PATENT DOCUMENT

Publication Number: US-9522468-B2
Application Number: US-201414273298-A
Country: US
Kind Code: B2

Title: Mass transfer tool manipulator assembly with remote center of compliance

Abstract:
Systems and methods for transferring a micro device or an array of micro devices to or from a substrate are disclosed. In an embodiment, a remote center robot allows on-the-fly alignment between a micro pick up array and a target substrate. The remote center robot may include a plurality of symmetric linkages that move independently and share a remote rotational center. In an embodiment, the remote rotational center may be positioned at a surface of the micro pick up array to prevent damage to the array of micro devices during transfer.

Claims:
What is claimed is: 
     
       1. A remote center robot, comprising:
 a first linkage having a first upper joint and a first lower joint separated along a first axis by a first link arm having a first length, wherein the first link arm is coupled to a first coupler link by the first lower joint; and 
 a second linkage having a second upper joint and a second lower joint separated along a second axis by a second link arm having a second length equal to the first length, wherein the second link arm is coupled to a second ground link by the second upper joint, and wherein the second ground link is fixed to the first coupler link. 
 
     
     
       2. The remote center robot of  claim 1 , wherein the first upper joint is coplanar with the first lower joint in a first plane, and wherein the second upper joint is coplanar with the second lower joint in a second plane orthogonal to the first plane. 
     
     
       3. The remote center robot of  claim 2 , wherein the first plane and the second plane intersect along a z-axis, and wherein a first angle between the first axis and the z-axis is equal to a second angle between the second axis and the z-axis. 
     
     
       4. The remote center robot of  claim 3 , wherein the first upper joint is coplanar with the second upper joint in an upper plane orthogonal to the z-axis, and wherein the first lower joint is coplanar with the second lower joint in a lower plane orthogonal to the z-axis. 
     
     
       5. The remote center robot of  claim 3  further comprising a third upper joint coplanar with a third lower joint in the first plane, wherein the third upper joint and the third lower joint are separated along a third axis by a third link arm, and wherein the third lower joint is coupled with the first lower joint by the first coupler link of the first linkage. 
     
     
       6. The remote center robot of  claim 5 , wherein a third angle between the third axis and the z-axis is equal to the first angle. 
     
     
       7. The remote center robot of  claim 6 , wherein the third upper joint is coplanar with the first upper joint in the upper plane. 
     
     
       8. The remote center robot of  claim 5  further comprising:
 a first linear actuator having a first end fixed relative to the first upper joint and a second end coupled with the first link arm, such that actuation of the first linear actuator changes the first angle; and 
 a second linear actuator having a third end fixed relative to the second upper joint and a fourth end coupled with the second link arm, such that actuation of the second linear actuator changes the second angle. 
 
     
     
       9. The remote center robot of  claim 8 , wherein the first axis intersects the z-axis at a remote tipping center, wherein the second axis intersects the z-axis at a remote tilting center, and wherein the remote tipping center is coincident with the remote tilting center at a remote rotational center. 
     
     
       10. The remote center robot of  claim 9  further comprising:
 a z-flexure having an upper portion coupled with a second coupler link of the second linkage and a lower portion separated from the upper portion along the z-axis; and 
 a distribution plate coupled with the lower portion of the z-flexure, the distribution plate configured to receive a micro pick up array having an electrostatic transfer head such that the remote rotational center is coincident with the electrostatic transfer head. 
 
     
     
       11. The remote center robot of  claim 1 , wherein a first combined stiffness of the first linkage is equal to a second combined stiffness of the second linkage. 
     
     
       12. The remote center robot of claim 11 , wherein the upper joints and the lower joints include a plurality of living hinges. 
     
     
       13. The remote center robot of  claim 1 , wherein the first linkage further includes an adjuster link between the first upper joint and an adjustment joint, wherein the adjustment joint is coupled with a first ground link of the first linkage. 
     
     
       14. The remote center robot of  claim 13 , wherein the adjuster link is adjustable such that a lateral distance between the first upper joint and the z-axis changes when the adjuster link is adjusted. 
     
     
       15. The remote center robot of  claim 14 , wherein the adjustment joint pivotally couples the adjuster link with the first ground link, such that the lateral distance changes when the adjuster link pivots about the adjustment joint. 
     
     
       16. The remote center robot of  claim 14 , wherein the adjuster link includes a variable length, such that the lateral distance changes when the variable length changes.

Description:
BACKGROUND 
     Field 
     The present invention relates to systems and methods for transferring micro devices. More particularly, embodiments of the present invention relate to systems and methods for rotationally aligning an array of micro devices relative to a substrate. 
     Background Information 
     The feasibility of commercializing miniaturized devices such as radio frequency (RF) microelectromechanical systems (MEMS) microswitches, light-emitting diode (LED) display systems, and MEMS or quartz-based oscillators is largely constrained by the difficulties and costs associated with manufacturing those devices. Miniaturized device manufacturing processes typically include processes in which miniaturized devices are transferred from one wafer to another. In one such implementation, a transfer wafer may pick up an array of miniaturized devices from a donor wafer and bond the miniaturized devices to a receiving wafer. 
     Miniaturized device transfer requires accurate and repeatable alignment in six spatial degrees of freedom between the transfer wafer and target wafer during the pick-up and bonding processes. Furthermore, alignment between the transfer wafer and the target wafer may be required after making contact between the target wafer and the transfer wafer. Methods and apparatuses for aligning two flat surfaces in a parallel orientation have been described, and may be applied to the problem of miniaturized device transfer. However, using some of the described methods, the wafers, or miniaturized devices on the wafers, may be smeared and damaged if alignment occurs after making contact between the wafers. This smearing may be caused by parasitic lateral motion, which is lateral motion of a point on an object accompanying rotation of the object about a center of rotation. That is, unless the point coincides with the center of rotation, the point will experience some lateral motion relative to the center rotation as it effectively pivots about the center of rotation. Some systems, such as hexapod robots, hybrid split-axis stages with tripod robot, and six-jointed serial arm robots, may use real-time motion control to provide rotational alignment about a point at the intersection of two planar surfaces, with negligible parasitic motion. However, such systems have some combination of limitations that may include slow response, inadequate stiffness, high cost, and excessive size and/or space requirements. 
     SUMMARY OF THE DESCRIPTION 
     A remote center robot and methods of using the remote center robot to transfer an array of micro devices to or from a substrate are disclosed. In an embodiment, a remote center robot includes a first linkage and a second linkage. The first linkage may include a first upper joint and a first lower joint separated along a first axis by a first link arm having a first length. The second linkage may include a second upper joint and a second lower joint, wherein the second upper joint is fixed relative to the first lower joint, and wherein the second upper joint and the second lower joint are separated along a second axis by a second link arm having a second length equal to the first length. 
     In an embodiment, the first linkage and the second linkage are positioned orthogonal to each other. More particularly, the first upper joint may be coplanar with the first lower joint in a first plane, and the second upper joint may be coplanar with the second lower joint in a second plane orthogonal to the first plane. 
     In an embodiment, the first and second linkages of the remote center robot are symmetric in any of several manners. For example, the first plane and the second plane may intersect along a z-axis, and a first angle between the first axis and the z-axis may be equal to a second angle between the second axis and the z-axis. Alternatively, the first upper joint may be coplanar with the second upper joint in an upper plane orthogonal to the z-axis, and the first lower joint may be coplanar with the second lower joint in a lower plane orthogonal to the z-axis. In an embodiment, a first combined stiffness of the first linkage is equal to a second combined stiffness of the second linkage. For example, the upper joints and lower joints of the linkages may include a plurality of living hinges have a same combined stiffness. 
     In an embodiment, a linkage of a remote center robot is symmetric relative to itself. For example, the first linkage may include a third upper joint coplanar with a third lower joint in the first plane, such that the third upper joint and the third lower joint are separated along a third axis by a third link arm, and the third lower joint is coupled with the first lower joint by a first coupler link of the first linkage. In an embodiment, a third angle between the third axis and the z-axis is equal to the first angle. Furthermore, the third upper joint may be coplanar with the first upper joint in the upper plane. 
     In an embodiment, a remote center robot includes an adjustment mechanism to adjust a remote tipping center of a first linkage to align with a remote tilting center of a second linkage, thereby forming a remote rotational center. In an embodiment, the adjustment mechanism is associated with the first linkage and includes an adjuster link between the first upper joint and an adjustment joint. For example, the adjustment joint may be coupled with a first ground link of the first linkage. Furthermore, the adjuster link may be adjustable such that a lateral distance between the first upper joint and a z-axis changes when the adjuster link is adjusted. In an embodiment, the adjustment joint pivotally couples the adjuster link with the first ground link, such that the lateral distance changes when the adjuster link pivots about the adjustment joint. In another embodiment, the adjuster link includes a variable length, such that the lateral distance changes when the variable length changes. 
     In an embodiment, linkages of a remote center robot are moved by one or more actuators. For example, a first linear actuator may have a first end fixed relative to the first upper joint and a second end coupled with the first link arm, such that actuation of the first linear actuator changes the first angle. Furthermore, a second linear actuator may have a third end fixed relative to the second upper joint and a fourth end coupled with the second link arm, such that actuation of the second linear actuator changes the second angle. 
     In an embodiment, geometry of a first linkage and a second linkage of a remote center robot may form a remote rotational center. For example, the first axis may intersect the z-axis at a remote tipping center, the second axis may intersect the z-axis at a remote tilting center, and the remote tipping center may be coincident with the remote tilting center at a remote rotational center. In an embodiment, the remote center robot also includes a z-flexure having an upper portion coupled with a second coupler link of the second linkage and a lower portion separated from the upper portion along the z-axis. A distribution plate may be coupled with the lower portion of the z-flexure and configured to receive a micro pick up array having an electrostatic transfer head such that the remote rotational center is coincident with the electrostatic transfer head. 
     In an embodiment, a method includes providing a remote center robot along a z-axis. The remote center robot may include a first linkage coupled with a first actuator and a second linkage coupled with a second actuator. A first coupler link of the first linkage may be fixed relative to a second ground link of the second linkage. Furthermore, a remote tipping center of the first linkage may be coincident with a remote tilting center of the second linkage at a remote rotational center on the z-axis. The method may further include receiving a signal from at least one of a tip sensor or a tilt sensor on a micro pick up array mount that is coupled with a second coupler link of the second linkage. In response to the signal, at least one of the first actuator or the second actuator may be actuated to rotate at least one of the first coupler link or the second coupler link about the remote rotational center. 
     In an embodiment, the first linkage and the second linkage of the method include symmetric link arm lengths. For example, the first linkage may include a first upper joint and a first lower joint separated along a first axis by a first link arm having a first length. The second linkage may include a second upper joint and a second lower joint. Furthermore, the second upper joint may be fixed relative to the first lower joint, and the second upper joint and the second lower joint may be separated along a second axis by a second link arm having a second length equal to the first length. 
     In an embodiment, the first linkage and the second linkage of the method are positioned orthogonal to each other. More particularly, the first upper joint may be coplanar with the first lower joint in a first plane, and the second upper joint may be coplanar with the second lower joint in a second plane orthogonal to the first plane. 
     In an embodiment, the first linkage and second linkage of the method include at least one of several geometric symmetries. For example, the first plane and the second plane may intersect along the z-axis, and a first angle between the first axis and the z-axis may be equal to a second angle between the second axis and the z-axis. Alternatively, the first upper joint may be coplanar with the second upper joint in an upper plane orthogonal to the z-axis, and the first lower joint may be coplanar with the second lower joint in a lower plane orthogonal to the z-axis. 
     In an embodiment, the method further includes adjusting an adjuster link of the first linkage to align the remote tipping center with the remote tilting center at the remote rotational center. The adjuster link may be located between the first upper joint and an adjustment joint, and the adjustment joint may be coupled with a first ground link of the first linkage. Adjusting the adjuster link includes pivoting the adjuster link about the adjustment joint. Alternatively, adjusting the adjuster link may include changing a length of the adjuster link. 
     In an embodiment, the method includes moving the remote center robot along the z-axis. As a result, an array of electrostatic transfer heads on a micro pick up array coupled with the second coupler link may be simultaneously moved toward a substrate surface. Thus, actuating at least one of the first actuator or the second actuator may include aligning the array of electrostatic transfer heads with the substrate surface. In an embodiment, the remote rotational center is coincident with the array of electrostatic transfer heads. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a mass transfer tool. 
         FIG. 2 , is a side view of a micro pick up array having a substrate supporting an array of electrostatic transfer heads. 
         FIG. 3  is a side view of a generic actuator assembly having a plurality of actuators. 
         FIG. 4  is a schematic view of a generic actuator assembly for adjusting an orientation of a micro pick up array. 
         FIG. 5  is a perspective view of a remote center robot in accordance with an embodiment. 
         FIG. 6  is an exploded view of a remote center robot in accordance with an embodiment. 
         FIG. 7  is a cross-sectional perspective view of a remote center robot in accordance with an embodiment. 
         FIG. 8  is a cross-sectional plan view of an x-linkage of a remote center robot in accordance with an embodiment. 
         FIG. 9  is a cross-sectional plan view of a y-linkage of a remote center robot in accordance with an embodiment. 
         FIG. 10  is a schematic view of a remote center robot adjusting an orientation of a micro pick up array in accordance with an embodiment. 
         FIG. 11  is a graph of parasitic motion of a point of interest as a function of micro pick up array tilt angle in accordance with an embodiment. 
         FIG. 12  is a perspective view of a z-flexure in accordance with an embodiment. 
         FIG. 13  is a cross-sectional view of a z-flexure in accordance with an embodiment. 
         FIG. 14  is a graph of parasitic motion of a point of interest as a function of vertical offset between the point of interest and a remote rotational center in accordance with an embodiment. 
         FIG. 15  is a cross-sectional plan view of an adjustment mechanism of a remote center robot in accordance with an embodiment. 
         FIG. 16A-16B  are a schematic view of an adjustment mechanism of a remote center robot adjusting a location of a remote tipping center in accordance with an embodiment. 
         FIG. 17  is a perspective view of a micro pick up array mount in accordance with an embodiment. 
         FIG. 18  is a schematic illustration of a control scheme for regulating a remote center robot in accordance with an embodiment. 
         FIG. 19  is a flowchart illustrating a method of aligning a micro pick up array coupled with a remote center robot relative to a target substrate in accordance with an embodiment. 
         FIG. 20  is a schematic illustration of a computer system that may be used in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention describe systems and methods for transferring a micro device or an array of micro devices to or from a substrate. For example, the micro devices or array of micro devices may be any of the micro LED device structures illustrated and described in related U.S. patent application Ser. Nos. 13/372,222, 13/436,260, 13/458,932, and 13/625,825. While some embodiments of the present invention are described with specific regard to micro LED devices, the embodiments of the invention are not so limited and certain embodiments may also be applicable to other micro LED devices and micro devices such as diodes, transistors, integrated circuit (IC) chips, MEMS, and bio-samples. 
     In various embodiments, description is made with reference to the figures. However, certain embodiments may be practiced without one or more of these specific details, or in combination with other known methods and configurations. In the following description, numerous specific details are set forth, such as specific configurations, dimensions, and processes, in order to provide a thorough understanding of the present invention. In other instances, well-known processes and manufacturing techniques have not been described in particular detail in order to not unnecessarily obscure the present invention. Reference throughout this specification to “one embodiment,” “an embodiment”, or the like, means that a particular feature, structure, configuration, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrase “one embodiment,” “an embodiment”, or the like, in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Furthermore, the particular features, structures, configurations, or characteristics may be combined in any suitable manner in one or more embodiments. 
     The terms “over”, “to”, “between”, and “on” as used herein may refer to a relative position of one layer or component with respect to other layers or components. One layer “over” or “on” another layer or bonded “to” another layer may be directly in contact with the other layer or may have one or more intervening layers. One layer “between” layers may be directly in contact with the layers or may have one or more intervening layers. 
     In an aspect, embodiments describe systems and methods for rotationally aligning a micro pick up array relative to a substrate. In an embodiment, the micro pick up array is carried by a remote center robot that manipulates an orientation of the micro pick up array. More particularly, the remote center robot may include a first linkage that moves independently of a second linkage and the micro pick up array may be coupled with the second linkage. In an embodiment, the first linkage carries the second linkage, but each linkage has an independent range of motion. For example, the first linkage may include a first coupler link that may tip without causing a second coupler link of the second linkage to move, and the second coupler link may tilt without causing the first coupler link to move. However, although motion of each coupler link may be independent from the other, each linkage may nonetheless share a common remote center of rotation. Furthermore, the common center of rotation may be located at a point of interest, such as at a surface of the micro pick up array. Thus, the surface of the micro pick up array may experience pure tipping about the common center of rotation when the first linkage tips and the micro pick up array may experience pure tilting about the common center of rotation when the second linkage tips. Therefore, when the surface of the micro pick up array contacts a substrate, the micro pick up array may be tipped and tilted to align the micro pick up array surface relative to the substrate without experiencing any parasitic translational motion that could damage the substrate or a micro device on the substrate. Adjustment of the micro pick up array may be dynamically controlled to adjust a magnitude and direction of a pressure gradient across the surface of the micro pick up array in addition to, or as a proxy for, micro pick up array alignment. 
     In an aspect, embodiments describe a remote center robot having symmetric first and second linkages. The linkages may share geometric symmetries. For example, link arms of both linkages may have equivalent lengths. Link arms may also be similarly oriented about a vertical axis, e.g., an angle between each link arm and the vertical axis may be the same. Similarly, an angle between link arms of the first linkage may be equal to an angle between link arms of the second linkage. The first and second linkages may also have symmetric geometries in that upper joints of all link arms may be coplanar within an upper plane and lower joints of all link arms may be coplanar within a lower plane. Furthermore, the linkages may share structural symmetries. For example, an overall stiffness of the first linkage may be the same as an overall stiffness of the second linkage. Thus, due to any manner of linkage symmetries, both linkages may have similar motion responses to similar actuation inputs. Also due to linkage symmetries, both linkages may have similar thermal responses to environmental changes, e.g., experience similar thermal expansion. Thus, a remote center robot with symmetric linkages may provide for an economic assembly for manipulating a micro pick up array that is robust and self-compensates for environmental changes during use. 
     In another aspect, embodiments describe a remote center robot that includes an adjustment mechanism functionally coupled with at least one linkage having a remote center of rotation. More specifically, an adjustment link may interconnect with a link of a first linkage such that movement of the adjustment link modifies the geometry of the first linkage. In an embodiment, movement of the adjustment link changes a location of a center of rotation of the first linkage, for example, by shifting the location of the center in space relative to a center of rotation of a second linkage. Accordingly, the adjustment link may be adjusted to move the center of rotation of the first linkage into alignment with the center of rotation of a second linkage such that the linkages share a common center of rotation about which an object may tip or tilt without parasitic motion. 
     In another aspect, embodiments describe a remote center robot that includes a z-flexure to move a micro pick up array along a z-axis within a frame of reference. More particularly, a z-flexure may incorporate at least one linkage that constrains motion of the z-flexure along the z-axis. Motion of the z-flexure may be passive, or it may be active and driven by a z-actuator. In an embodiment, the z-actuator applies a deformation load to the z-flexure in a direction orthogonal to the constrained direction of motion of the z-flexure. A micro pick up array may be coupled with the z-flexure to provide precise and repeatable movement in a known direction. Thus, the z-flexure may move a micro pick up array along a z-axis to a center of rotation of the micro pick up array with a surface of the micro pick up array. 
     In another aspect, embodiments describe a remote center robot having one or more actuators to adjust a linkage geometry in response to position and pressure-related control signals. In an embodiment, separate actuators adjust individual linkages and flexures of a remote center robot to cause a micro pick up array to tip, tilt, and move along a z-axis. The actuators may be controlled in response to positional inputs, and those positional inputs may be adjusted based on feedback signals provided by one or more sensor outputs representing a strain state of a micro pick up array mount mechanism carrying the micro pick up array. Thus, a closed control loop may be used to reorient the micro pick up array such that pressure is uniformly distributed across the micro pick up array. More particularly, the micro pick up array may be reoriented to distribute a pressure gradient across the micro pick up array in a predetermined manner. In an embodiment, an actuator aligns a center of rotation at the micro pick up array surface such that on-the-fly reorientation of the micro pick up array may be made while the micro pick up array contacts a target substrate without damaging the micro pick up array or associated micro devices. Accordingly, overall production rate may be increased and transfer error rates may be reduced. 
     Referring to  FIG. 1 , a perspective view of a mass transfer tool is shown. Mass transfer tool  100  may include a remote center robot  500  for picking up an array of micro devices from a carrier substrate held by a carrier substrate holder  104  and for transferring and releasing the array of micro devices onto a receiving substrate held by a receiving substrate holder  106 . Embodiments of mass transfer tool  100  are described in U.S. patent application Ser. No. 13/607,031, titled “Mass Transfer Tool”, filed on Sep. 7, 2012, which is incorporated herein by reference. Operation of mass transfer tool  100  and remote center robot  500  may be controlled at least in part by a computer  108 . Computer  108  may control the operation of remote center robot  500  based on feedback signals received from various sensors. For example, remote center robot  500  may include an actuator assembly for adjusting an associated micro pick up array  103  with at least three degrees of freedom, e.g., tipping, tilting, and movement in a z direction, based on feedback signals received from sensors associated with micro pick up array  103  or a component that carries micro pick up array  103 . Similarly, the carrier substrate holder  104  and receiving substrate holder  106  may be moved by an x-y stage  110  of mass transfer tool  100 , having at least two degrees of freedom, e.g., along orthogonal axes within a horizontal plane. Additional actuators may be provided, e.g., between mass transfer tool  100  structural components and remote center robot  500 , carrier substrate holder  104 , or receiving substrate holder  106 , to provide movement in the x, y, or z direction for one or more of those sub-assemblies. For example, a gantry  112  may support remote center robot  500  and move remote center robot  500  along an upper beam, e.g., in a direction parallel to an axis of motion of x-y stage  110 . Thus, an array of electrostatic transfer heads on micro pick up array  103 , supported by remote center robot  500 , and an array of micro devices supported by a carrier substrate held by carrier substrate holder  104  may be precisely moved relative to each other within all three spatial dimensions. 
     Referring to  FIG. 2 , a micro pick up array having a substrate supporting an array of electrostatic transfer heads is shown. Micro pick up array  103  may include a base substrate  202  supporting an array of electrostatic transfer heads  203 . Each electrostatic transfer head  203  may include a mesa structure  204  including a top surface  206  covered by a dielectric layer  208 . Furthermore, each electrostatic transfer head  203  may include electrical leads, electrodes, etc., necessary to generate an electrostatic gripping force on a micro device to be picked up. 
     In an embodiment, mesa structure  204  has a height of approximately 1 μm to 20 μm, or more specifically approximately 10 μm. In an embodiment, mesa structure  204  may have top surface  206  with surface area between 1 to 10,000 square micrometers. Furthermore, the top contact surface  210  of each electrostatic transfer head  203  may have a maximum dimension, for example a length or width of 1 to 100 μm, which may correspond to the size of a micro device to be picked up. For example, top contact surface  210  may have a surface area of about 5 μm by 5 μm or 10 μm by 10 μm. Thus, the height, width, and planarity of the array of mesa structures on base substrate  202  may be chosen so that each electrostatic transfer head  203  can make contact with a corresponding micro device during a pick up operation, and so that an electrostatic transfer head  203  does not inadvertently make contact with a micro device adjacent to an intended corresponding micro device during the pick up operation. Given the small geometry of micro pick up array and micro device geometry, movements between micro pick up array and micro devices must be accurately controlled to avoid damaging either electrostatic transfer heads  203  or micro devices on a target substrate. 
     Referring to  FIG. 3 , a side view of a generic actuator assembly having a plurality of actuators is shown. A generic actuator assembly  302  may include, e.g., a tripod or a hexapod robot to adjust a micro pick up array  103  relative to mass transfer tool  100  with at least three degrees of freedom, e.g., tipping, tilting, and movement in a z direction. Accordingly, actuator assembly  302  may include at least one actuator  304 , e.g., a piezoelectric linear actuator, which creates motion between mass transfer tool mount  306  and distribution plate  308 . More particularly, actuator assembly  302  may tip and tilt distribution plate  308  relative to mass transfer tool mount  306  that connects generic actuator assembly  302  to mass transfer tool  100 . As a result, an orientation of a micro pick up array  103  coupled with distribution plate  308  may be varied relative to mass transfer tool mount  306 . 
     Referring to  FIG. 4 , a schematic view of a generic actuator assembly  302  for adjusting an orientation of micro pick up array  103  is shown. A combined block representing distribution plate  308  carrying micro pick up array  103  may be mechanically coupled with mass transfer tool mount  306  through one or more actuator  304 . Thus, actuation of actuator  304  causes micro pick up array  103  to move relative to mass transfer tool mount  306 . More specifically, actuation of actuator  304  may cause an electrostatic transfer head  203  on micro pick up array  103  to move from an electrostatic transfer head position  402  to an electrostatic transfer head position  402 ′. Furthermore, the schematic illustration shows that the actuator assembly  302  includes a rotational center  404  about which micro pick up array  103  rotates. For example, as indicated in the schematic illustration, extension of a rightmost actuator combined with retraction of a leftmost actuator may result in a clockwise primary rotation  406  of micro pick up array  103  about rotational center  404 . 
     Rotational center  404  may be at a point above distribution plate  308 , and thus, micro pick up array  103  may pivot around rotational center  404 . More particularly, since electrostatic transfer heads  203  on micro pick up array  103  are not coincident with rotational center  404 , rotation of micro pick up array  103  about rotational center  404  may be accompanied by parasitic translation  408  of micro pick up array  103  as electrostatic transfer heads  203  shift from electrostatic transfer head position  402  to electrostatic transfer head position  402 ′. For example, parasitic translation  408  may be on the order of tens of microns of lateral motion. This range of motion may represent a significant distance in proportion to a width of electrostatic transfer heads  203 . Thus, if micro pick up array  103  is rotated about rotational center  404  after electrostatic transfer heads  203  make contact with a micro device on a target substrate, parasitic translation  408  may smear electrostatic transfer head  203  across a micro device on a surface of the substrate, potentially damaging the electrostatic transfer head  203 , micro device, or substrate. In an embodiment, an x-y stage  110  may be controlled to move beneath micro pick up array  103  to match parasitic translation  408  and compensate for relative movement between the electrostatic transfer head  203  and the micro device, which is inherent in tripod and hexapod robots. However, such compensation may be difficult to achieve over sub-micron distances and at the high motion rates required under product manufacturing conditions. Furthermore, hexapod robots may be expensive and complicated to incorporate in mass transfer tool  100 . 
     Referring to  FIG. 5 , a perspective view of a remote center robot is shown in accordance with an embodiment. A remote center robot  500  may be used in combination with mass transfer tool  100  to transfer micro devices to or from a substrate, e.g., receiving substrate or carrier substrate, using micro pick up array  103 . More particularly, remote center robot  500  may provide for negligible lateral or vertical parasitic motion for small movements of micro pick up array  103 , e.g., motion less than about 5 mrad about a neutral position. Accordingly, remote center robot  500  may be incorporated in mass transfer tool  100  to adjust a micro pick up array  103  relative to mass transfer tool  100 . Thus, remote center robot  500  may include mass transfer tool mount  306  that may be fixed to a chassis of mass transfer tool  100 , e.g., at a location along an upper beam or support. 
     In an embodiment, remote center robot  500  includes multiple linkages having independent ranges of motion. For example, remote center robot  500  may include an x-linkage  504  coupled with mass transfer tool mount  306  and having links interconnected at joints such that the links exhibit kinematics in a first plane, e.g., movement of x-linkage  504  may include a coupler link tipping relative to a ground link. Remote center robot  500  may also include a y-linkage  506  coupled with x-linkage  504  and having links that exhibit kinematics in a second plane different than the first plane, e.g., movement of y-linkage  506  may include a coupler link tilting relative to a ground link. Remote center robot  500  may also include z-flexure  508  coupled with y-linkage  506  and having a structure that lengthens and shortens along a z-axis  510 . 
     In an embodiment, x-linkage  504 , y-linkage  506 , and z-flexure  508  are structurally connected such that kinematics of each linkage is related but independent. For example, in an embodiment, a ground link of x-linkage  504  is fixed relative to mass transfer tool mount  306  and a first end of z-flexure  508  is fixed to a distribution plate  308 . Furthermore, a coupler link of x-linkage  504  may carry a ground link of y-linkage  506 , and a coupler link of y-linkage  506  may carry a second end of z-flexure  508  such that movement of any of x-linkage  504 , y-linkage  506 , and z-flexure  508  results in a relative movement between mass transfer tool mount  306  and distribution plate  308 . Thus, remote center robot  500  may be used to control a spatial orientation of an object, e.g., a micro pick up array  103  connected to distribution plate  308 . In an embodiment, a micro pick up array mount may intervene between micro pick up array  103  and distribution plate  308 . As discussed below, micro pick up array mount may be a coupling component suited to carry micro pick up array  103  on a first side and to connect to distribution plate  308  at a second side. 
     In an embodiment, the interrelated movement of x-linkage  504 , y-linkage  506 , and z-flexure  508  may nonetheless be independent, such that movement of any one of the components provides pure motion of distribution plate  308 . For example, movement of x-linkage  504  may cause distribution plate  308  to tip relative to mass transfer tool mount  306 , movement of y-linkage  506  may cause distribution plate  308  to tilt relative to mass transfer tool mount  306 , and movement of z-flexure  508  may cause distribution plate  308  to extend away from or retract toward mass transfer tool mount  306 . More particularly, such relative movement between distribution plate  308  and mass transfer tool mount  306  may be independently constrained within the ranges of motion of each linkage without motion in one reference frame causing motion in another. For example, tipping of distribution plate  308  within a first plane caused by movement of x-linkage  504  may not include any parasitic tilting in a second plane. Thus, decoupling remote center robot  500  linkages may provide pure motion of distribution plate  308  about different rotational centers and in different axial directions. 
     Referring to  FIG. 6 , an exploded view of a remote center robot is shown in accordance with an embodiment. X-linkage  504  and y-linkage  506  may each include a multi-link structure. For example, x-linkage  504  and y-linkage  506  may each include at least two links, e.g., a ground link and a link arm, or may include three or more links, e.g., a ground link, one or two link arms, and a coupler link. The linkages may further be aligned with planes that are substantially orthogonal, i.e., x-linkage  504  and y-linkage  506  may be substantially orthogonal to each other. For example, x-linkage  504  may act within a y-z plane encompassing a y-axis  602  and z-axis  510 , while y-linkage  506  may act within an x-z plane encompassing an x-axis  604  and z-axis  510 . 
     In an embodiment, components of remote center robot  500  may be monolithically formed or formed in pieces. For example, x-linkage  504  may be formed as a single piece of material with joints, e.g., living hinge flexures, which permit the single piece to flex and change geometry as a whole. Alternatively, such as in the case of y-linkage  506 , linkages may be formed in halves that are joined together directly or by being coupled with intermediate components to form a linkage structure. Remote center robot  500  may be formed from known materials, such as steel alloys, nickel-iron alloys, e.g., Invar, or other plastic, ceramic, or metal materials. Known manufacturing processes such as milling, laser cutting, electrical discharge machining, etc., may be used to form remote center robot  500  components. 
     In an embodiment, x-linkage  504  and y-linkage  506  are geometrically symmetric. For example, the links of x-linkage  504  and y-linkage  506  may have substantially equal lengths. More particularly, corresponding links of each linkage may or may not have substantially equal lengths. For example, link arms of each linkage may have a same first length and coupler links of each linkage may have a same second length, but the first length may or may not be equal to the second length. Equal length links may provide for a similar thermal response of x-linkage  504  and y-linkage  506  to environmental changes. For example, if temperatures local to remote center robot  500  change due to heating provided during use, each of the links may undergo similar thermal expansion. 
     In an embodiment, similar thermal expansion of x-linkage  504  links and y-linkage  506  links may be further facilitated through material choice. For example, corresponding links for each linkage may be formed from the same material, e.g., steel alloys, Invar, etc. Thus, corresponding links may have similar or equal coefficients of thermal expansion and may accordingly exhibit similar thermal expansion. As a result, x-linkage  504  and y-linkage  506  may exhibit self-thermal compensation because both linkage geometries may respond similarly to temperature changes. 
     X-linkage  504  and y-linkage  506  may have linkage angles that are symmetric about a given reference geometry. For example, an angle between link arms of each linkage and z-axis  510  may be equal, or approximately equal. Thus, as an example, an angle between each link arm of x-linkage  504  and z-axis  510  may be about 30 degrees and an angle between each link arm of y-linkage  506  and z-axis  510  may also be about 30 degrees. Therefore, linkage response to actuator inputs may be similar. For example, given that x-linkage  504  and y-linkage  506  may have similar geometric angles, actuation of respective link arms by respective actuators may cause similar angular changes of the link arms relative to z-axis  510 . More particularly, an actuator coupled with an x-linkage  504  link arm and an actuator coupled with a y-linkage  506  link arm may be moved similar amounts to cause similar tipping or tilting responses in x-linkage  504  and y-linkage  506 , respectively. 
     In an embodiment, x-linkage  504  and y-linkage  506  are structurally symmetric. For example, the overall structural stiffness of x-linkage  504  and y-linkage  506  may be similar. Overall structural stiffness may be measured by a motion response in relation to an input actuation. For example, in a case in which respective actuators place lateral loads on respective link arms to cause x-linkage  504  to tip and y-linkage  506  to tilt, the linkages may have a same composite stiffness if a same load applied by the respective actuators causes an equal degree of tipping or tilting in the respective linkages. The overall structural stiffness may be a function of joints that connect links in the linkages, e.g., living hinge flexures, but may also be a function of the system stiffness created by actuators, springs, and various couplers that hold the linkages together or impart loads on the linkages. 
     Referring to  FIG. 7 , a cross-sectional perspective view of a remote center robot is shown in accordance with an embodiment. As shown, the cross-sectional view passes through x-linkage  504  of remote center robot  500  and exposes several joints  702  connecting individual links of the linkage structure. Joints  702  may include living hinges having thin flexures that may repeatedly flex without failing. For example, a living hinge may be formed between x-linkage  504  links by forming the links as part of a single piece of material, in which the links are connected by a thin flap of material. The flap of material may be formed by removing material from the single piece of material using, e.g., electric discharge machining, or by forming the single piece of material with the thin hinge feature, e.g., during molding or casting. Living hinge flexures may provide low or no hysteresis and repeatable motion over a system service life. Alternatively, joints  702  may be other bearing structures, such as barrel hinges, ball and socket joints, etc. Joints  702  allow links of x-linkage  504  to move relative to one another and relative to other structures to which such links are connected. For example, a ground link of x-linkage  504  may be connected to mass transfer tool mount  306  and to a link arm of x-linkage  504 . Thus, movement of the link arm relative to the ground link also results in movement of the link arm relative to mass transfer tool mount  306 . These relative movements can be geometrically defined and modelled such that any point in remote center robot  500  may be predicted relative to another point in remote center robot  500  based on known motion inputs. 
     Motion inputs on the linkages of remote center robot  500  may be applied through loads imparted by a variety of actuators and loading elements. For example, in an embodiment, an x-actuator  704  imparts a biasing load to x-linkage  504  structure. More particularly, x-actuator  704  may be a linear actuator having two ends, and each end may be connected or constrained relative to x-linkage  504  such that linear motion of x-actuator  704  causes x-linkage  504  geometry to change. For example, a flexural coupler  706  may be located at one or both ends of x-actuator  704 . Flexural coupler  706  may transmit loading to opposing links of x-linkage  504 , e.g., between a ground link and a link arm, from x-actuator  704 . Simultaneously, flexural coupler  706  may allow some angular movement of x-actuator  704 . More particularly, flexural couplers  706  may act like ball joints to allow x-actuator  704  to passively change angle to accommodate a changing x-linkage  504  geometry. That is, flexural couplers  706  may provide a limited range of motion in two rotational directions, both of which are orthogonal to the line of x-actuator  704  action, between an end of x-actuator  704  and a location at which the x-actuator  704  end is to be connected, e.g., at a ground link of x-linkage  504 . In an embodiment, x-actuator  704  includes a fixed end with a first flexural coupler  706  fixed to an x-linkage  504  link, e.g., a ground link, and a moving end with a second flexural coupler  706 ′ movable relative to another x-linkage  504  link, e.g., a link arm. Thus, flexural couplers  706  and  706 ′ allow loading of x-linkage  504  to create linkage movement without over-constraining the linkage system. In an embodiment, actuators of remote center robot  500 , such as x-actuator  704  may be piezoelectric actuators. Although other linear actuators may be used, e.g., hydraulic, pneumatic, or electromechanical actuators, a piezoelectric actuator may exhibit fine positioning resolution through relatively short movements. 
     Y-linkage  506  may also include a four-bar linkage structure having links connected by joints  702 . Furthermore, forces may be imparted to y-linkage  506  by one or more actuators or loading elements, such as a y-actuator  708  and a spring stack  710  passing through remote center robot  500  orthogonal to x-actuator  704 . Y-actuator  708  may impart loads to y-linkage  506  to cause the linkage structure to move. Similarly, spring stack  710  may include a reactive load, such as by incorporating an extension or a compression spring, which counteracts the loading applied by y-actuator  708 . For example, whereas y-actuator  708  may push on a link arm of y-linkage  506 , spring stack  710  may pull on the link arm. X-linkage  504  loading may be similarly counteracted by a corresponding spring stack. As a result of these opposing loads, the linkage structure may be preloaded and biased toward one direction. The preload may also provide a known composite stiffness to the linkage. Therefore, linkage motion may be more uniformly controlled by actuation of y-actuator  708  since the actuator need only be precisely moveable in one direction and since the opposing loads to the actuation load may be known. 
     In addition to providing a known, repeatable opposing load to the actuation direction and to providing preloading bias and anti-backlash, spring stack  710  may also assist an actuator, such as y-actuator  708 , to retract to a neutral position. For example, in an embodiment in which y-actuator  708  generates more force in an extension direction than in a retraction direction, e.g., it pushes with greater force than it pulls, spring stack  710  may compensate y-actuator  708  in the retraction direction to return y-actuator to an initial, neutral position. 
     In an embodiment, z-flexure  508  is connected to y-linkage  506  such that y-linkage  506  carries z-flexure  508 . Furthermore, z-flexure  508  may be connected to z-actuator  712 , which may be capable of loading the structure of z-flexure  508 . More particularly, in an embodiment, z-actuator  712  extends and retracts in a direction orthogonal to a direction of deformation of z-flexure  508 . For example, z-actuator  712  may place a radial load on an annular structure of z-flexure  508  in a direction of y-axis  602 , and the radial load may cause z-flexure  508  to increase or decrease in length along an axial direction, e.g., z-axis  510 . 
     Referring to  FIG. 8 , a cross-sectional plan view of an x-linkage of a remote center robot is shown in accordance with an embodiment. In an embodiment, the cross-sectional plan view is taken about a y-z plane encompassing y-axis  602  and z-axis  510 . X-linkage  504  may include various elements that constitute links in a four-bar linkage structure. For example, x-linkage  504  may include an x-linkage ground  802 . As discussed above, x-linkage ground  802  may be connected with mass transfer tool mount  306 , e.g., by fastening x-linkage ground  802  to a flange of mass transfer tool mount  306 . Thus, x-linkage ground  802  may be fixed relative to mass transfer tool mount  306  of mass transfer tool  100 . 
     In an embodiment, x-linkage  504  includes at least one link arm connected to x-linkage ground  802 . For example, an x-linkage left link arm  804  may connect to x-linkage ground  802  at an x-linkage upper left joint  806 . X-linkage upper left joint  806  may include a living hinge flexure that allows x-linkage left link arm  804  to pivot relative to x-linkage ground  802 . X-linkage  504  may also include x-linkage right link arm  808  located opposite z-axis  510  from x-linkage left link arm  804 . More particularly, x-linkage right link arm  808  may pivot about an x-linkage upper right joint  810 , which may be located opposite the x-z plane, i.e., the plane encompassing x-axis  604  and z-axis  510 , from x-linkage upper left joint  806 . X-linkage  504  may also include x-linkage coupler  812  connected with one or both of x-linkage left link arm  804  and x-linkage right link arm  808 . For example, x-linkage coupler  812  may connect with x-linkage left link arm  804  at x-linkage lower left joint  814  and x-linkage coupler  812  may connect with x-linkage right link arm  808  at x-linkage lower right joint  816 . Thus, x-linkage  504  may include a four-bar linkage having a ground link, two link arms, and a coupler link, interconnected by four joints  702 . 
     Each link of x-linkage  504  may include a respective shape and volume. However, the shape and volume of each link may not be the same. For example, x-linkage left link arm  804  may include an elongated shape extending along x-linkage left axis  818  between x-linkage upper left joint  806  and x-linkage lower left joint  814 , and x-linkage right link arm  808  may include an elongated shape extending along x-linkage right axis  820  between x-linkage upper right joint  810  and x-linkage lower right joint  816 . However, even though each link arm may be generally elongated, each may include different shapes and volumes, e.g., x-linkage right link arm  808  may have a hole to allow x-actuator  704  to pass through x-linkage right link arm  808  while x-linkage left link arm  804  may not include such a hole. Furthermore, the shape and volume of each link arm may be substantially different from those of x-linkage ground  802  or x-linkage coupler  812 , which may both include substantially more volume or have a substantially different shape specific to their function. For example, x-linkage coupler  812  may be vertically arranged with substantially more volume along z-axis  510  between x-linkage  504  lower joints and one or more coupler mount  822  than x-linkage  504  link arm volumes. The vertical arrangement may allow for x-linkage  504  to carry y-linkage  506  such that y-linkage may be symmetric with x-linkage  504 . 
     In an embodiment, although volumes of links may vary, a mass of corresponding links in a linkage or between linkages may be kept the same. For example, x-linkage left link arm  804  may have a different shape than x-linkage right link arm  808  due, for example, to a hole for receiving x-actuator  704 , but a boss may be added to x-linkage right link arm  808  or x-linkage left link arm  804  may be made thinner to allow for the overall volume and mass of the link arms to be substantially equal. Furthermore, additional parts, such as a bolt formed from a material with a higher density than the link arm material, may be added to a link arm having less volume to compensate for the reduced volume and create a substantially equal mass for both link arm composite structures. Maintaining equal link arm mass may provide an additional symmetry within and between linkages to allow for uniform motion response to the same actuation loads. 
     Uniform motion response to the same actuation loads may be achieved in other manners. In an embodiment, the inertial characteristics of linkages about a given point may be asymmetric and yet the linkages may still exhibit similar motion about the point in response to loading from respective actuators. More particularly, motion of a linkage about the point may depend on a moment of inertia of the linkage about the point, as well as a load magnitude and a distance from the point at which a respective actuator applies the load. Thus, assuming similar load magnitudes are applied from respective actuators, motion response between linkages may be the same when the relationship between a location of the load on a linkage relative to the point of interest, and the moment of inertia of the linkage about the point of interest, remains the same. For example, in an embodiment, x-actuator  704  places a load amount on x-linkage  504  further from remote tipping center  826  than y-actuator  704  places the same load amount on y-linkage  506  relative to a remote tilting center. Nonetheless, x-linkage  504  and y-linkage  506  may have a similar motion about respective remote centers in response to the different loading conditions, if a moment of inertia of x-linkage  504  about remote tipping center  826  is correspondingly increased relative to a moment of inertia of y-linkage  506  about the remote tilting center. Accordingly, one of ordinary skill in the art may modify actuator loading location, linkage mass distribution, and linkage joint stiffness such that linkages exhibit uniform motion about remote centers of rotation in response to actuator loading. 
     Even in a case in which x-linkage  504  links do not share similar shapes, volumes, or masses, x-linkage  504  may nonetheless include geometric symmetries as described above. Accordingly, x-linkage left axis  818  may form a first angle with z-axis  510  and x-linkage right axis  820  may form a similar or identical second angle with z-axis  510 . For example, the first and second angle may each be approximately 30 degrees, resulting in a total sweep angle of about 60 degrees between x-linkage left axis  818  and x-linkage right axis  820 . In an embodiment, an additional symmetry includes x-linkage upper right joint  810  and x-linkage upper left joint  806  being coplanar within an upper plane  824 . Similarly, x-linkage lower right joint  816  and x-linkage lower left joint  814  may be coplanar within a lower plane  825 . Accordingly, x-linkage  504  may be symmetric about the x-z plane encompassing x-axis  604  and z-axis  510 , in numerous manners. 
     In an embodiment, x-linkage  504  includes a remote tipping center  826  located at an intersection of x-linkage left axis  818  and x-linkage right axis  820 . Remote tipping center  826  may be a virtual center of rotation with a spatial position that remains constant as x-linkage  504  link arms change orientation. For example, in an embodiment, as x-linkage left link arm  804  pivots about x-linkage upper left joint  806 , a corresponding motion of x-linkage right link arm  808  may cause the angles between x-linkage left axis  818 , x-linkage right axis  820 , and z-axis  510  to change. However, the location of remote tipping center  826  may remain stationary despite the change in linkage geometry. More particularly, as x-linkage  504  geometry changes, x-linkage coupler  812  may rotate about remote tipping center  826 . Thus, a point on an object that is fixed relative to x-linkage coupler  812  and located at remote tipping center  826  may experience pure rotation, unaccompanied by translational parasitic motion, when x-linkage  504  geometry is varied. 
     The phenomenon of pure rotation about remote tipping center  826  may be exploited by locating transfer elements for which parasitic motion is undesirable at remote tipping center  826 . For example, z-flexure  508  and distribution plate  308  may be fixed relative to y-linkage  506 , which in turn may be fixed relative to x-linkage coupler  812  at coupler mounts  822 , such that a micro pick up array mount  828  on distribution plate  308  may carry micro pick up array  103  with a surface co-located with remote tipping center  826 . More particularly, an electrostatic transfer head  203  on micro pick up array  103  may be co-located with remote tipping center  826  during movement of x-linkage  504 . As a result, as x-linkage  504  geometry varies, electrostatic transfer head  203  may experience pure tipping and remain in the same lateral location, rather than shifting under parasitic translation and potentially smearing a corresponding micro device on a mating substrate surface. 
     Referring to  FIG. 9 , a cross-sectional plan view of a y-linkage of a remote center robot is shown in accordance with an embodiment. In an embodiment, the cross-sectional plan view is taken about the x-z plane encompassing x-axis  604  and z-axis  510 . Like x-linkage  504 , y-linkage  506  may include several links constituting a linkage structure. For example, y-linkage  506  may include a y-linkage ground  902 . However, rather than being fixed relative to mass transfer tool mount  306 , y-linkage ground  902  may be moveable relative to mass transfer tool mount  306 . More particularly, y-linkage ground  902  may be fixed relative to x-linkage coupler  812  at coupler mount  822  or another location. Accordingly, when x-linkage  504  is moved by actuating x-linkage  504  link arms, x-linkage coupler  812  moves relative to mass transfer tool mount  306  and since y-linkage ground  902  is carried on x-linkage coupler  812 , so may y-linkage ground  902  move relative to mass transfer tool mount  306 . 
     In an embodiment, y-linkage  506  includes at least one link arm connected to y-linkage ground  902 . For example, a y-linkage left link arm  904  may connect to y-linkage ground  902  at a y-linkage upper left joint  906 . Y-linkage upper left joint  906  may include a living hinge flexure that allows y-linkage left link arm  904  to pivot relative to y-linkage ground  902 . Y-linkage  506  may also include y-linkage right link arm  908  located opposite z-axis  510  from y-linkage left link arm  904 . More particularly, y-linkage right link arm  908  may pivot about a y-linkage upper right joint  910 , which is located opposite the y-z plane, encompassing y-axis  602  and z-axis  510 , from y-linkage upper right joint  910 . Y-linkage  506  may also include y-linkage coupler  912  connected with one or both of y-linkage left link arm  904  and y-linkage right link arm  908 . For example, y-linkage coupler  912  may connect with y-linkage left link arm  904  at y-linkage lower left joint  914  and y-linkage coupler  912  may connect with y-linkage right link arm  908  at y-linkage lower right joint  916 . Thus, in an embodiment, y-linkage  506  includes a linkage structure similar to x-linkage  504 , having a ground link, two link arms, and a coupler link, interconnected by four joints  702 . 
     Like x-linkage  504 , each link of y-linkage  506  may include a respective shape and mass. However, the shapes and masses of each link may not be the same. For example, y-linkage left link arm  904  may include a triangular or polygonal shape through which y-linkage left axis  918  passes between y-linkage upper left joint  906  and y-linkage lower left joint  914 . Similarly, y-linkage right link arm  908  may include a triangular or polygonal shape through which y-linkage right axis  920  passes between y-linkage upper right joint  910  and y-linkage lower right joint  916 . However, even though each link arm may be generally triangular or polygonal, each may include different features, e.g., to account for a hole to allow y-actuator  708  to pass through y-linkage right link arm  908 . Furthermore, the shapes of each link arm may be substantially different from those of y-linkage ground  902  or y-linkage coupler  912 . Also like x-linkage  504 , y-linkage  506  geometry and configurations may be manipulated such that link arms include similar volumes and/or mass to facilitate equivalent motion response. 
     Y-linkage  506  may also be symmetric about the y-z plane in numerous manners. For example, y-linkage  506  link arms may exhibit similar lengths and/or make similar angles with z-axis  510 . Furthermore, in an embodiment, y-linkage upper right joint  910  and y-linkage upper left joint  906  are coplanar within upper plane  824 . Similarly, y-linkage lower right joint  916  and y-linkage lower left joint  914  may be coplanar within lower plane  825 . 
     In addition to exhibiting symmetries about respective planes passing through z-axis  510 , x-linkage  504  and y-linkage  506  may also be symmetric relative to each other. That is, upper joints  702  of x-linkage  504  may be coplanar within upper plane  824  relative to upper joints  702  of y-linkage  506 . Similarly, lower joints  702  of x-linkage  504  may be coplanar within lower plane  825  relative to lower joints  702  of y-linkage  506 . Furthermore, x-linkage left axis  818  may form a first angle with z-axis  510  that is equal to a first angle formed with z-axis  510  by y-linkage left axis  918 . Alternatively, an angle between x-linkage  504  link arms may be equal to an angle between y-linkage  506  link arms. Accordingly, although x-linkage  504  and y-linkage  506  may have links of different shapes and volumes, the lengths, locations, and angles of the links may be similar or identical between the linkages. 
     In an embodiment, y-linkage  506  includes a remote tilting center  922  located at an intersection of y-linkage left axis  918  and y-linkage right axis  920 . Remote tilting center  922  may be a virtual center of rotation with a spatial position that remains constant as y-linkage  506  link arms change orientation. For example, in an embodiment, as y-linkage left link arm  904  pivots about y-linkage upper left joint  906 , a corresponding motion of y-linkage right link arm  908  may cause the angles between y-linkage left axis  918 , y-linkage right axis  920 , and z-axis  510  to change. However, the location of remote tilting center  922  may remain stationary despite the change in linkage geometry. More particularly, as y-linkage  506  geometry changes, y-linkage coupler  912  may rotate about remote tilting center  922 . Thus, a point on an object that is fixed relative to y-linkage coupler  912  and located at remote tilting center  922  may experience pure rotation, unaccompanied by translational parasitic motion, when y-linkage  506  geometry is varied. 
     The phenomenon of pure rotation about remote tilting center  922  may be exploited by locating transfer elements for which parasitic motion is undesirable at remote tilting center  922 . For example, an electrostatic transfer head  203  on micro pick up array  103  connected with micro pick up array mount  828 , distribution plate  308 , and z-flexure  508 , may be co-located with remote tilting center  922  during movement of y-linkage  506 . As a result, as y-linkage  506  geometry varies, electrostatic transfer head  203  may experience pure tilting and remain in the same lateral location, rather than shifting under parasitic translation and potentially smearing a corresponding micro device on a mating substrate surface. 
     Referring to  FIG. 10 , a schematic view of a remote center robot adjusting an orientation of a micro pick up array is shown in accordance with an embodiment. In an embodiment, a remote rotational center  1002  represents a spatial location at which remote tipping center  826  associated with x-linkage  504  is coincident with remote tilting center  922  associated with y-linkage  506 . More particularly, although remote tipping center  826  and remote tilting center  922  are independently located according to link arm geometries of x-linkage  504  and y-linkage  506 , respectively, the x-linkage  504  and y-linkage  506  geometries may be symmetrically formed as described above to create a shared remote rotational center  1002 . Furthermore, remote rotational center  1002  may be located at a surface of micro pick up array  103 , e.g., at an electrostatic transfer head  203 , such that movement of x-linkage  504  causes pure tipping rotation at the electrostatic transfer head  203  and movement of y-linkage  506  causes pure tilting rotation at the electrostatic transfer head  203 . As a result, combined movement of x-linkage  504  and y-linkage  506  may cause pure rotation about the electrostatic transfer head  203  in any direction about z-axis  510 , to prevent smearing of a micro device that is in contact with the electrostatic transfer head  203 . 
     For ease of understanding, only x-linkage  504  movement is represented by  FIG. 10 . However, y-linkage  506  movement may be modelled identically since x-linkage  504  and y-linkage  506  may be symmetrically formed. X-linkage left link arm  804  is shown pivoting about x-linkage upper left joint  806  at x-linkage ground  802 . Similarly, x-linkage right link arm  808  is shown pivoting about x-linkage upper right joint  810  at x-linkage ground  802 . X-linkage coupler  812  spans between x-linkage lower left joint  814  and x-linkage lower right joint  816 . As shown, x-linkage  504  is not overly constrained, and may be acted upon by an actuator of some kind to generate movement of the linkage structure. For example, x-actuator  704  may be a linear actuator with a first end fixed relative to x-linkage ground  802  and a second end fixed relative to x-linkage right link arm  808 . As shown, x-actuator  704  may extend in length to cause x-linkage right link arm  808  to sway outward and cause x-linkage left link arm  804  to sway inward. More particularly, actuation of x-actuator  704  may move the actuator to an x-actuator  1004  orientation, accompanied by movement of x-linkage right link arm  808  to an x-linkage right link arm  1006  orientation and movement of x-linkage left link arm  804  to an x-linkage left link arm  1008  orientation. Alternatively, x-actuator  704  could be a lever, rotational motor, etc., to cause x-linkage left link arm  804 , or another link, to pivot relative to x-linkage ground  802 , or another link. 
     In an embodiment, movement of x-linkage  504  link arms is accompanied by a pivoting of x-linkage coupler  812  from an initial location to an x-linkage coupler  1010  orientation. More particularly, as x-linkage lower left joint  814  at one end of x-linkage coupler  812  moves to x-linkage lower left joint  1012  location and x-linkage lower right joint  816  at another end of x-linkage coupler  812  moves to x-linkage lower right joint  1014  location, x-linkage coupler  812  may pivot around remote rotation center  1002 , which remains virtually fixed in space. Furthermore, given that micro pick up array  103  may be fixed relative to x-linkage coupler  812 , the micro pick up array  103  may rotate around remote rotational center  1002  and an electrostatic transfer head  203  on micro pick up array  103  located at remote rotational center  1002  may experience pure rotation and/or minimal parasitic translational motion. 
     Referring to  FIG. 11 , a graph of parasitic motion of a point of interest as a function of micro pick up array tilt angle is shown in accordance with an embodiment. By way of example and not limitation, x-actuator  704  may be a piezo actuator having a linear motion range of about 90 micron. In an embodiment, actuation of x-actuator  704  over the full range of motion may result in x-linkage right link arm  808  pivoting through an angular range of about 2 mrad toward x-linkage right link arm  1006  location. Furthermore, such actuation may cause a similar tipping of micro pick up array  103  about remote rotation center  1002 , e.g., in the 2 mrad range. 
     In an embodiment, tipping or tilting of micro pick up array  103  about remote rotational center  1002  is accompanied by some degree of translational parasitic motion. For example, parasitic error  1102  may accompany tilting of y-linkage right link arm  908  under actuation of y-actuator  708 . However, such parasitic error  1102  may be substantially reduced as compared to parasitic translation  408  inherent in existing manipulator assemblies. For example, whereas parasitic translation  408  discussed above may be in a range of several tens of microns, parasitic error  1102  using remote center robot  500  may be less than about 200 nm over the entire range of actuator motion. Thus, remote center robot  500  may provide for negligible lateral or vertical parasitic motion for small motions, e.g., motion less than about 5 mrad about a neutral position. 
     Although remote center robot  500  may reduce lateral parasitic translation  408 , some degree of vertical movement of a point of interest may remain. For example, vertical error  1104 , corresponding to a degree of vertical motion that an electrostatic transfer head  203  at remote rotational center  1002  experiences during movement of remote center robot  500 , may accompany tipping or tilting of micro pick up array  103  about remote rotational center  1002 . In an embodiment, vertical error  1104  using remote center robot  500  may be less than about 350 nm over the entire range of actuator motion. Nonetheless, remote center robot  500  may incorporate additional features to adjust for, and reduce, vertical error  1104 . 
     Referring to  FIG. 12 , a perspective view of a z-flexure is shown in accordance with an embodiment. In an embodiment, z-flexure  508  may provide z-correction to compensate for vertical error  1104 . Z-flexure  508  may include a linkage structure that moves under actuation from z-actuator  712 . More particularly, z-flexure  508  may lengthen and shorten along z-axis  510 , and thus, a vertical location of an electrostatic transfer head  203  on micro pick up array  103  coupled with z-flexure  508  may be varied relative to mass transfer tool mount  306 . Accordingly, an electrostatic transfer head position on micro pick up array  103  may be moved vertically during tipping or tilting of linkages to compensate for vertical error  1104  and maintain electrostatic transfer head  203  in a constant vertical position along z-axis  510 . 
     In an embodiment, z-flexure  508  may have a generally annular shape such that a central opening is located along z-axis  510 . The annular shape may have a height in an axial direction and include an outer diameter in a transverse direction relative to z-axis  510 . Z-actuator  712  may be positioned inside of the central opening with a first end connected to a first lateral side of the annular shape and a second end connected to a second lateral side of the annular shape. Accordingly, z-actuator  712  may be lengthened or shortened such that the ends of z-actuator  712  apply a radial load on the annular shape, either outwardly or inwardly. 
     Radial loading of z-flexure  508  by z-actuator  712  may cause an axial change in height of the annular shape through a linkage structure formed in z-flexure  508 . For example, z-flexure  508  may include one or more associated linkages having z-flexure  508  links, e.g., a wedge link  1202  and one or more intermediate links  1208 . The z-flexure  508  links may form a double-back four-bar linkage with a range of motion within a single plane. More particularly, z-flexure  508  links may be rigid in a direction transverse to a plane encompassing z-actuator  712  and z-axis  510 , such that actuation of z-flexure  508  provide a change in z-flexure  508  height between an upper mount  1204  and a lower mount  1206 , but results in no lateral motion of upper mount  1204  or lower mount  1206 . Thus, z-flexure  508  provides a structure that is essentially immune to lateral flexure, such that lower mount  1206  moves only in a vertical direction and imparts motion to an associated object, e.g., micro pick up array  103 , only in the vertical direction. 
     In an embodiment, the z-flexure  508  linkage structure provides a relationship between wedge link  1202  position and a distance between upper mount  1204  and lower mount  1206 . More particularly, wedge link  1202  may be part of the annular shape acted upon by z-actuator  712 . Thus, as z-actuator  712  extends or retracts, e.g., in the case where z-actuator  712  is a linear actuator, wedge links  1202  may correspondingly move away from each other or toward each other. In either case, wedge links  1202  may be connected to each side of an upper mount  1204  and a lower mount  1206  through respective intermediate links  1208 . Intermediate links  1208  may be link arms of a double-back four-bar linkage that move based on wedge link  1202  position. More particularly, as wedge links  1202  move inward, intermediate links  1208  may be pushed away from each other, causing upper mount  1204  to separate from lower mount  1206  and causing the entire annular shape to increase in height. Alternatively, as wedge links move outward, intermediate links  1208  may be drawn toward each other, causing upper mount  1204  and lower mount  1206  to also be drawn together and causing the entire annular shape to decrease in height. Thus, actuation of z-actuator  712  may result in an overall change in height of z-flexure  508 . 
     In an embodiment, the structure of the z-flexure  508  linkage provides an amplification effect. For example, movement of z-actuator  712  may be amplified by a factor of about 5. Thus, in an embodiment, an increase in z-actuator  712  length of between 50-90 microns places a lateral load on the annular shape of z-flexure  508  that causes a distance between upper mount  1204  and lower mount  1206  to decrease by about 300 micron. Accordingly, an overall height of z-flexure  508  may be correspondingly reduced by about 300 micron. Z-flexure  508  height may be increased in a similar but opposite manner. 
     Referring to  FIG. 13 , a cross-sectional view of a z-flexure is shown in accordance with an embodiment. Given that z-flexure  508  height may be adjusted through transverse loading from z-actuator  712 , a vertical location of an electrostatic transfer head  203  on micro pick up array  103  may also be adjusted. More particularly, upper mount  1204  of z-flexure  508  may be connected to y-linkage coupler  912  and lower mount  1206  may be coupled to distribution plate  308 , or optionally to insulator  1302 . Furthermore, micro pick up array  103  may be connected with micro pick up array mount  828 , which may in turn be connected with distribution plate  308 . Thus, as the distance between upper mount  1204  and lower mount  1206  varies, so may the distance between micro pick up array  103  and y-linkage coupler  912  vary. Accordingly, a vertical location of an electrostatic transfer head  203  on micro pick up array  103  may be varied to compensate for vertical error  1104  created by tipping and tilting of remote center robot  500  linkages. 
     Referring to  FIG. 14 , a graph of parasitic motion of a point of interest as a function of vertical offset between the point of interest and a remote rotational center is shown in accordance with an embodiment. It is now evident that lateral parasitic motion of a point of interest depends upon whether the point of interest is aligned with remote rotational center  1002 . For example, as vertical distance between a point of interest, e.g., an electrostatic transfer head  203  on micro pick up array  103 , and remote rotational center  1002  increases, so may parasitic error  1102  resulting from a given tip or tilt of remote center robot  500  linkages increase. For example, for a first angular position  1402  of micro pick up array  103  about remote rotational center  1002 , e.g., about 0.5 mrad, parasitic error  1102  may increase by an additional parasitic error  1404  based on a given vertical offset. As the given vertical offset varies up to about 180 micron, the additional parasitic error  1404  for the first angular tip or tilt  1402  increase up to about 100 nm. Similarly, for higher tipping or tilting angles between micro pick up array  103  and remote rotational center  1002 , e.g., second angular position  1406 , third angular position  1408 , and fourth angular position  1410 , additional parasitic error  1404  may correspondingly increase for a given vertical offset of the point of interest relative to remote rotational center  1002 . For example, in an embodiment, as vertical offset between the electrostatic transfer head  203  and remote rotational center  1002  varies up to about 180 micron and micro pick up array  103  tilts to fourth angular position  1410  of approximately 2 mrad, parasitic error  1102  may be increased by additional parasitic error  1404  of up to about 375 nm. 
     Numerous factors may lead to vertical offset between a point of interest and remote rotational center  1002 . For example, thermal expansion of linkages during use may move remote rotational center  1002  relative to the point of interest. Accordingly, system features may be introduced to reduce thermal expansion of linkages. In an embodiment, insulator  1302  provides thermal and/or electrical insulation between micro pick up array  103  and z-flexure  508  or other components of remote center robot  500 . Micro pick up array  103  may be heated during micro device transfer, and thus, insulator  1302  may protect structural and electronic components from thermal degradation. Furthermore, thermal insulation may reduce thermal expansion of remote center robot  500  linkages that would change linkage geometries and potentially change remote rotational center  1002  location relative to a target surface, e.g., an electrostatic transfer head  203 . In a production environment, heating elements may be employed near micro pick up array  103  surface to facilitate micro device transfer. As a result, thermal expansion of link arms may be on the order of the movement of remote center robot  500  actuators, e.g., a 10 degree Celsius temperature change may cause a link arm length change of up to about 11 microns. This length change may cause a corresponding shift in remote rotational center  1002  location relative to a point of interest. Thus, insulator  1302  may be used to shield remote center robot  500  linkages from heating elements and reduce thermal expansion. In an embodiment, insulator  1302  may be a separate disk component fastened between distribution plate  308  and z-flexure  508 . Alternatively, insulator  1302  may be integrated within distribution plate  308 , e.g., distribution plate  308  may be formed from, or surrounded by, an insulating material. In any case, insulator  1302  may incorporate an insulating material, such as a ceramic material. 
     Other system and environmental variations, such as manufacturing tolerances inherent in the production of remote center robot  500 , may lead to remote rotational center  1002  drift, and thus, features may be needed to maintain remote rotation center alignment with electrostatic transfer heads. In an embodiment, z-flexure  508  may be used to maintain alignment between a point of interest and remote rotational center  1002 . For instance, if remote rotational center  1002  drifts downward due to thermal expansion of remote center robot  500  linkages, z-flexure  508  may be lengthened to extend micro pick up array  103  toward the relocated remote rotational center  1002  and maintain alignment between an electrostatic transfer head  203  and remote rotational center  1002 . 
     The same factors that can cause remote rotational center  1002  to drift vertically relative to a point of interest may also lead to relative movement between remote tipping center  826  and remote tilting center  922 . For example, even though the linkages of remote center robot  500  may be symmetric, thermal expansion of x-linkage  504  may not exactly match thermal expansion of y-linkage  506 . Thus, either remote tipping center  826  or remote tilting center  922  may become misaligned with a point of interest, causing additional lateral parasitic motion in the direction of the misaligned center of rotation. Accordingly, it may be advantageous to incorporate features in remote center robot  500  to adjust for misalignment between remote tipping center  826  and remote tilting center  922  to allow both centers to simultaneously align with a point of interest. 
     Referring to  FIG. 15 , a cross-sectional plan view of an adjustment mechanism of a remote center robot is shown in accordance with an embodiment. Remote center robot  500  may include a mechanism to adjust x-linkage  504  geometry such that remote rotational center  1002  is formed. More particularly, x-linkage  504  geometry may be varied to adjust a vertical position of remote tipping center  826  along z-axis  510  such that remote tipping center  826  coincides with remote tilting center  922  to form remote rotational center  1002 . 
     In an embodiment, an adjustment mechanism for altering x-linkage  504  geometry includes adjuster link  1502  connected between x-linkage ground  802  and x-linkage right link arm  808 . More particularly, adjuster link  1502  may pivot relative to x-linkage ground  802  link at adjustment joint  1504 , and adjuster link  1502  may pivot relative to x-linkage right link arm  808  at x-linkage upper right joint  810 . Adjuster link  1502  provides an additional degree of freedom to x-linkage  504 , and thus, an additional manner of adjusting x-linkage  504  geometry. More specifically, an adjuster actuator  1506  may alter adjuster link  1502  geometry. Adjuster actuator  1506  may have an adjuster rod length  1508  between an adjuster actuator  1506  end that contacts x-linkage ground  802  and an adjuster actuator  1506  portion fixed relative to adjuster link  1502 . Adjuster actuator  1506  may be actuated to increase adjuster rod length  1508 , and thus, cause adjuster link  1502  to be pushed away from x-linkage ground  802  and pivot about adjustment joint  1504 . As adjuster link  1502  pivots away from x-linkage ground  802  link, x-linkage upper right joint  810  may also move outward, adjusting the relationship between the x-linkage  504  link arms, ground link, and coupler link described above. More particularly, a lateral distance between x-linkage upper right joint  810  and z-axis  510 , or x-linkage upper left joint  806 , may change in proportion to adjuster rod length  1508 . Similarly, an angle between x-linkage right axis  820  and z-axis  510 , or x-linkage left axis  818 , may change in proportion to adjuster rod length  1508 . 
     In an embodiment, rather than relying on an adjuster actuator  1506  to move adjuster link  1502 , adjuster link  1502  may itself have a variable length that alters a distance between x-linkage upper right joint  810  and z-axis  510 . For example, adjuster link  1502  may be a linear actuator, e.g., a piezoelectric linear actuator, having a first end and a second end with a variable distance therebetween. The first end of adjuster link  1502  may be coupled with adjuster joint  1504  at x-linkage ground  802 , while the second end of adjuster link  1502  may be coupled with x-linkage upper right joint  810  at a location laterally offset from adjuster joint  1504 . Thus, the second end may be laterally offset from z-axis  510 . By way of example, adjuster link  1502  may be perpendicular to z-axis  510  between adjuster joint  1504  and x-linkage upper right joint  810 . Adjuster link  1502  may thus be actuated to increase or decrease the distance between x-linkage upper right joint  810  and adjuster joint  1504 , or z-axis  510 . As the lateral distance is changed, the geometric relationships of x-linkage  504  may be varied, e.g., a first angle between x-linkage right link arm  808  and z-axis  510  may change, resulting in a repositioning of remote tipping center  826  along z-axis  510 . 
     Referring to  FIG. 16A , a schematic view of an adjustment mechanism of a remote center robot adjusting a location of a remote tipping center  826  is shown in accordance with an embodiment. In an initial configuration, x-linkage  504  may include x-linkage left axis  818  and x-linkage right axis  820  that extend along the dashed lines to an intersection point at remote tipping center  826 . Although not shown in  FIG. 16A , y-linkage  506  includes similar geometry, e.g., symmetric with the geometry of x-linkage  504 , however remote tilting center  922 , which corresponds to an intersection between y-linkage left axis  918  and y-linkage right axis  920 , may be vertically offset from remote tilting center  922 . Such an offset may have numerous causes, including thermal expansion of link arms, manufacturing tolerance stack ups, or mechanical degradation of system components over time. The offset is exaggerated for illustration purposes, but in reality, the offset may be on the order of several microns. Such a small offset between remote tipping center  826  and remote tilting center  922  may nonetheless cause significant parasitic motion in the direction of movement of the linkage whose remote center is not located at the point of interest. Since such parasitic motion may result in damage to micro devices, in an embodiment, remote tipping center  826  and remote tilting center  922  may be adjusted to align with each other and be located at the point of interest. 
     Referring to  FIG. 16B , a schematic view of an adjustment mechanism of a remote center robot adjusting a location of a remote tipping center is shown in accordance with an embodiment. An adjustment mechanism may be used to alter x-linkage  504  geometry such that remote tipping center  826  is raised along z-axis  510  to align with remote tilting center  922  of y-linkage  506 . Alignment of the remote centers creates a remote rotational center  1002 —a point at which pure rotation may be experienced in any direction when x-linkage  504  and y-linkage  506  are moved. 
     In an embodiment, adjuster link  1502  is pivoted outward relative to x-linkage ground  802  by increasing adjuster rod length  1508 . Adjuster rod length  1508  may correspond to a length of adjuster actuator  1506 . For example, adjuster actuator  1506  may be a linear actuator, e.g., piezoelectric, pneumatic, linear motor, etc., that lengthens or shortens based on actuator loads controlled by computer  108 . In an embodiment, adjuster actuator  1506  may include a manual micrometer having a thumb screw that may be rotated manually to cause a micrometer length to change, and thus, to increase or decrease a distance between x-linkage upper right joint  810  and z-axis  510 , or x-linkage upper left joint  806 . Thus, actuation of adjuster actuator  1506  may cause x-linkage right axis  820 , which is geometrically coupled with x-linkage upper right joint  810 , to splay outward such that an angle between x-linkage right axis  820  and z-axis  510  increases. Similarly, x-linkage left axis  818  may simultaneously splay to maintain symmetry of the angles between the x-linkage  504  link arms and z-axis  510 . Accordingly, x-linkage coupler  812  may rise vertically, and remote tipping center  826  may be brought into alignment with remote tilting center  922 . As discussed above, after aligning remote centers to create remote rotational center  1002 , a location of remote rotational center  1002  may be aligned with a point of interest, such as an electrostatic transfer head  203  on micro pick up array  103 , by adjusting a vertical position of micro pick up array  103  until the point of interest is located at the remote rotational center  1002 . Z-correction enabled by z-flexure  508  may be used to vertically adjust the point of interest to coincide with remote rotational center  1002 . 
     In an embodiment, a control loop may be closed to achieve the goal of evenly distributing pressure across micro pick up array  103 . More particularly, the control loop may process a combination of position and stress inputs to move micro pick up array  103  toward a desired stress state, e.g., to evenly distribute pressure across micro pick up array  103 . Stress inputs may correspond to strain signals provided from strain gauges mounted on micro pick up array  103 . Alternatively, micro pick up array mount  828  may adapt micro pick up array  103  to distribution plate  308  and provide feedback signals corresponding to a stress state of micro pick up array  103 . Thus, micro pick up array  103  may be reoriented to distribute a pressure gradient across a surface of micro pick up array  103  in a predetermined manner. For example, micro pick up array  103  may be reoriented until a magnitude or direction of the pressure gradient across the surface of micro pick up array  103  is a predetermined value. 
     Referring to  FIG. 17 , a perspective view of a micro pick up array mount is shown in accordance with an embodiment. Micro pick up array  103  may be fixed to micro pick up array mount  828 , and micro pick up array mount  828  may include sensors and/or transducers to provide feedback related to a pressure distribution, e.g., a magnitude or direction of a gradient of pressure, throughout micro pick up array mount  828 . 
     For the purpose of reference, the illustrated view may be referred to as a “first side” of micro pick up array mount  828 . In an embodiment, micro pick up array mount  828  includes base  1702  and pivot platform  1704 . Base  1702  and pivot platform  1704  may be interconnected by one or more compliant elements. For example, in the illustrated embodiment, a compliant element may be represented by beam  1706 , which may connect with base  1702  and pivot platform  1704  at one or more pivot locations, such as inner pivots  1708  and outer pivots  1710 . 
     In an embodiment, the lateral extension of beam  1706  around pivot platform  1704  provides a lever arm that allows for bending and torsion in beam  1706 , inner pivots  1708 , and outer pivots  1710  when forces are applied to pivot platform  1704  or to micro pick up array  103  mounted on pivot platform  1704 . More specifically, micro pick up array  103  may be electrostatically clamped to micro pick up array mount  828  at clamp electrodes  1712 , and thus, when a force is applied to pivot platform  1704 , such as when an electrostatic transfer head  203  on a mounted micro pick up array  103  contacts a micro device on a carrier substrate, pivot platform  1704  may deflect relative to base  1702 . This deflection may be accompanied by the development of one or more high strain areas, as represented by dotted line region  1714 , near outer pivots  1710 . Similar strain regions may develop near inner pivots  1708  depending on the location that force is applied to pivot platform  1704 . 
     In an embodiment, one or more displacement sensors  1716  may be integrated with beam  1706  at or near a high strain area. Displacement sensors  1716  may be capable of sensing beam  1706  displacement resulting from loads applied to portions of micro pick up array mount  828 , such as pivot platform  1704 . For example, displacement sensors  1716  may detect movement of beam  1706  directly, or may detect internal deformation to infer movement of beam  506 . 
     Based on feedback from displacement sensors  1716 , remote center robot  500  may adjust a geometry of x-linkage  504 , y-linkage  506 , and/or z-flexure  508  to tip, tilt, or vertically move micro pick up array  103  until a desired amount of and/or a desired distribution of pressure across micro pick up array  103  is sensed by micro pick up array mount  828  sensors. Thus, remote center robot  500  may facilitate active alignment of an array of electrostatic transfer heads  203  on micro pick up array  103  with an array of micro devices on a mating substrate. Alignment within the scope of this description may include a spatial orientation between an array of electrostatic transfer heads  203  on micro pick up array  103  and an array of micro devices on a mating substrate. For example, the spatial orientation representing alignment may be predetermined to include a plane passing through the array of electrostatic transfer heads  203  being parallel to a plane passing through the array of micro devices. Alternatively, the spatial orientation representing alignment may include the planes not being parallel, but rather, being in some predetermined mutual orientation, such as angled such that only a portion of the array of electrostatic transfer heads  203  make contact with respective micro devices when the arrays are brought together. More particularly, the spatial orientation representing alignment of the array of electrostatic transfer heads  203  with the array of micro devices, may be any predetermined spatial orientation. Such spatial orientation may be monitored, sensed, and measured to determine system characteristics such as distribution of pressure across micro pick up array  103 . Thus, the measured system characteristics may be used as a proxy to represent alignment. Active alignment may increase the transfer rate of micro devices, since fine-alignment may be accomplished while picking up, and similarly while releasing, the micro devices. Furthermore, since the array of electrostatic transfer heads  203  may be co-located with remote rotational center  1002 , active alignment may be made on-the-fly without parasitic translation of the array of electrostatic transfer heads  203  that may otherwise smear and damage the array of micro devices. Such on-the-fly adjustments may be useful when a donor substrate, e.g., carrier substrate, and/or a display substrate, e.g., receiving substrate, include surface irregularities and non-planar contours. 
     Referring to  FIG. 18 , a schematic illustration of a control scheme for regulating a remote center robot is shown in accordance with an embodiment. More particularly, the control loop may include multiple sub-loops that process a combination of position and stress inputs. The actuators of remote control robot may be driven by the sub-loops, first toward an initial desired location, and if contact between micro pick up array  103  and a target substrate is sensed, then the initial desired location may be modified to move micro pick up array  103  toward a desired stress state, e.g., to evenly distribute pressure across micro pick up array  103  and/or to achieve a desired level of pressure at one or more locations on micro pick up array  103  based on a deflection of micro pick up array mount  828  compliant elements. 
     A primary input  1802  may define a set of reference signals that correspond to an initial desired state of micro pick up array  103 . More specifically, primary input  1802  may define a target spatial location of micro pick up array mount  828 . Primary input  1802  may correspond to x-linkage  504  and y-linkage  506  being symmetric about z-axis  510  with coupler links orthogonal to z-axis  510 . Furthermore, primary input  1802  may define a location along z-axis  510  toward which micro pick up array  103  is intended to be moved. For example, primary input  1802  may command z-flexure  508  to extend and bring micro pick up array  103  toward an anticipated location of a micro device array or substrate surface. 
     Primary input  1802  may be fed into one of several inner loops, each of which may correspond to an individual actuator. For example, x-actuator inner loop  1804  may correspond to a control loop for controlling x-actuator  704  to cause x-linkage coupler  812 , and thus micro pick up array  103 , to tip about remote rotational center  1002 . Similarly, y-actuator inner loop  1806  may correspond to a control loop for controlling y-actuator  708  to cause y-linkage coupler  912 , and thus micro pick up array  103 , to tilt about remote rotational center  1002 . Also, z-actuator inner loop  1808  may correspond to a control loop for controlling z-actuator  712  to change a height of z-flexure  508 , and thus a location of micro pick up array  103  along z-axis  510 . Therefore, the combination of inner loops allow for the control of actuators that adjust a tip, tilt, and z-spatial orientation of micro pick up array  103  relative to mass transfer tool mount  306 . 
     In an embodiment, inner loop control of remote center robot  500  actuators results in a primary output  1810 . More specifically, primary output  1810  may be an instantaneous geometric configuration of remote center robot  500  resulting from actuator movement. The geometric configuration may be inferred from data supplied by encoders or other sensors that track spatial position of individual remote center robot  500  components. That is, the geometric configuration may include a combination of individual geometric configurations for each remote center robot  500  linkage. For example, primary output  1810  may include a tip position related to a geometric configuration of x-linkage  504  links, a tilt position related to a geometric configuration of y-linkage  506  links, and a z-position related to a height of z-flexure  508 . 
     Primary output  1810  may also relate to a spatial position of micro pick up array mount  828  as inferred from known physical dimensions of remote center robot  500  components. For example, whereas encoder signals included in primary output  1810  may define a spatial position and orientation of a lower surface of z-flexure  508 , e.g., lower mount  1206 , a spatial position and orientation of micro pick up array mount  828  may be inferred through known physical dimensions of insulator  1302  and distribution plate  308  between micro pick up array mount  828  and lower mount  1206 . Alternatively, micro pick up array mount  828  surface location may be sensed directly using, e.g., laser micrometers, accelerometers, etc., to provide spatial orientation feedback that may be included directly in primary output  1810 . Thus, a position of micro pick up array mount  828  may be inferred or sensed to determine whether primary output  1810  has been achieved, i.e., equals the intended primary input  1802 . However, although micro pick up array mount  828  may be driven toward a target substrate to achieve the positional command of primary input  1802 , in some cases, micro pick up array mount  828  may contact the target substrate. Furthermore, once contact is detected, primary input  1802  may be modified by additional commands from several actuator outer loops, to achieve a neutral tip and tilt deformation of micro pick up array mount  828  with a desired pressure distribution across micro pick up array mount  828 . Accordingly, micro pick up array  103  may be driven to a tip deflection, tilt deflection, and z-compression target within an accuracy in the submicron range, e.g., on the order of less than about 250 nm. 
     After contact between an electrostatic transfer head  203  and a micro device has been made, micro pick up array mount  828  may be finely adjusted based on pressure feedback from micro pick up array mount  828 . More particularly, fine adjustment of micro pick up array mount  828  may be enabled in response to system recognition of a contact disturbance  1812 . In an embodiment, enable logic is included to determine whether a contact disturbance  1812  is sensed prior to primary output  1810  achieving the desired primary input  1802 , and if a contact disturbance  1812  is sensed, additional control loops may be closed to permit fine adjustment of remote center robot geometries. More specifically, additional control loops may be closed to drive micro pick up array mount  828  toward tip deflection, tilt deflection, and z-compression targets, rather than toward the initial positional target of primary input  1802 . 
     In an embodiment, a contact disturbance  1812  is sensed when, e.g., micro pick up array  103  contacts a mating substrate out of alignment. For example, if micro pick up array  103  and the mating substrate make contact in perfect alignment, the primary output  1810  may equal the primary input  1802  and micro devices may then be gripped by electrostatic transfer heads  203  without requiring additional adjustment. However, if micro pick up array  103  and the mating substrate are not perfectly aligned, displacement or strain measurements from each sensor on micro pick up array mount  828  may be substantially different from each other and/or the desired level of pressure may not be achieved. That is, in an embodiment, an expected or desired tip, tilt, and compression state must be satisfied prior to initiating electrostatic gripping. If the desired state is not achieved, displacement or strain measurements may be fed as feedback signals  1814 . 
     In an embodiment, feedback signals  1814  correspond to signals from separate sensors that monitor a physical state of micro pick up array mount  828 . For example, laser, proximity, or other distance sensors may monitor a position of different surface locations on micro pick up array mount  828 . Those distances may be correlated to a physical orientation of a portion of micro pick up array mount  828  surface. Alternatively, in an embodiment, a plurality of strain gauges, e.g., displacement sensors  1716 , are distributed across a surface of micro pick up array mount  828 . Each of the strain gauges may sense a strain state and output a corresponding analog signal. For example, feedback signals  1814  may include eight analog signals from eight separate strain gauges. The feedback signals  1814  may be conditioned by a signal conditioning and combination logic  1815  to transform the analog signals into a signal representing a strain state of a respective strain gauge. These conditioned signals may furthermore be combined by signal conditioning and combination logic  1815  to synthesize one or more of a micro pick up array mount  828  compression signal, a micro pick up array mount  828  tilt deflection signal, and a micro pick up array mount  828  tip deflection signal. The synthesized compression and deflection signals may be provided as inputs to dynamic control enable logic  1816 . More particularly, dynamic control enable logic  1816  may observe the one or more synthesized signals to determine that a contact disturbance  1812  has occurred in one or more of a tip, tilt, or z-direction. For example, if a non-zero compression signal is synthesized by signal conditioning and combination logic  1815  that exceeds predetermined limits, dynamic control enable logic  1816  may recognize the contact disturbance  1812 . 
     In response to observing that a contact disturbance  1812  exists, dynamic control enable logic  1816  may close respective outer loops, each of which may be configured to provide output commands to modify the positional command of primary input  1802 . Thus, closing the outer loops may drive the actuators to achieve a desired state of pressure and orientation, rather than driving them to achieve an initial position command. For example, if dynamic control enable logic  1816  observes that a compression contact disturbance  1812  exists, z-actuator outer loop  1818  may be closed to respond to the contact disturbance  1812  by adjusting z-actuator  712 . Likewise, dynamic control enable logic  1816  may respond to tip deflection signals or tilt deflection signals by enabling x-actuator outer loop  1820  or y-actuator outer loop  1822 , respectively. 
     Deflection and compression feedback signals may be passed from signal conditioning and combination logic  1815  to respective outer loops for comparison with deflection command inputs  1840  provided to respective outer loops. In an embodiment, micro pick up array mount  828  deflection command inputs  1840  may correspond to a desired pressure distribution across micro pick up array mount  828  or micro pick up array  103 . Thus, micro pick up array mount  828  deflection command inputs  1840  may represent tip deflection, tilt deflection, and z-compression targets of micro pick up array mount  828 . These targets may be compared to the synthesized compression and deflection feedback signals from signal conditioning and combination logic  1815 , which indicate an instantaneous pressure distribution across micro pick up array mount  828 , to determine a difference. The difference, if any, may then be fed as an error signal to drive respective remote center robot  500  actuators. For example, if tipping of micro pick up array mount  828  is sensed as a contact disturbance  1812  and dynamic control enable logic  1816  observes that the tipping exceeds an allowable amount, x-actuator outer loop  1820  may be closed and the tipping deflection signal may be compared with a micro pick up array mount  828  tip deflection command  1840  to generate a motion control signal that will tip micro pick up array mount  828  toward a desired stress state. The motion control signal may be fed to a servo filter and passed through inverse kinematics calculations to generate an outer loop command output  1830 . In an embodiment, the motion control signal may also be added with other remote center robot motion control signals at one or more of motion summation nodes  1850 . This may be the case, for example, when movement of both x-linkage and y-linkage actuators is required to cause tipping. 
     In order to close the control loop, the outer loop command outputs  1830  may be combined with primary input  1802  and passed back into actuator inner loops. For example, a tipping outer loop command  1830  may be summed with primary input  1802  for x-linkage  504  and passed through x-actuator inner loop  1804 , thereby controlling x-actuator  704  in such a manner that x-linkage  504  tips micro pick up array mount  828  toward a physical state of more even pressure distribution. Respective outer loop commands may be passed through to any actuator inner loop for which a contact disturbance  1812  was sensed. 
     The above control methodology may be performed and repeated until the remote center robot  500  is moved to a location at which pressure distribution across micro pick up array mount  828 , and hence micro pick up array  103 , is uniform and achieves a desired amount of pressure. Thus, remote center robot  500  may be controlled to bring an array of electrostatic transfer heads  203  on micro pick up array  103  into contact with an array of micro devices on a mating substrate. Using the control system described above, if alignment between micro pick up array  103  and the mating substrate is not initially perfect, which would be true of almost every transfer operation, pressure distribution control may be implemented to fine tune the alignment. The control methodology may be performed quickly, e.g., on the order of about 50 ms to sense a contact disturbance  1812 , enable the appropriate outer loop(s), and feed appropriate outer loop control commands to actuators, and thus, complete contact may be rapidly achieved between an array of electrostatic transfer heads  203  and an array of micro devices, enabling efficient transfer between a carrier substrate and a receiving substrate. 
     Although  FIG. 18  provides control loops for managing geometry of x-linkage  504 , y-linkage  506 , and z-flexure  508 , additional control loops may be added to control other linkages and mechanisms of remote center robot  500 . For example, an additional control loop may be used to control adjuster actuator  1506  in an embodiment that includes a remote rotational center  1002  position adjustment mechanism, such as the mechanism described with respect to  FIGS. 15-16B . Although adjuster actuator  1506  may be adjusted manually prior to beginning a transfer operation, such as via a manual micrometer adjustment, adjuster link  1502  geometry may also be controlled on-the-fly using an automated actuator, such as a piezoelectric actuator. Automated actuation of adjuster link  1502  may allow for on-the-fly adjustment of remote rotational center  1002  to compensate for thermal expansion, deformation due to external loads, etc. 
     Such adjustment may also be used to compensate for z-flexure  508  adjustment of micro pick up array  103  along z-axis  510 . For example, the automated adjuster actuator  1506  may be controlled based on z-flexure  508  movement. In an embodiment, if z-actuator inner loop  1808  moves z-flexure  508  a given amount, an adjuster actuator  1506  simultaneously adjusts adjuster actuator  1506  to move adjuster link  1502  in a manner that moves remote tipping center  826  along z-axis  510  by the same amount. A similar adjustment mechanism may be implemented for y-linkage  506  to also allow for on-the-fly adjustment of remote tilting center  922 . Accordingly, both remote tipping center  826  and remote tilting center  922  may be simultaneously adjusted to move remote rotational center  1002  in unison with z-flexure  508  movement of micro pick up array  103 . Thus, remote rotational center  1002  may coincide with a point of interest at all times. 
     Referring to  FIG. 19 , a flowchart illustrating a method of aligning a micro pick up array coupled with a remote center robot relative to a target substrate is shown in accordance with an embodiment. The method may be performed, e.g., during a pick-up or a placement operation as micro devices are transferred from a carrier substrate to a receiving substrate. At operation  1902 , mass transfer tool  100  moves remote center robot  500  along z-axis  510  toward a target substrate, e.g., carrier substrate held by carrier substrate holder  104  or receiving substrate held by receiving substrate holder  106 , according to primary input  1802 . More specifically, micro pick up array  103  held on micro pick up array mount  828  may be moved toward the target substrate along z-axis  510 . Movement of micro pick up array  103  along z-axis  510  may be achieved by adjusting z-flexure  508  height, or by actuating various actuators of mass transfer tool  100 , such as a vertical actuator associated with mass transfer tool mount  306  or a substrate holder. 
     Initially, remote center robot  500  may be in a neutral position, having x-linkage  504  symmetric with y-linkage  506 . Furthermore, there may be no compressive loading applied to micro pick up array  103  or micro pick up array mount  828 . This initial state may correspond to a range of travel over which array of micro devices are physically separated from array of electrostatic transfer heads. During this travel, micro pick up array  103  and the target substrate may have misaligned surfaces, but there may be no indication of this misalignment since the pressure distribution state of micro pick up array mount  828  may be uniform, i.e., all strain gauges may be outputting signals indicating zero strain. 
     At operation  1904 , an electrostatic transfer head  203  may contact a micro device while other electrostatic transfer heads  203  may remain separated from corresponding micro devices. That is, contact may be made while micro pick up array  103  is misaligned with the target substrate. This positional misalignment may be sensed as uneven pressure distribution in micro pick up array mount  828 . For example, a first strain output value from one strain gauge on micro pick up array mount  828  and a different second strain output value from another strain gauge on micro pick up array mount  828  may differ. The strain signals may be provided as feedback signals  1814  and conditioned and combined by into tip deflection, tilt deflection, and compression signals. Dynamic enable control logic  1816  may receive the deflection and compression signals, e.g., a tip deflection signal from a tip sensor on micro pick up array mount  828 . As described above, the tip deflection signal from the tip sensor may actually be a combination of signals from multiple strain gauges, and thus reference to a singular sensor here is not intended to be limiting. For example, at operation  1906 , a plurality of signals from strain gauges on micro pick up array mount  828  may be conditioned and combined by signal conditioning and combination logic  1815  into a tilt deflection signal indicating a contact disturbance  1812 . 
     Dynamic enable control logic  1816  may observe that the contact disturbance  1812  exists, and depending upon the level of contact disturbance  1812 , may activate actuator outer loops to determine driving signals for actuating various actuators of remote center robot  500  in order to adjust an orientation of micro pick up array  103  such that pressure distribution across micro pick up array mount  828  is uniform. For example, at operation  1908 , in response to the tip signal being recognized as a contact disturbance  1812  above a threshold, x-actuator outer loop  1820  may feed command signals  1830  to x-actuator inner loop  1804  in order to actuate x-actuator  704  and move x-linkage  504  such that x-linkage coupler  812  tips about remote rotational center  1002 . Similarly, at operation  1910 , in response to the tilt deflection signal being recognized as a contact disturbance  1812  above a threshold, y-actuator outer loop  1822  may feed command signals to y-actuator inner loop  1806  in order to actuate y-actuator  708  to move y-linkage  506  such that y-linkage coupler  912  tilts about remote rotational center  1002 . 
     At operation  1912 , in response to actuation of x-actuator  704  and y-actuator  708  based on the tip deflection signal and the tilt deflection signal, micro pick up array  103  may be rotated into alignment with the target substrate. Furthermore, with remote rotational center  1002  co-located with the contact surface of micro pick up array  103 , electrostatic transfer heads  203  on micro pick up array  103  may experience pure rotation about remote rotational center  1002 . Thus, as micro pick up array  103  is aligned with the target substrate, the electrostatic transfer heads  203  may experience minimal parasitic lateral motion and micro devices may remain undamaged. 
     Actuation of remote center robot  500  according to tip, tilt, and z-compression signals may continue until electrostatic transfer heads  203  on micro pick up array  103  are in contact with micro devices on the target substrate. More particularly, actuation may continue until primary output  1810  is within the limits set by primary input  1802 , at which point actuation may be stopped. As discussed above, primary output  1810  may be a positional output that is modified to reach a desired micro pick up array mount  828  state. For example, actuation of remote center robot  500  may continue until primary positional input is achieved and/or pressure distribution across micro pick up array mount  828  is uniform. 
     After contact between the array of electrostatic transfer heads  203  and the micro devices is made, a voltage may be applied to the array of electrostatic transfer heads  203  to create a grip pressure on the array of micro devices. An electrostatic voltage may be applied to electrostatic transfer heads  203  through various contacts and connectors, e.g., operating voltage leads, operating voltage traces, operating voltage vias, etc. Such electrical contacts and connectors may be integrated within remote center robot  500  components and powered by voltage supplies based on control signals from computer  108 . For example, computer  108  may implement a control algorithm instructing that electrostatic transfer heads  203  be activated if a predefined deformation is simultaneously sensed by each displacement sensor on micro pick up array mount  828  during a pick up process. As a result, the array of electrostatic transfer heads  203  may apply a gripping pressure to the array of micro devices after the entire array surface is in contact and uniform pressure is applied across the array. 
     After gripping the micro devices with electrostatic transfer heads  203 , the micro devices may be picked up from carrier substrate. For example, z-flexure  508  and/or mass transfer tool  100  actuators may be controlled by computer  108  to retract micro pick up array  103  from the target substrate. During pick up, the electrostatic voltage supplied to the array of electrostatic transfer heads  203  may persist, and thus, the array of micro devices may be retained on the electrostatic transfer heads  203  and removed from the carrier substrate. 
     During the pick up operation, a heating element may direct heat toward micro pick up array mount  828  and/or micro pick up array  103 . Thus, the micro devices may be heated through contact with electrostatic transfer heads  203  on micro pick up array  103  during pick up. For example, a heating element adjacent to micro pick up array mount  828  may be resistively heated to transfer heat to micro pick up array  103 , and thus, to the micro devices through the electrostatic transfer heads  203 . Heat transfer may occur before, during, and after picking up the array of micro devices from carrier substrate. 
     Although a pick up process is described in relation to  FIG. 19 , a similar methodology may be used to control the placement of micro devices onto a receiving substrate, such as a display substrate, held by receiving substrate holder  106 . For example, as the micro devices are gripped by the array of electrostatic transfer heads  203 , mass transfer tool  100  may move the receiving substrate under micro pick up array  103  using x-y stage  110 . Accordingly, micro pick up array  103  may be aligned with a target region of the receiving substrate. Micro pick up array  103  may be advanced toward, and aligned with, the receiving substrate using the control sequence described above until the array of micro devices held by the array of electrostatic transfer heads  203  are placed in uniform contact with the target region. Uniform contact may be inferred by sensing a strain state of micro pick up array mount  828 . Subsequently, voltage may be removed from the electrostatic transfer heads  203  to release the micro devices onto the receiving substrate and complete the transfer operation. 
     Referring to  FIG. 20 , a schematic illustration of a computer system is shown that may be used in accordance with an embodiment. Portions of embodiments of the invention are comprised of or controlled by non-transitory machine-readable and machine-executable instructions which reside, for example, in machine-usable media of a computer  108 . Computer  108  is exemplary, and embodiments of the invention may operate on or within, or be controlled by a number of different computer systems including general purpose networked computer systems, embedded computer systems, routers, switches, server devices, client devices, various intermediate devices/nodes, stand-alone computer systems, and the like. Furthermore, although some components of a control system, e.g., signal conditioning and combination logic  1815  and dynamic control enable logic  1816 , have been broken out for discussion separately above, computer  108  may integrate those components directly or include additional components that fulfill similar functions. 
     Computer  108  of  FIG. 20  includes an address/data bus  2002  for communicating information, and a central processor  2004  coupled to bus  2002  for processing information and instructions. Computer  108  also includes data storage features such as a computer usable volatile memory, e.g. random access memory (RAM)  2006 , coupled to bus  2002  for storing information and instructions for central processor  2004 , computer usable non-volatile memory  2008 , e.g. read only memory (ROM), coupled to bus  2002  for storing static information and instructions for the central processor  2004 , and a data storage device  2010  (e.g., a magnetic or optical disk and disk drive) coupled to bus  2002  for storing information and instructions. Computer  108  of the present embodiment also includes an optional alphanumeric input device  2012  including alphanumeric and function keys coupled to bus  2002  for communicating information and command selections to central processor  2004 . Computer  108  also optionally includes an optional cursor control  2014  device coupled to bus  2002  for communicating user input information and command selections to central processor  2004 . Computer  108  of the present embodiment also includes an optional display device  2016  coupled to bus  2002  for displaying information. 
     The data storage device  2010  may include a non-transitory machine-readable storage medium  2018  on which is stored one or more sets of instructions (e.g. software  2020 ) embodying any one or more of the methodologies or operations described herein. For example, software  2020  may include instructions, which when executed by processor  2004 , cause computer  108  to control mass transfer tool  100  or remote center robot  500  according to the control scheme described above for aligning a micro pick up array  103  with a target substrate. Software  2020  may also reside, completely or at least partially, within the volatile memory, non-volatile memory  2008 , and/or within processor  2004  during execution thereof by computer  108 , volatile memory  2006 , non-volatile memory  2008 , and processor  2004  also constituting non-transitory machine-readable storage media. 
     As used above, “coupling”, “fastening”, “joining”, “retaining”, etc., of one component against or with another may be accomplished using various well-known methods, such as bolting, pinning, clamping, thermal or adhesive bonding, etc. The use of such terms is not intended to be limiting, and indeed, it is contemplated that such methods may be interchangeable in alternative embodiments within the scope of the invention. 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope of the invention as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.

Metadata:
Filing Date: 20140508
Publication Date: 20161220
Grant Date: 20161220
Priority Date: 20140508
Inventors: PARKS PAUL ARGUS
LIGHT NILE ALEXANDER
BATHURST STEPHEN P.
HIGGINSON JOHN A.
BIBL ANDREAS
Assignee: APPLE INC
CPC Classifications: [{"code": "Y10T74/20354", "inventive": false, "first": false, "tree": "[]"}, {"code": "B25J18/007", "inventive": true, "first": false, "tree": "[]"}, {"code": "B25J9/0015", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2224/7565", "inventive": false, "first": false, "tree": "[]"}, {"code": "B25J9/0015", "inventive": true, "first": false, "tree": "[]"}, {"code": "B25J7/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "B25J7/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "B25J18/007", "inventive": true, "first": false, "tree": "[]"}, {"code": "B25J7/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "B25J18/007", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2224/75822", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y10T74/20354", "inventive": false, "first": false, "tree": "[]"}, {"code": "B25J9/0015", "inventive": true, "first": false, "tree": "[]"}, {"code": "B25J9/0015", "inventive": true, "first": false, "tree": "[]"}, {"code": "B25J7/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "Y10T74/20354", "inventive": false, "first": false, "tree": "[]"}, {"code": "B25J18/007", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2224/75822", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/7565", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 53005711