Self-assembly of semiconductor die onto a leadframe using magnetic fields

Integrated circuits may be assembled by placing a batch of integrated circuit (IC) die on a leadframe. Each of the IC die includes a magnetically responsive structure that may be an inherent part of the IC die or may be explicitly added. The IC die are then agitated to cause the IC die to move around on the leadframe. The IC die are captured in specific locations on the leadframe by an array of magnetic domains that produce a magnetic response from the plurality of IC die. The magnetic domains may be formed on the lead frame, or may be provided by a magnetic chuck positioned adjacent the leadframe.

FIELD OF THE DISCLOSURE

This disclosure relates to self-assembly of components, such as semiconductor die on a leadframe, using magnetic fields.

BACKGROUND OF THE DISCLOSURE

In electronics manufacturing, integrated circuit packaging is the final stage of semiconductor device fabrication, in which an individual die of semiconducting material is encapsulated in a supporting case that prevents physical damage and corrosion. The case, known as a “package,” supports the electrical contacts which connect the device to a circuit board. Typically, the die is mounted on a lead frame, which may be fabricated from a metal, for example, copper, and includes a number of leads which are secured to the frame. One well known method of connecting the contact pads on the die to the lead frame is wire bonding.

Flip chip technology is a surface mount technology in which the semiconductor die is “flipped” over such that the active surface of the die faces downward to the interconnect substrate. For flip chip packaging, a leadframe may be used as the interconnect substrate to produce a plastic molded enclosure, also referred to as a “molded package.” Electrical contact between the active surface of the die and the interconnect substrate is achieved by utilizing an area array of small solder “bumps” that are planted on pads on the active surface of the die. After the die is placed faced down on the interconnect substrate, the temperature is increased and the solder in the flip chip solder bumps reflows thereby bonding the die directly to the interconnect on the substrate. As such, the die makes electrical and mechanical connection directly to the interconnect substrate without the use of bond wires.

During assembly, a pick and place machine may be used to pick each individual die from a supply tray and place the die in a designated location on a lead frame strip that may hold dozens or hundreds of die. After packaging, the completed individual packages may be cut apart.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE DISCLOSURE

In the past, die placement has been done on a pick-and-place basis where a single die is placed one at a time by a machine. This is a serial process and may be a bottle neck in the integrated circuit (IC) product manufacturing line.

Embodiments of this disclosure may address the pick and place bottle neck by using magnetic self-assembly of dies on a lead frame through the implementation of selective magnetic pole induction on the lead frame and die. The magnetic fields may be configured such that the die is self aligning and self registering. The leadframe strip may then be “submerged” in a volume of dies and through random mechanical vibrations the magnetic fields are able simultaneously co-align and register a large number of die to the lead frame in desired places.

Embodiments of magnetic self-assembly disclosed herein relies on magnetic coupling and stochastic processes, also referred to as “random processes,” rather than mechanical handling and deterministic die placement. This method may be used to massively parallelize the die placement process and does not require direct placement of dies by handling machinery, as will be described in more detail below.

FIG. 1is a side view of an example component100positioned above an example substrate110to illustrate interaction of magnetic fields that may be produced therein. In this illustration, component100may be an integrated circuit (IC) die, for example. Example substrate110may be a portion of a lead frame strip, for example.

In the case that component100is an IC die, it may include a body101that is typically silicon on which may be formed transistors that are interconnected by multiple layers of conductive interconnect material, as is well known. As will be described in more detail below, a magnetically responsive structure102may be formed on a top surface or bottom surface of IC die100. Magnetically responsive structure102may include multiple individual magnetically responsive domains that each may produce a magnetic field, as indicated at103.

Similarly, as will be described in more detail below, a substrate110may include an array of individual magnetic domains112, such as domains1121-1123, that each may produce a magnetic field, as indicated at113. Various ones of the array of magnetic domains112may be positioned and/or activated so that component100is captured in a specific location due the magnetic attraction/repulsion of magnetically responsive structure102to the array of magnetic domains112.

In the case that that component100is an IC die and substrate110is a leadframe, an array of magnetic domains112may be positioned, or activated, at each location across substrate110where an IC die is supposed to be positioned during the packaging process. The leadframe strip may then be “submerged” in a volume of dies and through random mechanical vibrations the magnetic fields are able simultaneously co-align and register a large number of die to the lead frame in the desired place.

FIG. 2Ais a side view of a substrate200illustrating an embodiment of an array of magnetic domains202. In this example, the array of magnetic domains202include multiple individual domains, such as indicated at201. The arrow included within each individual domain indicates the direction of magnetic flux produced by that individual domain. Resultant flux fields such as indicated at203may then be formed on the surface of substrate200.

Each array202may contain several dozen, or evens several hundred, individual magnetic domains201. Each array202may cover an area on a surface of substrate200that conforms to the foot print of the component that is intended to be positioned in a particular location. Depending on the size of the intended component and the size of the individual magnetic domains201, the surface area size of array202may be the same as, larger, or smaller then the size of the intended component.

In some embodiments, array202may be formed in a layer that covers a large portion of substrate200. Individual domains201may be “programmed” by an external force, such as an electrical or magnetic field, a laser impulse, etc, that is applied to substrate200in order to activate specific regions of the layer and thereby activate an array of magnetic domains in a particular position on the surface of substrate200.

In some embodiments, substrate200may be reconfigured at different times by reapplying the external force in order to capture components in different locations at different times.

In some embodiments, array202may be formed by “printing” a magnetic material onto substrate200using a three dimensional (3D) additive process, for example.

In some embodiments, array of magnetic domains202may be embedded into substrate200. In other embodiments, array of magnetic domains202may be formed on the top surface of substrate200, or in some embodiments on the bottom surface of substrate200. In either case, the top surface of substrate200will be configured to be smooth enough to allow components to move around on the surface, as will be described in more detail below.

FIG. 2Bis a side view of a substrate210illustrating an embodiment of an array of magnetic domains212. In this example, the array of magnetic domains212include multiple individual domains, such as indicated at211. In this example, each magnetic domain is formed by an electromagnet that is activated by a wire/coil such as indicated at214. Resultant flux fields such as indicated at203may then be formed on the surface of substrate200.

Each array212may contain several dozen, or evens several hundred, individual magnetic domains211. Each array212may cover an area on a surface of substrate210that conforms to the foot print of the component that is intended to be positioned in a particular location. Depending on the size of the intended component and the size of the individual magnetic domains211, the surface area size of array212may be the same as, larger, or smaller then the size of the intended component.

In some embodiments, array212may be formed in a layer that covers a large portion of substrate210. Individual domains211may be activated by a control signal applied to each wire214in order to activate specific regions of the layer and thereby activate an array of magnetic domains in a particular position on the surface of substrate210. In this case, the magnetic domains may be controlled in a similar manner to pixels in an image device in which individual pixels may be turned on and off in order to form an image. The magnetic domains may be organized as “rows” and “columns” and controlled by circuitry in a similar manner as pixels in an image device, for example.

Substrate210may be reconfigured at different times by reapplying the control signals in order to capture components in different locations at different times, or to move components, as will be described in more detail below.

FIG. 2Cis a side view of another embodiment that may use a substrate such as substrate210behind another layer of material220to form flux fields213that extend through layer220that may be used to capture components that are placed on a surface of layer220. For example, layer220may be a copper leadframe strip onto which IC dies may be positioned by flux fields213. Once the IC dies are positioned and affixed, substrate210may be removed. In this example, substrate210may be referred to as a “magnetic chuck.”

FIG. 3is a top view of an example lead frame strip320. Lead frame strip320may include one or more arrays of individual lead frames. Lead frame strip320is typically fabricated from a copper sheet that is etched or stamped to form a pattern of thermal pads and contacts. Lead frame strip320may be plated with tin or another metal that will prevent oxidation of the copper and provide a lower contact surface that is easy to solder. An IC die may be attached to each individual lead frame.

Each individual leadframe may include a thermal pad, such as thermal pads321,322. Each individual lead frame also includes a set of contacts that surround the thermal pad, such as contacts323,324. A sacrificial strip of metal connects all of the contacts together and provides mechanical support until a sawing process removes it. An IC die, also referred to as a “chip,” is attached to each thermal pad during a packaging process. Wire bonding may then be performed to connect bond pads on each IC chip to respective contacts on the lead frame. The entire lead frame strip320may then be covered with a layer of mold compound to encapsulate the ICs. Lead frame strip320may then be singulated into individual packaged ICs by cutting along cut lines328,329.

FIG. 4is a top view of an example substrate410that includes an example arrangement of arrays of magnetic domains412. Substrate410may be constructed in a similar manner to substrate200as shown inFIG. 2A. In this case, each array of magnetic domains410may be similar to array202as shown inFIG. 2A. In some embodiments, an array of magnetic domains may be formed in a layer that covers a large portion of substrate410, as indicated at415,416. Individual domains within each array412may be “programmed” by an external force, such as an electrical or magnetic field, a laser impulse, etc, that is applied to substrate410in order to activate specific regions of the layer and thereby activate an array of magnetic domains in a particular position on the surface of substrate410. In some embodiments, substrate410may be reconfigured at different times by reapplying the external force in order to capture components in different locations at different times.

In another embodiment, substrate410may be constructed in a similar manner to substrate210as shown inFIG. 2B. In this case, each array of electromagnetic domains410may be similar to array212as shown inFIG. 2B. In some embodiments, an array of electromagnetic domains may be formed in a layer that covers a large portion of substrate410, as indicated at415,416. Individual domains within each array412may be activated by a control signal applied to each electromagnet, such as each wire214inFIG. 2B, in order to activate specific regions of the layer and thereby activate an array of magnetic domains in a particular position on the surface of substrate410. In this case, the magnetic domains may be controlled in a similar manner to pixels in an image device in which individual pixels may be turned on and off in order to form an image. The magnetic domains may be organized as “rows” and “columns” and controlled by circuitry in a similar manner as pixels in an image device, for example.

In some embodiments, substrate410may be used to position IC dies on a leadframe for packaging. In this case, in some embodiments substrate410may be the leadframe strip, as illustrated inFIG. 3, in which each array of magnetic domains412may correspond to a thermal pad such as321,322. In other embodiments, substrate410may be positioned adjacent a leadframe during the assembly process, as illustrated inFIG. 2C. The various arrays of magnetic domains412may be arranged to correspond to the placement of dies on the leadframe, for example.

FIGS. 5A and 5Billustrate a side view of an example configuration of a component540being magnetically assembled onto a substrate500. In this example, component540may be an IC die and substrate500may be a leadframe, for example. In this example, substrate500may be similar to substrate200as shown inFIG. 2A. As described in more detail with regards toFIG. 2A, an array of magnetic domains502may be formed on substrate500at a location where IC die540is to be placed. In this example, IC die540is positioned on thermal pad521that is part of leadframe500.

IC die540may include an epitaxial (epi) layer in which is formed various semiconductor devices. These semiconductor devices may be interconnect by conductive traces that may be formed in one or more layers of conductive material formed over the epi layer. One or more of these conductive layers may include metallic material that may have magnetic properties. For example, in this example, top interconnect layer544may include copper, nickel and palladium, for example. In this manner, a magnetically responsive structure may be an inherent part of IC device540.

In another embodiment, a magnetically responsive structure may be formed on a top surface or on a bottom surface of IC die540. In some embodiments, a magnetically responsive structure may be printed on the top surface or on the bottom surface of IC die540using a 3D additive process, for example.

In another embodiment, a magnetically responsive structure on the surface of IC die540may include a conductive loop that may be selectively powered by an external energy source. For example, IC die540may include a structure to receive energy in a near field communication (NFC) mode of operation that may then be used to activate the conductive loop to form an electromagnet. Alternatively, a radio frequency identification (RFID) structure may be implemented on IC die540to receive energy in a near field RFID mode of operation that may then be used to activate the conductive loop to form an electromagnet.

In this example, only a single IC540is illustrated for clarity; however, leadframe500may have locations for hundreds of IC die, for example, that may all be positioned simultaneously. As will be described in more detail below, multiple IC die540may be placed on the surface of leadframe500in a random manner. Leadframe500may then be shaken or vibrated, for example, to agitate the multiple IC die. Individual IC die540may then be captured in specific locations on the surface of leadframe500by magnetic attraction between the array of magnetic domains502at each specific location and the magnetically responsive structure on each IC die540.

Once the IC die are properly positioned, they may be affixed to that location, as illustrated inFIG. 5B. In some embodiments, an adhesive542may be used to affix IC540to leadframe500. For example, adhesive542may be a B-stage epoxy film that is applied to the surface of leadframe500, patterned, and etched using known or later developed IC fabrication techniques to form an adhesive pad on each thermal pad of leadframe500. While the multiple IC die are being agitated, the B-stage epoxy pad542may be in a partially cured state that is not sticky. B-stage epoxy pad542may be relatively thin and therefore does not impede the movement of IC die540while it is being positioned. Once the IC die are properly positioned, the entire leadframe and IC die may be heated to activate the B-stage epoxy and thereby permanently affix the IC die540to the leadframe500.

In another embodiment, the magnetic attraction between the array of magnetic domains502and the magnetically responsive structure in IC die540may be sufficient to affix the IC die in position for further processing without the need for an adhesive.

Further processing may then be performed to package the IC die. For example, wire bonds544may be installed between bond pads541on the IC die540and contacts523on leadframe500. The entire assembly may then be encapsulated and sawn into individual packaged ICs.

FIGS. 6A and 6Billustrate a side view of an example configuration of a component540being magnetically assembled onto a substrate600. In this example, component540may be an IC die and substrate600may be a leadframe, for example. A second substrate610may be positioned adjacent substrate600. In this example, substrate610may be similar to substrate210as shown inFIG. 2B. As described in more detail with regards toFIG. 2B, an array of magnetic domains612may be formed on substrate610at a location where IC die540is to be placed. In this example, IC die540is positioned on heat dissipation pad621that is part of leadframe600.

In some embodiments, array612may be formed in a layer that covers a large portion of substrate610. Individual domains may be activated by a control signal applied to an electromagnet in each magnetic domain in order to activate specific regions of the layer and thereby activate an array of magnetic domains in a particular position on the surface of substrate610. In this case, the magnetic domains may be controlled in a similar manner to pixels in an image device in which individual pixels may be turned on and off in order to form an image. The magnetic domains may be organized as “rows” and “columns” and may be controlled by circuitry in a similar manner as pixels in an image device, for example.

As described above, IC die540may include an epitaxial (epi) layer in which is formed various semiconductor devices. These semiconductor devices may be interconnect by conductive traces that may be formed in one or more layers of conductive material formed over the epi layer. One or more of these conductive layers may include metallic material that may have magnetic properties. For example, in this example, top interconnect layer544may include copper, nickel and palladium, for example. In this manner, a magnetically responsive structure may be an inherent part of IC device540. In another embodiment, a magnetically responsive structure may be formed on a top surface or on a bottom surface of IC die540. In some embodiments, a magnetically responsive structure may be printed on the top surface or on the bottom surface of IC die540using a 3D additive process, for example.

In this example, only a single IC540is illustrated for clarity; however, leadframe600may have locations for hundreds of IC die, for example, that may all be positioned simultaneously. As will be described in more detail below, multiple IC die540may be placed on the surface of leadframe600in a random manner. Leadframe600and substrate610together may then be shaken or vibrated, for example, to agitate the multiple IC die. Individual IC die540may then be captured in specific locations on the surface of leadframe600by magnetic attraction between the array of magnetic domains612at each specific location and the magnetically responsive structure on each IC die540.

As described above, once the IC die are properly positioned, they may be affixed to that location, as illustrated inFIG. 6B. In some embodiments, an adhesive542may be used to affix IC540to leadframe600. Once the IC die are properly positioned, the entire leadframe and IC die may be heated to activate the B-stage epoxy and thereby permanently affix the IC die540to the leadframe600.

Further processing may then be performed to package the IC die. For example, wire bonds544may be installed between bond pads541on the IC die540and contacts623on leadframe600. The entire assembly may then be encapsulated and sawn into individual packaged ICs.

FIG. 7illustrates a side view of an example configuration of a component740being magnetically assembled onto a substrate600. This example is similar to the example ofFIG. 6A. In this example, component740may have a magnetically responsive structure744formed on the back side of die740opposite from bond pads541. In some embodiments, a magnetically responsive structure may be printed on the top surface or on the bottom surface of IC die740using a 3D additive process, for example.

FIGS. 8A and 8Billustrate a side view of an example configuration of a component840being magnetically assembled onto a substrate800. In this example, component840may be an IC die and substrate800may be a leadframe, for example.

A second substrate810may be used as a magnetic chuck. In this example, substrate810may be similar to substrate210as shown inFIG. 2B. As described in more detail with regards toFIG. 2B, an array of magnetic domains812may be formed on substrate810at a location where IC die840is to be placed.

In some embodiments, array812may be formed in a layer that covers a large portion of substrate810. Individual domains may be activated by a control signal applied to an electromagnet in each magnetic domain in order to activate specific regions of the layer and thereby activate an array of magnetic domains in a particular position on the surface of substrate810. In this case, the magnetic domains may be controlled in a similar manner to pixels in an image device in which individual pixels may be turned on and off in order to form an image. The magnetic domains may be organized as “rows” and “columns” and may be controlled by circuitry in a similar manner as pixels in an image device, for example.

In this example, component840may have a magnetically responsive structure844formed on the back side of die840opposite from bond pads841. In some embodiments, a magnetically responsive structure may be printed on the top surface or on the bottom surface of IC die840using a 3D additive process, for example.

In this example, a set of IC die840may be first captured at designated locations using electromagnetic arrays812in a similar manner as described above. However, in this case, the IC die840are positioned with their bond pads841facing away from magnetic chuck810. After the IC die840are captured by magnetic chuck810, magnetic chuck810may be inverted so that the IC die840are suspended, as illustrated inFIG. 8A.

In this example, only a single IC840is illustrated for clarity; however, leadframe800may have locations for hundreds of IC die, for example, that may all be positioned simultaneously. As will be described in more detail below, multiple IC die840may be placed on the surface of magnetic chuck810in a random manner. Magnetic chuck810may then be shaken or vibrated, for example, to agitate the multiple IC die. Individual IC die840may then be captured in specific locations on the surface of magnetic chuck810by magnetic attraction between the array of magnetic domains812at each specific location and the magnetically responsive structure on each IC die840.

Magnetic chuck810may then lower the IC die840onto leadframe800where they may be further assembled as “flip chips,” as illustrated inFIG. 8B. In this example, bond pads841may be coated with solder or other material that may be used to provide a conductive connection between bond pads841and leadframe contacts823.

In this example, magnetic domains812are formed by electromagnets that may be deactivated after the IC dies840are positioned on leadframe800. In another embodiment, magnet chuck810may use permanent magnetic domains. In this case, the magnetic chuck may remain in place until the IC dies are affixed to the leadframe. The magnetic chuck may then be slid laterally to release it from the IC die, for example.

FIG. 8Cis a side view illustrating another embodiment in which a second IC die850is positioned on top of IC die840in a multichip module (MCM) configuration. In this case, IC die840may be positioned with magnetic chuck810and then captured on substrate800, as described above. Magnetic chuck810may then be exposed to another set of die to capture and place them in the same manner as described above.

Referring back toFIG. 5A, 6A, or7, for example, an MCM may be created by first flooding a substrate with a first type of chips, agitating them and capturing them as described above, then flooding the substrate with a second type of chips, agitating them and capturing them in a stacked MCM configuration.

FIG. 9is an illustration of magnet domains that may be inherently formed in an interconnect layer of an integrated circuit, such as IC die540as illustrated inFIG. 5A. IC die540may include an epitaxial (epi) layer in which is formed various semiconductor devices. These semiconductor devices may be interconnect by conductive traces that may be formed in one or more layers of conductive material formed over the epi layer. One or more of these conductive layers may include metallic material that may have magnetic properties. For example, in this example, top interconnect layer544may include copper, nickel and palladium, for example. Palladium has paramagnetic properties, which means it may be attracted to a magnetic flux field, but does not retain any permanent magnetism. In this manner, a magnetically responsive structure may be an inherent part of IC device540.

The various conductive traces in interconnect layer544may have different orientations, such as vertical traces such as trace9441and horizontal traces such as trace9442. Depending on the overall topology of interconnect layer944, there may be a dominant magnetic response direction. In this example, magnetic response direction946is approximately parallel to vertical trace9441.FIG. 10illustrates an example IC die1040that has a different topology in interconnect layer1044. In this example, the dominant magnetic response orientation1046may be skewed approximately 30 degrees from vertical, for example.

FIG. 11is an illustration of a calibration process that may be performed on a component, such as component1040, in order to determine a dominant magnetic response of the component. Each type of IC die may be calibrated to determine the shape and/or orientation of a magnetic response produced by a magnetically responsive structure that is part of the IC die. In a similar manner, other types of components that may have an inherent or an explicitly added magnetically responsive structure may be calibrated to determine the dominant magnet response of the component.

Based on the calibrated dominant magnet response orientation of a particular component, the array of magnetic domains in a substrate such as substrate200as shown inFIG. 2Aor substrate212as shown inFIG. 2Bmay be configured or controlled to produce a magnetic field that is aligned with the dominant magnetic response of the component so that the component is positioned correctly on the substrate in response to the magnet field produced by the array of magnetic domains in the substrate.

As illustrated inFIG. 11, the strength of various magnetic domains in array1112may be adjusted to cause a component, such as component1040as shown inFIG. 10for example, that is being calibrated to rotate as indicated at1047until it is positioned in a desired orientation. Array1112may be located on a test substrate. Alternatively, array1112may be part of a chuck, such as chuck810as shown inFIG. 8A. Alternatively, array1112may be a part of a substrate210as shown inFIG. 2B, for example.

FIGS. 12-14are illustrations of magnetically orienting and capturing a group of components1240on a substrate1200. In this example, substrate1200is representative of any of the substrates described above, such as substrate200,210,410, leadframe500, substrate610overlaid by leadframe600, and chuck810.

In this example, nine arrays of magnetic domains1212are illustrated for simplicity. It is to be understood that a typically embodiment may include several tens or hundreds of arrays of magnetic domains1212. Each array of magnetic domains1212is representative of an array of permanent magnets such as array202shown inFIG. 2Aor an array of electromagnets such as array212shown inFIG. 2B.

In this example, components1240are representative of any of the components described above in more detail, such as component540as shown inFIG. 5A, component740as shown inFIG. 7, component840as shown inFIG. 8A, or other components that include a magnetically responsive magnetic structure. In this example, the dominant magnetic response orientation of component1240is approximately perpendicular to one side of component1240, as illustrated at1246. As described above with regard toFIGS. 11 and 12, other components may have a dominant magnetic response that is oriented differently than component1240. In that case, the magnetic field produced by each array of magnetic domains1212may be adjusted accordingly so that when the component is captured by an array of magnetic domains1212it will be oriented properly.

Initially, a large number of components1240may be placed on a surface of substrate1200. This may be done in many ways, such as by “submerging” substrate1200in a container holding components1240, or by simply dumping a batch of components on substrate1200, for example. In any case, the components1240may initially have a random arrangement as illustrated inFIG. 12.

Substrate1200may then be agitated as illustrated at1250,1251with enough force so that components1240are encouraged to move around on the surface of substrate1200but not with too much force that prevents each array of magnetic domains1212from capturing one of the components1240using only magnetic attraction between the array of magnetic domains1212and the magnetic response of each component1240.

FIG. 13illustrates substrate1200after a period of time in which one component1240has been captured by each array of magnetic domains1212in a specific location determined by each array of magnetic domains1212. After all of the available locations are filled, excess components may be removed from substrate1200, as indicated by removed components1340. Components may be removed by further agitation of substrate1200, by tipping substrate1200, etc.

FIG. 14illustrates another aspect of magnetic self-assembly. In this example, a position indicated at1450has inadvertently been left open after the process of agitation, as described with regard toFIGS. 12 and 13. A visual inspection system indicated at1460may be used to detect such omissions. Visual inspections systems are well known and need not be described in detail herein.

In this example, substrate1400may be the same or similar to substrate1200as shown inFIGS. 12 and 13. In this case, under direction from visual inspection system1460, the array of magnetic domains14121that are holding component12401may be deactivated to thereby allow component12401to move towards array of magnetic domains14122in response to substrate1400being agitated. Visual inspection system1460may monitor the movement of component12401and reactivate the array of magnetic domains14121so that it may then capture component12402to thereby fill all of the locations.

In some embodiments, substrate1400may include additional arrays of magnetic domains such as those indicated at1413. In this case, various ones of arrays1413may be activated under direction of visual inspection system1460to encourage component12401to move towards location1450.

In some embodiments, the surface of substrate1400may be substantially covered with a large array of magnetic domains. In this case, a component such as component12401may be moved along a path from array14121to array14122by sequentially activating various small sets of magnetic domains along a path between array14121and array14122. Similarly, a component12402may be moved along a path from its current position to array14121by sequentially activating various small sets of magnetic domains along a path towards array14121. In this case, components may be moved without needing to agitate substrate1400.

FIG. 15illustrates a situation where one of the components1240is upside down at location1550. Visual inspection system1460may detect that component1240at location1550is upside down. Array of magnetic domains14122may be manipulated by turning on certain domains and turning off other domains so that a magnetic field is formed that repels one side of component1240at location1550in order to cause that component1240to stand up on edge as indicated at1551, which may be monitored by visual inspection system1460. Array of magnetic domains14122may then be manipulated to turn on a different set of domains to cause component1240at location1550to lie down in a correct position. In this manner, one or more components1240may be flipped over to lie in a correct orientation. While two steps are suggested here, more than two manipulations of array of magnetic domains14122may be required to cause component1240to flip over.

FIG. 16is an illustration of a quad-flat no-leads (QFN) IC package1600that was assembled using magnetic self-assembly as described herein. In this figure, the bottom side of QFN package1600is illustrated. Flat no-leads packages such as quad-flat no-leads (QFN) and dual-flat no-leads (DFN) physically and electrically connect integrated circuits to printed circuit boards. Flat no-leads, also known as micro leadframe (MLF) and SON (small-outline no leads), is a surface-mount technology, one of several package technologies that connect ICs to the surfaces of PCBs without through-holes. Flat no-lead is a near chip scale plastic encapsulation package made with a planar copper lead frame substrate. Perimeter lands on the package bottom provide electrical connections to the PCB. Flat no-lead packages include an exposed thermal pad to improve heat transfer out of the IC (into the PCB). Heat transfer can be further facilitated by metal vias in the thermal pad. The QFN package is similar to the quad-flat package, and a ball grid array.

QFN package1600includes a set of contacts1602arrayed around the perimeter of the package on the bottom side. Thermal pad1604has an exposed surface on the bottom side of QFN1600. An integrated circuit die (not shown) is mounted to the other side of thermal pad1604. The entire assembly is encapsulated in a molding compound1606, such as various types of epoxy compounds, for example. While a QFN is illustrated inFIG. 16, other embodiments may use other types of integrated circuit packages.

FIG. 17is a flow diagram illustrating magnetic self-assembly of semiconductor die onto a leadframe using magnetic fields as described in more detail above. A calibration process may be performed as described in more detail with regard toFIG. 11to determine the relative orientation of a dominant magnetic response of a magnetically responsive structure within a component as indicated at box1701. Once the orientation of the dominant magnetic response of the component is known, this information may be used to configure an array of magnetic domains to capture a similar component in a specific orientation.

A batch of components that include a magnetically responsive structure may be placed on a surface that includes an array of magnetic domains as indicated at box1702. In some embodiments, the surface may be part of a substrate in which the magnetic domains are formed, such as substrate200as shown inFIG. 2A. In another embodiment, the surface may be part of an overlay that is positioned adjacent to substrate that included the array of magnetic domains, such as surface220as shown inFIG. 2C. This may be done in many ways, such as by “submerging” a substrate that has the surface in a container holding a batch of components, or by simply dumping a batch of components on the substrate, for example. In any case, the components may initially have a random arrangement as illustrated inFIG. 12.

The substrate may then be agitated as indicated at box1703as illustrated at1250,1251inFIG. 12with enough force so that the batch of components are encouraged to move around on the surface of the substrate but not with too much force that prevents portions of the magnetic domain from capturing the components in specific locations as indicated at box1704using only magnetic attraction between the magnetic domains and the magnetic response of each component.

Selected ones of the array of magnetic domains may be activated to capture components at specified locations. In the case the magnetic domains are electromagnets, they may be activated by a control signal applied to each wire in order to activate specific domains and thereby activate an array of magnetic domains in a particular position on the surface of the substrate. In this case, the magnetic domains may be controlled in a similar manner to pixels in an image device in which individual pixels may be turned on and off in order to form an image. The magnetic domains may be organized as “rows” and “columns” and controlled by circuitry in a similar manner as pixels in an image device, for example.

In the case that the magnet domains are permanent magnets, they may be initialized by applying an external force to form selected field polarities. Depending on the material that forms the magnetic domains, the external force may be a directed magnetic field, a directed electric field, heat, energy from a laser, etc.

In some embodiments, components may be moved across the surface by selective activation of magnetic domains as indicated at box1705and described in more detail with regard toFIGS. 14 and 15. A visual inspection system may be used to determine which components need to be moved and/or flipped and to control the movement, for example.

In some embodiments, the surface may be magnetic chuck that is used to capture the components in specified locations. Once captured, the components may be transferred to a second surface, as describe in more detail with regard toFIGS. 8A-8B.

Once the components are correctly positioned in specified locations, they may be permanently or semi permanently affixed there as indicated at box1706. In some embodiments, an adhesive may be used to affix a component. For example, an adhesive may be a B-stage epoxy film that is applied to the surface, patterned, and etched using known or later developed fabrication techniques to form an adhesive pad at each specific location of the surface. While the batch of components is being agitated, the B-stage epoxy pad may be in a partially cured state that is not sticky. The B-stage epoxy pad may be relatively thin and therefore does not impede the movement of components while they are being positioned. Once the components are properly positioned, the entire surface and components may be heated to activate the B-stage epoxy and thereby permanently affix the components to the surface.

In other embodiments, other types of known or later developed adhesives may be used that may initially not impede the movement of components and that can be activated once the components are correctly oriented at the specific locations.

In this manner, large batches of components may be positioned on a surface and captured at specified locations in an efficient parallel manner.

Other Embodiments

While the disclosure has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various other embodiments of the disclosure will be apparent to persons skilled in the art upon reference to this description. For example, while positioning IC die on a leadframe was described herein, other embodiments may be used to position various types of electronic components on a different surface, such as on a printed circuit board.

In some embodiments, a first set of components may be captured while the magnetic domains are activated in one pattern, and then a second set of different components may be captured while the magnetic domains are activated in a second pattern. Additional types of components may be positioned by repeating this process.

In another embodiment, two or more IC die may be positioned and captured in close proximity to each other, even in a side-by-side arrangement. Such close placement is typically not possible with traditional pick and place machinery.

The techniques described in this disclosure may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the software may be executed in one or more processors, such as a microprocessor, application specific integrated circuit (ASIC), field programmable gate array (FPGA), or digital signal processor (DSP). The software that executes the techniques may be initially stored in a computer-readable medium such as compact disc (CD), a diskette, a tape, a file, memory, or any other computer readable storage device and then loaded and executed in the processor. In some cases, the software may also be sold in a computer program product, which includes the computer-readable medium and packaging materials for the computer-readable medium. In some cases, the software instructions may be distributed via removable computer readable media (e.g., floppy disk, optical disk, flash memory, USB key), via a transmission path from computer readable media on another digital system, etc.

Certain terms are used throughout the description and the claims to refer to particular system components. As one skilled in the art will appreciate, components in digital systems may be referred to by different names and/or may be combined in ways not shown herein without departing from the described functionality. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” and derivatives thereof are intended to mean an indirect, direct, optical, and/or wireless electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, through an indirect electrical connection via other devices and connections, through an optical electrical connection, and/or through a wireless electrical connection.

Although method steps may be presented and described herein in a sequential fashion, one or more of the steps shown and described may be omitted, repeated, performed concurrently, and/or performed in a different order than the order shown in the figures and/or described herein. Accordingly, embodiments of the disclosure should not be considered limited to the specific ordering of steps shown in the figures and/or described herein.