Abstract:
A method including forming a contact pad array on an integrated circuit substrate, the contact pad array including a first plurality of contact pads and a second plurality of contact pads, wherein an accessible area of each of the first plurality of contact pads is different than an accessible area of each of the second plurality of contact pads; and depositing solder on the accessible area of the contact pads. An apparatus including an integrated circuit substrate including a body having a nonplanar shape and a surface including a first plurality of contact pads and a second plurality of contact pads, wherein an accessible area of each of the first plurality of contact pads is different than an accessible area of each of the second plurality of contact pads.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    Integrated circuit packaging. 
         [0003]    2. Description of Related Art 
         [0004]    In an effort to improve interconnect speed, decrease power consumption and reduce integrated circuit package form factor, three-dimensional packages with die-to-die stacking has been promoted. 
         [0005]    Die-to-die stack minimizes the effort to place all technologies on to a single die. Instead, multiple dies may be stacked together. Such dies may allow a different fabrication technology optimized for a particular type of circuitry, such as memory, logic, analog and sensors. Wide I/O memory is a recent dynamic random access memory (DRAM) technology that contemplates a memory die stacked on a microprocessor die or vice versa. JEDEC standard JESD229, “Wide I/O Single Data Rate,” December 2011, specifies four 128-bit channels, providing a 512-bit interface to DRAM. An interface between the dice involves, in one embodiment, solder connections. 
         [0006]    In three-dimensional packaging, the assembly process flow depends on different variables, including package architecture (e.g., die size, substrate layout, etc.); fabrication materials and processes (e.g., silicon, back end of line (BEOL) metallization, die back side metallization, nitride stress); assembly materials and processes; and costs. The shape/topography of a chip during assembly is complex. Depending on the process flow variables, the chip or die shape can be concave, convex, saddle or other shape. During die-to-die bonding, the shape of one or both dies can effect the contact between the die dice and incompatible shapes can induce non-contact open, stretch solder joints and other defects that can induce process yield loss and reliability degradation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  shows a cross-sectional side view of a portion of an assembly that is suitable for use in a computing device. 
           [0008]      FIG. 2  shows a top view of a portion of a die through line  2 - 2 ′ of  FIG. 1 . 
           [0009]      FIG. 3  shows a side view of a portion die as shown in  FIG. 2 . 
           [0010]      FIG. 4  shows solder material on a contact pad. 
           [0011]      FIG. 5  shows a top view of a portion of a die through line  2 - 2 ′ of  FIG. 1 . 
           [0012]      FIG. 6  shows a side view of the structure of  FIG. 5  following the introduction of solder material. 
           [0013]      FIG. 7  shows a cross-sectional side view of a portion of a die having three-dimensional contact pads in accordance with another embodiment. 
           [0014]      FIG. 8  illustrates a computing device in accordance with one implementation. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    In an effort to improve the interconnect speed, decrease power consumption and reduce a package form factor, three-dimensional packages with die-to-die stacking are presented as approaches for alleviating the risk of non-contact open and/or stretched solder joints. 
         [0016]      FIG. 1  shows a cross-sectional side view of a portion of an assembly that is suitable for use in a computing device (computing device  10 ) including, but not limited to, a desktop computer, or a handheld device (e.g., a tablet, a smart phone, etc.). Assembly  100  includes die  110  that is, for example, a processor including device layer  120  and metallization  130 . Die  110 , in this embodiment, is connected to package  125  through, for example, solder ball interconnections  135  having a diameter on the order of, for example,  100  microns and a pitch on the order of  100  microns. A superior surface of die  110  (as viewed) includes metallization layer  140  terminating in a number of contact pads  150  for a connection to a secondary device. Thus, in one embodiment, die  110  includes through silicon vias (TSVs) for a connection to a secondary die in a surface to surface orientation. Overlying die  110 , in this embodiment, is secondary die  160 . Secondary die  160  is, for example, a memory die (e.g., DRAM) including device layer  165  and metallization layer  170 . Metallization layer  170  is terminated by a number of contact points or pads  175  or connection to contact points or pads  150  of die  110 . A connection between die  110  and die  160  is made, in one embodiment, through solder connections between aligned contact points or pads  150  (die  110 ) and contact points or pads  175  (die  160 ). The connections are illustrated as dashed lines in  FIG. 1 .  FIG. 1  also shows package  125  connected to printed circuit board  180  (e.g., a motherboard) through, for example, solder connections  185 . Representatively, the configuration of die  110  and secondary die complies with JEDEC standard JESD229 in implementing wide I/O. 
         [0017]    As noted above, one issue facing die-to-die stacking is the shape of a primary die (die  110 ) and a secondary die (die  160 ) and a desire for reliable connections between the dice. As illustrated in  FIG. 1 , due, in one aspect, to the processing of the individual dice, each die may have a non-planar shape and adopt, for example, a concave, convex, saddle or other shape relative to planar surface.  FIG. 1  shows die  110  having a generally convex shape and die  160  having a generally concave shape relating to a planar surface (e.g., representatively, a planar surface is illustrated as a surface of printed circuit board  180 ). 
         [0018]      FIGS. 2-4  illustrate one approach to improve die-to-die connection in three-dimensional packaging.  FIG. 2  shows a top view of a portion of die  110  through line  2 - 2 ′ of  FIG. 1 . As illustrated in  FIG. 1 , in this embodiment, die  110  has a generally convex shape while die  160  has a generally concave shape. Accordingly, in one embodiment, contact points or pads in or on a surface of die  110  are arranged in columns (as viewed) of points or pads of different sizes.  FIG. 2  illustrates contact points or pads  150 A,  150 B,  150 C,  150 D and  150 E extending left to right in a row toward edge  115  of die  110  with each numerical designation representing a column of contact points or pads of similar size. Where die  110  has a generally convex shape relative to a planar surface, contact points or pads closer to edge  115  of die  110  will tend to be further away from contact points or pads of a secondary die (e.g., contact points or pads  175  of die  160 ,  FIG. 1 ) than contact points or pads further away from edge  115  (e.g., closer toward the center of die  110 ). Thus, in one embodiment, contact points or pads  150 E have a larger diameter (and a larger accessible area) than contact points of pads  150 A- 150 D. Contact points or pads  150 A are illustrated with the smallest diameter (smallest accessible area) and the diameter (accessible area) gets progressively larger with each column of contact points or pads (points or pads  150 B- 150 E) as edge  115  approached. Contact points or pads  150 A- 150 E are illustrated in this embodiment as circular. In other embodiments, the contact points or pads may have other shapes, including but not limited to, rectangular, square and oval shapes. 
         [0019]    Contact points or pads  150 A- 150 E can be formed according to conventional techniques. Representatively, contact points may be formed by introducing a conductive seed layer; disposing a mask on the conductive seed layer in areas where contact points or pads are not desired; electroplating a material such as copper or a copper alloy to form the contact points or pads. The mask and undesired seed material may then be removed by etching. According to this method, openings in a masking layer can determine the accessible area of the contact points or pads. Representatively, a masking layer may be introduced and patterned to have openings of different diameter for column of contacts shown in  FIG. 2  (contact points or pads  150 A- 150 E). Alternatively, each of contact points or pads  150 A- 150 E may be formed of a similar diameter (similar accessible area) and, after forming the contact points or pads, a dielectric material, such as WPR, commercially available from JSP Micro, Inc. of Sunnyvale, Calif., may be introduced, such as introduced through a patterned mask, on portions of ones of the contact points or pads to reduce the accessible area of the contact points or pads. 
         [0020]      FIG. 3  shows a side view of the portion die  110  as shown in  FIG. 2 , following the introduction of solder material on the contact points or pads. In one embodiment, wave solder deposition is used to deposit solder on contact points or pads  150 A- 150 E. As indicated in  FIG. 4 , a height of an amount (volume) of solder transferred post wave solder deposition is proportional to a contact point or pad diameter. Since contact points or pads  150 E have an accessible area greater than contact points or pads  150 A- 150 D, a height, h, of solder material is greater on contact points or pads  150 E than on any of contact points or pads  150 A- 150 D; a height of solder material on contact points or pads  150 D is greater than a height of any of contact points or pads  150 A- 150 C; a height of solder material on contact points or pads  150 C is greater than a height of any of contact points or pads  150 A- 150 B; and height of solder material on contact points or pads  150 B is greater than a height of any of contact points or pads  150 A. 
         [0021]      FIG. 3  shows solder material  220 A of, for example, a tin-based solder introduced on contact points or pads  150 A- 150 E. Specifically,  FIG. 3  shows solder material  220 A on contact points or pads  150 A; solder material  220 B on contact points or pads  150 B; solder material  220 C on contact points or pads  150 C; solder material  220 D on contact points or pads  150 D; and solder material  220 E on contact points or pads  150 E. As illustrated, the amount of solder material  220 E on contact points or pads  150 E is greater than an amount of solder material on any of contact points or pads  150 A- 150 D. Accordingly, a height, h, of solder material  220 E is greater than a height of solder material on any of contact points or pads  150 A- 150 D. The greater height tends to reduce the effective solder material/pads co-planarity/flatness for a convex-shaped die, alleviating issue associated with die warpage (e.g., non-contact opens). It is appreciated that for different die shapes (e.g., concave, convex, saddle), a diameter of contact points or pads can be modified. For instance, where a shape or die  110  is concave, contact points or pads  150 A could have a greater accessible area (e.g., greater diameter) than contact points or pads  150 E. 
         [0022]      FIGS. 5-6  describe a second approach to address potential problems associated with non-planar dies in three-dimensional packaging arrangements.  FIG. 5  shows a top view of a portion of die  110  through line  2 - 2 ′ of  FIG. 1 . The portion is close to edge  115 . As illustrated, in this embodiment, die  110  includes a number of contact points or pads  150 A- 150 E. Where die  110  has a convex shape and die  160  has a concave shape such as illustrated in  FIG. 1 , contact points or pads  150 A- 150 E are progressively reduced in diameter going from left to right as viewed toward edge  115  of die  110 . Accordingly, contact points or pads  150 E have a smaller diameter than contact points or pads  150 A. 
         [0023]      FIG. 6  shows a side view of the structure of  FIG. 5  following the introduction of solder material. In this embodiment, solder material of the same amount (same volume) is deposited on each of the contact points or pads (each of contact points or pads  150 A- 150 E). The solder material is introduced and reflowed. Due to the difference in diameter of the contact points or pads, the smaller diameter contact pads (e.g., contact points or pads  150 D, contact points or pads  150 E) and the same solder material amounts (volumes) on each of the contact points or pads, the solder material on the smaller diameter contact points or pads will tend to be taller than those of the larger diameter contact points or pads. As illustrated in  FIG. 6 , solder material  320 A is reflowed on contact points or pads  150 A; solder material  320 B is reflowed on contact points or pads  150 B; solder material  320 C is reflowed on contact points or pads  150 C; solder material  320 D is reflowed on contact points or pads  150 D; solder material  320 E is reflowed on contact points or pads  150 E. As illustrated, the height, h, of solder material  320 E on contact points or pads  150 E is taller than a height of solder material  320 D on contact points or pads  150 D; a height of solder material  320 D on contact points or pads  150 D are greater than solder material  320 C on contact points or pads  150 C; a height of solder material  320 C on contact points or pads  150 C is greater than solder material  320 B on contact points or pads  150 B; and a height of solder material  320 B on contact points or pads  150 B is greater than solder material  320 A on contact points or pads  150 A. The difference in heights can reduce the effective solder material/pad/coplanarity/flatness alleviating issues related to die warpage. 
         [0024]    Contact points or pads  150 A- 150 E in  FIGS. 5-6  may be formed as described above with reference to  FIGS. 2-3  of different diameters. In one embodiment, an accessible area of a contact point or pad may be controlled by a dielectric material placed or introduced around the contact points or pads. Thus, for example, in one embodiment, the contact points or pads of die  110  may have a similar diameter (similar area) and a dielectric material may be introduced on die  110  where the dielectric material covers a portion of the contact points or pads reducing the accessible area of the contact points or pads for solder introduction. 
         [0025]    In the above embodiments, reference to an accessible area was described with respect to a two-dimensional contact points or pads (contact points or pad on a surface of a substrate). In another embodiment, contact points may extend a distance from a surface of a substrate.  FIG. 7  shows an example of a three-dimensional contact pad.  FIG. 7  is a side view of a portion of integrated circuit substrate  420  and illustrates contact pad  450  extending from a surface of substrate  420 . Representatively, contact pad  450  extends a distance, d, of 10 μm to 20 μm from a surface of substrate  420 . By extending from a surface of substrate  420 , an area of contact pad  450  includes a top surface of pad  450  (as viewed) as well as the sidewall surface(s) of the pad. The accessible area of the sidewalls of contact pad  450  that may be contacted by a solder material may include the entire area (including the top surface and the area attributable to the sidewalls surface(s) or some portion less than an entire area where, for example, dielectric material is present around a portion of the sidewall surface(s) (including the entire sidewall surface(s)). 
         [0026]      FIG. 8  illustrates a computing device  500  in accordance with one implementation. The computing device  500  houses board  502 . Board  502  may include a number of components, including but not limited to processor  504  and at least one communication chip  506 . Processor  504  is physically and electrically connected to board  502 . In some implementations the at least one communication chip  506  is also physically and electrically connected to board  502 . In further implementations, communication chip  506  is part of processor  504 . 
         [0027]    Depending on its applications, computing device  500  may include other components that may or may not be physically and electrically connected to board  502 . These other components include, but are not limited to, volatile memory (e.g., DRAM), non-volatile memory (e.g., ROM), flash memory, a graphics processor, a digital signal processor, a crypto processor, a chipset, an antenna, a display, a touchscreen display, a touchscreen controller, a battery, an audio codec, a video codec, a power amplifier, a global positioning system (GPS) device, a compass, an accelerometer, a gyroscope, a speaker, a camera, and a mass storage device (such as hard disk drive, compact disk (CD), digital versatile disk (DVD), and so forth). 
         [0028]    Communication chip  506  enables wireless communications for the transfer of data to and from computing device  500 . The term “wireless” and its derivatives may be used to describe circuits, devices, systems, methods, techniques, communications channels, etc., that may communicate data through the use of modulated electromagnetic radiation through a non-solid medium. The term does not imply that the associated devices do not contain any wires, although in some embodiments they might not. Communication chip  806  may implement any of a number of wireless standards or protocols, including but not limited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE 802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE, GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well as any other wireless protocols that are designated as 3G, 4G, 5G, and beyond. Computing device  500  may include a plurality of communication chips  506 . For instance, a first communication chip  506  may be dedicated to shorter range wireless communications such as Wi-Fi and Bluetooth and a second communication chip  806  may be dedicated to longer range wireless communications such as GPS, EDGE, GPRS, CDMA, WiMAX, LTE, Ev-DO, and others. 
         [0029]    Processor  504  of computing device  500  includes an integrated circuit die packaged within processor  504 . In some implementations, the package is formed in accordance with embodiments described above utilizes. The term “processor” may refer to any device or portion of a device that processes electronic data from registers and/or memory to transform that electronic data into other electronic data that may be stored in registers and/or memory. 
         [0030]    Communication chip  506  also includes an integrated circuit die packaged within communication chip  506 . In further implementations, another component housed within computing device  500  may contain a microelectronic package. 
         [0031]    In various implementations, computing device  500  may be a laptop, a netbook, a notebook, an ultrabook, a smartphone, a tablet, a personal digital assistant (PDA), an ultra mobile PC, a mobile phone, a desktop computer, a server, a printer, a scanner, a monitor, a set-top box, an entertainment control unit, a digital camera, a portable music player, or a digital video recorder. In further implementations, computing device  500  may be any other electronic device that processes data. 
         [0032]    In the description above, for the purposes of explanation, numerous specific details have been set forth in order to provide a thorough understanding of the embodiments. It will be apparent however, to one skilled in the art, that one or more other embodiments may be practiced without some of these specific details. The particular embodiments described are not provided to limit the invention but to illustrate it. The scope of the invention is not to be determined by the specific examples provided above but only by the claims below. In other instances, well-known structures, devices, and operations have been shown in block diagram form or without detail in order to avoid obscuring the understanding of the description. Where considered appropriate, reference numerals or terminal portions of reference numerals have been repeated among the figures to indicate corresponding or analogous elements, which may optionally have similar characteristics. 
         [0033]    It should also be appreciated that reference throughout this specification to “one embodiment”, “an embodiment”, “one or more embodiments”, or “different embodiments”, for example, means that a particular feature may be included in the practice of the invention. Similarly, it should be appreciated that in the description various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects may lie in less than all features of a single disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of the invention.