Patent Publication Number: US-2007099443-A1

Title: Memory modules and methods for manufacturing memory modules

Description:
TECHNICAL FIELD  
      The present invention relates to memory modules and methods for manufacturing memory modules. More particularly, the invention is directed to memory modules for use with a connector having a socket.  
     BACKGROUND  
      Conventional microelectronic devices are manufactured for specific performance characteristics required for use in a wide range of electronic equipment. A packaged microelectronic device can include a die, an interposer substrate or lead frame attached to the die, and a molded casing around the die. The die generally has an integrated circuit and a plurality of bond-pads electrically connected to the integrated circuit. The bond-pads are coupled to terminals on the interposer substrate or lead frame. The interposer substrate can also include ball-pads connected to the terminals by conductive traces in a dielectric material. A plurality of solder balls can be attached to corresponding ball-pads to construct a “ball-grid” array.  
      Several dies can be attached to a single substrate to form a multi-chip module (MCM), such as a single in-line memory module (SIMM) or a dual in-line module (DIMM), for applications in which the performance requirements exceed the capability of a single die. A SIMM is a memory module having several dies aligned in a row and connected to a printed circuit board to, in effect, create a single device with the memory capacity of the combined dies. The internal circuitry of the printed circuit board connects each die to contact pads that are disposed on one side of the module proximate to the edge. The contact pads are arranged for attachment to an edge-type connector. A DIMM is similar to a SIMM, except the DIMM provides additional memory capacity and includes contact pads on both sides of the module proximate to the edge.  
      Edge-type connectors receive SIMMs, DIMMs, and other types of memory modules to electrically couple the modules to external devices. For example, a conventional connector for use with a DIMM includes a socket having a plurality of pins arranged in two rows to contact the pads on each side of the module, respectively. When the module is inserted into the socket, the pads on the module contact and flex corresponding pins as the pads slide along the pins to a contact point.  
      One drawback of conventional memory modules is that the force required for inserting the modules into the connectors can be large. This is particularly true for high performance memory modules that require connectors with high pin counts. In applications in which the memory modules are manually inserted into the connectors, an individual may bend the pins, break the connector, and/or damage the module due to the large insertion force. It is also possible that some individuals may not be able to apply sufficient force to reliably insert the modules. To reduce the insertion force, the individual may first insert one end of the module into the connector and then pivot the module downward to insert the other end into the connector. This approach, however, exerts side forces on the pins of the connector, which tends to bend the pins and damage the connector. Another approach to reduce the insertion force includes beveling the portion of the memory module between the contact pads and the edge. This approach, however, does not reduce the insertion force because the pins typically do not contact the beveled portion of the module. Accordingly, there is a need to reduce the force required for inserting memory modules into connectors. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1A  is a schematic front view of a memory module and a connector in accordance with one embodiment of the invention.  
       FIG. 1B  is a schematic side cross-sectional view of the memory module and the connector of  FIG. 1A .  
       FIG. 2  is a schematic front view of a memory module in accordance with another embodiment of the invention.  
       FIG. 3  is a schematic front view of a memory module in accordance with another embodiment of the invention.  
       FIG. 4  is a schematic front view of a memory module in accordance with another embodiment of the invention.  
       FIG. 5  is a schematic front view of a memory module in accordance with another embodiment of the invention.  
       FIG. 6  is a schematic front view of a memory module in accordance with another embodiment of the invention.  
       FIG. 7  is a schematic front view of a memory module in accordance with another embodiment of the invention.  
       FIG. 8  is a schematic side cross-sectional view of a memory module in accordance with another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION  
      A. Overview  
      The following disclosure describes several embodiments of memory modules and methods for manufacturing memory modules. One aspect of the invention is directed to memory modules for use with a connector having a socket. In one embodiment, a memory module includes a card, a microelectronic device carried by the card, and a plurality of external contact pads on the card that are operably coupled to the microelectronic device. The card includes a first major surface and a second major surface opposite the first major surface. The first major surface has a first longitudinal edge and a second longitudinal edge opposite the first longitudinal edge. The external contact pads are disposed on the first major surface of the card proximate to the second longitudinal edge. The contact pads include a first contact pad with a first end proximate to the second longitudinal edge and a second contact pad with a second end proximate to the second longitudinal edge. The first end is spaced apart from the first longitudinal edge by a first distance, and the second end is spaced apart from the first longitudinal edge by a second distance different than the first distance.  
      In another embodiment, a memory module includes a body, a memory device carried by the body, and a plurality of external contact pads on the body that are operably coupled to the memory device. The body includes a first surface, a second surface opposite the first surface, a first longitudinal side between the first and second surfaces, and a second longitudinal side between the first and second surfaces. The second longitudinal side is nonplanar and can include teeth or have a V-shaped or other configuration. The external contact pads are arranged on the first surface proximate to the second longitudinal side for electrical connection with corresponding pins when the module is received in a socket.  
      In another embodiment, a memory module includes a board having a first surface, a second surface opposite the first surface, a first longitudinal side between the first and second surfaces, and a second longitudinal side between the first and second surfaces. The first longitudinal side defines a first plane and the second longitudinal side defines a second plane nonparallel with the first plane. The module further includes a microelectronic device attached to the board, a first plurality of external contact pads positioned on the first surface, and a second plurality of external contact pads positioned on the second surface. The first and second pluralities of external contact pads electrically couple the microelectronic device to an external device when the board is received in a socket and the first and second external contact pads contact corresponding pins.  
      In another embodiment, a memory module includes a card having a surface, a microelectronic device carried by the card, and a plurality of external contact pads operably coupled to the microelectronic device. The external contact pads are arranged on the surface such that at least several of the contact pads contact corresponding pins of a socket at different times as the card is inserted into the socket to reduce the insertion force.  
      Another aspect of the invention is directed to methods for manufacturing a memory module for use with a connector having a socket. The method includes forming a plurality of first external contact pads on a first surface of a card and forming a plurality of second external contact pads on a second surface of the card. The plurality of first external contact pads include a first contact pad with a first length and a second contact pad with a second length different than the first length. The method can optionally include mounting a microelectronic device to the card so that contacts on the microelectronic device are attached to the first and second external contact pads.  
      The following disclosure is directed to memory modules and methods for manufacturing memory modules. The term “memory module” is used throughout to include microelectronic devices, data storage elements, and other articles of manufacture. For example, memory modules include SIMM, DIMM, DRAM, flash-memory, ASICS, processors, and other types of electronic devices or components. Several specific details of the invention are set forth in the following description and in  FIGS. 1A-8  to provide a thorough understanding of certain embodiments of the invention. One skilled in the art, however, will understand that the present invention may have additional embodiments and that the embodiments of the invention may be practiced without several of the specific features described below.  
     B. Embodiments of Memory Modules for Use with Connectors  
       FIG. 1A  is a schematic front view of a memory module  100  and a connector  150  in accordance with one embodiment of the invention. The connector  150  is configured for receiving the memory module  100  and electrically connecting the module  100  to an external device. The memory module  100  includes a substrate  110 , a microelectronic device  128  (shown schematically in broken lines) attached to the substrate  110 , and a plurality of external contact pads  130  on the substrate  110 . The substrate  110  can be a card, board, or other structure to which one or more microelectronic devices  128  can be attached. The microelectronic device  128  can include one or more microelectronic dies, and the contact pads  130  are electrically connected to the microelectronic device  128  to provide external terminals for the device  128 . The microelectronic device  128 , for example, can be a memory device, a processor, or other type of device.  
      The illustrated substrate  110  includes a first surface  112 , a second surface  114  (shown in  FIG. 1B ) opposite the first surface  112 , a first longitudinal side  116  extending between the first and second surfaces  112  and  114 , and a second longitudinal side  118  opposite the first longitudinal side  116  and extending between the first and second surfaces  112  and  114 . The substrate  110  further includes a first longitudinal edge  120  at the interface of the first surface  112  and the first longitudinal side  116 , a second longitudinal edge  122  at the interface of the first surface  112  and the second longitudinal side  118 , a first transverse side  126  extending between the first and second surfaces  112  and  114 , and a second transverse side  127  opposite the first transverse side  126  and extending between the first and second surfaces  112  and  114 .  
      In the illustrated substrate  110 , the first longitudinal side  116  is generally planar, and the second longitudinal side  118  is nonplanar and has an inverted V-shaped configuration. As such, a first distance D 1  between the first and second longitudinal edges  120  and  122  at an outboard portion of the first surface  112  is greater than a second distance D 2  between the first and second longitudinal edges  120  and  122  at an inboard portion of the first surface  112 . The difference between the first distance D 1  and the second distance D 2  defines a depth C at the center of the second longitudinal side  118 . In other embodiments, such as those described below with reference to  FIGS. 2-8 , the second longitudinal side  118  can have other configurations.  
      The external contact pads  130  are arranged in (a) a row on the first surface  112  proximate to the second longitudinal edge  122  and/or (b) a row on the second surface  114  ( FIG. 1B ) proximate to a third longitudinal edge  123  ( FIG. 1B ). The individual contact pads  130  have a first end  132 , a second end  134  opposite the first end  132 , and a length extending between the first and second ends  132  and  134 . In the illustrated embodiment, the distance between the first longitudinal edge  120  and the first end  132  of the individual pads  130  generally is the same, and the distance between the first longitudinal edge  120  and the second end  134  of the individual pads  130  varies and depends on the length of the pad  130 .  
      The illustrated contact pads  130  have different lengths corresponding to the position of the pad  130  on the first or second surface  112  and  114  and the contour of the second longitudinal side  118 . For example, a first contact pad  130   a  at a center portion of the first surface  112  has a first length L 1 , and a second contact pad  130   b  at an outer portion of the first surface  112  has a second length L 2  greater than the first length L 1 . In the illustrated embodiment, the length of the individual contact pads  130  increases with the distance the pad  130  is spaced apart from the center of the first surface  112 . In other embodiments, however, the individual pads may not have a greater length than an adjacent inboard pad. For example, a group of pads can have the same length, and the individual pads in a single group can have a greater length than the pads in an adjacent inboard group.  
      In one aspect of the illustrated embodiment, contact pads  130  with similar lengths may have similar functions. For example, the longer pads may carry the power and ground, and the shorter pads may carry the signals. Because the capacitance of the individual pads corresponds to the length of the pad, pads carrying high frequency signals may have shorter lengths to reduce the capacitance. Moreover, pads carrying signals with similar frequencies may have similar lengths and therefore comparable performance. In other applications, however, longer pads may carry high frequency signals.  
       FIG. 1B  is a schematic side cross-sectional view of the memory module  100  and the connector  150  of  FIG. 1A . Referring to both  FIGS. 1A and 1B , the illustrated connector  150  includes a body  160 , a socket  165  defined by the body  160 , and a plurality of pins  170  attached to the body  160  for electrically coupling corresponding pads  130  of the module  100  to an external device. The socket  165  is sized to receive a portion of the memory module  100  proximate to the second longitudinal side  118 . The pins  170  include a plurality of first pins  170   a  arranged in a row to contact corresponding pads  130  on the first surface  112  of the memory module  100  and a plurality of second pins  170   b  arranged in a row to contact corresponding pads  130  on the second surface  114  of the module  100 . Although in the illustrated embodiment, the pads  130  on the second surface  114  ( FIG. 1B ) are aligned with and have a similar configuration as the pads  130  on the first surface  112 , in other embodiments, the second surface  114  may not include pads  130  or the pads  130  on the second surface  114  can be aligned differently or have other configurations. In such embodiments, the connector  150  may not include the second pins  170   b , or the second pins  170   b  can have a different configuration to be aligned with the pads  130  on the second surface  114 .  
      In the illustrated embodiment, the connector  150  also includes two latches  162  ( FIG. 1A ) configured to selectively engage notches  140  ( FIG. 1A ) in the first and second transverse sides  126  and  127  ( FIG. 1A ) for securing the module  100  to the connector  150  when the module  100  is received in the socket  165 . The connector  150  may also include a spacer  190  with a stop surface  192  between the first and second pins  170   a - b  to provide support to an inserted module  100 . In additional embodiments, the module  100  may not include the notches  140 , and/or the connector  150  may not include the latches  162  and/or the spacer  190 .  
      Referring only to  FIG. 1B , the individual pins  170  include a face  172  and a contact point  174  for contacting the corresponding pad  130  on the module  100 . The contact points  174  on adjacent first and second pins  170  are spaced apart by a first distance S 1 , and the external surfaces of corresponding contact pads  130  on the first and second surfaces  112  and  114  of the module  100  are spaced apart by a second distance S 2  greater than the first distance S 1  so that the contact points  174  contact corresponding pads  130  when the module  100  is received in the socket  165 . Although the illustrated substrate  110  has a thickness T greater than the distance S 1  between adjacent contact points  174 , in other embodiments, the substrate  110  can have a thickness less than or equal to the distance S 1  between adjacent contact points  174 .  
      The memory module  100  is inserted into the connector  150  by positioning the second and third longitudinal edges  122  and  123  on the face  172  of the first and second pins  170   a - b , respectively, and exerting a force in a direction F to slide the edges  122  and  123  and the contact pads  130  across the face  172  of the pins  170 . Because the distance S 2  between contact pads  130  on the first and second surfaces  112  and  114  is greater than the distance S 1  between adjacent contact points  174 , the first and second pins  170   a - b  flex outwardly away from the memory module  100  in directions X 1  and X 2 , respectively, as the contact pads  130  and the edges  122  and  123  slide across the face  172  of the pins  170 . The individual pins  170  continue to flex until the contact point  174  contacts the corresponding pad  130  on the module  100 . The module  100  is properly positioned in the connector  150  when the contact points  174  contact corresponding pads  130  and/or the second longitudinal side  118  rests on the stop surface  192  of the spacer  190 . The force required to flex the pins  170  and insert the memory module  100  into the connector  150  is affected by several parameters, including (a) an angle α of the face  172 , (b) a vertical length L 3  of the face  172 , (c) the difference between the distance S 1  separating adjacent contact points  174  and the thickness T of the substrate  110 , (d) the difference between the distance S 1  separating adjacent contact points  174  and the distance S 2  separating the contact pads  130  on the first and second surfaces  112  and  114 , (e) the position of the contact pads  130  on the first and second surfaces  112  and  114 , and (f) the material(s) from which the pins  170  are formed.  
      One feature of the illustrated memory module  100  is that the individual contact pads  130  contact corresponding pins  170  at different times when the module  100  is inserted into the connector  150 . An advantage of this feature is that the position of the contact pads  130  on the first and second surfaces  112  and  114  reduces the force required to insert the module  100  into the connector  150 . Because (a) the second ends  134  of the pads  130  are spaced apart from the first longitudinal side  116  by different distances, and (b) the second longitudinal side  118  has a nonplanar configuration, the individual contact pads  130  and sections of the second and third longitudinal edges  122  and  123  contact the pins  170  at different times. The outboard contact pads  130  and the outboard sections of the second and third longitudinal edges  122  and  123  contact the face  172  of the corresponding pins  170  before the inboard contact pads  130  and the inboard section of the longitudinal edges  122  and  123 . As such, the pins  170  corresponding to the outboard contact pads  130  flex and their respective contact points  174  contact the outboard contact pads  130  before the pins  170  corresponding to the inboard contact pads  130  begin to flex. By flexing only a portion of the pins  170  at any given time during the insertion process, the force required to insert the memory module  100  into the connector  150  is reduced. The reduced insertion force (a) decreases the likelihood that the module  100  and/or the connector  150  will be damaged during a manual insertion process, and (b) allows modules and connectors with higher pin counts to be used without increasing the insertion force.  
      Referring to  FIGS. 1A and 1B , in one aspect of the illustrated memory module  100 , the ratio of the depth C ( FIG. 1A ) at the center of the second longitudinal side  118  to the vertical length L 3  of the face  172  of the individual pins  170  is approximately 2:1. As such, the insertion force is reduced by approximately 50 percent because at any given time at most one half of the pins  170  are flexing. In other embodiments, the ratio of the depth C to the vertical length L 3  can be less than or greater than 2:1.  
     C. Additional Embodiments of Memory Modules  
       FIG. 2  is a schematic front view of a memory module  200  in accordance with another embodiment of the invention. The memory module  200  is generally similar to the memory module  100  described above with reference to  FIGS. 1A and 1B . For example, the memory module  200  includes a substrate  210 , a microelectronic device  128  (shown schematically in broken lines) attached to the substrate  210 , and a plurality of contact pads  230  arranged on the substrate  210  and electrically coupled to the microelectronic device  128 . The illustrated substrate  210  includes a first surface  212 , a second surface (not shown) opposite the first surface  212 , a first longitudinal side  116  connecting the first surface  212  to the second surface, and a second longitudinal side  218  opposite the first longitudinal surface  116  and connecting the first surface  212  to the second surface. The substrate  210  also includes a first longitudinal edge  120  at the interface of the first surface  112  and the first longitudinal side  116 , a second longitudinal edge  222  at the interface of the first surface  212  and the second longitudinal side  218 , a first transverse side  226 , and a second transverse side  227  opposite the first transverse side  226 . In the illustrated embodiment, the second longitudinal side  218  has a generally planar configuration and is oriented at an angle relative to the first longitudinal sides  116 . As such, the distance between the first and second longitudinal sides  116  and  218  at the first transverse side  226  is less than the distance between the first and second longitudinal sides  116  and  218  at the second transverse side  227 .  
      The contact pads  230  are arranged in a row on the first surface  212  proximate to the second longitudinal edge  222 . The individual contact pads  230  include a first end  232 , a second end  234  opposite the first end  232 , and a length extending between the first and second ends  232  and  234 . In the illustrated embodiment, the distance between the first longitudinal edge  120  and the first end  232  of the individual contact pads  230  is approximately the same, and the distance between the first longitudinal edge  120  and the second end  234  of the individual contact pads  230  varies and depends on the length of the pad  230 . The individual contact pads  230  have different lengths corresponding to the position of the pad  230  on the first surface  212  and the contour of the second longitudinal side  218 . For example, the contact pads  230  proximate to the first transverse side  226  have a shorter length than the contact pads  230  proximate to the second transverse side  227 . As such, the contact pads  230  of the illustrated module  200  contact the face  172  ( FIG. 1B ) of corresponding pins  170  ( FIG. 1B ) at different times during the insertion process and reduce the required insertion force. In other embodiments, the second surface of the module  200  may also include contact pads  230 .  
       FIG. 3  is a schematic front view of a memory module  300  in accordance with another embodiment of the invention. The memory module  300  is generally similar to the memory module  100  described above with reference to  FIGS. 1A and 1B . For example, the memory module  300  includes a substrate  310 , a microelectronic device  128  (shown schematically in broken lines) attached to the substrate  310 , and a plurality of contact pads  330  arranged on the substrate  310  and electrically coupled to the microelectronic device  128 . The illustrated substrate  310  includes a first surface  312 , a second surface (not shown) opposite the first surface  312 , a first longitudinal side  116 , a second longitudinal side  318  opposite the first longitudinal side  116 , a first longitudinal edge  120 , and a second longitudinal edge  322  opposite the first longitudinal edge  120 . In the illustrated embodiment, the second longitudinal side  318  is nonplanar and has a V-shaped configuration. As such, the distance between the first and second longitudinal edges  120  and  322  at an inboard portion of the first surface  312  is greater than the distance between the first and second longitudinal edges  120  and  322  at an outboard portion of the first surface  312 .  
      The contact pads  330  are arranged in a row on the first surface  312  proximate to the second longitudinal edge  322 . The individual contact pads  330  include a first end  332  and a second end  334  opposite the first end  332 . The distance between the first longitudinal edge  120  and the first end  332  of the individual pads  330  is approximately the same, and the distance between the first longitudinal edge  120  and the second end  334  of the individual pads  330  varies and depends on the length of the pad  330 . The individual contact pads  330  have different lengths corresponding to the position of the pads  330  on the first surface  312  such that the longest pads  330  are located at an inboard section of the first surface  312  and the shortest pads  330  are positioned at an outboard section of the first surface  312 . The configuration of contact pads  330  on the memory module  300  reduces the force required to insert the module  300  into the connector  150  ( FIG. 1B ) because the inboard pads  330  contact and flex corresponding pins  170  ( FIG. 1B ) before the outboard pads  330 . In other embodiments, the individual contact pads  330  can have generally the same length, and the first end  332  of the individual pads  330  can be spaced apart from the first longitudinal edge  120  by different distances so that less than all of the pads  330  contact corresponding pins  170  at the same time during insertion.  
      One feature of the memory module  300  illustrated in  FIG. 3  is that the longer contact pads  330  are located at an inboard section of the first surface  312 . Because the center portion of the connector  150  ( FIG. 1A ) typically flexes away from the module  300  when the module  300  is inserted, the longer center pads  330  ensure that the pins  170  ( FIG. 1A ) contact corresponding pads  330  even if the connector  150  flexes.  
       FIG. 4  is a schematic front view of a memory module  400  in accordance with another embodiment of the invention The memory module  400  is generally similar to the memory module  100  described above with reference to  FIGS. 1A and 1B . For example, the memory module  400  includes a substrate  410 , a microelectronic device  128  (shown schematically in broken lines) attached to the substrate  410 , and a plurality of contact pads  430  arranged on the substrate  410 . The illustrated substrate  410  includes a first surface  412 , a second surface (not shown) opposite the first surface  412 , a first longitudinal side  116 , and a second longitudinal side  418  opposite the first longitudinal side  116 . In the illustrated embodiment, the second longitudinal side  418  is nonplanar and includes a plurality of teeth  419 . In other embodiments, the second longitudinal side  418  can include a different number of teeth. For example, the second longitudinal side  418  can include a single tooth at an inboard portion of the module  400  or two teeth at outboard portions of the module  400 .  
      The contact pads  430  include a plurality of first pads  430   a  arranged on the first surface  412  and partially disposed on the teeth  419  and a plurality of second pads  430   b  arranged on the first surface  412  between adjacent first pads  430   a . The individual contact pads  430  include a first end  432  and a second end  434  opposite the first end  432 , and the second end  434  of the first pads  430   a  are disposed on corresponding teeth  419 . As such, the second end  434  of the first pads  430   a  are spaced apart from the first longitudinal side  116  a greater distance than the second end  434  of the second pads  430   b . In the illustrated memory module  400 , a single contact pad  430  is disposed on each of the teeth  419 , and the teeth  419  have a generally uniform height H. Other embodiments, however, may have other configurations. For example,  FIG. 5  is a schematic front view of a memory module  500  having a substrate  510  with a plurality of teeth  519  and a plurality of contact pads  530  partially disposed on each of the individual teeth  519 . Moreover,  FIG. 6  is a schematic front view of a memory module  600  including a substrate  610  having a plurality of the teeth  619  with various heights and a plurality of contact pads  630  partially disposed on the individual teeth  619 . The teeth  619  include first teeth  619   a  having a first height H 1  and second teeth  619   b  having a second height H 2  greater than the first height H 1 . The memory module  600  also includes contact pads  630  between the groups of pads  630  on the individual teeth  619 . In any of the modules  400 ,  500 , and  600  described above with reference to  FIGS. 4-6 , the teeth can be sized so that the contact pads on the teeth flex the corresponding pins  170  ( FIG. 1B ) on the connector  150  ( FIG. 1B ) before the other pads on the module contact and flex the other pins  170  to reduce the force required to insert the module into the connector  150 .  
      One feature of the memory modules  400 ,  500  and  600  illustrated in  FIGS. 4-6  is that the second longitudinal sides include generally flat teeth that partially carry contact pads. An advantage of this feature is that the memory modules do not exert side forces on the pins  170  ( FIG. 1B ) when the modules are inserted into the connector  150  ( FIG. 1B ). More specifically, although the teeth flex the pins  170  outwardly away from the module, the teeth do not exert a side force that causes the pins  170  to flex toward an adjacent pin  170 . Side forces can bend the pins  170  and damage the connector  150 .  
       FIG. 7  is a schematic front view of a memory module  700  in accordance with another embodiment of the invention. The memory module  700  is generally similar to the memory module  100  described above with reference to  FIGS. 1A and 1B . For example, the memory module  700  includes a substrate  710 , a microelectronic device  128  (shown schematically in broken lines) attached to the substrate  710 , and a plurality contact pads  730  arranged on the substrate  710 . The illustrated substrate  710  includes a first surface  712 , a second surface (not shown) opposite the first surface  712 , a first longitudinal side  116 , a second longitudinal side  718  opposite the first longitudinal side  116 , a first longitudinal edge  120 , and a second longitudinal edge  722  opposite the first longitudinal edge  120 . In the illustrated embodiment, the second longitudinal side  718  is generally planar and oriented parallel to the first longitudinal side  116 .  
      The contact pads  730  are arranged in a row on the first surface  712  proximate to the second longitudinal edge  722 . The individual contact pads  730  have a first end  732 , a second end  734  opposite the first end  732 , and a length between the first and second ends  732  and  734 . In the illustrated embodiment, the distance between the first longitudinal edge  120  and the first end  732  of the individual contact pads  730  is generally the same, and the distance between the first longitudinal edge  120  and the second end  734  of the individual contact pads  730  varies and depends on the length of the contact pads  730 . The individual contact pads  730  have different lengths corresponding to the position of the pad  730  on the first surface  712 . For example, the contact pads  730  positioned on an inboard portion of the first surface  712  have shorter lengths than the contact pads  730  positioned on an outboard portion of the first surface  712 . As such, the distance between the second end  734  of the individual contact pads  730  and the second longitudinal edge  722  at an inboard section of the first surface  712  is greater than the distance between the second end  734  of the individual contact pads  730  and the second longitudinal edge  722  at an outboard section of the first surface  712 . Accordingly, the contact pads  730  contact the face  172  ( FIG. 1B ) of corresponding contact pins  170  ( FIG. 1B ) at different times to reduce the force required for inserting the memory module  700  into the connector  150  ( FIG. 1B ).  
       FIG. 8  is a schematic side cross-sectional view of a memory module  800  in accordance with another embodiment of the invention. The memory module  800  is generally similar to the memory module  700  described above with reference  FIG. 7 . For example, the memory module  800  includes a substrate  810 , a microelectronic device (not shown) carried by the substrate  810 , and a plurality of contact pads  830  on the substrate  810 . The illustrated substrate  810  includes a first surface  712 , a second surface  714  opposite the first surface  712 , a first longitudinal side  116 , and a second longitudinal side  718  opposite the first longitudinal side  116 . The substrate  810  further includes first and second longitudinal edges  120  and  722  on the first surface  712 , and third and fourth longitudinal edges  823  and  825  on the second surface  714 .  
      The contact pads  830  include a plurality of first pads  830   a  on the first surface  712  and a plurality of second pads  830   b  on the second surface  714 . The individual pads  830  have a first end  832  and a second end  834  opposite the first end  832 . The first pads  830   a  have a first length L 4 , and the second end  834   a  of the individual first pads  830   a  is spaced apart from the second longitudinal edge  722  a first distance D 3 . The second pads  830   b  have a second length L 5  less than the first length L 4 , and the second end  834   b  of the individual second pads  830   b  is spaced apart from the third longitudinal edge  823  a second distance D 4  greater than the first distance D 3 . The difference between the first distance D 3  and the second difference D 4  reduces the force required to insert the memory module  800  into the connector  150  ( FIG. 1B ) because the first pads  830   a  contact and flex corresponding first pins  170   a  ( FIG. 1B ) before the second pads  830   b  contact and flex corresponding second pins  170   b  ( FIG. 1B ) when the memory module  800  is inserted into the connector  150 .  
      From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. For example, the features of any one of the memory modules described above can be combined with at least some of the features of another module described above. Accordingly, the invention is not limited except as by the appended claims.