Abstract:
An intercoupling component is provided that electrically connects the device leads of an integrated circuit package to a substrate. The package includes external device leads, each device lead having a downwardly extending section proximate a side of the package body, and the intercoupling component includes an insulating support member. The support member includes a first surface including first electrical attachment sites, each configured for making an electrical connection with a corresponding one of the device leads of the package. The support member also includes an opposite second surface including second electrical attachment sites in electrical contact with the first electrical attachment sites, each of the second electrical attachment sites including a plurality of solder balls associated with each device lead. The plurality of solder balls are used to form an electrical connection between each surface mount pad on the substrate and the corresponding conductive pad of the intercoupling component.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to making connections between integrated circuit packages (e.g., quad-flat packages) and printed circuit boards, and more particularly to intercoupling components for making such connections. 
       BACKGROUND 
       [0002]    Quad flat packages (QFPs) are popular in applications where packages are required to be manufactured in high volumes and at low costs. In general, a QFP is a surface-mounted integrated circuit package having leads extending from each of the four sides. The leads that extend from the QFP are generally soldered directly to corresponding surface mount pads of a printed circuit board. 
         [0003]    However, there are several circumstances in which it may be advantageous to be able to indirectly connect a QFP to a circuit board using an intermediate intercoupling device. In one example, such an intercoupling device can serve as a converter in cases where there is a mismatch in size between the QFP and contacts of the printed circuit board. This can occur when advances in size reduction of one component, for example the printed circuit board, outpaces that of the other component, for example the QFP. In another example, in certain applications, a QFP may have manufacturing temperature requirements which differ from that of the printed circuit board. Use of an intercoupling device permits the QFP to be manufactured and assembled independently of the printed circuit board, and then connected to the printed circuit board subsequent to the manufacture. 
         [0004]    Recent regulatory efforts to limit certain hazardous substances in some geographic areas and/or in some industries, such as the Restriction of Hazardous Substances in Electrical and Electronic Equipment (RoHS), have resulted in inconsistencies in the products that are manufactured, such that some electronic components, including QFPs and/or printed circuit boards, are compliant with regulations and some are not. Thus, it can be advantageous to provide an intercoupling device which permits, for example, a lead-free component to be assembled to a lead-containing component. 
       SUMMARY 
       [0005]    This invention relates to making connections between integrated circuit packages (e.g., quad-flat packages) and circuit boards, and more particularly to intercoupling components for making such connections. 
         [0006]    In some aspects, an intercoupling component of the type used to electrically connect the device leads of an integrated circuit package to a substrate is provided. The package includes a body and device leads, each device lead having a downwardly extending section proximate a side of the body, and the intercoupling component includes an insulating support member. The insulating support member includes a first surface including first electrical attachment sites, each configured for making an electrical connection with a corresponding one of the device leads of the integrated circuit package. The insulating support member also includes an opposite second surface including second electrical attachment sites in electrical contact with the first electrical attachment sites, each of the second electrical attachment sites including a plurality of solder balls associated with each device lead. 
         [0007]    Embodiments can include one or more of the following. 
         [0008]    The integrated circuit package can be a quad flat pack type package. The first electrical attachment sites can be electrically connected to the second electrical attachment sites by via holes. The plurality of solder balls can include at least three solder balls. Each of the plurality of solder balls can have a diameter of at most about 0.014 inches. The plurality of solder balls can include at least three solder balls arranged in a linear arrangement having approximately the same shape of the shape of as device leads of an integrated circuit package. 
         [0009]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is an exploded perspective view of an assembly in which an intercoupling component is used to electrically couple a QFP package to a printed circuit board. 
           [0011]      FIG. 2  is the exploded perspective view of  FIG. 1  as seen from below. 
           [0012]      FIG. 3  is a perspective view of a lower surface of the intercoupling component of  FIG. 1 . 
           [0013]      FIG. 3A  is a detail view of a portion of  FIG. 3  corresponding to dashed-line circle  3 A. 
           [0014]      FIG. 4  is a cross-sectional view of a portion of  FIG. 3  as seen along line  4 - 4 . 
           [0015]      FIG. 5  is a cross sectional view of a portion of the assembly of  FIG. 1  subsequent to soldering of the intercoupling component to the printed circuit board. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Referring to  FIG. 1 , an intercoupling component  16  for electrically connecting the device leads  12  of an integrated circuit package such as a quad flat package  10  to a printed circuit board  20  is shown. The quad flat package  10  includes a body portion  11  with downwardly extending conductive leads  12  proximate to one or more sides of the body  11 . The leads  12  are connected at one end to the body portion  11 , and at another end have a portion bent to form elongate feet  14  that are substantially parallel to the body  11 . When mounted to the intercoupling component  16 , the feet  14  are in electrical contact with, and are fixed to, corresponding electrically conductive pads  18  formed on the surface of the intercoupling component  16  using conventional surface mount technology. 
         [0017]    The intercoupling component  16  electrically connects the QFP  10  to the printed circuit board  20  and includes an electrically insulative member  28  having an upper surface  24  and a lower surface  26 . The terms “upper” and “lower” are used here and throughout this document for descriptive purposes rather than to imply any absolute relative orientation. 
         [0018]    The upper surface  24  supports conductive pads  18  that are provided in a pattern corresponding to a footprint of the feet  14  of the QFP  10 . In addition, each conductive pad  18  is formed having a size and shape corresponding to the size and shape of the feet  14  of leads  12 . The lower surface  26  of the intercoupling component  16  (as shown in  FIG. 3 ) supports electrical traces  30  that are provided in a pattern generally corresponding to a footprint of surface mount pads  22  of the printed circuit board  20 . 
         [0019]    Each upper conductive pad  18  terminates at one end in an electrical trace  40 . Each trace  30  provided on the lower surface  26  of the intercoupling component  16  is electrically connected to the corresponding trace  40  of a conductive pad  18  on the upper surface  24  by an electrically conductive via  52  ( FIG. 4 ). The via  52  extends from the upper surface  24  to the lower surface  26 , and forms an electrical current path through the intercoupling component  16  between the conductive pad  18  and the corresponding trace  30 . 
         [0020]    The upper and lower surfaces  24 ,  26  of the intercoupling component  16  are provided with a polymer solder resist coating  34 . The coating  34  serves to prevent solder from bridging between conductors and thereby creating short circuits. The coating  34  also provides some protection for the intercoupling component  16  from the environment. As seen in  FIG. 4 , at locations corresponding to each conductive pad  18 , the coating  34  is absent so that an electrical connection can be made between a lead  12  and the associated conductive pad  18 . In some embodiments, the coating  34  overlies the traces  40  extending from each conductive pad, as well as terminal ends of the via  52 . At locations corresponding to each trace  30 , the coating  34  masks some portions  36  of the trace  30 , while being absent from other portions  38 . More specifically, at the trace  30 , the solder resist coating  34  is configured to masks portions  36  of the trace  30 , leaving exposed portions  38  sized and shaped to permit connection to the solder balls  32 . In some embodiments, the trace  30  is widened in the vicinity of portions  38 . In these embodiments, the trace  30  may be provided with generally circular widened portions to facilitate receipt of, and contact with, a solder ball  32 . 
         [0021]    As shown in  FIGS. 2 and 3 , the intercoupling component  16  further includes multiple rounded solder balls  32  attached to each of the traces  30  provided on the lower surface  26  of the intercoupling component  16 . For each trace  30 , the solder balls  32  are disposed in a preconfigured arrangement that corresponds to the shape of the surface mount pads  22  of circuit board  20 , which in turn corresponds to a pattern of the leads of the QFP package  10 . As a result, multiple solder balls  32  are used to form an electrical connection between a single surface mount pad  22  on the printed circuit board  20  and the corresponding trace  30 . 
         [0022]    The number and arrangement of the solder balls  32  can vary based on the size, shape, and arrangement of the leads  12  of the QFP  10 , which determines the corresponding size, shape and arrangement of surface mount pads  22  of the printed circuit board  20 . For example, as shown in  FIGS. 2 and 3 , each lead  12  of the QFP  10  is associated with a set of three solder balls  32  arranged in a line along the trace  30 . As discussed above, the solder resist coating  34  masks portions  36  of the trace  30  between the solder balls  32 , such that each solder ball  32  is fixed to a corresponding exposed portion  38  of the trace  30  ( FIG. 4 ). 
         [0023]    In order to electrically and mechanically connect the intercoupling component  16  to the printed circuit board  20 , the solder balls  32  are soldered to corresponding surface mount pads  22  of the printed circuit board  20 . As shown in  FIGS. 3 and 4 , during use, the arrangement of the solder balls  32  is configured to control fluid flow (e.g., the flow of molten solder) and prevent the occurrence of a short circuit between two adjacent surface mount pads  22  of printed circuit board  20 , while substantially covering the entire surface mount pad  22 .  FIG. 4  shows a cross-sectional view of the intercoupling component  16  prior to being affixed to the circuit board  20 . After the intercoupling component  16  has been affixed to the printed circuit board  20  by application of heat to cause the solder to flow, the solder forms a connection region  50  that is similar in shape to the shape of the leads  12  of the QFP  10 , as seen in  FIG. 5 . 
         [0024]    The use of multiple solder balls arranged in the shape of the lead  12  of a QFP  10 , can provide various advantages in connecting the intercoupling component  16  to the printed circuit board  20 . For example, the leads  12  of a QFP  10  are often closely spaced to one another. As such, the use of a single, larger solder ball to provide an electrical connection between the intercoupling component  16  and the printed circuit board  20  can result in solder flowing into regions where the solder may form an electrical connection with solder from an adjacent connection region resulting in a short between two leads of the QFP  10 . The use of multiple, smaller solder balls arranged in a preconfigured layout can limit the flow of solder outside of the connection regions  22 , limiting the likelihood of formation of electrical shorts between adjacent leads of the QFP  10 . 
         [0025]    The size of the solder balls  32  can be selected to control the flow of solder. For example, the solder balls may have a smaller diameter than a typical solder ball used to connect two electrical components. More particularly, in some embodiments, each of the solder balls  32  can have a diameter in the range of about 0.012 inches to about 0.014 inches (e.g., at most about 0.014 inches). The size and arrangement of the solder balls  32  can be selected such that after causing the solder to flow the shape of the solder generally matches the shape of the lead  12  of the QFP  10 . 
         [0026]    The use of multiple solder balls and intercoupling component  16  to connect the QFP  10  to the printed circuit board  20  can also provide the advantage of increased mechanical stability. The leads  12  on the QFP  10  are formed of a metal or conductive material and can be bent with the application of too large of a force onto the QFP  10 . If QFP  10  is connected directly to the circuit board  20  and the leads  12  of the QFP  10  become bent during application, the leads  12  may fail to form an electrical contact with the circuit board  20 . In contrast, when using intercoupling component  16 , the QFP  10  can be pre-attached to the intercoupling component  16  which is then attached to the printed circuit board using the solder balls  32  disposed on the lower surface  26  of the intercoupling component  16 . The solder balls  32  are generally more robust to the application of force in comparison to the leads  12  of the QFP  10 . As such, the amount of force used to connect the intercoupling component  16  to the printed circuit board  20  is less likely to result in the loss of an electrical connection between the QFP  10  and the printed circuit board  20 . 
         [0027]    The use of multiple solder balls and intercoupling component  16  to connect the QFP  10  to the printed circuit board  20  can also provide the advantage of increased electrical contact area. 
         [0028]    A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. 
         [0029]    For example, the intercoupling component can be used with various types of quad flat packages such as a bumpered quad flat package (BQFP), a bumpered quad flat package with heat spreader (BQFPH), ceramic quad flat package (CQFP), a fine pitch quad flat package (FQFP), a heat sinked quad flat package (HQFP), a low profile quad flat package (LQFP), a metric quad flat package (MQFP), a plastic quad flat package (PQFP), a small quad flat package (SQFP), a thin quad flat package (TQFP), a very small quad flat package (VQFP), and/or a very thin quad flat package (VTQFP). In addition, while the above examples are described in terms of a quad flat package (QFP), a similar intercoupling component could be used for other types of packages. For example, a similar intercoupling component could be used for a ball grid array package (BGA), a quad flat package no leads (micro lead frame) (QFN(MLF)), a small outline integrated circuit package (SOIC), and/or a plastic leaded chip carrier (PLCC). 
         [0030]    In another example, while the above examples shows a set of three solder balls  32  forming the connection between the intercoupling component  16  and the printed circuit board  20 , other numbers of solder balls  32  could be used. For example, a set of 4, 5, 6, 7, 8, 9, or 10 solder balls  32  could be used to form each connection region between the intercoupling component  16  and a surface pad  22  on the printed circuit board  20 . In general, the number of solder balls used to form the connection region can be selected based on the size and shape of the leads on the QFP and the diameter of the solder balls such that the arrangement of the solder balls corresponds to the layout of the leads of the QFP. If the solder balls are smaller, more solder balls may be used to form the connection region. In addition, if the leads of the QFP are very closely spaced, it may be desirable to closely control the flow of solder by using more, smaller sized solder balls arranged to limit the flow in undesired directions. 
         [0031]    In another example, while the solder balls in at least some of the examples shown above are arranged in a linear arrangement, other arrangements are possible. For example, multiple rows of solder balls could be arranged side by side to form a rectangular contact region. 
         [0032]    Other embodiments are within the scope of the following claims.