Abstract:
A fully-molded or lidded circuit module assembly having edge-stiffening interlock features provides packaging for memory modules and other circuit modules, while preventing de-lamination of the housing from the circuit supporting structure. The interlock features are provided around the periphery of the circuit supporting structure, which is generally a laminated circuit substrate, and mating features are provided on a lid that interlock with the interlock features or are generated by molding an encapsulation around the circuit supported structure in a fully-molded assembly. The interlocked assembly has added strength in bending, twisting or dropping, preventing internal de-lamination or lid detachment from causing circuit module failure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is related to co-pending U.S. patent application Ser. No. 09/955,190, entitled “LEAD-FRAME METHOD AND ASSEMBLY FOR INTERCONNECTING CIRCUITS WITHIN A CIRCUIT MODULE”, filed Sep. 19, 2001 and Ser. No. 10/251,410 entitled “LEAD-FRAME METHOD AND CIRCUIT MODULE ASSEMBLY INCLUDING EDGE STIFFENER”, filed Sep. 20, 2002. Both of the above-referenced applications have at least one common inventor with the present application and are assigned to the same assignee. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to circuit module packaging, and more specifically, to a method and assembly for manufacturing a circuit module, including edge-stiffening features.  
       BACKGROUND OF THE INVENTION  
       [0003]     Removable circuit modules or cards are increasing in use to provide storage and other electronic functions for devices such as digital cameras, personal computing devices and personal digital assistants (PDAs). New uses for memory cards include multi-media cards and secure digital cards.  
         [0004]     Assembly of a circuit module typically involves attachment of one or more integrated circuit dies to a carrier or substrate. Carrier types include lead-frame assemblies as described in the above-referenced patent application. Substrates used in circuit modules are generally laminated circuit boards. For substrate-based multi-media cards, as well as other small form-factor applications, a cover is typically attached over the substrate to match the outline dimensions specified for the circuit module.  
         [0005]     Typically, the covers are manually assembled to a substrate-based circuit module using a silicone adhesive that is applied over the inside lower surface of the cover or over the top of an encapsulant covering the dies, and the cover is pressed onto the circuit module.  
         [0006]     However, when such a circuit module is flexed, bent or dropped, the adhesive attaching the cover to the substrate is stressed, and the cover will separate from the substrate.  
         [0007]     Therefore, it would be desirable to provide circuit modules wherein no cover separation occurs in bending or flexure.  
       SUMMARY OF THE INVENTION  
       [0008]     A substrate-based circuit module assembly and method therefor provides packaging for memory modules and other circuit modules. The circuit module assembly comprises one or more integrated circuits for providing an electronic function of the circuit module, a substrate for mounting the integrated circuits, and a housing providing the outside form factor of the circuit module.  
         [0009]     The housing may consist of an encapsulation attached to the substrate and surrounding the integrated circuits that extends to the outer dimensions of the circuit module on at least a top and the sides of the circuit module and may also extend around the substrate to provide the bottom side of the circuit module. The substrate may include interlock features for interlocking with mating features that are molded into the housing and the interlock features may constitute means for molding the mating features by molding the housing around a substrate with interlock features. The circuit module may also include an inner encapsulation covering the integrated circuits and a top side of the substrate which is subsequently covered by molding the housing over the inner encapsulation. Interlock features may be provided on the substrate, the inner encapsulation or both.  
         [0010]     Alternatively, the housing may comprise a substrate to which a lid having mating features is attached by an adhesive, providing resistance to separation of the adhesive by strengthening the mechanical interlocking of the lid to the substrate. The alternative embodiment may also include an inner encapsulant and interlock features may be provided on the substrate, the inner encapsulation or both. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1A  is a pictorial diagram depicting a top view of a substrate assembly forming part of a circuit module in accordance with an embodiment of the invention;  
         [0012]      FIG. 1B  is a pictorial diagram depicting a top view of a substrate assembly forming part of a circuit module in accordance with an embodiment of the invention;  
         [0013]      FIG. 1C  is a pictorial diagram depicting a side view of a lid forming part of a circuit module in accordance with an embodiment of the invention;  
         [0014]      FIG. 1D  is a pictorial diagram depicting a bottom inside view of a lid forming part of a circuit module in accordance with an embodiment of the invention;  
         [0015]      FIG. 2A  is a pictorial diagram depicting a cross-sectional side view of a fully-molded circuit module in accordance with an embodiment of the invention; and  
         [0016]      FIG. 2B  is a pictorial diagram depicting cross-sectional views of shapes for forming mating and interlocking features in a circuit module in accordance with various embodiments of the invention. 
     
    
       [0017]     The invention, as well as a preferred mode of use and advantages thereof, will best be understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings, wherein like reference numerals indicate like parts throughout.  
       DETAILED DESCRIPTION  
       [0018]     Referring now to  FIG. 1A , a substrate assembly  10  for forming a circuit module in accordance with an embodiment of the invention is depicted. Substrate assembly  10  is depicted as adapted for use in a circuit module as used in various multimedia memory applications. The present invention is also applicable to cards and modules having other outlines such as secure digital cards and various compact flash memory cards, etc. The present invention applies to peripheral device cards (I/O cards), as well.  
         [0019]     A substrate  11  to which integrated circuit dies  13  are attached and circuit terminals (contacts)  14  are included on the bottom side, is optionally covered by an inner encapsulant  12  that is bonded to substrate  11 . Circuit contacts  14  are electrically connected to integrated circuit dies  13  by conductive patterns  15  within substrate  11 . Substrate assembly  10  forms the electronic portion of the circuit module, which must be packaged with a housing which covers the top and edges and optionally the bottom of substrate assembly  10  to form a package that conforms with the outlines specified for the particular MMC, SD card, etc.  
         [0020]     A suitable housing can be provided by a lid or cover that is applied over substrate assembly  10  using an adhesive. Alternatively, a housing may be molded over substrate assembly  10 , forming a fully-molded circuit module. In either housing embodiment type, twisting or bending of the circuit module may separate substrate assembly  10  from the housing either completely or internally, causing distortion or separation of portions of the circuit module. The bending of the circuit module may also cause other internal failure such as cracking of substrate  11 , breakage of conductive patterns  15  and cracking or separation of dies  13 .  
         [0021]     The present invention is directed to various solutions to the separation problem described above. In general, the embodiments provide stiffening of the circuit module package so that an applied bending, twisting or impact force yields reduced bending of the circuit module. The circuit module is stiffened by adding one or more of various interlock features  16 A,  16 B and  16 C to substrate assembly  10  and either providing corresponding mating features on a lid, so that the lid interlocks with substrate assembly  10 , or in a fully-molded housing embodiment, molding the housing around the interlock features so that mating features are formed in the molded housing. Additionally, the circuit module may be made fully-molded, in which case the module can be constructed with or without interlock features.  
         [0022]      FIG. 1A  shows interlock features in the form of notches  16 A in substrate  11  disposed around the periphery of substrate  11  at regular intervals. Further interlock features shown in  FIG. 1A  are circular cutout  16 B and rectangular cutout  16 C provided through substrate  11 . Interlock features that strengthen a circuit module in bending axes may be located on the edge of substrate (as exemplified by notches  16 A), through the substrate (as exemplified by cut-outs  16 B and  16 C) or, as shown in  FIG. 1B , by interlock features formed in optional inner encapsulant  12 A. In general, interlock features may be located near the edges, stiffening the edges and therefore the circuit module as a whole, or interlock features may be located in convenient areas between circuits through the substrate, which will stiffen the entire circuit module.  
         [0023]      FIG. 1B  shows notches  16 D similar to notches  16 A of  FIG. 1A , but notches  16 D are formed around the periphery of inner encapsulant  12 . Any of the above interlock features may be used in combination, including the combination of notches  16 A on the edge of substrate  11  and notches or other interlock features provided on an inner encapsulation such as notches  16 D.  
         [0024]     Referring now to  FIG. 1C , a lid  20  is shown illustrating mating features  24 A suitable for interlocking with notches  16 A. Mating features for interlocking with interlock features on the substrate edge such as those illustrated will generally be tabs extending downward from the plane of the top surface of substrate  11  to the bottom surface of substrate  11 . A fully-molded housing can also be illustrated by the outline shown in  FIG. 1C , as the shape of the housing can externally be made identical to lid  20  and mating features (tabs)  24 A can be generated by molding around a notched substrate, such as substrate  11 , when molding a housing over substrate assembly  10 .  
         [0025]     Referring now to  FIG. 1D , a bottom perspective view of lid  20  prior to attachment to a circuit module is shown. Inner surface  22  of lid has mating features  24 B disposed to mate with interlock features of an inner encapsulation such as notches  16 D of inner encapsulation  12 A. Tab  24 A illustrates a mating feature for interlocking with interlock features disposed around the periphery of the substrate such as notches  16 A disposed around substrate  11 . Similarly, a fully-molded housing encapsulated over an inner encapsulant having interlock features will generate mating features such as those illustrated by bumps  24 B.  
         [0026]     Referring now to  FIG. 2A , a cross-sectional side view of a fully-molded circuit module  30  in accordance with an embodiment of the invention is depicted. Circuit contacts  14  are provided by a raised conductive layer on substrate  11 B, which is generally a laminated circuit board substrate. Dies  13  and passive components  17  are mounted on substrate and dies are wire-bonded via wires  18  to the substrate  11 B conductive patterns, that electrically interface the electronics to contacts  14 . Housing  20 A is molded around substrate  11 B on all sides, although alternatives to circuit module  30  may be made without molding encapsulant on the bottom side of substrate  11 B and/or without molding encapsulant around any or all of the sides of substrate  11 B, in which case the conductive material forming contacts  14  can be made thinner. Housing  20 A completely covers dies  13 , wires  18  and passive components  17  as shown, but an inner encapsulation may also be used prior to final molding of the housing and may provide inventory advantage in the protected encapsulated assemblies can be stored without the final encapsulation which may have a shape, color or embossing that is dictated by a particular application. Housing  20 A and substrate  11 B preferably include interlock features for stiffening the edges the circuit module  30 , providing enhanced protection against damage due to bending, flexure or impact.  
         [0027]     Referring now to  FIG. 2B , a variety of shapes that may be used to generate interlocking features and mating features in accordance with various embodiments of the invention are shown in a table. Interlock feature  16 E is an example of a shape suitable for use with cut-outs through a substrate such as interlock features  16 B and  16 C of  FIGS. 1A and 1B . Interlocking features  16 E can be located anywhere along the perimeter or inboard of the substrate edge.  
         [0028]     A housing may be molded over the substrate and mating feature  24 E will be generated through the cut-out having a counter-bore retaining shape as shown. Interlock feature  16 F is similarly suitable for such applications, showing a counter-sink shape generated as a mating feature  24 F through counter sunk cut-out  16 F.  
         [0029]     Interlock features  16 G,  16 H are examples of interlock features suitable for alternative shapes that may be applied to interlock features such as tabs  16 A of  FIG. 1A  or tabs  16 B of  FIG. 1B . Interlock feature  16 G generates a stair-step edge mating feature having an overlapping extension when over-molded, or provides a shape that is compatible with a separately fabricated lid having mating feature  24 G disposed thereon, by press fitting the substrate assembly to the from above, which will not cause any interference between the stairstep extension of the mating feature  24 G and the interlock feature  16 G. Interlock feature  16 G has a chamfered edge to generate or mate with an inverse chamfered edge of a mating feature  24 H on a molded housing or lid.  
         [0030]     Hemispherical interlock feature  16 J may be used at the edge of a substrate or as a cut-out mating feature (a vent hole may be provided through from interlock feature  16 J side to permit exit of air during a molding process. Corresponding mating feature  24 J can be fit from above in case of a lid or molded around interlock feature  16 J for a fully-molded application.  
         [0031]     Mating feature  16 A is depicted for comparison to the other examples, showing the profile of a tab interlock feature and a notch mating feature  24 A. The other examples have advantages in that they provide interlock in two or three axes (depending on the vertical profile), while the notch only provides interlock in the direction that the sides of the tab contact the notch. Other shapes that may be used will be apparent to those skilled in the art and the examples shown in  FIG. 2B  are intended to provide examples and are not limiting as to the shapes that may be employed to provide interlocking and mating features on the substrate assembly or housing of a circuit module.  
         [0032]     The above description of embodiments of the invention is intended to be illustrative and not limiting. Other embodiments of this invention will be obvious to those skilled in the art in view of the above disclosure and fall within the scope of the present invention.