Apparatus for stacking semiconductor chips

Abstract

A multi-chip memory module comprises multiple standard, surface-mount-type memory chips stacked on top of each other, and a pair of printed circuit boards mounted on opposite sides of the memory chips to electrically interconnect the memory chips. Each printed circuit board has vias that are positioned to form multiple rows, with each row of vias used to connect the printed circuit board to a respective memory chip. The vias falling along the bottom-most row of each printed circuit board are also exposed and are used to surface mount the multi-chip module to pads of a memory board.

What is claimed is: 
     
       1. A multi-chip memory module, comprising: a plurality of memory chips stacked on top of one another, each memory chip of said plurality having conductive surface mount pins; and   first and second side boards mounted to said memory chips such that said side boards are substantially parallel to one another, each side board having: vias for receiving said surface mount pins of said memory chips, said vias arranged in rows such that each row corresponds to a respective memory chip of said plurality, vias of a bottom-most row receiving surface mount pins of a bottom-most memory chip of said plurality, said bottom-most row falling along a lower side board edge such that vias of said bottom-most row serve as surface mount terminals for surface mounting the multi-chip memory module to pads of a printed circuit board; and   conductive traces for interconnecting said vias.     
     
     
       2. A multi-chip memory module as defined in claim 1, wherein said vias of said bottom-most row are exposed along said lower side board edge. 
     
     
       3. A multi-chip memory module as defined in claim 1, wherein all memory chips of said plurality are functionally identical. 
     
     
       4. A multi-chip memory module as defined in claim 1, wherein the total number of surface mount terminals on said first and second side boards is greater than the number of said surface mount pins on any one of said plurality memory chips. 
     
     
       5. A multi-chip memory module as defined in claim 1, wherein said memory chips of said plurality are interconnected by said traces such that all memory chips of said plurality are selected simultaneously. 
     
     
       6. A multi-chip memory module as defined in claim 1, in combination with a memory board having surface mount pads thereon, said vias of said bottom-most row soldered to said surface mount pads. .[.7. A module that includes at least one multi-chip module, said module comprising: a circuit board having at least first and second sets of surface mount pads;   a first plane side board including a plurality of surface mount contacts positioned along an edge of said first side board which abuts said circuit board, said plurality of surface mount contacts of said first side board being surface-mounted to said first set of surface mount pads of said circuit board such that said first side board is substantially perpendicular to said circuit board;   a second planar side board including a plurality of surface mount contacts positioned along an edge of said second side board which abuts said circuit board, said plurality of surface mount contacts of said second side board being surface-mounted to said second set of surface mount pads of said circuit board such that said second side board is substantially perpendicular to said circuit board and substantially parallel to said first side board; and   a plurality of standard surface mount chips stacked between said side boards, each chip including a plurality of pins, a portion of each pin extending beyond a chip surface which lies generally parallel to said circuit board with said chip positioned between said side boards, each chip of said plurality conductively connected to said first side board and   
     
     
        said second side board..].8. A module as defined in claim .[.7.]. .Iadd.12.Iaddend., wherein said first and second sets of surface mount 
     
     
        pads are arranged in respective first and second rows. 9. A module as defined in claim .[.7.]. .Iadd.12.Iaddend., wherein a surface area of a region between said first and second side boards on said circuit board is generally equal to a surface area occupied by one of said chips of said 
     
     
        plurality. 10. A module as defined in claim .[.7.]. .Iadd.12.Iaddend., wherein said standard surface mount chips of said plurality are stacked on 
     
     
        top of one another. 11. A module as defined in claim .[.7.]. .Iadd.12.Iaddend., wherein all chips of said plurality are functionally 
     
     
        identical. 12. A module .[.as defined in claim 7,.]. .Iadd.that includes at least one multi-chip module, said module comprising: a circuit board having at least first and second sets of surface mount pads;   a first planar side board including a plurality of surface mount contacts positioned along an edge of said first side board which abuts said circuit board, said plurality of surface mount contacts of said first side boards being surface-mounted to said first set of surface mount pads of said circuit board such that said first side board is substantially perpendicular to said circuit board;   a second planar side board including a plurality of surface mount contacts positioned along an edge of said second side board which abuts said circuit board, said plurality of surface mount contacts of said second side board being surface-mounted to said second set of surface mount pads of said circuit board such that said second side board is substantially perpendicular to said circuit board and substantially parallel to said first side board; and   a plurality of standard surface mount chips stacked between said side boards, each chip including a plurality of pins, a portion of each pin extending beyond a chip surface which lies generally parallel to said circuit board with said chip positioned between said side boards, each chip of said plurality conductively connected to said first side board and said second board, .Iaddend.wherein a lower-most chip of said plurality is   
     
     
        soldered to said first and second sets of surface mount pads. 13. A module as defined in claim .[.7.]. .Iadd.12.Iaddend., wherein each chip of said 
     
     
        plurality is a memory chip. 14. A module as defined in claim 12, wherein said lower-most chip is additionally soldered to vias of said first and 
     
     
        second side boards. 15. A module as defined in claim 14, wherein said lower-most chip is soldered to said vias with a first solder that has a first melting point, and is soldered to said first and second sets of surface mount pads with a second solder that has a second melting point, said second melting point lower than said first melting point. .Iadd.16. A module as defined in claim 12, wherein each surface mount contact of the first and second side boards is formed by a solder joint, and at least a portion of each solder joint extends below a lower edge of the respective side board. .Iaddend..Iadd.17. A low profile multi-chip module for mounting on a circuit board substrate, comprising: first and second support structures, each support structure including a plurality of electrically conductive paths and a plurality of surface mount contacts positioned along an edge thereof, the plurality of surface mount contacts arranged to align with corresponding surface mount pads on the circuit board substrate to electrically couple the first and second support structures to the circuit board substrate; and   at least first and second juxtaposed standard surface mount chips, the first and second chips being identical to each other, each chip having planar surfaces extending between at least a pair of opposing sides of the chip, the planar surfaces arranged generally between the support structures with the planar surfaces of adjacent chips positioned face to face, the opposite sides of each chip having a respective set of identical pins extending beyond the side of the chip toward respective ones of the support structures, at least some of each set of pins being electrically connected to respective ones of the support structures, the pins of the lower-most chip being disposed relative to the edges of the first and second support structures such that when the multi-chip module is surface mounted to the circuit board substrate the two sets of pins of the lower-most chip are soldered directly to the surface mount contacts of the first and second support structures, respectively, and to the circuit board substrate. .Iaddend..Iadd.18. The multi-chip module of claim 17, wherein the juxtaposed standard surface mount chips are interconnected by the plurality of electrically conductive paths such that all of the juxtaposed standard surface mount chips may be selected simultaneously. .Iaddend..Iadd.19. The multi-chip module of claim 17, wherein the electrical conductive paths are electrically coupled to at least some of the pins of the juxtaposed standard surface mount chips and are arranged so as to individually select at least one the juxtaposed standard surface mount chips. .Iaddend..Iadd.20. The multi-chip module of claim 17, wherein a total number of the surface mount contacts is greater than the total number of pins of the first chip. .Iaddend..Iadd.21. The multi-chip module of claim 17, wherein at least some of the pins of the juxtaposed standard surface mount chips are mechanically connected to one of the support structures. .Iaddend..Iadd.22. The multi-chip module of claim 17, wherein at least some of the pins of the juxtaposed standard surface mount chips are solder connected to one of the support structures so as to mechanically and electrically connect the pins to the support structures. .Iaddend..Iadd.23. The multi-chip module of claim 17, wherein all of the juxtaposed standard surface mount chips of the module are positioned to lie entirely between the first and second support structures. .Iaddend..Iadd.24. The multi-chip module of claim 17, wherein at least corresponding portions of the first and second support structures lie generally parallel to each other. .Iaddend..Iadd.25. The multi-chip module of claim 17, wherein the first standard surface mount chip is aligned above the second standard surface mount chip. .Iaddend..Iadd.26. The multi-chip module of claim 17, wherein the first and second support structures comprise opposing inner surfaces, and the pins of the juxtaposed standard surface mount chips extend outward beyond the inner surfaces of the first and second support structures. .Iaddend..Iadd.27. The multi-chip module of claim 17, wherein the first and second support structures are spaced apart from each other by a distance less than a distance between an outer end of a first pin on one side of the first standard surface mount chip and an outer end of a second pin on an opposite side of the first standard surface mount chip.   
     
     
        .Iaddend..Iadd.     The multi-chip module of claim 17, wherein said planar surfaces of each chip lie generally within respective parallel planes, and each pin of at least one of the chips connects to the corresponding support structure at a location outside the space between the plane. .Iaddend..Iadd.29. The multi-chip module of claim 24, wherein the first and second support structures comprise planar side boards. .Iaddend..Iadd.30. The multi-chip module of claim 24, wherein each of the first and second support structures extends along at least a side of one of the plurality of juxtaposed standard surface mount chips. .Iaddend..Iadd.31. The multi-chip module of claim 30, wherein each support structure is formed of a unitary piece of printed circuit board material. .Iaddend..Iadd.32. The multi-chip module of claim 30, wherein the planar surfaces of each chip lie generally normal to the parallel corresponding portions of the first and second support structures. .Iaddend..Iadd.33. The multi-chip module of claim 26, wherein said first and second support structures each include a plurality of vias that are arranged to receive 
     
     
        at least outer ends of at least some of the pins. .Iaddend..Iadd.34.  A low profile memory module comprising: a memory board having at least a pair of surface mount pads; and   at least one multi-chip module comprising a circuit board structure on the memory board and at least two identical, standard surface mount memory chips, each chip having a plurality of substantially identical pins extending outwardly from the respective chip, the chips being stacked one above the other with corresponding pins of two chips positioned above each other generally in vertical alignment, the corresponding pins which are in general vertical alignment being separated by solder, metal contacts and a portion of the circuit board structure, the portion of the circuit board structure having metal contacts on each side and the solder connecting each metal contact to an adjacent pin of a corresponding one of the chips, the pins of a lower-most one of the chips being soldered to the surface mount pads of the memory board and being soldered to metal contacts along a bottom side of the circuit board structure such that with the multi-chip module surface mounted onto the memory board the pins of the lower-most one of the chips are disposed between the circuit board structure and the   
     
     
        memory board. .Iaddend..Iadd.35.  A module as defined in claim 34, wherein the circuit board structure includes an interconnecting conductive path electrically connecting together the metal contacts. .Iaddend..Iadd.36. A module as defined in claim 34, wherein the portion of the circuit board structure between the metal contacts has a generally rectangular cross-sectional shape. .Iaddend..Iadd.37. A low profile multi-chip memory module having surface mount contacts for surface mounting to surface mount pads of a memory board, the memory module comprising: at least two identical, standard surface mount memory chips stacked one above the other, each chip having a plurality of identical pins extending outwardly from the respective chip; and   at least one circuit board structure including a plurality of electrically conductive paths and a plurality of surface mount contacts positioned along a bottom edge of the circuit board structure, the plurality of surface mount contacts aligned to align with corresponding surface mount pads on the memory board to electrically couple the circuit board structure to the memory board, the circuit board structure being electrically connected to at least some of the pins of the chips, each surface mount contact being formed by solder and one of the pins of a bottom one of the memory chips, said surface mount contacts extending below the bottom edge of the circuit board structure. .Iaddend..Iadd.38. A module as defined in claim 37, wherein each chip includes a pair of opposing sides with the pins extending from both sides, and the circuit board structure supports the pins on both sides of the chips.   
     
     
        .Iaddend..Iadd.39.  A module as defined in claim 37, wherein the circuit board structure includes a first circuit board side element and a second circuit board side element, each side element extending along a side of at least the bottom one of the chips and supporting a set of pins that extend from the respective side of an upper one of the chips, and each side element includes some of the plurality of electrically conductive paths and some of the plurality of surface mount contacts that are arranged along a lower edge of the respective side element. .Iaddend..Iadd.40. A module as defined in claim 39, wherein each side element has a generally uniform rectangular cross-sectional shape. .Iaddend..Iadd.41. A module as defined in claim 37, wherein the total number of surface mount contacts on the circuit board structure is greater than the number of the plurality of pins on any one of the standard surface mount chips. .Iaddend..Iadd.42. A module as defined in claim 37, wherein the circuit board structure is formed of a unitary piece of printed circuit board material. .Iaddend..Iadd.43. A module as defined in claim 37, additionally comprising a second circuit board structure including a plurality of electrically conductive paths and a plurality of surface mount contacts positioned along at least one edge of the second circuit board structure, the plurality of surface mount contacts arranged to align with corresponding surface mount pads on the memory board to electrically couple the second circuit board structure to the memory board, the second circuit board structure being electrically connected to at least some of 
     
     
        the pins of the chips. .Iaddend..Iadd.44.  A module as defined in claim 37, wherein each chip has planar surfaces that extend between at least a pair of opposing sides of the chip, and the chips are arranged in the module with the planar surfaces of adjacent chips positioned face to face. .Iaddend..Iadd.45. A module as defined in claim 42, wherein the circuit board structure has a generally uniform rectangular cross-sectional shape. .Iaddend.