Abstract:
The invention is to an array of stacked devices utilizing vertical surface mounted semiconductor devices stacked side by side and inserting the stack of devices into a casing. The packaged stack of devices creates a cube package which is capable of replacing SIMM boards, and saves considerable space. The casing dissipates heat generated in the devices, and may be of metal or thermally conductive plastic.

Description:
FIELD OF THE INVENTION 
     This invention relates to semiconductor devices, and more particularly to a system for stacking multiple semiconductor device packages in a casing and mounting the stacked packages onto a circuit board. 
     BACKGROUND OF THE INVENTION 
     Memory devices used, particularly in computers, are arrayed on the computer circuit board, or mounted on small circuit boards to group encapsulated memory device packages into a distinct amount of memory capacity. For example, SIMM (Semiconductor Integrated Memory Module) devices, utilize several memory device packages interconnected on a small circuit board to form memory modules. The devices comprise integrated circuit memory chips encapsulated into discrete protective packages, with electrical connections established by soldering exposed chip contact leads onto corresponding contacts of the circuit board. The sockets into which the memory circuit boards are mounted on the computer circuit board occupy considerable space, especially if the computer is to be designed to utilize 4-Mbytes or more of memory. As computer boards become more complex, and additional functions are integrated into the computer circuit board, the space required for individual memory devices and SIMM modules needs to be reduced to accommodate other circuitry. 
     SUMMARY OF THE INVENTION 
     The invention is to an array of stacked devices utilizing vertical surface mounted semiconductor devices stacked side by side and inserting the stack of devices into a casing. The packaged stack of devices creates a cube package which is capable of replacing SIMM boards, and saves considerable space. The casing dissipates heat generated in the devices, and may be of metal or thermally conductive plastic. 
     The casing has two side clips which clip directly onto the circuit board on which the devices are to be mounted. The devices, which normally are attached to a circuit board by solder reflow, may be tightly clamped to contact pads on the circuit board, avoiding the necessity to solder the devices to the circuit board, and allowing the devices to be removed, when defective, without the need to remove a solder connection. Larger memory arrays are possible in a smaller space by stacking or joining a number of arrays together. 
     The technical advance represented by the invention as well as the objects thereof will become apparent from the following description of a preferred embodiment of the invention when considered in conjunction with the accompanying drawings, and the novel features set forth in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a single vertical surface mount semiconductor device; 
     FIG. 2 shows an array f several vertical surface mount devices, and a casing for enclosing the devices; 
     FIG. 3 shows the encased devices; 
     FIG. 4 shows encased devices on a circuit board with a side cut-away showing the devices; 
     FIG. 5 is a side view of the cased devices; 
     FIG. 6 shows four sets of cased devices on a circuit board; and 
     FIG. 7 shows the top of the circuit board with the arrayed contact pads for mounting the devices. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     FIG. 1 shows a vertical surface mount device 1 which comprises an encapsulated integrated circuit memory chip having generally planar and parallel, rectangular front and rear side faces 2, 3 top left and right edges; and a plurality of contacts 11 extending out from a bottom edge 4 of the packaged device. Device 1 is usually flow soldered onto a circuit board having a contact pad for each contact 11. 
     FIG. 2 shows an array 10 of nine discrete identical vertical surface mount devices 1 stacked horizontally together, side by side with their side faces 2, 3 brought into adjacent superposed relationships so that a front face 2 of one device 1 package abuts a rear face 3 of a neighboring device 1 package and so that their top, left, right and bottom edges 4 are respectively aligned in common planes, with the contacts 11 of the device packages extending respectively out of the bottom edge plane of stack 10 of the arrayed devices. More or fewer device packages may be encased, depending upon the particular application. Aligned top edges, end ones of the front and rear faces, and aligned left and right edges of the stacked device packages respectively define a top, ends and sides of the array. A case 12 is shown positioned above the horizontally arrayed device packages. Case 12 is placed over the stacked device packages and encloses them as illustrated in FIG. 3. As shown, case 12 has a generally rectangular bottom parallelepiped box-like construction, with a bottom opening internal cavity 5 (see FIG. 4) defined by internal surfaces of top, front and rear end, and right and left side walls 6, 7, 8. The dimensions of cavity 5 are chosen so that the open bottom of case 12 can be placed over the array 10, to hold the packages together by bringing the top, ends and sides of array 10 into corresponding abutment with top, end and side surfaces 6, 7, 8 of cavity 5, leaving contacts 11 exposed and accessible through the open bottom of case 12. There are two clips 13, only one shown in FIG. 3, located in spaced positions, attached to respective opposite sides 8 of case 12. The clips 13 have depending leading ends 9 which are inserted respectively into correspondingly spaced holes in a circuit board, described below, to hold the case and arrayed device packages in contact with contact pads on a circuit board. The clips are made, for example from a spring-leaf material, and have a V-notch 13a for securing the clips by snap action within the holes in the circuit board. 
     FIG. 4 shows an end view of the arrayed packaged devices 1 in a case 12, with a portion of the case cut away to show the packaged devices in case 12. Contacts 11, which extend below the bottom of case 11, are in contact with circuit board 14. Clip 13 extends through a hole in circuit board 14. 
     FIG. 5 is a side view of the encased array 10 of packaged devices 1. Case 12 conforms at an angled cut-off top comer edge 12a with a correspondingly angled top edge of the stacked array 10 defined by aligned chamfered edges la of the package exteriors of devices 1, as shown in FIG. 1. The conforming of an angled top comer of case 12 with the corresponding aligned angled chamfered edges of the package exteriors of devices 1 helps hold devices 1 in position within case 12 and presents more surface area of each device package in contact with the case. This is important since case 12 also serves as a heat sink for the cased devices. Case 12 may be either metal or a thermally conductive plastic to assist in dissipating heat generated by the devices. Both clips 13 are shown in FIG. 5. The two clips securely hold case 12 over packaged devices 1 against a circuit board on which the packaged devices are mounted. 
     FIG. 6 shows four sets of cased devices. As an example, if devices 1 are 1-Mbyte memory devices, each cased array 10 represents a 9×1-Mbyte array, providing 1 Mbyte of memory. Eight devices are needed to provide a 1-Mbyte×8-bit memory array. Eight devices in a case provide the 1-Mbyte×8-byte memory array. The ninth chip provides a ninth bit for parity. The four cased arrays 10 then provide 4 Mbytes of memory, which is commonly used in computer systems. 
     FIG. 7 shows the top of a circuit board 23 with contacts 32 arrayed for the four cased arrays in FIG. 6. In the illustrated example, each packaged device has 16 pins. Therefore, to provide contacts to each pin on each chip, an array of 16×9 contacts is needed for each cased array. In practice, the mounting area required by the four cased arrays is less than the space required by four SIMM modules. 
     Circuit board 23 has four sets of holes 24-31, one set for each 16×9 array of contacts. Clips 19-22 lock in holes 25-31 and another set of clips (not illustrated) lock into holes 24-30, to hold cased arrays 15-18 on circuit board 23. When the clips are locked into the holes on circuit board 23, sufficient down-pressure is exerted on the device packages to hold the device contacts in electrical contact with contact pads 32. Therefore, it is not necessary to flow solder the contacts on the devices to the contact pads on the circuit board.