163 (H) S12/Storage Devices
    25-Jul-91  22:09:10
Sb: Card drives
Fm: John Feagans 75300,703
To: SYSOP*Marty Mankins 75300,1770 (X)

I had the good fortune (or bad) of running across a doa Portfolio RAM card. I
popped it open to see what was inside.  What I found was that they were using
32k x 8 SRAM die bonded to the board.  One chip =32k, two =64, four=128k. 
They also had a small custom chip which took care of the miscellaneous logic,
address decode, power detect, power down.  Die bonding means that instead of
mounting the die in a lead frame and encapclating it into expoxy, it is
actually bonded on the printed circuit board, wires attached to the
appropriate pads, and the whole works potted in exposy on the PCB.  Everything
is fine as long as the yield from the chips is good. Get one bad chip on a 32k
board, you just generated scrap.  Get one on a 64k card you just wasted one
potentially good chip.  Get one bad on a 128k you just wasted three
potentially good die.  You get the idea how the price gets out of hand quickly
with larger cards.  The PCMCIA cards on the other hand use already tested
bonded, and packaged parts.  I also disassembled one of those cards as well. 
The PCB has little square holes in it where the packages rest.    They were
gull wing and soldered to the board.  It seems that their is an additional
burden of cost on packaged parts but in the long run fewer parts resulting in
less cost would be used.


