Restoration: how far should it go??

"jamesd" <jdickens(a)ameritech.net> wrote: I don't think that's a sign of poor standards at IBM. The IBM parts were specifically engineered to be stacked. They didn't just take normal DIP RAMs, stack them up, and have some tech hand solder them together. The stacked DIP packages were a replacement for the earlier Mostek dual RAM packages that had two ceramic leadless chip carriers soldered to a ceramic DIP substrate. The stacked DIPs were less expensive to manufacture because they could mold both packages and simply use longer lead frames for the top, but still fundamentally use their normal plastic DIP production flow. The only additional manufacturing step was to ultrasonically weld the leads together. (At least, I think that's how they did it. I'm not 100% certain, and I don't have any close at hand to examine.) Note that the two stacked parts were bonded out with a slightly different pinout, since the RAS and CAS strobes had to be on different pins. However, since the top DRAMs were being bonded to a special lead frame anyhow, this was not a big issue. Both the CLCC on substrate and the factory-stacked DIPs were actually quite reliable. Until ZIPs, SIPPs, and DIMMs were invented, that was the highest packaging density in common usage for RAM.