IBM interconnect density prediction and C4 development

IBM developed controlled-collapse chip connection (C4) area-array bonding in the 1960s in anticipation of needs that wouldn't arise for decades. Tom uses it to illustrate forward-looking applied research.

IBM saw they were going to need more, and some folks got together and said, let's do C4 — controlled collapse chip connection. You'd have these little solder pads, just like that thing I passed around, which didn't have 2,000 of them on it, but your connections will be on these little pads, and you'll have a solder ball. You can get up to 2,000 theoretically before you start running into thermal expansion problems, of these things just shearing themselves apart. That's the way most of the chips are done today — not for 2,000 inputs and outputs, because I think Rent's rule has sort of pooped out. When we can get 100 million transistors on a chip, we don't need as many inputs and outputs.