|Re: 12c Platinum pictures: peanut CPU?|
Message #28 Posted by glynn on 13 May 2003, 11:57 a.m.,
in response to message #27 by Vieira, Luiz C. (Brazil)
The glob you see there in the center is epoxy. It indicates that underneath, you will find a "die"-- a piece of silicon, the chip without a lead-frame (for "pins") or casing. Usually there will be tiny wires leading from pads on the die to pads on the board. Sometimes though, it has pads on the bottom and just gets glued (not soldered) to the board. Then the glob gets put over it, to protect it.
This is a standard means of construction. Intel was one of the first companies to do this on a commercial product, on the "Wildcard '88" (a pc-board the size of a business card, 2 inches x 3-1/2 inches; it showed off a lot of new tech at the time, 1990 or so). It was subsequently picked up for use by others. It has some requirements: pick-n-place automation, clean-room standards, all the rest of the board pre-soldered.
It saves you money, IF you are equipped to do it. Chipmakers sell the dies cheaper than full chips. You connect 'em up, it's the same as the step which the chipmaker would have used to connect the die to legs. Once the epoxy is on it and hard, it will NEVER rust or be attacked by anything. It gets rid of heat a little less well than a ceramic chip carrier, but with something that uses power as frugally as this, I would not expect heat to be a problem.
All in all, they were doing right by making it this way-- but it doesn't LOOK as cool as a nice big chip with legs. It can never be "replaced". When this thing goes, you'll just throw the device away.
It is interesting, and thank you, Gene, so much for the pix. They really are useful to us all.