binder@fizbin.DEC.COM ("A few frilly words... 07-Aug-1987 1714") (08/08/87)
The original discussion of this came across the net around the end of July, but I got distracted. Here's my two cents' worth about chips and sockets. > Working at a computer store I found that in some cases a computer could be > fixed by pushing down on all of the chips, thereby re-seating ones that > worked themselves loose. > > Tom Arnold -- tra@j.cc.purdue.edu At least part of what Tom Arnold has experienced isn't due tochips working themselves loose. Sure, they are subject to vibration and thermal problems, and they do work loose sometimes whether the legs are bent to a right angle or not; but an often overlooked factor is lousy socket design, leading to poor contact caused by corrosion. The chip pins are tinned material, which is prone to corrode even in relatively clean air. There are two kinds of sockets, one that grips the chip pins on the outside and inside faces, called face-grip, and one that grips the pins on the edges between adjacent pins, called edge-grip. Face-grip sockets have a much larger surface area to grip, and it would seem that they would have better contact. In fact, that's not so. That larger area means that the unit gripping force per square millimeter is much less, and as a consequence these sockets do not form what is called a gas-tight seal with the pins. Edge-grip sockets do form a gas-tight seal. Without a gas- tight seal, corrosive agents can get between the pin and the socket, resulting in a poor contact. With a gas-tight seal, you actually have what amounts to a single piece of metal where the contact is made, and the potential for corrosive destruction is much less. An added benefit of the edge-grip design is that with the increase in gripping force, the coefficient of friction is increased, and there is less tendency to work loose. Cheers, Dick Binder (The Stainless Steel Rat) DEC Enet: FIZBIN::BINDER UUCP: { decvax, allegra, ucbvax... }!decwrl!fizbin.dec.com!binder ARPA: binder%fizbin.DEC@decwrl.DEC.COM