|answers to Paul and Luiz|
Message #16 Posted by Norm on 9 July 2003, 2:51 p.m.,
in response to message #15 by Vieira, Luiz C. (Brazil)
Yes, the article I posted described that there is a tendency to see melting of the plastic underlay. In fact, it was still quite useable, but nevertheless there was some melting, which was worrisome.
Yes, it was a precision temperature-controlled iron,
digital readout, using standard solder, set as low as is fair and reasonable. One could get into specialty low-melt point Indium solders, BUT, those stick lousy so you are back to where you started. You're triple-doomed if you don't have a precision controlled iron.
THE CONCLUSION is that the Luiz "clean it up and oil it and put it back together" is right on-target.
No, I dont think U want to use conductive epoxies. If they get a hairline crack, you are in trouble once again. You have no assurance that they will bond mechanically.
Back to the "keep it solderless" then what oil? A little unsure there, some kind of "tv tuner cleaner", etc. Just enough oily stuff to keep the oxygen from coming in and creating fresh corrosion.
I say keep it like the manufacturer intended. This is true for many situations, including car repairs. The more U modify, the more trouble U got. If you keep it solderless, U have the option of swapping chips later if there is a problem. Solder it, and its all over. Just clean it up enough so that it works OK. The article I posted says that the little 8-pin chips are seen to form a bluish oxide, which may contribute to not making a connection. Probably the oil would reduce the tendency to oxidize.
I use a "Leica Zoom 2000" microscope, a very low power (x7 to x30), yet exceptionally convenient inspection microscope. Just set it to 7 power. Flip the chip upside down and put it on the stage, then U start working on those chips to make the blue oxide go away, and see fresh metal.
What do you use? I dunno, maybe the finest wet/dry sandpaper U can buy at Home Repot.
In all of this, you are at grave risk of wrecking the chips w/o the MAXIMUM possible ESD protection. I would suggest some of those "chip clamps" from the early 1980's, that had a clip every 0.1" and you clamped it onto the chip. Short all the pins together on the clip. Now you've shorted out every pin on the chip, and can work on its oxidation problems quite freely.
Remember that if all pins are shorted together, ESD damage is impossible.
That STILL leaves you with 100 other issues about dealing with ESD, at other moments in time. But if you want to work on each pin of each IC, try those clamps, shorted out.
Put it back together at the end, avoid ESD trouble to avoid "2 disease" and it should be fine, even as a solderless unit. That's what I learned by trying to solder one.