| General > General Technical Chat |
| Beware of old AntiStatic foam |
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| TerraHertz:
'Pin Rot.' Many IC leads are made of soft iron, not copper. The iron is solder, tin or gold plated after the IC package is complete. The problem is, gold and tin plating is not hermetic - it is porous. And so some kinds of old chip leads gradually corrode away on the inside, often with no external visible effect. Then you touch the lead (or the board flexes) and because nothing was holding it on but the thin plating, it fractures and falls off. Or remains as a hairline fracture if the IC was soldered into a PCB. In OP's case, the porous-gold-plated iron legs were in contact with decaying rubber, which produces many chemical breakdown products that are corrosive. Resulting in super-boosted pin rot. Rather than try to salvage that ruin, maybe better to just find a nice one on ebay and buy it? I do feel your pain. A lesson learned too late... :( I'm currently sorting through and repacking a quite large collection of old ICs that came to me recently. Many of the chips are in anti-static foam, some of which is decaying. But fortunately it's all the 'dry crumbly' type of decay. No corrosion encountered so far. But ALL the foam has to be removed and binned. There are better ways. |
| DrG:
This guy does make some nice displays and IC tchotchkes https://chipscapes.com/collections/historical-series ...and you can get another (not as nice) for a not astronomical price https://www.donberg.ie/descript/s/scn_2650.htm It is interesting to watch the vintage IC market rise over the last decade....makes me a little "thirsty", not enough to get into it so late but I do like to see the history preserved. The BIN prices that never sell on $bay keep trying to push it harder....lots of boxes and boards and so many chips out there.... |
| David Hess:
--- Quote from: intabits on March 21, 2021, 11:44:49 am ---It looks like the pins on these ceramic packages are not part of the leadframe, but separate pieces that are welded(?) to the frame. I hope they are welded, rather than soldered, so that they won't come adrift when I solder them to the socket. --- End quote --- That package is a "side brazed" ceramic package. The pins are brazed onto the sides of the ceramic package in contrast to a plastic package where the plastic is molded around a lead-frame which holds the semiconductor die and includes the pins which are bent into position. There is no danger of the pins coming lose from soldering. Ceramic packages are preferred in high reliability applications because they are hermetically sealed and that extra reliability makes them more suited to expensive semiconductors. |
| intabits:
--- Quote from: Ian.M on March 22, 2021, 03:07:01 pm ---I don't like the direct to board mounting idea ... either by temperature extremes or the board flexing... you really don't want to get non-gold alloy solder... I'd suggest using a header even if you reject my loose pins idea... --- End quote --- I understand the concerns you raise, though I do struggle to visualize them actually causing problems. The header I envisage is something only about 25-30mm wide, so flexing risk would be low, and only while being (carefully) plugged into the main project board. Storage temperature would be unlikely to range outside 12C to 27C. (But then there is operating temperature) I like the adapter PCB idea for the more robust external pins and silkscreening for reference, and that could also incorporate the machined socket, or your (probably better) flat sided header idea. My major concern is to mount the chips once and for all, with no possibility of ever needing to touch them with a soldering iron again. The PCB plus DIP header/socket for the chip, with SIL headers for external connection seems to be the best answer. I'll get a DIP40 header (may even have one) and see how I feel about using that. --- Quote from: DrG on March 22, 2021, 03:28:53 pm ---Were there any of the same chips (2650s) nearby but not in the foam and not corroded? --- End quote --- No such luck. I have only two 2650s, and they were the only chips in black foam. --- Quote from: TerraHertz on March 22, 2021, 04:26:09 pm ---Rather than try to salvage that ruin, maybe better to just find a nice one on ebay and buy it? --- End quote --- Not without at least having a go with what I have. (and if that failed, I'd probably just drop the whole idea) --- Quote from: DrG on March 22, 2021, 04:38:21 pm ---This guy does make some nice displays and IC tchotchkes https://chipscapes.com/collections/historical-series --- End quote --- I'm planning an a working, rather than a static demo/display. With leds, hex displays and keypad, etc. Also variable clock speed (2650 can go down to DC), and single stepping. --- Quote from: David Hess on March 22, 2021, 07:53:33 pm ---That package is a "side brazed" ceramic package. --- End quote --- Brazing - that's would I should have said, something between soldering and welding. |
| coppercone2:
check old instruments with cards for this foam shit, they like using it to stabilize the cards from the top to save money on braces |
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