Advice on Desoldering an IC

[dwight]

Sometimes the IC has been installed with the pins under tension. This is typical of machine inserted ICs. When the solder is loose, bend the pin away from the side it is pressed against. Do this carefully, don't over bend. You want it to center in the hole. I recommend doing this with a separate iron than the desoldering tool, so you can see what you are doing. Once the pin is nicely centered in the hole use the desoldering tool to suck the solder out.
Make sure to always use a clean tip. An oxidixed tip will require excess pressure to transfer heatand damage the trace. Keep the solder shinny with a spung or soft metal wool. Do mot use a hard metal to clean an iron clad tip or it will damage the iron and rot it from the inside 🙁
When not using the iron but leaving it hot, always leave a blob of solder so that it won't have a thin oxide coating that is hard to remove. KEEP A CLEAN TIP!
After sucking the solder with the tool, with a small screw driver, give the pin a slight sideways pressure and let the screw driver slip off the pin. It should make a plink sound or a momentary ring. This is something that you'll just have to learn the sound of. If it doesn't sound right it means it isn't free of the sides. Add solder and try to bend the pin.
Often the body side of the IC will have a tiny film of solder right where the IC sits on the trace. If this is just the tiny amount to solder, one can break it loose with a pair of short needle nose pliers, By squeezing the two sides of the IC together. Don't expect to break loose a large blob.
Of course, if you expect to throw the IC away, use sharp pointed dikes to cut the pins at the package and pull each pin individually while the solder is hot. Use a small vice to hold the board so you can work from both sides. Tweezers are best but heat the solder first and when hot grab the pin from the top. Work quickly while the solder is hot.
You may need to refill the pin with fresh clean solder. Old oxidized solder does not remove easily. Use separate rosin flux if you have it ( not plumber flux!! ).
Like I said earlier, use a really clean tip. It should be shinny before trying to heat the board. It is hard to do with the higher temperature solders. There is some low temperature stuff you can use to remove solder more quickly.
I like using a large manual plastic solderpulit. Some like to use solder wick. The solder removal suckers are often hard to keep the tip clean. If you have to press hard on the tip to the work, the tip is not clean. It does help to have some really tiny flux core solder to touch right at the junction of the iron and work to start the heat transfer. Never use force to get the heat to start to transfer! Clean tip and a quick touch with solder is all that is needed.
When you are not using the iron for some time, but leaving it on, add a thicker blob of solder on it so it doesn't get a thin hard to clean oxide on it. KEEP YOUR TIP FREE OF THIN OXIDE!
Dwight



________________________________
From: cctalk <cctalk-bounces at classiccmp.org> on behalf of Rob Jarratt via cctalk <cctalk at classiccmp.org>
Sent: Friday, April 15, 2022 10:49 AM
To: General Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
Subject: Advice on Desoldering an IC

I am trying to remove an IC from my PDP 11/24 CPU, a DS8641. I am really
struggling to desolder it. I am using the technique of applying fresh solder
and then removing it. But after multiple cycles of this I think I am
starting to damage the PCB.



I am using a fairly cheap desoldering station (this one
https://cpc.farnell.com/duratool/d00672/desoldering-station-uk-eu-plug/dp/SD
01384?st=duratool%20desoldering). Its spec in terms of vacuum pressure is
equivalent to that of the professional Hakko ones though. I am also trying a
hand desoldering pump. None of these are able to clear many of the holes of
solder, although some are doing better than others. Nevertheless, the IC
remains stubbornly unmoving.



Are there any tips for removing ICs?



Thanks



Rob