Desoldering PGA IC - Page 1
Forum section: electronics / repair

author: hotdiode
author_rank: Newbie
timestamp: July 06, 2019, 04:01:32 am
content: I have been asked to swap out a MC68881 (ceramic PGA) IC with a different part. It is not socketed so I must desolder it.I do not have experience desoldering a PGA IC. Are there any recommended techniques?I was thinking to melt Chip-Quik to each pin with an regular soldering iron first, so that the old solder is mixed with the new Chip-Quik. And then use hot air from a cheap SMD rework station to heat up all the pins on the solder side of the board, so hopefully the IC will just drop straight down.But I don't know if this will work.The owner wants the original MC68881 too, so I want to prevent damage to it during desoldering. How can I keep it from getting too hot?

author: Bashstreet
author_rank: Frequent Contributor
timestamp: July 06, 2019, 06:22:40 pm
content: I cannot say i am any form of PGA expert but if we talk of MC68881 it should be relatively easy to de-solder.I think your approach with Chip-Quick is workable although depending of how many layers the board has etc it is advisable have sufficiently powerful heat gun so you do not end lingering too long.I do not see any major issues.1. Use the the chip-quick with soldering iron.2. Preheat the board if there is need (multilayered boards power planes etc)3. Use the hot-air station try use minimum heat needed but try not linger.I am sure we have some others here who are much more experienced than me and can give advice how to avoid any pitfalls but i would think this should be relatively straight forward job.Cheers.

author: amyk
author_rank: Super Contributor
timestamp: July 06, 2019, 06:34:38 pm
content: Just use hot air, heat the pins evenly from the backside and it should come out quite easily.The package itself won't get very hot --- definitely not any hotter than removing BGAs with this method, where the hot air must heat the body of the IC.If you don't have a hot air station or aren't too confident in its use, then a vacuum desoldering iron should work too, although you'll have to suck each pin individually.

author: coromonadalix
author_rank: Super Contributor
timestamp: July 07, 2019, 12:02:27 am
content: for a pga like this, if possible, preheat the board and use an desoldering pump, trying with a wick may be difficult and you can overheat the chip if you said to keep it working

author: Bashstreet
author_rank: Frequent Contributor
timestamp: July 07, 2019, 01:19:08 pm
content: Quote from: edavid on July 06, 2019, 11:39:52 pmNothing difficult about it if done right.Ceramic MC68881's are worth about 120 dollars (if you find one) so no point to bastardize one just for being super lazy

author: edavid
author_rank: Super Contributor
timestamp: July 07, 2019, 07:31:27 pm
content: Quote from: Bashstreet on July 07, 2019, 01:19:08 pmReally!?! Is there a better place to sell them than eBay?

author: basinstreetdesign
author_rank: Frequent Contributor
timestamp: July 07, 2019, 07:45:08 pm
content: 25 years ago this very problem was addressed by an assembler who put together 25 boards for me. The PGA uP was supposed to be installed with a plastic separator between the chip and the pcb but it wasn't. He had to get all of the 25 chips off and then re-solder with the separators in place. He did this by passing the boards over the solder wave a second time and plucking out the chips with tweezers at the right moment.I am still glad I wasn't there to see it done.

author: coromonadalix
author_rank: Super Contributor
timestamp: July 07, 2019, 08:02:09 pm
content: Doable, with a wire or somekind of puller put on top of the ic with a dab of sillicone, i would do it.

author: Bashstreet
author_rank: Frequent Contributor
timestamp: July 07, 2019, 08:54:26 pm
content: Quote from: coromonadalix on July 07, 2019, 08:02:09 pmWell using Chip-Quick and hot-air station the chip should just drop of . The ceramic MC68881's are relatively heavy and legs have quite a bit of thermal reserve.You do not really need any mechanical help unless there is large power plains etc that can soak up the heat and that can be combated with preheating.Of course one sometimes need to resort to all sort of "Ghetto engineering" at a pinch.Cheers.

author: Bashstreet
author_rank: Frequent Contributor
timestamp: July 07, 2019, 09:04:37 pm
content: Quote from: edavid on July 07, 2019, 07:31:27 pmWell i do not know the availability or prices of ceramic Motorola 68881's in U.S.In fact if you know any good sellers or retailers i would be interested.Cheers

author: hotdiode
author_rank: Newbie
timestamp: July 20, 2019, 07:18:19 pm
content: I had success desoldering the PGA without damage. I want to thank everybody for their advice and ideas.The original board has now been socketed and works fine, as does the removed MC68881.I took a different approach and bought the Hakko FR-301 desoldering tool. A little expensive, but I was amazed how effective it was. I assumed it would only be good for a first pass and then I'd need to do some additional work to get the more stubborn pins out, but the entire chip was loose after the initial attempt with no damage. The pins themselves were also quite clean, I guess thanks to the vacuum strength. I can strongly recommend this tool for PGA removal.About chip-quik: I had tried reflowing some on to an existing pin as an experiment and it stayed balled up in a blob and did not flow well or integrate into the existing solder. Maybe my technique was wrong, but it didn't seem useful in this application. I understand it's mainly for surface mount work but wanted to judge it for myself. In the end I did not need to use it.