How to desolder and resolder plastic connectors without damaging it - Page 1
Forum section: electronics / beginners

author: hitech95
author_rank: Regular Contributor
timestamp: February 15, 2020, 03:50:47 pm
content: Hi,I've a working mainboard with a couple of broken connectors and some broken mainboards with working and intact connectors.Unfortunatly I don't have a lot of experience on soldering and unsoldering SMD plastic connectors.I've tried to directly find a new connector but I didn't find any. (I don't have the P/N even if I have the schematics) It might be a custom one made just for Acer.Just for reference its like this, with smd pins; some of them are also under the plastic package:I'm tring to glue the connector with superglue but I think that this will not solve the main mechanical issue.BTW, its a NGFF Key b connector for a SATA M.2 SSD. The original one is from Lotes. It have some sort of printed serial number on it.Any suggestion would be perfect!

author: mvs
author_rank: Frequent Contributor
timestamp: February 15, 2020, 05:15:07 pm
content: You need hot air station to do this work.

author: hitech95
author_rank: Regular Contributor
timestamp: February 15, 2020, 05:27:47 pm
content: Yea, but the plastic connectors melts before the solder does.

author: mariush
author_rank: Super Contributor
timestamp: February 15, 2020, 05:35:09 pm
content: You'd use infrared hot plate or some kind of heat source on the other side of the board to bring the whole circuit board to a reasonable temperature ... then when you come with the hot air gun from the top it would take little time to heat up the solder.You'd put some kapton tape or aluminum foil over the plastic of the connector and paste or liquid flux all around the connector, then come with the hot air gun to desolder it.Do the same for installing the new connector...

author: Le_Bassiste
author_rank: Frequent Contributor
timestamp: February 16, 2020, 10:56:27 am
content: never used it myself, but would give it a try, if sufficiently desperate:https://www.chipquik.com/store/product_info.php?products_id=220001melting point is 90°C, so probably low enough to protect the plastics.

author: ebastler
author_rank: Super Contributor
timestamp: February 16, 2020, 11:25:36 am
content: Question about both, the Kapton-tape-plus-hot-air and the Chipquik solder proposal:How would that work for the row of pads which is hiddenbelowthe plastic body of the OP's connector?Lots of heat from the bottom side of the PCB, essentially enough to unsolder, might do the trick. But that would be bound to damage or unsolder other components in the neighborhood, wouldn't it?

author: jpanhalt
author_rank: Super Contributor
timestamp: February 16, 2020, 11:56:59 am
content: I believe ChipQuik is basically a low-melting bismuth-tin or bismuth-lead-tin alloy. There are lots of such alloys. "Woods" metal is one that has attained a little fame, but is not used in electronics. It is very low melting.On point, I saw some devices the other day (BGA packages) that came pre-balled with low-melting solder balls. There is a chance that the solder beneath the connector is low melting. In other words, a low-melting solder paste was used for reflow soldering the device. I would give heating from below a try as others have suggested. There seem to be few other options.If you heat from above, aluminum foil is a great protector.

author: hitech95
author_rank: Regular Contributor
timestamp: February 17, 2020, 12:26:53 am
content: Quote from: ebastler on February 16, 2020, 11:25:36 amI was thinking about the same. On the bottom side is full of passives. Bypass 0402 caps, pullups, and the audio codec with a lot of stuff around like LDOs.

author: mvs
author_rank: Frequent Contributor
timestamp: February 17, 2020, 07:12:26 am
content: Quote from: hitech95 on February 17, 2020, 12:26:53 amLight parts should stay in place due solder surface tension. But you need to have a steady hand and be very carefully.Look for some training videos on youtube. Try to solder/desolder components on some dead boards to gain experience.

author: Berni
author_rank: Super Contributor
timestamp: February 17, 2020, 11:14:39 am
content: It is possible to remove with hot air without damaging the plastic, but it takes some skill and practice to do it.The plastic can take these temperatures since it had to take them when it was originally soldered down. The problem when desoldering is that the large cold board is taking away the heat, so you want to make sure you heat up the board rather than the connector. Having a board preheater placed under the PCB helps a lot here.Other components wont fall off because of solder surface tension, it can happen only to very large heavy parts like inductors or large transistors like D2PAK.Quote from: jpanhalt on February 16, 2020, 11:56:59 amI'm guessing ChipQuik is mostly Bismuth since it will form low temperature alloys when mixed with both lead or tin(lead free solder). The melting point of pure bismuth is similar to that of lead free solder and you do need to melt the existing solder in order to get it to alloy quickly and fully with the bismuth.I have used QuickQuik low temp solder before and it does work well. It comes in useful when you want to desolder large chips of connectors where enough hot air to heat it all up might damage something. In that case i apply ChipQick to the pins and then use hot air to heat everything up at the same time and pull the part off. I don't use it everywhere but it comes useful in some more tricky situations.Also clean up the ChipQuik really well afterwards by tinning and wicking the pads again. These bismuth solders are not as strong and could have undesirable brittle properties when they are in a random mixture of both solders with the wrong proportions. So cleaning is important.