Solder mask coming off when soldering - Page 1
Forum section: electronics / beginners

author: djd_oz
author_rank: Contributor
timestamp: April 29, 2021, 10:15:40 am
content: Hey guys,I've been trying to solder the STM32F103CBT6 chip which is a LQFP-48 package ... and I'm finding that the solder masks around the tracks are coming off.The method that I've been using is to apply some flux using a flux pen ... solder a couple of pins to secure it and then apply another layer of flux and then using a soldering iron with the bevel tip at 355 degree C to drag solder the pins onto the board. Sometimes I may drag a few times as some parts are missed or if there is too much solder on some pins.Any ideas why this is happening? Is the iron too hot?HALP!

author: djd_oz
author_rank: Contributor
timestamp: April 29, 2021, 12:06:32 pm
content: Here is an image of this.

author: wraper
author_rank: Unknown
timestamp: April 29, 2021, 12:13:18 pm
content: You may apply too much force, and you should not touch solder mask with soldering iron to begin with. Trace covered with colder far away from IC cannot happen by just drag soldering normally. Also likely it's a crappy solder mask.

author: bobbydazzler
author_rank: Regular Contributor
timestamp: April 29, 2021, 05:13:54 pm
content: Have a rest between each row of pins to let the chip/board cool down?

author: thinkfat
author_rank: Unknown
timestamp: April 29, 2021, 08:26:22 pm
content: Temperatur might be a bit high, and too little Flux, but if the boards were made by a cheap prototyping house, it's not unusual to have the solder stop flake off. I had the same occasional thing, it's not a problem. Don't panic.

author: james_s
author_rank: Super Contributor
timestamp: April 29, 2021, 09:10:58 pm
content: Either scraping mechanically with the iron, or way too much heat. I suppose it's also possible that the solder mask is defective.

author: Bud
author_rank: Super Contributor
timestamp: April 29, 2021, 09:34:21 pm
content: Do not make PCB tracks too thin if it was not necessary. Thicker tracks will sink more heat and hold the solder mask better.

author: djd_oz
author_rank: Contributor
timestamp: April 29, 2021, 10:58:51 pm
content: Ok, I will try less heat ... 350 degrees C next time and be more careful to make sure the tip doesn't touch the solder mask.

author: wraper
author_rank: Unknown
timestamp: April 30, 2021, 12:33:36 am
content: Temperature is OK.

author: radiolistener
author_rank: Super Contributor
timestamp: April 30, 2021, 03:18:52 pm
content: Quote from: djd_oz on April 29, 2021, 10:15:40 amFrom my point of view you're using too high temperature.Usually I'm using 280 °C when soldering SMD components and this is well enough.Sometimes there is needs to solder very big copper terminals and other things which quickly remove heat from the soldering tip. In such case I'm set 320 °C, but such temperature leads to rapid charring of the tip if you leave the soldering iron for some time, so I switch back to 280 °C when high temperature is no longer needed.But I like to use lead solder, I don't like these "lead free" stuff, because they are not reliable and require high temperature.If you're using these RoHS lead free stuff, the temperature may be ok, I'm not sure because I don't use it.

author: tooki
author_rank: Super Contributor
timestamp: May 02, 2021, 06:38:55 pm
content: Quote from: radiolistener on April 30, 2021, 03:18:52 pmJust to be clear, there’s no evidence of lead-free being unreliable. Is it likelylessreliable than leaded? Yes. But only by a tiny amount.It’s not the horror so many people make it out to be.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 03, 2021, 05:45:59 pm
content: Reliability of lead-free is just fineif done correctly. Leaded solder also needs to be used correctly, obviously. The difference is, leaded solder has somewhat wider process window so is more forgiving than lead-free. I prefer leaded for prototyping for this reason, regulations also allow leaded to be used for prototyping and repair.During early transition of the industry, it is possible lead-free solder had slightly increased defect rate while the industry was learning and adjusting their processes. Those days are long gone.(In some rare applications (medical, aerospace, vacuum, for example), the tendency of lead-free solder to grow tin whiskers has to be taken into account and leaded may be used instead but this does not apply to 99.99% of members and projects of this forum.)Regarding the OP's problem, I'd vote for the combination of poor quality solder mask (crappy/cheap PCB manufacturer) and use of unnecessary force while drag soldering.

author: radiolistener
author_rank: Super Contributor
timestamp: May 11, 2021, 06:42:53 pm
content: Quote from: tooki on May 02, 2021, 06:38:55 pmThe evidence is RoHS electronics. For example just look at your PCB on HDD. For some reason, PCB contacts are oxidized and corrode very quickly over time and grow overgrown with some kind of metal moss or mold. And it make PCB non-repairable. I'm not sure if the root of cause is RoHS technology itself, or they using some special material which leads to a quick self-destruction. But most of RoHC electronics that I seen has the same issue with PCB self-destruction and it's hard to desolder components on such PCB.

author: tooki
author_rank: Super Contributor
timestamp: May 13, 2021, 01:25:39 am
content: Quote from: radiolistener on May 11, 2021, 06:42:53 pmThat’s anecdote, not evidence...

author: Whales
author_rank: Super Contributor
timestamp: May 13, 2021, 01:50:41 am
content: Quote from: radiolistener on May 11, 2021, 06:42:53 pmI've seen lots of different platings die in different ways, both new and old. Gold platings often rot in interesting ways. I can't causate this with RoHS however, so many other factors have changed at the same time: popularisation of cheap gold platings, highly competitive cost cutting competition between PCB fabs, etc.