PCB tracks crinkles: what caused this? Heat? Moisture? Both? - Page 1
Forum section: electronics / projects

author: mcinque
author_rank: Unknown
timestamp: January 27, 2014, 06:47:54 pm
content: Hi,I'm doing servicing a steam machine used for degreasing and I found this crinkles over some tracks of the PCB... I've never seen this before, what could be the cause?I suspect that since it's a 20 years old device with some leaks in the boiler, some steam can be trapped inside the case and condensing on the PCB could produce moisture.I guess it's not a heat issue, since the front face tracks are good, even if they are in the same area of the regulators which have produced the dark spot in the epoxy.

author: Flipp
author_rank: Contributor
timestamp: January 27, 2014, 06:53:20 pm
content: It is solder form the wave soldering process. Tin plating under the soldermask sucks the liquid solder in there. That´s why it is only at the bottom side.Flip

author: Zbig
author_rank: Frequent Contributor
timestamp: January 27, 2014, 06:53:54 pm
content: I believe that Dave was commenting on this phenomenon in one of his recent vintage teardowns/repairs and the conclusion was it's not the actual traces being crinkled but the solder mask which was applied using some earlier technology process.

author: free_electron
author_rank: Super Contributor
timestamp: January 27, 2014, 08:24:10 pm
content: old technology. they used dipped tin instead of tin flash. After applying solder mask and then sending the board through wave soldering the tin would 'redistribute' and cause this crinkling.

author: mcinque
author_rank: Unknown
timestamp: January 27, 2014, 08:35:06 pm
content: I've scratched the soldermask and yes, it is solder as Flipp and free_electron say.I wonder which effects this crinkles could cause to the circuitry, to capacitance for example.@free_electron: what's the difference between dipped tin and tin flash?

author: calexanian
author_rank: Super Contributor
timestamp: January 28, 2014, 05:15:55 am
content: At that time they were more concerned with trace continuity and current carrying than anything. I remember they used to tin them and try to blow off the excess with a hot air knife which never really worked that well, We used to hand tin our old boards, no solder mask, with 63/37. My father used to do the hand taping, and then I did it for a few designs. I still have the old light box and a big envelope with old pre-kut brand rub down footprints. Many of those boards are still out there running 30 years later! And these were irrigation controllers sitting out in the rain. The clock motors went bad before the boards did. I recall a 5 watt cement resistor on the board that only ran at about 2 watts dissipation, but the board would scorch just like that over the years, but I do not believe any of them ever failed from that. I still remember going to the shop that used to do our Litho. Somewhere I have some of our old acetates.

author: poorchava
author_rank: Super Contributor
timestamp: January 28, 2014, 07:06:57 am
content: Quote from: calexanian on January 28, 2014, 05:15:55 amActually, it's being used yet today in an evolved form - HASL.http://en.wikipedia.org/wiki/HASLCoplanarity after this method sucks, but if you don't have leadless packages or hyper fine pitches it's no big deal. It's also cheapst of allpopular methods

author: calexanian
author_rank: Super Contributor
timestamp: January 28, 2014, 04:05:28 pm
content: Yeah. I have seen it on things like power supplies and the like. There must be some ancient assembly lines out there somewhere cranking out commodity crap. "Shiver"