Author Topic: Solder that won't melt.  (Read 1289 times)

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Offline xavier60

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Solder that won't melt.
« on: November 16, 2017, 06:16:11 am »
In the photo it can be seen what looks like a solder bridge across a bunch of pins on the micro-controller. It is the motor controller board of Fisher & Paykel washing machine.
Whatever it is, I could not remove it with solder wick even after adding fresh solder and also adding chip quik smd removal alloy in an attempt to dissolve it.
I eventually scraped most of it out with a sewing needle and lifting 2 pins to clear a stubborn short.
The board is one of a bunch that I scored from a Gumtree seller, so I don't know much of its history except that the SMPS transformer had been removed revealing a badly charred LNK624 SMPS IC.
I'm really curious about what type of metal it's likely to be and how it got there. Maybe someone has seen the same thing.
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Offline DaJMasta

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Re: Solder that won't melt.
« Reply #1 on: November 16, 2017, 08:00:32 am »
It looks like the board is potted, so there's probably a layer of sealant on the pins that's just preventing good metal-to-metal contact.  Try chipping it off with a sharp knife (lightly enough not to chip the pins off too) and see if you can make better contact.
 

Offline capt bullshot

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Re: Solder that won't melt.
« Reply #2 on: November 16, 2017, 08:05:58 am »
Yes, IMO it's the remainders of the conformal coating that interferes with your soldering.
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Offline Rerouter

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Re: Solder that won't melt.
« Reply #3 on: November 16, 2017, 08:15:18 am »
Its a common industrial conformal coating, acetone and a toothbrush will clean it off pretty quickly,

The solder itself will be lead-free so should melt by 360C, but the coating is somewhat thermally insulating, which prevents you being able to get enough heat into a joint.
 

Offline xavier60

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Re: Solder that won't melt.
« Reply #4 on: November 16, 2017, 08:16:54 am »
It looks like the board is potted, so there's probably a layer of sealant on the pins that's just preventing good metal-to-metal contact.  Try chipping it off with a sharp knife (lightly enough not to chip the pins off too) and see if you can make better contact.
There was a light coating of lacquer that I had applied before I knew about  the bridged pins.
I took the photo after the first 2 attempts of applying a large blob of solder to the group of pins and removing it with solder wick. That remaining metal between the pins was rather tough yet brittle.
Hioki AS100D vom, HP 54645A dso, Fluke 87V dmm, AN8008 dmm, Agilent U8002A psu,  FY6600 function gen, New! Brymen BM857S-(With Battery)
 


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