Was trying to do a simple repair on a controller board that came out of a bread oven today and ran into a problem. The old solder will not melt/allow me to extract from the component I need to replace.
I first used my trusty Hakko 936 at around 350 C and then pumped it up to 400 C with no luck. It would take about 1-2 minutes and the solder would never flow. Instead it was acting like cement paste.
I started to think about the problem and wonder if the manufacturer of the board coated it with some kind of sealant after all of the components were soldered to the board. I took out my hot air rework gun and heated up a small section of board away from any components. In a 30 seconds I got my answer as it bubbled up off of the board. Upon scraping it away, the are looks like a normal board underneath.
Here is a picture of the board:
So my question is, What is this sealant they used? Is it a heat barrier or a dust barrier?
And the most important question. What do I use to remove the layer so that I can replace the component? Is there a chemical that will remove it without damaging the board?
The board is a Hobart Oven Control #0950003 (FFA303) board from a Hobart industrial oven that has been out of warranty for 7 or 8 years.
Thanks in advance Stack!