A short review/demonstration about using silver glue and UV-curable solder mask to repair damages to a PCB.
The PCB in question (see above) has a hole through the first layer — with the bottom layer traces shoving — and the trace on the top layer is missing a piece where the hole is. In order to repair the trace on the top layer, we need to repair the hole as well. We start by filling the hole with green UV-curable solder mask. I’m using green “MECHANIC UV Curable Solder Mask”, which is available in e.g. ebay or unionrepair for about 5 euros a tube.
The solder mask then needs to be cured using an UV-lamp for a couple of minutes. I got mine from unionrepair.com for about 5 euros, which is an USB-pluggable 7W lamp. The solder mask is quite resistant after curing, and tolerates high temperatures (400+ degrees?) without major problems.
After the hole was filled, I used “silver conductive wire glue paste” to repair the trace. Make sure to apply a generous amount of the glue to maximize conductivity. The glue is available in small syringes from ebay or unionrepair.com for about an euro or two per syringe. For this scale of work, one syringe is enough for at least a couple of dozens of repairs.
Right after placing/painting the silver glue, I measured the conductivity: no connection. However, after a couple of minutes with a hot-air blower @ 150 degrees Celsius, the paint started to dry and conduct. I measured 2.4 Ohm for the connection, which is already quite ok.
Next I tested how well the paint can withstand heat, and run the PCB on a rework machine with a top heat of about 260 degrees Celsius for a couple of minutes. I’m happy to report that the silver paint looked exactly the same — and what’s more, the connection even got better: resistance dropped to 0.4 Ohms, which is excellent for this type of repair.
Finally, I tried soldering new solder wire (both leaded and unleaded) on top of the silver glue. This would be very important if the glue were to be used for BGA pad repair in chip reballing. Sadly, this turned out to be a disaster. First, when the solder iron touched the silver glue, it looked like the glue part of the paste melted on top of the silver, which created a thick residue. After scraping this residue away and adding flux, the glue completely flaked away when I touched the glue/silver with a soldering iron. At no point did the solder attach to the silver glue.
As a conclusion, the silver glue is ok for many PCB trace repair jobs, but should not be used in, e.g., repairing pads, or anything which requires soldering work to be done on the trace afterwards. The UV-curable solder mask is excellent for anything needing masking on the PCB.
