Removing Old Glue from PCB
There is no easy way to remove old glue. If there is, I have not found it. The problem is that the glue will
become conductive as it dries and ages. Often, you will see the component leads with a fuzzy blue-green
build-up on them where the leads pass through the glue into PCB hole. This is copper oxide. It can be
caused by anything that allow an exchange of electrons, such as excessive moisture (condensation) on
the PBC. I have seen PCBs where components surrounded by glue all have oxidation and all the ones
in the clear were fine.
I use lacquer thinner as a solvent (sparingly). You should test a small area before using such a strong
solvent. I have seen some boards where lacquer thinner removed the component patterns. Seems some
boards have these patterns silk screened on with a lower quality paint (the newer the board, the more
prone it is to be like this). In such a case, try using alcohol, or naptha. I have a set of tools to prod and
scrape with. I use blunt tools for scrapping becuse sharp ones will scratch the board. One is a dental tool
for gum inspectiion. The other is the hook end of a wire-wrap tool. The hook works well for getting under
the leads. Tweezers to pick off the debris and a small bursh for applying the lacquer thinner.
First I brush a thin coat of thinner directly on the glue. I let it stand for a minute or so, and reapply. I do this
for about five minutes. This soften the glue and reduces the bond to the PCB (a little). I start scraping and
proding. Every minute or so I reapply thinner. If you are going to try this at home kids... be very careful! It is
very easy to take-out a componet doing this. Keep good control of the tool and remove just a little bit at a
time. Patients is the rule here. It took me 2 hours to clean  the power supply board seen below (both left and
right sides).  You will never get 100% of the glue. Just make sure the glue is removed from between
components and leads. I use the hook tool to scrape under the component leads.
Here it is... all cleand off
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