Severe corrosion of a PCB in salt spray testing
In our picture two weeks ago, we discussed about surfaces finishes and how poor surface finish can cause severe corrosion problems. This week our picture shows an example of severe corrosion in a printed circuit board (PCB) structure. Last time we were dealing with nickel-gold (ENIG) surface finish. This time immersion silver (ImAg) was used. The PCB was tested with a prolonged salt spray test to study its corrosion proterties.
The picture shows a cross-section of a copper pad on top of the PCB after salt testing. Additionally, a part of a copper trace in an inner layer can be seen. In the picture on the left side you can see how the structure looked before testing. After testing, the inner parts of the copper pad in the top layer have practically fully dissappeared. The silver surface finish can be seen forming the earlier shape of the pad. The gray material around the copper is oxidised copper. As mentioned, in this case the corrosion was very severe, so it was not a surprise that this PCB failed during the test.