Copper laminates in PCBs are fabricated with conductive metallic materials like Copper, Aluminum, Gold etc. However, the most commonly used metal is Copper due to its availability, low price and good electrical conductivity properties. In the open environment, due to different active elements, metals are prone to corrosion and the copper metal or copper alloys as well. Coppers exposed to the high sulfur environments with increased humidity become oxidized quickly. The PCBs assemblies are more prone to corrosion which are installed in the industries like cement manufacturing, water treatment, rubber manufacturing, paper mills, sulfuric and hydro-chloric acid production. The electronics products or PCB assemblies which are installed in marine applications are also very quickly attacked by corrosion.
A big ratio of field failed electronics products when analyzed are tagged as “no failure found but the product as a whole does not work”. One of the reasons of these products failures is corrosion, since these failures are hard to discern in the failure analysis. The cost of repairing such a failed product is very large as compared to its components cost.
The copper corrosion over a PCB is also called the PCB copper creep. In PCB creep or PCB corrosion the bright copper surface of the copper turns into tarnished white surface. The edges become powdered green and surface becomes less conductive or more resistive and leaky to the current. The copper corrosion grows at very negligible rate so the PCBs track complete corrosion occurs in the several months. This state gradually ruins the copper track and the finally product unserviceable. Although, in the room environment, the non-finished and unmasked PCBs’ tracks are seen working for the several years. Since the industry or field environment is more harsh than the room environment so the PCBA’s are more easily caught by the corrosion action.
The PCB surface finishing treatment can provide a good resistance to corrosion. However, there are different types of surface finish and every method is not resistive to corrosions. The HASL and InSn have the best resistance capability to corrosion and ImAg is the lowest to resist against the corrosion. On the other side to protect the vias or via barrels against the corrosion HASL and ENIG types are better, which fill the vias and protects them against corrosion, however the ENIG method is expensive relatively.
In Fig.1, corrosion occurred at different PCB electrical and non-electrical objects are shown. The tracks, vias and component pads are broken as corrosion propagates but the solder mask is damaged less. In Fig.2, a PCB installed in the high sulfur area is depicted that has ruined the solder mask level layer seriously and then the tracks.
Fig. 1:- Different PCB elements ruined due to corrosion
Fig. 2:- Corrosion over PCB tracks and vias due to high Sulfur in the environment
Fig. 3:- Comparison of different PCB structures and PCB creep growth.