RESISTANCE OF COMMON PWB SURFACE FINISHES AGAINST CORROSION IN HARSH ENVIRONMENTSAuthors: Mustafa Özkök, Mario Gensicke, Guenter Heinz; Hugh Roberts, Joe McGurran
Company: Atotech Deutschland GmbH; Atotech USA Inc.
Date Published: 10/24/2010 Conference: SMTA International
Depending on the final application and the environment to which the product is exposed, the requirements for corrosion resistance can be significantly different. Products used in military, automotive and medical applications typically demand higher corrosion resistance than products for lower performance or lifetime expectations, such as consumer electronics or similar products used in non-aggressive environments. As a result, to avoid corrosion on electronic products each industry sector has essentially adopted its own reliability testing procedures and standards. These facts all lead to the question, “What is the right corrosion resistance level of the surface finish for a particular product?”
One key function of surface finishes on printed wiring boards (PWB) is the protection of the underlying metal surface from environmental influences until assembly operations, such as soldering or wire-bonding, are performed. Also, after assembly there are areas on the PWB that are not covered by solder, including contact pads, test pads, heat seal and heat sink areas and the inside of through holes and vias. These areas are covered only by the surface finish and must still be resistant against any corrosive environment in the field. When corrosion occurs on a surface finish the metal decays and undefined corrosion products are created. The result of this process could be either an “open”, caused by attack of the underlying copper or a “short”, caused by creep from undefined corrosion products.
This paper investigates the performance of eight primary types of surface finishes using four different corrosion tests. The compiled data, findings and recommendations are offered as a guide to selecting the most suitable surface finish based on the end use application and required level of corrosion resistance.
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