Atomic layer deposition (ALD) for environmental protection and whisker mitigation of electronic assemblies

In this study, we demonstrate how metal-oxide thin-film conformal coatings grown by atomic layer deposition (ALD) can be exploited as an effective approach to mitigate tin whisker growth on printed circuit boards. First, we study the effect of different ALD coatings and process parameters on Sn–Cu-electroplated test coupons, by combining optical imaging and scanning electron microscopy and evaluating whisker distribution on the surface. On these samples, we found that one important parameter in mitigating whisker growth is the time interval between electroplating and the ALD coating process (pre-coat time), which should be kept of the order of few days (2, based on our results). Atomic layer-deposited coatings were also found to be effective toward whisker formation in different storage conditions. Furthermore, we show that ALD coating is also effective in limiting the need for outgassing of electronic assemblies (PCBAs), which is an additional stringent requirement for applications in space industry. Our experimental results thus demonstrated that atomic layer deposition is a suitable technique for aerospace applications, both in terms of degassing and whisker mitigation.