Tin whisker mitigation by means of a post-electroplating electrochemical oxidation treatment

Abstract

There are very few studies that have investigated directly the effect of an oxide film on tin whisker growth, since the 'cracked oxide theory' was proposed by Tu in 19941 . The current study has investigated the effect of an electrochemically produced oxide on tin whisker growth, for both Sn-Cu electrodeposits on Cu and pure Sn electrodeposits on brass. X-ray photoelectron spectroscopy (XPS) has been used to investigate the effect of the applied electrochemical oxidation potential on the oxide film thickness. Focused ion beam (FIB) has been used to prepare cross sections from electrodeposited samples to investigate the influence of the electrochemically formed oxide film on deposit microstructure during longterm room temperature storage. The XPS studies show that the thickness of electrochemically formed oxide film is directly influenced by the applied potential and the total charge passed. Whisker growth studies show that the electrochemical oxidation treatment mitigates whisker growth for both Sn-Cu electrodeposits on Cu and pure Sn electrodeposits on brass. For Sn electrodeposits on brass, the electrochemically formed oxide greatly reduces both the formation of zinc oxide at the surface and the formation of intermetallic compounds, which results in the mitigation of tin whisker growth. For Sn-Cu electrodeposits on Cu, the electrochemically formed oxide has no apparent effect on intermetallic compound formation and acts simply as a physical barrier to hinder tin whisker growth.

Atomic Layer Deposition (ALD) to Mitigate Tin Whisker Growth and Corrosion Issues on Printed Circuit Board Assemblies

“…For the thermally treated sample, the intermetallic compound was relatively uniform in thickness, whilst that present in the untreated control sample was much less regular and varied greatly in thickness, which is consistent with previous analyses of Sn-Cu deposits stored at room temperature. 30,31 The morphology of the IMC present within the ALD processed Sn-Cu coating from batch 4 (Fig. 12c) was similar to that of the thermally processed sample.…”

“…These results suggest that the ALD coating itself may act as a physical barrier to impede whisker growth, as shown by previous studies that have investigated the influence of applied surface oxides on whisker growth. 31,35,36 ALD processing may, therefore, provide greater long-term whisker mitigation than thermal treatment alone, which may simply retard the onset of whisker growth. Longer-term monitoring of whisker growth will more clearly elucidate the benefits of the ALD coating.…”

The effect of different post-electroplating surface modification treatments on tin whisker growth

“…In previous studies by the current authors [24,25], it was observed that an electrochemically formed tin oxide greatly reduced the growth of whiskers and that increasing the thickness of the tin oxide film promoted further reductions in whisker growth.…”

“…All surface modification treatments were carried out immediately after electrodeposition of the Sn or Sn-Cu coating using, if required, a Solartron SI 1286 Electrochemical Interface potentiostat and the 3-electrode cell described previously [24,25].…”

“…The thickness of the conversion coating and the microstructure of the electroplated Sn-Cu coating was investigated using a FEI Nova 600 Nanolab Dual Beam focussed ion beam milling scanning electron microscopy (FIB-SEM) using the method previously described [25].…”