Abstract
Introducing Bi in the coating of Sn on copper surfaces for chemical bonding with prepreg was proposed to inhibit the serious whisker growth of Sn in the post–application process. The desired bonding strength and low roughness of copper surfaces (Ra = 0.5 μm) coated with this Sn–Bi alloy were both obtained under characterizations of peeling strength test and roughness measurement. Scanning electron microscopy (SEM) and X–ray photoelectron spectroscopy (XPS) confirmed that the high bonding strength is related to the high content of SnO2 in as–coated Sn–Bi alloy and the plating time with 180 s gives rise to the optimized bonding strength. Agilent Vector Network Analyzer (VNA) affirmed the lower signal loss (7 dB/m@10 GHz) in comparison with that treated with conventional brown–oxidation. Accordingly, the Sn–Bi coating on copper surface is suggested to be a candidate for layer bonding in high frequency PCB.
Published Version
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