Wetting behaviour of SAC305 solder on different substrates in high vacuum and inert atmosphere
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The wettability between solder and substrate is a very important issue in reliability of soldering process. The contact angle θ is used to measure the degree of wetting. The contact angle of lead-free alloy Sn-3 % Ag-0.5 % Cu (wt%) was measured, as a function of temperature, for three different commercial surface finish substrates used in printed circuit boards (PCB): Sn, NiAu and Organic Solderability Preservative (OSP). The measurements were performed by the sessile drop method in two different atmospheres: high vacuum and inert gas. In high vacuum the results showed that on substrates of NiAu and OSP the solder started spreading suddenly at 225 °C and in Sn substrate the contact angle decreases slightly with temperature. In inert gas atmosphere the results showed different behaviours: the contact angle between molten solder in OSP and NiAu substrates is sensitive to temperature; and, in Sn substrate, the contact angle does not change with temperature. The NiAu and OSP substrates showed a better degree of wettability than Sn substrate, in inert atmosphere.
KeywordsSurface Tension Contact Angle Solder Joint Surface Finish Print Circuit Board
The authors acknowledge the financial support provided through project SI I&DT Projeto em co-promoção No. 36265/2013 (Projeto HMIEXCEL—2013–2015).
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