Issue link: https://iconnect007.uberflip.com/i/1406534
56 SMT007 MAGAZINE I SEPTEMBER 2021 June. at cost can be eliminated by using a sil- ver-free SnCX Plus alloy (an advanced SnCu0.7 alloy) or reduced by 26% using a SACX Plus 0807 alloy (Figure 2). Silver in lead-free solder has proven to en- hance thermal cycling performance in de- manding applications such as under-the-hood automotive assemblies (-40°C to 140°C THC), but typical consumer assemblies used in white goods, hand-held, remote control, and in- home audio-visual devices do not require the same thermal cy- cling resistance (0°C to 100°C). Low/no-silver soldering alloys are perfectly acceptable in these applications. In fact, data shows that reduced silver content in- creases the drop shock resis- tance of these devices [1] . Additional value from the low/no-silver alloys includes lower dross generation, partic- ularly in wave soldering pro- cessing (scrap required to be re- cycled), and longer process life through reduced copper disso- lution from OSP-finished sub- strates. is article will detail pre- vious findings in wave solder- ing barrel fill, copper dissolu- tion rates, dross generation, and as shown in Figure 2, the lower cost of metals in a way to inform users of bar solder to exploit the cost savings op- portunity of using SACX Plus 0807 (0.8% Ag) or SnCX Plus (no intentional added Ag) in their wave or selective solder- ing process. Barrel Fill Primary attach barrel fill re- sults, using SACX0807 alloy to assemble PTH connectors onto a 20-layer, 120-mil thick test vehicle were comparable to those test vehicles assembled using SAC305 with yield levels of 99.7% on standard designed connectors (Figure 3). Copper Dissolution When molten lead-free solder is in contact with copper plating, it results in copper disso- lution. is is particularly an issue with lead- free alloys due to the high tin content and lead- Figure 2: Silver contribution to alloy cost (silver at $28/troy ounce). Figure 3: Barrel fill vs. alloy. (Courtesy of Craig Hamilton, P.Eng., PMP, Black Belt, Process Engineering Consultant, Celestica)