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July 2017 • SMT Magazine 97 which resulted in outgassing that created the void. Measurement of the copper pad plating revealed a nonexistent nickel plating barrier, which allowed 50%–100% copper plating disso- lution of the BGA pad (Figures 3 and 4). A cross-sectional analysis of the reballed BGA component prior to assembly reflow sol- dering revealed damaged and degraded BGA pad plating that was exacerbated by the BGA re- balling process. Figure 5 illustrates the observed reballed BGA component pad condition. Func- tional testing of the BGA prevented a potential solder joint integrity field defect. A second methodology for using lead-free BGA components is to utilize a hot reflow pro- file during the tin/lead soldering process to har- monize the BGA solder joint microstructure and minimize solder joint microstructure segre- gation. Traditionally, the industry uses tin/lead solder paste reflow profiles with a maximum USING LEAD-FREE BGAs IN A TIN/LEAD SOLDERING PROCESS temperature limit of 200–225°C. Solder paste flux formulations and component fabricators have characterized and tested their construc- tion materials to not degrade up to this temper- ature range limit. However, the typical lead-free solder reflow profile has temperature excursions in the range of 235–260°C, which easily exceeds the 200–225°C tin/lead solder process reflow profile limit. Many component fabricators will void their tin/lead component warranties if the 225°C temperature is exceeded. Some high-per- formance product design teams have conducted testing and worked with their component fab- Figure 2: X-ray image of suspect BGA. Figure 3: Damaged BGA pad plating structures. Figure 4: Damaged BGA pad plating structures, micro view. Figure 5: Cross-sectional view of reballed solder- ball and component pad interface revealing pre- existing degraded conditions prior to assembly reflow process.