Issue link: https://iconnect007.uberflip.com/i/1379105
40 SMT007 MAGAZINE I JUNE 2021 rials and background/ experience with failure analysis work, the cause of the defect could be a contaminated substrate Cu pad before the HAL solder process and an inferior plat- ing condition. is could happen on both the PCB and components. Inferior plating would mostly be derived from an uncontrolled plat- ing process. An insufficient plating layer causes the inner layer to oxidize and removes the pur- pose of the plating in the first place. Solder cannot wet to the oxidized intermetallic com- pound (IMC) and results in solder de-wetting. Discussion on possible solutions to the board plating/surface finish quality defect One area to consider would be to improve the HAL treatment resulting in a thicker and more uniform coating. e preferred thickness of HAL coating is approximately 10 mm com- pared to 3.4 mm found with this board. e HAL coating should preferably be thicker than the IMC. e minimum HAL coating thick- ness would be around 5 mm and the maximum coating thickness would be around 10 mm. Other possible countermeasures to improve solder wetting would be to use a higher activity solder paste which can help to remove the oxi- dized film during reflow, or to reflow in a nitro- gen atmosphere to reduce oxidation of the Cu substrate. Contaminated plating (Case Study 2) e de-wetting issue on the pad substrates is shown in Figures 8 through 11. For Section B in Figure 6, the thickness of the HAL was 3.4 mm and the IMC thickness was 2.05 mm. For the thinner plating in Section C in Figure 7 there was no IMC layer observed. Assessment of the cause of the board plating/surface finish quality defect Based on company experience and knowl- edge with soldering defects, soldering mate- Figure 5: Microscope image showing areas analyzed. Figure 6: Section B: SEM image (thicker plating). Figure 7: Section C: SEM image (thinner plating). Figure 8: Dewetting issue on pad substrate.