Authored By:
Tony Lentz
FCT Assembly
Greeley, CO, USA
Summary
Solder powder size is a popular topic in the electronics industry due to the continuing trend of miniaturization of electronics. The question commonly asked is "when we should switch from Type 3 to a smaller solder powder?" Solder powder size is usually chosen based on the printing requirements for the solder paste. It is common practice to use IPC Type 4 or 5 solder powders for stencil designs that include area ratios below the recommended IPC limit of 0.66. The effects of solder powder size on printability of solder paste have been well documented.
The size of the solder powder affects the performance of the solder paste in other ways. Shelf life, stencil life, reflow performance, voiding behavior, and reactivity / stability are all affected by solder powder size. Testing was conducted to measure each of these solders paste performance attributes for IPC Type 3, Type 4, Type 5 and Type 6 SAC305 solder powders in both water-soluble and no clean solder pastes. The performance data for each size of solder powder in each solder paste flux was quantified and summarized. Guidance for choosing the optimal size of solder powder is given based on the results of this study.
Conclusions
This work shows major differences in solder paste performance for no clean and water-soluble solder pastes using SAC305 type 3, 4, 5 and 6 solder powders. When solder pastes with smaller solder powder sizes are used, the users should be aware of these performance differences so that the SMT process can be tuned accordingly.
Solder paste manufacturers are looking ahead to the future needs of the electronics industry. Smaller solder powder sizes are becoming increasingly common for miniaturized electronic applications. Solder paste manufacturers are formulating products for use with the smaller solder powder sizes in order to address these needs.
Initially Published in the SMTA Proceedings
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