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Assembly Process Feasibility of Low Silver Solder Paste
Assembly Process Feasibility of Low Silver Solder Paste
This paper presents performance/process capability of various low/no silver alloy solder pastes.
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Authored By:
Jennifer Nguyen, Ranilo Aranda
David Geiger, and Murad Kurwa
Flextronics International
Milpitas, CA, USA

Summary
Sn3.0Ag0.5Cu (SAC305) is the most popular near eutectic lead-free alloy used in the manufacturing processes. Over the last several years, the price of silver has dramatically increased driving a desire for lower silver alloy alternatives.

As the results, there is a significant increase in the number of alternative low/no silver lead-free solder alloys available in the industry recently. In this paper, we'll present the performance and process capability of various low/no silver alloy solder pastes. Data from printability, wetting test, slump test, solder ball test, voiding, etc... will be discussed and compared with the control SAC305 solder paste. Benefits and concerns of using low/no silver alloy solder paste materials will also be addressed.


Conclusions
There are many alternative low/no silver solder pastes in the market today. In general, alternative low/no silver solder pastes have higher liquidus temperature and require a higher reflow profile than SAC305 solder pastes. Thus, the process window of low/no silver solder paste is much narrower than the process window of SAC305 solder. Many alternative lead-free solder paste materials have good printing and wetting performance. However, low/no silver alloy solder pastes may result in more defects such as solder balling, voiding (especially on QFN components) and solder bridging. Flux chemistry and supplier play a critical role in the performance of alternative lead-free solder paste materials.

A good selected low/no silver solder can have similar performance as SAC305 solder pastes in many aspects when the process conditions are optimized. The higher reflow profile associated with alternative low/no silver alloy solder paste creates some concerns about the component's process temperature and its limitation. When alternative low/no silver solder paste is used, it is recommended to review the component's temperature limitation to make sure that they can survive the reflow profile. Further work on the reliability of lead-free solder joints assembled with alternative low/no silver solder paste is recommended.

Initially Published in the IPC Proceedings

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