Evaluation of Lead-free Solder Pastes
This paper discusses the strategy and methodology for selecting a good lead-free solder paste material for volume manufacturing uses.
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Authored By:
Jennifer Nguyen, David Geiger, and Dongkai Shangguan, Ph.D.
Flextronics International
Milpitas, CA, USA
Summary
Most of electronic components on a printed circuit board assembly (PCBA) are surface mount components assembled using solder paste material. Having a good solder paste material is very critical for having a high yield and reliable product. There is a strong correlation between the SMT defects to solder paste quality1, but there is limited published information on the evaluation procedure and requirements for a good solder paste material.
This paper discusses the strategy and methodology for selecting a good lead-free solder paste material for volume manufacturing uses. A statistical and methodological evaluation approach will be addressed in details. It shows how to screen the solder paste candidates for quality using printability tests, slump test, solder ball test and wetting tests and how to select a robust solder paste material using a design of experiment. The performance of lead-free no clean solder paste, lead-free water soluble solder paste, halogen containing solder paste and halogen free solder paste will be compared. Characteristics and requirements of a good lead free solder paste material are also outlined.
Conclusions
In general, at the present time, lead-free no-clean solder pastes are more robust and perform better than lead-free water soluble pastes, and lead-free no clean halogen containing solder paste typically performed better than lead-free no clean halogen free solder paste in the paste. This is most likely a reflection of the amount of efforts that the solder paste suppliers have spent on optimizing the formulation and performance of the various types of solder paste materials.
It is noticed that the performance of lead-free no clean halogen free solder paste has been significantly improved most recently; certain halogen free solder pastes can have equivalent (or even better) performance as many lead-free no clean halogen containing solder pastes. In the future, lead-free no clean halogen free solder paste will become more popular, and solder paste which helps mitigate HIP will also be in high demand.
Initially Published in the IPC Proceedings
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