Electronics Assembly Knowledge, Vision & Wisdom
Ultra-Low Voiding No-Clean Lead-Free Paste for Large Pads
Ultra-Low Voiding No-Clean Lead-Free Paste for Large Pads
In this work, a new halogen-free no-clean flux solder paste been developed. It exhibited ultra-low voiding and virtually zero solder beading performance.
Materials Tech

Materials Tech programs cover topics including:
Adhesives, Chemicals, Cleaning Solutions, Coatings, Components, Design, Embedded Technology, Fasteners, Finishes, Flex Circuits, Flip Chip, Fluxes, PC Fab, Solders, Solder Masks, Solder Paste and more.
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Authored By:
Li Ma, Fen Chen, and Dr. Ning-Cheng Lee
Indium Corporation

Summary
The miniaturization trend is driving industry to adopting low standoff components. The cost reduction pressure is pushing telecommunication industry to combine assembly of components and electromagnetic shield in one single reflow process. As a result, the flux outgassing is getting very difficult for devices. This resulted in more large voids. For a properly formulated flux, there is less outgassing at temperature above melting temperature of solder or the flux can be expelled out from interior of solder joints due to good wetting ability. Either approach will reduce the voids. In this work, a new halogen-free no-clean flux chemistry, F, has been developed. The solder paste using 96.5Sn3.0Ag0.5Cu and Alloy A exhibited ultra-low voiding and virtually zero solder beading performance.

The low voiding performance on Alloy A solder paste is particularly crucial since the automotive industry has been ailing by the poor voiding performance of this 6-element solder alloy system. The halogen-free F virtually enables the automotive to migrate toward full adoption of high reliability 6-element alloy system. Furthermore, the hot slump, wetting, solder balling, and graping performance are all acceptable. The printing performance of F showed excellent transfer efficiency under various printer setup and pad design conditions, indicating this flux system is a very robust system for SMT fine-pitch applications.

Conclusions
The miniaturization trend is driving industry to adopting low standoff components. The cost reduction pressure is pushing telecommunication industry to combine assembly of components and electromagnetic shield in one single reflow process. As a result, the flux outgassing is getting very difficult for devices. This resulted in more large voids. For a properly formulated flux, there is less outgassing at temperature above melting temperature of solder or the flux can be expelled out from interior of solder joints due to good wetting ability. Either approach will reduce the voids. In this work, a new halogen-free no-clean flux chemistry, F, has been developed. The solder paste using SAC305 and Alloy A exhibited ultra-low voiding and virtually zero solder beading performance.

The low voiding performance on Alloy A solder paste is particularly crucial since the automotive industry has been ailing by the poor voiding performance of this 6-element solder alloy system. The halogen-free F virtually enables the automotive to migrate toward full adoption of high reliability 6-element alloy system. Furthermore, the hot slump, wetting, solder balling, and graping performance are all acceptable. The printing performance of F showed excellent transfer efficiency under various printer setup and pad design conditions, indicating this flux system is a very robust system for SMT fine-pitch applications.

Initially Published in the IPC Proceedings

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