Electronics Assembly Knowledge, Vision & Wisdom
Selecting Fluxes for Lead-free Selective Soldering
Selecting Fluxes for Lead-free Selective Soldering
Paper touches on identifying flux properties, selecting low solids fluxes for lead-free selective wave, the soldering process and testing.
Production Floor

Authored By:
Mario Scalzo, Senior Technical Support Engineer
Indium Corporation, Utica, NY, USA

Todd O'Neil, Sales Manager
Juki Automation Systems, Morrisville, NC, USA
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Although many predicted the demise of through-hole components, they are alive and well with tens of billions used each year.

In mixed SMT/through-hole PCBs, through-hole components, and especially connectors, are often used for their mechanical robustness.

A typical example would be a USB connector in a laptop PC. Typically an SMT connection just doesn't have the mechanical robustness needed to support multiple connector plug-in and removals.

However, performing a full wave soldering process to assemble a few through-hole components on a mostly SMT PCB doesn't usually make economic sense and may damage the PCB.

In such situations, the best option is often to assemble the through-hole components and connectors with a selective soldering process.

This paper touches on identifying favorable flux properties, down-selecting low solids fluxes for lead-free selective wave soldering, the selective soldering process itself, and testing criteria.

Topics reviewed will be the flux selection, optimizing the selective soldering process by varying the flux concentration, pre-heat parameters, soldering temperatures, and dwell time.

The paper will finish with a summary of the work and a systematic process to select a flux and optimize the selective soldering process for high yields and quality.
Initially Published in the IPC Proceedings
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