Kester - Lead-free Reliability - Building it Right the First Time

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By Peter Biocca, Key Accounts Technical Manager, Kester


As lead-free implementation increases, it is more important than ever to build it right the first time. Leadfree assembly and RoHS will bring about numerous changes and the number of variables with which to contend is increasing, creating increased risk of defects and reduced product reliability. However, understanding what the variables are and their impact on the assembly can great increase product reliability.


Below is a summary of some of the changes that may occur during the transition to lead-free soldering. All aspects of the assembly process will be affected by the transition to RoHS compliant manufacturing.


  • Solder alloy
  • Component termination
  • Board finish
  • Board and component thermal limits
  • Component moisture sensitivity levels (MSD)
  • Flux Chemistry
  • Thermal profile requirements
  • Possible equipment changes
  • Cleaning process changes
  • Inspection processes


Due to the reduced wetting speeds of lead-free solders such as the most popular choices such as SnAgCu (SAC) and SnCu, optimizing the production process will be critical to the final reliability of the product. The alloy choice in wave soldering will directly impact hole-fill and a carefully chosen flux system designed for performance with the particular alloy is best. Optimization to maximize hole-fill without voids will then be necessary. In reflow soldering, SAC alloys are predominantly used and the wetting may be reduced if the profile is not optimized to the manufacturer’s recommended parameters.


Those experiencing the least issues with lead-free builds at this time are those assemblers using more active water washable flux systems. Higher activity flux systems will improve hole-fill in wave soldering and wicking and spread properties in reflow soldering. Such fluxes are often classified ORH1 per J-STD-004. Users of these active fluxes account for about 20% of the North American market and less than 5% elsewhere in the world. The added activity does offer better joints, which...

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