Ask the Experts
September 25, 2006 - Updated
July 4, 2007 - Originally Posted

Hand soldering process for lead-free

What is the right temperature for hand soldering of lead-free solder (Sn,Ag,Cu) composition is 96.5%,3%,.5% respectively? Please guide me for best hand soldering performance & precautions.

Veerendra Kumar Singh

Expert Panel Responses

Hand solder temperature is dependent on the density of the board. Typically a 750F iron tip is a good starting point. Please remember that SAC305 wets half as fast as Sn63. Therefore longer dwell times are needed this may take as long as 3 seconds with an iron as compared to 1.5 seconds with Sn63.

Karl Seelig

Deck Street Consultants
In his 32 years of industry experience, Mr. Seelig has authored over 30 published articles on topics including lead-free assembly, no-clean technology, and process optimization. Karl holds numerous patents, including four for lead-free solder alloys, and was a key developer of no-clean technology.

Hand soldering with the lead-free alloy SAC305 is most commonly done in the range of 700-750 F. Some have pushed the limit up to about 800 F, but anything beyond 800 F is definitely not recommended as it could induce damage to the assembly. You will need to carefully select the core flux and flux percent to achieve good soldering results. Most users have found that 2% or 3% flux by weight is required for good performance with lead-free alloys. Finally, it is also advised to monitor the usage of and selection of liquid flux that is being used to assist with the lead-free hand soldering process. Too many users have been attempting to "solve" the slow wetting behavior of lead-free alloys by adding a more aggressive or greater quantity of liquid flux to the operation. The type and amount of flux need to be controlled to be certain of the reliability of the final assembly.

Brian Smith
General Manager - Electronic Assembly Americas
DEK International
Mr. Smith has been supporting customers in the electronics assembly industry since 1994. His expertise is focused on solder paste printing and reducing soldering defects. He holds a BS in Chemical Engineering and an MBA in Marketing. He has authored several papers in trade magazines and at industry conferences. He is an SMTA Certified Process Engineer.
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