Dual Alloy SMT Process

Posted 07/12/2011 by espranzani

If the wave soldering step could be eliminated while still creating reliable solder joints and not damaging the temperature sensitive components, significant energy, material and labor cost savings could be realized. The processing time required for wave soldering would be eliminated. Wave soldering flux would not be needed. Purchasing bar solder, keeping the bar solder molten, and removing dross from the wave soldering bath would no longer be required. Also, the floor space, manpower and energy required to run a wave soldering process would no longer be costs added to the assembly process.

How can a paste in through hole (PITH) assembly process use temperature sensitive components in a lead-free process without the need for a wave soldering process? Consider a dual alloy SMT process with a lower peak temperature in the second reflow step.

What type of lead-free solder paste will enable low temperature PITH reflow soldering? Tin/Bismuth/Silver is a viable option. This family of alloys is known for high strength through hole solder joints, with excellent wetting to OSP/Copper surface finish. Its resistance to thermal cycling equals or exceeds tin-lead and SAC solder joints.

In addition to the savings from eliminating the wave solder processing, using lower temperature reflow also allows for the use of less expensive laminates and components, adding to the already significant cost savings in a dual alloy SMT process.

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