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Ask the Experts

July 13, 2009 - Updated
July 13, 2009 - Originally Posted

Wave Soldering Fine Pitch Through Hole Components

We are wave soldering very close pitch through hole components and see bridging. What is the finest pitch for through hole components that can be successfully wave soldered? Is there anything you can recommend we do to reduce bridging on this component?

A. N.

Expert Panel Responses

The article can be found in an of SMT Magazine titled Intrusive Reflow of Lead-Free Solder Paste.

Bill Coleman
Vice President Technology, Photo Stencil

For over 18 years, Dr. Coleman has been the vice president of technology for Photo Stencil, working closely with customers to understand their printing requirements. His efforts have resulted in several new stencil products.

We have seen very tight pitch wave soldering when the MS2 material is used on the solderpot. The MS2 works as a dross eliminator and allows the solder to wet and flow much better. The MS2 is available from PK Metal. Larry Kay is the contact.

Terry Munson
President/Senior Technical Consultant, Foresite

Mr. Munson, President and Founder of Foresite, has extensive electronics industry experience applying Ion Chromatography analytical techniques to a wide spectrum of manufacturing applications.

Bridging of close thru-hole terminations has long been an issue in design and assembly practices. There are a number of major contributors to this that may yield better results. When you start to reach a 20-25 mill pitch the process will be more difficult to maintain. Machine parameters,

Try not to run the assembly too deep into the wave. meaning immersion depth.
Make sure your back flow is not excessive from the main wave.
Make sure you are not burning off the flux prematurely from excessive preheat or excessive preheat exposure time.
And of coarse make sure you have enough flux on the assembly.

Design related issues and tools

Assembly direction through the wave, Connectors should run parallel with the conveyor.
Lead length, shorter leads have a tendency to not bridge as much or as easily.
Solder thieves. These are traces placed on the board surface at the exit end of a connector to provide a surface the solder can drain and adhere too.
Debridging tools. There are stationary hot airknives and X/Y area specific debridging tools that can assist. These devices can be limited by the thermal window as the solder must be in a liquid state for them to work effectively.

John Norton
Eastern Manager, Vitronics Soltec

John Norton started his soldering career in 1983 for Hollis Engineering. He has also worked with Electrovert as a technical training manager and Vitronics Soltec for the last ten years. He has held various technical development and sales positions.

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