Pan Pacific Symposium Conference Proceedings


IMPLEMENTATION OF A LEAD FREE WAVE SOLDERING PROCESS: AN IN-DEPTH LOOK AT THE CRITICAL ISSUES

Author: Denis Barbini
Company: Vitronics Soltec, Inc.
Date Published: 2/25/2005   Conference: Pan Pacific Symposium


Abstract: Many studies on lead free implementation have focussed on surface mount assembly with conventional reflow technology. As a result, wave soldering while no less important or impacted has received less attention. There exist similarities between the lead free implementation of surface mount and through hole assembly. An example is clearly observed in the tighter process window for assemblies using lead free alloys versus conventional eutectic tin lead alloy.

This investigation focuses specifically on two aspects: identifying the issues surrounding the implementation of a reliable, robust lead free wave soldering process and characterizing the impact various parameters have in achieving the optimized soldered joint. The critical aspects of the lead free wave soldering process can be broken down into several categories which include component reliability, board reliability, flux type and specifications, alloy and alloy composition, its melting behavior, wave equipment capacity and power requirements, profile attributes and flexibility.

This study will define the lead free soldering window, its impact on the soldering process, and address some of the critical issues surrounding lead free implementation including solderpot materials and compatibility which is known to be vulnerable to the formation of FeSn2 when exposed to lead free alloys. Rate of dissolution for board pad features when exposed to SnAgCu alloy increases significantly versus tin lead.

As a result of this, care must be taken to ensure that multiple soldering operations do not adversely impact joint strength and ultimately reliability. The impact of lead contamination on RoHS compliance as well as on cost to the end user is addressed. The relationship of solder temperature and dwell time on joint formation will be defined for various board types.

Overall, this investigation looks to bring an understanding of how these parameters correlate and provide the reader with the information necessary to make the critical decisions in selecting materials and equipment. This study will also provide insight into the process issues that one will encounter so that a rational implementation strategy for a reliable and robust lead free wave soldering process can be achieved.

Key words: Lead Free, wave soldering, process, power consumption.



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