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November 20, 2006
Lead levels in lead-free process
There is a lot being written on controlling the lead in lead-free soldering. Contamination is introduced in the solder process by way of component plating, board surface finish, migration from soldering iron tips/tooling and the original lead content in the solder. The RoHS Directive has and allowance of 0.1% for compliance with its standards.
From a manufacturing process control standpoint, I am interested in whether the industry has established a level/standard at which the percentage of lead results a significant reduction in solder joint strength. Has this been identified specifically for the SAC alloy, family of lead-free solders?
Richard Neblett
Applied Technologies Assoc.
This "Ask the Experts" page has been viewed 833 times.
Ask the Experts Comments
November 20, 2006
The introduction of lead does not, in of itself, reduce the inherent strength of the solder joint. The primary concern is where and how that lead is present in the solder. If the lead is segregated, especially preferentially in the interfacial regions, you can have a Pb-rich region which is very weak. If the Pb is well-mixed, Pb levels as high as 5, 10 ,15% do not seem to result in a reduction in solder joint reliability under temperature cycling. Less data is available on the behavior under mechanical loading.
Dr. Craig D. Hillman, CEO & Managing Partner
DfR Solutions
chillman@dfrsolutions.com
 Dr. Hillman's specialties include best practices in Design for Reliability, strategies for transitioning to Pb-free, supplier qualification (commodity and engineered products), passive component technology and printed board failure mechanisms. Dr. Hillman has over 30 publications and has presented on a wide variety of reliability issues to over 150 companies and organizations.
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