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Article: Underfills in Pb-free assemblies: increased stresses on assemblies--the result of lead-free soldering--raise the possibility of underfills as reliability enhancers.
- Article from:
- Circuits Assembly
- Article date:
- June 1, 2005
- Author:
CopyrightCOPYRIGHT 2005 UP Media Group, Inc. This material is published under license from the publisher through the Gale Group, Farmington Hills, Michigan. All inquiries regarding rights should be directed to the Gale Group. (Hide copyright information)
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Lead-free solder joints in grid arrays are vulnerable to failures resulting from CTE (coefficient of thermal expansion) mismatches. The chief causes are the lower ductility of lead-free alloys, combined with a greater tendency for the assembly to warp as a result of the higher peak reflow temperature for lead-free. (1) Diminishing interconnect pitches and general migration to thinner substrates are exacerbating the situation. As a result, underfills may now be necessary in assemblies using CSPs, [mu]BGAs or even BGAs, which have his torically not required the use of CTE countermeasures.
[FIGURE 1 OMITTED]
When mandatory use of lead-free solders for ...