Advanced Packaging Technology Conference Proceedings


LEAD-FREE REWORK PROCESS FOR CHIP SCALE PACKAGES

Authors: Arun Gowda and K. Srihari, Ph.D.
Company: SUNY, Binghamton
Date Published: 6/12/2001   Conference: Advanced Packaging Technology


Abstract: Legislation against the use of lead in electronics has been the driving force behind the use of lead-free solders, surface finishes, and component lead finishes. The major concern in using lead-free solders in the assembly and rework Chip Scale Packages (CSPs) is the relatively high temperatures that the components and the boards experience. Fine-pitch CSPs have very low standoff heights following assembly making inspection and rework of these components more difficult. One other concern pertinent to rework is the temperature of the neighboring components during rework. These issues, coupled with the limitations of rework equipment to handle lead-free reflow temperatures, make the task of reworking lead-free assemblies more challenging.

In this research endeavor, lead-free CSPs with tin-silver and tin-silver-copper solder balls were assembled and reworked. In addition, tin-lead CSPs were assembled and reworked as a baseline for comparison. Different rework sequences, redressing and fluxing techniques were evaluated. Post-assembly and post-rework analysis was done following assembly and rework using x-ray inspection, standoff measurements and cross-section microscopy. The reworked assemblies have completed 920 cycles of 0 degrees C to 100 degrees C Air-to-Air Thermal Cycling (AATC). No instances of time-zero electrical failures were found in post-rework tests Useful guidelines for lead-free rework of fine-pitch components and CSPs in particular were developed and are presented in this paper.

Key words: lead-free, CSP, BGA, rework.



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