Journal of SMT Article


Authors: Alan Donaldson and Raiyo Aspandiar
Company: Intel Corporation
Date Published: 1/1/2005   Volume: 18-1

Abstract: Due to pending legislation in Europe and Japan, the electronic industry is converting to lead-free (LF) solders. This paper focuses on the rework of LF ball grid array (BGA) packages and sockets, soldered to printed circuit boards (PCB), using hot air. Hot air rework profiles were developed for BGA package sizes from 15 to 37.5mm, soldered on immersion silver (ImAg), organic surface protectant (OSP) and nickel-gold (NiAu) PCB surface finishes. The BGA package solder balls were all Sn/Ag4.0/Cu0.5, attached to electroless nickel immersion gold at the package interface.

A hot air rework process for a 478 BGA lead-free socket with two different solder ball compositions (Sn/Ag3.5 and Sn/Ag3.0/Cu0.5) was also developed. The rework temperature range for these packages was from 230-250°C. Detailed inter-metallic compound (IMC) analysis was also conducted on some of these packages. Many packages were put through a series of reliability tests that included temperature cycling, static bake, mechanical shock, and vibration. A generic guideline for lead-free rework profiling was established based on the rework conducted in this study and will be described in this paper. From the results obtained, it was ascertained that lead-free hot air rework can be reliably done on a variety of boards and surface finishes.

Key words: lead-free rework, BGA, solder joints, IMC.

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