Pan Pacific Symposium Conference Proceedings


Author: Rahul Raut et al.
Company: SUNY Binghamton
Date Published: 2/25/2005   Conference: Pan Pacific Symposium

Abstract: The electronics industry is transitioning to lead-free soldering, and currently faces many process challenges. The primary issue is the effect on assembly processing of heat sensitive components, particularly BGAs, optoelectronic modules, certain connectors, and substrates at the higher melting temperature and this can shorten device life and degrade package reliability. Even under circumstances where the overall temperature profile is satisfactory, the profile of components at the edge of a PCB can be significantly different as the same component at the center.

This is further complicated by factors like PCB thickness, and the existence of hybrid "Pb-free" components that still contain Sn63Pb37 solders. In lead-free rework, components are subjected to multiple thermal cycles. Those components adjacent to the rework site regularly see temperatures that are high enough to compromise the integrity of their solder joints. In this paper, we discuss efforts made to solve these issues using an innovative thermal management approach.

In this thermal-management system, cooling caps are used for an efficient reflow and rework process. Performance of different cooling cap designs is discussed in the paper, along with procedures for use, and results on a range of test boards. Optimization for different cooling considerations has been achieved through empirical measurements, together with 2D and 3D models, using ANSYS. This technology can facilitate the assembly of legacy and other heat-sensitive components in lead-free reflow and rework. It can also aid in increasing the throughput of the overall manufacturing process.

Key words: Lead-free Assembly, heat-sensitive components, reflow and rework issues, thermal management, cooling caps / devices.

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