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Through-Hole Rework for Challenging Components



Through-Hole Rework for Challenging Components
The successful transition of low and mid-range servers to lead-free has come largely through wave solder process optimization and the use of alternate lead-free alloys.
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Authored By:


Brian Czaplicki
Air-Vac Engineering Company, Inc
Seymour, CT USA

Summary


Although the vast majority of electronic equipment has made the transition to lead-free without significant issue, some market segments still utilize tin-lead solder. The European Union's RoHS legislation currently exempts server, storage array systems and network infrastructure equipment from the requirement to use lead-free solder (exemption 7b).

The reliability of network infrastructure equipment in Finance, Health Care and National Security applications is critical to the health and safety of consumers, countries and the global community and the long term reliability of these end products using lead-free solder is not completely understood.

Conclusions


The solder fountain or "mini pot" has been the industry standard for tin-lead PTH rework as well as lead-free rework of PTH components on low and mid-complexity assemblies. The solder fountain process has been optimized for lead free rework by the use of lower dissolution solder alloys and by the addition of integrated preheating systems. In addition, BGA rework systems with convective and IR heating systems have been successfully used to remove lead free PTH components for applications where the optimized solder fountain process does not meet the rework objectives.

The current "lead in solder" exemption for Class 3 applications including server, storage and network infrastructure equipment is set to expire in 2014. Alternative rework solutions, including convection, IR, vapor phase and laser have been proposed, however none of the existing technologies was designed with lead-free rework of PTH components on large, high thermal mass assemblies in mind.

The PCBRM100 is a "clean sheet of paper" design approach to solving copper dissolution and barrel fill issues on Class 3 assemblies. In design and beta testing for over three years, initial production shipments will begin in the first quarter of 2013. The key to the 100 is the top and bottom focused convective heating (FCH) system which significantly reduces the required solder contact time which in turn significantly reduces copper dissolution. A two phased DIMM connector rework study on the 100 demonstrated that 100% of DIMM connectors reworked with the FCH process showed excellent results in regard to "post rework" copper thickness, barrel fill and fillet formation.

Void analysis showed excellent results on 86% of the joints analyzed, however some large, random voiding did occur. The combined phase one and phase two processes were based on the complete rework (i.e. removal, barrel cleaning and replacement) of twenty-six (26) DIMM connectors with fifty-two (52) cross sections, nine hundred and thirty-six (936) copper thickness measurements taken and one hundred and fifty-six (156) barrel fill and voiding calculations made and fillet formations assessed.


Initially Published in the IPC Proceedings

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