Electronics Assembly Knowledge, Vision & Wisdom
Converting Cable Assembly to Lead Free Solder
Converting Cable Assembly to Lead Free Solder
This paper reviews soldering applications associated with cable assembly. The focus is on process modification and qualification with lead free solders.
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Authored By:
Lynda L. Anderson, Robert Mahoney Jr.
IBM Corporation
Poughkeepsie, NY, USA

Summary
Lead free soldering presents many challenges to cable assembly manufacturing. Many assembly issues were easily solved with a little tin lead solder. However, the higher temperatures and lower ductility associated with lead free solder presents assembly challenges requiring adjustments to existing processes.

This paper will review the various soldering applications associated with cable assembly. The focus will be on process modification and qualification with lead free solders. The processes reviewed will include soldering of crimp terminals to enhance reliability, automatic or semiautomatic bulk cable solder attach to printed circuit boards, soldering of copper tape for shielded cables, soldering of splices and braid or drain wires.

Some process and design modifications are required when using lead free solder in cable assembly manufacture. Most are associated with temperature. High performance cable assemblies that have printed circuit boards exhibit changes in electrical performance with lead free solder but the variation is relatively minor. The more pressing issues are manufacturing and process control.

The forces transmitted to the solder joints from relative motion of the high performance bulk wire pairs have been a long standing concern. Lead free solder is stronger but that is not necessarily an advantage. Consistency is more critical to the quality and reliability of these cables. Handling during the process is also critical.

Converting processes to lead free solder is not without challenge. Accelerated reliability testing is not required for most cable assembly families. If proper cable assembly designs, cable manufacturing process designs and process controls are established, a wide variety of cable assemblies can be built using lead free solder without impact to the end customer.

Conclusions
Converting processes to lead free solder is not without challenge. The results support the conclusion that accelerated testing performance for lead free cables is not significantly different than those experienced using tin lead solder. This may, in part, be due to the small PCB used within cable assemblies. A larger thermal mass might significantly change the outcome.

It has also been learned that the key concern with lead free high performance cable assemblies is mechanical in nature. Handling and mechanical assembly design considerations are critical to success. It has also been shown that high performance electrical parameters need to be verified when moving an existing cable assembly from a tin lead to a lead free solder process. If adequate margins exist, the test results should be positive but data is needed to confirm.

Consistency is the ultimate goal to minimize variability in cable performance. If proper cable assembly designs, cable manufacturing process designs and process controls are established, a wide variety of cable assemblies can be built using lead free solder without impact to the end customer.

Initially Published in the SMTA Proceedings

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