Good practice guide to reduce copper dissolution in lead-free assembly.
- Author(s):
Di Maio, D, Hunt, C P, Willis, B
- Source:
- Measurement Good Practice Guide No. 110, December 2008
- ISSN:
- 1368-6550
- ISBN:
- NPL Doc. Ref:
- PDB: 5104 | DDB: 2769
- Document Type:
- Guide
- DOI:
Note: An asterisk after an author's name indicates a non-NPL author.
Abstract:
During a successful soldering operation to a copper surface a small amount of copper is dissolved to form a reliable interconnection and is perfectly normal. During the soldering operation copper is dissolved by tin to form a tin/copper intermetallic and the amount dissolved is dependent on the soldering process, solder alloy, surfaces to be joined, temperature, time and solder flow rate. Using lead-free alloys requires higher soldering temperatures and potentially longer contact times, and hence the propensity for higher dissolution of copper.A typical intermetallic produced with a tin/lead solder can range between 1-3µm. In the case of lead-free soldering process this thickness can increase above 5µm. The intermetallics are themselves soluble in solder, and hence potentially the overall copper dissolution rate is greater. Dissolution during lead-free soldering does not just impact copper pads on printed boards it can be a potential issue on thin copper wire, component terminations and hybrid metallisation. Examples of some typical problems previously experienced in industry are provided in this guide.
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