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Compatibility of lead-free solders with PCB materials.

Dusek, M; Nottay, J; Hunt, C (2001) Compatibility of lead-free solders with PCB materials. NPL Report. MATC(A)89

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This report presents the results of an evaluation of the compatibility of some lead-free alloys with other materials currently used in pcb assembly (flux systems, lead-tin solder, board and component finishes), and the consequential effects on the joint reliability. Three techniques have been used in these investigations: electrical continuity measurements, shear testing and observations of microstructural changes. Test boards were generated under a matrix of assembly conditions (three component termination styles, five board finishes and three solders), and subsequently comparative data were acquired following thermal exposure of the boards (-55 to +125 ºC for up to 2200 cycles). The work has benefited from the use of a new accelerated test method to obtain failure data in timescales much less than those traditionally experienced.
The electrical continuity findings indicated that for the larger components (2512-type resistors) the larger strain range can be better accommodated using traditional SnPb solder than using the new lead-free alloys. By contrast, when the strain range was smaller (e.g. with 0603-type resistors or SOIC devices) the lead-free solders were as good as, or better than, the traditional SnPb solder. There appears to be a benefit of adding Bi to the SnAgCu solder. The shear strength tests demonstrated that, over all the test cycle regimes used, the joints made using lead-free solders were stronger than those made using traditional SnPb solder. In the as-formed condition the ultimate shear forces required to break lead-free joints were significantly higher than those required to break lead-containing joints.

Item Type: Report/Guide (NPL Report)
NPL Report No.: MATC(A)89
Keywords: solder, reliability, PCB finish
Subjects: Advanced Materials
Advanced Materials > Electronics Interconnection
Last Modified: 02 Feb 2018 13:17
URI: http://eprintspublications.npl.co.uk/id/eprint/2326

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