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Measuring the impact of land size and solder joint volume on lead-free solder joint reliability.

Wickham, M; Zou, L; Dusek, M; Hunt, C P (2006) Measuring the impact of land size and solder joint volume on lead-free solder joint reliability. NPL Report. DEPC-MPR 044

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Abstract

In an attempt to ascertain the effect of pad size/design and solder joint volume on leadfree solder joint reliability, a range of test boards have been assembled using lead-free (SnAgCu) solder paste and assessed in a matrix experiment involving four components types (R0603, R1206, SOIC and BGA), ten pad designs and three stencil thicknesses. The assemblies were thermally cycled (-55 to + 125ºC) for a maximum of 2000 cycles, and the joints were studied visually, and using shear testing and electrical continuity monitoring.
The effect of using different thicknesses of stencil during the manufacture of lead-free assemblies was found to be quite limited. Thicker stencils did produce joints with higher shear strengths for chip resistors, but during thermal cycle testing of joints made using the thinner stencils, there was no evidence of increased crack propagation or failures. No electrical failures were noted for SOIC components up to 2000 cycles. There was some evidence that using thinner stencils resulted in BGA joints of poorer reliability, with twice as many BGAs joints made using the 100µm thick stencil failing after 2000 cycles, as compared with those from the thicker stencils.
The pad design also showed only a limited effect on the reliability of lead-free chip resistor joints after thermal cycling. Having a shorter pad did produce more electrical test failures, but only for the joints made using the thinner stencils, suggesting that this combination produced a narrower fillet, and thus a shorter time to electrical failure.

Item Type: Report/Guide (NPL Report)
NPL Report No.: DEPC-MPR 044
Keywords: pad design
Subjects: Advanced Materials
Advanced Materials > Electronics Interconnection
Last Modified: 02 Feb 2018 13:15
URI: http://eprintspublications.npl.co.uk/id/eprint/3690

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