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Measuring the reliability of electronics assemblies during the transition period to lead-free soldering.

Wickham, M; Zou, L; Dusek, M; Hunt, C (2005) Measuring the reliability of electronics assemblies during the transition period to lead-free soldering. NPL Report. DEPC-MPR 030

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A wide-ranging study of Pb-contamination of lead-free solder joints has been undertaken. Over 200,000 solder joints on assemblies incorporating the main types of surface mount and through components, have been manufactured with SnPb and LF terminated components using SnPb, LF and mixed alloy systems. The work has included manufacture of joints with specifically controlled levels of Pb-contamination between 1 and 10%. All these assemblies have subsequently been thermally cycled (-55 to 125 ºC) to 2000 cycles, continuity tested, shear tested, pull tested and vibration tested.
The work has indicated that there should be few solder joint reliability problems when mixing SnPb and LF components and solder alloys (with Pb contamination in the range 1 to 10%). Very few thermal cycle fatigue failures were experienced other than within two component groups. Shear testing of chip resistor components showed no difference in crack propagation rated between any of the component/alloy combinations. No failures were generated during vibration testing.
Some ball grid array joints did fail but these were largely restricted to SnPb alloy dominated systems, i.e. SnPb terminated components soldered with SnPb or SAC alloy solder pastes. Uncontaminated SAC systems or those systems contaminated with low levels of Pb showed fewer failures. Failures in Sn-plated QFP components were probably due to batch related solderability issues.
Work with hot peel testing of SOIC components has indicated that Pb-contamination may cause end-users problems during processing. The addition of small quantities of Pb (< 10%) to a LF joint significantly reduce its peel strength above 180 °C. This may cause the first side solder joint to separate or deform during second side reflow, if the assembly is subjected to mechanical forces during assembly.

Item Type: Report/Guide (NPL Report)
NPL Report No.: DEPC-MPR 030
Keywords: lead contamination
Subjects: Advanced Materials
Advanced Materials > Electronics Interconnection
Last Modified: 02 Feb 2018 13:16
URI: http://eprintspublications.npl.co.uk/id/eprint/3270

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