Authored By:
Chris Hunt, Martin Wickham, Ling Zou, Owen Thomas and Bufa Zhang
National Physical Laboratory
Teddington, UK
Summary
The banning of Pb in electronic component termination finishes has flushed through the supply chain making it impossible in some cases for hi-reliability users to purchase Pb containing interconnects. It has also led to increasing problems with tin whiskers.
Many end-users are now reterminating components with SnPb solder. This paper will discuss the results of a recent joint industry project undertaken at NPL to evaluate the retermination process on a range of electronic package styles. Details will be given of package styles covered, evaluation techniques employed, inter-comparison of reliability data, results and areas of concern.
Conclusions
A range of RoHS compliant components have been examined after retermination by two different retermination process suppliers. Few differences were noted between the suppliers, except that some damage to terminations of fine pitch gull wing leads was noted on the supplier who utilised manual handling during the retermination process. XRF measurements showed all components were RoHS non-compliant after retermination with at least 25% Pb present in all terminations.
Solderability was acceptable for all reterminated components, being as good as or better than the measurements for the
original components. In some examples, reterminated components showed increased solder thickness at the bend of terminations. This may lead to problems during component placement, particularly for fine pitch components. Additionally, thinner solder was noted around the edges of terminations compared to the original examples. After long term storage, these areas may present poor solderability during assembly.
Solder ingression along internal gull-wings of reterminated plastic bodied components was also noted. No solder was seen in the original components although the separation between the component body and lead-frame was present. No significant intermetallic thickening was noted as a result of the conversion process. Some through-hole components exhibited issues with poor coverage and package body damage. Poor coverage occurred when terminations exposed outside the package body were not solderable, due to the method of component manufacture or where the terminations extended into cavities within the component body.
Several examples of damage to TH component bodies were also seen in areas of components would not see molten solder temperatures in the soldering operation. Scanning acoustic microscopy did not locate any differences between original and reterminated components. Ball shear measurements on ball grid array components were acceptable. Thermal cycle solder joint reliability was improved for reterminated components compared to Sn originals. This was related to the increased solder joint volumes associated with the reterminated components, resulting in a greater stand-off.
Initially Published in the IPC Proceedings
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