Book Reviews

This report outlines the results from comparative testing of 12 variants of tin-silver copper type lead free solder paste products. The work is done in collaboration between Bang & Olufsen NS and DELTA and involves design of test board, production scale screen printing and paste reflow, qualification testing and technology studies. Tested solder paste products are selected and provided by the local paste suppliers, CYNCRONA NS, Teleinstrument NS, Venso Elektronik AB, Ketec NS, Interflux DK, PC-Trading NS, Boliden NS, HIN Horsens NS, Inimar KIF, KOKI NS and Tamura Kaken UK.

Single-sided FR4 glass-epoxy type test boards are supplied in two different board finishes – OSP & Immersion gold

The paste product properties have been evaluated by SEM examination, slump, hot slump, printability, reflow and SIR testing.

In general, the results show a relatively big difference in the hot slump performance, as only 2 solder paste products exhibit perfect performance. 5 solder pastes were found to have acceptable performance, however, the remaining products and in addition the reference tin-lead pastes are found to suffer from serious slump bridging.

On printing and reflow all of the tested pastes were found to have a wetting ratio of approx. 1.0, showing that the pastes only wets where it is printed. In contrast to this. the wetting ratio on immersion gold, is found to vary from 1.1 to 1.7, showing a relatively good wetability of some pastes and major difference between the solder pastes tested.

The ability to recover from overprinting is found to be perfect for all of the pastes tested and similar to what is seen for the reference tin-lead paste. Solder ball formation on no wetting epoxy laminate is also found to be perfect for all of the pastes, indicating a consistent paste reflow without solder splash/balling.

SIR testing confirmed perfect insulation resistance for 5 of the tested pastes 7 pastes were found to have acceptable insulation resistance.

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