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38 SMT Magazine • February 2014 approximately 10 seconds during the soldering process in order to ensure complete reflow and mixing of the solder joint. Prior to performing the pull testing on a sol- der joint the heating element temperature was monitored to be less than 30°C. Cooling of the pin is accomplished by a compressed air nozzle near the heating element. Pin and heating el- ements are identified in the image of the HB- P10kg head image in Figure 12. Care was taken not to disturb the liquid solder joint during the cooling of the pin. Several solder joints were reflowed followed by pin removal from the liquid solder in order to cross-section the solder joint and inspect the intermetallic condition. Intermetallic structures following the reflow soldering of the HBP tester TeSTING INTerMeTaLLIC FraGILITy ON eNIG uPON aDDITION OF LIMITLeSS Cu continues Cu pin appeared very similar in SEM analysis of the solder joints. Lead-free solder joints all appeared to have similar thickness intermetal- lic at the electroless Ni boundary (Figure 13). A similar observation was also made of the SnPb solder samples (Figure 14). experimental results In both HBP and CBP testing the failure mode produced were brittle failures within the intermetallic at the electroless Ni substrate (Fig- ure 15). As an aggregate the average peak load to failure of the HBP test samples was far lower than the CBP test procedure. This suggests ei- ther a dramatic decrease in the intermetallic strength or a difference in the mechanical load- ing between these two tests. FEATUrE Figure 11: Dage 4000 slow speed bond tester. Figure 12: hbP10Kg load cell. Figure 13: 10,000x SEM inspection of hbP intermetallic morphologies for Intel and Short ball attach profiles (A) Intel 845, (b) SnPb, (C) SnAg, (D) SAC304. a b C D