Issue link: https://iconnect007.uberflip.com/i/253291
February 2014 • SMT Magazine 37 TeSTING INTerMeTaLLIC FraGILITy ON eNIG uPON aDDITION OF LIMITLeSS Cu continues Cu6Sn5 intermetallic at the electroless Ni sur- face for short ball attach profiles (Figure 7 A &B). SEM inspection of the lead-free systems suggests that the SnAg Long (Figure 8C) had a unique morphology near the electroless Ni pad surface. Specifically a thinner intermetallic was observed in direct contact with the pad. Following addition of Cu powder the inter- metallic variation for the SnPb samples was far less dramatic than the lead-free samples. The long and short ball attach profile seemed to have little effect on the intermetallic morphol- ogy as determined by optical inspection (Figure 9) and SEM (Figure 10). Cold bump Pull (CbP) Testing CBP was performed on a Dage 4000 bond tester (Figure 11) using a tweezer of diameter 30 mils and a CBP5kg load cell. Pull rates were determined based upon the frequency of brittle failure modes observed. A speed was selected that generated nearly 100% brittle failure at the electroless Ni substrate. Hot bump Pull (HbP) Testing HBP testing was also performed on the Dage 4000 bond tester however a 30 mil diameter pin is heated and soldered to the solder joint using a HBP10kg lead cell. This load cell has an inte- grated heating element controlled by a temper- ature controller. Exact temperatures are difficult to quantify since the equipment thermocouple is attached to the heating element and not the tip of the Cu pin. A temperature was selected that induced reflow of the solder joint. The pin was brought in contact with the ENIG pad for FEATUrE Figure 8: 10,000x SEM images of lead-free morphologies following addition of limitless Cu (A) SnAg Short (b) SAC304 Short (C) SnAg long (D) SAC304 long. Figure 10: 10,000x SEM images of morphology IX (A) SnPb Short (b) SnPb long and (C) Intel 845. Figure 9: 500x optical images of SnPb morpholo- gies following addition of Cu powder (A) SnPb Short (b) SnPb long and (C) Intel 845.