by Jason Bragg, Russell Brush, Polina Snugovesky, Blake Harper, Simin Bagheri, Dr. Ning-Cheng Lee , Dr. Weiping Liu
Board-level drop test performance was evaluated and compared for the following four different solder combinations in BGA/CSP assembly: 1) SnPb paste with SnPb balls, 2) SnPb paste with SAC105Ti balls, 3) SAC305 paste with SAC105Ti balls, and 4) SAC305 paste with SAC105 balls. The presence of Ti improved the drop test performance significantly, despite the voiding side effect caused by its oxidation tendency. It is anticipated that the voiding can be prevented with the development of a more oxidation-resistant flux. The consistently poor drop test performance of 105Ti/SnPb is caused by the wide pasty range resulting from mixing SAC105Ti with Sn63 solder paste. The effect of Ti in this system is overshadowed by the high voiding outcome due to this wide pasty range material. In view of this, the use of a SAC105 BGA with an SnPb solder paste is not recommended, with or without the Ti addition. High reflow temperatures drove the fracture to shift to the interface at the package side, presumably through building up the IMC thickness beyond the threshold value. A lower reflow temperature is recommended. The electrical response is consistent with the complete fracture data, but the complete fracture trend is inconsistent with that of the partial fracture trend, and neither data can provide a full understanding about the failure mode. By integrating the complete fracture and the partial fracture into a “Virtual Fracture”, the failure mechanism becomes obvious and data sets become consistent with each other.
SAC305, solder paste, SAC105Ti, SAC, solder sphere, lead-free, drop test, Apex 2012
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Posted on 14 Oct 2011
