Study of five substrate pad finishes for the co-design of solder joint reliability under board-level drop and temperature cycling test conditions

The current paper evaluates the impact on solder joint reliability (SJR), using board-level drop test, temperature cycling on board (TCoB) test, and component-level high-speed solder ball shear (HSSBS) test, of five existing and under-development substrate pad finishes including electrolytic nickel-gold (NiAu), organic solderability preservative (OSP), stencil printed solder-on-pad (SoP), immersion tin (ImSn) and electroless nickel-electroless palladium-immersion gold (NiPdAu). The board-level drop test was performed following standard JEDEC conditions with 1500 G/0.5 ms. The TCoB test was performed following IPC-9701 with -40degC~125degC and 15 minutes dwell/ramp. The HSSBS test was performed using Dage 4000-HS machine with 500 mm/s shearing speed and 30mum shearing height. It is seen from drop test results that NiAu leg gives the poorest SJR. All of the other four pad finishes give very satisfactory drop test durability. In TCoB test results, however, it is observed that NiAu gives the best SJR. OSP gives very poor SJR as compared with the other four counterparts whose 2-parameter Weibull characteristic lives exceed 2000 temperature cycles with significant margin. Subsequent process improvements were made in an effort to improve the SJR of OSP in TCoB test. However, even with these improvements the characteristic lives of two improved OSP testing legs only marginally pass the SJR requirement of TCoB. HSSBS test was also performed to understand the resistance to brittle intermetallic compound (IMC) failure of the five finishes under time zero and ageing condition. It is observed that although SoP sees very good SJR in both drop and TCoB tests, it shows bad resistance to brittle IMC failure in HSSBS test. Encouragingly, NiPdAu, which shows good SJR in both drop and TCoB tests, is also found to give excellent resistance to brittle IMC failure in HSSBS test even after ageing at 125degC for 1000 hours.