Highly Productive Solder Interconnect Formation by Bump Stabbing for 3D-TSV Die Stacking

New high speed die stacking process using the originally designed stabbing pad combined with mass reflow for 2.5D and 3D has been developed. The top die having the bump of Cu pillar and solder cap was picked and placed on the bottom die which has the stabbing pad. The bump was stabbed by the pad with aligned. The stabbing pad has columns of 3 to 4 µm height, which were plated Cu coated by Ni/Au. The stabbing step took only 0.1 second. Well wetted solder joint between the bump the stabbing pad was formed. Sn-Ni-Cu alloy layer was detected by cross sectional EDX analysis at the interface of the column and the solder. Numerical analysis by finite element method revealed that the advantage of the bump stabbing process of the lower stress around the joint during reflow process comparing with TCB. The estimated UPH is 1440, which is much higher than that of conventional TCB process.