Development of 2.3D High Density Organic Package using Low Temperature Bonding Process with Sn-Bi Solder

Recently, 2.5D package structure such as using silicon interposer is used for high end sever and HPC (High Performance Computing) with high density connection between logic device and memory device. We are developing high density organic package called i-THOP® (integrated-Thin film High density Organic Package) 2.3D type combining organic interposer and build-up substrate. The organic interposer was mounted on build-up substrate. Interconnection between organic interposer and build-up substrate was consisted of copper post and Sn-Bi solder. The bonding process was applied by using the pre-applied NCF (Non-Conductive Film) method. Interconnection was achieved under 200 degrees C by using Sn-Bi solder. The good wettability of Sn-Bi solder was observed at joint portion with minimum 200 μm pitch and no NCF void was confirmed by SAT (Scanning Acoustic Tomography). After that, die assembly was evaluated. The good wettability of solder joints of assembled small die and large die was confirmed with minimum 40 μm pitch. Sn-Bi solder joints were also stable without re-melting after die assembly and stiffener attach process. The thermal warpages of i-THOP® 2.3D type was measured after organic interposer stacking, die assembly and stiffener attach. The warpage without die was small at approximately 20 μm at 30 degrees C and almost no change from 30 degrees C to 250 degrees C. However, the warpage with die was large at 300 μm at 30 degrees C. After stiffener attach process, the thick stiffener over 2.0 mm could reduce warpage below 200 μm that is the criteria of 1.0 mm pitch BGA (Ball Grid Array). The reliability tests of TC (Temperature Cycling), HTS (High Temperature Storage Life), u-HAST (unbiased-Highly Accelerated Temperature and Humidity Stress Test) and b-HAST (biased-Highly Accelerated Temperature and Humidity Stress Test) were carried out. The criteria of TC 1000cycles, HTS 1000 hours, u-HAST 192 hours and b-HAST 96 hours were passed.