A low-cost (with bare chips) and high (electrical, thermal, and mechanical) performance 3D IC integration system-in-package (SiP) is designed and described. This system consists of a silicon interposer with through-silicon vias (TSV) [1–24] and redistribution layers (RDL), which carries the high-power flip chips with microbumps on its top surface and the low-power chips at its bottom surface. TSVs in the high- and low-power chips are optional but should be avoided. The backside of the high-power chips is attached to a heat spreader with or w/o a heat sink. This 3D IC integration system is supported (packaged) by a simple conventional organic substrate. The heat spreader (with or w/o heat sink) and the substrate are connected by a ring stiffener, which provides adequate standoff for the 3D IC integration system. This novel structural design offers potential solutions for high-power, high-performance, high pin-count, ultra fine-pitch, small real-estate, and low-cost applications. Thermal management and reliability of the proposed systems are demonstrated by simulations based on heat-transfer theory and time and temperature dependent creep theory.

The present study evaluates the relative thermal fatigue life of tin-silver-copper (SnAgCu or SAC) lead-free and tin-lead (SnPb) solders with custom-made BGA assembly configurations generating various stress ranges under thermal cyclic loading. Although the SAC solder bears a lower creep strain rate compared with the SnPb solder in common thermal cycling conditions, it is found that there exits conditions at which the SnPb solder joint maintain a longer life than the SAC solder joint. The determination lies on the maximum normalized equivalent stress levels ( σ / E ) experienced by the two kinds of solder joint during the temperature cycles. Even under the same straining and thermal cycling condition, it is observed that the maximum σ / E induced in the two kinds of solder joint are normally different, as a result of their different rate of stress relaxation. The analysis shows that both the absolute and relative magnitude of σ / E experienced by the two kinds of solder joint affect the relative life. In general, the SAC solder joint sustain a longer life at low σ / E levels, while the SnPb solder joint outperform the SAC solder joint at high σ / E levels. There exists a critical σ / E level at which both solder joints acquire similar performance. However, this margin shifts with the relative magnitude of σ / E the two kinds of solder joint suffered. Having studied the variation of σ / E for the two kinds of solder joint under various loading conditions, this study uncovers the rationale for the difference in the relative thermal fatigue life of the two kinds of solder joint.