Low Temperature Fine Pitch All-Copper Interconnects Combining Photopatternable Underfill Films

Abstract

The trend to 3D and heterogeneous integration enable driving multi-functional blocks in one package. Flip-chip integration is currently playing an important role and is based on solder joints. To overcome the limitations of solder joints, allcopper interconnects have been investigated to meet electrical, thermal, and reliability demands in 3D integration. The underfill process is widely applied in flip-chip encapsulation technology. We propose a novel wafer-scale all-Cu interconnect method combining epoxy-based photo-patternable polymer as self-aligned underfill layer with the patterned copper nanoparticles interconnects. The resulting test wafers were able to pattern 20 μm pitch copper nanoparticle-paste interconnects on both substrates with and without photoimageable polymer. The Cu paste was applied to form the interconnects and was sintered after bonding process. Free-standing nanocopper is sintered to obtain mechanical properties with a Young's modulus of 112 GPa. All-Cu interconnects with diameter of 50 μm and 100 μm were measured to achieve the specific contact resistance, ranging from 1.4 × 10 −5 Ω•cm 2 to 1.0 × 10 −5 Ω•cm 2 at different sintering temperature when epoxy-based underfill existing. And its resistivity was 4.54 × 10 −4 Ω•cm, compared to 5.86 × 10 −4 Ω•cm for the all-Cu interconnects without underfill.