High-Density Interconnect Technology for LTCC Substrates in High-Reliability Hybrid Integrated Circuits

This work develops an advanced Ag co-fired/ENEPIG hybrid metallization system to overcome critical limitations in high-density LTCC substrates. The proposed technology simultaneously addresses: (1) the resolution barrier (≤120 μm line/space) of conventional thick-film processes, (2) due to Kirkendall effect and the mismatch of materials CTE, multiple sintering-induced defects including via protrusions and glass phase segregation, and (3) the cost inefficiency of pure Au systems. Through optimized single-step co-firing coupled with ENEPIG surface finishing, the system achieves exceptional pad coplanarity (±15 μm) and dimensional precision (≤10%-20% line width variation). The single-fire protocol effectively suppresses interfacial glass phase formation while promoting beneficial Ag-Au interdiffusion, resulting in outstanding mechanical performance (wire bond strength >15 gf, solder joint strength >1.6 Kg). The innovative seed-layer architecture, implemented via precision Ag paste deposition with Screen Mesh Technology, enables high-resolution patterning without lithography, reducing production costs by >40% versus conventional Au systems. These advancements establish a new benchmark for cost-effective, high-reliability packaging solutions suitable for demanding military and aerospace applications.