Cu redistribution layers on permanent glass-core substrates for advanced packaging: Direct-on-glass and polymer build-up architectures

Glass-core substrates are attracting increasing interest for advanced packaging because of their dimensional stability, high electrical resistivity, smooth surfaces, and compatibility with fine-pitch interconnect processing. This review compares Cu redistribution-layer (RDL) technologies implemented on permanent glass-core substrates through two principal architectures: direct-on-glass RDLs and polymer build-up RDLs. Direct-on-glass approaches reduce dielectric-stack complexity and can support low-loss lateral routing, but their scalability depends strongly on glass–Cu adhesion, seed-layer control, conductor dimensional fidelity, and stress transferred to brittle glass. Polymer build-up approaches enable multilayer routing and microvia-based redistribution while introducing additional constraints associated with dielectric properties, cure-induced dimensional change, moisture response, interfacial integrity, and multilayer registration. Reported studies demonstrate micrometer-scale wiring and vias, broadband signal transmission, multilayer integration, accelerated reliability testing, and large-area glass processing. However, the most aggressive dimensions, highest integration levels, and strongest electrical or reliability results have generally been demonstrated in different material stacks and test vehicles rather than concurrently within a single permanent glass-core platform. Accordingly, minimum feature size alone should not be interpreted as a manufacturing design rule. Future progress will require coordinated design of interfaces, dielectric materials, metallization, and routing architecture, together with statistically meaningful qualification of dimensional control, electrical performance, environmental reliability, and panel-scale manufacturability.