Physics / mechanism
Buildup (BF) and Ajinomoto Buildup Film (ABF) substrates are organic laminate interposers sitting between a flip-chip die and the PCB. ABF is a thermoset epoxy-based dielectric film developed by Ajinomoto; it enables fine-pitch copper redistribution layers (RDL) via semi-additive processing (SAP). Key parameters: line/space currently 2 µm/2 µm in leading HVM (down from 10/10 µm circa 2015), layer count 8–20+ for advanced packages, CTE ~13–17 ppm/°C (mismatch with silicon ~2.3 ppm drives warpage engineering). Substrate core is typically BT (bismaleimide-triazine) resin reinforced with glass cloth — mechanically stiff, low-loss at RF. Total substrate stack: BT core + multiple ABF buildup layers. Dominant suppliers: Ibiden, Shinko, AT&S, Unimicron. Severe capacity constraints drove ~$10B capex cycle 2021–2024. HVM yield at 2 µm L/S remains below 90% at most fabs.
Competitive landscape
ABF’s principal competitor at finer pitches is glass core substrates (Corning, AGC) — better CTE match to silicon, lower loss tangent, but immature SAP ecosystem. Silicon interposers (TSMC CoWoS, Intel EMIB) offer <1 µm RDL but at 5–10× cost. Fan-out panel-level packaging (FOPLP) eliminates the substrate entirely but struggles with die placement accuracy at scale. Embedded die approaches (AT&S ECP) compress z-height. For RF/mmWave, LTCC and liquid crystal polymer (LCP) substrates compete on loss but not density.
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.