OSAT (Outsourced Semiconductor Assembly and Test) Overview

OSATs are third-party companies that provide semiconductor packaging (assembly) and testing services for fabless chip companies and IDMs that choose to outsource these back-end operations.

Why OSATs Exist

• Capital Efficiency: Packaging and test equipment costs hundreds of millions of dollars. OSATs spread this cost across many customers.
• Specialization: OSATs focus exclusively on packaging/test, achieving higher expertise and efficiency.
• Flexibility: Fabless companies avoid owning assembly capacity—scale up or down with demand.
• Technology Breadth: OSATs offer many package types, while an in-house facility might support only a few.

Major OSATs

• ASE Group (ASE + SPIL): #1 globally. Headquartered in Taiwan. Full range of packaging and test.
• Amkor Technology: #2. Strong in advanced packaging (flip-chip, fan-out, SiP).
• JCET Group: #3. China-based. Acquired STATS ChipPAC for advanced packaging capabilities.
• PTI (Powertech Technology): Major DRAM/NAND memory packaging.
• Tongfu Microelectronics: Growing China-based OSAT.

Services Offered

• Wafer Probe/Sort: Test every die on the wafer before dicing.
• Assembly: Die attach, wire bonding, flip-chip bumping, molding, singulation.
• Advanced Packaging: Fan-out, 2.5D/3D integration, SiP, chiplet packaging.
• Final Test: Functional test, burn-in, reliability screening.
• Drop Ship: Ship tested parts directly to end customers.

Industry Trend

Foundries (TSMC, Intel) are moving into advanced packaging (CoWoS, InFO, Foveros), overlapping with OSAT territory. For cutting-edge AI chips, foundry-integrated packaging is becoming preferred. OSATs remain strong for mainstream and mid-range packaging.