Anatomy of a Chip

What ARM designs, what TSMC builds, and what an OSAT like Amkor assembles

ARM — Design
TSMC — Fabrication
OSAT (ASE / Amkor) — Assembly
Memory Supplier (SK Hynix / Samsung)

Cross-Section: What's Inside

A side view slicing through a modern AI chip package. Each layer is color-coded by who made or assembled it.

HEAT SPREADER (Metal Lid) OSAT Thermal Interface Material HBM Stack HBM Stack CPU DIE ARM-designed logic TSMC-fabricated silicon HBM Stack HBM Stack ARM designed SK Hynix / Samsung MICRO-BUMPS (~25μm) SILICON INTERPOSER Through-Silicon Vias (TSVs) connect dies above to substrate below TSMC fabricated C4 SOLDER BUMPS (~100μm) OSAT attaches ORGANIC PACKAGE SUBSTRATE Multi-layer PCB-like board — routes signals to the server motherboard (ABF substrate, made by Ibiden, Shinko, or Unimicron) OSAT assembles BGA SOLDER BALLS — connect to server motherboard OSAT attaches SERVER MOTHERBOARD (PCB) ~55–75mm wide (about the size of a large postage stamp) CROSS-SECTION VIEW (not to scale) — Modeled on NVIDIA H100 / ARM AGI CPU class packages
ARM's Part
CPU DIE

The Blueprint

ARM designed the logic — billions of transistors, arranged into CPU cores, cache, memory controllers, interconnects. This is the "tape-out" — a set of files describing every layer of the chip down to the nanometer. ARM never touches silicon. They hand TSMC a file.

TSMC's Part
CPU DIE + INTERPOSER

The Silicon

TSMC fabricates two things: the CPU die itself (3nm, ~80 billion transistors) and the silicon interposer (a thin wafer with through-silicon vias that act as highways between the CPU and memory). Both require EUV lithography — TSMC's core competency.

OSAT's Part (ASE / Amkor)
SUBSTRATE + LID + BUMPS + EVERYTHING AROUND THE DIES

The Assembly

The OSAT takes all the pieces — CPU die, HBM stacks, interposer — and assembles them into a finished package. They mount dies onto the interposer (micro-bumps), attach the interposer to the organic substrate (C4 bumps), add the heat spreader, attach BGA solder balls, then test everything.

Memory Supplier
HBM STACKS

The Memory

SK Hynix (80%+ market share) or Samsung makes the HBM (High Bandwidth Memory) stacks. Each stack is 8-12 memory dies stacked vertically and connected by through-silicon vias. These are fabricated separately and delivered to the packaging step.

Who Does What — The Full Breakdown

Think of it as architect → builder → general contractor

ARM

NASDAQ: ARM
The Architect
  • Designs the instruction set (ISA) — the "language" the chip speaks
  • Designs the CPU core microarchitecture — how instructions are executed
  • For the AGI CPU: designed the full chip layout (floorplan, I/O, power delivery)
  • Creates the "tape-out" — GDS files describing every transistor
  • Hands TSMC a file. Never touches a wafer.
  • Their value: The design IP. Energy-efficient compute per watt.

TSMC

NYSE: TSM
The Builder
  • Takes ARM's design file and prints it onto silicon wafers
  • 3nm process: ~80 EUV lithography layers, each aligned to nanometer precision
  • Also fabs the silicon interposer (the highway between chiplets)
  • For top customers: does CoWoS packaging in-house (die-on-interposer assembly)
  • Cuts wafer into individual dies ("dicing")
  • Their value: Only company that can print leading-edge silicon at scale

ASE / Amkor

NYSE: ASX / AMKR
The General Contractor
  • Receives bare dies from TSMC and HBM stacks from SK Hynix
  • Mounts chiplets onto interposer using micro-bump soldering
  • Attaches interposer assembly to organic substrate (C4 bumps)
  • Adds heat spreader, applies thermal interface material
  • Attaches BGA solder balls for board mounting
  • Runs burn-in testing, speed binning, quality assurance
  • Their value: Turn loose parts into a finished, tested, shippable chip
The Building Analogy

ARM is the architect who draws the blueprints. TSMC is the specialized factory that makes the steel beams and glass (the hard-to-manufacture precision parts). The OSAT is the general contractor who takes all the materials — beams, glass, electrical, plumbing — and assembles them into a finished building, then inspects it before handing over the keys. SK Hynix is the electrical subcontractor who supplies the wiring (memory).