Back-end

Notes

Advanced packaging has turned the back end from a cost centre into a differentiator, reversing decades of assumption.

Overview

In the semiconductor value chain, the back end is everything that happens after wafers leave the fab: thinning and dicing, attaching dies to packages, wire bonding or bumping, encapsulation, final test, marking and shipping. It is far less capital intensive and more labour intensive than wafer fabrication, which is why much of it is done by outsourced assembly and test companies in Asia.

How it works

Finished wafers, usually already tested at wafer sort, arrive at an assembly site. They are thinned, mounted on tape and diced into individual dies. Good dies are attached to a leadframe or substrate and connected by fine wires or by solder bumps in a flip-chip arrangement. The assembly is encapsulated in mould compound or capped, solder balls or leads are formed, and parts are marked. Final test then checks every part, often at temperature, sometimes with burn-in, before parts are packed and shipped.

Integrated device manufacturers often run their own back-end plants, while fabless companies and foundries frequently use outsourced semiconductor assembly and test (OSAT) providers. According to a 2021 SIA and BCG study, OSAT firms typically spend about 15% of revenue on capital equipment, compared with about 35% for foundries, so labour cost is a key competitive factor, and mainland China and Taiwan hold more than 60% of assembly, packaging and test capacity.

Advanced packaging, such as fan-out, 2.5D interposers, hybrid bonding and chiplet assembly, is changing this picture: it needs cleanroom-like processes and much more capital, and some of it is done by foundries rather than traditional assembly houses.

Examples

• A fabless company shipping sorted wafers to an OSAT for assembly in a ball grid array package and final test.
• An integrated device manufacturer running its own assembly and test plant in Southeast Asia.
• A foundry offering 2.5D packaging for AI accelerators, blurring the line between front end and back end.
• Final test with burn-in for an automotive processor before shipment.

Why it matters

The back end decides how a die becomes a usable product, sets much of its reliability, and is a large part of supply chain risk because capacity is concentrated in a few regions. Packaging and assembly engineers, test engineers, OSAT managers and supply planners work in it, and governments now target it in industrial policy alongside fabs.

Related terms

• Front-end
• Packaged part
• Downstream
• Heterogeneous integration

Where it appears on the Hub

Used on 39 pages of the Hub. In each group, the pages that mention it most come first.