OSAT Technology What Is OSAT and ATMP — and Why India Has Started There

When Micron Technology’s facility at Sanand started operations, news articles called it “India’s first semiconductor plant.” When Tata Electronics broke ground at Dholera, headlines said “India is finally building chips.” Both statements are accurate. Neither is complete.

The Sanand facility does not fabricate chips. The Dholera facility will. The distinction between these two types of manufacturing — and the deliberate sequencing of starting with one before the other — is fundamental to understanding India’s semiconductor strategy. Yet it is almost never explained clearly in public discourse.

I’ve spent 12 years at Micron Technology in the United States, working across both wafer fab and ATMP operations, and 12 years at Analog Devices in semiconductor manufacturing IT. This is the explanation I wish existed when I first encountered these acronyms.

What a Chip Looks Like Before OSAT Receives It

Picture a circular silicon disc — 300 millimetres across and roughly 775 microns thick. This is a completed wafer from a front-end fabrication plant (fab). On its surface, arranged in a repeating grid pattern, are hundreds or thousands of identical dies — each one a complete integrated circuit, with millions or billions of transistors etched into its surface in features smaller than a human hair.

This wafer, at this point, is entirely unusable. No one can put a bare silicon wafer into a phone, an automotive ECU, or a missile guidance system. The dies are fragile. They have no electrical connections to the outside world. Each die, sitting flush with its neighbours on the wafer surface, cannot be handled, mounted, or connected to anything without first going through a series of precision operations.

The series of steps that transforms this wafer into the black rectangular chip you see on a circuit board — packaged, tested, marked, and shippable — is what OSAT does. In India’s official terminology under the Semiconductor Mission: ATMP.

The 9 Steps of OSAT: What Actually Happens on the Floor

Having run manufacturing IT systems on fab floors for over two decades, I can tell you that the abstraction “assembly and test” covers an enormous amount of operational complexity. Here is what actually happens, step by step:

ATMP vs OSAT: Clearing Up the Terminology

In global semiconductor industry usage, this entire category — wafer thinning through final pack — is called OSAT: Outsourced Semiconductor Assembly and Test. The world’s largest OSAT operators are ASE Group and Amkor Technology (Taiwan/Korea), JCET (China), and Powertech Technology (Taiwan).

India’s government, under the India Semiconductor Mission, uses the term ATMP: Assembly, Test, Marking and Packaging. The practical scope is identical. ATMP was likely chosen to be descriptive of the complete workflow and to signal a broader ambition — from conventional packaging through to advanced packaging technologies. When you read “ATMP facility” in an ISM project announcement, it means an OSAT facility.

Conventional vs Advanced Packaging — Why This Distinction Matters Now

Not all OSAT is equivalent. There is an increasingly critical distinction between two categories of packaging operations:

India’s current OSAT facilities are starting in conventional packaging — and this is the correct decision. Advanced packaging capability cannot be built without first building the process knowledge, equipment infrastructure, materials supply chain, and trained workforce that conventional packaging develops. You build the foundation before the upper floors.

Why India Started with OSAT — Not a Front-End Fab

This is the most common question I receive from stakeholders new to India’s semiconductor ecosystem. The answer involves six interconnected strategic factors — and it is worth understanding each of them, because together they describe how India’s semiconductor capability will evolve over the next decade.

OSAT as a Foundation, Not a Ceiling

A common misconception: that starting with OSAT means settling for less. The precedent across every country that built a semiconductor industry tells the opposite story.

India is not choosing OSAT instead of a fab future. India is choosing OSAT as the correct first chapter of a semiconductor story that will have many more. The Tata Electronics / PSMC fab at Dholera — India’s first front-end wafer fab — would not have been feasible or fundable without Micron Sanand demonstrating first that India could attract global semiconductor investment, build compliant facilities, train workforces, and begin delivering qualified product.

For anyone evaluating India’s semiconductor opportunity — as a supplier, investor, equipment vendor, or talent builder — the key practical insight is this: OSAT is where the near-term commercial activity is concentrated, where procurement decisions are being made now, and where relationships established today will define who participates in India’s semiconductor ecosystem for the decade ahead.