OSAT, ATMP and advanced packaging: a plain-language guide.
Three terms that appear in almost every discussion of new semiconductor capacity, and are often used as if they meant the same thing. They do not, quite.
- Back-end manufacturing turns a finished wafer into packaged, tested chips.
- OSAT and ATMP describe the same work under two business models: as a service, or for a company’s own products.
- Advanced packaging is a set of newer techniques, not a third kind of company.
- All three run on operators at volume, tight quality systems and a dependable materials supply.
What happens after the wafer
A wafer fab produces wafers, each carrying many copies of a chip. Those copies, called dies, cannot be used until they are separated, connected, protected and tested. That work is back-end manufacturing, and it follows a broadly common sequence:
- Wafer sort. Every die is tested electrically while still on the wafer, and failing dies are marked.
- Dicing. The wafer is cut into individual dies.
- Die attach. Each good die is fixed to a leadframe or a substrate.
- Interconnect. The die is connected electrically, by fine bond wires or, in a flip-chip, through bumps on its face.
- Encapsulation. The assembly is sealed, usually in mold compound, to protect it.
- Final test. The packaged part is tested again, sometimes after burn-in.
- Marking and packing. Parts are marked, inspected and packed for shipment.
- 01Grind and diceThe wafer is thinned and cut into dies.
- 02Die attachGood dies are fixed to a frame or substrate.
- 03InterconnectWire bonds or bumps make the connections.
- 04MoldThe assembly is sealed in compound.
- 05Final testEach packaged part is tested, some after burn-in.
- 06Mark and shipMarked, inspected, packed, shipped.
OSAT and ATMP
| OSAT | ATMP | |
|---|---|---|
| Stands for | Outsourced Semiconductor Assembly and Test | Assembly, Testing, Marking and Packaging |
| Business model | A service provider that packages and tests chips for other companies | Usually a facility a company runs for its own products |
| Customers | Many: fabless companies, device makers, foundries | The owner’s own product lines |
| What decides success | Winning and passing customer qualifications, then utilisation | Cost, quality and delivery against internal targets |
| The work itself | The same steps, the same kinds of equipment, the same skills | |
In everyday use the two terms overlap, and a single site may do both. The useful distinction is commercial: an OSAT has to be qualified by each customer it serves, which makes audit-readiness central to the business.
Where advanced packaging fits
Advanced packaging is not a third kind of company. It is a family of techniques that either connect a die at a much finer pitch than wire bonding or place several dies in one package. Flip-chip, fan-out wafer-level packaging, 2.5D interposers and 3D stacking all belong to it.
These techniques borrow steps from the wafer fab, such as bumping and fine-line patterning, so the line looks more like front-end manufacturing: cleaner rooms, tighter process windows, more metrology and engineers with different experience.
What each needs in order to run
- People. Back-end lines employ large numbers of operators and technicians per shift. Consistency of manual and semi-automatic work shows up directly in yield, so operator training matters more than it might appear.
- Quality systems. Customers, particularly in automotive, audit the line against their own requirements and standards such as IATF 16949. The system has to describe the line as it really runs.
- Materials. Leadframes, substrates, bond wire, die-attach materials and mold compound must arrive on time and to specification, lot after lot.
- Test engineering. Test programmes, hardware and data analysis decide both what ships and what is learned from what does not.
| Wafer fabFront-end | OSATBack-end, as a service | ATMPBack-end, captive | |
|---|---|---|---|
| In | Bare wafers, gases, chemicals | Finished wafers from many customers | Finished wafers from the owner’s fabs |
| Out | Wafers carrying tested dies | Packaged, tested chips | Packaged, tested chips |
| Core steps | Deposit, pattern, etch, implant, polish, repeat | Dice, attach, bond, mold, test | Dice, attach, bond, mold, test |
| Cleanliness | Strictest: ISO class cleanrooms | Clean zones, less strict than a fab | Clean zones, less strict than a fab |
| People mix | Engineer- and technician-heavy | Operator-heavy at volume | Operator-heavy at volume |
| First hurdle | Process qualification and yield learning | Winning customer qualification | Meeting internal cost and quality targets |
Why the distinction matters when you plan a line
The label you use sets expectations for staffing, suppliers and customers. An OSAT plan that leaves out customer qualification will be late to revenue. An advanced-packaging plan staffed like a conventional assembly line will struggle with process control. Getting the description right at the start is the cheapest correction available.
Customers qualify the line, not the building.
For definitions of the terms used here, see the fab-to-OSAT glossary. For help staffing or preparing a back-end line, see Fab, OSAT and ATMP ramp.