Wafer probing equipment
The tools that electrically test each die while it is still on the wafer, so bad dies are found before the cost of packaging is spent on them.
In short
Wafer probing equipment touches tiny probes to each die's pads and runs electrical tests while the chips are still on the wafer. It identifies known-good dies so that only good ones move on to packaging.
Why it matters
Packaging a bad die wastes money and materials. Wafer test (probe) screens dies early, feeds yield learning back to the fab, and creates the wafer map of good and bad dies used downstream.
Beginner intuition
Before spending effort packaging each chip, you test them all on the wafer — a card of fine probes contacts each die and checks whether it works.
The result is a map of which dies are good, so only those get packaged.
Where it fits in manufacturing
Between wafer fabrication and assembly — the first electrical test, often called wafer sort or probe.
How it works
What goes in
- A finished wafer
- A probe card matched to the die's pads
- A test program (run on the test equipment)
What happens inside
- Align & contact: probes are aligned and lowered onto a die's pads.
- Test: the tester runs electrical tests through the probes.
- Step & map: the prober steps to the next die and records pass/fail into a wafer map.
What comes out
- A wafer map of known-good versus failing dies, and yield/parametric data fed back to the fab.
Major subsystems
Prober (stage)
Positions the wafer and steps die-to-die precisely.
Probe card
The array of fine contacts to the die pads.
Tester interface
Connects the probes to the test equipment.
Vision / alignment
Aligns probes to pads.
Process parameters that matter
- Contact accuracy
- Landing probes reliably on small pads.
- Parallelism
- How many dies are tested at once (throughput).
- Contact quality
- Good electrical contact without pad damage.
- Throughput
- Dies tested per hour.
A note on numbers
Common issues
What can go wrong:
- Poor contact → false failures (yield loss)
- Pad or probe damage
- Misalignment → missed pads
- Inadequate coverage → bad dies passed on
Yield implications
Probe both measures yield and prevents wasted packaging; contact reliability directly affects apparent yield.
Advanced & research
Emerging and research directions, beyond today’s established practice.
- Massively parallel probing
- Probing fine-pitch and bumped wafers
- At-speed and specialized test at probe
How this connects
Related process
Related concepts
Related equipment
Packaging connection
Wafer probing decides which dies are worth packaging — the gate between the fab and assembly.
Packaging →Supply-chain connection
It relies on probe cards and test systems from specialized suppliers.
Supply chain →