Step 14 of 17Test & assembly (back-end)
Wafer test
Testing each die before dicing.
Learn → Understand → Explore → Calculate
At a glance
Inputs
- Finished wafer
- Test program
- Probe card
ProcessWafer test
Outputs
- Wafer map of passing / failing dies; yield data
What is it?
Electrically testing each die while it is still on the wafer (wafer sort / probe), marking or logging which dies pass and which fail.
Why is it needed?
Packaging is expensive, so it makes no sense to package a bad die. Wafer test screens out failures early and produces the yield data that drives process improvement.
How does it work?
A probe card lands fine needles or contacts on each die's pads, and automated test equipment applies electrical stimuli and measures responses against the spec.
Results are recorded as a wafer map of good/bad dies; failing dies are inked or logged so they are discarded after dicing.
Critical parameters
- Test coverage
- Probe contact quality
- Test time per die
- Yield
Typical defects
- Probe-mark damage
- Escaped defective dies
- Contact / continuity failures
Equipment involved
- Wafer prober
- Automated test equipment (ATE)
- Probe cards
Materials involved
- Probe cards