Sampled Wafer Test

Sampled Wafer Test is a production strategy that tests only a subset of die on a wafer to reduce test time and cost while maintaining statistical quality control.

## What Is Sampled Wafer Test?

• Method: Test representative die across wafer, not 100% coverage
• Sampling: Statistical patterns (systematic grid, random, or adaptive)
• Purpose: Reduce test time for low-risk, high-yield products
• Risk: Some defective die may ship untested

## Why Sampled Testing Is Used

For mature products with >99% yield, testing every die is economically inefficient. Statistical sampling provides adequate quality assurance.

Sampling Patterns:
100% Test:           Grid Sampling:        Random Sampling:
● ● ● ● ● ●         ●   ●   ●   ●        ●     ●       
● ● ● ● ● ●           ○   ○   ○          ○   ●   ○   ● 
● ● ● ● ● ●         ●   ●   ●   ●            ●       ● 
● ● ● ● ● ●           ○   ○   ○          ● ○     ○     
● ● ● ● ● ●         ●   ●   ●   ●          ●   ●   ○ ● 

● = tested           ○ = not tested
Full coverage        Statistical coverage

Sampling Decision Factors:
| Factor | Full Test | Sampling OK |
|--------|-----------|-------------|
| Yield | <95% | >99% |
| Safety critical | Always full | Never sample |
| Margin to spec | Tight | Comfortable |
| Test cost | Low | High |