cost of test
**Cost of test** (or **cost of quality**) is the **total expense of testing and quality assurance across the entire manufacturing flow** — including wafer probe, final test, burn-in, failure analysis, and field returns, typically 10-30% of total product cost, making test optimization critical for profitability.
**What Is Cost of Test?**
- **Definition**: Total testing and quality costs from wafer to field.
- **Scope**: Probe, final test, burn-in, FA, returns, warranty.
- **Typical**: 10-30% of total manufacturing cost.
- **Impact**: Major component of product cost structure.
**Why Cost of Test Matters**
- **Profitability**: Significant impact on margins.
- **Competitiveness**: Lower cost of test enables better pricing.
- **Investment**: Test equipment is major capital expense.
- **Optimization**: High-leverage area for cost reduction.
**Components**
- **Wafer Probe**: First electrical test (20-30% of test cost).
- **Final Test**: Comprehensive package test (40-50%).
- **Burn-in**: Extended stress testing (20-30% for high-rel).
- **Failure Analysis**: Root cause investigation (5-10%).
- **Field Returns**: Warranty and replacement costs (variable).
**Total Cost Calculation**
```python
def calculate_total_cost_of_test(volume, probe_cost, final_test_cost,
burn_in_cost, fa_cost, return_rate,
return_cost):
# Manufacturing test costs
mfg_test_cost = volume * (probe_cost + final_test_cost + burn_in_cost)
# Failure analysis
fa_total = fa_cost
# Field return costs
returns = volume * return_rate
return_total = returns * return_cost
total_cost = mfg_test_cost + fa_total + return_total
cost_per_unit = total_cost / volume
return {
'total_cost': total_cost,
'cost_per_unit': cost_per_unit,
'mfg_test': mfg_test_cost,
'returns': return_total
}
```
**Optimization Strategies**
- **Test Time Reduction**: Minimize test duration while maintaining coverage.
- **Adaptive Testing**: Skip tests based on inline data.
- **Yield Improvement**: Reduce retest and rework.
- **Escape Prevention**: Invest in test to avoid expensive field failures.
- **Equipment Utilization**: Maximize tester uptime.
**Trade-offs**
```
More Testing → Higher test cost + Lower field failures
Less Testing → Lower test cost + Higher field failures
Optimal: Minimize total cost (test + field failures)
```
**Best Practice**: Optimize total cost of quality, not just manufacturing test cost. Preventing one field failure often justifies significant test investment.
Cost of test is **a strategic business metric** — optimizing it requires balancing manufacturing test costs against field failure costs to minimize total cost while maintaining customer satisfaction.