ORIGINAL COMPANY-CONTEXT PRACTICE
Estimate yield when inspection coverage differs
Original practice scenario: A hypothetical semiconductor analysis compares two process settings, but one setting has more inspected wafers and inspection selection depends on early warning signals. What would you examine?
Written for independent practice using company context; this is not a verified question from a company interview.
A REASONED APPROACH
Model answer.
Inspection outcomes come from a selected population. Comparing observed failure percentages directly can confound process quality with the rule that decided which material to inspect.
Work through it
- Define the experimental unit and eligible production population, then document inspection rates, selection triggers and outcome delays for each setting.
- Prefer randomized or otherwise justified comparable assignment; stratify by product and process stage, and assess whether selection probabilities can be estimated credibly.
- Report inspected yield and population coverage separately, with uncertainty and sensitivity analysis for unobserved outcomes rather than a single unsupported corrected estimate.
Tradeoffs to discuss
- Additional random inspections improve identification but consume capacity; weighting can use existing data while depending on overlap and a defensible selection model.
Common pitfalls
- Do not count multiple measurements of the same wafer as independent production units.
- Check for product-mix changes and post-treatment inspection rules before attributing an apparent improvement to the process setting.