Why is SS = 45 for Quals?

Guest

Why are the sample sizes for quals usually 45? Is this standard for the industry?

Assy Engr 2

Posted: Mon Sep 15, 2026 1:50 pm Post subject:

Hi Assy Engr 2,

A sample size of 45 is quite popular for quals because it corresponds to LTPD=5, which is the level of lot quality that you will reject 90% of the time if it has a defect rate of 5% and above. In other words, there's a 90% probability that you will catch a lot with 5% failures if you get 45 samples from the lot for rel testing. Of course, if you want higher confidence in your sampling, you can always increase your SS.

Pls see: http://www.semiconfareast.com/ltpd_aql.htm
for more details.

Thanks!
EE