Test Quality
Test Coverage
ICT is useless with a low test coverage. However, in practice a benchmark does not exist. It is however important that for all tests conducted (AOI, ICT, FCT, AXI) the combination delivers the highest possible confidence that a board is "OK" before shipped to a customer. On the contractual side we are astonished to see that some OEMs do not insist on a clear requirement for the supplier, even not for highly critical applications.
One test alone will not deliver a 100% coverage. In ICT the challenge is that board design will normally not allow to have test points in all areas where needed. Sometimes the result can be improved by the combination with boundary scan.
The more sophisticated a test platform, the more can be tested. Therefore there are big differences between a MDA and a true ICT system.
When using an external software partner we highly recommend to require an estimate for the test coverage before contracting. Otherwise you might compare apples with oranges when you have more than one offer.
First Pass Yield
The tracking of the "First Pass Yield" (FPY) is key to eliminate repeated tests, sometimes without real board problems. The stability of the test program ensures that all problems are found, and all "NOK" boards do actually have an electrical problem.
A high FPY is only a good performance indicator with a high test coverage. Therefore you have to be careful when tracking the FPY to prioritize the right process for improvement when you perform a Pareto analysis.
A high FPY is essential if you test panels of multiple boards. A problem with the test can easily result in the re-inspection of many panels and disrupt a smooth material flow.
We see on the market that external test houses (turn-key solution providers) can often achieve higher FPYs through their experience of the right test parameters. This can save an enormous amount of time and money and improve equipment efficiency (OEE).
