Poor QC on JLCPCB 4L boards

[thm_w]

Flying Probe Test: This is the final checkpoint for circuit continuity. It can test for open and short circuits.

Flying probe can detect this issue, but it depends on which pads are selected for testing each net. For nets with many pads (like a power rail) testing continuity between two random pads is not sufficient. If a net has 50 pads, do you check continuity from one pad to each of the other 49 pads? What if all pads are not on the same side of the board? Genuinely curious about this, I've asked this of other fabs about this and never got a clear answer

Its standard to test every pad. So continuity check would have to be done from pad 1 to 2, 1 to 3, etc. Or whatever the flying probe software determines is most optimal.

JLC has and uses double sided flying probe testers (15:34):
https://youtu.be/_XCznQFV-Mw?t=934

Whether its on all boards, no idea.

[bson]

Its standard to test every pad. So continuity check would have to be done from pad 1 to 2, 1 to 3, etc. Or whatever the flying probe software determines is most optimal.

Presumably it picks a good first pair, tests them, and then as it tests additional pads it's always against one that has already been tested.  Or comparable.  Otherwise you could get the equivalent of testing 1 to 2 and 3 to 4...

[Kasper]

Can you make the others fail?  Thermal cycle, pressure change, vibration, etc.

Maybe they passed testing but with a weak connection and that connection failed during shipping.

Maybe the ones that pass now will fail after a bit more stress.