1) Is it correct that bare boards electrical testers may not detect opens
caused by complete copper cracks (circomfrential) inside via holes because
the pressure from the test pins do close the crack? ( I personally do not
think so. The copper crack width measured from the cross section is
0.0004"). The boards I'm talking about are Immersion Silver plated.

It's possible the tester may 'close' the open but there are other variables
that would have to come into play first, for example, the pressure of the
test bed itself, most testers have adjustable pressures, with immersion tin
we would go light on the pressure to reduce the depth of probe marks, so you
'may' identify the opens there. Another factor is complete void, or is there
a 'sliver' of metal bridging this open. Adjusting Ohms is important.

2) How about via copper cracks if the boards are HASLed. Would the Tin/lead
inside the via holes allow enough conductivity to "hide" the copper crack?

If the 'crack' was 4/10 of a mil then solder may indeed close the 'open'. I
would expect though that enough vias and/or through holes contain these
voids (as they rarely if ever occur alone) that it would be detected. Visual
inspection before HASL should also include through-hole inspection. Start
International makes a prism eyepiece that works well in inspection of hole
wall quality (this should not replace sampling microsections as a process
control).

3) If the copper plating thickness inside the hole is considerably reduced
(for example, down to 0.0004" from 0.001") would that be detected by the
E-tester as high resistance?

It could, depending upon how much 'metal' is bridging the crack or void,
again, this is where a planned test program including sound parameters is
important.

4) How the test parameters affect the above issues?

Incorrect settings can allow the passing of defects, and rejection of
acceptable product. Again, plan your test program using parameters designed
for the type product you are fabricating as well as the defects or
conditions you are testing for.

Franklin

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