Hm.....struggling on this one!

Has anyone, when conducting solderability testing using the wetting balance
method experienced the following on alloy 42 leads.
Leads pass the force / time criteria but subsequent testing up to x5 exhibit
a strange phenomena

        Pass / Pass/ Pass / Pass / Pass
        Fail / Pass / Pass / Pass / Pass
        Pass / Fail / Fail / Pass / Fail
        Fail / Pass / Pass / Pass / Fail
        Pass / Pass / Fail / Pass / Pass

As can be seen there is absolutely no pattern. I know testing is normally
only carried out x1 but when determining the max force a lead is tested
several times and the result is not what I would have expected, though my
experience is typically with Cu leads.

Is this indicative of alloy 42?
If so what is actually happening?

These parts are ASIC QFP's (gull wing) which are reflow soldered where quite
a large # of joints are easily detachable by probing though the solder
appears to form the basis of a good joint but with demarcation lines along
the foot of the lead

One last thing, when testing leads using an aggressive water soluble flux
the pass / fail results appear no different.

Any help / understanding would be appreciated!

Regards,
        Iain.





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