Earl
Well, I think some acceptance criteria is necessary since if there isn't even no solder is accepted. However, I agree that in many cases I feel that the acceptance criteria mare more designed in a manner that they can be controlled rather than in respect to reliability.

Regarding your comment of IMC and the discussion we had offline I thought abut the thing at home:
- Suppose you do a good job in designing your solder profile. This means, in my understanding, that just enough heat is brought into a PCB that all joints are formed and as little heat as possible stresses the components. As an effect the IMC will be very thin.
- Suppose again that you rework. Again you do a good job in removing the remaining tin thoroughly. To do so you need to keep the pad to be cleaned at elevated temperature for quite a while.

The result will be, that 
- Because of thoroughly removing the solder you expose IMC or
- Because the IMC is thin and the pad is warm for some time the remaining little amount of tin that covers the IMC is transformed into IMC.

Hence, one can say that a job too well done leads to a poor solder joint. And thus ( just to steer the pot a bit as you like it) if you instruct people for repairing solder joints and it works, your instruction wasn't too accurate? ( HeHe)

Have a great weekend

Ps: What do you mean by : you spoke with someone who is also much respected in this field?



Guenter Grossmann

Swiss Federal Institute for Materials Testing and Research EMPA
Centre for Reliability
8600 Duebendorf
Switzerland

Phone: xx41 1 823 4279
Fax :      xx41 1823 4054
mail:     [log in to unmask]

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