Brian,
Hey, Good! One I can answer, I think.
Laminate voids (IPC 600 3.1.1) and Delanination IPC 600 2.3.2 are two different
defects, with two different causes, with two different long term reliability risks.
Laminate voids indicate the lamination process went wrong. It indicates that
sufficient prepreg resin was not present during MLB lamination press, or that the
lamination process (temperature, rate or rise) was not proper. Large voids in the
laminate, prior to thermal stress, indicates a failure of prepreg to insulate all the
areas between adjacent copper layers. Small voids, less than 3 mil, are typical of air
entrapment, especially if vacuum lamination is NOT used. The expectation is that there
are MANY more voids in the board that are probably worse than the ones observed in the
cross section. It is likely that somewhere on the board, plating solution has been
trapped in some of these voids, just waiting to leak out and create havoc in the field.
Delamination is caused by moisture in the laminate being heated to a sufficient vapor
pressure within the epoxy-resin laminate to break the laminate apart, i.e. blow-up.
This is a result of improper heating/preconditioning of the PWB, but not a indicator
that the board has grave reliability risks, (assuming the delam is within the
parameters given in the spec.) The expectation is also that you can see and evaluate
EVERY instance of delamination on the board, and that the acceptance decision will be
made on the worst case present on the board. The expectation is also that the
delaminated area is very clean since it has never been exposed to process chemicals or
anything else for that matter. Therefore there should be little or no ionic
contaminates in the void region.
George Franck
"My opinions are just that."
Brian Lane wrote:
> To All,
> I am interested in finding out what the difference is between what is
> called a laminate void, and a spot of delamination or blister.
> Because of the great difference in acceptable size between the 2 defects,
> it seems to be important to be able to differentiate them.
> Why is such a small (anything greater than .003") void unacceptable (IPC
> 600 3.1.1), but a larger delamination spot acceptable as long as it doesn't
> violate conditions spelled out in IPC 600 2.3.2.
> Any information as to how to identify the differences, and why one is more
> "acceptable" in terms of size would be greatly appreciated.
> Thank you,
> Brian Lane
>
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