Rudy,
I don't know that I agree with your assessment.
> 
>  This fabricator is required by their customer to run, and pass, an SIR
type
>  test, immediately after Tin stripping.   When I heard this, my initial
>  reaction was what sort of daft beaurocrat thought this one up, but,
>  subsequently, it seems it may not be so daft.

As a former daft bureaucrat, I resemble that remark.  SIR testing at this
point in the process would show if you had absorbed any harmful materials
into the laminate and or solder mask.  It would also show if your rinsing
regimen was up to par.  You can do SIR testing after almost any point in any
process with an eye towards determine the effects of that process.  If SIR
drops way down, there are potential problems with that step that need to be
addressed.
>  
>  They passed the test easily, for some extended length of time, until, one
>  day, seemingly apropos of nothing, they stopped passing it.   Cleaning the
>  boards in an alkaline cleaner seemed to help, but they could not figure
out
>  why they suddenly could not pass the test.   Then they examined the bare
>  laminate.   Certain supplier(s), when the bare laminate was run through
the
>  solder stripper, could not pass the test.  Others did easily.
>  
>  So, if this problem surfaces suddenly, the problem is likely the laminate.

Having seen lots of SIR data from OTHER facilities, the problem could be a
fault in the tester, or technique.  Did good old Bob retire around that time?
 Did water quality in the rinse system change?  Did the DI water unit
suddenly go south?  There are lots of factors that can cause poor SIR.  Don't
assume any one factor is the problem.  

I do agree that no two laminates are the same.  Varying levels of porosity
and varying resin compositions can dramatically effect SIR, or at least their
processing characteristics.

Doug Pauls
CSL Technical Director


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