I measured some tin/lead thickness on some 20 mil pitch pads (12 mil 
     width, 8mil spacing) on some raw fabs and found the largest majority 
     of the measurements to fall in the 450-600 microinch range (These 
     measurements were made on a SFT 7455 X-ray fluorescence system.)  
     However, there were a number of isolated pads with thicknesses 
     exceeding 850 microinches which were were considerably more 'dome' 
     shaped compared to those pads in the nominal 450-600 microinch range.  
     SMT is decidedly having more problems (i.e., shorts) with the boards 
     with the isolated 'thick' pads, but incoming QA says the boards are 
     within spec.  Can anyone share their experiences or data on an upper 
     threshold thickness for tin/lead on 20 mil pitch boards? I'm not sure 
     whether we have a part problem, process problem or both.
     
     Ed Tidwell
     DSC Analytical Lab
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