Jim, i'm not up on IPC-A-600. But, if you want to find a representative
HASL thickness measurement you can live with, i suggest the following;

(Assuming you are using XRay Flourescence)

1) Agree on a site that will be measured.  i recommend you select the
smallest, most populous pad site. (like QFP or SOIC leads).  These are
the areas most vulnerable to planarity discrepancys.

2) Use the largest collimator that will not overlap the site.

3) Measure the center of each pad.

I think you will find that this method will produce data you can live
with.

Hope this helps,

Mark Simmons, V-Score Central, Inc.

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