Victor - I've never seen a finished microvia size checked with a pin gauge
like you might use for a larger hole.  Optical methods could be used after
plating, but I'd question the accuracy, and many microvias are plated
"full", or filled/overplated.  Cross section could be used, but care must be
taken on vertical sections to make sure the sample is at the center of the
via (otherwise it will appear smaller).  A vertical cross section could be
used.  But obviously, these are destructive methods.  The finished hole size
(FHS) of microvias is usually specified with a wide tolerance (generally FHS
+0/-FHS), so there is no real reason for a fabricator to try and measure the
finished size.  In cases where the size is critical, the drill size is
usually specified on the fab drawing.  If verification of drill size is
needed, this could be done easily with a calibrated optical microscope prior
to plating (non-destructively).

Morgan Viggers
Field Applications Engineer
ISU Petasys
503.675.3877

-----Original Message-----
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Sent: Friday, June 19, 2020 3:50 AM
To: [log in to unmask]
Subject: [TN] Micro Via Terms and Definitions

Fellow TechNetters:

   IPC-2226  3.1.1  (Aug 2003):

   3.1.1   Microvia (Build-Up Via)   A blind or subsequently buried hole
that is ?0.15 mm  (0.00591 in) in diameter having a pad diameter that is
?0.35 mm  (0.0138 in) and formed either through laser or mechanical
drilling, wet/dry etching, photo imaging or conductive ink-formation
followed by a plating operation.

Note:   Formed holes >0.15 mm   (0.00591 in) in diameter will be referred to
as via within this standard.

Question:    What is the proper/correct method to measure microvia diameter.

Victor,