Tom, just a easy one, what type of tool do you use to measure the thickness
of solder? Is it accurate for that specific application? If you know some
tools that  should be enough accurate, any hint would be appreciated.

Thanks in advance   


>
>          Don:
>               The thickness of solder from a solder level operation
>          is dependent upon pad geometry, amongst other things.  Board
>          fabbers walk the tightrope between blowing enough solder out
>          of the holes yet leaving enough remaining on the surface
>          mount pads.
>               I would strongly urge you to specify a horizontal HASL
>          process from your board vendors.  Boards should also be
>          cocked at a 45 degree angle when going into the solder to
>          offset a "north-south, east-west" bias on QFPS.
>               Getting back to the pad geometry, the larger the pad,
>          the thinner the solder coat is apt to be, because the solder
>          has a larger surface over which to retreat.  Worst case
>          would probably be discrete pads, where we have a stated
>          minimum of 50 microinches at the pad center.  Maximum solder
>          thickness can be held to .0015".
>               Where the solder is measured is another issue.  We
>          always ask our customers to measure from the pad centroid so
>          that outgoing and incoming measurements are apples and
>          apples.  The pad center may or may not be the crest, and it
>          usually isn't.  When I see thicknesses called out in specs
>          that say "as measured at the crest", I chuckle because it
>          would take too long just to find the crest of a given pad.
>          In all cases, your board fabricator should guarantee
>          solderability.
>               In summary, the most workable callout would be a solder
>          thickness of .0001" nominal, .00005" minimum, .0015" maximum
>          (all measurements taken at pad center).  Again,
>          solderability is to be guaranteed.
>          Regards,
>          Tom Coyle
>          Field Services Engineer
>          HADCO Corporation
>
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-------------------------------------------------
Patrick Ducas
Process Quality Engineer 
Matrox Electronic Systems Ltd
E-mail: [log in to unmask]
Tél:(514)969-6000 ext.2971   Fax:(514)685-3415
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