Patrick Ducas wrote:
> 
> 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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Hi,TechNetters,
Patrick asked Tom how he measures the solder thickness on SMT pads.
I measure the thickness with X-Ray,which gives me the following
opportunities:
1:I can perform several measurements on the same pad.
2:I see WHERE I measure,and usually I find the crest-don't ask me how
much time it takes.
3:I can determine also the composition of the solder.
Tom's suggestion about 45 degrees is very correct, I think, I have seen 
differences of 40 micrometers or more between N-S and E-W.
Here my experience ends,and because there is always Dave,I will also ask
one question:
Why do I get different Tin content levels on the same board,depending on
the solder thickness I found?
In the range of ~1micrometer I get higher readings,although the alloy is
"recognizable".
Is it a calibration error, the real thing, or me?
Bye
Gaby

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