Hey, thanks, Mark.

I thought the numbers were in the range you mentioned, I was hoping for
some confirmation from the wealth of knowledge out there.  And I got it!

You folks all have a great weekend and next week. I have just signed off of
Technet for some vacation time.

Tennessee and W. Va mountains, here I come. I sure hope its cooler there
than here!  Will rejoin you later.

Charlie B.




Please respond to [log in to unmask]

To:   "TechNet E-Mail Forum." <[log in to unmask]>, Charles Barker/US/I-O INC
cc:
Subject:  Re: [TN] Solder thickness needed after HASL




Charlie, intermetalic formation is a function of time and temp. on the
solder dip portion of the HASL process. And, to some lesser extent the
porosity of the CU.  With acid copper plated on clad "normal"
conditions,
and with Solder temp at 460f, the range will be from 30 U-inches to as
much as 70 to 80 U-inches.  Horizontal levellers with good pre heaters
produces the shortest dwell times and the thinnest intermetallics.
Vertical levellers with no pre heat tend to produce the thicker layers.

As far as the free metal above the intermetallic, what your looking for
is a "fused" condition of the surface.  This occurs in the HASL process
at approx. 100 U-inches.  The mil spec for years was 300 U-inches, this
was borrowed from the venerable T/L plate with oil or IR fusing process.
And this is because T/L as plated won't fuse (get shinny) at less than
300 U-inches.

The reason you are getting such a large range from your suppliers may be
their attempt to account for all coated areas (pads and lands)
regardless of shape and size.

Try agreeing on specific areas to measure (the smallest are best) this
will reduce your range.

Hope this helps, if you need more, contact me directly,

Mark Simmons

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