It was back in the soldermask over tin-lead days. The tin-lead would
reflow in wave solder (regardless of whether it was directly associated
with a land) and cause the soldermask to blister. In the present days of
SMOBC, and SMD IR convection reflow (instead of wave solder), the
technique is still used for the same reason, but the chances of
soldermask blistering is greatly reduced due to the lack of reflowing
metal beneath the soldermask. It was a requirement of MIL-STD-275 and
carried over to IPC-D-275.

Chris Taylor
Senior Printed Circuit Designer
LXE, Inc.
125 Technology Parkway
Norcross, GA 30092
voice: (770) 447-4224 X3242
fax: (770) 447-6928
[log in to unmask]


>----------
>From:  Davis Ben[SMTP:[log in to unmask]]
>Sent:  Friday, May 01, 1998 3:47 PM
>To:    [log in to unmask]
>Subject:       [DC] Solid vs. Hatch
>
>Greetings fellow designers...
>
>I'm having a bit of trouble explaining the reasoning behind using hatch
>fill vs. solid fill on outer layers.  I have, in the dark recesses of my
>brain, a memory of a rule of thumb saying to hatch any fill areas larger
>than 1 sq. inch.  I believe this was to prevent sucking too much heat
>during the soldering process, sucking too much solder during wave
>soldering (in uncoated use), and/or to prevent warping of the board.
>
>We currently have a board approx. 6x5 inches, predominately fill
>(chassis ground) on the secondary side.  We are using soldermask over
>bare copper on this 2-sided, .062, FR4 board..  The previous incarnation
>of this board was somewhat smaller and used solid fill with no
>problems.  Now I find myself trying to defend my choice of using hatch
>fill on the new board.  Perhaps my "rule of thumb" is no longer valid or
>was a myth originally.  It is easy convince others about the sucking up
>solder when uncoated issue, but since we have SMOBC they don't see this
>as a problem.  Are the warping and heat sinking issues valid?  Are there
>other issues/concerns I should address or use in my defense?  On the
>other hand, I don't mind if I'm wrong - solid/hatch is just a button
>push away!!!
>
>Thanks for any assistance you can provide.
>
>Ben Davis
>Systems & Electronics, Inc.
>[log in to unmask]
>
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