Alan Hilton wrote:

Does this have any effect on hand-manufacturing? ie. Do you have to 
apply heat for a longer period in order to get a proper solder joint? 
Does it take appreciably longer to cool?

At Rockwell, we do NOT put vias under smt pads.  Because the 
stringers act as "thermal spokes", there are no soldering problems.

----- Begin Included Message -----

>From [log in to unmask] Wed Jun 26 09:36:55 1996
Resent-Date: Wed, 26 Jun 1996 11:34:54 -0700
Resent-Sender: [log in to unmask]
Old-Return-Path: <[log in to unmask]>
Date: Wed, 26 Jun 96 09:08:03 MDT
From: [log in to unmask] (Gary Peterson)
To: [log in to unmask]
Subject: Re: DES:,FAB: - Thermal relief for via holes ??
Resent-Message-Id: <"AOxd93.0.Or6.f1Lqn"@ipc>
Resent-From: [log in to unmask]
X-Mailing-List: <[log in to unmask]> archive/latest/4865
X-Loop: [log in to unmask]
Resent-Sender: [log in to unmask]
Content-Length: 1946

We sometimes do the same (no thermals on SMT designs)...however there is
always a price to pay.  With buried planes, especially multiple planes
for impedance control, lack of thermals make it necessary to preheat the board 
before hot-air removal/replacement of dead ICs.  This is especially problematic
when we have designed the board with vias-in-pads to cram too many parts on
too small a board.  The vias that connect directly to the planes take a lot
of heat to reflow.  Many a board has been burned by impatient individuals
who turn up the temp on the hot-air tool instead of increasing the board
pre-heat and increasing the hot-air tool airflow...and waiting 'till the solder
flows on the power and gnd pins to lift the part.

Gary P.
---
                                  Gary D. Peterson
    _/_/_/   _/    _/  _/        SANDIA NATIONAL LABORATORIES     _/_/_/
   _/       _/_/  _/  _/        P.O. Box 5800, M/S 0503            _/_/
  _/_/_/   _/ _/ _/  _/        Albuquerque, NM 87185-0503     _/_/_/_/_/_/
     _/   _/  _/_/  _/        Phone: (505)844-6980           _/  _/_/  _/
_/_/_/   _/    _/  _/_/_/_/  FAX: (505)844-2925             _/  _/_/  _/
                            E-Mail: [log in to unmask]        _/_/_/




----- Begin Included Message -----

HOWZITGOIN?

Gary Willard wrote:

...are there any major concerns or advantages in having the vias
connecting directly into the plane without relief...

At Rockwell, flooded (no thermal relief) vias have been standard
operating procedure for the last 5 years.  We just photo plot a
round circle that is smaller than the hole size (ie: .004") for
each plane connection.  It's small enough to get drilled away
but large enough so the fab house doesn't think we forgot about
those holes.

Thank you and have a FANTASTIC day!

Kevin L. Seaman (714) 221-4752

P.S. If your "reply" bounces back, then "send" to:
[log in to unmask]



----- End Included Message -----




----- End Included Message -----