We use thermal reliefs for all plated vias that have through hole 
     parts.  This makes assembly so much easier.  If you don't your design 
     will not be robust for wave assembly.  This is much worse for higher 
     layer counts with multiple power/ground planes.  
     
     We do not use thermal reliefs for microvias that are not associated 
     with through hole parts.   This is common practice for many major 
     computer OEMs.
     
     For our mixed SMT/TH designs this means that over 75% of the plated 
     through holes have no thermals.
     
     Advantages:  
     
        1.  Less perforation to the ground plane.  The EMI guys like this.
     Less emmisions.
     
        2.  For designs where microvias are densely packed near each other 
     the thermal relief pads on the ground/power planes don't overlap.  
     This prevents problems of making sure all 4 spokes in the thermal are 
     connected.
     
     Disadvantages:
     
        1.  It is more difficult to "inspect" artwork manually.  You don't 
     know where ground and power via connections are.  This can be solved 
     if you use a 5 mil flash instead of a thermal.  Also use your CAM 
     station for these checks.
     
        2.  I've heard concerns about pink ring for "no-thermal" designs.  
     I haven't had any problems with this.
     
     Hope this helps.
     
     [log in to unmask]
     
     
     



______________________________ Reply Separator _________________________________
Subject: Re: DES:,FAB: - Thermal relief for via holes ??
Author:  [log in to unmask] at dell_unix
Date:    6/26/96 9:59 AM


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 -----