The advantage of not having the thermal relief on the inner layers where 
something is not being soldered into the hole is that with surface mount 
components and the newer technologies in general the speed of our products 
is going up exponetially. Not having a restriction on the inner layer allows 
for much better current flow in the substrate and quicker supply of power to 
our components. Thermal relief use should be eliminated when ever possible.

 Phil Elias
 Honeywell Air Transport Systems
 ----------
From: [log in to unmask]
To: [log in to unmask]
Subject: DES:,FAB: - Thermal relief for via holes ??
Date: Wednesday, June 26, 1996 7:38AM

     Hello TechNet users
        I am in need of some input about the necessity of having thermal 
     relief patterns on inner planes for vias that are being used to 
     connect surface mount devices to the inner plane.
        The design in question is 1.6mm thick, 4-layer, mixed technology 
with      via size of 0.6mm. The leaded devices that connect directly to the 
     plane have the IPC recommended thermal relief patterns.
        My main question is, are there any major concerns or advantages in 
     having the vias connecting directly into the plane without relief, I 
     vaguely recollect concern expressed over reliability of these 
     connections if extreme thermal cycling is undertaken.
        Can anybody help
           Regards  Gary Willard (Substrate Design Engineer - UK)