Thermal relief pads reduce the excess heatsinking on the plane layers, but they are not 100%.  Those joints are the hardest to do.  Look at your topside temps as the board hits the wave. I have found if you can run these type of boards at 20-30° F hotter on top than you normally run,  it really helps.

Richard

>>> "Stephen R. Gregory" <[log in to unmask]> 08/10/00 11:59AM >>>
Hi all!

Been trying to dial a profile in on the wave today with a board that's fairly
thick, probably around .090", polyimide, all PTH with a fair amount of the
IC's being ceramic. We use a spray fluxer and a RMA flux.

The first boards have been coming off without the preferred topside fillets
at a number of locations. I've been playing with the pre-heat, belt speed,
and even did something that I don't like to do, which was to flux the topside
of the board.
All to no avail...I still had quite a few places that didn't have topside
fillets, and that is something that doesn't go over well here at all.

I started noticing that the places that didn't have topside fillets were at
the same locations. So I came back to my 'pooter and looked at the gerber for
the board. What's really weird was that everyplace there's a thermal for a
pin is where I have no topside fillet??? I thought that thermals were
supposed to help prevent that from happening? But it's true, every single
place there is a thermal= no top solder. Has anybody ever seen that before?

-Steve Gregory-

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