Re: gEDA-user: "soldermask via caps"

[Stefan Salewski <mail@xxxxxxxxxxxx>]

On Fri, 2010-05-21 at 12:55 +0100, andrew whyte wrote:
> 
>   There is a known problem in layouts with vias inside pads, where
> solder wicks down into vias and causes the joint to be poorly
> soldered.  I found this link  about how to avoid this problem:

I have absolutely no experience with this problem...
I know that open vias in small pads can give problems -- solder can flow
by capillary forces from the pad into the via.

I have never heard about this problem for large pads. For that case the
amount of solder on the pad should be large compared to the volume of
the vias, so there is no problem if some solder flows in the via hole.
And you have a large area for electrical and thermal contact, so
soldering should be not too critical. Capillary forces should move the
fluid from width to narrow areas, so I do not really believe that all
solder will propagate from the contact area of your device into large
vias.

Just a guess of someone with no experience but physical background.

My next task, coming soon, is to solder a few of such thermal pads with
a soldering iron: My plan: have some open 0.3 mm vias in the thermal
pad, fill them with 0.2mm copper wire to improve thermal conductivity.
Put some soldering past on the pad and via, mechanical fixate the device
and heat the vias from backside with a really hot iron. Ok, that may
fail, but gives me at least some experience...

Best regards

Stefan Salewski




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