[sdiy] SMD experiences

[Dave Manley]

 On Fri 11/09/09  6:03 PM , "Tim Parkhurst" tim.parkhurst at gmail.com sent:
> On Fri, Sep 9, 2011 at 1:08 AM, Tom Wiltshire <tom at ele
> ctricdruid.net> wrote:>
> >
> > What's a "thermal relief pad" and why
> would I only need one for through-hole?>
> 
> Hi Tom,
> 
> A thermal relief isn’t really meant to keep solder out of vias. A
> thermal relief is designed to allow a via (or any other plated through
> holes) and a copper plane to expand / contract at different rates
> without cracking.  For the uninitiated, a via is basically a tiny
> plated through hole that is used to connect one layer to another on an
> SMT board. A thermal relief is made by connecting a via to the copper
> plane with four small strips at each quadrant of the via (rather than
> a continuous solid connection, which could become a stress point under
> thermal expansion). If a via is near a solder pad, it should be
> separated from the pad by a short, thin trace (with solder mask over
> the trace). Vias in pads should be avoided whenever possible, as they
> can actually wick too much solder in and create an unreliable joint.
> However, if you absolutely have to have a via in a pad, it should be
> located in a corner of the pad to minimize the amount of solder that
> gets pulled in.
> 
> 
> Tim (did my time installing pick and place machines) Servo

Interesting* discussion/pics here: http://i.screamingcircuits.com/docs/Via_In_Pad_Guidelines.pdf

I like the small dot of solder mask on top of the via, in the center of the pad on page 3.

-Dave

For some values of "interesting".