Homebrew PCBs

> The chips wiggle themselves into place during reflow. Not only is
> self-centering one of the benefits of solder paste, there is little 
> you can do to prevent it.

At least two things prevent it actually;

1. Pads not designed for reflow
2. No solder mask

Again, your idea of self centering may be different from mine. All 
boils down to taste and expectations.

--- In Homebrew_PCBs@yahoogroups.com, "Mike Young" <mikewhy@s...> 
wrote:
>
> Solder mask has absolutely no effect there. Aside from BGA, the 
entire 
> footprint including the pads and spaces is not masked.
> 
> It's one of those things you'll have to take on faith until you see 
it for 
> yourself. The chips wiggle themselves into place during reflow. Not 
only is 
> self-centering one of the benefits of solder paste, there is little 
you can 
> do to prevent it.
> 
> There's nothing magic about paste. You don't even need paste and an 
oven to 
> prove it to yourself. Point a heat gun at a hand soldered 0402 or 
SOIC and 
> see.
> 
> ----- Original Message ----- 
> From: "derekhawkins" <eldata@m...>
> To: <Homebrew_PCBs@yahoogroups.com>
> Sent: Tuesday, January 31, 2006 2:11 PM
> Subject: [Homebrew_PCBs] Re: Question: using surface mount 
resistors/caps ?
> 
> 
> >> Why would you think you need soldermask?
> >
> > Exposed tracks leading to the pads will cause unpredictable 
imbalances
> > as the solder "wicks" away on them. Self centering is not one of 
the
> > benefits of solder paste in the absence of solder mask.
> >
> > --- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan"
> > <stefan_trethan@g...> wrote:
> >>
> >> Most of us, actually, i guess ;-)
> >>
> >> Of those that using smd paste that is.
> >>
> >> Why would you think you need soldermask?
>