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@...>
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?