Homebrew PCBs

> I think he might mean stencils.

I mean't the usually green stuff called solder mask. You cannot get 
perfect or near perfect centering of SMD components during reflow 
without it. BTW, even though stencils are more efficient, there are 
still shops that use CNC solder paste dispensers.

> Bridging isn't a concern

It is a concern if a track runs under a SMD component and there is no 
solder mask when solder paste is used. Lots of talk about solder 
paste but very few proficient in its actual use so far. Personally, 
it would be my soldering method of choice on a board done 
professionally. Doubt if I'll ever use it on something made at home. 


--- In Homebrew_PCBs@yahoogroups.com, "Mike Young" <mikewhy@s...> 
wrote:
>
> I think he might mean stencils. The answer is still the same: few 
of us and 
> it doesn't make much difference. The stencil's job is to mask the 
paste into 
> an even thickness only where it's needed. Typically, the stencil is 
3 to 5 
> mil thick. Adding the solder mask thickness, it leaves about 8 mil 
of paste 
> on the pads after troweling off.
> 
> Why might you not need a stencil? Conversely, why are they used if 
you can 
> do without? Very briefly: surface tension, and manual application 
versus 
> automated production line. Apply the paste where it's needed, not 
too much 
> and not too little. Bridging isn't a concern. Experiment a little. 
Prove it 
> to yourself.
> 
> 
> ----- Original Message ----- 
> From: "Stefan Trethan" <stefan_trethan@g...>
> To: <Homebrew_PCBs@yahoogroups.com>
> Sent: Tuesday, January 31, 2006 12:21 PM
> Subject: Re: [Homebrew_PCBs] Re: Question: using surface mount 
> resistors/caps ?
> 
> 
> > On Tue, 31 Jan 2006 17:20:01 +0100, derekhawkins <eldata@m...> 
wrote:
> >
> >>> You could also use paste and reflow if appearance is an issue, 
it
> >>
> >>> self-centers exactly due to surface tension and looks perfect.
> >>
> >>
> >> No kidding! How many of us are reflowing on boards without solder
> >>
> >> masks?
> >
> >
> > Most of us, actually, i guess ;-)
> >
> > Of those that using smd paste that is.
> >
> > Why would you think you need soldermask?
>