Homebrew PCBs

For prototyping you can make your own solder stencils using a 3-4 mil copper gasket material from a good hardware store.  I use toner transfer to apply the solder mask and then etch as you normally would a board.  Very fast, clean, and simple.

For fine pitch parts in prototyping or rework I always tin the pads with a solder, wick up any bridges and then use a hot air rework tool to solder the part in place.  Much easier than hand soldering the fine pitch leads and then trying to wick up the bridges.

Using a 3-4 to 1 solder paste/flux mix ratio usually thins the solder paste enough to apply on very small pads.

--- In Homebrew_PCBs@yahoogroups.com, "Boman33" <boman33@...> wrote:
>
> For regular SMT assembly I use commercial stencils to screen print the
> solder paste but I am having problems dispensing solder paste by hand in
> small amounts for rework or prototypes.  
> 
> I have seen somewhere that individual stencils are sold but that adds the
> requirement to accurately align the stencil which will be very difficult on
> a rework board.
> 
> Using a syringe and placing a single long bead across all the IC pin pads
> work fine on wider pitch ICs but as the pitch is getting smaller I am having
> trouble getting the line thin enough.  In other words, there is too much
> solder so when I reflow there are solder bridging.
> 
>  
> 
> If I use a finer tip on the syringe I cannot squeeze it hard enough for the
> paste to come out.  If I add some flux it gets thinner but too runny.  I
> like the normal consistency since it helps to keep the ICs in place with its
> stickiness.  My current smallest bead diameter is 0.5mm (20mils).  I like to
> be able to get about half of that size.
> 
>  
> 
> I am basically looking for a solder paste with less solder and more thick
> flux material so I can squeeze out a reasonably sized bead but after reflow
> there is less solder than a normal paste.
> 
> Any suggestions on a paste like that?
> 
>  
> 
> Any other suggestions on how to place a very small amount of solder on the
> IC pads?
> 
> Thanks in advance for suggestions.
> 
> Bertho
> 
>  
> 
>  
> 
> 
> 
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