Homebrew PCBs

Hi Tom,

I already did that but adding 50 % liquid flux to the solder paste I get a very liquid runny mixture that does not stay on the pads.  I am hoping to find paste flux and mix it with the solder paste.

What do other people do?

I know I can remove the extra solder afterwards with solder braid but I rather do it correctly in the first place.

Bertho

 

From: Tom Biery    Sent: Saturday, May 07, 2011 17:29



Why don't you mix a 50%/50% bactch and try it with a smaller needle,

Tom

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________________________________
From: Boman33 <boman33@... <mailto:boman33%40vinland.com> >
To: Homebrew_PCBs@yahoogroups.com <mailto:Homebrew_PCBs%40yahoogroups.com> 
Sent: Sat, May 7, 2011 4:05:41 PM
Subject: [Homebrew_PCBs] Controlled solder paste dispensing

  
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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