Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

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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