What type of laser cutter are you using?
And ditto on the stencil. If I don't have several boards it's just not worth the effort/time.
--- In Homebrew_PCBs@yahoogroups.com, Henry Liu <henryjliu@...> wrote:
>
> Using Zeph paste and a 25 gauge plastic syringe + hot air gun , I can solder
> a 128 pin .5mm pitch QFP in under 10 seconds (including the pasting time)
> with no bridging.
>
> I cannot usually solder .4mm pitch devices without some bridging. However,
> I just use kester flux in a syringe and a wide soldering iron and drag it
> across the pins and this moves 99% of bridges as long as I made my pcb pads
> big enough.
> Syringes have no cleanup.
>
> I have a laser cutter and it's pretty effortless for me to make a stencil
> but I don't use it unless I need to make more than 2 boards because the
> cleanup time is more than my syringe time.
>
> On Mon, May 9, 2011 at 5:27 PM, Terry <twgray2007@...> wrote:
>
> >
> >
> > 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
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > [Non-text portions of this message have been removed]
> > >
> >
> >
> >
>
>
> [Non-text portions of this message have been removed]
>