[sdiy] matrix ICs

[Jay Schwichtenberg]

Howdy,

When doing surface mount stuff there are a couple of key things. Use a good
iron, if you can afford a Metcal get it. Next use very fine solder 0.015 or
0.02 at the biggest. One of the hardest things to do when soldering SMD
stuff is not put to much solder down. When you use a fine solder you have to
work harder to get more solder down so you have more control over it. Also I
think that the water solualable stuff is great for this. There are a couple
of issues. You have to let your dry before you use it. Heat guns can dry
stuff out pretty good. NEVER, EVER, USE A HAIR DRYER! Heat guns are grounded
and take care of static, hair dryers aren't. Also never solder anything with
it that you can not wash. This includes both sides of the boards if they are
thru hole. What I do is solder the part down not being over critical. Then I
come back with some fine solder wick and wick up any excess solder. If I do
it right you can't tell the difference between that and a machine doing it.

When connecting adjacent pads do not run traces between pads. Run them away
from the chip and back to the other pad. This can create problems when
soldering/unsoldering fine pitched pins.

One of the analog guys that I worked with has used some of integrated cross
point switches. They were a major pain but they finally got the project done
to spec. While the chip has very good crosstalk specs you have to be very
critical of the PCB layout to avoid crosstalk. So make sure that you are
careful here use a good ground plan and try to isolate analog signals from
one another as much as possible. Use guard traces (grounded traces between
signals) if you have the room. Also keep the digital and analog seperate as
much as possible. Run digital and analog signals at 90 degrees from each
other.

Good luck.
Jay

> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Theo
> Sent: Saturday, October 06, 2001 10:00 AM
> To: Alex Stettler; DIY Synth List
> Subject: Re: [sdiy] matrix ICs
>
>
> May I suggest the "blob" method for soldering the TQFP?
> I got this from a friend who works at a SMD assembly line, where 1 minute
> for a 100 pin TQFP is already too slow. There is a web-page around about
> this soldering method, but I don't have the URL, sorry.
>
> - Flux your PCB (spray works fine), this is rather essential.
> - Place the TQFP on the board.
> - Next take a normal soldering iron with a +/- 2mm bit, larger is also OK.
> - Now put a nice "blob" of solder on the tip of the iron and drag
> this over
> the pins of the IC.
> Done.
>
> It takes some practice and you might want to keep a 0.8mm iron handy to
> remove a occasional solder bridge.
> (just reheat the offending pins)
> But the emphases in on occasional, most of the time it works like a charm.
>
> There is one thing though you need to take in account.
> While designing your PCB you should make sure there is a
> copper-area (large
> trace, ground plane, ect.) next to the pads of the IC your gona "blob".
> Your "blobbing" ends on this copper-area so the excess of solder
> has a place
> to go.
>
> I "blob" all my SMD ICs and am quite happy with it :)
>
> Theo
>
>
> From: Alex Stettler <alex at xatomic.ch>
>
>
>
> > Hi all,
> >
> > I'm currently designing a 32-channel patch-cordless patchbay
> (PCLPB) with
> > four AD8113 chips.
> > These are 16x16 crosspoints and are specially designed for
> audio purposes.
> > They have -100dB channel crosstalk, 100dB isolation at 20kHz
> and a +/-12V
> > supply.
> > The outputs are buffered.
> > They come in a 100pin TQFP package.
> > So I'm very curious on the results of the finished product and I hope I
> > could manage
> > to solder the chips properly to the PCB as such a 100pin TQFP
> is a rather
> > small chip.
> > But it should be possible with a hot air gun and solder paste.
> >
> > Regards,
> > Alex
> >
> > > -----Ursprüngliche Nachricht-----
> > > Von: owner-synth-diy at dropmix.xs4all.nl
> > > [mailto:owner-synth-diy at dropmix.xs4all.nl]Im Auftrag von Glen
> > > Gesendet am: Samstag, 6. Oktober 2001 08:57
> > > An: synth-diy at dropmix.xs4all.nl
> > > Betreff: Re: [sdiy] matrix ICs
> > >
> > > Just to pass some time, I compiled a list of known cross-point
> > > switches where
> > > are still considered to be in active production. You can find
> > > that list here:
> > >
> > http://users.ezwv.com/~mclilith/electronics/cross-point.html
> >
> > Perhaps it will be of interest to someone.
> >
> >
> > Later,
> > Glen
> >
>
>
>