[sdiy] Surface mount

[Craig Critchley]

I've done a little bit of surface mount, both by hand-soldering and by the
"toaster oven method," which involves "reflowing" solder paste in a toaster
oven. It works well, and is pretty fast once you have a PCB made, although
when using fine pitch ICs like QFPs you have to be sparing with the paste,
and still expect to do a little manual cleanup.

I got myself one of those big magnifiers with a circular flourescent light
around the lens, which really helped me see what I was doing.

Doing PCB design for surface mount can be more challenging and
time-consuming: things are smaller, you can't route between pins on
fine-pitch packages, and you don't get the free vias you get with
through-hole leads. Fine-pitch packages are more of an issue when doing
digital than analog, what with all those CPUs and gate arrays in QFP
packages.

The Seattle Robotics Society describes toaster oven reflow here:
http://www.seattlerobotics.org/encoder/200006/oven_art.htm

				...Craig

________________________________

From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of Jay Schwichtenberg
Sent: Thursday, January 01, 2004 8:30 PM
To: Synth DIY
Subject: RE: [sdiy] Surface mount


Laurie,
 
In general if you use the same parts you will have the same performance.
Main difference is circuit board layout. When you're doing SMT the traces
are typically smaller and closer together. This can create problems if you
are not careful. You'll need to pay attention to the amount of current that
a trace can carry (trace width) and to cross talk issues (distance between
traces). With the thin traces power layout and decoupling may be more of an
issue. Pay particular attention to circuits that are capacitive sensitive
when doing layout and spread the traces out. With traces that are carrying
large signals you may want to run guard traces between them or use distance.
So keep these things in mind when doing your PCB layout. Another thing which
comes to mind is temperature sensitive circuits like expo converters. With
the smaller parts there is less thermal mass which may make the circuits
more acceptable to temp changes. So thru hole/larger components may make a
difference here.
 
Some other thoughts about doing surface mount stuff are:
 
Just because you can get 603 parts doesn't mean you have to use them. You
might use 1206 parts to start out with. With my eyes and hands I don't do
anything smaller than 805 unless I absolutely have to.
 
If you do your own boards it cuts down on the number of holes you have to
drill. This can save a lot of work.
 
Clean your boards real well before soldering.
 
If you are going to hand solder the stuff it will take some time to get a
technique down for doing it. So don't be discouraged if your first few tries
don't come out looking all that good. Keep working at it. I was forced into
doing SMT at work but once I was there it isn't all that bad.
 
Having a good temp controlled soldering iron, non-magnetic tweezers,
magnifier/lighting and plenty of tooth picks helps.
 
I found that having 0.015 dia. solder helps a lot if you can afford it.
Having the smaller dia. solder lets you control the feed better so you don't
get more than you need.
 
Learn the issues with and how to use water soluble flux solder it will make
your boards clean up real nice.
 
Good luck.
Jay
 

	-----Original Message-----
	From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Laurie Biddulph
	Sent: Thursday, January 01, 2004 1:25 PM
	To: Synth DIY
	Subject: [sdiy] Surface mount
	
	
	Hi, Hope everyone had a good Xmas holiday and New Year.
	 
	I would like to get some feedback on how you feel about using
surface-mount components in analogue synths as opposed to the good old
thru-hole component.
	Would two identical circuits built using the two different
technologies sound the same?
	
	Best Regards
	Laurie Biddulph
	http://www.elby-designs.com