All that is undoubtedly true... but if you still want to try it, I would
think you would get better results with a convection kind of toaster oven.
Larry N8LP
Henry Gardiner wrote:
SMT soldering was designed to obtain high volume and high quality
solder joints with great uniformity so that detailed inspection and
rework are not necessary. It does this at considerable investment
expense up front.
The paste solder must be applied in a precise amount. This means a
stencil printer (most use optical alignment) and multi-hundred dollar
stencils, or a robot that applies dabs in precisely metered amounts.
Hand application will not work adequately. Smear the solder on those
narrow smt ics even slightly and a solder short results. Not enough
solder, and the lead won't wet. Too much, and the joints short or are
hard to inspect. You end up with the extra step of inspecting every
joint (which is not done often in the industry) and doing a lot of
touch-up by hand.
Then the component must be placed precisely on the pads of solder
without lateral motion that would smear the solder and cause solder
joint problems. In industry, robots do this at high speed and
precision using software that determines from coordinates and optics
where to put each component. Just about impossible to do by hand
unaided at any speed. But a person could rig up some very slow manual
pick and place device.
Circuit boards that have been sitting around for months start to
lose their wettability. This adversely affects the uniformity of the
solder joints. The high volume of a factory provides considerable
protection against this problem.
Most smt ovens heat the air and blow the air around the boards at
high volume. Compared to radiant heating this provides much better
regulation of component temperature-time profiles despite differences
in component colors and geometries, and the biggest factor, the
thermal mass of the circuit board itself. The circuit board forms
half the joint.
To obtain the temperature vs time profile needed, most factory smt
ovens are actually a chain of several ovens connected together
linearly over a moving belt. Each oven operates stabilized and
uniform at a different point in the temperature profile.
Unless you want to buy good equipment, you will be inspecting every
joint, doing a lot of touch up and replacing fried components. You'll
have a lot of field failures from intermittent joints. Toaster ovens
don't make sense. Single cavity ovens could be made to work well if
there's a lot of moving air and if the walls of the oven and the air
can be kept very close to the temperature profile, including the
cool-down phase.
For experimenters, it makes much more sense to stick with the larger
smt sizes and solder them in by hand with a soldering iron and
hand-held solder.
Henry AC5LA
_______________________________________________
Elecraft mailing list
Post to: [email protected]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com
_______________________________________________
Elecraft mailing list
Post to: [email protected]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com
