[geeks] wave soldering

[Kris Kirby]

On Mon, 22 Jul 2002, Joshua D Boyd wrote:
> What is wave soldering?  Google of course returns lots of links, but
> mostly of people trying to sell it to me, not people explaining what
> it is.  I say a boutique effects shop advertising that one particular
> pedel they sell is wave soldered.

I used to work in a factory on SMT lines, right next to the `wave'. Wave
soldering is typically used when you can't do SMT or you're installing
hand-loaded parts that are uneconomical to be installed one at a time by a
dedicated operator.

Typically, you have an `assembly line'. This is a `hollow' conveyor that
has adjustable spacing and places on both sides to allow chairs to come up
to, shelves to support arms and trays of parts, and usually foot rests.

The boards to be manufactured (wave soldering is usually the last step in
production, except for washing and putting the case / cover on and packing
it out.) are placed in `pallets'. These pallets are usually fiberglass (in
some cases, teflon, but teflon is hella-expensive, so only in certain
conformal coating operations do they use it) and have holes cut out on the
bottom to allow the solder to come up to the holes to be soldered. The
pallets usually have a mechanism to secure the board to the pallet, so no
solder comes up in places that it isn't expected.

The pallets are loaded onto the assembly line, where the operators place
components in specific locations, usually doing one, two, or three parts
and locations per operator. Then the finished work is inspected by a
single operator who usually does a touch inspection -- touching every part
and making certain it is installed correctly then passing it on to the
`wave'

The Wave is a large, oven like apparatus that has a piece of motor-driven
assembly line inside of it, usually made of a different material. This
line runs from one end to the other, starting on the left at about 25 - 30
inches from the ground and finishing on the right at about five feet off
of the ground. There is a mechanism on the right-hand side for catching
the pallets and cooling them.

When the product enters the wave, the first action is that flux is
applied. Usually, this is a no-clean flux (since `clean' flux requires
something called sponificators in the board wash machine to get all of the
residue off) that is applied by either a `bubble line', a robotic spot
spray-head, or by hand. The `bubble line' is my term; it's a device that
takes the liquid flux and nitrogen and makes a foam of bubbles that flows
downward. As the board passes over the top, it gets a uniform coating all
over it's bottom. This isn't nearly as efficent as the spot-sprayer, which
is controlled by a program as to where to spray and how much to spray.

>From there, the board passes over two or three sets of heater elements,
each progressively hotter than the one before it. Finally, beyond the
heaters, sits the solder pot.

Imagine a 1,000 pound pot of molten metal sitting at 550 degrees F. Yeah.
Anyway, inside the solder pot are two pumps -- one simply circulates the
solder, the other provides pressure to `solder jets'. The solder jets are
to push the solder further up into the pallet, should that be needed to
reach a hard to get to part. Just beyond the jets is a raise platform that
the circulation pump pushes the solder to. As the board passes over this
platform it *just* comes in contact with the solder, finishing the job.
Then the board exits, is cooled, inspected, and washed, if need be.

More often that not, the wash step is skipped.

That's a wave-solder machine, in a nutshell. I was almost trained to
operate one, but I'd rather stick to machines that will only posion me;
not cook me alive[1].


[1]: I used to be a `screen printer' operator. Those of you who have been
     in manufacturing know what I am talking about, but all this typing is
     killing me, so that explaination will have to wait a short while
     while my hands recover. Two of my closest friends were wave
     operators, until they quit working in manufacturing.

--
Kris Kirby, KE4AHR  <kris at nospam.catonic.net>  TGIFreeBSD IM: 'KrisBSD'
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