Homebrew PCBs

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Everybody,

I am interested in trying to solder whole pcboards at once, with something like a solder pot.  Has anyone here had any experience with that?  Has anyone done it "at home"?   Anything to share about it?

I'm thinking of using a rectangular stainless steel or cast iron kitchen-type dish, on an electric hotplate (or, maybe an electric skillet, or possibly even a converted deep-fryer) instead of a commercial solder pot, to keep the cost as low as possible.  Any foreseeable problems with that part of it?  

For everyone's reference, below are pasted copies of parts of two message-threads that I found, on Google Groups (http://groups.google.com), that seem to contain a lot of valuable information about the process.

By the way: The messages' URLs are: 

http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&safe=off&selm=q23q5tgenqeso1ni414v9m5c9uj5co3ves%404ax.com&rnum=7  

and 

http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&safe=off&threadm=KUiN4.3529%24dj5.56108%40news.swbell.net&rnum=18&prev=/groups%3Fq%3Dsolder%2BOR%2Bsoldering%2Bpot%2BOR%2Bdip%2BOR%2Bdipping%26hl%3Den%26lr%3D%26ie%3DUTF-8%26safe%3Doff%26start%3D10%26sa%3DN

--------------------------- Copy of Google Groups message #1:

Solder pots are simple things and can be used to solder PCBs with through-hole/leaded components quickly and cheaply. Be sure to get one with setable temperature. It costs more, but is worth it. A simple solder pot and a 600W lamp dimmer works well as a power controller if you want to save money, but the temperature regulator is you.

The 'pot' at the top should be rectangular or square, large as you can afford. Turn the heat on to max, then add the bar solder, 63/37% tin/lead is best, to the pot. Keep adding solder until the molten metal mounds up above the lip, brimming. You want it to be just on the verge of spilling over. Now it's time to set the temperature, get a strip of newspaper and touch one end to the solder. Perfect temp is when the paper just turns a light tan. (Remember Ray Bradbury's Fahrenheit 451? Same temp!) Black or flaming is bad, so is no change. Keep at it, until you get it right, it's really, really important to set the temp right. 

By this time the solder has probably got a dull or corroded surface, this is 'dross'. Lightly scrape it off with the newspaper strip, leaving a bright shiny surface that looks like a pool of mercury. Add more solder if the surface is below or even with the pot lip... you want it brimming. 

In a separate glass tray, pour some liquid rosin flux, Kester makes a good one. It's a reddish color and very fluid. About a 1/4" depth is fine. Put the tray next to the solder pot.

Ok, now it's time to solder the PCB. Make sure the leads of all the parts on the PCB are trimmed to less than 3/16 of an inch, but more than 1/16". The copper PCB pads should be shiny and clear of any tarnish or corrosion. 

Pick the PCB by the sides up with a pair of steel tongs or very long nose pliers. Lightly 'skim' the bottom of the PCB flat onto the surface of the flux, don't drown it! You just want to wet the all the bottom of the board. Spilling it over on the top won't hurt anything, just wastes flux and makes the PCB look ugly later. 

Then skim the PCB, flat, across the brimming solder surface, slow enough that it takes three to five seconds to make a complete pass. If the board is wider than your solder pot, make several passes in strips. Try not to overlap too much. 

Once you've made a pass, hold the PCB in air, still, over a piece of tin foil for a few more seconds. (The tin foil will catch any drips.) This stillness is important, any parts moving about will increase the odds of bad solder joints. After 20 or 30 seconds, carefully inspect the bottom of the PCB for solder joint quality. If you have a lot of bad joints, check the rosin level in the tray and the solder temp again. Then run the PCB through the same steps again. 

After a few boards, you'll likely need to add more solder and flux. If you have to add a lot of solder wait a few minutes afterwards before soldering more boards. This allows the solder temp to come back up. Scrape the dross off too. (Check the temp again! It's worth it!) 

Ok, after you've done all your boards, time to shut down. Turn off the solder pot, clean off any dross that's accumulated with a scrap of newspaper, then leave the solder in the pot. It won't go anywhere once it cools. Pour the unused flux back into it's bottle then seal tightly. It'll all be ready for your next run. 

Done right, this works great and doesn't cost an arm and a leg. I did this for small PCBs years ago and never had a problem, once I was told how to set the temp right by a kindly old timer. I would have never thought to use newspaper as a temp indicator, but it does work. 

--------------------------- :END of Copy of Google Groups message #1

--------------------------- Copy of Google Groups message #2:

> Actually, The pot I purchased is supposed to solder up an entire board 
> at once. Kinda like wave soldering..... The distributor (Jameco) says 
> it will work great for that. I was just looking for more input on 
> procedures. Don't want to mess up any boards. 
> 

Someone else recently bought a solder pot from Jameco. Here's what I said then: 

"We use 63/37 solder at 250-260 degrees Celsius and Kester 951 "no-clean" flux, which is a clear thin liquid (mainly alcohol). For soldering small, double-sided, tinned circuit boards dip the whole board, parts and all, just into the surface of the flux so the entire top and bottom of the board is wetted. Don't get flux onto the components beyond their leads. Make sure you use sealed capacitors, switches, etc. Drain for a few seconds by tipping up the board (watch the parts!) or by applying an air knife. Then preheat the board over a radiant heater for about 1 minute to evaporate the flux solvent. The board should reach around 150-180 degrees while in preheat. Then dip the board onto the solder for 3 to 4 seconds. Don't just drop it straight down or many of the components will float up - slide it into position." 

"After soldering there should be almost no visible flux residue. If there is you are not draining properly or your flux is too strong. You can thin it with Kester 110 flux thinner. The flux gradually increases in strength as it is used (evaporation of the solvent) so you'll need to thin it periodically. We try to keep it as thin as possible. You'll know your flux is too thin when you start getting unsoldered joints. Just out of the bottle, Kester 951 seems to be a bit too strong - thin it by about 5% initially. If that seems OK, try thinning by another 5%. You have to watch the solder temperature carefully. If it gets too hot you can damage components. If it gets too cool, the solder will form ugly blobs on the bottom surface of the board. We use a Fluke high temperature thermocouple probe to monitor the solder temperature." 

"Our soldering is done in a vented fume hood - it's smelly business. We skim the dross after every dipping - we haven't tried dross reducing agent. Don't throw the dross in the garbage. Save it and donate it to a PCB assembly house - they know what to do with it. Wash your hands carefully when you are done or you'll get bits of lead and its compounds in your food." 

--------------------------- :END of Copy of Google Groups message #2

Thanks for any comments, information, or advice on this.

Regards,

Tom Gootee

http://www.fullnet.com/u/tomg

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[Non-text portions of this message have been removed]

A few things.

1. Do not use no clean flux, if you want your board to
last in a humid or possibly corrosive environment.
Temperature control is critical for most no clean
fluxes. It is unlikely one could get consistant,
uniform profiles at home... and is such, if you make
an error in temperature settings or dwell time, your
board may die in a year or two due to corrosion.
2. Preheat is important, and a hot plate or radiant
heating element will do fine. Try to match the thermal
profiles as presented in the parts datasheets.
3. fumes as mentioned are bad news, use an exhaust
fan, but keep the air movement low over the pot so as
not to shock cook the board after removal. After a few
seconds quick cooling is a good idea. Again check the
profile.
4. Material selection for the solder container is
important. Some metals will react with the hot solder
and deteriorate, others will rapidly contaminate it.
5. Put a tray filled with sand under the solder bath.
You don't want to have molten solder roll off your
workbench onto your shoe, or floor. (no tennis shoes
btw, leather is much safer
6. skim the dross before each board

An outfit I know built their our own machines for
selective soldering. They did however use solder
pumps, skimmers, and tight temperature control. It
saves a lot of labor if you have mixed through hole
and SMD parts to not to have to solder 50-100 pins by
hnad. The machines were roughly 12"X18" so they could
easily put them right on a production workbench.

Ron


		
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----- Original Message ----- 

From: "Thomas P. Gootee" <tomg@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Sunday, August 15, 2004 8:17 PM
Subject: [Homebrew_PCBs] Soldering a whole board at once?


>
> ---------------
>
> Everybody,
>
> I am interested in trying to solder whole pcboards at once, with something
like a solder pot.  Has anyone here had any experience with that?  Has
anyone done it "at home"?   Anything to share about it?
>
> I'm thinking of using a rectangular stainless steel or cast iron
kitchen-type dish, on an electric hotplate (or, maybe an electric skillet,
or possibly even a converted deep-fryer) instead of a commercial solder pot,
to keep the cost as low as possible.  Any foreseeable problems with that
part of it?

Someone told me recently about how he'd seen boards soldered like this in
China. Holding a board in tongs it was first dipped into liquid flux, then
swept through the molten solder bath, whilst it was turned, to create
something like the wave that is used when doing it with the proper
flow-soldering equipment. You'll probably need to practise a lot to get it
right.

Leon

In a message dated 8/15/2004 2:33:20 PM Central Standard Time, 
tomg@... writes:
I am interested in trying to solder whole pcboards at once, with something 
like a solder pot.  Has anyone here had any experience with that?  Has anyone 
done it "at home"?   Anything to share about it?
If you have never DONE that for hours in a "professional assembly house", you 
are asking for PAIN and damage!  

This process is done by "wave soldering" where a WAVE or "linear bump" of 
solder is pumped up with the rig, in the middle of a tank of molten solder, so 
that the crest of the wave just-touches the bottom of the PCB as it moves along 
on a speed-controlled track. 

Go trying to "dip-solder" an entire board will WARP the boards, NOT solder 
every point, cause a general mess with lots of "solder-bridges" that will have 
to be cleaned off manually, which will take even LONGER than simply soldering 
the entire PCB with a good clean iron of the correct size/tip!

Solder-alloy (tin/lead) costs a FORTUNE, these days, and if OSHA ever gets 
wind of your hopes of doing this, they will come knocking at your door, asking 
for the assay of your solder, to insure there is less than 0.003% lead in it 
(or whatever bureacratically-chosen number), and that all the equipment you are 
using is approved by the FDA, FEC, surely several federally sanctioned 
labor-unions, etc.  Next, DOING a few boards, assuming you manage to get it working 
as you want, will result in contamination of the solder-pot, requiring some 
metal-purification proceedures I don't even KNOW where/what/ how-much!  Not to 
mention the effects dissolved COPPER has on the solder (same story).

COOKING UTENSILS are not DESIGNED for melting 20 kG of solder, and even if 
you DO manage to find something that will make a giant solder-pot that will melt 
60-40, it probably won't remain mechanically intact long enough for you to 
shut it down, after the first trial, and you will become an involuntary 
track-star, running from the giant hungry puddle of molten solder chasing you across 
the floor and out into the street!

If you think I sound like a pessimist, read this again while you are laid-up 
with your feet bundled in greasy medicated gauze in a "cranked up" 
hospital-bed, as you read your medical invoice!

Jan Rowland, OLD troll who has BEEN there, but (barely) had sense enough NOT 
to have DONE that!


[Non-text portions of this message have been removed]

> If you have never DONE that for hours in a
> "professional assembly house", you 
> are asking for PAIN and damage!  
Having been there done that, if care is taken, I don't
see the problem. But, one must not be sloppy about it,
as molten solder is not something to play with.
 
> This process is done by "wave soldering" where a
> WAVE or "linear bump" of 
> solder is pumped up with the rig, in the middle of a
> tank of molten solder, so 
> that the crest of the wave just-touches the bottom
> of the PCB as it moves along 
> on a speed-controlled track. 
> 
It can be done, and is done with small benchtop units
as well. They do create a liner bump, which can be
smooth or turbulent depending on your process, and a
motor controlled track or positioner. Solder pots are
useful for tinning, and in some cases soldering small
areas. I think with practice on small boards, one can
do it successfully.

> Go trying to "dip-solder" an entire board will WARP
> the boards, NOT solder 
> every point, cause a general mess with lots of
> "solder-bridges" that will have 
> to be cleaned off manually, which will take even
> LONGER than simply soldering 
> the entire PCB with a good clean iron of the correct
> size/tip!
I disagree to a point, a small board with low density
should work ok.... But to take even a 4"X4" board
would result in much havoc without some type of motion
control, as well as a wave.

> Solder-alloy (tin/lead) costs a FORTUNE, these days,
> and if OSHA ever gets 
> wind of your hopes of doing this, they will come
> knocking at your door, asking 
> for the assay of your solder, to insure there is
> less than 0.003% lead in it 
> (or whatever bureacratically-chosen number), and
> that all the equipment you are 
> using is approved by the FDA, FEC, surely several
> federally sanctioned 
> labor-unions, etc.
OSHA is not concerned with the home hobbyist, as long
as employess are not involved. The FDA does not
regulate production equipment. Not even food
processing equipment (they do however approve some
materials). The FEC has zero interest. However, the
vapors and or flux may fall into community right to
know, and or EPA regs which are a pita. As far as the
lead issue goes, the European no lead requirements may
force the issue through market demand, as less and
less 63/37 will be available and the prices will go
up. There are however regulatory issues to be dealt
with concerning lead exposure and periodic testing.
This is critical if you have employees.

  Next, DOING a few boards,
> assuming you manage to get it working 
> as you want, will result in contamination of the
> solder-pot, requiring some 
> metal-purification proceedures I don't even KNOW
> where/what/ how-much!  Not to 
> mention the effects dissolved COPPER has on the
> solder (same story).
With proper temperature control, flux chemistry, and
testing, its not a big deal. We ran solder pots as
well as wave soldering machines for years with little
tweaking. Sure if its a govt contract, or a customer
requirement, thats different. But for most, its not an
issue, just follow the vendors recommendations.

> COOKING UTENSILS are not DESIGNED for melting 20 kG
> of solder, and even if 
> you DO manage to find something that will make a
> giant solder-pot that will melt 
> 60-40, it probably won't remain mechanically intact
> long enough for you to 
> shut it down, after the first trial, and you will
> become an involuntary 
> track-star, running from the giant hungry puddle of
> molten solder chasing you across 
> the floor and out into the street!
I agree 100%, do not use cooking utensils for a large
vat. I also question 20KG. Thats a fairly large pool
for home use, and if something goes wrong, you have
problems. Many years ago, one of our waves lost a
board, and it jammed itself right where the wave
ended. As such, solder went everywhere. The operator
got it shut down in 30 seconds or so... but it took 2
guys almost 3 days to clean it up and fix it. And yes,
molten solder was flowing onto the floor.

What you may find is that benchtop waves are going to
become super cheap in the next year or two. The
residual lead contamination, coupled with the
reduction in wave soldering should allow one to pick
them up for a song. That way, you have the solder
pump, motion control, and everything you need.

Ron, who has been there, done similiar things, and see
it as less of a problem if you are careful.

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