Soft Soldering
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Concepts
This is one skill that needs some basics
understood, before you can be really achieve good results.
In the years that I spent as a
Coppersmith, this was a day to day activity and I was taught how to solder
by several gentlemen who have probably forgotten more about the subject
than I remembered. But what I do remember are some very basic things that
make a real difference.
The key things to remember are;
 | Cleanliness is next to Godliness.
| Solder will only go where the heat is.
| The right flux for the job is a must.
| Be patient. |
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Soft Soldering, as we called it, is a
simple task if this things are taken into consideration.
Cleanliness
Regardless of what type of material you
are trying to solder, if the area you are trying to solder is not clean,
you will not get anywhere. Make sure that both parts or the area are free
from oil, paint, rubber, etc. Anything that stops you seeing the bare
metal.
If it is not, then scrape it, file it,
sand it, grind it, do anything you have to get to the bare metal. One word
of caution with steel and stainless steel, do not burn or blacken the
metal as a result of too much heat. Once this occurs you will get a black
oxide skin on the metal and you will not be able to solder over this.
If you do get this, then you have to
clean it off with either sandpaper, file or some other abrasive action
that does not overheat the metal. You can also use Hydrochloric Acid to
"pickle" the metal. This usually gives good results with all
metal, but please ensure you have the correct safety equipment. It should
also be noted that if you do use acid to clean the metal, you must wash off
the residue.
Acid cleaning should only be used for non
electrical components. If you are soldering electrical or electronic
components, please clean only with the abrasive methods and treat the
components with some respect. In general you usually do not have to clean
electronic components that much.
Just remember your output will be as good
as your input, the cleaner it is the better it will be.
Solder will only go where the heat is.
This is a fact of physics, as you melt
the solder with a soldering iron, gas torch or any other means of heat you
choose, the molten solder can only travel to the areas that have enough
heat to allow it to flow.
If it is not hot enough for the solder to
flow of its own free will and you "blob" the solder on to the
area, you will not have created a good mechanical bond with the parent
metals. The correct heat allows the solder and the parent metal to form an
alloy between them, this is the actual joining part of the process. Not
enough heat, no join. It should also be noted that too much heat will burn
the parent metal and the solder, this will have two effects.
| If the parent metal gets too hot and
it is steel based, it will get a black oxide skin on it and you will
not be able to solder anything to it. |
| If the solder gets too hot, it will
burn some of the alloys out of it and you will end up with either a
weak or brittle joint. |
This is one of the basic mistakes that
most people make and the easiest way to deal with it is to be patient and
let the heat do its job.
The right flux for the job is a must.
This is another area that is really
misunderstood and has major effects on the quality of the soldering job.
There are basically two families of flux;
| Acid Based
| Resin Based |
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The Acid based solders use different
types of acid that have been chemically treated to give them certain
properties for the expected use. They usually come in a liquid form and
need to be brushed onto the solder joint.
The Resin (pronounced Rosin) based
solders are made up of chemicals that have been treated to make them into
a firmer form. Most solder that you by for electronics is resin cored.
This fluxes are safe to use with most electronic components.
Why the difference, many reasons, but
mainly heat type, the type of components being soldered.
From a type of heat perspective;
| Acid based solders work well when you
are using an exposed flame to solder with.
| Where as the resin based solder work
best with a soldering iron. This is does not mean you cannot use
either them with the other method of heating, but there are
limitations.
| Acid based fluxes work well with a
soldering iron as long as you remember that they will cool the solder
area, so a little more heat may be required.
| Resin based fluxes work ok with a
flame, but you cannot put the flame directly on the flux, it burns and
usually burns black and sooty. This undoes all your efforts in trying
to get the area clean. To use them this way you will need to heat the
joint area first and then introduce the flux. You can "play' the
flux with the very end of the flame as long as you watch the
temperature. |
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From a purpose perspective;
| Electrical / Electronic components
should only be soldered with Resin.
| Steel, Stainless Steel, Bright Steel,
Iron usually solder better with Acid.
| Brass, Copper, Gold usually solder
with either it is dependant on the sensitivity of the components. Acid
delivers the best results, however if it was anything electrical use
resin first.
| Galvanised, Zinc, and Cadium Plating
try acid first, but watch the fumes. |
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Be patient.
Take you time and if you are not sure try
it on a small area and see what happens. If it works, great, if not then
try the other method.
As my first tradesman said to me
"son patience is a virtue and you learn it from soldering!"
Soldering Usage Matrix
I have put this simple matrix together to
make it a little easier for you;
| Soldering Job |
Suggested Method |
Notes |
| Electrical Wire to a
PCB |
Resin Cored Solder and
a Soldering Iron |
|
| Two Electrical Wires |
Resin Cored Solder and
a Soldering Iron |
|
| Electronic Components
into a PCB |
Resin Cored Solder and
a Soldering Iron |
|
| Steel to Steel |
Acid Flux, 60%/40%
stick solder and a flame. |
The flux I use is made
by BOC is it called 956 Soldering Flux and is the best I have ever
used as it is not as sensitive to heat as some are. Use what you
can, but get used to it with some scraps. |
| Copper to Copper |
Acid Flux, 60%/40%
stick solder and a flame. |
|
| Brass to Brass, |
Acid Flux, 60%/40%
stick solder and a flame. |
|
| Stainless Steel to
Stainless Steel |
Acid Flux, 60%/40%
stick solder and a flame. |
This is tough stuff,
be really carefull with the heat and you may find you have trouble
with the flux if it is not correct. |
| Silver to Silver |
Acid Flux, 60%/40%
stick solder and a flame. |
Be careful with the
amount of heat, silver melts quickly and you cannot tell how hot
is it by looking at it. |
| Gold to Gold |
Acid Flux, 60%/40%
stick solder and a flame. |
As above |
| Steel to Stainless
Steel, Copper, Brass |
Acid Flux, 60%/40%
stick solder and a flame. |
|
| Nicad Battery Pack |
Resin Cored Solder and
a Soldering iron |
Make sure the battery
terminal are clean. Give them a light sandpaper even if they look
clean as the manufacturers coat them with chemicals that actually
make it harder to solder.
Make sure you use a big soldering
iron and do not hang around. It is also worthwhile to
"tin" the ends of the battery before you start. This
will make sure you get a good result.
|
Fluxes
I have used many different types of flux,
below is an outline of my thoughts
| Flux |
Maker |
Notes |
| Comweld 956 |
British Oxygen Company
formally CIG in Australia |
The best for any flame
based soldering. I have not used anything better ever. Get a
bottle if you can. |
| Bakers Soldering Flux |
Bakers (not sure too
many years since I looked at the bottle) |
It is pretty good, but
really suffers when you get it too hot. |
| Resin Cored Solder |
Everyone |
Great on electrical
components and has some use with a flame. Not too good if the
surface is a little dirty. |
| Killed Spirits |
You if you like, it is
Sulphuric Acid that has been "killed" by dropping blocks
of Zinc into it. Be careful this give off lots of dangerous
vapours and should only be done with the correct safety equipment. |
Really good on heavy
galvanised iron sheets, but it does not like the flame too much.
You have to use a big soldering iron, most plumbers used this
stuff to solder roofing iron.
In an emergency you can take a
small amount of battery acid and a zinc coated bolt to get a flux.
|
| Pork Fat |
You laugh!!!
|
This is an emergency
resin flux replacement. It does work but you need to coax it
along. Mind you it smells great when you put a flame on it....mmmm...crackling!! |
| Coca Cola |
You laugh again!!! |
This is an emergency
flux, don't even try a flame it just burns the sugar. You have to
be patient with it and it take a while for the acid in Coke to
clean stuff. But you can use it. |
Tips and Techniques
Here a few simple things that will
improve your success.
| Item |
Notes |
| Tin the area you want
to solder first. |
If you can coat the
area that you want to solder with a thin coat of solder prior to
trying to solder anything to it. Just run over the area with the
iron or a flame and coat it. This will help ensure that you get a
good bond when you go to solder the other parts on.
This is really important with
Ni-Cad batteries.
|
| Avoid "Dry"
joints |
A "dry"
joint happens when you solder something and it moves while it is
setting. This actually partially breaks the joint and can lead to
connectivity problems with electrical connections or strength
problems with mechanical joints.
Set the joint up that is to be
soldered so that you can solder it and not have to hold it with
your hands.
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| Don't use to small of
a Soldering iron |
If you are not sure if
your soldering iron is too small for the job, then let it warm up
to its normal operating temperature, then try to tin a small area
where you want to solder. If you cannot get the solder to flow
freely, the soldering iron is to small. If you leave it on the
area for a small while and the solder flows then it may be ok,
however if it does not, then stop.
You will need to get a bigger
soldering iron to do the job properly. if you don't then you will
get a bad joint, which may cause more problems.
|
| Don't use too big a
Soldering iron |
This is very rarely a
problem, because you can usually control the heat of the area you
want to solder by the amount of time you have the iron in touch
with the area you want to solder. However be aware that if the
solder burnt you will have a weak joint. |
Copyright © 2002
- 2003 Craig Tarlington
This material cannot be used for
any commercial purpose without my written approval.
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