Soldering

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(De)soldering a contact from a wire.

Soldering, brazing, and welding are techniques used to join metals together. Of the three, soldering is arguably the weakest. It is still strong enough for our needs with DCC model building.

[edit] General Definition

Soldering is a method of joining metal parts using an alloy of low melting point (solder) below 450 °C (800 °F). Heat is applied to the metal parts, and the alloy metal is pressed against the joint, melts, and is drawn into the joint by capillary action and around the materials to be joined by 'wetting action'. After the metal cools, the resulting joints are not as strong as the base metal, but have adequate strength, electrical conductivity, and water-tightness for many uses. Soldering is an ancient technique that has been used practically as long as humans have been making articles out of metal.

[edit] Soldering - as applied to modeling

Soldering is used to join two or more wires together for electrical connectivity, to join decorative bits of metal to brass locomotives, to fasten rail to printed circuit board ties while hand-laying track, to join the lead came strips between pieces of stained glass (see Lead came and copper foil glasswork), and to join sections of copper tubing used in plumbing.

The main differences in the above examples are the size of the pieces of metal being joined, and the amount of heat needed to make the joints. Copper tubing usually requires a propane (or hotter) torch to supply sufficient heat, while a wire junction requires considerably less heat, such as that from a handheld soldering iron.

In general, soldering consists of physically joining the bits of metal to be connected, applying heat to the joint, then touching the solder to the joint and allowing it to flow into the joint through capillary action. In the case of work with an iron, the iron is NOT used to smear the solder around!

[edit] About Solder

Solder is an alloy of metals, usually tin and lead for electrical connections, although the lead component is being phased out because the lead ends up in landfills and can leach into the ground water supplies. The melting point of solder depends on the metals involved and their ratios.

Pure tin melts at 450 degrees F. Pure lead melts at 621 degrees F. An alloy of 63% Tin and 37% lead (a common electrical solder) melts at 361 degrees F, the lowest temperature soldering alloy composed of just tin and lead -- yes, the temperature at which solder melts is BELOW the temperature at which either component will melt! The more lead, the higher the melting point; tin lowers the melting point.

Some solders include silver, and have a much higher melting temperature, and other formulations include other metals. Only Tin/Lead solders should be used for electrical connections. Silver based solders are used for other purposes, such as soldering pipes and other pieces of metal together. The only application of silver solder for electrical purposes is where there will be a lot of heat-- hot enough to melt the typical solder alloys used for electrical work. Some examples: connecting wires to a heating element, or a shunt (A device used to measure large currents.) The additional cost of silver solder isn't justified for typical electrical soldering.

Only a 60/40 or 63/37 tin/lead solder should be used for electronics, and only rosin flux core solders. Acid flux core solders - meant for other uses - should not be used, and will in time damage circuit boards and electrical connections. The rosin flux removes the oxidation on the surface of the metals, allowing them to bond cleanly. The flux should be cleaned from circuit boards after soldering using a flux remover.

One source (http://www.tpub.com/neets/book4/12n.htm) indicates that soldering is more than just melting-there is a chemical change that occurs as well.

[edit] Warnings and Precautions

WARNING! Solder is liquid metal. It melts anywhere between 361 degrees F and 621 degrees F. This is hot! Burns are common-both to your surroundings and your skin!

Please follow safe soldering techniques at all times!

• DO NOT TOUCH the hot iron.
• DO NOT TOUCH the heated joint.
• Wear eye protection
• Wear gloves, even thin leather is better than nothing at all.
• Work in a well ventilated area due the fumes created while soldering.
• As with all power tools, it's recommended to remove all jewelery beforehand.

[edit] First Aid

If you do burn yourself, here is what to do (we are not doctors, but offer this advice):

• Immediately cool the affected area with cold running water for at least 5 minutes.
  • Some people keep a cool, wet sponge near the work area. Use this to cool the burn on your way to a faucet for further cooling.
  • Cooling a burn immediately will help prevent blisters (second and third degree burns) so scarring will be prevented or greatly minimized.
  • See BurnSurvivor.com for details and treatment.
• Although you should have removed any rings, or other jewelery before working, remove them now if you haven't - before swelling starts
• Apply a sterile dressing to protect against infection.
• Do not apply lotions or ointments.
• Do not touch, poke, or prick any blisters which form later.
• Seek professional medical advice if needed.

[edit] Tools and supplies required for electrical and most model work

A. Different types of soldering irons

1. Electrically heated, direct plug-in

An iron in the 30-40 watt range is adequate for soldering wires. For soldering on electronic boards, consider purchasing a temperature controlled model instead to avoid damaging electronic devices on the board. Pen soldering irons have tip temperatures creaed by heating the tip with the same amount of power (the wattage) until equilibrium heat transfer is achieved with the air, which usually results in extremely high tip temperatures if the iron is not used for a few minutes, and this temperature can easily damage electronics.

2. Electrically heated, temperature controlled unit

Melting metals near delicate electronic components requires the proper tool, so when working on connections to printed circuit boards, consider purchasing a temperature controlled soldering station, which allows application of a precise amount of heat for a short period of time to a very precise area.

3. Resistance soldering unit

4. "Cold Heat" battery powered portable

5. Butane torch portable

B. Tip (copper or pre-tinned)

Soldering iron tips are usually base metals plated in copper and must be tinned before use to encourage heat transfer to the junction. Never file a soldering iron tip, or you may remove the copper, causing the tip to oxidize which will prevent it from transferring heat properly to the junction being soldered. But the copper also need tinning before use to ensure even heat transfer and to prevent oxidation. For ease of tinning, consider using a product such as the Plato Tip-Tin paste, which you simply dip the tip of the soldering iron in.

1. Pointy (pencil tip)

2. Chisel

C. Solder - rosin core, NEVER acid core!

D. Flux - rosin, NEVER acid!

The rosin core in solder (or the paste flux available separately) is designed to clean away oxidation on the surface of the metals when the heat of soldering is applied and to prevent the metals from oxidizing further as they are heated. While rosin flux is generally neutral and helpful to soldering, acid flux is just that -- an acid, that will dissolve whatever gets in its way. And unless it is quickly neutralized, acid flux will continue to nibble away at whatever it is in contact with. This means electrical connections will corrode, things will fall off of that brass locomotive, etc. Neutralizing means daubing on a base (ie a baking soda paste), then cleaning up the residue. The problem is that it is likely that a bit of the flux will escape the cleanup (ie a bubble inside the joint), and will continue the corrosion process. Acid flux should not be used for electrical work. Do not use 95/5 lead free acid core solder often found in hardware stores!

E. Wire-cage soldering iron holder (with sponge for cleaning the tip of excess solder or grit)

F. Solder sucker (for desoldering)

G. Unsoldering braid (for desoldering)

H. Heat sink clamps (to draw heat away from heat sensitive components)

1. Specially made

2. Hemostats

3. Alligator clips

I. Vinyl electrical tape

J. Wire Strippers.

Wire Strippers. The one on the left is an inexpensive one, but it can be a little difficult. The one of the right is a heavy duty tool, capable of handling 22 to 8 AWG wires.

Wire strippers are a quick and easy way to remove insulation from the wires prior to soldering. They are better than using a knife (and you should not use your teeth!) as knives and other more brutal techniques can nick the conductors, leading to failure later.

Strippers work by cutting the insulation, then pulling it toward the end of the wire. Simple tools like those sold with sets of crimp on terminals just cut the insulation, then you have to pull the tool toward the end of the wire. Better strippers, like those shown in the picture, will strip the wire when you squeeze the handles.

[edit] Preparing a new soldering iron for use

1. Screw on/in a new tip
2. Heat the iron
3. Soak the sponge on the soldering iron holder in water. It should be heavily damp, but not dripping.
   • Remember to clean and dry the sponge when done soldering
   • If possible, use distilled water with the sponge.

1. "Tin" the iron
   • Dab solder on the tip until the solder 'sticks.' Coat the tip evenly. Wipe off any excess on the sponge.
   • From time to time while soldering, wipe the tip of the iron on the sponge to remove the dross and excess solder that accumulates during your soldering session. Re-tin as necessary.
2. If you are using an adjustable base, adjust...

[edit] Renovating an 'old reliable' soldering iron

A. File off any scuzzy crusty residue on the tip

This can be done while the iron is cold or hot. Actually, most soldering tips are plated with iron. Filing them can remove the plating and then they're ruined. They also wear out and become pitted with time anyway. The good news is that tips are almost always replaceable and relatively cheap.

A knife can also be used to scrape any dross that has accumulated on the tip.

Filing the tip will fill the file with solder and bits of crud. You may choose to dedicate a file to the soldering kit; it will need cleaning if you need to use it for other purposes.

B. Make sure the tip is firmly screwed in/on to the iron

Loosening and then tightening a tip will break any corrosion that has formed and may improve performance in the process.

If the iron is hot, use a pair of pliers and keep your fingers away from the hot bits!

C. Re-tin the tip.

Heat the tip, then dab on fresh solder until the tip is shiny with molten solder.

From time to time while soldering, wipe the tip on the sponge to remove the dross (technical term is 'crud') that accumulates in the process

A tip cleaning device made from brass turnings is also useful. Electronics suppliers carry these and other accessories.

[edit] Types of Soldering

I have never used a torch or resistance soldering tool, so those topics are up for grabs!

A. Direct application of heat

1. Torch

2. Iron

A soldering iron is an electrical appliance that consists of a handle, a heating coil, and a metal tip. In appearance, it is similar to a curling iron, but most like a wood burning tool.

B Resistance soldering

[edit] How To Solder (using a standard iron)

Generally speaking, all types of soldering follow the same basic steps:

A. Clean the parts being joined

Remove all coatings, grease, dirt, and other crud from the joint. Solder and flux do not clean the joint! Flux will remove corrosion from the metal, but that's it! If you're soldering copper pipe, use a wire brush or crocus cloth to remove the tarnish.

B. Physically connect the parts

The joint should be strong enough to stay together without solder. Solder is not intended to provide a lot of mechanical strength!

C. Stabilize the joint so it won't move while being soldered

You will be pressing on the joint with the soldering iron, so it must be restrained. You can use a "third hand" rig, with alligator clips on swivel arms, you can prop it up or weight it down, or otherwise keep it from moving

D. Heat the joint

Make sure the iron is hot. Unwind a few inches of solder from the spool. Don't cut it off, just unwind a bit! Dab a bit of fresh solder on the tip of the iron. Make sure the tip of the iron is 'shiny' with molten solder. You may need to wipe the tip on the sponge on the base of the iron holder to clean off the tarnish, then add the dab of solder.

Press the iron to the joint to be soldered. Make sure as much of the tip as possible is touching the joint. Make sure BOTH parts of the joint are being touched!

E. Dab on the solder

After a second or so, touch the end of the solder between the iron and the joint. If things go well, the solder should melt and be 'sucked into' the joint. If not, wait another second and try again. Keep adding more solder to the joint until you see it 'surfacing' at the edges of the joint.

DO NOT attempt to 'mush' the solder with the iron; DO NOT push the solder around with the iron. The solder must melt and flow into the joint!

F. Allow the joint to cool without moving

Remove the iron. Do NOT move the joint until you see the solder solidify. This is usually easy to see-the shiny, molten appearance of the solder turns more of a dull silver-gray.

You can accelerate this cooling by gently pressing the tip of a small screwdriver to the joint. This works because the screwdriver is being heated by the blob of solder, and as the screwdriver is heated, the solder is cooling (faster than if the heat just dissipates into the air).

• A commercial video (free for the downloading) showing how to solder turnouts using Fast Track brand jigs for PC-board tie turnouts is available at http://www.handlaidtrack.com/turnout-videos.php
• The demonstrator uses good technique (IMHO), but does use acid flux (which I do not recommend) to good effect, and does show the problems of corrosion if the acid is NOT neutralized! On wire, where you won't be able to wash off the acid, nor rinse with a baking soda solution, do NOT use acid flux!!
• Also shown is an example of trying to solder on a dirty surface, with the solder 'beading up' and not flowing properly.
• Some nice examples showing how solder should -flow- into a joint.
• During the 'how to solder trackwork' demo the demonstrator does tell you to do one thing, but demonstrates a slightly different technique: he starts to hold the tip of the iron on the base of the rail, but after a second slides it so it touches both the rail and the PC board tie-- necessary to heat both parts of the joint when there might be a slight gap between the 2!
• He does push the solder around a bit with the iron, but the joint is hot, the solder is liquid, and the solder does -flow- into the joint, and does not lie on the surface!
• The largest "Building Turnouts" video is 201 Megabytes, so guide yourself accordingly.

[edit] Soldering different things

[edit] A. Joining Electrical Wires

1. Since wires are covered with insulation, the first step is to strip 1/2 to 3/4 inch of insulation from each wire. Cleaning is not usually necessary, since the wire has been protected by the insulation.

2. Make a secure mechanical connection. There are several ways of joining the wires together:

a. Line up the stripped ends together and twist them together. This is similar to preparing the ends for using a wire nut.

b. Cross the stripped ends of two wires at 90 degrees, about half-way down the stripped end. Then wrap the free end of each wire around and around the remaining stripped portion of the -opposite- wire. This will result in a joint that is in line with the remaining lengths of the wires.

c. Remove 3/4" of insulation from the center of a length of wire. Strip the end of the joining wire, then wrap the entire stripped end around and around the stripped center section. This results in a "T" shaped conection.

3. Stabilize the joint so it won't move.

In some cases, if the joint is mechanically secure enough, you can place tension on the wires with the soldering iron itself.

4. Heat the joint.

5. Dab on the solder.

6. Allow the joint to cool without moving.

[edit] B. mounting scale rail on PC-board ties

• A commercial video (free for the downloading) showing how to solder turnouts using Fast Track brand jigs for PC-board tie turnouts is available at http://www.handlaidtrack.com/turnout-videos.php The demonstrator uses good technique (IMHO), but does use acid flux (which I do not recommend) to good effect, and does show the problems of corrosion if the acid is NOT neutralized! On wire, where you won't be able to wash off the acid, nor rinse with a baking soda solution, do NOT use acid flux!!
• The largest "Building Turnouts" video is 201 Megabytes, so guide yourself accordingly.

[edit] C. Adding decorative metal bits to brass locomotives

The best method of doing this is using a resistance soldering rig. They are not cheap, but will make life a lot less stressful.

Resistance soldering uses the metal body, and the part to be soldered on, to complete the circuit. A lead is clipped onto the body. The part to be soldered is held with a tool that is connected to the resistance soldering system's power supply. When the part is positioned correctly, the circuit is completed and energy flows. The metal of the body and the part at the point gets hot quickly, and can be quickly soldered into place. Stopping the energy flow allows the solder to freeze and complete the bond.

The advantage of this method is that the heating is local to the joint, and will not have enough time to spread to nearby solder joints. Using a hot iron runs the risk of melting more solder than planned, resulting in other details shifting or falling off.

For more information, see the American Beauty website here: American Beauty wesite

[edit] D. Soldering rail joiners to improve connectivity

This is easiest when done prior to installation, but not always possible. Soldering the joints improves conductivity and strengthens the mechanical joints. Curves laid with flextrack are easier, smoother, and less stressful when the sections are soldered together prior to forming and installation.

Requirements:

- Flux

- Chisel tip iron

- Light gauge solder

- assorted track laying tools

For soldering track, a chisel tip is best, as the rail will draw the heat out of the tip. The larger thermal mass of the chisel tip, and it's area, will minimize this. If it takes too long to complete the operation, any plastic ties near the joint may melt or deform. Cold solder joints, or joints with excessive amounts of solder may also result.

Using a light gauge solder allows more precise control over the amount applied to the joint.

Flextrack: trim away any ties, trim the rails square, and install the joiners. Then butt the second section against the first. If adjustments are needed, now is the time.

Once the two sections are mechanically aligned and connected, prepare the joint for soldering. Apply a small amount of rosin flux to the area of each joint, clean and tin the iron, apply the iron to the joint, and then touch the solder to the joint. The solder should flow and wick into the joint almost instantly. Remove the heat.

It may be easier to flip the track over and apply the heat to the bottom of the rails, directly on to the joiner.

Flextrack curves: leave, if possible, a straight section before finalizing the curve. It will be easier to trim, join, and solder. Once the joint is completed, continue to form the curve, adding additional sections as needed. Otherwise kinks and poorly butted joints can occur.

With previously installed track, apply rosin to the joints, touch a hot, tinned iron to the joint and add a little solder. Work from the outside of the rails, if possible.

For sectional track, soldering may be more difficult if the plastic ties surround the joint. A hot chisel tipped iron, flux, speed, and dexterity are the keys. Heatsinks should be used to prevent excessive heat from melting the plastic ties. Any metal device, such as aligator clips, that can be clipped onto the rails on either side of the joint should work. Damp paper towels also work. A narrow chisel tip may also improve access to the joint. Flux and a hot iron minimize the time needed to complete the joint, reducing the ties' exposure to heat.

After the joints have cooled, clean off any excess flux residue, and check for a smooth, proper joint. If there is excess solder, reheat the joint and draw off the excess. For a cold solder joint, reheat the joint to reflow the solder. Application of flux may also improve the joint during the reflow process.

Flux isn't a necessity, but it will make the task a lot easier and cleaner.

[edit] E. Adding power feeds to track

[edit] Shooting Troublesome Problems

• Symptom - Solder won't "take;" solder 'beading up' on the surface
  • Probable Cause 1 - Dirty Joint-- Grease or dirt present
    • Explanation - A dirty joint will usually cause smoking (ie overheated flux), darkening of the joint, and problems with solder flowing through the joint.
      • How To Fix Problem - Desolder and clean up the parts, then try again.

• Symptom - Solder won't "take;" solder 'beading up' on the surface;
  • Probable Cause 2 - Material not be suitable for soldering with lead/tin solder (eg aluminium).
    • Explanation - Aluminum won't solder with lead/tin solder
      • How To Fix Problem - ????

• Symptoms - Joint is crystalline or grainy-looking; solder 'beading up' on the surface; solder does not appear to have 'wet' the joint. These symptoms are generally classed as a "cold" solder joint.
  • Probable Cause 1 - The objects you wish to solder together have been moved before being allowed to cool
  • Probable Cause 2 - Not enough heat used during soldering to allow solder to flow into the joint via capillary action
    • Explanation 1 - The joint was not heated adequately due to too small an iron, or too large a joint
    • Explanation 2 - Wiggling a solder joint before it cools doesn't allow the solder to bond to the pieces being joined
      • How To Fix Problem - Sometimes re-heating the joint and adding more solder is sufficient; otherwise, desolder and clean up the parts, then try again. If the problem is due to a too-small iron or too-large parts, obtain a larger iron, soldering gun, or soldering torch to supply additional heat. Be careful of 'collateral damage;' ie melting of the surrounding materials.
      • Preventing joint movement problems - When solder goes from liquid to solid, it passes through a pasty state. That's when moving the joint ruins it. One solution is to use eutectic solder. It has a slightly different tin/lead ratio (63/37 instead of 60/40). It goes much more rapidly from liquid to solid and spends almost no time in the pasty state. Therefore, moving the joint is much less of a problem. (btw. If you ask for eutectic solder, the store clerk won't know what you're talking about. Just ask for 63/37.)
      • Re-working a joint - As a general rule, a joint can be remelted three times. After that, it's best to face the fact that the joint was not properly prepared. You have to remove all the solder and start over. You can remove solder with a 'solder sucker' or 'solder wick'. Generally, as long as the joint is shiny you have a good joint. A dull colour indicates trouble. If you re-melt a joint and the colour goes dull then the solder has probably become oxidized.

• Symptom - Solder joint forms a "spike"
  • Probable Cause - Overheating the joint and/or the flux.
    • Explanation - Flux can be burned away if heated too high
      • How To Fix Problem - Desolder and clean up the parts, then try again.

• Symptom - Large blobs of solder on joint
  • Probable Cause - Too much solder used
    • Explanation - Although the main problem with too much solder is unsightly appearance, excess solder can cause short circuits if it connects things it's not supposed to, or blocks trains from running down the rails!
      • How To Fix Problem - This is where the "solder sucker" comes into play. Make the solder sucker ready- if it's spring loaded, make it ready. If it's a squeeze syringe, squeeze it. Heat the joint until the solder turns shiny (ie-it's melted). With careful coordination, press the tip of the solder sucker into the molten solder and let it go! Much of the solder should disappear into the tool. You may have to poke a stiff wire into the business end of a solder sucker to unclog it from time to time. Make sure there is sufficient solder remaining in the joint!

• Symptom - strands of wires not embedded in solder; parts wiggle
  • Probable Cause - Not enough solder used
    • Explanation - Solder should surround all strands of wire; parts should be held firmly by the solder
      • How To Fix Problem - Sometimes re-heating the joint and adding more solder is sufficient; otherwise, desolder and clean up the parts, then try again.

• Symptom - Surrounding objects charred, melted, otherwise damaged.
  • Probable Cause - "Collateral Damage" due to soldering in too-tight quarters; poor control of business end of the iron
    • Explanation - The soldering iron is HOT! Plastics will melt, other materials will char.
      • How To Fix Problem - Repair damage. Be more careful in the future.

Notice that many of the problems are fixed in the same way - "Desolder and clean up the parts, then try again." This does cure a lot of problems; soldering is generally a reversible process, except for a thin coating of solder on the parts (they are 'tinned').

• Symptom -
  • Probable Cause -
    • Explanation -
      • How To Fix Problem -

[edit] External Links

• Another Soldering Guide