Soldering

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Summary: Soldering is a process whereby similar or dissimilar metals are joined using a soldering alloy that typically includes Tin with another metal such as Silver, Lead, Copper, Antimony, Bismuth, Indium or other alloys. Solder covers a temperature range of 60 - 445°C.

Most solders for electronic and other purposes are an alloy of lead (Pb) and tin (Sn). Some solders also contain Silver (Ag), and others are lead free.

The solder used for electrical work is a tin/lead alloy. Tin has a melting point of 232° Celsius, and lead melts at 325.5° C. When alloyed 60/40 (SnPb) the melting point is 188° C. The most common solder alloy used for electronic/electrical work is 63/37 SnPb, which is a eutectic solder, meaning its melt/freeze point is 183° C, it also has the lowest melting point found in Tin/Lead alloys.

Some solders also contain Silver (Ag), which is used to reduce erosion of silver plating, or for joints that have to withstand higher temperatures. Some silver solders are also used with integrated circuits during manufacturing to solder microprocessors and other ICs to the PCB. Silver solders require more heat, and make a stronger joint as well.

(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 Digital Command Control.

Contents

Solder

Solder is used to join two or more wires together for electrical connectivity, apply detail parts brass locomotives, and fasten rail to printed circuit board ties while hand-laying track

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.

In general, soldering consists of physically joining the pieces 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. The iron is NOT used to smear or push the solder around!

What is Solder

60-40 Solder.jpg

Solder is an alloy, usually tin (Sn) and lead (Pb) 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. Lead free solders have higher melting points.

Pure tin melts at 232°C while lead melts at 328°C . An alloy of 63% Tin and 37% Lead is Eutectic, which melts and freezes at 183°C, 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.

A 60Sn Alloy has a working range of 183-238°. There is a lower temperature alloy Sn43Pb43Bi14 has freeze/melt temperatures of 144-163°.

Some solders include silver, which have a much higher melting temperature, and some formulations include other metals. Only Tin/Lead solders should be used for electrical connections. Silver based solders are used for other purposes where strength is important, such as track work and specifically, soldering the point rails to the throwbar when making your own turnouts. The only application of silver solder for electrical purposes is where there will be a lot of heat, enough to melt 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.

A 60/40 or preferably 63/37 tin/lead solder should be used for electronics, and only rosin flux core solders. Solder is available in solid wire, or rosin (flux) core. Solid wire solder requires flux, or it will not work. A 60/40 solder is a little cheaper than 63/37. For large volume soldering, the cost may make enough of a difference. 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.

Rosin Core Solder, such as those alloys in the table below, and related fluxes, have a shelf life of three years from date of manufacture.

Solder Alloys for Electrical and Electronic Applications

Alloy Freeze/Melt, °C Eutectic Comments Sn Pb Ag
Sn60Pb40 183/190 No Sn60, ASTM60A, ASTM60B. Common in electronics, most popular leaded alloy for dipping. Low cost and good bonding properties. Used in both SMT and through-hole electronics. Rapidly dissolves gold and silver, not recommended for those. Slightly cheaper than Sn63Pb37, often used instead for cost reasons as the melting point difference is insignificant in practice. On slow cooling gives slightly duller joints than Sn63Pb37. 60 40 -
Sn63Pb37 183 Yes Sn63, ASTM63A, ASTM63B. Common in electronics; exceptional tinning and wetting properties, also good for stainless steel. One of the most common solders. Low cost and good bonding properties. Used in both SMT and through-hole electronics. Rapidly dissolves gold and silver, not recommended for those. Sn60Pb40 is slightly cheaper and is often used instead for cost reasons, as the melting point difference is insignificant in practice. On slow cooling gives slightly brighter joints than Sn60Pb40. 63 37 -
Pb92Sn5.5Ag2.5 286/301 No For higher-temperature applications. 5.5 92 2.5
Sn62Pb36Ag2 179 Yes Sn62. Common in electronics. The strongest tin-lead solder. Appearance identical to Sn60Pb40 or Sn63Pb37. Crystals of Ag3Sn may be seen growing from the solder. Extended heat treatment leads to formation of crystals of binary alloys. Silver content decreases solubility of silver, making the alloy suitable for soldering silver-metallized surfaces, e.g. SMD capacitors and other silver-metallized ceramics. Not recommended for gold. General-purpose. 62 36 2
Pb97.5Ag1.5Sn1 309 Yes Ag1.5, ASTM1.5S. High melting point, used for commutators, armatures, and initial solder joints where remelting when working on nearby joints is undesirable. Silver content reduces solubility of silver coatings in molten solder. Not recommended for gold. Standard PbAgSn eutectic solder, wide use in semiconductor assembly. Reducing protective atmosphere (e.g. 12% hydrogen) often used. High creep resistance, for use at both elevated and cryogenic temperatures. 1 97.5 1.5
See note above regarding shelf life of solders.

(Reduced version of the table found on Wikipedia)

Acid flux core solders, meant for other uses, must not be used. In time damage will occur on circuit boards and to electrical connections. When heated the acid becomes very aggressive and acidic fumes are created too. The acid will eat connections in electrical applications, making it unsuitable for any electrical work. The corrosive action continues long after the joint was soldered. It can be mitigated with cleaning to remove the flux, but it will still remain and slowly eat away at the metals.

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.

Flux

Basic Rule: Flux follows Heat, and Solder follows Flux.

Flux comes from the Latin fluxes, meaning flow. Flux is used as a chemical cleaning and flowing agent when joining metals.

The role of a flux in joining processes is typically dual: dissolving of the oxides on the metal surface, which facilitates wetting by molten metal, and acting as an oxygen barrier by coating the hot surface, preventing oxidation. In some applications molten flux also serves as a heat transfer medium, facilitating heating of the joint by the soldering tool or molten solder.

Why Use Flux?

Flux core in solder wire.

In soldering, flux serves a threefold purpose:

  1. Flux removes oxides from the surfaces to be soldered,
  2. Flux blocks oxygen thus preventing further oxidation, and
  3. Facilitates amalgamation, which improves the wetting characteristics of the liquid solder.

Some fluxes are corrosive, so the parts have to be cleaned with a damp sponge or other absorbent material after soldering to prevent acid damage later.

Several types of non-corrosive flux are used in soldering electronics. Flux should be cleaned off after soldering a joint.

Warning Regarding Flux Usage

Some decoder manufacturers include a warning instructing the decoder installer not to apply any flux during soldering.

The reason: Many modellers refuse to take advice and apply an acid flux. Such as plumbing flux from the tins found in the plumbing sections of hardware stores. Another culprit often praised online is the TIX brand flux. It contains zinc chloride, which is inappropriate for electrical work.

Be aware that many solder preparations which are available also contain acids. Solder pastes are an example. These solders, as well as acidic fluxes, are not recommended for use with electrical or electronic applications. The flux can never be completely removed nor neutralized by cleaning.

If in doubt ask for and read the Material Data Sheet. If the ingredients include zinc chloride, ammonium chloride, hydrochloric acid, phosphoric acid, citric acid, or hydrobromic acid, the flux is acidic and is not recommended for electrical work. These aggressive fluxes are meant for use with plumbing, steel, and other materials not normally used in electronics, and at higher temperatures.

Acid Flux

Do Not Use Acid Flux, That is for Plumbing!
A major decoder manufacturer stated that the most common reason for decoder failures is the use of acid based flux. Some decoder manufacturers actually include a warning regarding flux, and may not honour a warranty if any flux is used.

Acid fluxes used in plumbing and automotive applications are very aggressive, often containing hydrochloric acid. These fluxes will dissolve small wires over time, and their residues are conductive. Therefore, they are not recommended for electrical and electronic work. If the flux contains Ammonium Chloride or Zinc Chloride they are acidic and not appropriate for electrical work.

Rosin Flux

The correct flux for electrical work is Rosin Flux.

Many solders sold for electrical purposes are rosin-core. The solder wire has a core filled with rosin flux which is activated by the heat of the iron. For better results, apply additional flux. Rosin flux can be purchased in liquid and paste form, there are various devices to aid in application, available from a store that deals in electronic components. Solid wire solders (often used for plumbing) require the use of flux.

The flux within a rosin core solder will in time dry out and be less effective, hence the need for additional flux. Rosin Core Solder with less than 70% lead content has a shelf life of three years, from the date of manufacture, so it won't hurt to add some additional flux.
Flux also has a lifespan, check the manufacturer for details. Typically it is 3 years.

The application of a small amount of flux to the work prior to soldering will improve the results substantially, as well as speeding the process, which is important if you are soldering track with plastic ties. When heated the flux is activated and facilitates the wetting process, allowing the solder to quickly wick into the joint.

Brushes for applying flux are available in many hardware stores, often in packages of a dozen or more. Another application for flux brushes is sweeping ballast during application and bonding.

What is Rosin Flux?

The terms resin flux and rosin flux are ambiguous and somewhat interchangeable, with different vendors using different assignments. Generally, fluxes are labeled as rosin if the vehicle they are based on is primarily natural rosin. Some manufactures reserve the "rosin" designation for military fluxes based on rosin (R, RMA and RA compositions) and label others as "resin".

Rosin has good flux properties. A mixture of organic acids (resin acids, predominantly abietic acid, with pimaric acid, isopimaric acid, neoabietic acid, dihydroabietic acid, and dehydroabietic acid), rosin is a glassy solid, virtually nonreactive and noncorrosive at normal temperature, but liquid, ionic and mildly reactive to metal oxides at molten state. Rosin tends to soften between 60-70 °C and is fully fluid at around 120 °C; molten rosin is weakly acidic and is able to dissolve thinner layers of surface oxides from copper without further additives. For heavier surface contamination or improved process speed, additional activators can be added.

There are three types of rosin: gum rosin (from pine tree oleoresin), wood rosin (obtained by extraction of tree stumps), and tall oil rosin (obtained from tall oil, a byproduct of kraft paper process). Gum rosin has a milder odor and lower tendency to crystallize from solutions than wood rosin, and is therefore preferred for flux applications. Tall oil rosin finds increased use due to its higher thermal stability and therefore lower tendency to form insoluble thermal decomposition residues. The composition and quality of rosin differs by the tree type, and also by location and even by year. In Europe, rosin for fluxes is usually obtained from a specific type of Portuguese pine, in North America a North Carolina variant is used.

(From Wikipedia)

Flux Removal

After soldering, use flux remover and a small brush to clean the area. Flux remover is available in various packages, including aerosols. This is important with track, as the wheels will pick up the sticky flux residues and spread them everywhere, resulting in intermittent operation, especially at joints that were soldered. The residues will attract and hold dust, moisture, and other contaminants.

Always remove the flux after soldering on a PCB. The residue can become conductive over time. In small circuits, this can lead to failures due to components being shorted by the flux residues.

A number of commercial preparations are available for removing flux. Isopropyl alcohol (IPA) and water will also work. Mixtures of IPA and acetone can also be effective. A quick search on the internet will yield many possibilities and processes.

Hazards

Safety with Solder and Flux

Acid flux types (not used in electronics) may contain hydrochloric acid, zinc chloride or ammonium chloride, which are harmful to humans. Therefore, acid flux should be handled with gloves and goggles, and used with adequate ventilation.

Prolonged exposure to rosin fumes released during soldering can cause occupational asthma (formerly called colophony disease in this context) in sensitive individuals, although it is not known which component of the fumes causes the problem.

While molten solder has low tendency to adhere to organic materials, molten fluxes, especially of the resin/rosin type, adhere well to fingers. A mass of hot sticky flux can transfer more heat to skin and cause more serious burns than a comparable particle of non-adhering molten metal, which can be quickly shaken off. In this regard, molten flux is similar to molten hot glue. (From Wikipedia)

Warning

WARNING! Solder is molten metal. Soldering irons are even hotter to melt the solder. 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 jewellery beforehand.

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.

Preparations for Soldering

For soldering to be effective, everything has to be clean.

The work (the materials to be joined) should be clean and free of corrosion, paint, oils, etc. Rosin flux will clean the work when activated by heat, but can only do so much. Just like glue, solder can't stick to a dirty surface. If the solder balls up, the surface needs to be cleaned.

The work can be cleaned using a Dremel tool with a wire brush, steel wool, sandpaper, and/or a cleaning solvent, as required.

Clean and tin the tip of the iron.

The tip can be cleaned using a moistened sponge (use distilled water if available), a rag, or a paper towel. Tin the tip with some solder, the dross should float on the solder, then wipe clean. Wet the tip with a little more solder and it is ready for use.

Tip cleaners made from brass shavings are also available, which can scrap the dross off the tip. The brass is soft enough to avoid damage to the tip. Never use files or sandpaper to clean the tip, as that will remove the iron plating. Once the copper underneath is exposed, the solder will erode the tip very quickly. Remember, the process of soldering involves alloying several metals together.

Wire-Cage Soldering Iron Stand

(With sponge or similar device for cleaning the tip of excess solder or grit). You can also use a cotton rag or paper towels to clean the tip. If you do use the sponge, it should be moistened with distilled water. Too much water cools the tip during cleaning.

Miscellaneous

  1. Solder sucker (for desoldering)
  2. Unsoldering braid (for desoldering)
  3. Heat sink clamps (to draw heat away from heat sensitive components)
  4. #Specially made
  5. #Hemostats
  6. #Alligator clips

Vinyl electrical tape

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.


Soldering

Tools and Supplies Required for Electrical and Model Work

Soldering Station Weller 2.jpeg

Types of Soldering Irons

An ESD safe soldering iron is recommended to avoid damage to electronic devices from current leaking from the iron or static discharge.

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 created 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.
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. You can adjust the heat, and often the tips are interchangeable, allowing the best combination of tip and temperature.
Resistance Soldering Rig
Resistance soldering rigs are expensive. But they do work, and they do work well. They do not have a hot tip either.

Resistance soldering works by connecting one side of the work to the power supply, and the piece to be soldered is usually held with a pair of tweezers in place of the iron. A solder paste is usually employed in the process. The piece held by the tweezers is then positioned where it is to be soldered, and a foot-switch energizes the system. A high current flows between the two pieces, which results in a very localized hot spot. The solder melts and wicks into the joint as the work is pressed together then operator releases the foot-switch and the solder freezes. This process is excellent for work on brass models, as the heat is intense but localized, and happens so quickly that the rest of the workpiece doesn't get hot. Trying to do this with a conventional iron would result in a large amount of heat being sunk by the work, causing other nearby solder joints to melt or soften in the process. You would also need a very big iron to transfer the heat quickly, which isn't easy to do or position correctly on a model.

Resistance soldering can also be used for track.

Resistance soldering stations are expensive, but if you do a lot of work with brass or metal models, they are a worthwhile tool. They can be purchased from companies such as American Beauty Tools, or MicroMart, which offers a model made by American Beauty.

"Cold Heat" (Battery Powered)
Butane Torch (Portable)

Exactly as the name implies. It can be torch with an open flame, or a metal tip indirectly heated by the flame.

There also are soldering irons which are heated in a small gas fuelled furnace, and then used to heat the work. You will probably never see one of those.

Digital Command Control Decoders and Soldering

This symbol means the device is static sensitive and precautions must be taken during handling.
This symbol means ESD Protected. A soldering station with this symbol is safe for soldering electronics.

It is recommended that an ESD (Electrostatic Discharge) safe iron be used when soldering DCC decoders during installation. Many soldering stations are ESD safe, ask the vendor to verify at the time of purchase or consult the manufacturer. Older, non-ESD safe irons can actually have significant voltages present on the tip, which can damage electronics.

ESD can destroy the audio or motor control circuit during the soldering operation.

An ESD safe iron is designed to be used to solder electronics, especially static sensitive components. Most electronic devices can be damaged by a static discharge, or even destroyed outright. Even after a shock the device may still work, but hours of life were lost because of the discharge. To minimize the possibility, an ESD safe iron with a wrist strap and mat keeps the operator and all the components at the same potential, minimizing the chance of ESD occurring.

Additional ESD Precautions

In addition to an ESD Safe soldering station, a wrist strap and an antistatic mat should be used on the workbench. This will minimize the possibility of ESD destroying or damaging something. DCC Decoder manufacturers report that many of the failures seen during an install are a result of ESD.

Always follow the instructions for the mat and wrist strap (you can also get heel straps to ground you) with respect to their use and grounding. The mat may need an antistatic treatment as well. Keep in mind that dry, cool weather is very advantageous to static electricity production. Dry winter weather is all you need to charge yourself up to tens of thousands of volts while walking across a carpet. Synthetic fabrics also generate static.

Minimizing static charges is a good idea with Digital Command Control Electronics.

Soldering Iron Tips

Soldering iron tips are usually copper, plated with base metals (such as iron) which must be "tinned" or "wetted" before use to encourage heat transfer to the junction.

Never file a soldering iron tip, you will remove the plating, causing the tip to oxidize, which prevents it from transferring heat properly to the junction being soldered. Also, exposing the underlying copper damages the tip, as the solder alloys with the copper and in time the tip is destroyed. The copper is eaten away or eroded by the process, making the tip useless as you cannot get a good contact surface with the work. 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 into.

Pencil Tip

Useful for soldering in tight areas, such as leads onto a PCB. Not very good for large items.

Chisel

Larger tips have more thermal mass, so choose accordingly. Too big is not good either. Chisel tips are useful for track work, etc. Their larger thermal mass takes longer to heat, but also has more energy to transfer to the work. When using with track to solder feeders or construct turnouts, it will allow you to complete the task quickly. A hot iron with a chisel tip that maintains the temperature will do less damage than one with a small tip which takes longer to make the joint.

Solder

Rosin core, NEVER acid core!

Over time, the rosin used in the manufacture of rosin core solder loses effectiveness. Solder which dates from the Soviet era, or better, the Apollo Program, is not as effective as the rosin will have dried out, and reacted with the solder. The shelf life of solder is only several years from date of manufacture.

If the solder isn't working well, age would be the reason. Thus, additional flux goes a long way to solving any problems. Fresh solder may also be a solution.

Wire type solders are available in many gauges, from heavy to very light (thin) wire. Lighter gauge solders are useful for delicate work, as they allow better control of the amount of solder applied in the process of making the joint.

Flux

Rosin, NEVER Acid Flux! Acid flux is for plumbing!

Additional flux will make the job go easier, and it is best not to rely on the rosin core of the solder. The flux will dry out over time, and solder often does not have enough flux for the job at hand. Plumbing solders typically are solid wire solders, unlike solders sold for electronics. Small gauge solders are useful for precise work, and they usually are not large enough to accomodate the flux core found in heavier gauge solders sold of electronic work.

A dispenser bottle or a syringe is useful for applying liquid rosin flux. Paste versions are also available. A small amount goes a long way.

The rosin core in solder (or the paste/liquid 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 the 95/5 lead free acid core solder often found in hardware stores!

Flux and Lead Free Solder

Flux is corrosive, that is the way it works. When heated, it is activated and begins cleaning the surfaces to be soldered.

If you are using lead free solder, chose a flux formulated for that type of solder. Flux meant for tin/lead solder is a little too aggressive for this type of solder alloy.

Preparing a New Soldering Iron

  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.
  4. Remember to clean and dry the sponge when done soldering
  5. If possible, use distilled water with the sponge.

"Tin" the iron

  1. Dab solder on the tip until the solder 'sticks.' Coat the tip evenly. Wipe off any excess on the sponge.
  2. 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.
  3. If you are using an adjustable base, adjust...

Renovating an Old Iron

Remove 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.

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!

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.

Types of Soldering

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

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 more like a wood burning tool.

Soldering guns are not for precision work.

HowToSolder.SolderingIron.gif

Resistance soldering

The workpiece is connected to the power supply, usually via an alligator clip.

Often the system has a tweezer or plier type of "iron". With this, the part to be soldered is grasped with the hand-piece, positioned, and power is applied, usually via a foot switch. The joint between the two pieces gets hot, a small amount of solder is applied, and power is disconnected, allowing the solder to freeze. The process is extremely quick.

For track work, a pencil like tool can be used in much the same manner as an iron. Touch the probe to the joint, close the circuit with the foot switch, apply solder, open the circuit and the task is complete.

How To Solder (Using an Iron)

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

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.
Soldering feeds to weathered track can be difficult. The rails must be clean and all surface coating removed to bare metal. Flux will also be very useful in attaining a proper soldered joint.

Physically mate the parts.

    • The joint should be strong enough (if possible) to stay together without solder. Solder is not intended to provide a lot of mechanical strength!
  • Stabilize the work so it won't move during soldering.
    • 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.
  • If you will be using flux, this is the time to brush some onto the work.
  • Heat the work
    • Make sure the iron is hot. Unwind a few inches of solder from the spool. Don't cut it off, just unwind a bit! Tin, using fresh solder, the tip of the iron. Make sure the tip is 'shiny' with molten solder. You may need to first wipe the tip to clean off the dross, then add solder. The tinning process aids in heat transfer by using liquid solder to increase the surface area and improves heat transfer from the iron.
  • Apply the iron to the joint. Make sure as much of the iron's surface (part of the reason for tinning the iron) as possible is touching the joint. Make sure BOTH parts of the joint are heated!
  • Solder: To the Work, Not the Iron!
    • After a second or so of heating, apply solder to the work. If things go well, the solder should melt and flow into the joint. Keep adding solder to the joint until you see it 'surfacing' at the edges of the joint. A small amount of solder is all that is needed. Two seconds is about the maximum time you should need to complete this process.

If there is no wetting action or the solder will not melt and flow, there is a problem. Your iron may not be hot enough or there is corrosion preventing the solder from wetting and flowing into the joint. Clean the joint, apply flux, and try again.

    • DO NOT apply solder to the iron; DO NOT push the solder around with the iron. The solder must melt and flow into the joint!
  • Allow the solder to cool (freeze) by removing the heat source without disturbing the work. If the solder is still molten you may end up with a misaligned part or other issues.
    • 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 absorbing the energy, and as the screwdriver is heated, the solder is cools (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 HandLaidTrack The demonstrator has good technique, but does use acid flux (not recommended) 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, so 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. Other examples show 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 them. 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.

Soldering Different Things

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:
    1. Line up the stripped ends together and twist them together. This is similar to preparing the ends for using a wire nut.
      HowToSolder.Twisted.gif
    2. 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.
      HowToSolder.Electrical.StraightLine.gif
    3. 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 connection.
      HowToSolder.Electrical.Tee.gif
  3. Stabilize the joint so it won't move.
    1. 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. Apply solder.
  6. Allow the joint to cool without moving.

Mounting 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 HandLaidTrack 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.

A chisel tip works best. Clean the ties and the rail. Apply a small amount of flux. Position the iron so it can heat the rail and the tie. Tinning the iron beforehand allows the solder to form a bridge to conduct heat to the work. The flux should boil, and then apply a little solder, from the opposite side. It should melt and flow under the rail towards the heat source. Remove the iron and let the solder freeze.

Properly done, there should be a small amount of solder on either side of the rail, flowing up onto the base of the rail. The entire process should take no more than two seconds.

Resistance soldering rigs are great for trackwork.

Adding Details 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

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.

TrackJoint.jpg

Requirements:

  1. Flux
  2. Chisel tip iron
  3. Light gauge solder
  4. 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.

Adding Power Feeds to Track

Similar to soldering the joints, except you will be using a light gauge wire to connect the rail to your power bus This is usually done after the track is laid, from the bottom of the rail. When done in the gauge, care must be taken to avoid causing a lump which will touch the flanges and possibly derail the truck. The secret is to plan your attack so the wire is hidden as best as possible with as little evidence of the connection as possible.

Problem Solving

Solder won't "Take;" Solder 'Beading Up' on the Surface

This is what wetting is. The solder will alloy with the metal and form a bond. If the solder will not wet, the result is solder which can be removed completely using a tool.

Oil, grease or dirt present
A dirty joint will usually cause smoking (i.e. overheated flux), darkening of the joint, and problems with solder flowing through the joint.
Desolder, clean up the parts, try again.
Material not be suitable for soldering with lead/tin solder (e.g. aluminium).
Aluminum won't solder with lead/tin solder

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 applied to allow solder to melt and flow into the joint via capillary action
Explanation 1 - Wiggling a solder joint before it freezes doesn't allow the solder to bond to the pieces being joined
Explanation 2 - The joint was not heated adequately due to too small an iron, or too large a joint
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;' i.e. melting of the surrounding materials. A soldering iron should be at least 60W, or use a temperature controlled station and increase the heat/change tips.
When solder changes from liquid to solid, it passes through a plastic 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 rapidly from liquid to solid and spends almost no time in the plastic 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.)
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.

Solder Forms a "Spike"

Probable Cause - Overheating the joint and/or the flux.
Flux can be burned away if heated too high
Desolder and clean the parts, then try again.

Large Blobs of Solder on Joint

Too much solder!
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!
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 (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!

Strands of Wire not Embedded in Solder; Parts Loose

Not enough solder used.
Solder should surround all strands of wire; parts should be held firmly by the solder, sometimes re-heating the joint and adding more solder is sufficient; otherwise, desolder and clean up the parts, then try again.

To tin a wire, start in the middle, add a little solder and move the iron toward the insulation, then move toward the end. You should be able to identify strands of wire when properly done.

Surrounding Objects Charred, Melted, or Damaged

Probable Cause - "Collateral Damage" due to soldering in too-tight quarters; poor control of business end of the iron.
  1. Iron is too hot, or tip is too large. Reduce temperature and/or replace the tip.
  2. Iron isn't hot enough, or tip is too small.
    1. If it is not hot enough to make the joint within two seconds, continued application of heat will allow the energy to travel further into the work (heatsink), possibly melting or damaging something. At the joint it just doesn't get hot enough to melt solder effectively.
The soldering iron is HOT! Plastics will melt, other materials will char.
Be more careful in the future.
Make changes to the tip and temperature used to minimize the time needed to heat and solder the work.

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 now 'tinned').

External Links

Additional Reading on Soldering:

PACE Electronics Basic Soldering Course on YouTube: https://youtu.be/vIT4ra6Mo0s?list=PL926EC0F1F93C1837 Soldering Pt 1

Look on YouTube for the SolderingGuru channel for more soldering information.

Kester, shelf life of various solder products, Datasheet