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 metals. Solder covers a temperature range of 60 - 445°C.
Soldering isn't hard, so don't be intimidated. With a bit of practice, anyone can make complete a solid solder joint. There are some very technical aspects within this article, but don't let that put you off.
- Main article: Soldering/Solder
Solder comes in different forms, thicknesses, and materials. However, they all have the same goal: join metals together to form physical and electrical connections using high heat. The solder article goes into details all this. It's important to note that proper selection of solder and flux is important to protect your items from excessive corrosion.
- Main article: Soldering/Flux
Flux comes from the Latin fluxes, meaning flow. Flux is used as a chemical cleaning and flowing agent when joining metals. This assists solder in adhering properly to the materials being soldered. Flux also helps remove previous oxidization, and prevent additional oxidation during the soldering process.
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 skin. A mass of hot sticky flux can transfer more heat to the skin and cause 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! 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 is recommended to remove all jewellery beforehand.
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 jewelry before working, remove them now if you have not - 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. If you are having no success, this is often the cause, aside from metals which are incompatible with soldering.
The work (the materials to be joined) must 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.
Read the Electrostatic Discharge page for further precautions when soldering DCC decoders and track.
How Much Heat is Needed?
That depends on a number of factors.
- What is being soldered
- The size of the work
The iron must be much hotter than the melt point of the solder. When the iron is applied to the work, the heat energy must be transferred to the work to melt the solder. A hot iron will have enough energy that after losing energy to the work, it will still be hot enough to melt the solder.
If the iron is not hot enough:
- It will take too long to heat the work to the required temperature
- A cold solder joint may occur
- Damage to surrounding materials, as the heat travels over an extended period of time.
Rule of Thumb: It should take no more than a few seconds to complete the joint.
Digital Command Control Decoders and Soldering
Read the page on ESD for more information.
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.
An ESD safe iron is designed for soldering electronics, especially static sensitive components.
ESD can destroy the audio or motor control circuit during the soldering operation. A hard failure is easy to spot, latent damage from ESD is not.
Rosin core, NEVER acid core!
Rosin core Solder manufactured during the Apollo Program or the Soviet era is not effective as the rosin will have reacted with the solder's lead content. The shelf life of solder is only several years from date of manufacture. Since many modellers are not doing large volumes of soldering on a yearly basis, the majority will be using solders which are well past their best before dates.
If the solder is not working, age would be the reason. Thus, additional flux goes a long way to solving 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. It is also available in various alloys. For DCC and electrical work the preferred alloy is a 63/37 tin/lead solder. A 60/40 alloy will also work. Purchase a rosin core solder for electrical work.
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 accommodate the flux core found in heavier gauge solders sold for electronic work.
Additional Reading on Soldering:
- Another Soldering Guide
- Wikipedia article on Flux
- Soldering on the Wikipedia
- Brazing and Soldering Category on Wikipedia
Look on YouTube for the SolderingGuru channel for more soldering information.
Kester, shelf life of various solder products, Datasheet
The following videos may be helpful when soldering: