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Soldering A guide for Beginners

PLEASE NOTE - This article was previously published in the form of a 'Data Sheet' on the ol dweb site. It was written some time ago by Mr Brian Lewis, whilst he was the owner of C&L


Health & Safety Notice

Mains electricity, hot irons, raw acids and lead are not exactly user friendly. Hand washing is essential after handling any lead product. Some folk find Phosphoric acid fumes to be highly irritating to their nose and lungs. Inhaling Cadmium fumes is linked to throat cancers. All products should be treated with respect and used where possible, in well-ventilated rooms. Should you be unlucky enough to get burned, cool the affected area with cold water. There is a commercial product, an aerosol called ‘Burneze’ which is useful to have around. Apply a sterile plaster or dressing to guard against infection. If you have spilt flux onto your skin, was off with large amounts of water. Minor burns may respond to proprietary antiseptic creams. If in doubt, seek medical help. Soldering is looked upon by many folk as a ‘black art’. If you have problems, if ‘balling and spiking’ are frequent visitors to your soldered work, then read on. In simple terms, successful soldering is achieved by a combination of five essentials:

1. A soldering iron of sufficient wattage.
2. A bit of suitable size.
3. The right flux.
4. The right solder.
5. Clean metals to be soldered.

Ignore any one of the above and you risk creating ‘dry’ joints that fail.

Soldering Irons

It is unlikely that you will have a need for anything smaller than a 25-watt iron. This is ideal for electrical wiring and also for adding detail to previously soldered work. For general soldering a 50-75 watt iron is ideal. Both should be purchased with a range of bits. Do be aware that the wattage of an iron is no indicator of how quickly it will reach an operating temperature, or how quickly it will replace heat lost at the tip, when being used. These factors vary from manufacturer to manufacturer. One has a range of 150-200 watt irons that are eminently suitable for large soldering jobs. However, they take 25+ minutes to reach a working temperature. This is no problem as long as you know the characteristics of each iron you use.

Temperature Controlled Soldering Stations


These are excellent, especially the digital type, but please check the temperature range of any model you wish to purchase. With some models, the minimum temperature obtainable is 150 deg C. You really need one that goes down to 80 deg C. (Be aware also, that the accuracy of the digital readout will be plus or minus 6 Deg C). There still is a place for flame soldering and a ‘cook’s torch’ - a tiny blowlamp, with a small pencil flame, used by cooks for caramelising sugar, etc. is useful. Some large brass castings act as heat sinks and can be difficult to heat up sufficiently in order that the solder will flow. A small gas blowlamp is ideal for this purpose. Resistance soldering units are useful, but certainly not essential.

Soldering irons do not switch themselves on and off. They are continually generating heat. The tip absorbs this and when not in use, dissipates this heat into the surrounding air. Thus, when it is not being used, there is a gradual temperature increase above that normally used in the soldering process. This makes the tip more likely to corrode. Human nature being what it is, we all switch the iron on and leave it there for as long as we are at the workbench. In a perfect world, if you are not using the iron for say 10-15 minutes, it should be cleaned and switched off.

Soldering Iron Bits


The function of a soldering iron bit is to store heat and transfer this, via the tip, to the work to be soldered. Bits invariably have a solid copper core. A combination of heat, active solders and leaching of the copper by certain solders will eat this away in a short time. So, in order to protect the copper, bits are usually electroplated with an iron and then nickel coating. The barrel, but not the tip is then often plated with a chrome coating. The purpose of this latter coating is to keep the solder concentrated at the tip.

If you file the tip coatings away, the life of the bit will be seriously reduced. There are times when a tip of a specific size or shape is required. By all means adapt the tip to your requirements, but before doing so, check with the manufacturer’s catalogue. Most will offer at least half a dozen variables and one may suit your needs.

Good soldering is dependent on the fast transfer of heat from the heating element to the work surfaces. The monitoring factor controlling this is the size of the tip you are using. When it touches the work surfaces, the temperature of the tip reduces as heat dissipates into the work. This is why, when you are using too small a wattage iron with perhaps too small a diameter bit, the solder at first melts, but them partially solidifies again. Good soldering is difficult under these circumstances. The larger the tip, the more heat will be transferred. So, when selecting a bit, always choose one with the largest tip diameter you can work with.

Treatment for new Bits


Accept on faith that how you treat a new bit in the first few minutes after you switch the iron on, has a significant effect on subsequent life and performance. Most folk switch on and wait until the iron reaches it’s working temperature, before tinning. In many instances, this is too late - the heat has coated the bit with a difficult to remove oxide layer. Instead, dip your bit into our 188 Solder paint and wipe this into the surface with a rag. Now switch on. It will spit and smoke, but as it reaches normal working temperature it should be tinned and ready for use. If it is not completely tinned, follow the procedure outlined below, starting with paragraph 2.

Tinning your Iron and Keeping it Clean


Solder will not flow with a dirty iron. Flux residue and oxidized lead from the solder coat the tip in a gunge universally known as ‘clag’. This has to be removed, but this can be minimized by clean working practices. So here are a few house rules.

      1. C1040 - Carr’s 188 Solder Paint is an ideal tip cleaner. Simply plunge the tip into the container.Do be aware that some iron-coated bits can be difficult to tin - the solder just drops off in balls. You have to persevere - they will ‘season’ in time. However, see paragraph 4. Below for a solution to this problem.

      2. After you have made a solder joint, dip the tip of the bit into a 50/50 mixture of water and Cleaner Degreaser, then wipe it on a sponge that you have wetted in the same mixture. Now this is something that you have probably never heard of and folk will be reluctant to tell you about it because of the possible dangers of electrocution when plunging something connected to the mains into water. So it is just the tip and nothing more that you dip into the liquid. A water/alcohol mixture is in itself a flux, but is so gentle in action that it is not active enough for general use. However, this makes it ideal as a tip cleaner.

      3. If the bit is really filthy, wipe it with a copper pot scourer. This is obtainable from hardware stores, sometimes under the trade name ‘Goldilocks’. NB. It must be made of brass - brass coated steel pan scourers will not do. An alternative is a brass wire type suede brush.

      4. Be wary of tip cleaners. They tend to corrode the bit. However, we have recently reformulated our 188 deg Solder Paint. Our aim was to improve it by adding compounds that lowered the melting temperature of the flux. But there is an added bonus in that our Solder paint now makes an excellent tip cleaner - especially for new or hard to tin bits. Simply wash with the water/Cleaner Degreaser mixture, dip it into the Solder paint and rub the surplus off with a pan scrubber. Your bit should now be clean, tinned and ready for use.

      5. Clean and tin your iron immediately before switching it off.



What we call ‘solder’ is actually ‘soft solder’, normally having a melting point of below 400 deg, C. Above this temperature they are usually known as ‘brazing alloys’. Soldering involves the joining of metals by the addition of a filler metal, which is molten and free flowing at a temperature below that of the metals being joined. Solder can simply ‘fill and adhere’ - rather like gluing two pieces of glass together with silicone adhesive, where the glass and the silicone remain discrete materials. Or, it can ‘alloy’ - in the same way polystyrene cement will alloy Plastikard. The process of alloying aids ‘wetting’ and ‘flow’, two characteristics we will enlarge upon later. Obtaining the optimum degree of alloying is quite an exact science - too much and the metals can degrade. Zinc alloys - brasses,
gunmetal, phosphor bronze, nickel silver, etc. can suffer from, ‘Dezincification’. (These metals will also alloy with solders containing antimony to form brittle joints.) However, you are not likely to find solders and fluxes causing such problems, if you stick to Carr’s products, which are specifically ‘tailored’ for the hobbyist.

Solders we use are predominately tin/lead alloys, with the addition of small amounts of silver, 
antimony, cadmium and bismuth. They are detailed in BS 219:1977. Lead free solders consist almost entirely of tin, with the addition of a small amount of copper or silver. Solders are normally available as wire, bar and paste. In wire form, it is often ‘cored’ with a resin or acid based flux. If you go into a normal retail outlet and ask for a reel of solder, you will probably be offered 60/40 alloy - the 60/40 being 60% tin and 40% lead. This starts melting at 183 deg C and is fully molten at about 188 deg C. This narrow band (melting transition) is important, as it does not make for tidy work to have semi molten ‘puddles’ cooking away! They are specifically designed for soldering electrical joints. Modellers rarely use this and have preference for solders that are tailored to a specific use. Solders have an important secondary purpose, in that they aid the transfer of heat from the tip to the work. ‘Dry’ irons will not conduct heat as well as one that has been tinned.

Solders - Stick, Wire, Paint or Cream - Which to use?


This is an area where individual taste loom high over pure physics. With some items, 70 Deg C solder for example, there is no choice. It is only manufactured in blowpipe form. With others, you have a choice. 145 Deg C solder is available in stick, wire and cream. As a general guide, relate the type to the work. If you have fairly large items to solder, perhaps where you will need to use a large iron or perhaps a flame heating, you should use stick or wire solders. For delicate work and anything electronic, creams are the obvious choice. If you are assembling etched brass kits, creams can be your first choice. Although they may seem more expensive, the micro nozzle allows you to apply tiny amounts. So the job is neater and you do not have to spend time scraping off excess solder.



Some general points:

     1. They remove oxides from the metals to be joined and to prevent re-oxidation during the soldering process. This is to enable the molten solder to flow over the work and perform a bond.
     2. They will not clean dirt, oil & grease, etch resist, etc. For that you must use Cleaner Degreaser and/or Surface Conditioner.
     3. They carry heat into to area to be jointed. Heat transfer can be a problem. Experiment with a dry iron, no flux and the tip applied to only one surface. Touch the other surface with a piece of solder. See how much extra heat is required - heat that could well be destroying delicate electronic parts or un soldering nearby joints that have been soldered previously. Now try with a tinned iron, fluxed joints and heat applied to both surfaces. The difference is significant.
     4. Fluxes ‘creep’ between two items to be jointed, by virtue of capillary action. More importantly, molten solder will ‘follow’ this flux into the joint. Solder also ‘follows the heat’ of an iron. But solder is reluctant to flow where there is no flux.

Remember these facts, for understanding and using them is the key to successful soldering Fluxes are chemical compounds, variously based upon zinc chloride, phosphoric, hydrobromic and hydrochloric acids. They are usually called ‘active fluxes’ and the residues of the soldering process are corrosive. Resin based fluxes leave a hard deposit that are said to protect the joint. For this reason, they are widely used for electrical connections. Water-soluble organic fluxes and cored solders containing these leave residues that can be removed with warm water.

Never rely on the flux contained in cored solder alone - except perhaps for PCB work. Always use a separate flux. Please understand and accept that, although alloying does aid wetting and flow, it is the active elements in the fluxes which remove surface oxidation - an absolute prerequisite for successful soldering.

We strongly suggest you avoid all paste fluxes. There are doubts that you can remove paste flux residues completely and we all have seen lifting paintwork on locomotives - sometimes years after they have been painted. Paste flux is invariably used on normal domestic plumbing so, if you need convincing, go and look at the corrosion on some of your capillary joints.

The Carr’s range includes a wide variety of solders and fluxes. All are specifically chosen with the modeller in mind and some have been specially formulated to our requirements. For this reason, you can use our products with confidence. Some are specific to a single process, whilst others will perform several tasks perfectly. For this reason, you will see more than one suggested product for a specific task. It is all a matter of choice - and of course, what you have to hand…

Pre Treatment

It is important to understand that fluxes do not remove the need for basic surface preparation. That pristine looking piece of etched brass or nickel silver that you have just removed from the pack, is oxidized, coated with etch resist and is probably greasy as well. (Even the grease from your fingers will interfere with the soldering process). So basic cleaning must still be carried out. The full treatment sounds complicated, but can be accomplished in not much more time that it takes to read the next paragraph. Here’s what you do.

Take your pieces of metal and brush them with Surface Conditioner. Wash well with water and dry. Brush over with Cleaner Degreaser and wipe dry. Finally, brush over with Yellow Label Flux. There is no need to dry; simply removing the surplus will be OK. The residue will aid ‘wetting’. This is the ability of solders to spread thinly, which makes for cleaner work and stronger joints. (Solder in itself has little strength. As a rule of thumb, the thinnest joints are also the strongest. This treatment should be all you need to do. However, if the metals are rusty, corroded or perhaps painted over, then some physical cleaning may be necessary. A fibreglass brush is ideal for this purpose, but please remember that fibreglass particles are highly irritating to your skin and so the wearing of latex gloves is recommended. As an alternative, you can always use an abrasive rubber block - the type used as a track cleaner is suitable. Be sure to remove glass fibre or rubber particles before soldering your work.

What you certainly should not do is be tempted to apply heat for a longer period in an attempt to ‘burn off’ dirt and grease. It just does not work and can not only distort the work, but anneal and so change the physical properties of the metal. Sadly, that may not be apparent at the time, but will reveal itself by way of failed joints at a later date.

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