How to Solder #101

Never used a soldering iron? Does the art of soldering seem a bit of a mystery to you? Have you tried your hand at soldering and found it difficult to produce results you’re happy with? Do you feel your soldering technique could do with some improvement? If you answered any of the above questions in the affirmative, you’re in the right place!

It is widely known in the hardware hacking community that you simply cannot take over the world if you don’t know how make connections. Connections which are both electrically and physically sound, that is. Welcome to Soldering 101 – here you will learn the basics of soldering, allowing you to make reliable electrical connections for all those projects you have in mind or in progress.


Items Required

  • Soldering Iron
  • Solder
  • Damp sponge/Tip cleaner
  • Scrap wire to practise soldering
  • Cardboard or newspaper to protect your work surface
  • Heat shrink
  • Heat gun or gas stove to shrink the heat shrink


Preparation

Clear and prepare your workspace – keep in mind that you will be wielding an implement which will be reaching over three hundred degrees Celsius. Remove anything that could be accidentally melted or could result in the application of such temperatures to any unintended surfaces (like human skin – it hurts!). Place down an old newspaper or cardboard, something with a bit of thickness to it in order to protect your work surface by insulating it from the heat of any molten solder which could fall from your connection during the process. Though it seems counter intuitive what with paper and cardboard being relatively flammable, the temperature you will be soldering with is well below the ignition point of these materials.

Prepare your soldering iron. Power it up – you’ll know you’re ready to go when the tip of your iron can melt your solder! Ensure that your tip cleaning sponge is wet – not just damp, but wet. ‘Tin’ your soldering iron tip – the process of ‘tinning’ in soldering is applying a layer of fresh solder. This is done by feeding solder onto the hot tip of your iron – you should notice a small amount of smoke followed by a nice shiny-looking soldering iron tip. Your soldering iron tip should always be clean and shiny for successful soldering.

If you cannot complete step three successfully, a set of ‘helping hands’ from your local electrical supplier may be the next best thing. During soldering, the items to be connected need to be held in contact long enough for the solder to dry – and this is more often that not easier said than done without something to hold it in place for you.


Procedure

Strip 2-4mm of insulation from the two ends of wire you wish to join. Once the insulation has been stripped, twist the conductor strands together. This prevents fraying during the soldering process.

Tin each end. This is done by squashing some solder between the wire you wish to tin and the tip of your soldering iron. Successful tinning results in a fresh, shiny appearance. You should also notice that once the solder is dry, the once flexible stranded conductor behaves more like solid wire where you have tinned it.

It is important to ensure your connection is electrically insulated to prevent any unwanted electron movement shenanigans. For a neat, secure, and professional look, use heat shrink tubing. Heat shrink is a type of electrical insulator which shrinks in diameter when heat is applied, holding it in place over bare electrical connections. The heat shrink I am using has a 2:1 shrink ratio, which means it will end up half the diameter it started with when fully shrunk. Choosing the correct diameter heat shrink for your connection is simple – it needs to be large enough to slide over the wire(s) you wish to join, but small enough so that before it shrinks to half its size, it has a firm grip on the connection!  Cut the heat shrink to a length which is longer than the length of your connection by about 4-6 times. This allows you to leave 2-3 times the length of your connection worth of heat shrink on either side of the connection, so that a seal is formed between the insulation of the wire and the heat shrink.

Slide your heat shrink over one side of the connection BEFORE soldering the two together. This is a great habit to develop for situations that would require unsoldering of the connection if the heat shrink is not slid into position before joining. This can be due to the other end of the wires being terminated with connectors that are too large to fit the appropriately sized heat shrink over, or in this particular situation where the wire is to be soldered into a loop for demonstration purposes, there is no way to slide the heat shrink into position once the ends are joined!

Time to make the join! At this stage you should have:

  • Two nicely tinned and shiny wire ends to join.
  • Heat shrink slid over one end, far enough back to prevent premature shrinking from the heat of the soldering process.
  • A nice clean, shiny soldering iron tip. If your tip is dull or covered in browny-blackish yuck, quickly and gently wipe tip through your wet sponge. Melt some fresh solder onto your tip if necessary to get that clean, shiny look.

Place the two wire ends to be joined in contact with each other. It is often easier to set up one end in a stationery position, while holding the other end in one hand, and your soldering iron in the other. This allows you to position the two ends while you apply heat to them both with the soldering iron. You should notice the point at which the solder on both ends melts and joins the two ends – this is the trickiest part! Remove the soldering iron tip from the connection the moment you notice both ends melt together, but you must hold the two ends in position until the solder hardens! If you observe closely you will notice the surface of the solder change slightly as it hardens. For connections this size allowing 5-10 seconds is enough to ensure to solder has hardened. For much larger connections this process may take a longer period of time – learn to spot that subtle visual change when solder changes from molten to solid!

Once you have made a satisfactory join (don’t be afraid to play around and practice until you get the join to your liking), it is time to install the heat shrink. The heat shrink is to be positioned such that its centre aligned with the centre of the join. To begin with, you may find the centring technique pictured useful.

Once the heat shrink is in position, fire up your heat gun (a hairdryer is inconveniently not hot enough).  Pictured you will see a gas-powered flameless heat gun which is ideal for shrinking heat shrink.

A direct flame is too hot and will damage the heat shrink, while a hair dryer does not get it hot enough to begin shrinking. While holding the connection clear of anything that could melt (think plastics), bring your heat gun closer to the heat shrink slowly until you notice it beginning to shrink. Maintain this distance while rotating your connection or moving your heat gun around your connection to ensure complete shrinkage. If you do not have access to a heat gun but have a gas stove, you’re in luck! Ignite your smallest burner and turn it down to the lowest setting. From a height of approximately 300mm slowly lower your connection toward the burner until you notice shrinking. Once shrinking begins, maintain this distance from the burner while slowly rotating your join in order to ensure complete shrinkage. You should notice the shape of the insulation and wire join start to appear through the heat shrink as it clings snugly to your connection.

And there you have it! A nice, neat, mechanically and electrically sound connection! …or is it? How do we know? We must test it, of course! Try tugging your connection apart firmly – it should hold just fine if done correctly – if not, you’re going to have to try again. If your connection can’t stand up to a controlled tug, it is a failure waiting to happen! Be thankful that you have found this flaw in your work so early allowing you to rectify it! The connection should also be electrically conductive. A simply continuity test with a multimeter is a nice way of confirming this.


Wrap it up....

And there you have it! A nice, neat, mechanically and electrically sound connection! …or is it? How do we know? We must test it, of course! Try tugging your connection apart firmly – it should hold just fine if done correctly – if not, you’re going to have to try again. If your connection can’t stand up to a controlled tug, it is a failure waiting to happen! Be thankful that you have found this flaw in your work so early allowing you to rectify it! The connection should also be electrically conductive. A simply continuity test with a multimeter is a nice way of confirming this.

Effective soldering is a wonderfully useful skill to possess in the electrical world – be sure to dedicate some time preparing connections like the one described in this tutorial until you are familiar and competent with the process, selecting some scrap wire and cutting it in order to join it again is great practice.

Be sure to ask any questions you may have in the comments section!