by George Szymanski, DU1GM
Now that there are a number of construction articles on the PARA website which require soldering, I thought it might be useful to collate a few hints and tips from the internet on how to solder and de-solder.
Soldering is a skill and will develop as you build your own electronic projects.
Soldering irons of various wattages, including gas powered types for those heavy duty or outdoor jobs. A good iron to have is a temperature controlled one with a knob to set the required temperature. This is much more flexible and the temperature is shown on a digital display.
De-soldering tool and de-soldering braid.
Magnifying glass - the type with a built in circular fluorescent lamp. Head mounted binocular types are good too.
Solder. NEVER use acid cored solder; this will corrode printed circuits and component leads. Use a rosin cored solder with a thickness of 0.75mm for fine electronic work and larger diameters for soldering bigger wires etc. Be careful not to overload a joint with solder, so the thinner solders are better in this respect. Solder is an alloy (mixture) of tin and lead, typically 60% tin and 40% lead. It melts at a temperature of about 200°C. Coating a surface with solder is called 'tinning' because of the tin content of solder.
Solder for electronics use contains tiny cores of flux, like the wires inside a mains flex. The flux is corrosive, like an acid, and it cleans the metal surfaces as the solder melts. This is why you must melt the solder actually on the joint, not on the iron tip. Without flux most joints would fail because metals quickly oxidize and the solder itself will not flow properly onto a dirty, oxidized, metal surface.
Protection and safety considerations: Try to avoid breathing the solder fumes as they are irritating to the air passages. Be careful of hot solder splashes which will burn your skin instantly. Try to clean the tip using a wet sponge instead of flicking off the excess solder! Eye protection is also advised. Never touch the tip of the iron as it is very hot! You will come in to contact with it at some time however! Also, return the iron to a metal stand with a protective spring cage. NEVER leave it lying on a work bench or dangling over the side. YOU WILL PUT YOUR HAND ON IT! Be careful of touching the iron power cable with the tip as it will melt the plastic and may burn through to the power wires. The iron should have a heat proof flex to avoid this sort of problem. Finally, when you are finished soldering, wash your hands carefully as solder contains lead which is a poisonous metal.
If you have a brand new soldering iron, the first thing you need to do is to heat it up and then "tin" the soldering bit. This will prevent the copper from wasting away too quickly. Before each time you solder a component to the board, clean the hot tip using a wet sponge or cloth to remove black deposits, then add a little solder to "tin" the tip and this will ensure a good heat transfer to the component lead and track. Heat the component lead for a couple of seconds then apply the solder to the lead and track so that the solder flows cleanly onto them. Remove the iron but make sure you do not move the component lead before the solder has hardened. A good joint will be clean and shiny. If you have made a poor connection, or a "cold" joint it will look grey and grainy. You will need to remove the solder by heating the joint and use the solder sucker to remove the old solder and start again. Practice makes perfect and you will soon find that soldering is second nature, a bit like riding a bike!
Of prime importance is the cleaning of component leads and printed circuit board copper tracks before applying solder. Corroded leads and tracks will not solder so well despite the effect of the solder flux. Clean the copper pcb track with a fine grade of emery paper until it shines. Similarly clean the component leads you want to solder so that they also shine.
If you are soldering onto a large area of copper, you will find that a 15W iron will not do the job because all the heat will be "sucked" into the copper and the bit will cool too much. You will then need to use a higher wattage iron, such as 30W or even up to 75W. Soldering guns can provide even more heat but you should be careful of using these as they work by passing a large current through a loop of copper used as the soldering tip. Stray voltages may be induced into the circuit you are soldering. Solder guns are fine for joining copper pcb's together to make a small box or shield sections.
If you are soldering delicate components you should use a clip on heat sink to divert the heat on the component side of the pcb while you are solder on the track side. A crocodile clip can be used very successfully as a heat sink and is much cheaper than a custom designed tool. You could solder a couple of small pieces of flat copper onto the jaws to provide better thermal conductivity. A pair of small long nose pliers can also be used with an elastic band around the handle to hold the jaws shut on the component lead.
Some components require special care when soldering. Many must be placed the correct way round and a few are easily damaged by the heat from soldering. Appropriate warnings are given in the table below, together with other advice which may be useful when soldering.
The Components list in the table has embedded url's which will lead you to more interesting information about each type of component.
For most projects it is best to put the components onto the board in the following order:
|Components||Pictures||Reminders and Warnings|
Connect the correct way
round by making sure the notch is at the correct end.
|2.||Resistors||No special precautions are needed with resistors.|
Small value capacitors
(usually less than 1µF)
|These may be connected
either way round.
Take care with polystyrene capacitors because they are easily damaged by heat.
(1µF and greater)
|Connect the correct way round. They will be marked with a + or - near one lead.|
Take care with germanium diodes (e.g. OA91) because they are easily damaged by heat.
The diagram may be labeled a or + for anode and k or - for cathode; yes, it really is k, not c, for cathode! The cathode is the short lead and there may be a slight flat on the body of round LEDs.
|7.||Transistors||Connect the correct way
Transistors have 3 'legs' (leads) so extra care is needed to ensure the connections are correct.
Easily damaged by heat.
|8.||Wire Links between points on the circuit board.||
If there is no danger of touching other parts you can use tinned copper wire, this has no plastic coating and looks just like solder but it is stiffer.
|9.||Battery clips, buzzers and other parts with their own wires||Connect the correct way round.|
|10.||Wires to parts off the circuit board, including switches, relays, variable resistors and loudspeakers.||You should use stranded
wire which is flexible and plastic-coated.
Do not use single core wire because this will break when it is repeatedly flexed.
Many ICs are static sensitive.
Leave ICs in their antistatic packaging until you need them, then earth your hands by touching a metal water pipe or window frame before touching the ICs.
Carefully insert ICs in their holders: make sure all the pins are lined up with the socket then push down firmly with your thumb.
After you have completed soldering all the components on a pcb, you should clean off the excess rosin deposits using steel wool and some solvent such as lacquer thinner. Once the pcb is clean and dry you might want to apply a spray coating of varnish to protect the tracks and solder joints from corrosion.
Surface Mount Devices
These are really small and you should be very confident of your soldering ability before you tackle projects using these. SMD resistors and capacitors, for example, are typically only 2mm or less in length and have no leads. Contact is made by soldering the ends of the component to the tracks. You will find smd's in most electronic/computer pcb's these days. Assembly of these units is usually done by automatic machinery, but if you feel like doing it manually you will need a steady hand, magnifying glass and a small soldering iron, as well as small tweezers. You will also need a big supply of patience when you drop these miniscule components onto the floor, or worse into the carpet! I find a stainless steel dental probe is an ideal tool as it can be used for manipulating and holding down the device and solder will not stick to stainless steel.
Some typical SMD components. A ¼W resistor is shown as a size reference.
|1. 1 Watt 1218
2. 1206 1/4 Watt
3. 0805 1/8 Watt
4. Potentiometer (Top and Bottom)
|1. A-Case Tantalum
2. D-Case Tantalum Capacitor
3. Electrolytic Capacitor (Side View)
4. Electrolytic Capacitor (Bottom View)
5. 0805 Ceramic
6. 1206 Ceramic
7. 1210 Ceramic
8 . High Q Porcelain RF
9. Variable Trimmer (Top and Bottom)
|1. SMT Power Transistor
2. SMD Led
3. Melf Diode
4. 4 Leg SOT
5. SMB Diode
1. With a de-soldering pump (solder sucker)
2. With solder remover wick (copper braid)
After removing most of the solder from the joint(s) you may be able to remove the wire or component lead straight away (allow a few seconds for it to cool). If the joint will not come apart easily apply your soldering iron to melt the remaining traces of solder at the same time as pulling the joint apart, taking care to avoid burning yourself.
Now get going and build something. There are many kits available locally, as well as from USA and Europe. Once you start building your own equipment and accessories you will be hooked on soldering. I wonder if the solder flux is addictive......
© Philippine Amateur Radio Association, Inc. 2009