Technical Section - Soldering
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Soldering Soldering is a delicate manual skill that only comes with practice. Remember that your ability to solder effectively will determine directly how well your motor control boards function. Bad soldering technique can be a cause of major disappointment which damages your confidence. It needn't be like that: soldering is really easy to learn, and like learning to ride a bike, once mastered is never forgotten! You should be given a small piece of stripboard and some gash components to practice soldering. Tools As well as a soldering iron (ideally temperature controlled) you will need a pair of pliers to bend component leads, a pair of wire cutters to cut the leads to length and a screwdriver to attach the heat sink. Solder Joints Solder joints should possess some degree of mechanical strength. The components' wires are bent to fit through the holes in the board until the component is flush against the board's surface. Use some masking tape to hold the component flush with the board whilst you turn it over. It's generally better to snip the surplus wire leads off before you solder to make the joint more accessible. Leave about 3mm of wire poking through the board.
The perfectly soldered joint will be nice and shiny looking, and will prove reliable in service. The key factors affecting the quality of the joint are:
A little effort spent now in soldering the perfect joint may save you - or somebody else - a considerable amount of time in troubleshooting a defective joint in the future. It only takes a second or two, to make the perfect joint, which should be nice and shiny. Cleanliness Firstly, and without exception, all parts - including the iron tip itself - must be clean and free from contamination. Solder just will not "take" to dirty parts! It will "bead" into globules, going everywhere except where you need it. Dirt is the enemy of a good quality soldered joint! Hence, it is an absolute necessity to ensure that parts are free from grease, fingerprints, oxidation and other contamination. Before using the iron to make a joint, it should be "tinned" (coated with solder) by applying a few millimetres of solder, then wiped on a damp sponge preparing it for use. Then re-apply a very small amount of solder again, mainly to improve the thermal contact between the iron and the joint, so that the solder will flow more quickly and easily. Historically, electronics grade solder was usually 40% tin - 60% lead or 40/60, however concern over the nvironmental effets of lead and recent changes in legislation have removed this from common use. Modern lead-free (Pb-free) solders are available, but these have a higher melting point than the older tin/lead mixture. Electronics grade solder already contains cores of "flux" which helps the molten solder to flow more easily over the joint. Flux removes oxides which arise during heating, and is seen as a brown fluid bubbling away on the joint. Temperature Another step to successful soldering is to ensure that the component lead and the PCB track are heated QUICKLY and SIMULTANEOUSLY to roughly the same temperature. Press the chisel or conical tip of the soldering iron against both the PCB track and the component lead and apply a few millimetres of solder until it melts and flows readily over the joint onto the track. Then remove the iron and allow the joint to cool naturally. This should take only a few seconds. Do not move parts until the solder has cooled. Heating one part but not the other gives a far less satisfactory joint, so strive to ensure that the iron is in contact with all the components first, before touching the solder to it. The melting point of Pb-free solders is in the region of 220°C and the iron tip temperature is typically 330-350°C. Inexperienced solderers often use a small clip-on heat-shunt, which resembles a pair of aluminium tweezers. In the case of, say, a transistor, the shunt is attached to one of the leads near to the transistor's body. Any excess heat then diverts up the heat shunt instead of into the transistor junction, thereby saving the device from over-heating. Remember that the tip of the iron must be ‘tinned’ first to improve the thermal contact between the iron and the joint. 
Time It only takes two or three seconds at most, to solder the average PCB joint. Excessive heating time will damage the component and perhaps the circuit board copper foil too! The heating period depends on the temperature of your iron and size of the joint. Larger components and large areas of copper need more heat than smaller ones - but some parts such as semiconductor diodes, transistors and integrated circuits (ICs), are sensitive to heat and should not be heated for more than a few seconds. Soldering Horrors 1 – The Dry Solder Joint A well soldered joint will be nice and shiny looking. If it looks dull and crystalline you have made what is called a ‘dry joint’ and you should reheat the joint until the solder flows. A "dry joint" usually results from dirt or grease preventing the solder from melting onto the parts properly and is often noticeable because of the tendency of the solder not to "spread" but to form beads or globules instead, perhaps partially. Alternatively, if it seems to take an inordinately long time for the solder to spread, this is another sign of possible dirt and that the joint may potentially be a dry one. Solder should cover the joint completely. If you can see the hole through which the component lead passes, or if the solder forms a round bead, the joint is likely to be dodgy. 
Remedy. Sometimes it's enough to simply remelt the existing solder. If this doesn't produce visible results, add more solder. Soldering Horrors 2 - Solder Bridges The final key to a successful solder joint is to apply an appropriate amount of solder. Too much solder is an unnecessary waste and may cause a solder ‘bridge’ which short circuits adjacent tracks. 
Remedy. A bridge can usually be got rid of by melting it with the soldering iron and then wiping the soldering iron along the copper track at right angles to the bridge. If it's a massive blob of solder, use a desoldering pump(sometimes called a solder sucker). 
Too little solder and it may not support the component properly, or may not fully form a working joint. How much to apply, only really comes with practice. A few millimetres of solder is enough for an "average" joint. A soldered joint that is improperly made will be electrically "noisy", unreliable and is likely to get worse in time. It may even have made no electrical connection at all, or could work initially and then cause the equipment to fail at a later date! Removing and Resoldering Components There will undoubtedly come a time when you need to remove the solder from a joint: possibly to replace a faulty component, to fix a dry joint or remove a solder bridge. The usual way is to use a desoldering pump which works like a small spring-loaded bicycle pump, only in reverse! A spring-loaded plunger is released at the push of a button and the molten solder is then drawn up into the pump by suction. The pump has a P.T.F.E. nozzle which is heat proof. 
Troubleshooting Guide
Next The next section is on Constructing The Chassis. |