Soldering is one of the most important technique that an Engineer(Or anyone dealing with PCBs) should know. So, today I am going to give you guys a few tips about it.
DESCRIPTION:
Soldering is a process of joining two or more metal pieces. Its best suited for metals in form of wire or sheet. Unlike welding, here the metal pieces to be joined are not melted, instead a “filler” is used. The filler is melted and placed between the metals to be joined. On cooling, it binds the metals fairly strongly and have good conductivity and do not allow liquids to pass through(in case liquid containers). The filling used is called as solder, which is an alloy. For electronic applications, it consists of 60% Tin(Sn) and 40% Lead(Pb). It has a melting temperature of about 185 °C. But, Lead is a poisonous chemical and is a threat to environment and life as it can get into the food chain. Hence solders without lead that melt at around 240 °C are being used widely these days. But these alloys are not as reliable as the ones containing Lead. The metal that provides the heat is called as Soldering Iron( or the Solder Gun). It is heated to about 400 °C and this will easily melt the solder and the melt can be suitable placed.
Soldering Iron and a roll of Solder
PROCESS:
- Plug in the Soldering Iron and place it on the stand. Now the stand should be such that it will hold the Iron in place and will not be affected by its heat. Dont use a plastic stand. Use metallic stand. Wait for the Iron to heat up properly. DO NOT touch it to see if its hot or not. Try melting the solder instead to test it Clean the.
- surfaces that you are soldering. Clean the PCB with some abrasive that is not too Strong. Sand paper is NOT a good material for this. Some people use steel wool or even a hard fabric. The leads of the components MUST be cleaned to form strong joints. The leads may have residues of glue or they may have corroded. Hence you must clean them properly before using them. Not cleaning properly will lead to weak joints and the joints will have high resistance.Plan the placements of each components before you actually solder it.
- Try to work out different positions and choose the one that you find suitable. I usually Place them in such a way that they occupy less space and not care about its representation as in the given circuit. This may, at times, be tedious to debug. But if you are using a PCB and not a general purpose board, you wont have to worry about placement of components.
- Bend the leads of the components to fit them properly into the holes. Now insert them and bend the leads on the other side a little so that the component sits there without slipping back. Hold your soldering iron as if it were a pen. Place the iron on the lead you are about to solder and now touch the solder wire at the bottom of the now hot lead using your other hand. At this point it melts and surrounds the lead. If the metal is not cleaned properly, the melt wont flow properly and you will have to use more solder to cover the missing parts. Once you are satisfied, remove the solder wire. The solder formed should be conical, that indicates perfect soldered joint with least resistance.Note : The shape of the joint need noe be a PERFECT cone. It should be simillar to a cone. So even if its not pointed dont worry as long as its simillar to a cone.
- Cut the extra leads using a wire-stripper or you can also use a nail cutter.
PRECAUTIONS :
- DO NOT touch the soldering iron for ANY reason. You will get burnt even for the shortest possible contact.
- Try not to inhale the fumes that come out when you melt the solder. Also sit in a well ventilated room so that the fumes can escape easily.
- DO NOT place the soldering iron on plastic, sponge or any such materials as they will melt and they may reach your work table.
- Do not heat the leads for a long time as the components will be damaged due to over-heating. Components are heat resistant and will survive the heat of soldering. But if it is heated for very long time, the component will be damaged
EXTRA TIPS:
- Always use an IC holder instead of soldering an IC directly into your board. Since ICs have many pins, you will be heating the IC too much if you solder it directly thereby risking damage to it. If the IC is damaged while operatiing, you can easily replace it with a new one if a holder is used.
- If the soldered joint appears globular instead of conical, that means that there is either too much solder or air gap is created. Both will increase the resistance at the joint. To remove the extra solder, heat it and simultaniously scrub it with the Soldering Iron. This can be tricky at the beginning, but practice makes you perfect. And to get rid of the air bubble, you just heat the lead and the solder will melt and redistribute uniformely thereby attaining the conical shape.
- Always clean the Soldering Iron tip off the carbon deposition. This is the reason why the Soldering iron will not provide the required heat. You can use a radium cutter to clean the surface.
- Do not touch the components as soon as you solder them as they will be hot and you will get burnt.
- Always use single strand wire to connect within the Circuit board. Just to be on the safer side, use insulated wire rather than open wire.
- To connect from the circuit board to OUTSIDE world, use multistranded wires. Single stranded wires will break if you bend them repeatedly. Multistrand wires are made to be flexible and hence they are suitable.
- Always double check the polarities of the components you are soldering as an error will lead to desoldering and things will get messy.
- To know whether any two points on the board that are NOT supposed to join have joined, hold a light behind the board and observe it from the opposite side with your eyes, the board and the light source in a straight line. You will clearly be able to see the solder on the board and whether or not its touching the adjacent joints.
DESOLDERING :
I ususally do desoldering the hard way. You first melt the solder and try to pull the component from behind. But this method requires two people and simultaneously melting two or more points. You can also try to shift the solder to the adjacent holes. But this is possible only in the general purpose boards and not in PCBs. The other alternatives are
Desoldering pump :
The pump usually looks like large syringes. There is a spring loaded plunger, and a button to release it. The plunger is pushed down. When you want to suck up the solder, you position the nozzle over the molten solder and hit the button. The plunger moves up, creating a vacuum and sucking up the solder.
Solder remover wick :
It looks like wick used in oil lamps, except that it is made of copper. To use it, you put the wick over the joint and heat it with the Soldering Iron. The molten solder gets sucked by the wick. First remove the wick and then the iron.The desoldering pump is advisable as the copper wick is expensive.
First Aid in case of burns :
- Use cold water to keep your wound cool. Even ice will work. Keep it under cold water or ice for atleast 15 minutes.
- Although any ointment is not prescribed, you can try a small amount of Aloe Vera.
- Cover it with bandage if necessary
Hope this guide helped you. For any queries or suggestion please comment 
