PCB fabrication does not stop with the etching of the pattern, or the circuit. For the PCB to fully function and do things such as compute numbers, receive inputs, display images, and store data, components such as transistors, resistors, capacitors, integrated circuits, LEDs (light emitting diodes), and switches must be mounted and connected together via soldering. Soldering glues the components and the copper foil together with a stick of lead that is heated with a soldering iron.
Careful soldering must be done to prevent damage to the conductive foil and render the entire PCB inoperative. Skilled hands, therefore, play an important part in the successful soldering. These skilled hands are also important in PCB fabrication, since a specific and intricate pattern must be created with closely-followed procedures.
Small-scale or homebrew soldering is done with a 30- to 40-watt soldering iron, which is available in hardware stores. For industrial-scale soldering, higher-wattage irons are used. Soldering irons come in various tips and are made with copper coated with iron or tin. Copper is an excellent conductor of electricity and heat, while iron and tin are hardeners that make the tip last longer. To ensure a stable heat transfer, clean the tip regularly. If the tip is full of dirt and oxidation, replace it with a new one.
Soldering errors can be corrected without replacing the entire PCB and redoing the PCB fabrication process again. The correction is done with a desolderer, which is a special tool that either sucks the molten lead like a vacuum cleaner or blows it away from the PCB.
Another important tool in soldering a PCB is the soldering aid. It is a bladed, pointed, and double-ended stick that serves many purposes: to remove excess solder from soldered joints, to get rid of insulation around the terminal that will be soldered, to separate soldered joints that were joined by accident, and to act as a heat sink for the component’s terminals during the soldering process.
The solder is the adhesive for the components’ terminals and the conductive copper and is usually made of an alloy that is composed of 60% tin and 40% lead. Inside the alloy is a semi-liquid flux which disintegrates the oxide and helps the alloy bind to the metals of the terminals and the foil.
One step that is done between the PCB fabrication process and the soldering of components is the drilling of holes into the finished PCB. These holes, where the components’ terminals will be inserted to, are called donuts. These terminals can be interchanged with the terms leads and wires.
Drilling the donuts can be done manually for homebrew PCBs by using a drill, a vertical drill stand, and small drill bits. Automatic drilling, which involves programming a drilling pattern, is done by PCB manufacturers and is therefore more expensive.
Before the actual soldering, one must ensure proper and consistent clearance when installing the components into the board. Installation is done by inserting the components’ terminals into the PCB’s donuts.
To start soldering, the person performing the soldering must heat both the lead and the donut evenly for 3 to 5 seconds and then apply the solder to the meeting point of the two, which is located underneath the board, until the solder flows to the foil. Overheating is unacceptable. Otherwise, the foil might be damaged. The performer then removes the iron once enough solder has been applied, and the solder is left to cool down.
Once all the components have been soldered, the excess terminal wires are cut off. Finally, the soldered PCB must be checked for cold solder, or short circuits caused by the solder overflow.
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