Printed circuit boards can be assembled in manufacturing plants or by hand. Hobbyists often use single or 2-sided boards and components threaded through the holes for PCB assembly. Manufactures most often use multi-layered boards with surface mounting devices.
For hobbyists, assembling printed circuit boards needs a set of tools in order to become successful. The most essential tools needed for the assembly are the following:
- Soldering iron
Soldering irons are available from simple plug-in-the-wall soldering irons to thermostatically controlled irons. The plug-in-the wall iron does not have any temperature regulation mechanism and has to be turned on and off frequently during the entire PCB assembly process. For best function, choose an iron with 30 to 50 watts. Thermostatically controlled irons have dials that adjust the temperature of the tip of the iron.
Solders attach the through-the-hole components to the board. There are 2 categories of solder used for electronics: the lead/tin alloy and the lead free solder. Commonly used lead/tin alloy is the 63% tin-37% lead alloy and the 60% tin-40% lead alloy. The melting point of these alloys is at 360˚F.
Some manufacturers prefer the lead-free solder over the use of lead because of environmental concerns. Alloys used in lead-free solder include copper, tin and silver. The melting point of lead-free solder is at 423˚F.
- Small wire cutter
- Small pliers
- Dental probe
- Volt/ohm meter
- Anti-static mat
- Solder removal tools
- Damp sponge
Procedure for PCB assembly
To solder, heat the solder until it melts and flows freely. Use solder sparingly, just enough to bond the surfaces that are being soldered. Double check for cold solders. These are areas wherein the solder has not been heated enough and the solder does not flow properly. This will cause the soldered surfaces to detach while in use. When using 2-sided boards, use enough solder so that the melted solder flows from one side to the other.
To start, thread the through-hole PCB components in pre-cut holes in the desired circuit pattern. Bend the leads of the components slightly for better anchorage. Then solder the components properly. Keep the soldering iron at 45 degrees angle to the soldered surface. The tip of the iron should be in contact with the PCB and the lead at the same time. Be careful when soldering to avoid overheating the pad. Overheating can lift the pad off and damage the PCB.
A good place to start is by placing the resistors. Bend the leads at the body in a 90-degree angle then insert the leads through the hole. The body of the resistor should be tight against the surface of the board. If the resistor has a tendency to heat up during operation, lift it about a quarter of an inch from the surface of the board. This will allow air circulation to cool the resistor to prevent damage and malfunction. Once in place, turn the board over and solder the leads. Next, place the capacitors, diodes and transistors. Then add the ICs. The leads on the ICs tend to come bent outwards. Readjust the angles and thread through the holes, then solder in place.
When soldering, make sure to avoid overheating any of the components, especially the semiconductors. Using small plies and dental probes help in handling the tiny components. Also, manual PCB assembly requires skill and patience, especially with soldering. It is recommended to practice soldering in a separate board before doing it on an actual circuit board. Also, reworking the entire board is also a huge possibility. Be careful when removing the solders and reworking the circuit pattern to prevent damaging the entire board.