Basics of how to solder circuit boards

The electronic circuits are made of PCBs, components connected to each other in a meaningful way to function as per the design specifications.

These connections between the components is achieved by wiring or by PCB tracks. For a circuit on Vero Board, the multiple and single strand wires are commonly used and soldered with components in through hole package to form electrical connection. PCBs do use soldering of through and SMT type components by means of pads, vias and holes. However the breadboard do not require soldering because of all ready built in electrical tracks inside.

What is soldering..?

A soldering is the process of creating an electrical joint between components by melting the solder wire through applying heat and pouring that melted solder wire on leads/terminals of component to make a joint.

The Tools Required For Soldering:

The following tools are required for proper soldering

  • Soldering Iron:

A soldering iron is device that is electrical 220/110V operated and is like pen and its tip/end is made of heating element. The soldering iron works simply. Plug into AC220V/110V outlet and starts to heat up. When you feel the heat and smoke starts then apply solder wire to "Tin" the tip.

                                                                                                                                                                                                                                                                           Tinning:

Tinning the solder iron tip is also good, it helps the iron to grasp the solder quickly.

The tinning of copper wire is made so that the copper wire catches the solder and it will not break or bend and have the ability to create good electrical joint.

  • Solder Sucker:

The solder sucker is used in "De-Soldering" process. When removing components from PCB or removing any leg/terminal of component from PCB then the solder sucker will remove the solder and relieves the component to pull out of PCB. Be careful while using solder sucker because some low quality PCB hole pads are weak and can breakout due to high vacuum of sucker thus rendering the hole useless.

  • Tweezers:

The tweezer can be used as a tool to remove components from Vero board or PCB.

  • Solder Wire:

There are many types of solder available in market. The solder that is lead free, is a combination of tin 96.3%, copper 0.7% and silver 3% is a good option. Gauge # 21 is 0.032" dia. The best melting point temperature for this type is 217OC - 221OC.

  • Solder Flux:

The flux is very important in soldering process. It reduces the oxidation and used to chemically clean the metal surface joint before and during soldering. The flux used in electronic circuits soldering is basically rosin flux or ammonium chloride. The flux helps enhance the soldering and “wetting” process. Flux prevent the formation solder balls by dissolving the oxide from metal joint surface.

Wetting is the adhesive force between the molten solder and solid copper wire that causes the molten solder drop to spread-out across the surface to form strong electrical joint. Cohesive force on the other hand causes the formation of solder balls and hinders the contact with metal/copper surface.

  • Soldering Station:

The temperature of soldering iron can be controlled by means of a “Regulator” which has the internal regulatory electronic circuit to control the amount of current flowing through heating element. This is possible only in “Soldering Stations”. There are numerous soldering stations manufactures like Weller QB, and others. The have the “Control Knob”, “Toggle Switch”, “Temperature Display Unit” on the front panel and is operated by AC 220/110 V.

  • Soldering Iron Stand:

The solder stand is the place where you can put your iron at rest when not in use.

  • Soldering Gun:

The soldering gun is actually gun shape tool used for soldering purpose. It has a trigger when pressed to initiate soldering and when released to stop.

  • Soldering Clamp Stand / PCB Holder Jig

It is normally very difficult to handle wires that are being soldered. So there are clamp stands having crocodile clips to hold the wire. They also have PCB holding vise to ease soldering.

  • Wet cloth for cleaning iron tip

This is very important. It is the wet sponge or cloth to clean the iron tip regularly.

Soldering Tips.

  • Use the thinnest, 60/40 solder wire if you are a beginner
  • Select the appropriate size of solder iron tip. The thinner the tip the lesser the wattage and vice versa. 12Watt, 40Watt and 60 Watt irons have different applications. For precise SMT soldering use thinner tip and for THT use large tip iron.
  • Typical solder iron tip temperature is 330OC to 350O Allow iron to achieve this temperature. If iron do not attain this temperature then the cold solder joint will result. The cold solder joint is due to insufficient heat or movement of joint when cooling.
  • Keeping the iron ON will damage the soldering iron tip. Turn it off when not in use.
  • The plastic or wooden body side of solder iron is for holding. This is the cool side and hold it by your hand.
  • Touch the iron to the connection/joint/lead first, then apply solder and spread it. Look out for the drenched solder.
  • Too much solder is not useful. Appropriate solder is sufficient for good joint.
  • Do Tinning before making joint/connection
  • On regular basis check your soldering iron tip for any oxidation or residual flux. This hinders the soldering process. Try to clean it using wet sponge.
  • While cooling the solder joint, do not move.
  • Practice on scrap boards before working on actual board
  • Select the place of soldering where there is proper air ventilation.
  • Wear mask to avoid hazardous solder smoke
  • Be calm while soldering. Try not to shiver your hand while soldering.

Temperature Sensitive Components:  Some of the components are sensitive to heat and high temperature, applying iron for longer time will damage the components. So to avoid thermal shock or high temperature, proper heat sinks in form of sheet metal clips may be clamped to dissipate the excessive heat away from PCB and components.

Solder Bridge:  The solder bridge can form due to insufficient amount of solder mask on PCB. The solder bridge is the connection between the two points on PCB that were not meant to be connected. This solder bridge is formed accidently during soldering PCB components because of inappropriate solder mask