Electronics Made Easy - a Complete Introduction to Electronics - Martin Denny [20]
Connections to and from the board should be made in multistrand cable. Again keep these connections reasonably short for high frequency applications. For audio circuits low level signals should be connected with screened cable.
3.3 Soldering
Before starting work give the soldering iron enough time to heat up properly, test the temperature by applying multicore solder to the bit. The solder should flow easily when the iron is up to temperature.
Before soldering anything ensure that the components to be soldered are clean and free of oxide. Printed circuit boards, not already tinned can be cleaned with paper, stubborn areas can be polished with a fine abrasive paper but be careful the copper layer is very thin. Connectors on switches, potentiometers etc can also be cleaned with a fine abrasive paper if absolutely necessary. Component leads generally will not require cleaning especially if the component is new.
Multicore solder contains flux within the solder wire, when heated the flux will flow fractionally before the solder. The flux has two functions to coat the area to be soldered to prevent oxide build up and to facilitate the flow of the solder. A common fault when soldering is to apply solder to the bit and then attempt to stick two components together. This can sometimes be done to temporarily hold a component in position ie DIL sockets on a PCB but will inevitably result in a poor joint sometimes called a dry joint.
When soldering first clean the soldering iron bit by applying a small amount of multicore solder to the bit and wiping the bit on a damp sponge. The bit should then appear shiny with no pitting. If the surface is damaged temporary repairs can be made with abrasive paper then repeating the process but it is better to accept the inevitable and change the soldering iron bit immediately.
Allow the soldering iron to cool down then fit a new bit and re-heat and tin the new bit. In many cases a new soldering iron bit will not immediately tin properly if this is the case hold a piece of paper flat on the workbench and polish the bit adding solder occasionally until the tip of the bit is properly tinned and has a shiny finish, do not use abrasive paper as this will permanently damage the bit.
Hold the soldering iron as you would a pen or pencil only providing enough force to maintain contact with the work piece.
Soldering techniques vary slightly between connecting two components together and a component to a PCB. When connecting two components tin the contact area of each of the components after first cleaning the bit on the damp sponge. Apply multicore solder to the component and the bit with the bit in contact with the area to be tinned. The tinned area of the component should appear shiny and have a consistent coating. Repeat the process with the second component then with the components in position apply sufficient heat to join them, applying additional solder as necessary.
At first sight it may appear that you need three hands but remember you can usually use the soldering iron in its stand, or use a small vice to hold the component. A probe or crocodile clip can also be useful.
When soldering components to a PCB locate the components on the component side then push the leads through the holes. To retain the components bend the leads slightly on the copper side, this should prevent movement when you turn the board over to solder it.
To solder the component to the board, clean the bit then position the bit on the track and the component lead then apply the solder to the joint. Never use more solder than absolutely necessary as it can result in bridging of tracks on the board. It is usually possible to do two or three joints in this manor before cleaning the bit but do not allow surplus solder to remain on the bit.
The resultant joints should appear shiny not matt and have a concave appearance. If they appear convex or rounded solder them again using a solder sucker