Soldering tutorials

Beginners guide to soldering

These tutorials set out to give guidance about how to solder using the most basic low cost methods.  These are the techniques used by engineers who do not have access to professional tools and machines.  With care, good results can be achieved, but do not expect the consistent quality and accuracy achieved by industrial processes.

The two main type of components

There are two main types of components. Through-hole components (also known as leaded components - as in cables or wires, not the poisonous metal) are fitted through drilled holes in the printed circuit board.  This makes them more physically secure and more suitable for switches, connectors, heavy components and anything else likely to bear heavy force.   Surface-mount components (SMD) are simply placed upon copper pads (without holes) on one side of the board, which means they take up less board area than their through-hole equivalent. Surface-mount components also tend to be cheaper and there is an increasing shift towards using them as a way to reduce the unit costs of a product since they are easy to machine place.

Soldering surface mount components - hand soldering

The first tutorial is a video showing how to solder surface-mount components with basic tools. The simplest way to do this is with similar equipment you'd use for through-hole components. You will need a soldering iron, solder and tweezers. To clean up the board you will need some flux, alcohol wipes or spray and a stiff brush.

Soldering surface mount components - reflow soldering

As the number of surface-mount components on a board increases, it becomes more inefficient to solder components individually. An alternative is to use the reflow soldering process. This involves placing solder paste (solder particles suspended in a thick flux) on the components' pads, positioning components on their pads so that the solder paste holds them in position and finally placing the board in a reflow oven. The reflow oven heats the solder paste, melting the solder and evaporating the flux, creating a good solder connection. The control of the temperature profile (board temperature over time) is very important as each solder paste will have a different "ideal" profile.

There are two ways to apply solder paste manually. The first is to use a syringe, but this requires steady hands and is not suitable for boards with a large number of pads. The second is to use a stencil, which is a sheet of material with holes (apertures) that correspond to pads on one side of a board. Low-cost stencils tend to be made of mylar (a transparent polymer), while higher quality ones are made from stainless steel. Often a single sheet of stencil material will have a set of apertures for each side of a board, or possibly even multiple boards.

Solder paste printing using a stencil (by hand)

This video demonstrates how to print solder paste using basic workshop materials. To apply solder paste using a stencil, you will need a stencil, masking tape, alcohol wipes, spacers (these need to be the exact height of the board, so a good choice is the off-cuts from the board's panel), solder paste and a squeegee. A squeegee is a flat piece of metal used to push solder paste over a stencil and through the holes.

Reflow soldering

Once the pcb has been solder pasted and the SMD components have been mounted, it is necessary to reflow or fuse the solder paste at high temperature in an oven.  This link shows how to reflow using low cost domestic equipment.