Basics of Printed Circuit Board Assembly

Printed circuit board assembly is a multi-step processes that involves the use of either or both through-hole and surface mount technologies/assembly techniques. During this process, the bare board is assembled and populated with all the electronic components necessary to create a functional PCA or printed circuit assembly (also PCBA or printed circuit board assembly).

In through-hole assembly, component leads are put in place by inserting contacts through holes, while surface-mount assembly involves gluing of components on pads or lands attached to the surface of the PCB. After assembly, component leads are then mechanically fixed and electrically connected to the board through soldering.

Different soldering techniques are also used to secure and attach components to a printed circuit board. In high-volume production, soldering is usually done using SMT (Surface Mount) placement machines and reflow ovens, which allow for bulk wave soldering. Skilled technicians on the other hand, have the ability to solder even the tiniest parts by hand using only tweezers, a fine tip soldering iron, and a special microscope, such as in the case of 0201 packages, which are a wee 0.02 by 0.01-inches in size. Manual soldering, however are only practical for small-volume prototypes as they can be quite time-consuming and labor intensive, although they do offer extreme precision. Some parts and components, on the other hand may be extremely difficult or impossible to solder by hand.

In many cases, through-hole and surface mount techniques and construction must be performed and combined in one assembly as some components might only be available in surface-mount packages and others in through-hole. Another possible reason why both methods are required is when components require additional strength or might be prone to physical stress, for which through-hole mounting can provide added security. When components are expected to go undisturbed or untouched, surface mount techniques are preferred because SMT packages take up less space.