Design and manufacture of rigid printed circuit boards

The PCB designer will have the satisfaction of obtaining good results, if he takes account of manufacturing imperatives, which means he must have a good knowledge of processes, different methods, equipment and, of course, the personnel needed to build the product. The drift can be rapid, and we often encounter the case of circuits that are not industrially feasible because their mechanical characteristics are outside the limits of most manufacturers' know-how. Of course, a solution will be found to obtain the finished product, but at what price?

One of the aims of this document is to make the designer aware of the advantages he can bring to his company, if he takes into account the difficulties a manufacturer will have in producing the printed circuit board. Before starting any work, the designer should ask himself questions such as :

• what functions will the PCB have to perform?

• what types of components will be installed (through-hole, surface-mounted, active, passive, etc.)?

• Do the lines have to have a specific, tolerated impedance?

• will future PCB technology require shielding with grounded lines to avoid potential crosstalk problems?

• Are signal propagation speeds and dielectric losses imposed?

• how many circuits will be required?

• where will the products be manufactured? What is the manufacturer's level of "know-how"?

Already, from the answers provided, we will see appearing elements that will determine, later, the construction of the circuit, such as :

• the base material ;

• the trimmed PCB format ;

• the drilling grid ;

• diameter of component holes and vias (without components).

Starting with the component to be installed on the circuit, the product is designed progressively, since the diameter of the hole is already imposed on the designer (traditional component or surface-mounted component (SMD)), then that of the pad that will receive this hole, which will determine the width of the tracks, their spacing and the possible number to be placed between two pads. This rigid printed circuit board technique benefits from more than 70 years of experience, and this document will guide the designer through the basic rules, enabling him to define a design with full knowledge of the facts.