2.2.1 Basic PCB classifications

PCBs may be classified in many different ways according to their various attributes. One fundamental structure common to all of them is that they must provide electrical conductor paths that interconnect components to be mounted on them.

There are two basic ways to form these conductors:

1. Subtractive. In the subtractive process, the unwanted portion of the copper foil on the base substrate is etched away, leaving the desired conductor pattern in place.

2. Additive. In the additive process, formation of the conductor pattern is accomplished by adding copper to a bare (no copper foil) substrate in the pattern and places desired. This can be done by plating copper, screening conductive paste, or laying down insulating wire onto the substrate on the predetermined conductor paths.

The PCB classifications given in Fig. 2.1 take into consideration all these factors, i.e., fabrication processes as well as substrate materials. The use of Fig. 2.1 is as follows:

Figure 2.1: Classification of printed circuit boards.

• Column 1 shows the classification of PCBs by the nature of the substrate.

• Column 2 shows the classification of PCBs by the way the conductor pattern is imaged.

• Column 3 shows the classification of PCBs by their physical nature.

• Column 4 shows the classification of PCBs by the method of conductor formation.

• Column 5 shows the classification of PCBs by the number of conductor layers.

• Column 6 shows the classification of PCBs...