The printed wiring board (PWB), also known as the Printed Circuit Board (PCB), is essential for every electronic device. The printed wiring board was introduced in the early 1950s as a building block for electronic packaging. The critical feature of the printed wiring boards is to get the maximum components count per square inch of PWB. This is known as component density. Hence many advanced packaging techniques were introduced like Ball Grid Array (BGA), Chip Scale Packaging (CSP), and Chip on Board (CoB).
The surface mount components are miniature size and are extensively used in many PWBs to provide maximum component density while maintaining the device’s electrical, thermal, and signal integrity performance. There is a variety of materials used for PCB substrate, the most common is FR4. The below-shown figure-1 shows the evolution of Computer CPU and associated PWBs.
1.The main factors affecting the performance of PWBs
1.1 Speed of operation of the printed wiring board
The speed at which the electronic device operates is a significant factor in the design of PWB interconnections. The signal propagation speed is inversely proportional to the square root of the dielectric constant of the substrate material of PWB. Time of flight is the signal’s propagation time, which is directly proportional to the length of conductors and must be kept short of ensuring the optimum electrical performance of a system. Above 25MHz, the PWBs use the strip-lines and micro-strips for this purpose.
1.2 Printed Wiring Board–Power Consumption
Increasing clock rates and increasing the number of gates will result in increased power consumption. Special care must be taken for high-speed switching circuits where ground return current flow is channeled optimally. The separate ground plane must be made in multilayer PWBs to ensure low resistance current flow. A different bus bar system is also preferable for high-power circuits.
1.3 Thermal Management
The PWBs are poor conductors of heat, so proper care must be taken to use methods to dissipate the heat generated by power components in PWBs. Heat sinks, heat vias, conductive planes in PWBs, and metal slugs are good techniques.
