Multilayer printed circuit boards (PCBs) consist of multiple layers of conductive tracks and electronic components, reducing size and interconnecting wiring. They offer advantages in space, weight, and signal integrity, particularly in aviation and aerospace. Multilayer PCBs were developed in 1961 and have revolutionized the electronics industry.
Printed circuit boards (PCs) are thin boards made of materials that don’t conduct electricity, but have electronic components mounted on a network of conductive tracks that join the components together to form a complete circuit. The term multilayer boards refers to PC boards that consist of a composite wafer made up of multiple boards joined together to reduce the size of the finished board while maintaining circuit size or complexity. These boards can consist of as few as two layers and as many as 50, depending on the complexity of the circuit. The separate layers are isolated from each other to prevent short circuits and are interconnected by plated or conductive through-holes.
Printed circuit boards (PCBs) first saw the light of day in 1936 when an Austrian engineer, Paul Eisler, incorporated one into a radio set. The PCB grew steadily in popularity and sophistication throughout the 1940s and 1950s with the first multilayer board being developed in 1961. The enormous benefits offered by multilayer PC boards were immediately apparent and their development has continued rapidly ever since.
Multilayer boards have many advantages over traditional double-sided and single-layer PCBs. They save significant space, allow simple and simultaneous shielding of a large number of components, and reduce the amount of interconnecting wiring that would be required if separate circuit boards were used. These interconnects represent a considerable addition to the floor space occupied by a circuit and significantly increase the overall weight of the system.
These savings are of particular value in industries such as aviation, where space and weight are important considerations when designing and building aircraft. The internal connection characteristics of multilayer boards also allow the outer surfaces of the completed board to be used to mount larger heat sinks that allow for cooler operation. Again, industries such as aviation and aerospace benefit greatly from this feature.
The use of multilayer boards also offers numerous advantages for applications where high levels of uniformity in conductor wave impedance are required. Additionally, multilayer boards offer superior reductions in signal propagation and distortion in applications where signal integrity and “crosstalk” levels are critical. The high levels of overall uniformity of these characteristics can also be maintained across all panels in the laminate through the use of multilayer construction. While multilayer boards are relatively expensive to manufacture and very expensive to repair, their benefits are extensive and have revolutionized the electronics industry and defined the future of printed circuit board technology as a whole.
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