Multi-layer PCBs are circuit boards made up of a lot more than two electrical layers (copper layers) superimposed on each other. The copper layers are bonded together by resin layers(prepreg). Multi-layer boards represent probably the most complex form of printed circuit boards. Their expense is relatively high, owing to the complexity of the manufacturing process, lower production yields and difficulty of re-working on them. The need for multi-layer boards has been necessitated by the increasing packaging density of PCB Spring Terminal Block, which give rise to high concentration of interconnecting lines.
The printed circuit layout results in unpredictable design problems like noise, stray capacitance, cross-talk etc. The PCB design, therefore, must aim at minimizing the size of the signal lines and avoiding parallel routing etc. Obviously, such kind of requirements could not really met satisfactory in single-sided and even double-sided printed circuit boards as a result of limited cross-over which could be realized. Thus, to achieve satisfactorily performance from the circuit in the existence of an extremely large number of interconnections and cross-over, the PCB should be extended beyond two-plane approach.
This offers rise to the idea of multi-layer circuit boards. Hence, the main intent of fabricating a multi-layer printed circuit board would be to provide an additional degree of freedom in your selection of suitable routing paths for complex Feed Through Terminal Block. Multi-layer boards have at the very least three layers of conductors, by which two layers are on the outside surface as the remaining the initial one is incorporated into the insulating boards. The electrical connector is often completed through plated through-holes, which can be transverse for the boards. Unless otherwise specified, multi-layer PCBs are assumed to become plated through hole similar to double-sided boards.
Multi-layer boards are fabricated by stacking several circuits on top of every other and establishing a trusted set of pre-determined interconnections between the two. The technique starts off with a departure from conventional processing in that all the layers are drilled and plated before these are laminated together. The 2 innermost layers will comprise conventional two-sided PCB as the various outer layers will likely be fabricated as separate single-sided PCBs.
Just before lamination, the inner layer boards will likely be drilled, plated through, imaged, developed and etched. The drilled outer layers, which are signal layers, are plated through in a manner that uniform donuts of copper are formed on the underside rims of the through-holes. This can be then lamination from the various layers in to a composite multi-layer with wave-solderable interconnections. The lamination may be done in a hydraulic press or in an over-pressure chamber (autoclave). Inside the case of Transformer Terminal Block, the prepared material (press stack) is put within the cold or pre-heated press (170 to 180 °C for material having a high glass transition point). The glass transition temperature will be the temperature in which the amorphous polymers (resins) or the amorphous areas of a partially crystalline polymer change from the hard and relatively brittle state to a viscous, rubbery state. Multi-layer boards find applications in professional eqrfdn (computers, military equipment), particularly whenever weight and volume are the over-riding considerations.
However, there should be a trade-off which is simply the cost for space and weight versus the board’s costs. Also, they are very beneficial in high-speed circuitry because more than two planes are offered to the PCB designer for running conductors and providing for big ground and offer areas.