For a proper circuit routing and placing, i.e. to design a circuit, stepping from the electrical schematic to the printed circuit board, it is necessary to follow some basic guidelines. In this article we will examine all focal points and basic notions to design a proper professional printed circuit board. We will analyze about how to place and route the tracks in a circuit and examine all criteria and rules behind this process dealing with a correct flux of work.
1. Electrical Schematic: A good start...
The electrical schematic should be complete. All information about routing can be put directly inside the schematic both in a graphical form or in a component library, and whenever this is not possible, a simple text could be inserted (Figure 1).
Figure 1: Example of electronic circuit
It is important to put labels on all possible links, to simplify the reading of the schematic but also to easily recognize the NET on the LAYOUT. It is also important to tag all links that do not have visible LABELS, to increase the optimization in the routing CAD. In addition to an easy individuation of the circuit, it will be possible to assign a different color to each RATNEST, this will make the routing more visible.
Figure 2: Adjustable Output Voltage Regulator
In the figure 2 is shown another example of a schematic which has been optimized to give information about the CAD routing. The ground node portrayed clearly means that all links shown must be as short as possible and must be directly connected without deviations or STUBS (Stubs are T terminations, we will talk about them in other articles).
2. Mechanical dimensions and anchoring
One of the most annoying (and burdensome) things that an electrical designer can experience is to insert a drill or to need a free surrounding zone, at the end of a routing process and to literally bend over and backwards to find a free area, or again to dismantle half the circuit and do the routing again. Here, you will find something to keep in mind BEFORE starting your work:
Always define your mechanical layout;
External dimensions and tolerances must be precise;
Always define your anchoring drills;
Identify the maximum heights of components.
It is, thus, really important to define the mechanical layout at the beginning of your work, with all its dimensions and obstacles. Anchoring drills must also be defined and inserted in advance inside the schematic. They will surely need a free surrounding zone (as an example, for the head of a screw), so always get some information about it if this is not declared in the technical specifications. Tolerances can play an important role in the grid for components placing. Do not even underestimate the maximum heights for components, sometimes a resistor assembled in a vertical position can solve a critical situation in routing, but it will be important to have enough height available in that area. [...]
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