PCB trace

Tracing of printed circuit boards is one of the stages of the design of electronic equipment (CEA), which consists in determining the location of the conductors on the printed circuit board manually or using one of the CAD systems designed for the design of printed circuit boards.

Content

1 Tracing Methods
2 Setting the trace task
3 Tracing Algorithms
4 References

Trace Methods

There are three ways to trace:

manual tracing , in which a person independently, using certain software tools, applies a drawing of conductors to the board drawing;
automatic tracing , in which the program independently conducts the conductors on the board drawing, using the restrictions imposed by the developer. The developer controls the result, if necessary, adjusts the initial parameters of the task and repeats the trace. Correction includes changing the location of components, preliminary drawing of circuits manually, etc. At the moment, all modern design systems have complex and efficient automatic tracing systems;
interactive tracing , in which the program (automation) does the rough job of drawing the circuit and controlling the tracing rules, and the person tells the program (robot) the sequence of actions on complex tracing sections, controls the result of its work step by step. Interactive PCB tracing can be used both for fully manual tracing and for PCB improvements after automatic tracing.

Setting the trace task

Tracing connections is, as a rule, the final stage in the design of electronic equipment (CEA) and consists in determining the lines connecting the equipotential contacts of the elements and the components that make up the designed device.

The trace task is one of the most time-consuming tasks that arise when automating the design of electronic equipment. The complexity is explained, in particular, by the variety of ways of constructive and technological implementation of compounds, for each of which, when solving the problem algorithmically, specific optimization criteria and restrictions are applied. From a mathematical point of view, tracing is the task of choosing the optimal solution from a huge number of options.

Simultaneous optimization of all connections during tracing due to enumeration of all options is currently impossible. Therefore, locally optimal tracing methods are developed mainly when the trace is optimal only at this step in the presence of previously made connections.

The main task of the trace is formulated as follows: according to the given connection diagram, lay the necessary conductors on the plane (circuit board, crystal, etc.) in order to realize the given technical connections, taking into account predefined restrictions. The main ones are restrictions on the width of the conductors and the minimum distances between them.

The initial information for solving the connection tracing problem is usually a list of circuits, parameters of the design of elements and the switching field, as well as data on the placement of elements. The tracing criteria can be the percentage of realized connections, the total length of the conductors, the number of intersections of the conductors, the number of mounting layers, the number of interlayer transitions, the uniformity of the distribution of conductors, the minimum trace area, etc. Often these criteria are mutually exclusive, therefore, the quality of tracing is assessed by the dominant criterion when fulfilling restrictions by other criteria, either the additive or multiplicative form of the evaluation function is used, for example, of the following form:

$F=\sum _{i=1}^{p}\lambda _{i}f_{i},$ ${\ displaystyle F = \ sum _ {i = 1} ^ {p} \ lambda _ {i} f_ {i},}$

Where:

$F$ ${\ displaystyle F}$ - additive criterion;
$\lambda _{i}$ ${\ displaystyle \ lambda _ {i}}$ - weight coefficient;
$f_{i}$ ${\ displaystyle f_ {i}}$ - private criterion;
$p$ ${\ displaystyle p}$ - the number of particular criteria.

Trace Algorithms

Well-known PCB trace algorithms can be divided into three large groups:

wave algorithms based on Lee's ideas and developed by Yu. L. Ziman and G. G. Ryabov. They are widely used in existing CAD systems , because they make it easy to take into account the technological specifics of printed wiring with their own set of design limitations. They guarantee the construction of the route, if the path for it exists;
orthogonal algorithms with higher speed than the algorithms of the first group. To implement on a computer, they require 75-100 times less calculations in comparison with wave algorithms. They are used in the design of printed circuit boards with through metallized holes. The disadvantages of this group of algorithms are associated with the receipt of a large number of transitions from layer to layer, the absence of a 100% guarantee of the routes, a large number of parallel conductors;
heuristic type algorithms. Partially based on a heuristic technique for finding a path in a maze, in which each connection is carried out along the shortest path, avoiding obstacles encountered on the path.

Links

Detailed descriptions of the PCAD trace process in PCAD .
"PCB layout technique" (article).