PCB wiring methods continue to improve, and flexible wiring techniques can reduce wire length and free up more PCB space. Conventional PCB wiring is limited by fixed wire coordinates and the lack of arbitrarily angled wires. Removing these limitations can significantly improve the quality of wiring.

Let’s start with some terminology. We define arbitrary Angle wiring as wire wiring using arbitrary Angle segments and radians. It is a kind of wire wiring, but is not limited to using only 90 degree and 45 degree Angle line segments. Topological wiring is wire wiring that does not adhere to grids and coordinates and does not use regular or irregular grids like shape-based wiring. Let us define the term flexible wiring as wire wiring without fixed shape that enables real-time wire shape recalculation to achieve the following transformation possibilities. Only arcs from obstacles and their common tangents are used to form the line shape. (Obstacles include pins, copper foil, forbidden areas, holes and other objects) part of the circuit of two PCB models. The green and red wires run on different layers of the PCB model. The blue circles are the perforations. The red element is highlighted. There are also some red round pins. Use only line segments and models with an Angle of 90 degrees between them. Figure 1B is a PCB model using arcs and arbitrary angles. Wiring at any Angle may seem strange, but it does have many advantages. The way it is wired is very similar to how engineers wired it by hand half a century ago. Shows a real PCB developed in 1972 by an American company called Digibarn for complete hand wiring. This is a PCB board based on Intel8008 computer. The arbitrary Angle wiring shown in Figure 2 is actually similar. Why would they use arbitrary Angle wiring? Because this type of wiring has many advantages. Arbitrary Angle wiring has many advantages. First, not using the angles between line segments saves PCB space (polygons always take up more space than tangents). Traditional automatic cablers can place only three wires between adjacent components (see left and center in Figure 3). However, when wiring at any Angle, there is enough space to lay 4 wires on the same path without violating design rule checking (DRC). Suppose we have a positive mode chip and want to connect the chip pins to two other pins. Using only 90 degrees takes up a lot of space. Using arbitrary Angle wiring can shorten the distance between the chip and other pins, while reducing the footprint. In this case, the area was reduced from 30 square centimeters to 23 square centimeters. Rotating the chip at any Angle can also provide better results. In this case, the area was reduced from 23 square centimeters to 10 square centimeters. It shows a real PCB. Arbitrary Angle wiring with rotating chip function is the only wiring method for this circuit board. This is not only a theory, but also a practical solution (sometimes the only possible solution). Shows an example of a simple PCB. Topology cabler results, while automatic cabler results based on optimal shape are photos of the actual PCB. An automatic cabler based on optimal shape cannot do this because the components are rotated at arbitrary angles. You need more area, and if you don’t rotate the components, the device has to be made bigger. Layout performance would be greatly improved without parallel segments, which are often a source of crosstalk. The level of crosstalk increases linearly as the length of parallel wires increases. As the spacing between parallel wires increases, crosstalk decreases quadratic. Let’s set the level of crosstalk produced by two parallel 1mm wires spaced d to e. If there is an Angle between the wire segments, then as this Angle increases, the level of crosstalk will decrease. The crosstalk does not depend on the length of the wire, but only on the Angle value: where α represents the Angle between the wire segments. Consider the following three wiring methods. On the left side of Figure 8 (90 degree layout), there is the maximum wire length and the maximum emi value due to parallel line segments. In the middle of Figure 8 (45 degree layout), the wire length and emi values are reduced. On the right-hand side (at any Angle), the wire length is shortest and there are no parallel wire segments, so the interference value is negligible. So arbitrary Angle wiring helps to reduce the total wire length and significantly reduce electromagnetic interference. You also remember the effect on signal delay (conductors should not be parallel and should not be perpendicular to the PCB fiberglass). Advantages of flexible wiring Manual and automatic movement of components does not destroy the wiring in flexible wiring. The cabler automatically calculates the optimal shape of the wire (taking into account the necessary safety clearance). Flexible cabling can therefore greatly reduce the time required to edit the topology, nicely supporting multiple recabling to meet constraints. This shows a PCB design that moves through holes and branch points. During automatic movement, wire branch points and through-holes are adjusted to the optimal position. In most computer-aided design (CAD) systems, the wiring interconnection problem is reduced to the problem of sequentially finding paths between pairs of points in a maze of pads, forbidden areas, and laid wires. When a path is found, it is fixed and becomes part of the maze. The disadvantage of sequential wiring is that the wiring result may depend on the wiring order. When topological quality is still far from perfect, the problem of “getting stuck” occurs in locally small areas. But no matter which wire you rewire, it’s not going to improve the quality of the wiring. This is a serious problem in all CAD systems using sequential optimization. This is where the bending elimination process is useful. Wire bending refers to the phenomenon that a wire in one network must walk around an object on another network to access an object. Rewiring a wire will not correct this. An example of bending is shown. A lit red wire travels around a pin in the other network, and an unlit red wire connects to this pin. Automatic processing results are displayed. In the second case (on another layer), a lighted green wire is automatically rewired by changing the wiring layer (from green to red). Eliminate wire bending by automatically optimizing wire shape (approximate arcs with line segments just to show any Angle examples without arcs). (top) original design, (bottom) after eliminating bending design. Red bent wires are highlighted. In a Steiner tree, all lines must be connected as segments to vertices (endpoints and additions). At the top of each new vertex, three segments must converge and no more than three segments must end. The Angle between the line segments that converge to the vertex shall not be less than 120 degrees. It is not very difficult to construct a Steiner with these sufficient conditional properties, but it is not necessarily minimal. Gray Steiner trees are not optimal, but black Steiner trees are. In practical communication design, different kinds of obstacles must be considered. They limit the ability to construct minimum spanning trees using both algorithms and Steiner trees using geometric methods. The obstacles are shown in gray and we recommend starting at any end vertex. If there is more than one adjacent terminating vertex, you should choose one that allows you to continue using the second vertex. It depends on the Angle. The main mechanism here is a force-based algorithm that calculates the forces acting on the new vertices and repeatedly moves them to an equilibrium point (the magnitude and direction of the forces depend on the wires at the adjacent branch points). If the Angle between a pair of line segments connected to a vertex (terminus or addition) is less than 120 degrees, a branch point can be added, and then a mechanical algorithm can be used to optimize the vertex position. It’s worth noting that simply sorting all angles in descending order and adding new vertices in that order doesn’t work, and the result is worse. After adding a new node, you should check the minimum of a subnet consisting of four pins:

1. If a vertex is added to the vicinity of another newly added vertex, check for the smallest four-pin network.

2. If the four-pin network is not minimal, select a pair of “diagonal” (belonging to the quadrilateral diagonal) endpoints or virtual terminal nodes (virtual terminal nodes – wire bends).

3. The line segment that connects the endpoint (virtual endpoint) to the nearest new vertex is replaced by the line segment that connects the endpoint (virtual endpoint) to the distant new vertex.

4. Use mechanical algorithms to optimize vertex positions.

This method does not guarantee to build the smallest network, but compared with other methods, it can achieve the smallest network length without grazing. It also allows for areas where endpoint connections are prohibited, and the number of endpoint nodes can be arbitrary.

Flexible wiring at any Angle has some other interesting advantages. For example, if you can automatically move many objects with the help of automatic real-time wire shape recalculation, you can create parallel serpentine lines. This cabling method makes better use of space, minimizes the number of iterations, and allows for flexible use of tolerances. If there are two serpentine lines interlaced with each other, the automatic cabler will reduce the length of one or both, depending on rule priority.

Consider the wiring of BGA components. In the traditional peripheral-to-center approach, the number of channels to the periphery is reduced by 8 with each successive layer (due to a reduction in perimeter). For example, a 28x28mm component with 784 pins requires 10 layers. Some of the layers in the diagram have escaped wiring. Figure 16 shows a quarter of a BGA. At the same time, when using the “center to periphery” wiring method, the number of channels required to exit to the periphery does not change from layer to layer. This will greatly reduce the number of layers. For a component size of 28x28mm, 7 layers are sufficient. For larger components, it’s a win-win. Figure 17 shows a quarter of the BGA. An example of BGA wiring is shown. When using the “center to periphery” cabling approach, we can complete the cabling of all networks. Arbitrary Angle topological automatic cabler can do this. Traditional automatic cablers cannot route this example. Shows an example of a real PCB where the engineer reduced the number of signal layers from 6 to 4 (compared to the specification). In addition, it took engineers only half a day to complete the wiring of the PCB.