Quickly learn irregular-shaped PCB design

The complete PCB we envision is usually a regular rectangular shape. Although most designs are indeed rectangular, many designs require irregularly shaped circuit boards, and such shapes are often not easy to design. This article describes how to design irregular-shaped PCBs.

Nowadays, the size of PCB is constantly shrinking, and the functions in the circuit board are also increasing. Coupled with the increase in clock speed, the design becomes more and more complicated. So, let’s take a look at how to deal with circuit boards with more complex shapes.

As shown in Figure 1, a simple PCI board shape can be easily created in most EDA Layout tools.

However, when the circuit board shape needs to be adapted to a complex enclosure with height restrictions, it is not so easy for PCB designers, because the functions in these tools are not the same as those of mechanical CAD systems. The complex circuit board shown in Figure 2 is mainly used in explosion-proof enclosures and therefore subject to many mechanical limitations. Rebuilding this information in the EDA tool may take a long time and is not effective. Because, mechanical engineers are likely to have created the enclosure, circuit board shape, mounting hole location, and height restrictions required by the PCB designer.

Due to the arc and radius in the circuit board, the reconstruction time may be longer than expected even if the circuit board shape is not complicated (as shown in Figure 3).

These are just a few examples of complex circuit board shapes. However, from today’s consumer electronic products, you will be surprised to find that many projects try to add all the functions in a small package, and this package is not always rectangular. You should think of smartphones and tablets first, but there are many similar examples.

If you return the rented car, you may be able to see the waiter read the car information with a handheld scanner, and then wirelessly communicate with the office. The device is also connected to a thermal printer for instant receipt printing. In fact, all these devices use rigid/flexible circuit boards (Figure 4), where traditional PCB circuit boards are interconnected with flexible printed circuits so that they can be folded into a small space.

Then, the question is “how to import the defined mechanical engineering specifications into PCB design tools?” Reusing these data in mechanical drawings can eliminate duplication of work, and more importantly, eliminate human errors.

We can use DXF, IDF or ProSTEP format to import all the information into the PCB Layout software to solve this problem. Doing so can save a lot of time and eliminate possible human error. Next, we will learn about these formats one by one.

DXF is the oldest and most widely used format, which mainly exchanges data between mechanical and PCB design domains electronically. AutoCAD developed it in the early 1980s. This format is mainly used for two-dimensional data exchange. Most PCB tool vendors support this format, and it does simplify data exchange. DXF import/export requires additional functions to control the layers, different entities and units that will be used in the exchange process. Figure 5 is an example of using Mentor Graphics’ PADS tool to import a very complex circuit board shape in DXF format:

 

A few years ago, 3D functions began to appear in PCB tools, so a format that can transfer 3D data between machinery and PCB tools is needed. As a result, Mentor Graphics developed the IDF format, which was then widely used to transfer circuit board and component information between PCBs and mechanical tools.

Although the DXF format includes the board size and thickness, the IDF format uses the X and Y position of the component, the component number, and the Z-axis height of the component. This format greatly improves the ability to visualize the PCB in a three-dimensional view. The IDF file may also include other information about the restricted area, such as height restrictions on the top and bottom of the circuit board.

The system needs to be able to control the content contained in the IDF file in a similar way to the DXF parameter setting, as shown in Figure 6. If some components do not have height information, IDF export can add the missing information during the creation process.

Another advantage of the IDF interface is that either party can move the components to a new location or change the board shape, and then create a different IDF file. The disadvantage of this method is that the entire file representing the board and component changes needs to be re-imported, and in some cases, it may take a long time due to the file size. In addition, it is difficult to determine what changes have been made with the new IDF file, especially on larger circuit boards. IDF users can eventually create custom scripts to determine these changes.

In order to better transmit 3D data, designers are looking for an improved method, and STEP format came into being. The STEP format can convey the board size and component layout, but more importantly, the component is no longer a simple shape with only a height value. The STEP component model provides detailed and complex representation of components in three-dimensional form. Both circuit board and component information can be transferred between PCB and machinery. However, there is still no mechanism to track changes.

In order to improve the exchange of STEP files, we introduced the ProSTEP format. This format can move the same data as IDF and STEP, and has great improvements-it can track changes, and it can also provide the ability to work in the original system of the subject and review any changes after establishing a baseline. In addition to viewing changes, PCB and mechanical engineers can also approve all or individual component changes in layout and board shape modifications. They can also suggest different board sizes or component locations. This improved communication establishes an ECO (Engineering Change Order) that has never existed before between ECAD and the mechanical group (Figure 7).

 

 

Today, most ECAD and mechanical CAD systems support the use of the ProSTEP format to improve communication, thereby saving a lot of time and reducing the costly errors that can be caused by complex electromechanical designs. More importantly, engineers can create a complex circuit board shape with additional restrictions, and then transmit this information electronically to avoid someone wrongly reinterpreting the board size, thereby saving time.

If you have not used these DXF, IDF, STEP or ProSTEP data formats to exchange information, you should check their usage. Consider using this electronic data exchange to stop wasting time to recreate complex circuit board shapes.