How to design an irregular shaped PCB?

- Aug 28, 2018-

The complete PCB we envisioned is usually a neat rectangular shape.While most designs are indeed rectangular, many require a circuit board with an irregular shape, which is not always easy to design.This paper introduces how to design irregular PCB. 

As PCB sizes continue to shrink and more functions are added, the design becomes more complex as the clock speed increases.So, let's see what we can do with more complicated circuit boards. 

    

However, when the circuit board shape needs to be adapted to a complex case with high limitations, it is not so easy for PCB designers because the functions in these tools are not the same as those in mechanical CAD systems.The complex circuit board shown in figure 2 is mainly used in the explosion-proof enclosure, so it is subject to many mechanical restrictions.Rebuilding this information in the EDA tool can take a long time and is not productive.Because mechanical engineers have probably created the shell, circuit board shape, mounting hole location, and height restrictions that PCB designers require. 

Since there are radians and radii in the board, even if the board shape is not complicated, the reconstruction time may be longer than expected. 

These are just a few examples of the complex circuit board shape.However, from today's consumer electronics, you'll be surprised to see many projects that try to add all the functionality to a small package that isn't always rectangular.Your first thoughts should be on smartphones and tablets, but there are many similar examples. 

If you return a rented car, you might see a waiter reading the car with a handheld scanner and then communicating wirelessly with the office.The device also connects to a thermal printer for instant receipt printing.In fact, all of these devices use rigid/flexible circuit boards, where traditional PCB boards interconnect with flexible printed circuits so that they can be folded into small Spaces. 

The question, then, is "how do you import the defined mechanical engineering specification into a PCB design tool?"Reusing this data in mechanical drawings eliminates duplication of work and, more importantly, human error. 

We can solve this problem by importing all the information into the PCB Layout software using the DXF, IDF, or ProSTEP format.Doing so can save a lot of time and eliminate possible human errors.Next, we'll look at each of these formats. 

Graphics interchange format - DXF

DXF is the oldest and most widely used format for exchanging data electronically between the mechanical and PCB design domains.AutoCAD was developed 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 functionality to control the layers, different entities, and cells that will be used during the exchange.Figure 5 is an example of importing very complex circuit board shapes in DXF format using the PADS tools of Mentor Graphics:

A few years ago, three-dimensional capabilities began to appear in PCB tools, requiring a format that could transfer three-dimensional data between mechanical and PCB tools.Accordingly, Mentor Graphics developed IDF format, which was then widely used to transmit circuit board and component information between PCB and mechanical tools. 

While the DXF format contains circuit board size and thickness, the IDF format USES the X and Y position of the component, the component bit number, and the z-axis height of the component.This format greatly improves the ability to visualize PCB in 3d views.Other information about the restricted areas, such as the height limit on the top and bottom of the circuit board, may also be included in the IDF file. 

The system needs to be able to control what is contained in the IDF file in a similar manner to the DXF parameter setting.If some components do not have height information, IDF exports can add missing information during creation. 

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

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

To improve the STEP file exchange, we introduced the ProSTEP format.This format moves the same data as IDF and STEP, and is greatly improved - it can track changes or provide the ability to work in the discipline's original system and review any changes after the baseline is established.In addition to viewing the changes, PCB and mechanical engineers can also approve all or individual component changes in layout, circuit board shape modifications.They can also suggest different circuit board sizes or component locations.This improved communication creates an ECO (engineering change order) that has never existed before between the ECAD and the mechanical group.

Most ECAD and mechanical CAD systems now support the use of the ProSTEP format to improve communication, thus saving time and reducing costly errors that can result from complex electromechanical designs.More importantly, engineers can create a complex circuit board shape with additional limitations and then transmit this information electronically to avoid someone misinterpreting the circuit board size, thereby saving time.