PCB Technical - Is it difficult to design irregularly shaped PCBs?

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

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

Simple PCI board outlines 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. Complex circuit boards are mainly used in explosion-proof enclosures, so they are subject to many mechanical restrictions.

Rebuilding this information in EDA tools may take a long time and is not very effective. Because, mechanical engineers are likely to have created the housing, 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.  

However, from today's consumer electronics 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. Your first thought should be smartphones and tablets, 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, where traditional PCB circuit boards are interconnected with flexible printed circuits so that they can be folded into a small space.  

How to import the defined mechanical engineering specifications into the PCB design tool?

Reusing these data in mechanical drawings can eliminate duplication of work, and more importantly, eliminate human error.  

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

DXF

DXF is a long-standing and widely used format that mainly exchanges data between mechanical and PCB design domains through electronic means. AutoCAD developed it in the early 1980s. This format is mainly used for two-dimensional data exchange.

Most PCB tool suppliers 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. 

Three-dimensional functions began to appear in PCB tools, so a format that can transfer three-dimensional data between machinery and PCB tools is needed. As a result, Mentor Graphics developed the IDF format, which was then widely used to transmit circuit board and component information between PCB and machine tools.

IDF

Although the DXF format includes the size and thickness of the circuit board, the IDF format uses the X and Y position of the component, the component location number, and the Z-axis height of the component. This format 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. 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 shape of the circuit board, 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 which 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.

STEP&ProSTEP

In order to better transmit 3D data, designers are looking for an improved method, and the STEP format came into being. The STEP format can convey the size of the circuit board and the layout of the components, but more importantly, the components are no longer a simple shape with a height value.

The STEP component model provides a detailed and complex representation of the components in a three-dimensional form. Both the circuit board and component information can be transferred between the PCB and the machine. However, there is still no mechanism that can be changed.  

In order to improve STEP file exchange, we introduced the ProSTEP format. This format can move the same data as IDF and STEP, and has a great improvement-it can be changed, it can also provide the function of working in the original system of the subject and reviewing any changes after the benchmark is established.

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 circuit 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.  

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 may 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 circuit board size, thereby saving time.