Useful Information | How to solve the design problem of irregular shaped PCB?

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Today, PCBs are shrinking in size, with more and more features on the board, and with the increase in clock speeds, designs are becoming more complex. So, let’s take a look at how to handle boards with more complex shapes.

Simple PCI board outlines can be easily created in most EDA Layout tools. However, when the board outline needs to fit into a complex enclosure with height restrictions, it is not so easy for PCB designers because the capabilities in these tools are not the same as those of mechanical CAD systems. Complex boards are mainly used in explosion-proof enclosures and therefore have many mechanical restrictions.

Trying to recreate this information in an EDA tool can be time consuming and unproductive since the mechanical engineer has most likely already created the enclosure, board outline, mounting hole locations, and height constraints required by the PCB designer.

Because of the curvature and radii in the board, rebuilding may take longer than expected, even if the board shape is not complex.

However, if you look at today’s consumer electronics, you’ll be surprised at how much engineering has gone into trying to fit all that functionality into a small package, and that package isn’t always rectangular. Smartphones and tablets are probably the first examples that come to mind, but there are many more.

If you've ever returned a rental car, you've probably seen the valet use a handheld scanner to read the car's information, which then communicates wirelessly with the office. The device is also connected to a thermal printer for instant receipt printing. Virtually all of these devices use rigid/flex circuit boards, where traditional PCB circuit boards are interconnected with flexible printed circuits to enable them to be folded into a small space.

How do you import defined mechanical engineering specifications into your 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 DXF, IDF or ProSTEP formats. Doing so can save a lot of time and eliminate possible human errors. Next, we will look at these formats one by one.

DXF is the oldest and most widely used format for electronically exchanging data between the mechanical and PCB design domains. It was developed by AutoCAD in the early 1980s. This format is primarily used for 2D 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 units that will be used during the exchange process.

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

While the DXF format contains the board size and thickness, the IDF format uses the component's X and Y position, component reference number, and component Z-axis height. This format greatly improves the ability to visualize the PCB in a 3D view. Additional information about keepout areas may also be included in the IDF file, such as height limits on the top and bottom of the board.

The system needs to be able to control what will be included in the IDF file in a similar way to DXF parameter settings. If some components do not have height information, the IDF export can add the missing information during the creation process.

Another advantage of the IDF interface is that either party can move components to new locations or change the board outline and then create a different IDF file.

The disadvantage of this approach is that the entire file representing the board and component changes needs to be re-imported and in some cases this can take a long time due to the file size.

Additionally, it was difficult to determine from the new IDF file what changes had been made, especially on larger boards. IDF users eventually created custom scripts to determine these changes.

In order to better transmit three-dimensional data, designers are looking for an improved way, and the STEP format came into being. The STEP format can transmit circuit board dimensions and component layouts, but more importantly, components are no longer a simple shape with only a height value.

STEP component models provide a detailed and complex representation of components in 3D. Both board and component information can be transferred between PCB and mechanical. However, there is still no mechanism to track changes.

To improve STEP file exchange, we introduced the ProSTEP format. This format moves the same data as IDF and STEP, but with major improvements – it tracks changes and also provides the ability to work in the discipline’s original system and review any changes after a baseline has been established.

In addition to reviewing changes, PCB and mechanical engineers can approve all or individual component changes in layout, board outline modifications. They can also suggest different board sizes or component locations. This improved communication creates an ECO (Engineering Change Order) between the ECAD and mechanical groups that never existed before.

Most ECAD and Mechanical CAD systems now support the use of the ProSTEP format to improve communication, saving considerable time and reducing costly errors that can arise with complex electromechanical designs.

More importantly, engineers can create a complex board outline with additional constraints and then electronically communicate this information to avoid someone incorrectly reinterpreting the board dimensions, saving time.

If you are not already exchanging information using these DXF, IDF, STEP or ProSTEP data formats, you should check out their use. Consider using this electronic data exchange and stop wasting time recreating complex board outlines.

Source: Compiled from the Internet. If there are any copyright issues, please contact us in time to delete it.

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