Design Con 2015

Moving to open-source PCB design

-January 24, 2014

Electronic design trends include the use of open-source hardware designs and the open-source schematic and PCB layouts that accompany them. This growing trend is explained by the ease with which engineers can adopt existing designs and, in turn, improve their efficiency and time to market. With better understanding of the design differences between traditional PCB designs and open-source designs, this trend will likely continue.

There are several advantages over traditional PCB design that make open source a more appealing option for engineers. These include re-use of the power and digital sections, as well as high-speed data sections. Engineers have always had to struggle with the power layout, but now with higher speed and RF structures on the board, the task has become much more complex. Engineers must now pay closer attention to the board’s trace width, proximity and through-hole vias. In an open-source PCB design, layouts that have already proven effective can be copied – eliminating the need to start the design from scratch.


Figure 1: Electronic design trends include the use of open-source hardware designs and the open-source schematic and PCB layouts that accompany these designs. (Image shows a BeagleBone Black.)

Growing Trend
When designing for higher-speed layouts (or layouts of a similar nature) many engineers have traditionally gone to application notes , asked manufacturers for assistance, or even used PDF copies of boards to measure the traces on the paper, hoping they are to scale. For applications involving many of these more complex layouts, open source has become a more appealing option. The ease with which open source designs can be adopted removes the burden placed on engineers to be “layout experts” in all areas of the PCB design process, particularly when facing uniquely difficult sections in the design. To give an example, power supply, a traditionally difficult section to design, has become easier to lay out when using existing open-sourced designs. The complicated PCB layouts of power supply, high-speed interfaces and lines, or even impedance-matching lines, can be re-used or replicated via open source quickly and easily.

Challenges & Benefits
There are challenges when integrating open -ource designs. For example, engineers are faced with more noise issues.  With high-current switching supplies now being brought on the board, noise radiates onto other lines. But perhaps the largest and most important of these challenges is the learning curve change. Simply put, when copying and pasting layouts that are open-sourced, engineers risk losing the opportunity to learn the fundamentals that come with designing from scratch. These fundamentals include spacing methods, recognizing necessary line widths, and impedance matching.

The trade-off is a complicated one: engineers who do not use open-sourced designs will have a difficult time with certain components of the design process, but engineers who do open-source designs risk losing a deeper knowledge of design. If the fundamentals are missing, it becomes difficult to adapt to unique design challenges in the future.

On the other hand, using open-source designs can give engineers the experience of looking at the PCB design process from a new perspective. The same learning challenge of open-sourced designs then becomes a learning opportunity, provided the right approach is taken.

Using open source designs give engineers a starting point in the process. Engineers can “dive” deeper into PCB design if open-sourced layouts are treated as a reference point. From that reference point, engineers can work backwards to better understand why certain layouts are organized in a particular way. This facilitates a new way of learning from existing designs, a process not necessarily available in the traditional PCB design format.

To return to the example of power supply designs, an engineer who has employed open-source layouts can analyze particular components of the power-supply design, line spacing, or the amount of copper used to work backwards from the end result. The ability to work backwards to learn those lost fundamentals – thermal management, impedance matching and power supply layout, to name a few – gives engineers the opportunity to learn empirically.

Some Tips
Before making the switch to open-sourced designs, it is important to remain cautious. Remember that not all open-source is truly “vetted.” When creating an open-source layout, for example, an engineer may not have the proper understanding of how applicable it is to another engineer’s layout. Thermal management is, again, another area in which open-source designs can fail an engineer if a complete understanding of the differences in the designs are not understood. Simply put, sometimes we do not know where an open source layout is coming from, so it is difficult to predict how reliable it will be.
In the power supply example, an engineer using an open source layout may initially believe the board is running properly and integrate it into the design. When the design moves into the testing phase, however, it may fail if the original design was not fully tested to meet certain specifications or requirements, such as EMI from radiated or conducted emissions.

Fortunately, there are  precautionary steps you can take when new to designing with open-source layouts. If the PCB layout is sourced from a semiconductor supplier, odds are the layout will be more robust and reliable compared to a layout sourced from an online bulletin, website, or forum. Forums can be a way to confer with fellow PCB design engineers on the successes and failures of specific open source layouts, as engineers at the element14 open source group do. As PCB design methods continue to migrate toward open source formats, recognizing the challenges, advantages and unique learning opportunities this approach presents will yield results that benefit not just engineers and manufacturers, but the PCB industry as a whole.

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