3/25/2023 0 Comments Seven habitsWithout a detailed analysis, which every engineer should do, we can only follow some general design guidelines that will reduce the risk that these problems will bring your product down. The goal in the physical design of the board, including the layout, is to follow general design guidelines to reduce these two problems. Figure 2 is an example of the measured ground bounce in an Arduino Uno board as multiple digital outputs are simultaneously switched on and off. While there are many signal and power integrity problems that can arise, the two most common and with the largest impact, are cross talk due to excessive mutual inductance between signal and return path loops (ground bounce) and switching noise on the power rails due to large transient current swings. Once the connectivity is established, the interconnects can only screw up the performance of your product. It says nothing about the signal or power integrity performance of the design. The two problems we are trying to avoidĪ schematic identifies the components used in a design and how they are connected. In my course we use the Arduino as an example of how NOT to design a board and then re-design it using the following Best Design Practices. This unfortunately reinforces bad design habits. You can use almost any design rules and it will work. The Arduino Uno is a pretty robust product. An example of this board is shown in Figure 1. In the graduate class I teach at CU, Boulder, on Practical Printed Circuit Board Design, we use the venerable Arduino Uno board as an example of a 2-layer board that works but violates almost every one of the seven important habits. But, many consumer products, microcontroller and IoT applications are built in 2-layer boards. Generally, it is hard to route a BGA package such as an FPGA or high-end microprocessor in a 2-layer board. In most 2-layer board designs, performance is limited. But, if performance matters, if the interconnects are not transparent, or if you want to develop good habits, you will want to incorporate these seven habits in your next two layer board design. All you need to worry about is design for manufacturing at low cost and maybe design for test. If you can build your product using a solderless breadboard with wires going every which way, and it works, and the interconnects are transparent, then it probably doesn’t matter how you design your circuit board.
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