7 Common Misconceptions about PCB Design
After years of PCB assembly you probably know about a decoupling capacitor, a solder mask, and schematic symbols like the back of your hand. Right? Brace yourself. We’re about to challenge everything you ever thought you knew about printed circuit board design. Well, maybe not everything. Seven things. Everyone holds to certain misconceptions when designing: things they’ve been taught, things they heard, things they learned firsthand that simply don’t apply anymore… Clinging to these misconceptions is a hindrance to your designs and can lead to defective boards and field failures, as well as higher overall production costs. It’s essential, every now and then, to take a look at the rules of thumb and standard design guidelines that you’ve been taught, and see if they really make sense in your current design environment.
The 7 PCB Design Misconceptions
1. Rigid and Flexible Circuits Have the Same Design Rules. The materials are different, but the functionality is basically the same, so there shouldn’t be much difference in design schematics, right? There’s more than you’d think. For one thing, flexible circuits need to be designed to minimize locational stresses as they’re folded and bent. There’s also a difference in the dimensional stability of the base materials. No matter how well you know rigid circuit design, if you’re just starting in flexible circuits, you have some catching up to do.
2. Via in Pad Will Damage Your Circuit Board. In certain situations this can be true—if it’s not used properly. Plating chemicals can get trapped if you don’t cap your via in pad, or don’t mask it (from the opposite side). But even so, this is not a reason to avoid via in pad entirely, as many designers say you should. In fact, via in pad can have a number of important uses. They’re great for placing close bypass caps. They also help with thermal management and grounding, and make any pitch BGA routing easier. Via in pad is nothing to be afraid of. It can be a great tool for certain situations, if you have the right guidance.
3. 90 Degree Angles Are Acid Traps. This used to be true. When PCBs were etched with acid, 90 degree angles would collect acid in the corners, leading to problems. Therefore, PCBs have for many years been almost exclusively designed with only 45 degree angles. However, etching is now done with alkaline, rather than acid, so acid traps are no longer a problem. Feel free to use 90 degree angles all you want.
5. PCBs Are Bad for The Environment. Our society replaces its electronics practically every other week. What happens to those old circuit boards when everyone is upgrading to a new iPhone, and getting rid of their old ones? Well, a solution is on the horizon. Engineers are currently developing biodegradable PCBs, which will break down harmlessly after they’re discarded, rather than sitting in a landfill for millennia.
6. A Beautiful Design Is Everything. Engineers are artists. They want their designs to be as elegant and fluid as possible. Unfortunately, while within your EDA design tool, you’re not constrained to any boundaries, your finished product has to abide by the laws of physics, the materials available, the tools being used for manufacture, and a host of other limitations. For example, in design, you can have virtually any annular ring size, any track width, any spacing, and any material properties you desire. However, the board that actually gets produced needs to take these factors and limitations into consideration in order to function properly in the real world. Though their designs may work well on paper, they don’t always function practically when applied in the real world. Within those limitations are also variations that need to be kept in mind as well. You can’t design in a vacuum. Being aware of real world limitations and design constraints will help you design more practically the first time around, saving time and money in the long run.
7. Your PCB Design Software Doesn’t Matter. What PCB design tool will you invest in? Which PCB manufacturer will you go with? Will you get the cheapest one? The one with the most bells and whistles? Or will you stick with the tools you already have, no matter how many bugs they have, because you’re used to the way they function? Choosing the right PCB design software is an important decision that involves a lot of factors. And remember that in addition to the set of features, there are other important aspects to keep in mind, such as the type, quality, and quantity of readily available content to jump start your design. Does the platform you choose have a community and support for when you have questions or experience problems? Is the supply chain integrated within the tool? How is their MCAD integration? How well do they manage library components and designs? Carefully outline what it is you need from your software, what kind of user interface it needs, what your price range is, and any other important information. Then use that outline to find the software solution that best meets your needs.