I grew up in the era before the PlayStation ever existed. Back then, generic consoles reigned alongside premium counterparts like Super Nintendo and Sega. I first discovered my stubborn streak while playing Super Mario, a game where a funny looking character starts shooting fireballs after getting power-ups from mushrooms. I lost count of how many times I repeated the entire game even though I was always ultimately defeated at the last level. As there were no ‘saves’ and ‘continues’ back then, I spent countless hours trying to get the better of the villain crocodile boss character.
Thankfully, I was slightly smarter in dealing with problems routing my PCB due to size constraints. When starting your career as a hardware designer, you may assume that PCB design is a fun process of arranging components and linking connections. That misconceived notion will soon disappear as you struggle to route a seemingly simple design for several days.
PCB Design Tips for an Unroutable Board
Various factors can contribute to an unroutable PCB: limited dimensions, strict compliance to routing practices, and component choice. Rather than throwing in the towel, however, you can follow various tips to make your PCB routable. Note that some of these tips require a compromise in terms of cost.
1. Use smaller form factors
If you’re still using through-hole components, you should have good reasons for doing so. They occupy larger areas compared to their surface mounted counterparts. With that said, surface mounted components are available in various form factors and opting for a smaller form factor may clear the path for copper traces to pass.
Sometimes, opting for a Ball Grid Array (BGA) instead of a Quad Flat Package (QFP) for microcontrollers can increase area efficiency during the routing process. Of course, using smaller form factors may make manual repair more difficult, as they demand a higher level of precision and technical skill.
Go smaller if you have to.
2. Rearrange the components
You’ve probably read enough about how analog and digital components must be separated from each other. Other best practices dictate the appropriate component placements to reduce electromagnetic interference (EMI) susceptibility. However, these are not the only reasons you should understand how the components are placed on the PCB.
Simple common sense can sometimes help in ensuring that components are neatly organized and no precious space is wasted. For example, cascaded components ought to be placed close to each other so that the interlinking traces do not become a nuisance in other areas of the PCB.
3. Use smaller traces, vias, and clearance
Most of us inherited hardware designs from our predecessors that may be subject to manufacturing limitations that are no longer applicable today. These days, PCB manufacturers have no problems supporting traces and clearances as tiny as 3 or 4 mils. Unless they are traces that carry a substantial amount of current, you can reduce the width to complete routing the PCB.
4. Use a multilayer PCB
Cost is definitely an important factor when it comes to the business aspects of electronics design. A single or double layer design is usually preferable if there are no immediate needs for a multilayer PCB. However, shifting the power and ground connections to the middle layers of a PCB will do wonders in freeing up enormous spaces on the outer layer. Besides, having a large power and ground plane provides a stable power supply for PCB components.
Use multilayer PCB for more free routing areas.
Prioritize Autorouting After Making These Changes
I come from an age where engineers were limited to manual routing tools as autoroute features were not as developed as they are today. Imagine the frustration of spending hours with different design rules to complete the PCB only to give up in vain. Luckily, the PCB design world of today offers more options.
After making the needed changes on your PCB, I strongly suggest using a powerful autoroute feature, like the one in Altium Designer, to ensure that your PCB is routable. After confirming that your PCB is physically routable, you can start manually making certain critical connections before letting the autoroute tool to complete the rest.
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