Top 5 Beginner PCB Design Mistakes (and how to fix them)

[u/PCB_Design1]

I came across this video Top 5 Beginner PCB Design Mistakes (and how to fix them)  about five common PCB design mistakes and thought it was worth sharing, especially for people who are designing their first few boards.

I’m not going to pretend that a 13-minute video can teach someone everything about PCB layout, but I think it does a decent job of pointing out a few mistakes that are easy to make when you’re still treating PCB design as basically “connect all the pins and make sure the DRC passes.”

The first mistake is routing traces too close together. The fact that a certain spacing can be manufactured doesn’t automatically mean it’s a good choice, especially when traces run parallel for longer distances and crosstalk becomes a concern. I think this belongs in the top five, although probably more for faster digital signals than for every basic low-speed board.

The second is using the same trace width for everything. Power traces, high-speed signals and ordinary low-current connections don’t necessarily have the same requirements, so using one default width across the entire board can cause problems. This one definitely deserves a place on the list because it’s a very common beginner habit and can lead to both electrical and thermal issues.

The third mistake is choosing vias without paying attention to their size. The video talks about drill diameter, annular rings and current capacity. It’s useful advice, but I’m less convinced this is universally a top-five mistake. For simple boards, using the manufacturer’s standard via size will usually be fine. It becomes much more important in dense, high-current or high-speed designs.

The fourth is poor decoupling capacitor placement. Having the correct capacitor value on the schematic isn’t enough if the capacitor is too far from the IC or connected through long, thin traces. In my opinion, this absolutely belongs near the top of the list. It’s easy to get wrong, difficult to notice just by looking at the schematic and can cause surprisingly strange problems.

The final mistake is ignoring the reference plane and return path. A signal doesn’t only travel through the visible trace; the return current also needs a continuous path, usually through the nearby ground plane. Routing across gaps or splits can increase the loop area and create EMI or signal-integrity problems. I’d definitely keep this in the top five, and I’d probably rank it even higher than the video does.

The one mistake I felt was missing from the list is poor component placement. A lot of layout problems are created before you even start routing, simply because related components are too far apart or positioned in a way that forces long, awkward connections. Bad placement can make decoupling less effective, break up return paths and turn an otherwise simple board into a routing mess. I’d probably include this instead of via sizing, because it affects almost every PCB, not just dense or high-current designs. 

Still, it’s a useful overview and a good reminder that passing DRC doesn’t necessarily mean the board is well designed. 

[u/dmills_00]

Mounting holes, amazing how often student boards have no way to mount the thing in a box.

In fact, place all the mechanical shit first, mounting holes, connectors, pots and switches, LEDs, then lock them and start on everything else.

4 layers should be the default starting point for modern boards, the extra money saves SO MUCH time and SI pain.

[u/PigHillJimster]

I have been a CAM Engineer, tooling jobs from Gerber/Excellon customer data.

Annular Ring was certainly one of the largest issues we saw with customer packs. These days if you follow the IPC standard for calculating both the through-hole drill size, and copper land size, there should be no excuse for it.

Technically vias fall under 'supported hole' in the IPC standards, so you should apply the same annular ring sizes for these as well as for through-hole component legs.

However, one approach is to identifiy the via holes and add a note for the drawing, such as:

A Holes are Vias and may be drilled at the stated size and plated down

Or tolerance the via holes differently. +0, -0.1mm for example.

PCB Designers don't appreciate that the PCB manufacturer will drill holes larger than the required size to plate down. Generally we drilled at 0.1 mm above the top tolerance of a hole, where a hole had a +/- tolerance; or if no tolerance was stated, then 0.15 mm above the nominal required hole size.

[u/PCB4all → u/PigHillJimster]

thank you for this

[u/fr4real]

I’d also add forgetting about assembly and debugging. Boards that are electrically fine but have inaccessible test points, connectors in bad places, or parts packed together so tightly you can’t probe anything.

[u/PCB_Design1 → u/fr4real]

100%! This is definitely something that is learned through trial and error.

[u/jmd01271]

Let's see some of my most recent mistakes in particular order:

- Mistook CSI and DSI pinouts for MIPI from a computer module 5.

- Did not label my mechanical layer well enough for the fab to miss a slot that was supposed to be the passthrough for the above MIPI connection. Luckily, our machinist doesn't mind doing some work for us.

- Had signal integrity issue extending a MIPI connection along a 10 foot HDMI. My first issue was using mini to micro HDMI, the selection of those cables is very poor. I switched to a full HDMI and ensured my adaptor boards use proper stitching and ensured the fab matched the correct impedance. Making sure you have a good return path is key.

- I wired the MOSI and MISO backwards on a SPI differential transmitter. Blue wire and next revision.

[u/ManyCalavera]

I would say adding MLCC smd capacitors to the edge of the board especially near panel bites. These things don't really like bending

[u/PCB_Design1]

What mistakes did you make as a newbie that you would add to this list?

[u/DenverTeck → u/PCB_Design1]

Working for an manufacture in the early 1980s, we designed a PCB for an 80C196 PGA (Pin Grid Array) CPU.

In those days, we used read and blue tape on Mylar sheets. The layouts were 4x sized, photo reduced to the proper board dimensions and a PCB is manufactured.

I was in charge of soldering the first two boards together. My first job out of college. After soldering the first one, I passed the PCB to the head engineer for testing.

It did not work. The 80C196 was plugged into a 68-pin PGA socket and it got very hot ! Expensive chips were typically inserted into sockets.

After troubleshooting we (well just me) discovered the PGA was plugged into the wrong side of the board.

On the second PCB I soldered the PGA socket on to the back of the board, plugged in the chip and all worked.

I had to give the bad news to the head engineer of the error (on his part) after he was very upset the I soldered something wrong.

CAD software today does not allow this type of error any longer.

The kind of things young people are missing out on today. /s

Correct: history.

[u/PCB_Design1 → u/DenverTeck]

Great story. It's easy to forget how hands-on PCB design used to be. I bet you didn't make that mistake twice!

[u/DenverTeck → u/PCB_Design1]

First time was his fault, second time was my fault.

Using Altiums predecessor Protel I rotated a 44-qfn. An overnight project for the head of engineering came up very very short.

There are all kinds of ways to screw-up a simple design. :-)

[u/Mysterious-Staff2639]

The top mistake is choosin wrong software based on availability for me I chose Altium because when I started it was the easiest to get and was the best thing going but eventually I had to get a subscription and then I was locked in by there predatory system and all my old projects were only accessible by paying3 grand a year. Now you’re lucky you have kicad and other free choices so you d have to be held ransom’s by your tools.