EEVblog #1176 - 2 Layer vs 4 Layer PCB EMC TESTED!

What difference does a 4 layer PCB make to EMC radiated emissions compared to an identical 2 layer PCB? And why?

Dave does H-Field near-field probe testing on two otherwise identical PCB's.

Electromagnetic waves and the difference between near field and far field, and H-Field and E-field probes and wave impedance is also explained.

The PCB layout is then examined to look at loop area and by-passing and what effect this has.

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#PCBdesign #PCBdesign #EMC

[iamdarkyoshi]

So this is what the metalised plastic on cheap laptops is for, shielding the board from radiating EMI. Neat.

[williamvaverka]

I am a PCB designer in a small electronics designing company and we are aiming a lot on the low price, so most of thw stuff we do is 2 layer. It caused a lot of problems to us when we go to EMC testing. Biggest problem is the fast switching, you can put 10R to 22R resistor in series in the high speed traces, this helps a lot. Also keep your traces as short as possible and always look for the ground loop.

[oly]

This is great, the first time I have ever seen someone do this on the same pcb as a 2 layer and 4 layer with groundplane.
Thanks Dave this is a really really useful emc video.

[ELECTRONOOBS]

This is so nice to see the effects directly and the difference between 2 and 4 layers. I made a lot of PCBs for my DIY projects that are using radio connection. I always had problems with the radio module because the SPI for that was very "sensitive", but once I place that on the exterior of the PCB and made a ground and Vcc plane, the board had no more radio errors. Especially that my board was using PWM signals and MOSFET control and that made a lot more noise. Thank you for all that you show us!

[michaelmoorrees]

FCC Part 15 is the compliance regs in the US. In the late 70's these new personal computers (Apple II, CP/M systems, but NO IBM PC, yet) plus video game consoles, and other microprocessor based products needed to be added to the compliance standard. So subpart J was added. The whole Part 15 reg has been since realigned, so there is no subpart J anymore. I'm old enough, and had was in the electronics business when subpart J was added. The company gave me the task of making sure our product designs complied with the new regs. Some of these RFI/EMI testing houses are better than others. The first one we went to just ran the test, and we had to fix it back at the shop, before retesting. Another house, let us try things while at their facility, and ran shortened tests to check our intermediate results. They also gave us suggestions. That was a good test facility !

Now products come out of China, and testing boils down to applying a compliance sticker.

[JonathanDFielding]

I'm an electrical engineer and I love these type of videos. I'm still pretty young a very hungry and eager to improve my skills. Work for a large company and so there are other engineers whose careers have been dedicated to Signal integrity. So I don't really get to learn this as they are the ones who are the real experts on these topics. Then again I don't think we've ever done anything smaller than a 6 layer board. We ground flood the top and bottom layers and all signals are inside the board. That's how they deal with Emi and EMC. They just surround everything in ground. Please do more videos on practical engineering tips and tricks. I enjoy these types of teaching the young engineers much more than I like an unboxing video. I do really like your tear-downs to as they can teach a lot

[noakeswalker]

Great to see A-B-A comparison of the same layout in 2 and 4 layer. Thanks Dave.

[qwerty]

Good work Dave, amazing video. I have never seen a 2 to 4 layer PCB comparison before, and to have a board for the test with this level of complexity is really a bonus.

[ayitsyaboi]

Just dropping in to say how refreshing it is to see a content creator who actually interacts whit their viewers. I barely understand any of what I'm watching, but as a hobbyist going nowhere I still find it all super interesting.

[MaxWattage]

I'm delighted to see this high-quality educational content.

[ElmerFuddGun]

Ah yes, the Gigatron Computer is back. Almost forgot about your 4 layer version. Watching with interest!

[Graham_Wideman]

Great credit to Dave for going to the effort of making this board and exhibiting the measurements! Some of Dave's videos can be relatively blab or rant oriented, of which there is much on YouTube :-), but videos like the current one really distinguish this channel. Well done Dave!

[dotdissonance]

This was super helpful! Thank you. Short loops, via stitching and watch out for bypass caps. Perfect timing for a current project as well. Still killin' it after all these years!

[drjmansplace]

Sometimes, as professionals, we overlook some basics. Thanks for the post. Great refresher.

[Damien.D]

DaveCAD, now in 3D and augmented reality.

[bossssie]

It used to be a challenge to route everything on a 2 layer board. Since I've had a couple of products compliance tested I go straight to the 4 layers.

[PlasmaHH]

Regarding the heatmat, a rather different ("real") kind of heatmap I have seen many years ago in a video (that I can't find):

The guy took some thin layer pcb ground planes (full, with split etc.), painted them black and took some prepreg with signal traces, overlayed them and then ran high power high frequency signals through them. In the end he took an image with a thermal camera. The result was very neatly showing how the low frequency components chose the intuitive shortest path, but the high frequency ones were following the signals, or spreading out in places nobody would have thought of.

[namty]

Great job Dave. I love your video not only the technical aspect, but the way you spit out your knowledge with so much emphasis. Keep doing more and more video.

[RobertFeranec]

@Dave, please take it to an official EMC lab to compare the boards (if a lab would measure it for you for free)

[ewafelber]

I love your explanation about near and far field extra to the main subject. When it comes to layers, I newly redesigned an RF board (up to 6 GHz) from 4 to 6 layers. A lot of other changes had to be made, mostly because of the last problems with delivery of the components and because of the heat issue. But I have taken care of the appropriate routing of the RF lines and of grounding in general, in the same time REMOVING many decoupling capacitors (after watching Eric Bogatin presentation at Altium Live) and... the PLL on the board is soooo less noisy!! The biggest Spourious reduced from ca. 30 dBc to less than 50. Sadly I could not compare the grounding alone so nicely as you did