FEDEVEL
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, 09-15-2025, 05:42 PM

Hi @Robert Feranec and all. I need opinions about to use all dielectrics using FR-4, and an opinion to use L5 Signal and L6 GND Plane. Thanks in advance. Its so difficult find videos or real information about medical devices PCB design.

Robert Feranec , 09-15-2025, 10:55 PM

usually I would like to use the materials that are used and stocked by PCB manufacturers ... otherwise there are many problems. Also, material will influence what is the minimum track width you can have for example for 50OHM tracks and it inflences how far the GND layer will be from signal layer. So I normally just check what stackups the manufactuerer can build and select the one wich canoffer narrow traces (for high density PCB) or the stackup that has signal layer close to GND reference plane.
What problem are you expecting with L5 and L6 layers?

, 09-16-2025, 12:09 AM

Usually on stackup we use GND at L2 and L5 and L1 referenced to L2, and L6 referenced to L5. But, consulting web, using L6 as GND plane we achive a cage faraday in respect to L5 (signal).

QDrives , 09-16-2025, 07:30 PM

1) You have a "reverse build-up" stack-up. A Normal stack-up has prepreg as the outermost dielectric.
2) If you want L6 as Gnd, then I assume L2, L4 and L6 are Gnd?
3) You cannot use Altium's symetrical stack-up when using planes that way.

Karthik , 09-20-2025, 10:18 AM

The question is what is the routing and component density on the board. Also, components only on top or both sides? I like to have 2 routing layers - one for horizontal runs and one for vertical. To shield them properly, and to provide reference to the components on both sides, i'd be tempted use L2 and L5 ground, L3 and L4 as signal routing and power split planes (assuming its a low power device). In this case, i will keep the L3 -L4 core thicker (like you have) so that the signal return path is on ground layer that is closer compared to the other signal layer.