Quiz Answer – PCB Layers stackup


PCB-STACK

On the picture above you see 4 layer PCB. The layer stckup is very important if your board will have controlled impedance, i.e. if you route high speed signals.

For most of our designs we use this standard stackup:

  • TOP copper signal layer 35 um finished copper thickness.
  • P2116 prepreg which have 100 um thickness.
  • internal copper GND plane with 35 um copper thickness.
  • Core 1.2 mm
  • internal copper GND plane with 35 um copper thickness.
  • P2116 prepreg which have 100 um thickness.
  • BOTTOM copper signal layer 35 um finished copper thickness.

When add all above we get total PCB thickness = 0.035+0.1+0.035+1.2+0.035+0.1+0.035 = 1.54 mm +-10%

Why we use this stackup? Because with it, the traces with 5 mils width have about 50 ohm characteristic impedance and 5 mils is convenient for high speed signal routing.

 

10 Comments (+add yours?)

  1. GeeKen
    Dec 23, 2015 @ 03:05:48

    Thats a fascinating PCB layout approach – are the two central layers both grounds ? Or is one the +ve supply layer ?

    I guess it has to be that way so that signals are not coupled to the +ve rail ??

    Thanks for the Info !!!!

    * *

    Reply

  2. Zivko
    Dec 23, 2015 @ 14:57:18

    In any case a properly decoupled powr is signal ground

    Reply

  3. Dylan
    Dec 24, 2015 @ 21:59:39

    Can’t the trace on the left be a bit more curvy?😉

    Reply

    • LinuxUser
      Dec 25, 2015 @ 16:53:04

      😀 nice catch, that was a part of previous quizz on highspeed boards routing. Uhm, well, still, a good picture to show it some competitors, and somesuch. Let ’em get some ringing in their circuitry, he-he 🙂

      Reply

    • Arturas
      Jan 06, 2016 @ 18:00:56

      No need. The this trace is going through via, which is already “90 degrees” in signal path😉

      Reply

  4. __BriKs__
    Jan 06, 2016 @ 00:36:36

    Hi guys, take a tour on http://www.icd.com.au/ and you can download some usefull pdf about impedance and stackup relative stuff. I build a 8 layer ddr3 design using theyr consideration and the associated free eval software, using the explanations I took the opportunity to benchmark my layout with high end industrie pcb simulation tools (polar 9000, allegro sigrity, hyperlinx) to seee how with just following recommandation my ddr3 design (simple desing onlye 2x16bits ddr chips running @ 400mhz) was top of the art. Have fun desing with passion!

    Reply

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