How to connect SMD components to ground plane

[matrixofdynamism]

Like most people I am have encountered confusion with regards to ground planes on PCB.

(1) As far as I understand, the hole drilled for via is platted so I can connect to it at top or bottom. Is this assumption wrong?

(2) First I made top as power plane and bottom as ground plane. This works for through hole components quite well. I could easily connect to power and ground without needing trace. Is this approach wrong?

Main problem:
(3) I have SMD components, how do I connect them to ground plane? One idea is to make top as ground plane and use trace for VDD. I can still have bottom plane as VDD too for the through hole components. Is this the best approach?

(4) As far as I understand, the ground plane must be below the signal path, thus if I make the bottom ground plane, what is the best way to connect it to the ground plane to SMD components since I also need to use decoupling capacitors, probably several of them for different SMD components? Should these decoupling capacitors go onto the top or bottom of the board?

 

[KlausST]

HI,

I think there is no general answer.

I don´t like the idea of using the GND plane at the component side.
The ground plane should be as solid as possible, this can´t be done when all the components need that much space.

Therefor I recommend to put the GND plane at the bottom or in an inner layer.
Often it is good to connect each single GND signal with an extra via to the gnd plane. With high currents and/or switching currents you should use multiple vias.

For low power (logic) devices there is no need for a power plane. You could use single traces but with individual capacitors at each VCC pin. (but a power plane will have it´s improvements)

Often i place all components on one side, so the VCC capacitors are on the component side, too.
But sometimes - when teher is not enough board space - I place the VCC capacitors at the bottom side. I think there is not much deviation in impedance compared to top side.
top: GND_plane - via - capacitor - VCC_pin
bottom: GND_plane - capacitor - via - VCC_pin
(if you place them all in same orientation it might be able to solder them with a wave. )

Klaus

 

[matrixofdynamism]

Thanks.

How about ground plane on both top and bottom with many vias connecting the two? And trace for vcc.

 

[KlausST]

Hi,

I often saw this, but I (personally) don´t find it usefull.


Klaus

 

[marce]

I second the use of a SOLID CONTIGUOUS ground plane, how many of these ground planes I will add to my design depends on...
Signal/power requirements.
Cost, adding layers does add to the cost.
Just done a design where I upped the layers from 8 to 10 to get 2 extra ground planes in, so I had all the long signals routed as stripline between two ground planes, but also the power layers each had an adjacent ground plane... (12 layers would have made me even happier...)

Like most people I am have encountered confusion with regards to ground planes on PCB.

I would expect most professional people involved with PCBs not to say that, there is a wealth of information out their regarding ground planes, decoupling etc. Here's a basic list (that one day given some time I will update!!!!)

And here's some pretty pictures of the electro-magnetic fields and how they interact with a ground plane....

- - - Updated - - -

Look up splits in ground planes, it will explain why top and bottom outer layer ground planes are a bit of a waste, and in fact they are ground copper pours not plains........