GND Connected but ... not?[RESOLVED]

Hello guys,

i’m doing some reverser enginering and i got a big problem. I can’t found the connection between two GND (but there is a connection, with multimeter it “biiiiiip”). There is no component on the card…

other face :

but there is connection with others GND…

My assumption: There is a third layer. What do you think ?

Thank you guys :slight_smile:

I think you shouldn’t reverse engineer a board which looks like that :slight_smile:

It’s difficult to say anything about the problem, you should at least mark some corresponding vias in each side. And even then, if you can’t see and can’t find a connection with the board in your hands, how could we just by looking at some photos?

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I had almost finish the card… the only think which i have to do it’s make all GND the same but i don’t know how they did… Pictures are not here to make you find me connection, just to prove you there is not. I’m here just to know if there is other way to connect two things together

0-ohm resistor or an inductance with (very) low resistance.

There is no component on the board.

Maybe a multi layer pcb but there is no reason

You can try to cut those GND areas into smaller pieces with a knife and see which of the parts is connected.

I don’t want to cut the board :slight_smile: This card is pretty expensive

Internal ground plane.

See if you can shine light through the board. Not? There’s copper in there.

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It’s unlikely. I bet you have not found any type 2 via, so no reason for a type 3 via. But if you find a type 2 via (a hole on top or bottom without its related hole on bottom or top) it could be possible to find type 3 vias; odd but possible.

multi layer boards do not necessarily use blind or buried vias. So just because all vias are full through hole does not mean that it is a two layer board. (A full through hole via can still connect to an inner layer.)

There is no type 2 via and the most odd : there is many GND area which are connected by via between GND area on the top and on the bottom. If there is an hide layer why do that ?

Of course, Rene. I make a lot of 4 or 6 layer pcbs with only through vias.

But the OP doesn’t find (yet) a via not connected to top and bottom, meaning this via is connected somewhere to a inner layer.

I choose to use a multilayer pcb and i got a question, what is the best for GND area ? IN1.Cu or In2.Cu? which is nearest the F.Cu ?

Ty :slight_smile:

The board looks like emissions or impedance etc. don’t matter at all. Actually it looks like it’s been thrown together with a bad autorouter which hasn’t found a route for one connection and the third layer was used because of that (if the guess about 3rd layer is correct). Therefore the layer or nearness to another layer doesn’t matter at all. Just remember that the price of the board will be at least 5x if it’s 4 layers instead of 2, and with a little bit of work you would probably find better routes with only 2 layers. (This is based on what you said, namely that you have already done everything else with 2 layers.)

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That board does not look like new…
Are you sure the ground connection you found is intentional? It might come from a short circuit or solder bridge somewhere.

I was so surprised with that info (I supposed it is 2x) that I have checked at www calculator of the PCB manufacturer we use. I think it is the biggest (not the chippest) one in Poland and continuously improving his technology. Now they offer PCB with 4/4mils. But I have checked prices for their worst technology = 6/6mils.

Their 5 days offer (you have to order at least 1m²). So I have checked prices (netto) for 100PCBs 10x10cm (1,55mm width).
2 layer - 1784 PLN (about $465)
4 layer - 3783 PLN (about $985)

Their prototype offer - I have checked the price for 3PCBs 5x5cm:
2 layer - 108,75 PLN ($28)
4 layer - 195 PLN ($51)

I didn’t checked their standard production offer (if you order less then 1m²). It is more expensive and slower so if we order PCBs ourself we try to order at least 1m².

It was based on lower quantity and smaller board from China. There, too, 100 pcs. of larger 4 layer seems to be relatively much cheaper.

In1.Cu is just under F.Cu

Does anything show up in the gerber viewer?

What do you mean ? I finally resolve my problem by doing a multilayer PCB