SMD Pads through top and bottom layer without via

[Anonymous]

Hi,

I have a question: I have to design a flex PCB with Pads, which will be welded during production process.

For this it is required to have a SMD Pad, which is on all two layers (Top and Bottom).

I attached for reference a flex PCB and marked it with a red circle, where they did also. I'm not quite sure how they did this. Because for me it seems like, it is just an one layer PCB. But how did they insert the pads on both sides?

Can you help me which approach would be the best to achieve this? 

Thanks in advance

Paul

[sdalling]

It looks like they just used a normal pad on the top and bottom.

Physically its not possible to have a pad on the top and bottom connected without having a via. This is due to how PCBs are manufactured. They drill the holes, then etch the pads. If they didn't do it this way there would be no connection between the pads on the top and bottom of a PCB.

With this in mind you could have pad on the top and bottom and then run a trace away from the pads and use the smallest via size your manufacture supports and tent the via. This way the pads would be connected.

[Anonymous]

Thanks for your quick answer.

That was also my understanding of PCB manufacturing, that a top and bottom pad on the same location are not connected. Thats why I'm so curious how they have done it. Because there is no via on this PCB between top and bottom pad... Is this kind of a special manufacturing process? Did they maybe leavout the Polymide core in that specific area? I can also imagine, they did only one layer PCB and left out all covering in that specific area, so no adhesive, no coverlay. Then I would also get this result, wouldn't I?