SMT Pad Vias: Is it OK? | PCB Layout

  • Thread starter Jdo300
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In summary, the conversation discusses the potential use of small vias on the pads of SMD components for a board layout in ExpressPCB. There are concerns about manufacturing and mechanical issues, but some have successfully used this method for lower inductance and connecting to heatsinks. It is suggested to consult the PCB manufacturer before implementing this method.
  • #1
Jdo300
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Hi All,

I'm working on a board layout in ExpressPCB and I am wondering if it is considered OK to place a small via on the pad of a SMD part. To be specific, I have a bunch of 0805 bypass caps that I am placing on the underside of the board for various ICs, and I want to add a via through the pad of the cap to the top layer to connect to the power pins. I am using the smallest via size the program supports (0.36mm hole) which the manufacturer says is usually filled due to the size tolerances.

Would placing these small vias in the middle of the pads present any problems, particularly when it comes to soldering the parts down? Has anyone ever tried this?

Thanks,
Jason O
 
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  • #2
It probably depends on the order of steps done during manufacturing. If they plate vias after plating pads, there's a good chance such vias will not be plated properly.

I would call up whatever PCB house you're using to manufacture the board and ask them. It's definitely not normal practice, and will certainly reduce the mechanical strength of the mounting. That alone may be a reason not to do it.

- Warren
 
  • #3
I often place a via within the pad, as it results in lower inductance. When this method has produced a problem, there have been others. That is, there have been no problems with an otherwise well-manufactured board.
I also use arrays of vias to connect surface mounted devices to a heatsink on the other side of the board. In this case, plated over vias rather than solder-filled are easier to produce.

Humber
 

1. What are SMT pad vias and why are they used in PCB layout?

SMT pad vias are small holes in the printed circuit board (PCB) that are used to connect the surface-mounted component pads to the inner conductive layers of the board. They are used to route signals and power between different layers of the PCB, allowing for a more compact and efficient layout.

2. Can SMT pad vias be used on all types of PCBs?

Yes, SMT pad vias can be used on all types of PCBs, including single-sided, double-sided, and multi-layer PCBs. However, the placement and design of the vias may vary depending on the type of PCB and its intended application.

3. Are there any limitations to using SMT pad vias in PCB layout?

While SMT pad vias are a common and useful component in PCB layout, there are some limitations to consider. The size and placement of the vias can affect the overall performance and reliability of the PCB. Additionally, the number of vias used must be carefully planned to avoid overcrowding and potential signal interference.

4. How are SMT pad vias typically incorporated into PCB layout?

SMT pad vias are typically incorporated into the PCB layout using CAD (computer-aided design) software. The designer will determine the necessary placement and size of the vias based on the components and circuitry of the PCB. The CAD software then generates a layout that includes the placement of the vias.

5. Is it possible to use through-hole vias instead of SMT pad vias in PCB layout?

Yes, it is possible to use through-hole vias in PCB layout instead of SMT pad vias. However, through-hole vias take up more space on the PCB and are not as efficient for routing signals between layers. SMT pad vias are generally preferred for their smaller size and better signal integrity.

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