Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Vias in SMT pads

  1. Dec 6, 2007 #1
    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
     
  2. jcsd
  3. Dec 6, 2007 #2

    chroot

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    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
     
  4. Dec 12, 2007 #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
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Vias in SMT pads
  1. FFT zero padding issue (Replies: 7)

  2. 12 volt heating pad (Replies: 8)

Loading...