General PCB mounting question

Discussion in 'The Projects Forum' started by stoopkid, Sep 6, 2011.

  1. stoopkid

    Thread Starter Member

    Mar 3, 2011
    136
    1
    So I got my PCB all drawn up and transferred to a copper board before I realized that there's no room for mounting screws or anything. The board will have some large components and will need to be very stationary to my wood case. I realized I don't really know about any PCB screw standard or anything. Google results are vague. Is there a standard size I should clear for screws or do I just need to grab what I can find and make it work for my project?

    Basically I just want to know how it ought to be done. I'm looking for dimensions and such.

    Thanks
     
  2. debjit625

    Well-Known Member

    Apr 17, 2010
    790
    186
    Their are options in PCB CADs for creating drill holes like that,but if you forgot,its ok just use any screw that will go with your PCB to mount it properly just don't mess up with your tracks.

    Good Luck
     
  3. mcasale

    Member

    Jul 18, 2011
    210
    12
    You did not say anything about your application. Is this a "one-off" project, or will this be a product? Note that much of the heat generated on a PCB (especially SMT) goes through the board to the mounting holes and to a metal chassis (unless you have a fan in the package). You also need good grounds and shielding to help minimize RFI issues.
     
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Photo of the PCB?

    Ken
     
  5. #12

    Expert

    Nov 30, 2010
    16,346
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    I use 6-32 screws and threaded plastic or metal spacers.
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Pick any screw.. Typically #4-40 or #6-32 (or comparable metric for those across the pond) are pretty standard for regular pcb assemblies.. But its all up to how much support you need and how much area you have. But typically you would provided enough clearance for the diameter of the head (make sure to think about slop from the actual hole in the board and the screw not being perfectly centered) then add the required clearance based on your voltage levels (higher voltage = more clearance to prevent arcing..
     
  7. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    I use 4-40 machine screws, .125" holes in the PCB, and try to keep a .25" diameter area clear around the center of the hole. The 4-40 machine screw heads are .200" in diameter, so that leaves .025" clear all around the screw head. Of course, if you are placing a nut on the PCB surface, that takes more clearance and you should leave .300" diameter clear around the center of the hole.
     
    Last edited: Sep 6, 2011
  8. paulktreg

    Distinguished Member

    Jun 2, 2008
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    If it's a one-off project just use plastic and drill an hole in your PCB wherever is convenient.
     
  9. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Or if you have no place for the screws, no high voltage present on the pcb and you are confident it will work, you can use something like sanitary silicone to stick it to the bottom. Don´t power it up until the silicone is completely hardened.
     
  10. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    For a one-off hobby project don't forget about hot melt glue. You can find the glue and the gun in many dollar stores. I keep a gun and some sticks in my tool box.
     
  11. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Well yes, but it´s the melting when hot which makes it a little tricky to use, because when the device should for any reason overheat the pcb might fall off and cause even more damage when it comes in contact with something else.
     
  12. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Be very selective in the silicon adhesive/caulk you use. Ones containing acetic acid will corrode metals on PCBs. You can recognize them by the strong, pungent odor. There are electronics-compatible silicon adhesives.

    Ken
     
  13. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    If it gets hot enough to re-flow hot melt glue then it shouldn't be inside a wooden case to begin with.
     
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