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 Drill Hole in a SMD Pad 

Last post Sun, Jan 27 2013 7:30 PM by ScottCad. 3 replies.
Started by ScottCad 25 Jan 2013 11:43 AM. Topic has 3 replies and 1034 views
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  • Fri, Jan 25 2013 11:43 AM

    • ScottCad
    • Top 50 Contributor
    • Joined on Fri, May 25 2012
    • Roswell, GA
    • Posts 176
    • Points 2,775
    Drill Hole in a SMD Pad Reply

    Hi guys, kind of a general question this time. I have a farily dense board with lots of decoupling caps "0603" footprint. I was wondering has anyone used drill in a pad to get to the internal power ground layers without seeding a via. What I was thinking of doing is putting a small 10 mil drill hole in the center to the 0603 pad to connect to the inner layers, kind of make that 0603 pad a th pad.

    I dont believe the solder paste will wick through the 10 mil hole to the bottom side of the board, kind of wanted to put the idea out there to see what you think

    Thanks Scott

    • Post Points: 35
  • Fri, Jan 25 2013 11:22 PM

    • hithesh
    • Not Ranked
    • Joined on Tue, Dec 18 2012
    • Posts 9
    • Points 165
    Re: Drill Hole in a SMD Pad Reply

    Scott,

    Puttin vias on pad is what I really like as a designer. It connects the cap directly to the power plane.

    Don't put just one via, put 4 small ones. 

    I remember reading a app note by ultracad(I think), that showed the difference in power integrity.

    I think the problem will be with manufacturing. Check if it increases cost. 

     

    • Post Points: 5
  • Sat, Jan 26 2013 11:37 AM

    Re: Drill Hole in a SMD Pad Reply

    I believe you should investigate blind vias with your fabricator.  The cost increase comes from having to do the multilayer lamination and drill steps at least twice.  The b-stage epoxy will become liquid and fill in the via holes so you won't have paste wicking problems.

    Including the drill with the pad is not a good idea.  Common practice is to keep flexibility in moving those vias around to avoid bumping into other things.   Investigate same-net DRC checking.

    • Post Points: 20
  • Sun, Jan 27 2013 7:30 PM

    • ScottCad
    • Top 50 Contributor
    • Joined on Fri, May 25 2012
    • Roswell, GA
    • Posts 176
    • Points 2,775
    Re: Drill Hole in a SMD Pad Reply

    Guys, thanks for the advice and assistance, I am going to contact the company that assemble our boards to confirm if they can apply solder paste to a land that has a small drillhole in it. Off the cuff I dont see a problem in doing this but it is better to confirm before I push the go button.

    Normally I use a 25 Mil via with a 12 mil drill, but on a dense design a via sometimes just wont fit. The thing I do like about the drill in pad is that when used with a decoupling cap for a pin you are connected directly to the plane with the shortest possible distance to the pin.

    Thanks Again Scott

    • Post Points: 5
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Started by ScottCad at 25 Jan 2013 11:43 AM. Topic has 3 replies.