2 Replies Latest reply on Sep 12, 2008 4:24 PM by happy_holden

    Via in pad usage- minimum board thickness

    randall.j.echelbarger

      My name is Randy and I have been a designer for twenty five years with an automotive component parts supplier. We presently use a finished .2mm via in pad in 0603,0805  & BGAs. My question is what in the industry using as drill sizes to accomadate drill stackup wander?

        • 1. Re: Via in pad usage- minimum board thickness
          carlos-m-monica

           

          Hi Randy

           

           

           

           

           

          My pcb fabricators, tell me to use a max of 2,2mm pcb thickness for a 0,2mm via hole.It should be near the 1/10 ratio

           

           

          Thas a safe ratio for plating the holes of the vias

           

           

          Carlos

           

           

          • 2. Re: Via in pad usage- minimum board thickness

             

            Randy,

             

             

            Drill wander is a functionof the stackup height and the drill diameter.  A FHS of 0.2 mm is pretty much the minimum size of normal drilled holes.  You need to ask your fabricator what his stack-height is for this drill size.  My guess it would be only 2 high.  But if he is using 3 or 4 panels high, then you will get a LOT of drill wander.  If he drops the stack-height he may want to increase the board price, so ask what is the minimum drill diameter for 3 high, for 4 high.  If your SMT pad can take that height, switch to the larger diam.  Hopefully you are having these vias filled (carefully!).  Otherwise all your solder is going to run down the hole and your joint will be 'starved' and probably fail.  The filling of these holes WILL cost  more than the stack-height costs.