> -----Original Message----- > From: Abd ul-Rahman Lomax [mailto:[EMAIL PROTECTED] > Sent: Friday, 16 January 2004 12:25 > To: Protel EDA Forum > Subject: Re: [PEDA] Gerber output problems > > > At 10:54 PM 1/14/2004, Drew Mills wrote: > >I completed the layout of a small PCB (99SE) designed for > enclosure in a > >moulded case, then realised I needed an additional hole for > mechanical > >locking. So I added a free pad, with no copper - just the > correct hole size. > >Everything looks good in PCB, but now, when I output the > gerber files I need > >to panelise in Camtastic, there is no trace of the hole, > except for a tiny > >pin-prick on the top soldermask layer. Why is it so? > > Here is what is going on. The soldermask layer is a > calculated layer, it is > generated from the pad size. In order to make a "pad with no > copper" you > made the dimensions of the pad zero. The solder mask is > generated as an > oversize from the pad size, so that it clears the pad. That's what is > creating the "pin-prick," it would probably be a pad with a > diameter of > twice your solder mask clearance, perhaps 20 mils, about the > size of a pinhole. > > What did you expect to see on the gerbers? > > I usually create mechanical holes as a pad with clearance, > the pad being > made the size of, for example, the MMC of a screw head for a > screw going > into the hole. That way my DRC guarantees that a screw can't > bite into a > track.... I've often left it just like that, but there is > some thought that > hole plating in mounting holes can create problems with fragments of > copper. I'm not sure how much of a real problem it is, but if > you don't > want the hole plated, then you can request that from the > fabricators (it > may be enough to uncheck the Plated box on the Advanced tab > of the pad edit > dialog). Unplated holes can be a bit of extra cost, they have > to be treated > specially. > > If you don't want the pad to be there, you can made the pad > size smaller > than the hole. I wouldn't make it zero, though. Invisible > pads give me the > creeps.... If you want solder mask to be clear of the hole, > you can set a > rule for that pad. You might give the pad a name like "MH" > for "mounting > hole" and then you can create design rules for the pad > Free-MH. This would > allow you to define sufficient clearance rules to prevent > possible shorts, > if that is relevant for this design, as well as a solder mask > expansion > that will make the solder mask opening be larger than the hole.
Abdul, being familiar with this design (Drew works in the same office as me), I can comment on the clearence problem - there is not one. The "missing" hole is for a plastic locating pin in a blow moulded housing. Hence no need for copper to allow for screw head size, as there is no screw. Tom L. * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * To post a message: mailto:[EMAIL PROTECTED] * * To leave this list visit: * http://www.techservinc.com/protelusers/leave.html * * Contact the list manager: * mailto:[EMAIL PROTECTED] * * Forum Guidelines Rules: * http://www.techservinc.com/protelusers/forumrules.html * * Browse or Search previous postings: * http://www.mail-archive.com/[EMAIL PROTECTED] * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
