| T O P I C R E V I E W |
| Kruse |
Posted - 17 Jun 2007 : 03:13:11
I regularly need to add holes to fix something as a heatsink or display frame to the PCB with a screw.
So far I add a pad and minimize the anual ring as much as possibel.
Isn't it possibel to add just a hole without any anual ring at all ? |
| 1 L A T E S T R E P L I E S (Newest First) |
| Peter Johnson |
Posted - 18 Jun 2007 : 05:37:06
You are allowed to create a pad style with a pad diameter smaller than the hole diameter. however, there are issues that arise as a result of this.
Firstly, it can be very difficult to spot the hole. Easy-PC does show a 'ghost' of a ring round it, but it's not very obvious. Secondly, (unless you disable the check) you WILL get annular ring errors, as the pad diameter IS too small for the check. The design rule check will take the larger of the pad or drill size when checking clearances, so that shouldn't be an issue.
I would urge you that if you're mounting using screws, leaving a pad on the board at least the diameter of the screw head does two things. It avoids the risk of accidentally shorting to a track running close to the hole, and it provides some reinforcement to the board surface if the screw is repeatedly removed for maintenance. You can use pad exceptions to leave the extra copper only on the side in contact with the screw head. |
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