Hi JF,
I didn't find a soldermask spec for unplated holes, however the spec
according to IPC-7351 is: "PCB Manufacturer are required to keep
soldermask material off the land. Clearance conditions can vary from
0.0mm(0.0") to 0.1mm (0.004")".
I recommend you to choose the best one that fits your design rules
requirements. There are clearance requirements from copper to mounting hole
(hardware, screws, etc) you should look into it.
Hope this helps,
Regards,
Glennys de Jesús, CID+
2013/2/25 Greg Smith <[log in to unmask]>
> The answer is, of course: It depends.
>
> The size of the mounting hole, the distance the copper is pulled back from
> the hole, and the board material used can all affect the location of the
> mask edge. And also your design intent.
>
> You want to be sure the mask does not leave any copper exposed so the
> tolerances for your shop/processes determine that.
>
> If the mounting hole is for a typical sized screw it will be large enough
> you can have the mask opening dia just a bit smaller than the hole dia as
> there will be little chance of the mask clogging the hole. Do not make the
> mask opening dia zero as the shop will have to make there own choice there
> as a large opening in the screen will mean too much mask gets squeegied
> thru and will need to be cleaned off the back of the screen too often.
>
> If you are using a board material such as teflon, for RF for instance, do
> not run the mask to the edge of the hole or beyond (or the edges of the
> board). Since the mask does not adhere well to those materials an edge can
> be a location where the mask can catch and be easily peeled back, espcially
> by hardware going through the hole.
>
> Greg Smith
>
>
>
> On 2/25/2013 11:37 AM, JF wrote:
>
>> Hi All,
>>
>> This should be basic, yet I can't remember the requirement nor where to
>> find the info (which spec).
>>
>> We have a board with some unplated holes and a copper plane on both the
>> top and the bottom. Of course, the copper planes are recessed from the hole
>> but I can't remember if the Solder Mask should be flush to the holes (some
>> are mounting holes), or just covering the planes + a certain distance.
>>
>> Thanks in advance!
>>
>> JF
>>
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