Especially if using star lock washers!! They will bite into trace on inner layers.
Also Veronika stated .2 for caps as stress clearance we have been able to live with .15
If room really is an issue.
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Greg Smith
Sent: Tuesday, January 15, 2013 1:46 PM
To: [log in to unmask]
Subject: Re: [DC] Component to Mounting Clearance
Just a couple of things to add:
If you allow for the needed tolerances, as Tom Hausherr points out, you
are good for the assembled PCB product.
As far as needing a courtyard, there is another aspect: If the hardware
used in the hole is not installed when the PCB is assembled or reworked,
then there is no "component" there, just an empty pad. So there is no
need to worry about access for component placement or rework. So then
electrical clearances are primary. But you do need to know how the
hardware will be installed as there is the potential for damage if the
tool slips. If you think you may have issues with EMI etc, placing an
active part so close to what might be "chassis" or "earth" ground could
be an issue for isolation. There is another potential gotcha: Do not
route any traces, on inner layers, under the large pads for the mounting
hole. The compression force of the hardware after installation can crush
the board material and cause shorts. This type of short may go away when
the board is removed from the assembly, making it hard to find.
Greg
On 1/15/2013 8:07 AM, Tom Hausherr wrote:
> Jack,
>
> Mounting Holes have a placement courtyard just like any other footprint.
> Consider Mounting Holes just like any other component. As long as you've
> compensated for the hole slop for the screw and the washer hole slop
> tolerances and placed your placement courtyard 0.25 mm (10 mils) larger than
> the total slop everything will be fine.
>
> You can't find any recommendations in an IPC spec because it does exist.
> There is no reason to do anything different than normal component to
> component spacing rules.
>
> Tom
>
> Tom Hausherr
> President
> 13730 Sorbonne Court
> San Diego, CA 92128
> 858.592.4826 Office
> 858.859.5371 Cell
> [log in to unmask]
>
>
> -----Original Message-----
> From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Robert
> Wolfe
> Sent: Tuesday, January 15, 2013 7:52 AM
> To: [log in to unmask]
> Subject: Re: [DC] Component to Mounting Clearance
>
> The only references to mounting hole clearances I roughly remember seeing
> were only related to the electrical clearance. So one would have to do the
> math with tolerances hole Hole size vs screw head& washers sizes to
> determine worst case so there would be The MIN required electrical clearance
> per the design. I don't remember seeing anything related To mechanical
> reasons other that ya gotta make it fit without interference based on
> Assembly requirements (insertion machine, placement machine, test machine
> requirements etc) of any parts in the design.
>
>
> -----Original Message-----
> From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Jack
> Olson
> Sent: Tuesday, January 15, 2013 10:44 AM
> To: [log in to unmask]
> Subject: [DC] Component to Mounting Clearance
>
> Is there any guidance in IPC publications about acceptable clearance between
> components and mounting hardware? I can't find anything, but one of our
> designs has a QFP144 near a screw (more than 100 mils), and someone is
> wondering if it will be a problem.
>
> Here is a partial picture:
> https://console.mxlogic.com/redir/?hPPPbUVZcSMC--M-qekPo0dSdojgHmf1j0I93aRoP
> Q_075MIyMMHczN6jFK_8I9LfzAm4PhOrKrGoxYiW7QAhxYrlrxqhUaAJrw09JxNMQsCQmnTAT673
> hPsSOUrdbos96BQQg2lllGM-4Ph1eFEw6WJMDa14Qg2h_X7omYTfM-ub7Xa1J4SyrojvvovvjdO0
> rk
>
> There's also a crystal to the left of the mounting hole, and they were
> wondering about that one, too. Should I be worried?
>
> (always feelin' like "the new guy")
> Jack
>
>
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