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IPC-7351 Mounting Hole Naming Convention & Info

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Tom H View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post Topic: IPC-7351 Mounting Hole Naming Convention & Info
    Posted: 13 Feb 2013 at 1:31pm
Let's break it down like IPC would -
 
MTG - component family
P - Plated + pad Size - value in millimeters (2 places to each side of decimal point and drop leading zero's)
NP - Non-plated + pad Size - value in millimeters (2 places to each side of decimal point and drop leading zero's)
H + hole size - value in millimeters
K + keepout size - value in millimeters (this normally maps to the placement courtyard diameter)
V + Number of vias _ via hole size (this is a modifier and not necessary when there are no vias)
T - Tight Fit
L - Loose Fit
 
Example: MTGNP1000H360K1050L
 
We need to think of all the options and how they  need to be arranged.
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JZsori Quote  Post ReplyReply Direct Link To This Post Posted: 13 Feb 2013 at 2:08pm
OK - but in my case I will likely simplify it some.  My placement courtyard will be slightly larger than the pad size.  I will put in actual keepout areas as mine is a little more complicated in that I have different keepout areas for primary and secondary sides.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post Posted: 13 Feb 2013 at 2:39pm
Don't forget that all non-plated mounting holes still need a pad to support the hardware: 
 
Here is a Mounting Hole with a Keepout:
 
 
Here is Mounting Hole with sattelite support vias. The vias are usually connected to the ground plane.
 
 
 
Here is a Non-plated hole example:
 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dale Quote  Post ReplyReply Direct Link To This Post Posted: 13 Feb 2013 at 3:20pm
Tom, in your last image you show a copper-free annulus between pad and hole.
However I consider a non-plated mounting hole as analogous to every hole on a single-sided board - and we don't provide a copper-free annulus on those.
Can you educate me/us on the differences?
Thanks.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post Posted: 13 Feb 2013 at 3:25pm
The non-plated hole drill bit cannot hit any copper (metal), just a clean hole through the FR4 material.
 
The mfr. desmears plated holes, but non-plated holes are plugged or masked during the plating process.
 
IPC has a rule on this and I think it's in the newly released IPC-2221B standard (which I don't have yet, but I'll get it at APEX next week.
 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JZsori Quote  Post ReplyReply Direct Link To This Post Posted: 13 Feb 2013 at 3:28pm
My understanding is that it is preferable to have a donut pad for the screw head so that the screw does not crush the epoxy glass material as much as it has a copper pad in between.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dale Quote  Post ReplyReply Direct Link To This Post Posted: 13 Feb 2013 at 4:56pm
Originally posted by Tom H Tom H wrote:

The non-plated hole drill bit cannot hit any copper (metal), just a clean hole through the FR4 material.

But why? The plated hole drill bit hits copper on every hole.

Originally posted by JZsori JZsori wrote:

My understanding is that it is preferable to have a donut pad for the screw head so that the screw does not crush the epoxy glass material as much as it has a copper pad in between.

The copper pad might help distribute the force, but I don't see how this has anything to do with keeping the copper away from the hole.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post Posted: 13 Feb 2013 at 6:22pm
Both statements are correct.
 
1. Donut Pad so that the pad center is pulled away from the drill bit so the drill does not go through metal to avoid metal fragments and produce a clean hole. Like I mentioned, there is an excellent reason and description of the non-plated mounting hole in the newly released IPC-2221B.
 
2. The Donut Pad acts as mechanical support during the torque process when tightening the screw to the board to prevent the FR4 glass from crushing. i.e.: It's best to have metal on metal and avoid having the screw hardware make any contact with the FR4 material.
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dale Quote  Post ReplyReply Direct Link To This Post Posted: 13 Feb 2013 at 6:40pm
Originally posted by Tom H Tom H wrote:


...there is an excellent reason and description of the non-plated mounting hole in the newly released IPC-2221B.
Thanks. I look forward to it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jameshead Quote  Post ReplyReply Direct Link To This Post Posted: 14 Feb 2013 at 2:19am
In addition to Tom's two points:

A non-plated hole can have copper around it but it affects the fabrication of the board.

If a non-plated hole is clear of copper then it can be drilled at the first stage drilling along with all the plated holes and is then "tented" by the film to prevent it being plated.

If you have a non-plated hole with the drill going through copper then as well as the points Tom mentions, the drill will have to be drilled at the second stage drilling along with the route.
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