Author Topic: PCB holes and mechanical drawings  (Read 898 times)

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Offline RobK_NL

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PCB holes and mechanical drawings
« on: January 13, 2018, 03:17:57 am »
I just received a batch of PCBs with the wrong size mounting holes  :(

The drill file clearly states they should be 5.2mm, but they are 6mm

The manufacturer now says that they have made it according to the mechanical drawing I provided. The affected holes have an outline* on this drawing and so,
according to 'ancient rules of PCB manufacturing' (says they!), this takes precedence over the actual drill file.

I have *never* heard about this rule and would be much interested to find out what the combined wisdom of the forum has to say about this.


*The outline is actually a keepout area I defined to get a bit more clearance around the holes. It ended up on the drawing by accident and I didn't think anything about it when I sent the files out |O
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Offline mars01

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Re: PCB holes and mechanical drawings
« Reply #1 on: January 13, 2018, 03:40:09 am »
If the outline is on a mechanical layer it can be interpreted as you want it milled.
If it's on a overlay layer than they did a mistake.
 

Offline RobK_NL

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Re: PCB holes and mechanical drawings
« Reply #2 on: January 13, 2018, 04:29:55 am »
Well, yes, you can "interpret" 'till the cows come home, but if you have two clearly conflicting pieces of information (three, actually because there is a list of drill sizes on the same very drawing!), you might want to ask for clarification I would think.

My main problem is with their rigourous application of some Very Old Rule I have never heard of in almost 30 years of designing.
But that could be just me, so I'm asking here.
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Offline phil from seattle

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Re: PCB holes and mechanical drawings
« Reply #3 on: January 13, 2018, 05:58:03 am »
I think the best thing they could have done is contact you to resolve the conflict but it's not surprising they didn't.  A good practice is to not give them conflicting instructions in the first place. Given that the holes are slightly large it's not a disaster.

What is the vendor's name?
 

Offline DerekG

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Re: PCB holes and mechanical drawings
« Reply #4 on: January 13, 2018, 08:07:12 am »
The drill file clearly states they should be 5.2mm, but they are 6mm

It is usual for any holes greater than 4.0mm to only be offered in 0.5mm increments unless you discuss the matter with the board manufacturer before production.
I also sat between Elvis & Bigfoot on the UFO.
 

Offline RobK_NL

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Re: PCB holes and mechanical drawings
« Reply #5 on: January 13, 2018, 09:15:49 am »
I think the best thing they could have done is contact you to resolve the conflict
I agree  :)

Quote
but it's not surprising they didn't.
Here I have to disagree. My experience with European vendors is that at times they seem to be overly cautious. The Chinese vendor in question has, in the past, also checked back with me on some issue. Even on this very board, when I had mixed up my units and specified 1µm gold thickness for the ENIG, in stead of their standard 1µ".

Quote
A good practice is to not give them conflicting instructions in the first place.
Well, duh. 't was an honest mistake guv'!
Which is, of course precisely why it should have been checked.

Quote
Given that the holes are slightly large it's not a disaster.
No, but given that they've done an almost perfect job on a board that few other vendors would even make, it's a real shame.

Quote
What is the vendor's name?
Not gonna say as it is not germane to the discussion.


It is usual for any holes greater than 4.0mm to only be offered in 0.5mm increments unless you discuss the matter with the board manufacturer before production.
Is it? Never had any problems with that. This same vendor is certainly capable of making 4.2mm, 5.2mm and 6.2mm holes, as they have done so previously.
Even so, with 5.2mm specified you'd expect either 5.0 or 5.5mm, not 6.
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Online Richard Crowley

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Re: PCB holes and mechanical drawings
« Reply #6 on: January 13, 2018, 09:25:33 am »
Can you tell if they were actually drilled?  Or were they routed? (along with the perimeter?)
Perhaps their process is more efficient to route holes over a certain diameter (vs. stocking and mounting lots of different sizes)?
It is easy to imagine that the Chinese vendors are more focused on throughput and language is a greater barrier than for European vendors.
 

Offline RobK_NL

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Re: PCB holes and mechanical drawings
« Reply #7 on: January 13, 2018, 10:02:56 am »
I'm pretty certain they were drilled. The reason I caught it in the first place is that they send a complete test report with each batch. This mentioned two npt holes; 3.2 and 6.0mm ...
There are some 16mm holes as well, that are not mentioned in the report, so these surely must have been routed.
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Offline Mattylad

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Re: PCB holes and mechanical drawings
« Reply #8 on: January 14, 2018, 12:56:15 am »
They are correct, a drawing always overrules what the data says.
This may be an ancient rule but its a damn good and proper one.

This is because the designer must have put details on the drawing deliberately, a drill hole in a component may not always be what was intended.
I.e. if your hole says its 4mm in the data yet you put 6mm on the drawing then either your making a mistake or you mean for it to be 6mm.
Generally, this should flag up a problem at the fab house front end, the job gets stopped and your contacted for a resolution.

You should always check your data, import it into the free GC-Prevue and check it matches what you think it should be.
Do a manufacturing drawing, clearly identify it as such. (used to be called a "drill drawing" but should contain a lot more info).
This drawing should contain lots of info such as board dimensions, tolerances, materials, plating required etc.

Sadly many people do not do nor understand the importance of a good drawing to convey the designers intent to the manufacturer.

Matty
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Matty
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The following users thanked this post: Alex Eisenhut, Richard Crowley, RobK_NL

Offline donotdespisethesnake

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Re: PCB holes and mechanical drawings
« Reply #9 on: January 15, 2018, 09:45:35 pm »
My experience with European vendors is that at times they seem to be overly cautious. The Chinese vendor in question has,

You used the Chinese vendor because they are cheaper. Now you found out why. It sounds like you already used up their support budget catching your mistakes.

Anyway, you made a mistake, you can hardly blame the Chinese vendor for doing exactly what you asked them.

Bob
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