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  1. #1
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    PCB milling accuracy

    Hi All,

    There are several PCB based module on the market which can be populated like an IC to the main PCB. Some of them looks like a QFN package and the contour of them looks pretty clear.
    I am thinking on something similar but (as I am not a PCB specialist) I am lost... and after several hours of search I could not figure out what accuracy can be reached by the contour milling. (I also tried to find the milling machine specs but that looks confusing...)

    Could someone help me?

    Thaks

    •   Alt16th May 2017, 19:01

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  2. #2
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    Re: PCB milling accuracy

    IPC Standard usually +/-0.2mm. That said I use to get pretty much spot on from most manufacturers (China direct and UK/USA based fabricators) and if I don't I am not a happy bunny and will not use said manufacturer again.


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    •   Alt17th May 2017, 09:59

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  3. #3
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    Re: PCB milling accuracy

    I found similar values (+/-0.2mm and +/-0.25mm) at some manufacturer, but after I checked some of the module's tolerance (eg http://www.ti.com/product/TPS82675) it looks quite loose.
    Is there any way to get more accurate shape with a standard PCB manufacturing process?

    (Is this +/-0.2mm comes from IPC610 ?)



    •   Alt17th May 2017, 11:35

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  4. #4
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    Re: PCB milling accuracy

    Hi,

    I think marce has focussed this already: --> contact the manufacturer that will produce the PCB.

    ***
    If there is a forum member that tells you that 0.01mm is possible, but your recived PCB is off this limits.. who is to blame?
    If one manufacturer tells you that 0.01mm is possible, but you choose another manufacturer and your recived PCB is off this limits.. who is to blame?

    ***
    There are several tolerances.
    * Milling dimensions (without respect to copper)
    * Milling to THM drills.
    * Copper_to_milling.

    For tight copper_to_milling tolerance you may need to add some passer markings on you PCB. But the manufacturer will tell you this.

    Klaus



  5. #5
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    Re: PCB milling accuracy

    No blame at all! I appreciate every comment/advice.

    If one say that +/-0.01mm is possible then I have a chance to make a module testable in standard IC socket and I will look for PCB supplier which can provide at least +/-0.05mm edge accuracy (milling dimension). If you say that +/-0.2mm is the standard and noone will promiss better I would not spend too much time on it.

    Thanks,
    gabor



    •   Alt17th May 2017, 21:14

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  6. #6
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    Re: PCB milling accuracy

    I have done PCB interposer's (basically a small thin PCB that you mount bare die and components on to make another device), these were assembled in a panel then routed out afterwards, the routing being controlled and the copper pattern used as a cross reference with the panel tooling holes. You pay a bit extra to get the required accuracy becasue they cant just throw the boards on a standard jig and let it go.



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