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 A question about the pad size? 

Last post Tue, Feb 25 2014 3:43 PM by pilav. 9 replies.
Started by Leeya 27 Jan 2014 04:28 PM. Topic has 9 replies and 3696 views
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  • Mon, Jan 27 2014 4:28 PM

    • Leeya
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    A question about the pad size? Reply

    Have a question about the pad size?

    I am new about Cadence design. And now, I am making a footprint for a part. The pdf file shows you the min/average/max of each pin. 

    when you make a footprint, which number are you going to use? I know the bigger pad the better, but I still want to run tace between pins.

    For example,e1 could be 8.20-0.55 =7.65mm or also could be 7.40-0.95=6.45mm. that makes a lot of different about the footprint~~

    all also each pin width, should I use0.22 or 0.38 or ?  

    Thanks 


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  • Mon, Jan 27 2014 5:00 PM

    • Leeya
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    Re: A question about the pad size? Reply
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  • Mon, Jan 27 2014 11:22 PM

    • kabalee
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    Re: A question about the pad size? Reply
    hi leeya, better use nominal value for example add the minimum and maximum value and then divided by 2
    kabee
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  • Tue, Jan 28 2014 1:22 AM

    • steve
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    Re: A question about the pad size? Reply

     Have a look at www.pcblibraries.com This uses the IPC-7351 standard to build footprints automatically for many CAD tools incuding Allegro and OrCAD. You can design the footprint based on Min, Nom or Max values.

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  • Tue, Jan 28 2014 5:36 AM

    • padmaster
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    Re: A question about the pad size? Reply

    Leeya:
    when you make a footprint, which number are you going to use?

     I typically use the max # for size and nominal # for location.

    Leeya:
    I know the bigger pad the better

    Not true, if the pad is too large then you will have too much solder paste and a greater possibility of shorts.

    Leeya:
    I still want to run tace between pins

    I would not recommend trying to route traces between pins on fine pitch parts. You would need a very small trace and it is likely you will not have any solder mask covering the trace so you will have shorts. 

     

     

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  • Tue, Jan 28 2014 9:55 AM

    • KEN13
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    Re: A question about the pad size? Reply

    You can also Web search for IPC-SM-782A.

    Have a good day, Ken Capture 16.5 S022, Layout 16.2.0p001, PCB Editor 16.5 S025
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  • Wed, Jan 29 2014 9:22 AM

    • Leeya
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    Re: A question about the pad size? Reply
    Thanks Kabalee, That is good idea
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  • Wed, Jan 29 2014 9:29 AM

    • Leeya
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    Re: A question about the pad size? Reply

    Hi Steve,  I am using this software,and it is really helpful~~

    Have another question, if you use PCBlibraries,when you type the max min,the software will give you a design margin (or call it side solder fillet 0.35mm).

    So if I type the pin width or length in Cadence Symbol wizard, does  allegro symbol wizard automatic add design margin(side solder fillet) for us or it doesn't??

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  • Thu, Jan 30 2014 1:28 AM

    • steve
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    Re: A question about the pad size? Reply

     The Cadence symbol wizrad won;t add anything automatically. It build the footprints based on the dimensions you enter. Remeber you build the pads first then use these in your footprint. PCB Libraries does this all completely - makes the pads, then creates the footprint. If you don't do this using PCBLibraries you need make the pad size that the IPC calculator generates using Pad Designer then use this as part of the symbol wizard.

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  • Tue, Feb 25 2014 3:43 PM

    • pilav
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    Re: A question about the pad size? Reply

    @Leeya. Using the optimum size for pads is always recommended. It gives you an extra safety in case if the PCB soldering has any issues or the PCB solder mask has any overlaps. Now one thing that you mentioned in your first post is that you need to pass track through the pads, I’d completely advise against it. If you have to send data or do quick switching through that particular track, it will create interference for the pads nearby. Also, there could be issues with soldermasking which could lead to pads and track getting short.

     printed circuit board fabrication

    • Post Points: 5
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Started by Leeya at 27 Jan 2014 04:28 PM. Topic has 9 replies.