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A question about the pad size?

Leeya

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 

  • kabalee
    hi leeya, better use nominal value for example add the minimum and maximum value and then divided by 2
  • steve

     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.

  • padmaster

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

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

    Leeya said:
    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 said:
    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. 

     

     

  • KEN13

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

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