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Via tenting and plugging

autodeskguest

I want to put vias in the central pads of several QFN/MLF devices to

improve grounding and dissipate heat. To reduce costs, the vias are

0.3mm which is fairly large compared to a small QFN20 part's central

pad. To prevent solder paste from draining away during reflow, I believe

I need to plug those vias.

 

I'm considering plugging and tenting the vias from the bottom-side only

so that there is no top-side solder mask to interfere with good reflow

bonding to the chips. Another approach might be to only plug the vias

from the top (no tenting), but I'm not sure how accurately this can be

done in "prototype" runs.

 

Two questions:

 

1. Do either of those approaches seem practical?

 

2. If I go with bottom-side tented vias, how can do this in Eagle? I

have only been able to turn off the stop mask entirely, not for just one

side. I was looking for a way to draw a polygon on the board that would

"subtract" any stop masks inside its bounds, but I haven't found a way

to do that.

 

Thanks for any input.

 

-Brad

 

Parents

  • Brad Schick schrieb:

    On 02/23/2008 12:27 AM, Tilmann Reh wrote:

    That's easy: Turn the stop mask completely off, and then manually draw

    whatever mask you want into the appropriate layer. This must be done for

    each via separately, but hopefully there are not too many of these

    special ones...

     

     

    Actually, putting the vias inside the package is a hassle. One of my

    devices will be used more than once and I'll have to create new package

    variant each time I want the via to be in a different location within

    the central SMD pad. I'll also have to create a bogus pin on the symbol

    to make the via grounded.

     

    Richard, why is it not possible to turn off stop masks on the board

    directly? It would be much simpler to just add the gnd via to the board,

    turn off its automatic stop masks, then draw the stop mask I want.

     

    Its rather strange that the board editors has a button for "change,

    stop, off" that does nothing. Could making that work as expected be

    considered for 5.0 still?

     

     

    -Brad

     

    It works for vias in the Layout:

      ==> http://www.cadsoft.de/faq.htm.en#06062601

     

     

    --

    Mit freundlichen Gruessen / Best regards

    Richard Hammerl

    CadSoft Support -- hotline@cadsoft.de

    FAQ: http://www.cadsoft.de/faq.htm

     

Reply

  • Brad Schick schrieb:

    On 02/23/2008 12:27 AM, Tilmann Reh wrote:

    That's easy: Turn the stop mask completely off, and then manually draw

    whatever mask you want into the appropriate layer. This must be done for

    each via separately, but hopefully there are not too many of these

    special ones...

     

     

    Actually, putting the vias inside the package is a hassle. One of my

    devices will be used more than once and I'll have to create new package

    variant each time I want the via to be in a different location within

    the central SMD pad. I'll also have to create a bogus pin on the symbol

    to make the via grounded.

     

    Richard, why is it not possible to turn off stop masks on the board

    directly? It would be much simpler to just add the gnd via to the board,

    turn off its automatic stop masks, then draw the stop mask I want.

     

    Its rather strange that the board editors has a button for "change,

    stop, off" that does nothing. Could making that work as expected be

    considered for 5.0 still?

     

     

    -Brad

     

    It works for vias in the Layout:

      ==> http://www.cadsoft.de/faq.htm.en#06062601

     

     

    --

    Mit freundlichen Gruessen / Best regards

    Richard Hammerl

    CadSoft Support -- hotline@cadsoft.de

    FAQ: http://www.cadsoft.de/faq.htm

     

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