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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

  • On 02/26/2008 04:35 AM, Richard Hammerl wrote:

     

    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?

     

     

    It works for vias in the Layout:

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

     

     

    Thank you Tilmann and Richard for the pointers. I should be able to do

    what I wanted now.

     

    But I'd still says Eagle's implementation is rather odd. It seems like a

    much simpler (and more useful) behavior would be for the "change, stop,

    off" command to always work for all components on a board.

     

    Eagle could auto-generate mask openings for vias based on the DRC but

    still let me turn them off individually (irrespective of the limit

    setting). Likewise, I should be able to turn of a device's stop mask on

    a board and draw my own. It seems odd to force the creation of a new

    package just to change stop mask in what might be a one-off situation.

    Particularly when the "change, stop" command already exists at the board

    level.

     

    I'm not sure how common tented vias are, but another nice feature would

    be to let users change the stop mask setting to the following 4 values:

    "off, on, top only, bottom only". Then I wouldn't have to draw it

    manually and make sure it gets moved together with the via (which is

    currently one advantage of putting in into the package).

     

    Thanks again,

    -Brad

     

Reply

  • On 02/26/2008 04:35 AM, Richard Hammerl wrote:

     

    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?

     

     

    It works for vias in the Layout:

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

     

     

    Thank you Tilmann and Richard for the pointers. I should be able to do

    what I wanted now.

     

    But I'd still says Eagle's implementation is rather odd. It seems like a

    much simpler (and more useful) behavior would be for the "change, stop,

    off" command to always work for all components on a board.

     

    Eagle could auto-generate mask openings for vias based on the DRC but

    still let me turn them off individually (irrespective of the limit

    setting). Likewise, I should be able to turn of a device's stop mask on

    a board and draw my own. It seems odd to force the creation of a new

    package just to change stop mask in what might be a one-off situation.

    Particularly when the "change, stop" command already exists at the board

    level.

     

    I'm not sure how common tented vias are, but another nice feature would

    be to let users change the stop mask setting to the following 4 values:

    "off, on, top only, bottom only". Then I wouldn't have to draw it

    manually and make sure it gets moved together with the via (which is

    currently one advantage of putting in into the package).

     

    Thanks again,

    -Brad

     

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