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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

  • 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.

     

    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...

     

     

    Thanks that makes sense, particularly if I put the vias inside the

    package itself. Two more (probably obvious questions). 1. How do you

    draw a filled circle? Using the polygon tools works, but its sort of a

    hassle. 2. I actually have not found a way to turn off stop masks on the

    board itself. Only seems to work in packages. Is it possible on boards?

     

    -Brad

     

Reply

  • 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.

     

    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...

     

     

    Thanks that makes sense, particularly if I put the vias inside the

    package itself. Two more (probably obvious questions). 1. How do you

    draw a filled circle? Using the polygon tools works, but its sort of a

    hassle. 2. I actually have not found a way to turn off stop masks on the

    board itself. Only seems to work in packages. Is it possible on boards?

     

    -Brad

     

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