Topic: Via in SMD pad

Via in SMD pad
I have read your FAQs and would like to place vias directly inside the pad of my decoupling capacitors (was already a question of Martin Silbernagl, 18.08.2002, 04:30:14 "Via in SMD Pad"). On my design, each capacitor has a via centered in each pad and one track on the top side that goes to the component power supply.

I would like to be sure that automatic placement will work properly with this solution and do not want to put any unecessary constraints that may drive the price up.

Do you commonly have such requests and are you experienced with this pad-in-vias process? Is it a good way to do it? Will a 603 capacitor move during automatic soldering?
02/06/2003 12:46:58
Laurent Guinnard
Re: Via in SMD pad
Hello Laurent Guinnard,
a via in a SMD-Pad will be filled with solder after the reflow-process. This solder is then missing on your SMD-Pad.

Example:
The printed volume on a 0805-Pad is

Padlength x Padwidth x Printheight =
approx. 1,0 mm x 1,5 mm x 0,2 mm = 0,3 mm^3.
Your via in the pad will use
drilldiameter^2 /4 x Drilllength =
approx. (0,3 mm^2) /4 x 1,6 mm = 0,036^3 mm .

This is about 30% of the printed solderpaste. It exactly means, that a third of your solderpaste will disapear in your hole.
To compensate this, you could increase your solderpasteheight, for example by increasing your stencilthickness to +30% but decrasing all areas where Pads are without vias to -30%.

To answer your question: It absolutely will increase the costs for manufacturing your assembled board.

Your Beta LAYOUT Team



03/06/2003 14:41:17
Beta LAYOUT GmbH Service Team
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