Hi Heather,
My first reaction to your question is a question... what size and type of via do you want to use... is it a thru hole via, blind via? Laser drilled via? Capped and plugged via? Back drilled via? There are so many flavors... :)
Usually you will find that there is a way to do what you want... but it may cost more and have undesirable impacts on the design and/or its manufacture...
A good designer will look at all the options and find the most cost effective, functional and simplest solution to solve the deign challenge.
A thru hole via typically if placed into a pad of a 0805 resistor without any special consideration will most likely wick the molten solder away from that pad it is embedded in when reflowing the board causing the part to be 'solder starved'... under those conditions, while in the reflow oven, I would not be surprised if the part didn’t 'tombstone' (or stand up erect) due to the surface tension of the solder on the opposite pad... The larger the diameter of the hole in the via, the more the capillary action and movement of solder down the hole... the smaller, the less...
I have put small .008 in. vias in TO-220 package or thermal pads under IC's like SO-8 or SO-14 packages and had them solder successfully. A larger diameter via would steal the solder from the part as it wicked down the plated thru hole... Other types of vias like blind or buried vias can be more expensive than standard thru hole vias... but they have their proper applications...
An 0805 package is a large part compared to some of the parts we use these days...maybe a smaller part would allow you to get a thru hole via in without putting it into the pad?
Just a thought... :) Maybe an 0603 or 0402 package? Would the design tolerate that?
William Brooks, CID+
Senior MTS (Contract)
2747 Loker Ave West
Carlsbad, CA 92010-6603
760-930-7212
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-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Heather Gregg
Sent: Friday, August 08, 2014 4:31 AM
To: [log in to unmask]
Subject: [DC] Vias in pads
Hello,
It has been a number of years since I was active in the PCB design realm. I was asked a question yesterday about the possibility of placing vias inside a component pad. My first response was "no way", but then I thought maybe things have changed.
I have used vias in heatsink pads for thermal reasons, but this designer was asking about placing a signal via inside one pad of an 0805 resistor.
What are the guidelines these days?
Thanks,
Heather Gregg
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