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So, I am trying to figure out what pad size to use for 0603 (imperial) SMD capacitors. The datasheet for the particular capacitors I plan to use provides part dimensions but does not recommend a land pattern.

Googling, I found that the land pattern is typically parameterized as X=pad width, Y=pad height, C=center-to-center pad spacing.

As a first pass, IPC-SM-782A recommended X=1.00, Y=1.10, C=1.70 (all mm).

http://tinymicros.com/mediawiki/images/3/3c/IPC-SM-782A.pdf

Then, I found a document from Kemet that contains a bunch of maths and stuff to conclude that X=1.08, Y=1.05, C=1.73 would theoretically be more effective than the standard at countering possible tombstoning. But in their comparison table (pg 12) they misquote the standard as having specified X=1.2, which is incorrect AFAICT. This makes their maths and stuff seem somewhat less impressive but maybe it's just an isolated typo. I really don't want to try to understand the maths itself, "estimation of error" techniques were always a giant weak point for me.

http://www.kemet.com/kemet/web/homepage/kfbk3.nsf/vaFeedbackFAQ/2209BDBA03843BBF85256BCD004EBC11/$file/f2100e.pdf

Finally, I downloaded some component libraries for KiCad, and everyone seems to use slightly different pad sizes (e.g., "walter"'s library is close to X=0.9, Y=1.0, C=1.5).

I've soldered before, but only larger stuff w/ iron and solder wire. I've never used the solder paste + hot air method before nor handled components as small as 0603, so I am worried about the tombstoning and it seems to make sense to try and input the pad dimensions that will work best, and have the greatest chance to avoid tombstoning ... problem is, all the sources have conflicting advice.

So, the question is: what pad sizes should I use? the standard's? kemet's? walter's? an average of these? also, if you use other sizes that you have practical experience with and they work well, please share ...

I guess a pertinent higher-level question is, do the few fractions of millimeters make any practical difference at all?

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  • \$\begingroup\$ Just found related question electronics.stackexchange.com/questions/13072/the-right-0805-footprint-land-pattern that points to an updated standard. Will check that out ... \$\endgroup\$
    – Andrei
    Commented Oct 27, 2013 at 8:27
  • \$\begingroup\$ The only real answer here is to talk to your PCB manufacturer and your assembly house. \$\endgroup\$
    – Connor Wolf
    Commented Oct 27, 2013 at 8:42
  • \$\begingroup\$ Hmm, well, I order PCBs from oshpark.com, it's only $13 for 3 boards, so it doesn't feel right to bug them with support questions specific to my design. Since my design is still in the early prototype stage I'll be doing the assembly myself. Apparently you have to pay like 100 bucks for a copy of the updated standard IPC-7351B which doesn't seem worth it for getting three values -- I'll probably just go with Kemet's calculations if nobody has better advice. \$\endgroup\$
    – Andrei
    Commented Oct 27, 2013 at 8:50
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    \$\begingroup\$ If you're doing the assembly yourself, they'll all work fine. It's only really when you're trying to squeeze the crap out of your yield ratio that it's important. \$\endgroup\$
    – Connor Wolf
    Commented Oct 27, 2013 at 8:59

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It depends very much on how the boards will be assembled and soldered. If you are doing it manually then it will not matter too much. I try to pick a slightly larger footprint for my DIY boards because that makes it easier.

If the boards will be professionally assembled then the footprint will definitely matter. There are often slightly different requirements for e.g. reflow soldering vs. wave soldering. This is when you'll need to work closely with the assembly house to work out what size and tolerances they can work with.

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