SMD Resistor & Capacitor Footprint, Do a Golden Guideline Exist? - Page 1
Forum section: electronics / beginners

author: MuriTheMyth
author_rank: Contributor
timestamp: August 01, 2024, 10:19:02 pm
content: Hi folks,I hope you're all doing well.I'm a absolute newbie in ECAD and I felt like this is a stupid question to ask: Is there a golden guideline for the sizing of SMD footprints?I tried to do some searching online but the information is surprisingly mixed:- Not a single guideline covers all the packaging I'm using (0201 for the smallest and 1210 for the largest).- Also that some guidelines differentiate between footprint for capacitors and resistors, while some don't.Is there a agreed guideline on the sizing for the footprints? I'm really really confused.Thank you so much for any bits of advice!Many Thanks,Muri

author: Sensorcat
author_rank: Regular Contributor
timestamp: August 01, 2024, 10:54:29 pm
content: There are two sources of information on footprints:Data sheets and other documents from device manufacturersFootprints stored in PCB design softwareIn both cases, this information is a recommendation. These footprints are known to work well under a large set of applications and manufacturing processes. You can choose different sizes, but there's not much you can gain from choosing differently.

author: tautech
author_rank: Super Contributor
timestamp: August 02, 2024, 04:57:32 am
content: Typically in your footprint libraries you will/should have a choice of different density footprints.High density will have the shortest pad and low density the longest and best suited to hand population and soldering.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 02, 2024, 05:49:16 am
content: Quote from: Sensorcat on August 01, 2024, 10:54:29 pmAnd maybe third: hidden information from those who design boards and have made and fine-tuned footprints that work well in actual production.And the difference can be huge. For example long time ago Altium Designer came with completely broken bogus SMD footprints, and I'm sure it's not the only CAD package doing this kind of shit. And quite notoriously, part manufacturers usually do not have the best advice how to use the parts they manufacture.There are probably more "golden guidelines" than you'd ever need, the problem is, as usually, who to trust?

author: MuriTheMyth
author_rank: Contributor
timestamp: August 02, 2024, 08:16:12 am
content: I think that's exactly where my confusion comes from! Do folks in this forum have a agreed credible source?I personally prefer less to use whatever footprint given by manufacturers, because the sizing and notation look too messy.

author: PGPG
author_rank: Frequent Contributor
timestamp: August 02, 2024, 12:18:49 pm
content: To give you an overview some words about 0603 only.Till 2017 I was using the same footprint for resistors and capacitors and didn't even get an idea I could use different once (if you don't ask you the question you will not answer it).In 2017 I decided to move from Protel 3 to KiCad and I found KiCad has separate 0603 for capacitors and resistors. I specially liked the R one. It had 1mm distance between pads, and I found manufacturer datasheet with exactly the same footprint (his resistors had short pads). I am using minimum clearance of 0.2mm and minimum track of 0.2mm so my conclusion was: "at least I will be able to run with two tracks under each R". All my PCBs were 2 layers with whole bottom being continuous GND so it could help a lot in unraveling connections.But before using it I asked my contract manufacturer and they said that resistors they use has longer pads so absolute maximum distance between pads should be 0.85mm. To have a reasonable margin I decided to have 0.8mm there (0.85 don't gives me nothing extra).Soon KiCad changed its footprints. I have just checked - now KiCad has 0.85mm there.

author: mtwieg
author_rank: Frequent Contributor
timestamp: August 02, 2024, 01:27:49 pm
content: There is, in fact, a standard for SMT footprints: IPC 7351. It's a generic standard which is meant to cover all types of SMT footprints (not just R and C). There are of course exceptions which the standard can't address, and applying the standard is by no means a guarantee of success. But in general if you apply the standard you will have an easier time, especially if you work with contract manufacturers.