What Units Are Used In Footprint NAMES: Inches or MM?

Layout
#1

Starting my first KiCAD project with a very simple schematic. One IC and two capacitors, repeated five times. What could go wrong? I found and added the IC to the schematic and then tried to add the capacitors. They are 10 and 25 uF, electrolytics in surface mount packages. In the default symbol library I tried the manufacturer’s name and part number but no luck. So I choose “C_polarized_US”. OK.

But then I needed to choose a footprint, apparently from a drop down list. That list contains a number of surface mount footprints with descriptions like “Capacitor_SMD:CD_Elec_4X3”. There is absolutely no hint as to what units those numbers, 4 and 3 refer to. I have seen footprints described both in hundredths of inches and in tenths of mm. Many datasheets will even have both. I do not see any numbers in that list of footprint NAMES that look like multiples of 2.54 or 1.27 or 0.63 so I suspect they are using inch values. Can anyone confirm this? Or correct me?

I hate to get off to a bad start with my first PCB and need to take corrective action later or just start over from scratch.

One more quick question. As I said, my basic circuit is repeated five times. I am assuming/hoping that I can just draw it once and then copy it for the other four instances. Is this possible? Are there any things to look out for while doing it?

Thanks in advance!. My first post got closed before I thought to thank everyone who responded, but I do appreciate the help.

#2

The Item box expands to the right. You will find the description there. first number is diameter, second is height.

The procedure is to consult manufacturers date sheets to find the size, or, if you have the part, measure it, then find a suitable footprint.

Edit: The part outline is drawn on the F.Fab layer (see layers on far right). Under the drawing space and to the right, beside the layers, are measuring tools. Using these tools will confirm if you have the right footprint (measure the grey circle diameter).
Note, although most electrolytics are cylindrical, they are often different diameters and heights. You really need to have the electrolytic present and measured, then select an appropriate footprint.

#3

The standard SMD parts contain both units, for example C_1210_3225Metric is about 0.12x0.10 inches or 3.2x2.5 millimeters.

Otherwise look at the part description, for example CP_Elec_4x3 is described as “SMD capacitor, aluminum electrolytic, Nichicon, 4.0x3mm”

#4

Yes, use the "duplicate " function after selecting the group of components and then Right Mouse Click.

#5

Go support these guys to finally abolish those other silly units.

Apparently George Washington himself proposed to adapt the metric system, but all attempts fail because of an army of housewives that are afraid they can’t cook anymore because they get lost in their recipies or something. And in the mean time it’s an ongoing waste of money and energy that leads things like emergency landings for planes to space probes crashing on mars.

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#6

Speaking of ‘Mars’… Awhile back I watched a YouTube video of Mars’ landscape - there are many of them on YouTube. Something caught my Eye in the video; the scene was a large expanse and not easy to see without enough effort.
Once, I was finally able to Zoom-into what I thought was, perhaps, some rocks falling, I discovered someone Jogging along a path… You can’t trust anyone!!!

Here’s the snippet of the Video…

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#7

Short answer, this is just a graphical representation of the electronic function of the part; in or mm doesn’t matter.

Short answer, choose the footprint the corresponds to the datasheet dimensions that match the actual part you have in hand.

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#8

Those “other silly units” are sometimes not that silly. Lots of electronic stuff is in 1/10ths of inches, which is a sort of “Metric Imperial”.
It is much easier to work in .1s than 2.54s… eg. 17x.1= 1.7 and 17x2.54= hang on 'till I find my calculator.

Sometimes it is convenient to be fluent in both languages. :grin: :grin: :grin:

Edit: Sorry, three languages. US Imperial, Real Imperial and, that sometimes awkward, Metric. :crazy_face:

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#9

Jmk, Thank you for a straightforward answer to my second question.

Apparently, no one knows the answer to my first one.

#10

mm

ksnip_20230124-223551
ksnip_20230124-2235511881×915 227 KB

Place cursor on RH “Item” border, hold left mouse button down and drag border to right to expose “Description”.

#11

There were good answers to your questions in the posts above. Your specific question in the thread title was answered above, shown quoted below.

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#12

I am working in the schematic editor. This photo shows one of many footprints just after selecting it. The NAME of that footprint has the dimensions of “4x3” as part of that NAME. I want to know it that is 4x3 tenths of a mm or 4x3 hundredths of an inch. That’s all I need to know.

If I need to use the footprint editor to examine the footprints, then just say so. It just seems like someone must have used these included footprints and in order to use them, you need to know what units they are NAMED with. But perhaps no one ever uses them? Do you all just draw new footprints for every part you use?

ChoosingFootprint
ChoosingFootprint1571×681 185 KB

#13

You can easily measure it yourself, right? You should know which component you are going to use, and you can read the datasheet and compare it with the footprint dimensions.

EDIT: there may be some standard in naming those footprints, but I don’t know what it could be.

#14

I have been reading datasheets and measuring parts for longer than most of those here have been alive. I started making PCBs with paste-on donut holes and black tape on a Mylar grid. The only thing that is new to me here is KiCAD.

The only thing I was asking about was how the NAMES in the footprint library were created. The naming convention! That’s all.

I just asked a simple question that was stated in very precise English. Has anyone actually read it instead of ASSUMING that I was asking something else?

Forget the question. I will figure it out for myself. Thanks for …

Well, I don’t know what for. But thanks anyway.

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#15

@ChipsAndChips : Already the third answer (and again the 9.answer) stated that 4x3 for your example smd electrolytic cap refers to 4mm diameter x 3mm height. And it was written in very precise English. Do you actually read it?

Forget the question. I will figure it out for myself.

This solution is often faster than writing the first thread-opening text.

#16

For the patience of those who answered your question time and again. Your tone and attitude is inadequate and not conducive to anyone helping in the future.

#17

Hi @ChipsAndChips ,

As I stated above, the dimensions were in millimetres and were height and diameter. To confirm which was which, use one of the measuring systems I mentioned above to measure the diameter, which is the grey circle in the footprint which I also mentioned above. However, as I also mentioned above, different brands of electrolytics have different sizes, so, unless you know the brand of electrolytic you are purchasing and have the data sheet for that electrolytic, it is wise to first obtain then measure the electrolytic before finding a suitable footprint from the Kicad library.

What I did NOT mention was, YES, you do need to go into the footprint editor to confirm the measurements of the footprint. All my comments were regarding the footprint editor as can be seen in the screen shots I posted.
You wrote about footprints, so I assumed (incorrectly), you had ventured from the symbol editor to the footprint editor.
My apologies.

Finally,

ABSOLUTELY!!! in my case.

Edit: I also use my own symbols. :slightly_smiling_face:

#18

KiCad has the KiCad Library Convention, and it also has some suggestions for filenames.

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#19

I never select a footprint in that dialog, i always just place the symbol with no or the default footprint and then (if necessary) use the assign footprints dialog later, which I believe shows the footprint descriptions.

#20

Hi @ChipsAndChips
I feel your pain ! I do not draw my own footprints for the jellybean passives either :disappointed: and a good few years ago I had the same head scratching moment as you are enduring. I have no idea about naming conventions but I realized that it was diameter x height and the units are ‘mm’ also the information for the dimensions can be found in a multitude of places which is great as you will find it at any point in your workflow. I use a lot of the capacitors that you are choosing in various sizes, lets say a 6.3x5.4 I roughly measure the product in my hand and read 6x5 I know its the right footprint. A final point with the SMD caps and res there is an option for hand soldering that provides bigger footprints. I hope this helps a little :smiley:
Andy :nerd_face: