Confused again ... pad size

Layout
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OK … either I am way overthinking this or PCB’s are rocket science.

So … designing my first board (well at least in 20 years).

Think I have KiCad under control …

Needed a few custom components no in the library.

How do you go about figuring out the pad size?

These are all through hole parts.

The hole makes sense … did some reading … pin size plus .3 -.4 mm … easy

Now for the pad … and boy I got lost in reading here.

They start talking about manufacturing error … minimal annular ring before breakthrough …

I did see notes on things like do not exceed 3 mm or you need to think about changing the shape.

Formulas and manufacturing standards and …

This is a simple circuit … the fuses are only 300 mA so no high power stuff. 115 to 12 transformer …

So, for example … I need to use a special fuse holder (touch safe per the customer) … 1.2 pins or 1.5 hole.

Now, what size pad ?

The transformer and the input connector have had similar size pins (1.4 hole) and I went with a 3 mm pad … but this is more of a guess.

Now that the hole is getting a bit larger (1.5) I am wondering if 3 is too small ( and maybe it was for the other also)?

I am hand soldering this … don’t know if that makes a difference.

Just looking for some simple guidelines to follow.

Thanks!

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Maybe this is helpful? How to calculate PTH hole and pad diameter sizes according to IPC-7251, IPC-2222 and IPC-2221 standards? - PCB 3D

I would generally follow the IPC recommendations for most cases (you may want to go larger than them if the component will be under mechanical stresses)

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So basically for Level A (easiest for hand-soldering), it appears to be lead diameter + 0.95mm.

Sometimes the data sheet has advice on pad size.

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Worth consideration:

Syntax (what things are called, from Parts, Symbols, Footprints, automobiles…) can mean different things to different Software.

Kicad Schematics use ‘Symbols’. The PCB’s use Footprints.

Symbols are simply a Graphic to represent something such as a DIP-socket. What it looks like only matters if you care that it matters.

Symbols can have a Link to a Footprint but, not necessary (it’s used only for the PCB).

Footprints can have a Link to a 3D-Model or WRL but, they are used for only the 3D-viewer - a pretty picture.

Pads can be of different shapes - there are several to choose from (if you double-click a Pad).

Size of the Pad depends on several things - Manufacturability, Current-load… Personal-Preference…

Stock-Pads on Parts are usually small but, can be re-sized/shaped.

Example: I CNC Mill my PCB and I like big Oval Pads. Holes size depends on the Part’s Pin’s/Contacts…

If making your own PCB, do what makes Common-Sense to you.

Make a Footprint with some example Pad/Hole sizes and that will trigger your thinking with better clarity toward the end-goal…

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Way better example than I found … this one makes sense … Thanks!

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This is what I am looking for … just a good “rule of thumb”. If is was a critical board it might be different but this a large board with few parts. Thanks!

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Now milling is something I understand … I am a machinist by trade.

I think I am getting the hang of this.

I did find a symbol for a fuse but the for the pads, I needed a special fuse holder … so I started to draw one.

Got to sizing the pad and started way overthinking this.

“Common” sense is something I understand… just didn’t want to break rules that are in place for manufacturing.

Heck, wayyyyy back in the day (making PCB’s in my mom’s laundry tube) I would leave as much copper as possible as a heat sink and or ground plane.

Thanks!

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@xtal_01
PCB manufacturer’s have requirements commensurate with their manufacturing capability so, look at info on their site. If making your own PCB, consider that, whether you use:

Print-transfer
CNC-Milling
Etching…etc…

there is always enough variability such that Bigger Pad’s are your friend…

How are you going to make this?

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I am making a one off first for approval … they with some luck say 10.

Kind of a long story … I do a lot off odd jobs for this client … all industrial electric work (patch cords … push button stations … simple starter boxes).

They have a very simple air monitoring system (just a diff press switch … buzzer … relay … back up battery).

These boxes were designed 30 plus years ago … made by one guy (we worked at the same place for a while … both contractors).

He has long since retired … maybe even passed away … no one can get a hold of him.

The boxes are starting to fail … they wanted me to reverse engineer them and make a few.

Most of it is industrial electrical stuff but it has a PCB in it.

There are so few parts on the board … maybe 20 … that it is almost like making a kit when I was a kid.

They don’t want me to change the design.

Some of the parts are obsolete so I am just updating the ones I need to.

Anyway … I have made PCB’s but that was years ago. I downloaded KiCad … I knew I needed a Gerber file … just trying to figure out all the little details.

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