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Electronics => Beginners => Topic started by: jrozner on March 20, 2017, 06:17:32 am

Title: Hole sizes for packages in an EDA
Post by: jrozner on March 20, 2017, 06:17:32 am
When creating packages for parts in an EDA should the holes be slightly larger than the pin size in the documentation to allow for any tolerance in the manufacturing and to allow the pin to not be the exact same size? If so, is there a good general rule about how much larger to make it?
Title: Re: Hole sizes for packages in an EDA
Post by: ElektronikLabor on March 20, 2017, 07:21:49 am
Yes, slightly bigger hole sizes for THT components are recommended.
How much bigged depends on the size of the pin. For example: I use holes that are twice as big as the leads for small electrolytic capacitors, because of their thin leads.
Fot bigger leads as TO-220 packages I use 20% - 30% bigger holes.
For really big leads maybe 10% bigger hole.

But it's my personal preferences. I believe that the next one will have different biases ;)
Title: Re: Hole sizes for packages in an EDA
Post by: Fire Doger on March 20, 2017, 07:56:11 am
It's good to have big holes, if you are using THT I assume that you are not really tight in layout so 0.2mm diameter more won't cause any troubles. I like tight holes but better safe than sorry.
Every lead has tolerance in data sheet, fab house too so take for example worst case scenario both for component and PCB, go up to the next (or more) standard bit size and you are good.

Also try to keep the same hole sizes.
This may give you the ability to fab it an a low cost CNC (or home?) which cannot handle 20 different bit sizes.

You can practice on that with some bits from eBay and scrap boards or download some libraries to see what most of them uses.

If you are inexperienced it's good to test blocks of the board as small modules in diy PCB before manufacturing so this will give you an Idea if the footprints needs rework
Title: Re: Hole sizes for packages in an EDA
Post by: mariush on March 20, 2017, 08:51:27 am
I'd also add : round those diameters to values that are most likely to be supported by pcb manufacturers.

For example, here's what Eurocircuits recommends : http://www.eurocircuits.com/PCB-design-guidelines/#holes (http://www.eurocircuits.com/PCB-design-guidelines/#holes)

Quote
2. All PCB drills are manufactured in increments of 0.05 mm. So we convert the drill sizes given in the drill files or tool lists into millimeters and round to the nearest 0.05mm.

For example:

    Drill size of 31mil is converted to 0.7874mm and then rounded to 0.80mm.
    Drill size of 32mil is converted to 0.8128mm and then rounded to 0.80mm.
    Drill size of 33mil is converted to 0.8382mm and then rounded to 0.85mm.


and so on...

Plenty of good advice in that document.