Five 0805 resistors and five different footprints


#1

I really support the idea of a community parts library but I don’t understand why there are so much variations between the same footprints. I placed five different value 0805 resistors choosing verified parts only. Each part has a different footprint and it just makes me want to edit each one and break the whole concept of a community library. Especially when I know there is almost zero chance that the changes I make will roll back to the community library.

There are good reasons to have different kinds of 0805 footprint for different manufacturing methods, but that should be agnostic to the resistor part/value. Upverter really needs to push IPC standard footprint for something as common as 0805 and the verified status should reflect this. Then allow a simple part property to oversize the pads for those that need more area for hand soldering.


#2

Hey @combatcqb can you share the parts you had this issue with? I’ll take a look but my guess is that the datasheets actually do call for minor variations between the footprints of the different parts.

We do have an 0805 footprint which we use for generics, and its identically every time you use it - maybe you should try using generics instead of specific parts? And we also have an IPC footprint generator which is very deterministic - in case you want to create parts of your own, or tweak the footprints of the parts you were testing.

Either way, once I have the parts list I’ll make sure we didn’t screw up on our side and fix it if we did.

In case you’re interested, the backstory on why it works like this is that early on we decided that every part should have an explicit footprint and an explicit symbol that belong to that part. Rather than having three databases: symbols, footprints and parts where the parts database would link into the symbol and footprint databases.

We felt that the 3 databases would lead us and our users to try and best-fit parts. Instead of creating the correct footprint or the correct symbol as specified by the datasheet, we would instead use whatever we already had that was “close enough”. And from my experience building hardware at scale this burns you hard when you get into big volume, standard footprints and yield issues.

We built a bunch of helper tools to copy symbols and copy footprints out of existing parts, a footprint generator to make footprints fast to make, and a symbol generator to make symbols fast to make. All added up our assumption was (and still is) that this will lead to a higher quality parts library where every part has exactly the correct symbol, and exactly the correct footprint as specified by the manufacturer.

Thats probably why you have 5 “0805s” that are all a little different. But assuming there hasn’t been a breakdown somewhere its because they are each designed exactly as their manufacturer recommended.


#3

Hi Zak,

Thanks for explaining the rational. I do share your view that the “close enough” mentality can breed complacency. Looking at it again, my concerns really had two roots: FIrst, I can overcome the OCD of wanting all my resistor footprints to look the same simply for aesthetics. Second is how much work it would take to edit each part for what I would consider hand soldering compatible as I add more parts.

I will concede that my initial reaction did not consider that each manufacturer would specify unique footprints for something as common as 0805. I still think there is a valid case for having a simple “oversize pad” property that can simplify making footprints more friendly to hand soldering. I can also sympathize that it is hard to come up with a one size fits all rule in footprints and I wouldn’t expect such a rule to apply to BGAs; but basic discreet parts are everyone’s bread and butter so they really should have multiple footprints to cover more usecases.

Here are the parts I’m using to illustrate the variations, all verified 0805 resistor/capacitors:
CL21B104KCC5PNC - https://upverter.com/upn/revision/ba9d0de8071a5573/
GCM21BR71C225KA64L - https://upverter.com/upn/revision/d3149798698ed33a/
RT0805FRE07100RL - https://upverter.com/upn/revision/eba0a7b3ac598740/
CRCW080510K0FKEA - https://upverter.com/upn/revision/c495844112187454/
CRCW08054K70FKEA - https://upverter.com/upn/revision/703d66bf4b770ce8/


#4

Sorry its taking me a few days longer than I thought to get back to you on this. I need a little more time though.


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