Electronics advantages to different pad shapes?

Hi - I'm just wondering - I've been doing alot of layout work with Eagle as of late - and I've noticed that most components have round pads, but some have oval pads. Why is this? For example - most DIP components have oval pads. At first I thought that it was a way to leave space between each pad, but to also leave plenty of space to solder. But then I noticed some other components that have much wider pin spacing also use oval pads (like many relays, for example). So - does anybody know why some would be oval, and others circular? Is there some advantage to one or the other that I'm not thinking of? Thanks!

 

I am guessing this is a case of over-thinking. For all we know, they just ran out of one type, and heck, use whatever what was available then.

Maybe there is a physic rationale involved when working with very tiny traces and very precised dimensions. U hobbiests doing it by hand is not gonna make didly of difference.

 

hmm this is a puzzler!

I'd guess its because with the DIL stuff, theres another thing near it, so it squashes the pad to make the gap bigger, but keeps the same(ish) area for the solder's benefit.

Thats a complete and utter guess thou. It might just be some zaney convention.

 

I know that a square pad is often used to mark pin 1.

 

Polarised components often use a different pad shape to denote which leg is the cathode or negative.

If there is sufficient space between legs to use round pads then there is no reason as to why you shouldn't use them. It's just the preference of the designer.

 

I've done it when I need to run a trace between pins of the component. The more pins something has the more likely your are to want/need to run a trace between pins. Can't as easily do this with round pads.

Also it lets you get a pad of larger surface area into less space, can only go so wide, but can often go way longer... the result... ovals.

Just my experience/2 cents for what it's worth.

 

There's also the thing that the glue between copper and board melts at highish temperature, so a very small round pad would be more likely to lift and maybe break the track or leave a weakness when soldering. May be less of a problem these days with automatic flow soldering, but it wasn't always like that...