PSU Design Part 9 - PCB Layout

[IanB]

Hi Dave,

You mentioned in the introduction that SMT components use a metric grid. However, I was under the impression that sizes like 0805 were 80 thou x 50 thou? Or is it that the sizes are nominal and in fact metric/imperial grids are interchangeable at this scale?

[shebu18]

As far as i know 0805 is in imperial.
A comparison:



Edit: Corrected stupid mistake.

[metalphreak]

Things like resistors, capacitors, and surface mount leds that are 1206/0805/0603 etc are usually in imperial units.

Things like that aren't terribly important for grid alignment since they are a single pad either end. Pretty much all of the SMD ICs use metric pin spacing which is where you definitely want the correct grid spacing.

[siliconmix]

cool video.works out about 7 hours work.

[EEVblog]

You mentioned in the introduction that SMT components use a metric grid.

There is a mix (e.g. SO is 50thou/1.27mm), but generally all modern SMD packages use metric, so it's advantageous to use metric when doing SMD.
Resistors and caps don't matter because they don't have a pin pitch as such, and the centre line is usually in the centre of the component, so with any grid the traces go directly through the centre. The old imperial sizes like 1206, 0805, 0603 etc slowing being replaced with their metric equivalents e.g 0805 is 2012 metric. Bloody annoying for anyone who been bought up on imperial.
And modern CAD packages like Altium have "smart" snap features anyway, so will automatically snap your cursor to any pad centre, even if off the routing grid.

Dave.

[EEVblog]

cool video.works out about 7 hours work.

Yeah, about that. it was a good days work.

Dave.

[electrode]

As far as i know 0805 is in metric.
A comparison:

Hmm? That clearly shows it's imperial.

A "metric 0805" would be something a bit smaller than an imperial 0402.

[JimmyM]

7 hours!? Christ. I'd be at it all week. Juuuust a little bit of experience there. Eh, Dave?

[EEVblog]

7 hours!? Christ. I'd be at it all week. Juuuust a little bit of experience there. Eh, Dave?

I spent years as a full time PCB layout guy, so yeah, I've done a few 
But even so, I don't consider myself very productive, I do a lot of dicking around...

Dave.

[Rerouter]

I would also be going at it for more than a day :/ but I would like to think that's just because I'm never happy with small details like "what if i rotated this IC the other way?" and spend half my time digging up sections of the board and relaying it

[sacherjj]

I spent years as a full time PCB layout guy, so yeah, I've done a few 
But even so, I don't consider myself very productive, I do a lot of dicking around...

So you design boards like you make videos?