PSU Design Part 9 - PCB Layout - Page 1
Forum section: electronics / general

author: IanB
author_rank: Super Contributor
timestamp: February 13, 2012, 09:35:19 am
content: 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?

author: shebu18
author_rank: Frequent Contributor
timestamp: February 13, 2012, 09:42:40 am
content: As far as i know 0805 is in imperial.A comparison:Edit: Corrected stupid mistake.

author: metalphreak
author_rank: Frequent Contributor
timestamp: February 13, 2012, 10:53:26 am
content: 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.

author: siliconmix
author_rank: Frequent Contributor
timestamp: February 13, 2012, 10:57:10 am
content: cool video.works out about 7 hours work.

author: EEVblog
author_rank: Unknown
timestamp: February 13, 2012, 10:57:43 am
content: Quote from: IanB on February 13, 2012, 09:35:19 amThere 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.

author: EEVblog
author_rank: Unknown
timestamp: February 13, 2012, 10:58:57 am
content: Quote from: siliconmix on February 13, 2012, 10:57:10 amYeah, about that. it was a good days work.Dave.

author: electrode
author_rank: Regular Contributor
timestamp: February 13, 2012, 11:20:59 pm
content: Quote from: shebu18 on February 13, 2012, 09:42:40 amHmm? That clearly shows it's imperial.A "metric 0805" would be something a bit smaller than an imperial 0402.

author: JimmyM
author_rank: Regular Contributor
timestamp: February 14, 2012, 02:06:20 am
content: 7 hours!? Christ. I'd be at it all week. Juuuust a little bit of experience there. Eh, Dave?

author: EEVblog
author_rank: Unknown
timestamp: February 14, 2012, 02:26:59 am
content: Quote from: JimmyM on February 14, 2012, 02:06:20 amI spent years as a full time PCB layout guy, so yeah, I've done a fewBut even so, I don't consider myself very productive, I do a lot of dicking around...Dave.

author: Rerouter
author_rank: Super Contributor
timestamp: February 14, 2012, 02:29:34 am
content: 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

author: sacherjj
author_rank: Frequent Contributor
timestamp: February 14, 2012, 04:11:00 pm
content: Quote from: EEVblog on February 14, 2012, 02:26:59 amSo you design boards like you make videos?