Where is Pin 1? - Page 1
Forum section: electronics / beginners

author: Brumby
author_rank: Unknown
timestamp: July 11, 2016, 02:18:04 pm
content: I thought it would be straightforward....I bought a cheap kit which had a mix of SMD and TH components. For an extra couple of dollars, I could get one assembled - but I just felt it was more honest to do it myself.Starting out, everything was fine. I could identify all the components, read the SMD markings and found everything was there, but then I came across this TL084C in an SO-14 package. As I went to place it - I went looking for Pin 1. I could not see a notch, a dot, a dimple or any other mark to indicate Pin 1. Have I missed something?(Apologies for the poor quality photo, my close-up camera is on the fritz.)

author: Brumby
author_rank: Unknown
timestamp: July 11, 2016, 02:26:14 pm
content: I just found a datasheet that helped.Pin 1 is the bottom left, isn't it?It's the chamfered edge.

author: Kilrah
author_rank: Unknown
timestamp: July 11, 2016, 02:28:07 pm
content: Should be bottom left (that package has one of the edges that's 45° slanted as reference)EDIT: Too slow...

author: Andy Watson
author_rank: Super Contributor
timestamp: July 11, 2016, 02:29:26 pm
content: Yes. The chamfer on that edge is ever-so slightly bigger than the other edge!

author: MarkF
author_rank: Super Contributor
timestamp: July 11, 2016, 02:32:12 pm
content: Why in the world do manufactures use such packages? Absolutely insane.

author: Andy Watson
author_rank: Super Contributor
timestamp: July 11, 2016, 02:37:09 pm
content: Quote from: MarkF on July 11, 2016, 02:32:12 pmI guess that it has some advantage - possibly for orientating the package with automatic tooling.

author: bktemp
author_rank: Super Contributor
timestamp: July 11, 2016, 02:37:19 pm
content: If you can't see a pin 1 marking look at the marking text:Pin 1 is always at the left side of the text.

author: Kilrah
author_rank: Unknown
timestamp: July 11, 2016, 02:44:05 pm
content: I particularly hate STM32's in that regard.Do I take one of the 2 dimples in the plastic (which one?), the printed "dot" (isn't really one, but when looking with naked eye it's not obvious), or the top left of the marking? That gets you exactly all possibilitiesThe "dimple in plastic on the left of the text" is correct, but talk about ways of getting confused

author: bktemp
author_rank: Super Contributor
timestamp: July 11, 2016, 02:47:10 pm
content: Quote from: Kilrah on July 11, 2016, 02:44:05 pmIf there are multiple dots, it is always the smallest one.If you can't identify the smallest one, combine it with the orientation of the marking text (pin 1 is at the left side of the text), so pin 1 must be at the bottom left corner.

author: Brumby
author_rank: Unknown
timestamp: July 11, 2016, 02:50:03 pm
content: Quote from: bktemp on July 11, 2016, 02:37:19 pmI was getting the 'feeling' that was the case - probably from years of handling DIP packages ... but I hadn't made the conscious connection.Funny thing is that I went looking for just that sort of asymmetry, examining it closely with a headband magnifier, but I was not looking at it top down and the asymmetry wasn't all that obvious. When I took the photo, it was a straight top down shot, but I didn't even notice it then.It was only when I came across the manufacturer's datasheet I noticed the SO package line drawing was clearly showing the difference.That was my revelation - and facepalm moment. Another 5 minutes of research and I would have not exposed my ignorance......Murphy lives on.

author: tatus1969
author_rank: Super Contributor
timestamp: July 11, 2016, 03:04:45 pm
content: Quote from: Kilrah on July 11, 2016, 02:44:05 pmThey probably want to sell more parts, it already happened to me twice that I got it wrong and made the chip "burn"

author: SeanB
author_rank: Super Contributor
timestamp: July 11, 2016, 07:25:44 pm
content: As 99.999% of these devices will be taken from a tape and mounted with a pick and place, they probably wanted to reduce the amount of work needed on the die compounding the package, thus the chamfer so there is no need for a projecting pin to be added to the die. Has to be small so the vacuum pickups do not fumble if they are not perfectly placed on the part in the tape, so it is a compromise all round, driven by the need for a small overall package with large flat surface.

author: Gyro
author_rank: Super Contributor
timestamp: July 11, 2016, 07:41:45 pm
content: You putting a DSO138 together Brumby?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 11, 2016, 11:30:01 pm
content: FYI, I've seen some -- very old -- TTL chips that were printed "sideways". So the text direction wouldn't necessarily help you much there.To make matters worse, one was a 7404, manufactured in February 1974. Or maybe it was a 7406 from January, I forget...Tim

author: Brumby
author_rank: Unknown
timestamp: July 12, 2016, 01:42:55 am
content: Quote from: Gyro on July 11, 2016, 07:41:45 pmSprung.Yes. I know it doesn't have mouth watering specs - but it is rather compact, so I can throw it in the toolbox. For the money, it's not a big risk and (I hope) it will be adequate for some basic signal checking in the field - or if I need a floating scope on the bench. I'll find out.

author: Gyro
author_rank: Super Contributor
timestamp: July 12, 2016, 08:57:11 am
content: QuoteHaha, thought so. I noticed the slightly suspect looking molding flash on the package (seems ok though), and it's about the only cheap kit worth the effort of building. Watch your solder joints, those TH pads are too small for good heat transfer.Yes, I think it's worth it, for exactly the reasons you mentioned, in the same way as keeping a cheap dmm is. There's a short thread on it:https://www.eevblog.com/forum/testgear/jye-tech-dso-138-review-and-performance-testing/msg857888/The JYE forum also has some useful info if you skip the random 'I built it and nothing happens' threads (soldering and misplaced components). It's worth carrying out the h/w noise reduction mod while you're building it, even if you have the latest f/w.http://www.jyetech.com/forum/viewforum.php?f=18