Guess who is *really* not happy right now. - Page 1
Forum section: electronics / general

author: back.to.battery
author_rank: Contributor
timestamp: October 08, 2016, 02:20:08 pm
content: So, I don't know if this is normal for SMD LEDs, and I guess it's my fault for not checking the datasheet and assuming two very similar SMD LEDs from the same manufacturer would follow the same marking convention, but I'm still pretty miffed about this...

author: bitslice
author_rank: Frequent Contributor
timestamp: October 08, 2016, 02:39:12 pm
content: It's a power saving feature

author: AndyC_772
author_rank: Super Contributor
timestamp: October 08, 2016, 02:44:58 pm
content: I've seen this with different colours in the same range before.At least the parts can be rotated, you don't need to respin your PCB.

author: back.to.battery
author_rank: Contributor
timestamp: October 08, 2016, 03:00:22 pm
content: Quote from: AndyC_772 on October 08, 2016, 02:44:58 pmTrue. Unfortunately I was also too rushed (read: stupid) to check the first PCB for functionality before proceeding with the whole batch. Looks like I'll be paying for my impatience with a day's worth of rework. >.<

author: wraper
author_rank: Unknown
timestamp: October 08, 2016, 04:01:27 pm
content: They mount different dies on the same substrate. However dies themselves most likely have different polarity (top/bottom). As the substrate is not symmetric at all, they cannot just reverse the polarity internally.

author: TJ232
author_rank: Frequent Contributor
timestamp: October 08, 2016, 05:35:26 pm
content: Quote from: back.to.battery on October 08, 2016, 03:00:22 pmI know somebody else (me, lol) who learned few years ago, on the hard way, the valuable lesson about cheking that EACH new batch of new received components has been checked twice, even if they are the same thing as previous and from the same supplier, and do a 3-5 pcs testing boards before full batch processing. LED's are notorius for your situation, I really hope that you don't need to rework thousands of them.

author: CraigHB
author_rank: Regular Contributor
timestamp: October 08, 2016, 06:05:30 pm
content: I had that happen with a MOSFET. They always have the drain common with the thermal pad. I designed a PCB and almost sent it to the fab, but then I checked the part data sheet. Sure enough this one had the source common with the thermal pad. That would have been a batch of coasters. But yeah you can never assume a standard even though parts seem to be common across the board. It's ridiculous to reverse that connection for seemingly no reason, but they do that stuff for whatever reason.

author: Ice-Tea
author_rank: Super Contributor
timestamp: October 08, 2016, 06:39:18 pm
content: With SMD LEDs never assume anything, ever.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 08, 2016, 07:04:39 pm
content: IME the taping orientation is always cathode to the hole edge.

author: Ice-Tea
author_rank: Super Contributor
timestamp: October 08, 2016, 07:40:16 pm
content: Quote from: mikeselectricstuff on October 08, 2016, 07:04:39 pmI have no indication to the contrary but I wouldn't trust it with LEDs. Ever. Ever.

author: razberik
author_rank: Frequent Contributor
timestamp: October 08, 2016, 09:03:40 pm
content: Exactly the same experience here.

author: stj
author_rank: Super Contributor
timestamp: October 08, 2016, 09:37:15 pm
content: i always test them before soldering.not just polarity, but too make sure it's the right colour!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 08, 2016, 10:31:45 pm
content: Quote from: CraigHB on October 08, 2016, 06:05:30 pmI've never seen a "standard" part that's made that way. Surely you had an RF part?Tim

author: JPortici
author_rank: Super Contributor
timestamp: October 09, 2016, 07:02:36 am
content: Quote from: back.to.battery on October 08, 2016, 02:20:08 pmbeen there. a whole production lot

author: Psi
author_rank: Super Contributor
timestamp: October 09, 2016, 07:36:41 am
content: Yep, i've seen this exact issue before on 0805 LEDs.One color is anode dot, another is cathode dot.

author: peter.mitchell
author_rank: Super Contributor
timestamp: October 15, 2016, 10:30:28 am
content: Quote from: T3sl4co1l on October 08, 2016, 10:31:45 pmNot just RF, but GaN power fets also do it for lower inductance for higher switching speeds.

author: aandrew
author_rank: Frequent Contributor
timestamp: October 17, 2016, 01:23:50 am
content: I've run into this enough times that when I am hand-assembling a board I *always* use the diode check function of my meter to make sure which terminal a particular batch of LEDs is indicating. Very, very frustrating.It's the same kind of issue with every f#*$ing polarized capacitor indicating negative... except for tantalum capacitors! I'd love to ask the person who decided to change that why they did so.

author: tszaboo
author_rank: Super Contributor
timestamp: October 17, 2016, 11:25:33 am
content: Quote from: aandrew on October 17, 2016, 01:23:50 amIt is the demonstration for the volatility of tantalum capacitors. Why have white papers and application notes, explaining that it is bad, if you can demonstrate it with hellfire.

author: chris_leyson
author_rank: Super Contributor
timestamp: October 17, 2016, 11:36:23 am
content: In general for T-1 and T-1 3/4 LEDs the cathode is usually the long lead, but I always check the data sheet because occasionally you ind one where the anode is the long lead.

author: Skashkash
author_rank: Regular Contributor
timestamp: October 17, 2016, 11:53:59 am
content: I remember this issue from a blog post a while ago.Yep,http://blog.screamingcircuits.com/2013/01/how-not-to-mark-a-diode.htmlSince reading that I always triple check the data sheets and worry about any substitutions.I understand the manufacturing difficulties. But you would still expect (hope?) for consistently from the same manufacturer.

author: MagicSmoker
author_rank: Super Contributor
timestamp: October 19, 2016, 11:21:41 am
content: Quote from: back.to.battery on October 08, 2016, 02:20:08 pmAww, man... I got burned by this very same thing, with these very same part numbers!