Rendered at 13:30:59 GMT+0000 (Coordinated Universal Time) with Cloudflare Workers.
exmadscientist 1 days ago [-]
Why is this posted here? It's old, and it's not terribly relevant, though it's not useless.
For anything larger than 2 pins, pin 1 at upper left and pin 1 at lower left are both quite common. Components are also reeled more or less randomly. (There are some patterns, but you'll be better served by pretending there aren't.)
Put that all together and it means... it's all a cluster and gets manual intervention for every build. You can't automate it, but you can automate the intervention (that's what JLCPCB has done to enable scaling to lower volumes).
Just pick "lower left" or "upper left" for your library and stick to it. That's the best you can realistically do.
Also, LEDs are terrible and everyone hates them.
gregsadetsky 18 hours ago [-]
(I'm the OP) I got interested in PCBA, one thing lead to another, and I ended up posting this document which hopefully can provoke some good discussions :-)
I was also specifically interested in how critical the manual intervention seems to be - and how accepted it is. What are the barriers to automating this completely?
If the assembly fab had access to the schematic (I know a lot of people wouldn't want to share the schematic, but if we suppose that's not a problem), would that clarify most situations?
Is 100% automation possible at all?
exmadscientist 5 hours ago [-]
> If the assembly fab had access to the schematic (I know a lot of people wouldn't want to share the schematic, but if we suppose that's not a problem), would that clarify most situations?
Haha, no, not at all; that's a disaster!
No, really, the schematic usually makes it worse. CMs don't speak schematic, as a general rule. EEs don't usually draft good schematics either. And, honestly, a good schematic usually won't have this information at all. The needed information might be found in the BOM, in theory. In practice, it's probably actually also in the PLM. If your company uses a PLM system. It might not be there either.
The actual barrier here is that there's really only one guy who has all the necessary information, and that's the guy who's loading the reel into the pick-and-place machine. He's going to have to check the work no matter what. So he often ends up having to do the work instead of just check it.
This is because what orientation is required depends on what part was purchased. Not the component type; not the manufacturer; not even the specific part number. The actual dead-ass specific part purchased, and how they decided to reel it that week at the packaging subcontractor facility. This is stable over time for the major chip vendors (unless they just issued a PCN this week! hope it wasn't retroactive!); for the Shenzhen specials, don't bother. But it is not consistent among second sources for the same part, and guess what -- your purchasing department will buy the cheapest thing you allow them to buy. And those two orderable PNs that are completely identical according to the datasheet, so you listed them as fully qualified alternates, and one is way cheaper this week for some reason? Yeah, that's a reeling code difference: same part, different orientation in the tape. And it's cheap this week because some big company (probably medical...) bought the wrong one and is unloading it instead of dealing with it.
So things end up different week to week.
And only the guy loading the reels knows which reel he's grabbing. So he's got to do the work.
> Is 100% automation possible at all?
No. No one genuinely cares. This is a throughput-optimized industry: the first board takes a while to get set up to build. Then there's thousands and thousands of them.
At the end of the day, the manufacturing data packages have (should have) centroid, orientation, and pin 1 data. That's enough to get the job built. Any more information is very likely to overconstrain things, leading to conflicting information, leading to build stops (conflicting information should always stop the build, always), leading to the engineer who did the overconstraining getting called in to fix it. Probably by not realizing what they did and saying "uh, just, uh, you know what to do, so just do that I guess".
The good professionals learn to make the manufacturing data files say that from the beginning.
gregsadetsky 23 minutes ago [-]
I’m extremely grateful for your informative answer, thanks a lot! I may have been wrong about everything I thought I knew, but at least I was not wrong about the interesting conversation that would come out of posting this pdf :)
If I could ask one more thing, and be even more direct about it - I’ve been curious whether it would make sense to start doing board assembly in NY. I don’t have a plan, and I don’t have the necessary knowledge - but in some sense it seemed like a “more” automated assembly line, … better software (?)…, and fast/guaranteed turnaround could interest some part of the market - especially those doing small runs and hating to wait 2-3 weeks per revision. That, and tariffs.
Is this crazy and silly, or worse? Is there any juice in trying to run any pick and place operation? In or near Brooklyn?
brotchie 1 days ago [-]
Luckily never been bitten by component orientation issues. But every time I get a PCB assembled at JLCPCB with WS2812b or WS2816b LEDS they always email me to confirm LED orientation. I'm assuming customers have messed this up frequently enough to require a customer ACK.
15155 1 days ago [-]
They will send this email for all LEDs and generally all polarized components (capacitors, diodes, etc.)
JLC is also extremely unique because they offer the component orientation configuration GUI. This GUI's output is likely used for PNP tape orientation configuration as well.
Karliss 1 days ago [-]
ws2812 family is a mess. The pin 1 is not the pin which has the corner mark and pinout varies between specific packages and variations.
CableNinja 1 days ago [-]
What an awful set of things to do!
exmadscientist 18 hours ago [-]
All LEDs are like this. It's horrible. The only good thing about it is that every professional in the entire industry has come to expect that if it's an LED, something somewhere will be wrong with it.
Karliss 5 hours ago [-]
By all LEDs do you mean addressable and other multipin LEDs? Never seen anything weird with classic 5mm/3mm. The flat side+leg length is quite reliable. 0805/1206 smd LEDs also seem mostly fine.
exmadscientist 4 hours ago [-]
No, I mean all LEDs.
The cathode marks are basically randomly assigned. This is because each company more or less designs one leadframe/package structure per size or type of LED. Sounds reasonable, right? But LED dice aren't made of silicon. They're made of weirdo high-bandgap materials, and every color is different in its own way. From physics alone, some of the colors end up with cathodes on top of the dice and some of the colors end up with anodes on top. They all get bonded in to the package the same way. So... that marking built in to the package? That's always the "top of die" wire next to it. But "top of die" might be cathode, or it might be anode. Flip a freaking coin!
If you want to see this clearly, find a datasheet that covers an entire series of LEDs. Vishay often does this, here's one: https://www.vishay.com/docs/82437/vlmo1300.pdf . They'll tell you the marking locations for each color individually. Notice how they're all completely different? Yeah.
Could the manufacturers do better? Yes. Yes, they could. We all wish they would do better. But they do not. So LEDs are the stuff of nightmares for people who assemble boards.
Through-hole parts are somewhat better (but there are certainly rogues!), but this is 2026: the volume's in surface mount.
Multipin LEDs are no better. The SMD no-lead versions are again fairly randomly marked. The PLCC-4 types are usually "cutoff corner near pin 1", but I've seen it as pin 4... or pin 2... constant vigilance is the only solution. Constant vigilance!
For anything larger than 2 pins, pin 1 at upper left and pin 1 at lower left are both quite common. Components are also reeled more or less randomly. (There are some patterns, but you'll be better served by pretending there aren't.)
Put that all together and it means... it's all a cluster and gets manual intervention for every build. You can't automate it, but you can automate the intervention (that's what JLCPCB has done to enable scaling to lower volumes).
Just pick "lower left" or "upper left" for your library and stick to it. That's the best you can realistically do.
Also, LEDs are terrible and everyone hates them.
I was also specifically interested in how critical the manual intervention seems to be - and how accepted it is. What are the barriers to automating this completely?
If the assembly fab had access to the schematic (I know a lot of people wouldn't want to share the schematic, but if we suppose that's not a problem), would that clarify most situations?
Is 100% automation possible at all?
Haha, no, not at all; that's a disaster!
No, really, the schematic usually makes it worse. CMs don't speak schematic, as a general rule. EEs don't usually draft good schematics either. And, honestly, a good schematic usually won't have this information at all. The needed information might be found in the BOM, in theory. In practice, it's probably actually also in the PLM. If your company uses a PLM system. It might not be there either.
The actual barrier here is that there's really only one guy who has all the necessary information, and that's the guy who's loading the reel into the pick-and-place machine. He's going to have to check the work no matter what. So he often ends up having to do the work instead of just check it.
This is because what orientation is required depends on what part was purchased. Not the component type; not the manufacturer; not even the specific part number. The actual dead-ass specific part purchased, and how they decided to reel it that week at the packaging subcontractor facility. This is stable over time for the major chip vendors (unless they just issued a PCN this week! hope it wasn't retroactive!); for the Shenzhen specials, don't bother. But it is not consistent among second sources for the same part, and guess what -- your purchasing department will buy the cheapest thing you allow them to buy. And those two orderable PNs that are completely identical according to the datasheet, so you listed them as fully qualified alternates, and one is way cheaper this week for some reason? Yeah, that's a reeling code difference: same part, different orientation in the tape. And it's cheap this week because some big company (probably medical...) bought the wrong one and is unloading it instead of dealing with it.
So things end up different week to week.
And only the guy loading the reels knows which reel he's grabbing. So he's got to do the work.
> Is 100% automation possible at all?
No. No one genuinely cares. This is a throughput-optimized industry: the first board takes a while to get set up to build. Then there's thousands and thousands of them.
At the end of the day, the manufacturing data packages have (should have) centroid, orientation, and pin 1 data. That's enough to get the job built. Any more information is very likely to overconstrain things, leading to conflicting information, leading to build stops (conflicting information should always stop the build, always), leading to the engineer who did the overconstraining getting called in to fix it. Probably by not realizing what they did and saying "uh, just, uh, you know what to do, so just do that I guess".
The good professionals learn to make the manufacturing data files say that from the beginning.
If I could ask one more thing, and be even more direct about it - I’ve been curious whether it would make sense to start doing board assembly in NY. I don’t have a plan, and I don’t have the necessary knowledge - but in some sense it seemed like a “more” automated assembly line, … better software (?)…, and fast/guaranteed turnaround could interest some part of the market - especially those doing small runs and hating to wait 2-3 weeks per revision. That, and tariffs.
Is this crazy and silly, or worse? Is there any juice in trying to run any pick and place operation? In or near Brooklyn?
JLC is also extremely unique because they offer the component orientation configuration GUI. This GUI's output is likely used for PNP tape orientation configuration as well.
The cathode marks are basically randomly assigned. This is because each company more or less designs one leadframe/package structure per size or type of LED. Sounds reasonable, right? But LED dice aren't made of silicon. They're made of weirdo high-bandgap materials, and every color is different in its own way. From physics alone, some of the colors end up with cathodes on top of the dice and some of the colors end up with anodes on top. They all get bonded in to the package the same way. So... that marking built in to the package? That's always the "top of die" wire next to it. But "top of die" might be cathode, or it might be anode. Flip a freaking coin!
If you want to see this clearly, find a datasheet that covers an entire series of LEDs. Vishay often does this, here's one: https://www.vishay.com/docs/82437/vlmo1300.pdf . They'll tell you the marking locations for each color individually. Notice how they're all completely different? Yeah.
Could the manufacturers do better? Yes. Yes, they could. We all wish they would do better. But they do not. So LEDs are the stuff of nightmares for people who assemble boards.
Through-hole parts are somewhat better (but there are certainly rogues!), but this is 2026: the volume's in surface mount.
Multipin LEDs are no better. The SMD no-lead versions are again fairly randomly marked. The PLCC-4 types are usually "cutoff corner near pin 1", but I've seen it as pin 4... or pin 2... constant vigilance is the only solution. Constant vigilance!