How LEDs Are Made 93
An anonymous reader writes "The SparkFun team took a tour of a factory in China that manufactures LEDs. They took lots of pictures showing the parts that go into the LEDs, the machines used to build them, and the people operating the machines. There's a surprising amount of manual labor involved with making LEDs. Quoting: 'As shipped on the paper sheets, the LED dies are too close together to manipulate. There is a mechanical machine ... that spreads the dies out and sticks them to a film of weak adhesive. This film is suspended above the lead frames ... Using a microscope, the worker manually aligns the die, and, with a pair of tweezers, pokes the die down into the lead frame. The adhesive in the lead frame wins (is more sticky), and the worker quickly moves to the next die. We were told they can align over 80 per minute or about 40,000 per day.'"
Re:Somewhat off-topic: why not uncut LED panels? (Score:3, Informative)
Attach ONE set of leads to the LED silicon panel.
LEDs emit light from the diode junction, not the surface. If you wired up the entire wafer, light would just come out only from the edge of the wafer and the rest would be trapped inside and turn to heat.
Re:great photowork there (Score:4, Informative)
My interpretation is as follows. The equipment shown is stuff that could have existed in the 1960s. In the West, that's pretty much how machines looked like in the 60s. The #1 company that made and still makes these machines is Kulicke & Soffa.
http://www.kns.com/en-us/Pages... [kns.com]
China basically scoured North America for all the old machines they could find. Ribbon machines that make incandescent lightbulbs. Pick and place machines. Board plating shops. Wire and ball bonders.
All this stuff that used to the define the West's technological prowess. K&S is now based in Singapore.
https://www.youtube.com/watch?... [youtube.com]
Oh, and if you want to see something fast and automatic, look up chip shooter on youtube...
Re:left out the most important steps (Score:5, Informative)
Note: I am speaking as a material engineer who spent about 6 years in R&D for the 65W LED bulbs you can now buy at HomeDepot. The articled failed to mention the most important aspects of the LED manufacturing: wafering and the MOCVD that deposits the light emitting materials (the PN junction) onto the wafer. In short, the steps would include:
1) Crystal growth / wafering / surface prep; (make the wafer)
2) Nitrite epitaxial growth; (grow the light emitting part)
3) Wafer fabrication (cut big wafers down to die-sized chunks)
4) Packaging and testing (encapsulating the die) -- what the article was describing
The article only touched upon the 4th step of LED manufacturing, and concidently, the most automated aspect of manufacturing, as well as the part that contains the least amount of patents / trade secrets. The first 3 steps were marginalized as "This is a sheet of LED dies. YunSun buys their dies from a high quality Taiwanese company". To my knowledge, there is no high quality manufacturer in Asia outside of Japan. Samsung makes a great quantity of ok stuff, and China / Taiwan makes a great quantity of shitty stuff that is ruining the entire high profit margin products. Also, all of the major manufacturers of LED dies dare not introduce step (2) and (3) into China / Taiwan due to IP issues.
Wafering is important because larger wafer sizes (2in to 4in to 6in) means more dies per area. However, crystal quality becomes harder to control as sizes go up, especially for US-based LED manufacturers that is based on silicon carbide instead of sapphire. The real issue is with the MOCVD, the deposition technique that grows the PN junction which actually emits light. In the world of deposition, MOCVD is archaic voodoo magic and we spent a lot of time praying to deities of deposition that our process would repeat for more than a day. Fab is more systematic than epitaxial growth, and the real science here has to do with light extraction. Again, big money is spent on R&D here, and we dare not bring the manufacturing process to Asia (except for Japan).
Re:Somewhat off-topic: why not uncut LED panels? (Score:3, Informative)
I work in a part of the commercial lighting industry, and the current technology is indeed surface-mount LEDs, sort of like what you see on strip lighting, only on a metal PCB (for heat dissipation, naturally). Just run everything through a pick-and-place machine and roll it through the reflow oven. The lenses are clear plastic light pipes mounted through holes in a metal fascia. (And I was lucky enough to be able to pick up a bunch of LEDs that fell out of the PnP when we were making some a couple of years ago. Heavy parts do that.)
I doubt they're ever going to move to mounting bare dies (like in seven-segment displays) because they'd have to have their own wire bonder and epoxy, and I'm going to guess that white LEDs need the phosphor applied between mounting the die and molding the lens, so that's one more step. Some customers want Made in USA stuff, and that would be a true pain in the ass to do die-mount in the US vs. a tube of surface-mount LEDs and a normal pick-and-place machine.
I'm pretty sure just from the way they look that traffic lights are using regular 5mm or 8mm LEDs. Even if they used surface-mount LEDs, they'd still need a lens somewhere, and die-mounts would of course be even more trouble. You would have to buy the whole thing pre-made from China with die-mount. The only reason seven-segment (and presumably matrix) LEDs use die mounts is that they can be sold as a single pre-packaged part, and they're too small to even use 3mm molded LEDs.