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A close look at a COB-style LED module as used for signage illumination. I chose blue so we would be able to see the bare LED chips.
These low voltage modules are used as an alternative to neon and fluorescent tubes inside signage. They have the huge advantages of being relatively safe to install and being very flexible about how they can be placed inside channel letters.
As always with LED strips and modules, it makes sense to slightly under-run them for longer life at the cost of slightly reduced intensity.
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Let's explore some more led signage modules, and this time it's cob based led modules, so these are basically strings of modules that are used inside signage either inside this are blocked, channel letters or inside the boxes to illuminate from behind. Sometimes they rather nauseatingly use them around shot windows as well, just as bright points of light. They could be quite ferocious that way the difference between this type and the others. Well, let me show you some others.

Let me show you some really crap ones. These are just awful: these are the very generic ebay, cheapy ones, with very badly matched leds, slightly defective leds and the common strip in the back, and you presumably just cut them apart when you need them very thin, wire, very horrible modules. These are better, i think, the other ones i could show you are the modules like this. This is a more common style where there's individuals of leds in different sections behind lenses, but the theory is the same.

You, basically, you cut it to the dire length. Each one is approximately two watt. It just gives you a nice source of light these ones. It's notable that, instead of the separate adhesive tape in the back, you do have to cut it apart as needed.

I suppose it keeps them all clustered together, so i shall show you these lit up and the reason i got blue ones because that's what the blue represents here. The blue plastic color is because it means that the the led chips are just bare. There's no phosphor over them. If this these were white, led cob modules that would have the yellow phosphor.

If they were the red ones, it would have the red, phosphor and so on, but by getting the blue ones, it's just beer modules and we can explore them closer well. Now, you've seen them lit i'll turn that off i'll get this out. The way i shall zoom down a bit and we'll take a look at this one, so the cob module zoomed down the cob module is molded round and you can actually see on one of those other modules. Let me just grab them back in again, then that was bad timing on one of those other cob modules you can see.

The plastic has molded over the top, but it's not stuck onto the silicony schmooze. So that's something that you can just pick off. It's not that bad, but these er modules are start off as the aluminium pcbs with the wires on them with the little dam and the resin for the little chips, and that is using cobb chips. Chip on board flip chips, the um are the tiny little chips that are bonded directly to pcb, we'll take a closer look at that afterwards, but in the meantime, before we go there, i'm going to try and delaminate this one.

So i'm going to cut the wires here and crop those down there and i'm going to see how easy it peels off it might be well bonded on. But to be honest, i don't think the plastic is going to go super onto the aluminium. It's not bad! It's not bad, it's being held on to degree by the wires here, but it's not super bonded on, although the plastic is molded around the resistors and things like that, it means that uh. I wonder if, over time with expansion, contraction, water would end up seeping in and do things like corroding these connections in here.

I suppose there's only one way to find out well ask signage guys: that's the way to find out right, taywar, i'm going to take a closer look at this, i'm going to take a picture of it and then we can explore it in greater detail. One moment please and continue with a nice high resolution picture. Let's take a look at this, so the area under the gel here that you've got the white dam that is poured around the chips are physically sorted on. These are just bare leds, they're, very thin leds that are placed onto pads with the a little blob of the soda paste and then it's they they're just treated like the surface.

Mount components they're just float on, but in this case they are microscopic. I really don't know how to place these because they are absolutely excruciatingly small but the basically, the bare led chips with metallization formed on them, so they can just be sold in place without actually having to have a package around them. So we've got three in parallel. Then three and then three so effectively: it's nine leds but they're as a 3x3 parallel series array and in series with that are two 8.2 ohm resistors.

That will add up to 16.4 ohms. The current the power drawn by these at 12 volts is about 170 milliamps, which is 2 watts. If we just validated that by saying uh, i equals v over r. So that's the voltage dropped across the resistors, which it's going to be 9 volts being dropped across these roughly from the 12 3 volts left to drop across the two resistors divided by 16.4, gives us roughly 180 milliamps.

So that means the voltage across these leds. For the 170 milliamps is just a little bit higher than three volts. I could have worked out the exact voltage across them, but that's slightly pointless. So there's an oddity about this over here they've got the number of the module and they've done that thing that they have uh left off.

Some of the uh solder, resist and they've done that over here and it's kind of tinned the pads and it's uh. Given this a silver look, there they've left the resist off, but it's just going through to the printed circuit board material, which is a layer of fiberglass on the aluminium. But in doing so they could have moved this logo onto here, but they've actually compromised they've reduced. This volume of copper here down to this area here just for their local, that's very odd because they could have just moved that logo down a bit and then just run that track right across and it would have increased the current carrying capacity, because this is part Of the bus bar that passes right through the whole system, so that is the narrowest bit and it's purely because that logo - that's very strange.

I guess these two things are test points, maybe not not really sure, maybe for testing during manufacture. I see other little dots around here, but they've gone for the max amount of copper covering the area. There's very little copper left removed. So this array of leds here then couples down to the next ones by the solid mass, and this is going to help couple.

The heat into the background into this metal plate, but that's more or less it there's not really much to say about them. It is just basically um two resistors in series with a three by three array of the led chips. Um, but that's interesting, it'll be interesting to see. I may inquire on suitable forms and see who's had led modules fail in a widespread manner and what styles they were.

These are fairly generic, ebay ones. I'm not sure the quality is, i think, really, if you're considering putting this stuff in signage, you have to potentially buy from companies that buy in and test it and they've got predictable quantities because they buy large quantities because because, if you uh, if you spend a Lot of time putting modules like these into signage and it turns out they don't last too long, then it means you have to do all the work again under warranty and also get all the access equipment for going out to the signage, but they have other uses And interesting i discovered recently is that the weight modules grab sweep modules are used in some television sets now behind the behind the lcd screens and likewise suppose, really because these are designed they just six them zag them backwards and forwards and large quantities, because they're designed For eliminating signage quite brightly, i suppose it makes sense to use them as retrofits for tv screens or backlighting lcd panels, but that is it that is what's inside. The cob based led modules, they're quite smart um, maybe i'll, put some intestine a long-term basis and just see if they fail over time, but it was certainly worth exploring and quite an interesting construction. Although with that delaminating thing, i don't think that i don't think.

I trust these for use in a very wet environment, but in signage they may well be okay.

13 thoughts on “Led signage cob module teardown”
  1. Avataaar/Circle Created with python_avatars Fred Fred says:

    Aren't the LED chip die ultrasonicly bonded? I can't imagine that the surface tension of the 'solder' would work holding something that small. The miniscus of the wet solder would have a radius larger than the LEd chips… Clive please get a microscope with a camera attachment! They're great… ๐Ÿ˜€๐Ÿ‘๐Ÿป๐Ÿ‡ฌ๐Ÿ‡ง

  2. Avataaar/Circle Created with python_avatars scamin sam says:

    Hey bud. I am finding your videos becoming very repetitive. You get something and tear it apart. Your schematics are all starting to blur into one. I am not really bitching, just some advice on what I would like. You are completely ignoring your strongest suit. You are a stage and lighting tech. I think that your audience might like to see things they can't buy at pound-land, like likos and Fresnels along with pro sound equipment etc.

  3. Avataaar/Circle Created with python_avatars twocvbloke says:

    So, a string of these spliced with other colours will be the christmas tree lights then? ๐Ÿ˜›

  4. Avataaar/Circle Created with python_avatars Alec Kristi says:

    several years ago, we were installing the 3-led type signage lights, except the whole string was in series… the driver was rated at 150mA, 60 to 1200 volts… absolutely crazy in my opinion. I cannot remember the manufacturer, but is was a local US company

  5. Avataaar/Circle Created with python_avatars Sqweeky Badger says:

    Hi Clive

    I have a range rover rear light unit that has a faulty led strip and I've replaced it,

    Just wondered if you wanted the old one for a tear down as it looks like a complex set up in there.

    Checked out the website and failed to find how to send you thing for your videos


  6. Avataaar/Circle Created with python_avatars Paul Drake says:

    It's always funny when they do that "kind of sort of" phony 3M logo on the adhesive strip. Seems to be a common thing among Chinese goods.

  7. Avataaar/Circle Created with python_avatars Sany0 says:

    Only knew what COB meant from watching one of your videos a few years ago….a nugget of info i doubt very much ill ever use!

  8. Avataaar/Circle Created with python_avatars Kevin Hardisty says:

    These seem very versatile. Any links to the source for the 120 volt version in smaller quantities?

  9. Avataaar/Circle Created with python_avatars Raymond Richmond says:

    I wonder how these would fair as under cabinet lighting. They are low profile, can place them however for your desires, and 2W per unit would do well. The 120/240v version would be an easier setup however…..

  10. Avataaar/Circle Created with python_avatars DC Allan says:

    Interesting lights, I dont think they would last long outside. In a sogn they will last a bit longer but they way the cover just peeled off is not a great confidence builder. ๐Ÿ‘

  11. Avataaar/Circle Created with python_avatars George Dorn says:

    It'd be interesting to get these in grow lamp colors; I recently made a bunch of linear grow lamps using aluminimum extrusions and luxeon stars, and it was more work than I'd like. These would have made the job a whole lot faster, though I wonder about the heat dissipation if they're facing down…

  12. Avataaar/Circle Created with python_avatars zh84 says:

    When you etch a circuit board, is it possible to recover the copper from the etching solution? On the scale you do it at home this would be insignificant, but in a factory it might be enough to matter. Or are circuit boards like this prepared by some other method which leaves no waste copper?

  13. Avataaar/Circle Created with python_avatars FarmerSteve says:

    Those dots look to be fiducial marks to help the assembly machines locate & align to the boards. Particularly important when dealing with such tiny parts as any misalignment when placing them can cause issues.

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