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LED footprint is very uninformative?

Discussion in 'Circuit Simulation & PCB Design' started by Flyback, Apr 21, 2017.

  1. Flyback

    Flyback Well-Known Member

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    Hello,
    The following “WICOP2 Z8 Y19” LED, on page 21, shows its footprint.
    It says on page 21 that “Undefined tolerances are +/-0.2mm”

    So do they mean that the gap between the pads is 0.3mm +/-0.2mm?, and that the pad dimension is 0.56mm +/-0.2mm?

    How can we lay out a decent footprint with that kind of slack information?

    Also, what does "Cu open" mean?

    WICOP2 Z8 Y19” LED datasheet
    http://www.seoulsemicon.com/_upload/...Y19_Rev5.2.pdf
     
  2. alec_t

    alec_t Well-Known Member Most Helpful Member

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    They must do, since neither dimension has a tolerance specified. Unless ..... if there's a typo and the tolerance should be ±0.02mm ?
    "Cu open" presumably indicates a copper-free area.
     
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  3. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    Fly What type of PCB you mounting these on?
     
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  4. dave

    Dave New Member

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  5. Flyback

    Flyback Well-Known Member

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    Its on IMS, (AKA Aluminium cored PCB), 1.5mm thickness with 1oz copper
     
  6. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    The speca call for 2oz copper on a metal based board for heat dissipation. Have you double checked all the heat specs? I didnt have time to wade through and work it out, but a quick scan didnt add up to me.

    The lumens given for optimum temp, dosnt fit with the heat dissipation for the board size given in the data sheet, or maybe I read it too fast and didnt add it up correctly. Better double check though mate.
     
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  7. Flyback

    Flyback Well-Known Member

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    Thanks, so there is some advisory spec that it must really be 2oz copper on Metal core PCB?
     
  8. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    The heat sink problem is hard:
    You must design for worst case.
    Measure the temperature of the LEDs and increase/decrease current to regulate the temp. Now you do not have to over design the heat sink for a very hot day. In very hot situations you just back down the power a little.
     
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  9. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    The data sheet mentions the temp specs, but it also says the specs are based on 2 oz copper. There is alot in the data sheet temperature wise, I didnt look in too much detail, but what struck me was the optimum light output, dosnt actually look realistic compared to the temperatures they give for it. Off my head I think 85C is max temperature, but heat dissipation figures given . Make me think that to stay inside the working temp, your going to be operating at a lower current than the one that gives the best output.

    Or I guess your going to have to get creative with the heat removal. the other thing was they make a big deal out of not using tweezers or fingers, it reads like its only suitable for precise size suction pick and place. But they could just be covering themselves. I dont know Flyback I havnt used silicon coated Leds, but they do mention the outer material is not like normal leds etc etc etc.

    Whats the application? I cant help thinking you might be better with a ON semiconductor Led, they do some good high powered Leds. If I get a chance I will read the datasheet properly, it was a quick read but gave me a gut feeling the temp figures need a close look at.
     
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  10. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    What Wattage one you using?
    led1.PNG

    It mentions 5W there, but all the other figures are based on around 7.8W output as the max. Also look at the graph on page 11, everything else points at 1.5A being optimum current for max Lumens, but the graph on page 11 puts you outside the envelope on the lower wattage one.

    Hard to tell I am not sure which of the Leds your using. Maybe I missed exactly which one your using as the datasheet covers several.
     
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