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From time to time I come across a solution in which uses an LED as in below picture:

enter image description here

This particular component is placed inside the module located in car interior. Button backlight application.

The base LED [PLCC-2 Package] is blue color LED. The top cover material changes the light to white, so I assume this cover material is actually a phosphorus layer. This is a common approach of achieving white color but usually the phosphorus layer is integrated inside the PLCC-2 package (The die is sunk in phosphorus line on below picture.)

enter image description here

What is the purpose of this additional cover? My guesses are:

  • Specially mixed phosphorus layer is added to finished LED in order to achieve exact white color coordinates.
  • Manufacturing process improvement: one line for blue and white LEDs with additional process for white.

Is there any LED expert that could confirm this?

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  • \$\begingroup\$ Does it not simply shine at the bottom side? I.e. flip chip? \$\endgroup\$
    – winny
    Nov 19, 2019 at 11:08
  • \$\begingroup\$ @winny No, underneath the phosphorus layer there is a standard PLCC-2 blue LED. This assembly shines in a standard way 90 degree angle to PCB surface. \$\endgroup\$
    – KJA
    Nov 19, 2019 at 11:27
  • \$\begingroup\$ Then I don’t understand your question. Are you asking why the phosphorus layer is there? \$\endgroup\$
    – winny
    Nov 19, 2019 at 11:46
  • \$\begingroup\$ The question is why the phosphorus layer is not directly on a die as on Picture number two, which is much simpler from production point of view. \$\endgroup\$
    – KJA
    Nov 19, 2019 at 12:48
  • \$\begingroup\$ I can't tell from the photo but the most common answer to all questions of this type is: price. If it makes it cheaper in any way, someone will do it. \$\endgroup\$
    – winny
    Nov 19, 2019 at 12:49

1 Answer 1

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I received confirmation from LED supplier:

  • This solution results in better light homogeneity than die sinking method.
  • It is very rare because it's patent protected.
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