Abstract
Summary
The low-profile package is very straightforward in concept and design, and
uses materials which are typical in the high-power LED industry. As the LED
die substrate is electrically insulating, there is no back-side contact to the
die. Three bond wires for anode and three for cathode connect to the die
front. Die attach is by an unfilled and probably insulating adhesive of
unusually thin and apparently well controlled glue line thickness, probably to
minimize thermal resistance to the heat sink.
The included protection device is a silicon Zener diode providing ESD and
possibly overstress protection.
The fluorescent medium coating of the blue LED die is unusually thick, but has
a correspondingly low density of Gd/YAG fluorescent particles.
The die is an InGaN/GaN hetero-structure with a multiple quantum well (MQW)
active region, on a sapphire substrate. A thick In-rich InGaN layer serves as
the pside (top) current spreader layer. The MQW (also InGaN/GaN) is between
GaN layers, below the InGaN /GaN interface. Interdigitated p-side (surface)
and n-side (recessed) contact fingers handle current distribution.
The optical concept is conventional, with upward emission dominating and side
emission directed upward by a silvered conical reflector in the package. There
is no anti-waveguiding feature incorporated. There is no device-level
back-side reflector either, but back-side reflectance is aided by the
transparent substrate and die attach material and the silvered heat slug.
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