ASMT-JB11-NMP01 Datasheet, PDF (1/2 Pages) AVAGO TECHNOLOGIES LIMITED – Silicone Encapsulation for LED Advantages and Handling Precautions

Silicone Encapsulation for LED
Advantages and Handling Precautions
Application Note 5288
Introduction
In recent years, LED brightness has improved tremen-
dously due to advancement in LED die in terms of lumi-
nous efficiency and its ability to be driven under higher
powered conditions. Due to these developments, the
LED has been adopted in more applications, including
high brightness illumination, backlighting and ESS that
require high flux output and high driving current. Apart
from the improvement in die technology, the challenges
for the high brightness LED lies in the packaging technol-
ogy, especially the encapsulation material, to ensure and
further enhance its reliability.
Conventionally, epoxy has been used as the encap-
sulation material. Optical grade epoxy has good light
transmission and high glass transition temperature (Tg)
that is suitable for LED application. With expectation of
higher luminous flux output, higher driving current and
better long term reliability, silicone materials has been
introduced to Avago’s LED product line-up as the new
generation of encapsulation material for LEDs.
Advantages of Silicone Encapsulant
Silicone can be formulated in different hardness proper-
ties, which are gel, elastic and hard types. Silicones used
in optoelectronic products are generally elastic type to
give the flexibility to encapsulated wire bond and die
attach. This characteristic provides the ability to absorb
thermal stress during the soldering process and during
operation as well.
The chemical structure of silicone provides several ad-
vantages over epoxy encapsulant used in optoelectronic
products. Its structure consists of bonding between Si
and O called siloxane bond which has higher energy
compare to the carbon (C) bond and oxygen (O) exist in
epoxy. This characteristic gives the thermal and UV stabil-
ity of silicone, which are the main characteristics needed
for new generation LED products.
R
O Si
R
R = Organic groups
Figure 1. Example of Siloxane bond in silicone material
Prolonged exposure to high temperature, either from the
environment or the internal LED die junction tempera-
ture, will cause deterioration of the encapsulation mate-
rial including reduction of transmittance and yellowing of
material. A similar deterioration issue applies to exposure
to UV emission from sunlight for outdoor products and
to the blue or white LEDs own near-UV emission. Silicone
material exhibits superb stability towards heat and UV
thanks to the strong siloxane bond, enabling long life
performance of high brightness LEDs with little intensity
degradation.