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One Part, Dual Cure
One Part, Dual Cure
• Dual cure formulation utilizes UV light and heat
Cures at 80°C in shadowed out areas
• Dimensionally stable & abrasion resistant
• Optically clear
Refractive index: 1.52
High-power (HP) LED
Chip-scale package (CSP) LED
Plastic leaded chip carrier (PLCC)
Plastic chip carrier
submounts. These submounts were made from alumina (Al2O3) or
aluminum nitride (Al N) and offered the required heat spreading ability while maintaining ease of
surface mounting. These high-power LEDs (HP LEDs) provided
the perfect solution, except for
one significant downside: cost.
And for AlN, in particular, that
cost could be a showstopper.
The dilemma the industry
faced was how to reduce the
cost of mid- and high-power LEDs without compromising both the
thermal requirements and the SMT advantages gained by using standardized packaging.
From ceramic packaged LEDs to CSP
The general semiconductor industry dealt with a similar challenge
some time ago by switching to a chip-scale packaging technology.
To make a CSP LED, the p and n junctions on the base of a flip-
chip structure are metallized and the top and sides are covered with
phosphor. Fig. 2 depicts the differing LED architectures. The finished
CSP must be no more than 20% larger than the chip itself to qual-
ify as a CSP (the next level is wafer-level packaging, WLP, where the
package must be the same size as the chip). Clearly, elements of the
traditional mid- and high-power LED had to be removed for it to
slim down to a CSP LED. For HP LEDs, the ceramic submount and
the lens had to be eliminated, and for PLCC it
was the entire chip case that was eliminated.
For mid-power PLCC LEDs, losing the chip case
wasn’t such a problem and for this reason mid-
power CSPs have been operating happily in back-
lighting applications for several years. In 2015,
Lumileds introduced a white CSP and started to
push the technology into general lighting applica-
tions ( http://bit.ly/1KQ1wiV). They were followed
by other manufacturers such as Samsung, Seoul Semiconductor, and
Nichia. The market was (and remains) fluid and different manufactur-
ers have competing visions of how the market will develop (http://bit.
Samsung will sell arrays of four or more CSPs joined together,
and Seoul has opted for the term wafer-level integrated chip on PCB
(WICOP), while Nichia has branded its CSPs as direct mountable chips
(DMC) and uniquely they only emit light from the top surface, reducing crosstalk. These different approaches make for a very dynamic
market, one that industry analysts Yole Développement estimate will
account for 34% of all HP LEDs by 2020. The products are beginning
to find usage in a variety of applications including street lights (Fig. 3).
CSP opportunities and challenges
However, the benefits of the CSP approach are not in doubt. In addition
to being smaller, they are cheaper to produce. All this while the CSPs
are still able to go through standard surface-mount technology (SMT)
PCB assembly lines so the products can be used as direct replacements
for PLCC and ceramic HP LEDs. CSPs allow Level 2 integrators (who
tend to run PCB assembly lines to build modules with packaged LEDs)
to enjoy many of the benefits usually only afforded to integrators working with bare die — the chip-on-board (COB) manufacturers. This isn’t
FIG. 2. The structures of mid-power LEDs, high-power LEDs,
and CSP LEDs all differ considerably.
The fnished CSP must be
no more than 20% larger
than the chip itself to
qualify as a CSP.