Examine the heated question
of chip-scale packaging
in the LED industry
JOHN CAFFERKE Y discusses the growing popularity of CSP LEDs for general lighting and how thermal
management solutions need to adapt to keep pace.
The primary reason LEDs are sold as a packaged product is to pro- tect the fragile bare die from damage. Standardized packaging also makes it
far easier for manufacturers to work with
LEDs on production lines. However, there is
another consideration: LEDs are only around
40% efficient, which means 60% of the power
that goes into an LED will come out as heat.
As with any electronic device, too much
heat can cause serious damage so it needs
removing as quickly as possible. This is
where thermal management comes in. As
LEDs increase in power while shrinking in
size, thermal management becomes a critical aspect of LED packaging. The solid-state
lighting (SSL) industry has long dealt with
the thermal challenges of mid- and high-power LEDs, but the latest move to a chip-scale package (CSP) has introduced all new
thermal design challenges.
LED package evolution
Early LEDs used through-hole packaging.
The die was mounted onto an anvil and
post structure and covered in an epoxy lens.
The negative and positive anvil and post
were then pushed through holes drilled in
a printed-circuit board (PCB) and soldered
into place. This type of package was ubiquitous throughout the early development of
LEDs and is still used for applications such
as power indicators today.
With ever-increasing automation, man-
ufacturers needed LEDs capable of being
easily surface mounted, particularly for
backlighting applications for TVs and mon-
itors, which led to the development of plas-
tic leaded chip carrier (PLCC) LEDs — low-
and mid-power LEDs. These standardized
PLCC LEDs were a victim of their own suc-
cess as they were manufactured in such high
volumes that there was a massive oversupply
— with repercussions that still reverberate
around the LED industry to this day.
One side effect of this excess capacity
was LED manufacturers that looked to new
markets to sell their PLCC LEDs, particularly the nascent general lighting market.
Mid-power PLCC LEDs were well suited for
replacement bulb and tube lighting appli-
cations, which in turn helped push the price
of consumer LED lighting down (Fig. 1). A
push from the LED manufacturers with
huge stocks of LEDs to ship, coupled with
incoming regulations banning inefficient
technologies such as incandescent lighting,
helped to create the perfect environment
for LED lighting to go mainstream.
As the market developed, the requirement
for smaller, higher-power devices for applications such as automotive headlamps and
spotlights grew. This in turn presented a
new challenge for the LED manufacturers
— how to keep the LED die cool enough to
operate effectively. PLCC designs were not
thermally conductive enough for the job, and
while through-hole designs can be thermally
effective they are not surface mountable, so
they lacked scalability.
The industry turned to mounting the LED
die, covered with an encapsulant, onto thermally conductive, but electrically isolating,
JOHN CAFFERKEY is marketing manager at
Cambridge Nanotherm ( camnano.com).
developer forum | THERMAL MANAGEMENT
FIG. 1. Mid-power LEDs gained traction in general lighting applications starting with