Packaging &
Interconnects
placed tightly together without the corresponding pins, reduced
costs since several LEDs comprise a single part, faster time to
market, and desirable heat distribution. This has been a boost for
lighting manufacturers, who can put more emphasis on traditional
industrial design process such as forming metal and molding.
Robbie Paul, lighting sales director at Digi-Key explains the plug
and play benefits of COB: “You would take a COB package, you
would have an appropriate connection, or you would solder the
leads on the package and away you go. So you would not need
any electronic processing to come up with a lighting fixture.”
What was once a niche packaging technology is now
ubiquitous, as most LED vendors offer some sort of COB-based
product. One of the more interesting packages belongs to
Bridgelux’ Vero LED array, which includes an onboard connector
port that interfaces with the Molex Pico-EZmate connector for
plug & play solder-free electrical interconnectivity. According
to Brandon Noska, applications engineer at Bridgelux, “the
connector is made from the same plastic and color, so it has the
same reflective properties as the housing.“ With little training
necessary to attach the connector, the connections are reliable,
repeatable and consistent. The company also helps make things
easier by using common (industry standard) driver currents in its
LEDs. Noska asserts, “luminaire manufacturers do not have to use
unique drivers that are harder to procure, are more expensive,
and cannot be leveraged across other products – causing sku
management complexity.”
High heat fluxes raise thermal challenges
The tight spacing between the LEDs and small light emitting sur-
face that make chip on board LEDs attractive also present high
heat fluxes that must be addressed -- the natural convectional
cooling that is present in more traditional solid state lighting is
hindered with the small surface area of COB. “The biggest chal-
lenge is the power density,” says Lee Jones, director of advanced
development at thermal solution provider Nuventix. “COBs cre-
ate a tough cooling challenge in terms of Watts per square cen-
timeter. These high lumen packages just keep the heat coming.”
Like any other solid state lighting applica-
tion, COB-based solutions can pay a price for
being pleasing to the eye. Brandon Noska of
Bridgelux says, “The fixture must have aes-
thetic appeal that can negatively impact ther-
mal management.”
To address thermal management with COB-
based solutions, lamp manufacturers have
to consider a number of variables. There are
many cooling options out there, and designers
will have to choose between passive cooling
strategies – those that spread heat over a
large surface area without adding more power
to the design, or active cooling strategies
involving fans or synthetic jet technology.
The environment in which the lamp will
ultimately reside should be a consideration
(ex. a spotlight in an ambient room, or a high
bay many feet above a factory floor), the power
involved in the solution, and cost should be a
factor. As always, there’s tradeoffs.
There’s no single formula to cooling
COB-based designs
Robbie Paul of Digi-Key notes a cooling strategy does not come down to a simple formula
or flowchart. “An active cooling system is
more expensive, but a passive cooling system
brings raw materials costs into parity. For
