10-Watt Lednium SMD
OVTL09LG3x Series
Thermal Resistance
Optek Lednium Series 1-watt Cup – Measured value 2
o
C/w
Optek Lednium Series 10-watt Matrix – Measured value 2.5
o
C/w
Theory
In line with industry practice, the thermal resistance (Rth) of our LED packages is stated as Rθ
j-b
, thermal
resistance from the junction region ( j ) of the die, to the board (b) - PCB or other mounting surface. What this
means in a practical sense, is that when operating at rated input (1watt approx.) the junction of a die in a cup prod-
uct will attain a temperature that is 2
o
C higher than a reference point on the mounting surface beneath it. In the
case of a 10-watt Matrix product, the maximum temperature difference between any junction and the reference
point is 25
o
C (2.5
o
C/w x 10w). The thermal path thus quantified is a composite of a number of thermally resistive
elements in a series and or parallel configuration, but lumped together into a single parameter for convenience.
For an end user of LED products then, this constant allows the junction temperature to be determined by a
simple measurement of the temperature of the mounting surface. Optek recommends that the design value of sus-
tained die junction temperature be limited to 80
o
C. In an ambient temperature of 25
o
C, the board temperature of a
10-watt device must be constrained below 55
o
C to comply with this recommendation, and for a 1-watt cup the board
can theoretically operate at up to 78
o
C.
(OVTL01LGAxx)
(OVTL09LG3xx)
From the diagram above it can be seen that the heat generated in the junction region follows a somewhat
serial conductive path through the package to the major radiating surface – which in this example is a single sided
PCB. Some additional radiation may occur directly from the upper surface of the package (not shown). This would
be conducted upward from the die surface through the transparent encapsulating material to the package surface
and be radiated from there. To all practical purposes this is a very minor effect. The polymer encapsulants in normal
use are poor conductors of heat.
OPTEK reserves the right to make changes at any time in order to improve design and to supply the best product possible.
Issue B 0507
Page 8 of 11
OPTEK Technology Inc. —
1645 Wallace Drive, Carrollton, Texas 75006
Phone: (972) 323-2200 or (800) 341-4747 FAX: (972) 323-2396 visibleLED@optekinc.com www.optekinc.com
OPTEK [ OPTEK TECHNOLOGIES ]
