AN1149-6 Lumileds Lighting, LLC, AN1149-6 Datasheet - Page 4

• Manufacturer Part Number: AN1149-6
• Description: Reliability Considerations for SuperFlux LEDs
• Manufacturer: Lumileds Lighting, LLC

SuperFlux LED durability. One of the two typical
wear out mechanisms in thermal cycle testing is
separation between the plastic encapsulant and
the sides of the reflector cup in the leadframe as
shown in Figure 6.1. This type of separation lifts
the semiconductor die off of the leadframe and
causes an open circuit or intermittent open
circuit. The second typical failure mechanism is
a necked down wire break above the ball bond
(wire bond) as shown in Figure 6.2. In order to
Simultaneous Power & Temperature Cycle
Simultaneously cycling both power and
temperature can accelerate typical LED failure
modes. Although these conditions are much
more extreme than those seen in actual field
use, this type of test is very helpful in comparing
the performance of different designs.
Performance under these conditions is
benchmarked during initial LED product
validation and then checked during subsequent
validation tests for process or material changes.
This test should also be used when validating
assemblies containing SuperFlux LEDs to
ensure that excessive self heating will not result
in premature failure of SuperFlux LEDs.
Figure 6.1 Example of LED die
delamination.
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avoid these failure mechanisms, it is important
that the maximum junction temperature listed in
the SuperFlux LED Technical Data Sheet is not
exceeded (refer to Application Brief AB20 4
Thermal Management Considerations for
SuperFlux LEDs). Lumileds used the three
temperature cycle tests listed in Table 6.1 to
validate SuperFlux LED performance after
thermal cycle testing.
Although SAE J1889 describes a power
temperature cycle test, Lumileds used more
extreme power temperature cycle conditions to
validate SuperFlux LED performance. SAE J1889
recommends powering the device while
warming and hot and leaving it unlit when
cooling and cold. Lumileds’ tests, which are
summarized in Table 6.1, are similar to SAE
J1889, but the power is cycled by excessive
solder heat, or improperly manufactured
SuperFlux LEDs. Lumileds also extends the test
from the 25 cycles recommended in SAE J1889
to a minimum of 50 cycles.
Figure 6.2 Example of neck-down
wire break.