AUSTIN – Effective removal of heat is critical for controlling junction temperatures of LED chips, ensuring long device lifetimes, and maintaining the spectral and efficiency characteristics of the light source, says a new report on LEDs.

TechSearch International’s report finds as much as 50% of failures in lighting are attributed to thermal issues. The stability of packaging materials (encapsulants and lenses) is affected by exposure to elevated temperatures and to UV and other wavelength radiation.

High Brightness LED Assembly Trends, Materials, and Issues provides examples of various packages for high brightness LEDs.

Ineffective removal of heat from the LED source can also degrade the phosphors in the LED package and other packaging materials, causing yellowing of the encapsulation material and higher absorption losses at reflective surfaces. Depending on the temperature changes, the thermal expansion coefficient and glass transition temperature of the materials used can create mechanical stresses that cause failure of the package or the LED die. If failure is not total, these effects will still reduce the lumens output of the package, and thus the overall efficiency (lumens per watt) of the source.

Excess heat can also lead to premature failure of the LED package as a result of delamination and die fracture.

The report discusses these issues, as well as material requirements for LED packaging and assembly. Future trends such as wafer-level assembly of LEDs are also discussed.

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