By Debra Vogler, senior technical editor
April 1, 2011 — Daniel Duffy, research scientist in Henkel’s Advanced Technology Group, was a presenter at MEPTEC’s The Heat is On event (3/21/11, Santa Clara, CA). Summarizing the encapsulant materials used for high-brightness LEDs (HB-LEDs), he noted the pros and cons of epoxy and silicone. The material challenges for epoxies are temperature stability and color (aging); and for silicone, contamination and adhesion, as well as barrier properties. In the future, epoxies will have to be stable with respect to blue light (T>150ºC); and silicone material will have to fulfill the condition T<Tg CTE <60ppm/K. "Silicone encapsulants are very stable," said Duffy. "But it is not enough — future power demands require higher levels of photo-thermal stability."
Die attach material challenges include transparency, CTE, interfacial TC, and adhesion properties. Such materials will need to have stable thermal resistance, high TC, matched TCE, and good adhesion properties. Duffy specifically mentioned adhesion as a critical property for LED packaging. "Delamination leads to increased interfacial thermal resistance," said Duffy. "Localized temperature increases can shorten device life." Furthermore, cracking can lead to weakening of wire bonds and cracks; also, delamination weakens barrier protection.
In this podcast interview, Duffy discusses the outlook for new materials and/or enhanced materials for HB-LED applications, including quantum dots. "Quantum dots are very interesting materials…when we learn how to tune the interactions between then and the rest of the materials involved in LED packaging, they will play a continuous role in the future," said Duffy. "They offer a wide variety of colors, tunability of color, and lots of options for tuning their performance with temperature, with time and, maybe even other optical effects we’re not even considering now…they’re here to stay." The challenge, he noted, will be getting them into materials for higher-power applications.