LED (Light Emitting Diode) components are widely used in large-size displays, traffic signals, lighting and other fields for their advantages of high efficiency, low power consumption, and high durability.Along with the rapid development of LED application technologies, the performance requirements for packaging materials are getting higher and higher.
Thermosetting epoxy resin, featuring good mechanical properties, low curing volume shrinkage, excellent adhesion force to substrates, and strong controllability of its operating processes, is one of the major packaging options for LEDs at present.Among them,cycloaliphatic epoxy resins, especially 3 4 epoxycyclohexylmethyl 3 4 epoxycyclohexanecarboxylate (TTA21), are preferably and widely applied in LED and optical device encapsulants for their excellent processability, high Tg point and good weather resistance.
It should be noted that cycloaliphatic epoxy resins feature very high curing cross-linking strength, making it easy to cause cracks in the cured substance due to excessive internal stress, and limiting the product performance (during the packaging process, moisture absorption and mechanical stress are two main factors that affect the product reliability, where the mechanical stress is the product of curing stress and cooling stress that are caused by mismatching coefficients of thermal expansion (CTE)). In practical applications, they are usually paired with bisphenol A epoxy resin (or hydrogenated bisphenol A epoxy resin) to adjust the tenacity of the system. This article provides a brief analysis about the basic characteristics of resin matching for reference.
Viscosity-temperature Curves of TTA21 and E51 Epoxy Resins
E51：Bisphenol A epoxy resin, (epoxy equivalent of 184~194g/eq)
Relationship between the Mixing Ratio and the Viscosity of TTA21（25℃）
EP-4080：Hydrogenated bisphenol A epoxy resin, (epoxy equivalent of 205g/eq, and viscosity of 1800mPa·s)
It can be seen from Fig that when E51 and EP-4080 are mixed with an appropriate amount of TTA21, the viscosity of them both decreases significantly, and TTA21 may act as a high heat-resistant epoxy resin diluent.
Due to their good transparency and heat resistance, cycloaliphatic epoxy resins are suitable for the application of demanding LED encapsulation, which is in line with the market performances.
Featuring an obvious viscosity reduction effect in the formula, cycloaliphatic epoxy resins can pair with ordinary epoxy resins to effectively control the viscosity while improving the overall performances, thus leaving a larger space for operation.
Considering the differences in water absorption and mechanical strength, the formulation should be reasonably matched with the proportion of several specialty epoxy resins according to the actual performance requiremnts.