Novel Siloxane-Modified Epoxy Resins as Promising Encapsulant for LEDs

Abstract

This study investigated a new category of transparent encapsulant materials for light-emitting diodes (LEDs). It comprised a phenyl group that contained siloxane-modified epoxy (SEP-Ph) hybridized with a cyclic tetrafunctional siloxane-modified epoxy (SEP-D4) with methylhexahydrophthalic anhydride (MHHPA) as a curing agent. The SEP-Ph/SEP-D4 = 0.5/0.5 (sample 3) and SEP-D4 (sample 4) could provide notably high optical transmittance (over 90% in the visible region), high-temperature discoloration resistance, low stress, and more crucially, noteworthy sulfurization resistance. The lumen flux retention of the SEP encapsulated surface mounted device LEDs remained between approximately 97% and 99% after a sulfurization test for 240 h. The obtained comprehensive optical, mechanical, and sulfurization resistance proved the validity and uniqueness of the present design concept with complementary physical and chemical characteristics.Polymers 2020, 12, 21 2 of 11 of anhydride hardener and accelerator [14,15]. Huang et al. developed a series of cyclic silicone epoxies with various numbers of epoxy groups. By curing with aluminum acetylacetonate (Al(acac) 3 ) and diphenylsilanediol (Ph 2 Si(OH) 2 ), enhanced ultraviolet stability was achieved compared with an anhydride-cured cycloaliphatic epoxy [16]. Hue et al. prepared a transparent composition using the diglycidyl ether of bisphenol A and a phenylmethylsiloxane-modified epoxy (PMSE) hybrid resin. Curing with methylhexahydrophthalic anhydride (MHHPA) revealed that the addition of an appropriate amount of PMSE could effectively improve high-temperature thermal stability, dynamic mechanical stability, and performance of LEDs [18].Currently, surface mounted device LEDs (SMD LEDs) are advancing and their packages are becoming smaller and thinner. This allows harmful contaminants in the atmosphere such as hydrogen sulfide (H 2 S) to easily permeate an LED's package through its transparent encapsulation material.In this case, the bottom silver electrodes would darken because of the formation of silver sulfide, which would be accompanied by a significant decrease in the LED's light output. Although transparent epoxy-based encapsulants exhibit suitable gas barrier properties, the high thermal stress of epoxy resins that is generated during the soldering or temperature-cycling process would cause catastrophic damage. By contrast, silicone materials possess relatively low thermal stress compared with conventional epoxy resins, but their higher gas permeation properties would pose a problem for thin SMD LED packages, especially in outdoor applications.Many research studies have been conducted to enhance the gas barrier properties of transparent polymers, one of which added nanoscale lamellar fillers with a large aspect ratio, such as clay or graphene, into the polymer matrix [19,20]. The addition of clay can alter and extend the gas molecule diffusion pathway; furthermore, the incorporation of graphene can effectively prevent gas molecules from permeating into the polymer matrix; ho...

Curing Regime-Modulating Insulation Performance of Anhydride-Cured Epoxy Resin: A Review

“…The acid anhydride curing agent relies on the hydroxyl group in the epoxy to open the ring of the acid anhydride to form a carboxylic acid, which further reacts with the epoxy group. At the same time, the hydroxyl group can also open the ring of the epoxy group to form a cross-linking network [ 34 ]. The reaction temperature between anhydride curing agent and epoxy resin is high.…”

Superior hydrophobic silica-coated quantum dot for stable optical performance in humid environments

“…Therefore, the epoxy resin shell need proper light stabilizers or stable groups to deactivate the free radicals. As a result, the preparation of epoxy resin-coated QD is more complex, expensive, and time-consuming than that of the SiO 2 shell-coated [26,27]. The SiO 2 shell is usually generated by the hydrolytic polycondensation at ambient temperature, which is simple and economic.…”

Novel aspects derived from the influence of dispersion properties of poly(4‐vinylpyridine)/aluminum nitride nanocomposite encapsulants on light‐extraction efficiency of light emitting diodes

“…Focusing on encapsulation materials, it was reported that silicone, 13 fluororesin, 14 siloxane‐modified epoxy resins, 15 diminish the abrupt change in refraction properties between the semiconductor and air, generating a larger light‐escape cone. However, these transparent encapsulation materials display a refractive index of about 1.35–1.50, which is still much smaller than those of III–V phosphides and nitrides.…”