應用於OLED封裝之紫外光硬化環氧樹脂膠材之性質與改善研究

Abstract

本論文研究應用在有機發光二極體元件（OLEDs）封裝用之紫外光硬化樹脂的特性和改質方法。OLEDs需要氣密性優良的封裝結構以防止發光層及高活性的陽極金屬因水氣入侵而劣化，良好的黏著性質為達成此一目標的必要性質之一；本研究因此探討紫外光硬化環氧樹脂之組成對黏著以及各種相關物理性質之影響，進而提出改善黏著等性質的方法。 本論文的主要研究項目包含：（i）單體種類對於樹脂黏著強度的影響；（ii）偶合劑對於樹脂黏著強度的影響；（iii）三級胺對樹脂之紫外光/熱硬化、黏著強度及黃化的影響；（iv）含hBN（六方氮化硼）無機填充材之環氧樹脂做為覆晶IC封裝之填充底膠之研究。第一部分研究聚醇類、乙烯酯類和壓克力酸類單體，對於樹脂縮收率、紫外光轉化率及玻璃接著強度的影響，實驗結果顯示聚醇類單體效果最佳，其在進行陽離子光聚合反應時，擁有最小的縮收率（1.72%）、最慢的光聚合轉化率（0.09 sec□1）和最大的黏著強度（153.35 kg/cm2）。第二部分研究填加不同種類之偶合劑的樹脂在ITO玻璃上之黏著強度的影響，偶合劑種類包含乙烯類、胺類、環氧類，乙基類及壓克力酸類；實驗結果顯示乙烯類偶合劑可以促進自由基聚合，當其添加量在1.0 wt.%時，樹脂在ITO玻璃及玻璃基板有最大的接著強度，其值分別為91.42 kg/cm2及153.35 kg/cm2。第三部分研究添加不同種類三級胺的紫外光硬化樹脂之特性，其種類包含咪唑、1,2-二甲基咪唑、2,4,6-三(二甲基胺-甲基)酚、1-甲基咪唑和2-甲基咪唑；實驗結果顯示2,4,6-三(二甲基胺-甲基)可提高樹脂的玻璃轉化溫度（Tg = 72.3□C）、降低熱膨脹係數（CTE = 70.8 ppm/□C），在玻璃（> 199 kg/cm2），ITO玻璃（> 182 kg/cm2）、PET（約115 kg/cm2）和不□鋼（約232 kg/cm2）等基板上亦有最大的黏著強度，此外，2,4,6-三(二甲基胺-甲基)酚亦有最高的紫外光反應性和最佳的黃化改善效果（黃化指數 = 11.27；顏色參數 = 6.48）。 前述之研究成果亦被應用於IC之填充底膠製備研究，其利用六方氮化硼（hBN）做為無機物填充物，添加量為9.2至25.7 vol.%，並對電氣性質、熱性質、硬化動力學、接著強度及黏度進行探討。與商用含二氧化矽之底膠比較發現，當hBN添充量在15 vol.%以上時，擁有較高的Tg與較低的CTE值；當hBN添充量在25.7 vol.%時則有最大的熱傳導係數（= 1.08 W/m□K）；hBN添加量愈高對於基材的黏著強度愈低，對於不同的基材之黏著強度大小依序為氧化鋁 > 矽晶片 > 錫鉛基板。

This thesis studies the properties and modifications of UV-curable epoxide resins applied to the packaging of organic light-emitting devices (OLEDs). A hermetic packaging structure is essential to OLEDs since the light-emitting layer and highly active cathode electrode inside the devices are rather vulnerable to moisture attack. Since good adhesion is one of the key properties for sealing resins to achieve such a purpose, a thorough study on the UV-curable epoxide resins was hence carried out so that an in-depth understanding on the effects of resin constitution on adhesion and methods of property improvements could be obtained. The main topics included in this works are: (i) the effects of monomer types on adhesion strength of resins; (ii) the effects of organo-functional silanes on adhesion strength of resins; (iii) the effects of tertiary amines on UV/thermal curing, adhesion strength and etiolation of resins; (iv) epoxide resins containing hBN (hexagonal boron nitride) as inorganic filler for underfill of flip-chip interconnection. In part (i), epoxide resins containing polyol, vinyl ether and acrylate monomers were prepared and their effects on resin shrinkage, conversions and adhesion strength on glass substrate were investigated via a pull test. The polyol monomer was found to be the best since it provided the smallest shrinkage (1.72%) for cationic photopolymerization, the slowest rates of polymerization at 0.09 sec□1 and the highest adhesion strength (153.35 kg/cm2). In part (ii), epoxide resins containing various organo-functional silanes including vinyl, epoxy, amino, methacrylic and acrylic groups were prepared and the adhesion strengths on indium tin oxide (ITO) substrate were studied. The vinyl silane was found to be able to promote the free-radical polymerization and the sample containing 1.0 wt.% of vinyl silane possessed the highest adhesion strength of 91.42 kg/cm2 on ITO glass and 153.35 kg/cm2 on glass substrate. In part (iii), various tertiary amines including imidazole, 1,2-dimethylimidazol, 2,4,6-tris(dimethylamino-methyl)phenol, 1-methylimidazole, and 2-methylimidazole were respectively added into the UV-curable epoxide resins. The addition of 2,4,6-tris(dimethylamino-methyl)phenol offered the highest glass transition temperature (Tg = 72.3□C), the lowest coefficient of thermal expansion (CTE = 70.8 ppm/□C) and the highest adhesion strengths on glass (> 199 kg/cm2), ITO (> 182 kg/cm2), PET (□ 115 kg/cm2), and stainless steel (□ 232 kg/cm2) substrates. 2,4,6-tris(dimethylamino-methyl)phenol also exhibited the highest UV reactivity and the best efficiency on the etiolation improvement that the values of □YI and □E*ab as low as 11.27 and 6.48 were achieved in the UV-curable epoxide resins. The knowledge acquired from the studies presented above was also applied to the preparation of underfill resin containing hBN filler for flip-chip interconnection. It was found that the hBN-resin possesses better dielectric properties in comparison with conventional underfill resins containing SiO2 filler. The hBN-resin also exhibited a lower CTE and a higher Tg and, for the resin containing 25.7 vol.% hBN, it possessed the largest thermal conductivity (1.08 W/m□K). The adhesion strengths of the composite resins decreased with the increase of hBN content and the adhesion strengths on various substrates was found to be in the order of alumina (Al2O3) > Si wafer > eutectic PbSn solder.