Alexandra Debray

High-performance epoxy casting resins for SMD-LED packaging

In order to come up with high volume SMD-LED production encompassing 1.9 billion devices for current fiscal year we did basic exploratory work to establish structure-processing- property relations for robust epoxy casting resin packages with identical ppm level of one. Bisphenol A-based epoxy casting resins (DGEBA) with acidic ester modified Hexahydrophthalic anhydride (HHPA) hardeners using strictly controlled high-grade raw materials were formulated and thermally transferred to highly transparent polyester networks. For 1 mm thick samples transparency in the 400 to 800 nm region is above 90%. Thermal aging tests for 6 weeks at 120 degrees Celsius reveal only slight discoloration with a color distance of 2. To avoid significant light losses within the LED operating life of 100,000 hrs stress on mechanically sensitive light-emitting chips was reduced by matching glass transition temperature Tg and E-modulus to 115 degrees Celsius and 2,800 MPa, respectively. Total chloride content below 1,000 ppm imply low corrosion potential. Further, resin composition, epoxy-hardener mixing ratio as well as curing profile were adapted to materialize fast curing for demand quantities while introducing effective low stress moieties in the final structure. Low internal stress, superior thermal shock and crack resistance were derived from supreme fracture toughness: KIC and GIC values were 1.350 MPam1/2 and 560 J/m2. With favorable water absorption behavior LED-packages withstand all soldering processes including TTW (through the wave) soldering. Thus, SMD-LEDs fulfill electronic industry standard JEDEC LEVEL 2.