A model for spectra of the phosphor-coated white LED (p-W LED) with a blue chip, a red chip, and green and yellow phosphors is presented. The optimal spectra of p-W LEDs with correlated color temperatures (CCTs) of 2700-6500 K have been obtained with a nonlinear program for maximizing luminous efficacy of radiation (LER) under conditions of both color-rendering indices (CRIs) and special CRIs of R9 strong red above 98. The simulation results show that p-W LEDs with one InGaN blue (450 nm) chip, one AlGaInP red (634 nm) chip, and green (507 nm) and yellow (580 nm) silicate phosphors can realize white lights with CRIs of about 98 and special CRIs of R9 for strong red above 98. The average of the special CRIs R9 to R12 for the four saturated colors (red, yellow, green, and blue) is above 95. R13 for the skin of women's faces at about 100, as well as LERs above 296 lm/W at CCTs of 2700-6500 K. LERs of excellent CRI p-W LEDs with one InGaN blue chip, one AlGaInP red chip, and green and yellow silicate phosphors increased by 19-49% when compared with that of excellent CRI p-W LEDs with one InGaN blue chip and green and yellow silicate phosphors, as well as red nitride phosphor.
The optimal spectra of the warm-white LED (WWLED) lamp consisting of AlGaInP red LED and the p-W LED packaged by combining silicate green and orange phosphors with a InGaN blue LED die was obtained by nonlinear program for maximizing the luminous efficacy of radiation while both color rendering index (CRI) and special CRI of R9 for strong red above 90 at correlated color temeratures (CCTs) of 2700 K. The optimal peak wavelengths of red LED, blue LED die, silicate green and orange phosphors are 626 nm, 454 nm, 535 nm and 584 nm, respectively. Their optimal relative radation fluxs are 9.7%, 33.4 %, 26.1 %, 30.8 %, respectively. The real WWLED lamp with CCT of 2653 K, CRI of 90, R9 of 94 and R(9-12) of 88, as well as luminous efficacy (LE) of 80.2 lm/W have been realized. Furthermore, the WWLED lamp can realized CCT tunable warm-white-light with CRIs of 86 ∼ 93, R9s of 86 ∼ 95 and LEs of 78.2 ∼ 80.3 lm/W at CCTs of 2392 K to 3014 K by adjusting drive current of the red LED
Die attach materialsSilver Sn96.5Ag3CuO.5 AuSn20 epoxyThe structure of HP-LED samples is shown in the Fig.l, for the substrate, the bottom is ceramic layer and the conductive layer is copper layer with gold plating. Except the differences in die attach materials, the HP-LED chips and other components are the same. For die attach processes, here take the solder paste as example. First, dispend the solder paste on the ceramic substrate by a dispenser. Second, load the LED chip on the solder paste. Third, put the ceramic substrate on the heating plate and undergoes eutectic process. Last, assemble the device to an aluminum substrate. The solder paste and AuSn20 interconnection eutectic process curve are as Fig.2 (a) and (b) respectively. When design the eutectic curve, considering the heating platform is bottom heating and there are temperature difference between the heating platform and real eutectic temperature, the curve setting temperature was set up as 260°C 13 80°C to achieve the substrate surface temperature about 230°C and 330°C been moved to metallic eutectic interconnection and the better performance also have been demonstrated [1][2]. Investigated results show that the thermal resistance of AuSn20 eutectic bonding is lower than that of the solder paste and silver epoxy [1]. However, the thermal characteristics and optical durability of the HP-LED with different die attach materials need more data and investigations to speed up the industrial application.In order to further understand the thermal characteristics and reliability of HP-LED interconnected by different dieattach materials, the AuSn20 eutectic, solder paste (Sn96.5Ag3CuO.5) and silver epoxy are applied to HP-LED respectively as the experimental samples. The transient thermal resistance, steady state junction temperature and optical durability of the HP-LEDs are tested and studied. ExperimentsThe silver epoxy and solder paste are commercial products. AuSn20 is already coated on the bottom of the HP-LED chip by the manufacturer. Table 1 shows the value of the thermal conductivity coefficient. Table 1 Thermal conductivity coefficient of die attach materials (WImK) AbstractDie interconnection layer is one of the main factors to improve the HP-LED thermal issue as it is the main thermal transfer media from the HP-LED chip to the substrate or heat sink. Silver epoxy is now widely used for LED interconnection, but it becomes more and more difficult for efficient heat dissipation as the HP-LED electric power density becomes higher and higher. Nowadays more and more attentions have been moved to metallic eutectic interconnection, especially for solder paste and AuSn20 eutectic interconnection which have big potential to be used for HP-LED. In order to further understand the thermal characteristics and reliability of HP-LED interconnected by different die-attach materials, the AuSn20 eutectic, solder paste and silver epoxy were applied to HP-LED respectively. The transient thermal resistance, steady state junction temperature and optical durability of th...
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