Via-Hole-Type Flip-Chip Packaging to Improve the Thermal Characteristics and Reliability of Blue Light Emitting Diodes

Abstract

We investigated the effect of via-holes in the lead-frame on the reliability of blue flip-chip light-emitting diodes (FCLEDs). For bonding, conventional Sn-Ag(3.0%)-Cu(0.5%) solder (SAC) and Ag sintered paste were adopted. Lateral LED, conventional FCLED (c-FCLED), and via-hole FCLED gave efficacies of 218.5, 221.6 and 225 lm/W at 30 mA. The lateral LED sample (bonding material: silicone), c-FCLED sample (SAC), via-hole-type sample (Ag sinter), and via-hole-type sample (SAC) exhibited total thermal resistance of 15.24, 10.19, 8.95, and 11.79 K/W, respectively. The humidity/temperature/H 2 S gas reliability examinations showed that unlike the via-hole-type samples, the lumen of the c-FCLED was fallen by 15.0% after exposure for 500 h. Furthermore, the c-FCLED exhibited a 19.6% higher forward voltage than the via-hole FCLED after 1,000 thermal-cycles. SEM results showed that unlike the via-hole type FCLED, the c-FCLED underwent cracking after thermal cycle of 1000 times.

Selective Coating of White Silicone to Improve the Optical and Thermal Characteristics of White LED Packages

“…8a), coating the Ag plating area and Ag epoxy paste bonding area using white silicone could be an important process for the maintenance of high lumen. 10,25,27 In addition, as can be seen in Fig. 8b, after aging at 85 °C for 1000 h the lumen maintenance rate is almost the same for both the uncoated and coated white LED packages, namely, it was 99.21% and 99.32% for the uncoated and coated white LED packages, respectively, after 1000 h.…”

“…Thus, such plastics-incorporated leadframes have rather poor heat dissipation efficiency, resulting in high thermal resistance and device failure. 10 As an example, it was shown that owing to efficient heat dissipation, flip-chip (FC)-LEDs with viaholes in the leadframe resulted in lower thermal resistance and higher efficacy than conventional FC-LEDs. Consequently, after thermal cycle (from −40 to +125 °C) of 1000 times, the via-hole type FC-LED remained stable, whereas the conventional FC-LED underwent cracking.…”

“…Consequently, after thermal cycle (from −40 to +125 °C) of 1000 times, the via-hole type FC-LED remained stable, whereas the conventional FC-LED underwent cracking. 10 Furthermore, in order to protect LED chips from electrostatic charge failure, they are equipped with a Zener diode, where metal area (Ag plating area) and Ag epoxy paste are needed. However, upon the operation of LEDs, these areas could cause internal optical loss in the packages, reducing the heat dissipation and consequently deteriorating the performance of LED packages particularly when exposed to high temperature/high moisture ambience for long time.…”

“…However, upon the operation of LEDs, these areas could cause internal optical loss in the packages, reducing the heat dissipation and consequently deteriorating the performance of LED packages particularly when exposed to high temperature/high moisture ambience for long time. [8][9][10][11] So far, to improve the efficacy of LED packages, white silicone was coated over the LED chips and plastic reflectors (e.g., PCT) of LED packages. It was reported that TiO 2 having high refractive index was often mixed with epoxy to improve the output performance of LEDs.…”

Improvement in the Reliability of AlGaInP-Based Light-Emitting Diode Package Using Optimal Silicone and Leadframe Structure

“…For encapsulation, silicones have been widely used as a suitable encapsulant because of their advantageous characteristics such as high transmittance, thermal resistance, low-impurity contents, low moisture absorption, and low modulus. [8][9][10][11][12][13][14][15][16][17][18][19] For outdoor applications, e.g., headlamps or rear lamps for vehicles, LEDs should have higher electrical and thermal reliability under harsher conditions. In particular, moisture was known to be one of the main causes for the degradation of LED packages.…”