Introduction to the Factors Causing Luminous Degradation of Small Butterfly LED Chips

Release Date:

2020-11-21

　　Many materials can contribute to luminous degradation in small LED butterfly lamps, including the LED chip, the phosphor used in white-light LEDs, the encapsulant, the LED lead frame, and the LED lamp holder and housing. The following sections provide a detailed overview.

 

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　　1. Chip pair Small butterfly LED light beads Impact of Luminous Decay

　　Based on the current experimental results, the impact of the chip on light degradation can be categorized into two types: First, the chip material leads to varying degrees of degradation. The commonly used substrate materials for blue wafers are silicon carbide and sapphire; silicon carbide typically features a single-electrode structure, which offers superior thermal conductivity, whereas sapphire usually employs a dual-electrode design, making heat dissipation more difficult and resulting in poorer thermal performance. Second, chip size plays a role: when the chip material is the same, chips of different sizes exhibit different degradation rates.

　　2. The Impact of Phosphor on Light Degradation in Small Butterfly LED Chips

　　There are numerous approaches to realizing white LED chips. The most common and well-established method involves applying a layer of yellow phosphor onto a blue-light-emitting chip, thereby mixing the blue and yellow emissions to produce white light. Consequently, the quality of the phosphor material has a significant impact on the performance and degradation characteristics of white LEDs. The prevailing phosphors on the market include YAG (yttrium aluminum garnet) phosphor, silicate phosphor, and nitride phosphor. Compared with blue-light LED chips, phosphors can accelerate the aging of white LEDs; moreover, the degree of light output degradation varies among different manufacturers, largely depending on the raw-material composition of the phosphor.

　　3. Influence of Die-Attach Adhesive on Luminous Degradation of Small Butterfly LED Chips

　　In the white-light LED chip packaging industry, the solid die-attach adhesives commonly used include epoxy insulating adhesive, silicone insulating adhesive, and silver paste. Each of these three has its own advantages and disadvantages, and their selection should be based on a comprehensive consideration. Epoxy insulating adhesive has poor thermal conductivity but offers high luminance; silicone insulating adhesive exhibits slightly better thermal conductivity than epoxy and also provides higher luminance, yet because it contains a certain proportion of silicone, residual silicone and fluorescent phosphor in the adhesive can form a barrier when bonding the chip to the substrate, especially when combined with the epoxy matrix. This barrier effect can lead to delamination under thermal shock, ultimately causing the LED to fail. Silver paste boasts superior thermal conductivity compared with the other two, which can extend the service life of the LED chip; however, its relatively high light absorption results in lower luminance. For double-electrode blue chips, precise control of the amount of silver paste applied during die attachment is critical—too much or too little can easily cause short circuits, directly impacting product yield.

　　4. Bracket Pair Small butterfly LED light beads Impact of Luminous Decay

　　LED brackets are mainly available in copper and iron versions. Copper brackets offer excellent thermal and electrical conductivity but come at a higher price, whereas iron brackets have relatively poorer thermal and electrical conductivity and are more prone to rusting, though they are more affordable.

　　Most LEDs on the market use iron brackets. The material of the bracket significantly affects LED performance, particularly light depreciation. This is primarily because copper has much better thermal conductivity than iron: copper’s thermal conductivity is 398 W/(m·K), whereas iron’s is only about 50 W/(m·K)—roughly one-eighth of copper’s value. In addition, the thickness of the bracket’s electroplated coating also plays a critical role. When selecting a bracket, it is essential to ensure that the cup-shaped cavity size matches the LED chip and the encapsulant bead; the quality of this match directly influences the optical performance of small butterfly-type LED beads. Otherwise, issues such as asymmetrical light spots, yellow halos, and black spots may arise, severely compromising product quality.

　　5. The Impact of Fluorescent Adhesive on Luminous Degradation of Small Butterfly LED Chips

　　For conventionally packaged white-light LEDs, epoxy resin or silicone is typically used as the phosphor encapsulant; among these, white-light LEDs incorporating silicone powder exhibit a significantly longer service life than those using epoxy resin. One reason is that, in both cases, the encapsulation process involves curing the phosphor within the encapsulant. Silicone offers superior UV resistance and better thermal dissipation compared with epoxy resin; however, under identical conditions, silicone powder delivers higher initial whiteness than epoxy resin. The lower light output of silicone-based formulations is primarily attributable to silicone’s lower refractive index (1.3–1.4) relative to epoxy resin’s refractive index (above 1.5), resulting in inferior initial luminous performance.

 

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