With the continuous advancement in LED packaging technology and the global implementation of energy-saving and emission-reduction policies, the adoption of LED light sources in the lighting industry is steadily increasing. New packaging technologies are constantly emerging to meet growing demands for efficiency and performance. Despite these developments, key factors such as heat dissipation, luminous efficiency, reliability, and cost-effectiveness remain central concerns for LED performance. Without significant breakthroughs in these areas, or if alternative technologies surpass LEDs in the future, the dominance of LEDs in the lighting market may be challenged.
In this context, COB (Chip on Board) has emerged as a promising LED packaging solution. Compared to traditional discrete LED packages, COB offers superior primary heat dissipation and high-density light output. When designing an LED package, minimizing the junction temperature of the chip is critical. The COB structure provides the shortest heat dissipation path, allowing heat from the working chip to be directly transferred to the metal substrate and then to the heat sink. As a result, COB packages exhibit better thermal management than conventional discrete components.
The materials used for COB metal substrates include copper, aluminum, aluminum oxide, and aluminum nitride. Among these, aluminum is widely preferred due to its balance of cost, thermal conductivity, and corrosion resistance. With ongoing innovations in LED packaging and increasing environmental regulations, the role of COB technology in improving LED performance is becoming more prominent.
**3. Angle Analysis of Heat Dissipation Performance of LED Based on COB Technology**
The power loss in an LED during operation is typically converted into heat. Any component with electrical resistance becomes a heat source, leading to a sharp rise in local temperature. This increase affects both the device itself and the surrounding environment, impacting the LED’s reliability, performance, and lifespan. Studies have shown that higher temperatures can significantly increase the failure rate of LED chips. Therefore, effective thermal design and heat control are essential to enhance the overall reliability of LED systems.
In the electronics industry, the "10°C rule" states that for every 10°C increase in ambient temperature, the failure rate of a device increases by an order of magnitude. While many current solutions focus on using materials with high thermal conductivity—such as copper, aluminum, and ceramics—improving only the circuit board is insufficient. Additional thermal design strategies are necessary to address the heat dissipation challenges of LEDs effectively.
**Heat Dissipation Technology**
All electronic devices generate heat during operation, and managing this heat is crucial for maintaining performance and longevity. Proper heat dissipation techniques are key to minimizing thermal stress and ensuring reliable operation.
Heat transfer occurs through conduction, which is the most common method. It involves the transfer of energy between particles in direct contact. In contrast, thermal diffusion occurs in gases where the molecular spacing is larger. The basic formula for heat conduction is:
$$ Q = K \times A \times \frac{\Delta T}{\Delta L} \quad (1) $$
Where:
- $ Q $ is the heat transferred,
- $ K $ is the thermal conductivity of the material,
- $ A $ is the heat transfer area,
- $ \Delta T $ is the temperature difference,
- $ \Delta L $ is the distance over which heat is conducted.
This equation shows that heat transfer is directly proportional to the thermal conductivity and surface area, and inversely proportional to the distance. Higher thermal conductivity, larger area, and shorter distances all contribute to more efficient heat dissipation.
**LED Thermal Performance and Packaging**
As a next-generation light source, LEDs are increasingly used in general lighting applications. One of the primary optical requirements is luminous flux. To increase this, two main approaches are used: boosting the brightness of the chip or using dense arrays. However, these methods require higher power input, and only a small portion of the energy is converted into light. Most of it is lost as heat, which can cause overheating in densely packed designs, especially in small spaces.
Like traditional light sources, LEDs produce heat during operation. Only about 30%–40% of the electrical energy is converted into light, while the remaining 60%–70% is transformed into heat through non-radiative recombination. As the junction temperature rises, this process intensifies, reducing luminous efficiency and shortening the LED's lifespan. Effective heat dissipation is essential to maintain low junction temperatures and extend the life of the LED.
Figure 1 illustrates the relationship between the light decay and junction temperature of a Lumileds 1W LED under constant current. It clearly shows that higher junction temperatures lead to faster light degradation and reduced lifetime.
**LED Heat Dissipation**
The key thermal parameters for LEDs include junction temperature and thermal resistance. Junction temperature refers to the temperature at the PN junction, while thermal resistance measures how easily heat is conducted from the junction to the surrounding environment. Lower thermal resistance means better heat dissipation and a lower junction temperature, which improves light efficiency and extends the LED's lifespan.
When the junction temperature rises, it causes a drop in forward voltage, potentially leading to further temperature increases. If the temperature exceeds the critical threshold, the LED may be damaged. Different packaging materials and processes affect the critical temperature, making thermal design a crucial factor in LED performance.
**The Impact of Packaging Process on Thermal Performance**
Currently, most LED chips are packaged individually, suitable for small-scale applications like 1–4 LED lamps. These lamps have limited usage time, so heat accumulation is not a major issue. However, when applied to fluorescent lamps, which operate continuously in compact spaces, heat dissipation becomes more challenging.
LED chips generate a large amount of heat in a very small volume, and their low heat capacity means that heat must be removed quickly. While chip architecture and materials influence thermal resistance, the most effective way to improve heat dissipation is through advanced packaging techniques.
Table 1 compares the thermal resistance of LEDs in various packaging methods. It shows that COB technology results in the lowest thermal resistance, making it the most effective solution for heat management in LED applications.
From the data, it is clear that COB packaging offers the best thermal performance, making it a preferred choice for high-performance LED systems.
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