Detailed explanation of LED packaging technology: ceramic COB technology

LED packaging The method is to connect the chip (die) to its heat dissipation substrate Submount (sub-adhesion technology) through wire bonding, eutectic or flip chip packaging technology to form an LED chip , and then fix the chip on the system board to form a light source module.

At present, LED packaging methods can be roughly divided into lens -type and reflector-type. The lens can be molded or bonded; while the reflector-type chip is mostly formed by mixing glue, dispensing glue, and packaging. In recent years, epitaxy, die bonding and packaging design have gradually matured, and the chip size and structure of LEDs have been miniaturized year by year. The power of a high- power single chip reaches 1~3W, or even more than 3W. As the power of LEDs continues to increase, the heat dissipation and heat resistance requirements for LED chip carriers and system circuit boards are becoming increasingly stringent.

In view of the comprehensive considerations of insulation, voltage resistance, heat dissipation and heat resistance, ceramic substrates have become one of the important materials for chip sub-attachment technology. Its technology can be divided into thick film process (Thic film ), low temperature co-fired process (LTCC) and thin film process (DPC) and other methods. However, thick film process and low temperature co-fired process are sintered by screen printing technology and high temperature process, which are prone to rough circuits, inaccurate alignment, and shrinkage ratio problems. For high-power LED products with increasingly fine circuits, or LED products produced by eutectic or flip chip processes that require accurate alignment, thick film and low temperature co-fired ceramic substrates are gradually insufficient.

Therefore, high heat dissipation coefficient thin film ceramic heat dissipation substrates are made by sputtering, electro-/chemical deposition, and yellow light lithography. They have the characteristics of precise metal lines and stable material systems, and are suitable for the development trend of high-power, small-size, high- brightness LEDs. They also solve the stringent requirements of eutectic/flip-chip packaging processes on the resolution and accuracy of metal lines on ceramic substrates. When LED chips use ceramics as carriers, the heat dissipation bottleneck of this LED module is transferred to the system circuit board, which transfers heat from the LED chip to the heat sink fins and the atmosphere. As the functions of LED chips are gradually improved, the material is gradually changed from FR4 to metal core printed circuit boards (MC PCB ). However, with the development of high-power LED demand, the heat dissipation coefficient of MCPCB materials (2~4W/mk) cannot be used for higher power products. Therefore, the demand for ceramic circuit boards has gradually become popular. In order to ensure the material stability and light decay stability of LED products under high-power operation, the trend of using ceramics as heat dissipation and metal wiring substrates has become increasingly clear. The cost of ceramic materials is currently higher than that of MCPCB. Therefore, how to use the high heat dissipation coefficient of ceramics to save material usage area and reduce production costs has become one of the important indicators for the development of ceramic LEDs. Therefore, in recent years, the integration of polycrystalline packaging and system circuits with ceramic COB design has gradually attracted the attention of various packaging and system manufacturers.

COB is not a new technology in the electronics manufacturing industry. It refers to directly pasting the bare epitaxial wafer on the circuit board and directly soldering the wire/bonding wire on the gold-plated circuit of the PCB, which is also commonly known as wire bonding. Then, through the sealing technology, the packaging steps in the IC manufacturing process are effectively transferred to the circuit board for direct assembly. In the LED industry, as modern technology products are increasingly light and highly portable, in addition, in order to save the system board space problem of multiple LED chip designs, the COB technology of directly pasting the chip on the system board has been developed in the demand for high-power LED systems.

The advantages of COB are: high cost-effectiveness, simple circuit design, and space saving on system boards, but there are also technical barriers to chip integration brightness, color temperature coordination, and system integration. Taking a 25W LED as an example, a traditional high-power 25W LED light source must use 25 1W LED chips to package into 25 LED components , while COB packaging packages 25 1W LED chips in a single chip, so the required secondary optical lenses will be reduced from 25 to 1, which helps to reduce the light source area, reduce materials, and system costs, and thus simplify the secondary optical design of the light source system and save assembly labor costs. In addition, a high-power COB package only requires a single high-power LED to replace multiple 1-watt (inclusive) or more LED packages, making the product thinner and smaller.

Currently, the production of COB products on the market is still mainly based on MCPCB substrates. However, MCPCB still has many problems of heat dissipation and large light source area that need to be solved. Therefore, the fundamental way is to update the heat dissipation material as the most effective solution. Ceramic COB substrates have the following advantages: 1. Thin film technology makes the basic circuit more precise, (2) large quantity reduces costs, and (3) high plasticity, which can be designed according to different needs.

LED bulbs made of COB chips on MCPCB substrates cannot be dimmed, but LEDaladdin has launched dimmable LED bulbs assembled with ceramic COB chips, which are available in 5W, 6W, and 7W. They have better performance, color temperature of 2200K-8000K, and lumen of more than 60LM/W.

The development of ceramic MCOB/COB is a trend to simplify system boards. The practicality, brightness, heat dissipation and cost control of lighting fixtures are all important key factors.