Foreword
LED can be divided into components fixed on two parallel wires, covered with resin sealed into a shell type, and LED components directly fixed on the printed wire substrate, and then sealed with resin into surface-encapsulated two.
The shell-type resin seal does not have the lens function, and it is easier to control the light collection and beam collection; the surface-mount type directly fixes the LED component on the substrate, suitable for high-density packaging, although small, light, and thin are more advantageous, but the brightness is It is lower than the cannonball type, and a reflector must be used to achieve high brightness requirements; the surface package type is mainly used in the fields of lighting and backlight modules of liquid crystal displays.
This article will focus on surface-mounted LEDs, introduce the characteristics and functions required for surface-mount substrates, and often face heat dissipation technical issues in design, and discuss the optical design techniques of O2PERA (OpTImized OutPut by Efficient ReflecTIon Angle).
Function of package substrate
Surface-mounted LED chips are usually only about the size of rice grains. The basic structure is shown in Figure 1. It encapsulates the light-emitting components on the electrodes of the printed substrate, and then is sealed with resin.
One of the functions of the printed circuit board when manufacturing LED chips is to integrate the semiconductor device. The other function is to allow the emitted light generated by the component to be efficiently reflected in the front, thereby improving the efficiency of the LED.
In order to improve the luminous efficiency of the LED module, it is also very important to efficiently reflect the light emitted from the substrate side, so a substrate with a high reflectance is required. Printed substrates with gold or silver plating can improve reflectivity. However, when gold plating is used, the reflectance of low-wavelength light in the blue light field is very low, and silver plating has a problem of low long-term durability. Therefore, the researchers reviewed the use of LED white substrates.
The white substrate for LED requires 400 ~ 750nm, and the visible light has a uniform high reflectance in the entire wavelength area. When the wavelength dependence of the reflectance is very strong, the LED chip design will become a light source with a different wavelength from the design. It has a uniform reflectance in the entire wavelength range of visible light.
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