1 LED chip type

LED chip types are mainly divided into three categories from a structural point of view: horizontal electrode chips, flip chips and vertical electrode chips.

2 LED packaging

Packaging is an intermediate link necessary to realize the LED from the chip to the final product. The function of the packaging is to provide enough protection for the chip to prevent the chip from failing due to long-term exposure in the air or mechanical damage, so as to improve the stability of the chip; for LED packaging, also It needs to have good light extraction efficiency and good heat dissipation. Good packaging can make the LED have better luminous efficiency and heat dissipation environment, thereby improving the life of the LED.

The role of packaging: to realize the function of inputting electrical signals, protecting the normal operation of the chip, and outputting visible light.

3 Commonly used LED chip packaging forms

1) Lead type package

2) Planar package

3) Surface mount package

4) Piranha Package

5) Power package

4-pin package structure

The LED pin-type package uses lead frames as the pins of various package shapes. It is the first package structure that has been successfully developed and put on the market. There are many varieties and high technology maturity. The internal structure of the package and the reflective layer are still being continuously improved.

The LED chip is bonded to the lead frame. The positive pole is connected to a bracket with gold wire, and the negative pole is connected to the bracket reflection cup with gold wire or directly bonded in the bracket reflection cup with silver paste. The top is encapsulated with epoxy resin to form a cylinder + hemisphere. The shape of the epoxy acts as a lens, controlling the beam divergence angle. At the same time, the refractive index of epoxy resin plays a role in the transition between the chip and the air, which improves the luminous efficiency of the chip. The refractive index of the chip is high, and the total reflection angle to the air is small. more light output.

Generally, the size of this LED chip is 0.25mmX0.25mm, the radius of the packaged component is 5mm, the luminous power is 1~2 lumens, and the working current is 20~30mA. Traditional small-chip LEDs have limited applications due to their low luminous power. Most of them are used for display or indication. Such as the indicator light of the instrument.

4.1 The process of pin package

5 Flat Package

Flat packaging is a combination of multiple LED chips packaged into a flat structural package. Through the appropriate connection (series and parallel) of LEDs and suitable optical structure, the light-emitting segments and light-emitting points of the light-emitting display can be formed, and then various light-emitting displays, such as digital tubes, "meter" character tubes, can be composed of these light-emitting segments and light-emitting points. and matrix tubes, etc.

Taking the Xlamp XP-E product of Cree Company in the United States as an example, it adopts a packaging manufacturing process with higher production efficiency. Ceramics are used as packaging substrates. Together. Chips are mounted on each substrate unit, and then a layer of silica gel is encapsulated on the ceramic substrate to form the required optical lens structure. Its structure includes ceramic substrate, new product, Au wire and plastic-encapsulated silicone.

6 Surface Mount Package (SMD)

Surface Mount Package (SMD) is a new type of surface mount package. It has the advantages of small size, large scattering angle, good luminous uniformity and high reliability. Its luminous color can be various colors including white light, which is very suitable for keyboard display lighting of mobile phones, backlight lighting of TV sets, and electronic products that require lighting or instructions. In the direction of development, three or four Led chips are packaged in one patch, which can be used to assemble lighting products.

7 Piranha Package

The piranha encapsulation is square and uses a transparent resin encapsulation, because its shape is very similar to the piranha in the Amazon River, so it is called the piranha encapsulation. It has four pins, with a missing pin at the negative side. Piranha is an astigmatism-type LED, with a luminous angle greater than 120 degrees, high luminous intensity, and can withstand greater power. Since the bracket used by the piranha LED is made of copper and has a large area, the heat transfer and heat dissipation are fast. After the LED is lit, the heat generated by the PN junction can be quickly transferred from the four legs of the bracket to the copper tape that goes out to the PCB.