packaging technology

LED light-emitting part of the core is a p-type and n-type semiconductor pn junction consisting of the die, when the pn junction into the minority carrier and majority carrier recombination, it will send visible light, ultraviolet light or near infrared light. However, photons emitted pn junction non-directional, and immediately fired in all directions have the same probability, therefore, not all the light generated by the die can be released, depending on the quality of semiconductor materials, structure and geometry of the die , the package internal structure and encapsulation materials, improved LED applications require internal and external quantum efficiency. Conventional-type LED package Φ5mm is a square of side length 0.25mm die bonding or sintering the shelves in the lead, the positive die and the gold contact points through the sphere, bonded to the lead with a pin connected to the negative through the reflection Cup and the lead frame is connected to another pin, and then the top with epoxy resin coating. The role of reflective glass is to collect the die side of the screen the light emitted within the desired direction angle fired. Top of the envelope made of epoxy resin to shape, there is some role: to protect the die from outside such as erosion; using different shapes and material properties (doped or not doped bulk reagent), or diffuse from the lens lens function, control the light divergence angle; tube core refractive index associated with too much air, causing the die is very small within the total reflection critical angle, the light generated by the active layer is removed only a small part of the most easily in by multiple reflections within the die has been absorbed, prone to loss of ATR leads to too much light, choose the appropriate transition of the refractive index of the epoxy resin to improve die efficiency of the light emitted. Used as a form of epoxy resin shell must have moisture resistance, insulation, mechanical strength, the die emits light on the refractive index and transmission rate. Select a different refractive index of packaging materials, packaging geometry of the photon escape efficiency is different, the angular distribution of luminous intensity and the die structure, light output, encapsulated lens material and the shape used. The use of a tapered resin lens, can focus light to the LED in the axial direction, the corresponding small angle; If the top of the resin lens is round or flat type, the corresponding angle will increase.
In general, LED's emission wavelength with temperature change is 0.2-0.3nm / ℃, spectral width increases, the degree of bright colors. In addition, when forward current flows through the pn junction, the junction loss fever temperature rise at room temperature near the temperature rises 1 ℃, LED luminous intensity will be correspondingly reduced by 1%, the package heat dissipation; to maintain color purity and luminous intensity is very important, in the past to use more ways to reduce the drive current and lower junction temperature, the majority of LED drive current is limited to 20mA or so. However, LED light output with the increase of current, at present, a lot of power type LED drive current up to 70mA, 100mA or 1A level, need to improve the packaging structure, the new LED package design concepts and structure of low thermal resistance package and technology, improved thermal characteristics. For example, the use of large area flip-chip structure, using a good thermal conductivity of silver plastic, metal stents increase the surface area of ​​the silicon carrier solder bump heat sink mounted directly superior method. In addition, application design, PCB circuit board thermal design, thermal performance is also very important.
In the 21st century, LED's efficient, high brightness of, and continuously developed panchromatic, red, orange LED light effect has been reached 100Im / W, the green LED is 501m / W, the luminous flux LED alone has reached tens of Im. LED chip and package is no longer the traditional design concepts along the Gong and manufacture production patterns, increasing the chip's light output, changes in materials research and development is not limited to the number of impurities, lattice defects and dislocations to improve internal efficiency, while improving the internal structure of the die and package, enhanced LED internally generated photons emitted chance to improve the light efficiency, solve the heat, get light and heat sink optimization of design, improved optical performance, speed up the process of SMD surface mount technology is the main direction of industry R & D .