LED packaging technology elements have three points: the package structure design, use the appropriate packaging materials and process level.
At present, there are more than 100 kinds of LED packaging structure, the main packaging types are more than 40 kinds of lamp series, SMD (chip LED and TOP LED) series of more than 30 kinds, COB series of more than 30 kinds, PLCC, high power package, Modular packaging, etc., the development of packaging technology to keep up and meet the needs of LED application product development.
LED packaging technology, the basic content
LED packaging technology, the basic requirements are: to improve the light efficiency, high light color performance and device reliability.
(1) to improve the efficiency of light
LED package light efficiency is generally up to 80 ~ 90%.
① use more transparent packaging materials: transparency ≥ 95% (1mm thickness), the refractive index is greater than 1.5 and so on.
② use high excitation efficiency, high dominant phosphor, particle size appropriate.
③ mounted substrate (reflective cup) to have a high reflectivity, high optical design of the appearance.
④ choose the appropriate packaging process, especially the coating process.
(2) high light color performance
LED main light color technical parameters are: height, glare, color temperature, color, color tolerance, light flashing and so on.
Color rendering index CRI ≥ 70 (outdoor), ≥ 80 (outdoor), ≥ 90 (art museum, etc.).
Color tolerance ≤ 3 SDCM ≤ 5 SDCM (full life)
Encapsulation to use multi-primary combination to achieve, focusing on improving the spectral distribution of LED radiation SPD, to the sun's spectral distribution close to the spectrum. We should pay attention to the development and application of quantum dot phosphor to achieve better light color quality.
(3) LED device reliability
LED reliability includes different conditions of LED device performance changes and a variety of failure mode mechanism (LED packaging material degradation, the impact of integrated stress, etc.), which is mainly referred to the reliability of the characterization value - life, the current LED device life is generally 3 to 5 hours, up to 5 to 10 million hours.
① use the appropriate packaging materials: binding force to large, small stress, good match, good air tightness, temperature, moisture (low water absorption), anti-ultraviolet light.
② package heat dissipation material: high thermal conductivity and high conductivity of the substrate, high thermal conductivity, high conductivity and high strength of solid crystal materials, stress is small.
③ the appropriate packaging process: loading film, welding, packaging and other strong combination of stress to be small, combined to match.
LED light integrated packaging technology
LED light integrated package structure has more than 30 types, is gradually moving into the system integration package, is the future direction of packaging technology development.
(1) COB integrated package
COB integrated package existing MCOB, COMB, MOFB, MLCOB more than 30 kinds of package structure, COB packaging technology matures, the advantage is low cost COB package is about 40% of the LED light source market, light efficiency of 160 ~ 178 lm / w, thermal resistance up to 2 ℃ / w, COB package is the recent trend of LED packaging development.
(2) LED crystal grade package
Crystal-level package made from the epitaxial LED device as long as a scribe, LED lighting is the demand for multi-system integrated package form, the general substrate with silicon material, without solid crystal and pressure welding, and dispensing, forming a system integrated package , Its advantages are good reliability, low cost, is one of the direction of packaging technology development.
(3) COF integrated package
COF integrated package is a large area in the flexible substrate assembly in the power LED chip, it has a high thermal conductivity, thin layer flexibility, low cost, light uniform, high light efficiency, flexible surface light source, etc., can provide line light source, Three-dimensional light source of various LED products, but also to meet the LED modern lighting, personalized lighting requirements, but also as a general-purpose packaging components, market prospects.
(4) LED modular integrated package
Modular integrated package generally refers to the LED chip, drive power, control part (including IP address), parts and other systems integrated package, collectively referred to as LED module, with material conservation, reduce costs, can be standardized production, easy maintenance and many other advantages , Is the direction of LED packaging technology development.
(5) flip chip packaging technology
Flip chip packaging technology is formed by the chip, substrate, bumps a space, so that the package out of the chip with small size, high performance, short connection, the use of ceramic substrate, flip chip, eutectic process, direct pressure Combined to achieve high power lighting performance requirements.
With gold and tin alloy chip will be pressed on the substrate, instead of the previous silver plastic process, "direct pressure" instead of the past "reflow", with excellent conductive effect and thermal area. The packaging technology is an important trend in high-power LED packaging.
(6) free package chip technology
Free packaging technology is a technology integration, the use of flip chip, without solid crystal, gold and stent is a semiconductor packaging technology 70 kinds of technology in the formation of one.
PIF chip-free chip products can enhance the luminous efficiency to 200lm / w, light angle greater than 300 degrees ultra-wide-angle all-week design, do not use secondary optical lens, will reduce the loss of light efficiency and reduce costs, but to put expensive equipment.
PFC new products main LED lighting market, especially in the application of candle lights, not only can simulate the shape of tungsten filament, while breaking the heat volume limit.
(7) LED other package structure
① EMC package structure: is embedded integrated package form (Embedded LED Chip) will not directly see the LED light source.
② EpC encapsulation technology: (Epoxy Molding Compound) Epoxy Molding Compound as a stent packaging technology, with high heat resistance, high integration, anti-UV, small size, but poor air tightness, is now mass production.
③ Cog package: (Chip On Glass) LED chip on the glass substrate for packaging.
④ QFN packaging technology: small pitch display pixel unit is less than or equal to P.1, the package used, will replace the PLCC structure, the market prospects.
⑤ 3D packaging technology: three-dimensional form of packaging technology, is being developed.
⑥ power frame packaging technology: (Chip-in-Frame Package) in the small frame on the package power LED chip, the industrial light effect has reached 160 ~ 170 lm / w, up to 200 lm / w or more.
LED packaging materials
LED packaging materials a lot of varieties, and is constantly evolving, here only a brief introduction.
(1) packaging materials
Epoxy, epoxy plastic, silicone, silicone, etc., technically on the refractive index, internal stress, adhesion, air tightness, high temperature, anti-ultraviolet and other requirements.
(2) solid crystal material
① solid crystal: resin and silicone, internal filler metal and ceramic materials.
② eutectic: AuSn, SnAg / SnAgCu.
(3) substrate material: copper, aluminum and other metal alloy materials
① ceramic materials: Al2O3, AlN, SiC and so on.
② aluminum ceramic materials: known as the third generation of packaging materials AlSiC, AlSi and so on.
③ SCB substrate material: multi-layer die substrate, good heat dissipation (thermal conductivity 380w / m.k), low cost.
④ TES polycrystalline semiconductor ceramic substrate, heat transfer speed.
(4) heat dissipation material: copper, aluminum and other metal alloy materials
Graphene composites, thermal conductivity 200 ~ 1500w / m.k.
PCT high temperature special engineering plastics (poly-terephthalic acid 1,4-cyclohexanedicarboxylate), plus ceramic fiber, high temperature, low water absorption.
Thermal engineering plastics: non-insulated thermal conductivity engineering plastics, thermal conductivity 14w / m.k.
Insulated thermal conductivity engineering plastics, thermal conductivity 8w / m.k.