The elements of LED packaging technology have three points: packaging structure design, selection of suitable packaging materials and process level.
At present, there are more than 100 LED package structures. The main package types are more than 40 Lamp series, more than 30 SMD (chip LED and TOP LED) series, more than 30 COB series, PLCC, high power package, optical integrated package and Modular packaging, etc., the development of packaging technology must closely follow and meet the needs of LED application product development.
The basic content of LED packaging technology
The basic requirements of LED packaging technology are: improved light extraction efficiency, high light color performance and device reliability.
(1) Improve light extraction efficiency
The light-emitting efficiency of the LED package is generally 80 to 90%.
1 Use a more transparent packaging material: transparency ≥ 95% (1mm thickness), refractive index greater than 1.5 and so on.
2 Select high-efficiency, high-dominance phosphors with appropriate particle size.
3 The mounting substrate (reflecting cup) should have an optical design with high reflectivity and high light extraction rate.
4 Choose the appropriate packaging process, especially the coating process.
(2) High light color performance
The main light color technical parameters of LED are: height, glare, color temperature, color rendering, color tolerance, light flicker, etc.
Color rendering index CRI ≥ 70 (outdoor), ≥ 80 (outdoor), ≥ 90 (art museum, etc.).
Color tolerance ≤3 SDCM≤5 SDCM (full life period)
The package should be implemented with a multi-primary color combination, focusing on improving the spectral amount distribution SPD of the LED radiation, and the spectral distribution to the sunlight is close. Pay attention to the development and application of quantum dot phosphors to achieve better light color quality.
(3) LED device reliability
LED reliability includes changes in LED device performance under various conditions and various failure mode mechanisms (degradation of LED package materials, effects of integrated stress, etc.), which is mainly referred to as the characterization value of reliability - lifetime, currently LED device life is generally 3 to 5 hours, up to 50,000 to 100,000 hours.
1 Use suitable packaging materials: large bonding force, small stress, good matching, good air tightness, temperature resistance, moisture resistance (low water absorption), anti-ultraviolet light, etc.
2 package heat-dissipating materials: high thermal conductivity and high conductivity of the substrate, high thermal conductivity, high electrical conductivity and high strength of the solid crystal material, the stress is small.
3 suitable packaging process: loading, pressure welding, packaging and other bonding strength, stress should be small, the combination should be matched.
LED light integrated packaging technology
There are more than 30 types of LED light integrated package structures, which are gradually moving toward system integration and packaging, which is the development direction of future packaging technology.
(1) COB integrated package
The COB integrated package has more than 30 kinds of package structures such as MCOB, COMB, MOFB and MLCOB. The COB packaging technology is becoming more and more mature, and its advantage is low cost. COB package now accounts for about 40% of LED light source market, light efficiency of 160~178 lm/w, thermal resistance up to 2 °C/w, COB package is the trend of recent LED package development.
(2) LED crystal garden grade package
The crystal-scale package is made of epitaxial LED devices. Once dicing, it is a multi-system integrated package for LED illumination sources. The general substrate is made of silicon material, which does not require die bonding and pressure bonding, and is formed by dispensing to form a system integrated package. The advantage is that the reliability is good and the cost is low, which is one of the development directions of the packaging technology.
(3) COF integrated package
The COF integrated package is a large-area assembled medium-power LED chip on a flexible substrate. It has the advantages of high thermal conductivity, thin layer flexibility, low cost, uniform light emission, high light efficiency, and flexible surface light source, and can provide line light source, surface light source and The various LED products of the three-dimensional light source can also meet the requirements of LED modern lighting and personalized lighting, and can also be used as a general-purpose package component, and the market prospect is promising.
(4) LED modular integrated package
Modular integrated package generally refers to system integration and packaging of LED chip, driving power supply, control part (including IP address), parts, etc., collectively referred to as LED module, which has many advantages such as saving materials, reducing cost, standardizing production, and convenient maintenance. Is the direction of LED packaging technology development.
(5) flip chip packaging technology
The flip chip packaging technology forms a space from the chip, the substrate and the bump, so that the packaged chip has the advantages of small volume, high performance, short connection, etc., using ceramic substrate, flip chip, eutectic process, direct pressure Meet to achieve high power lighting performance requirements.
The chip is pressed onto the substrate with a gold-tin alloy to replace the conventional silver glue process, and the "direct press-fit" replaces the "reflow soldering" in the past, and has excellent electrical conductivity and heat-conducting area. This packaging technology is an important development trend of high-power LED packaging.
(6) Package-free chip technology
The package-free technology is a technology integration, using flip chip, without solid crystal glue, gold wire and bracket is one of the 70 process formation of semiconductor packaging technology.
The PFC package-free chip product can be upgraded to 200lm/w, and the ultra-wide-angle full-period design with an illumination angle greater than 300 degrees. Do not use secondary optical lenses, which will reduce the loss of light efficiency and reduce costs, but it will cost expensive. device.
PFC's new products are mainly used in the LED lighting market, especially on candle lamps, which can not only simulate the shape of tungsten lamps, but also break through the limitation of heat dissipation volume.
(7) LED other package structure
1EMC package structure: Embedded LED chip does not directly see the LED light source.
2EMC packaging technology: (Epoxy Molding Compound) with epoxy molding compound as the packaging technology, with high heat resistance, high integration, anti-UV, small size and other advantages, but the airtightness is poor, has been mass-produced.
3COG package: (Chip On Glass) The LED chip is placed on a glass substrate for packaging.
4QFN packaging technology: When the pixel unit of the small-pitch display is less than or equal to P.1, the package form used will replace the PLCC structure, and the market prospect is promising.
53D packaging technology: The technology of packaging in three-dimensional form is under development.
6 Power-frame packaging technology: (Chip-in-Frame Package) The power LED chip is packaged on a small frame, and the industrialized light efficiency has reached 160~170 lm/w, which is more than 200 lm/w.
LED packaging material
There are many types of LED packaging materials, and they are constantly evolving. They are only briefly introduced here.
(1) Packaging materials
Epoxy resin, epoxy molding compound, silica gel, silicone plastic, etc., technically have requirements for refractive index, internal stress, bonding force, air tightness, high temperature resistance, and ultraviolet resistance.
(2) Solid crystal material
1 solid crystal glue: resin and silica gel, filled with metal and ceramic materials.
2 eutectic: AuSn, SnAg/SnAgCu.
(3) Substrate material: metal alloy materials such as copper and aluminum
1 ceramic material: Al2O3, AlN, SiC, etc.
2 Aluminum-based ceramic materials: called third-generation packaging materials such as AlSiC, AlSi, and the like.
3SCB substrate material: Multi-laminated mold substrate, good heat dissipation (thermal conductivity 380w/m.k), low cost.
The 4TES polycrystalline semiconductor ceramic substrate has a fast heat transfer rate.
(4) Heat dissipating material: metal alloy materials such as copper and aluminum
Graphene composite material, thermal conductivity 200~1500w/m.k.
PCT high temperature special engineering plastics (polybutylene terephthalate 1,4-cyclohexane), with ceramic fiber, high temperature resistance, low water absorption.
Thermal engineering plastic: non-insulated thermal engineering plastic, thermal conductivity 14w/m.k.
Insulation type thermal conductive engineering plastic with thermal conductivity of 8w/m.k.