High power LED encapsulation base plate development trend - (AddTime - 2013-01-25)

For a long time display application has been LED luminous element main appeal, does not require LED high heat resistance, therefore LED most direct packaging in the general resin system base plate, but 2000 years later with the degree of micromixer mixing effect LED and qualitative change efficient development, especially the blue LED luminous efficiency of components for improve drastically, LCD, home appliances, automobile and other companies also began actively review the suitability of LED.

Now the digital home appliance with the graphic display rapidly became popular, and LED monomer cost continues to decline, that LED the scope of application, and intend to use LED industry expanded, especially the LCD panel companies face the European Union issued harmful material limited guidance (RoHS: Restriction of Hazardous Substances Directive) standard, and put forward in the future must be the mercury system Cold Cathode Lamp (CCFL: Cold Cathode Fluorescent Lamp) comprehensive no mercury change development policy, the result caused by high power LED needs more urgent.

Technology on high power LED package after the goods, when using cooling measures is very difficult, and this background have high cost efficiency, and is similar to the metal base plate contour cooling package base plate products development trend, become LED high efficiency change after the other one is main purpose focus.

Epoxy resin is not in high power demand

In the past LED output power is lesser, can use traditional FR4 and glass epoxy resin encapsulation base plate, however 200W led Flood light high power LED luminous efficiency of only 20% ~ 30%, and the chip area is very small, although the overall power consumption is very low, but the calorific value per unit area is large.

Automobile, 200W led Flood light and common people's livelihood industry has begun to actively review LED the applicability of the industry of high power LED to characteristics were save electricity, degree of micromixer mixing effect, long service life, high color reproducibility, this means that the cooling property better is high power LED packaging base plate integrality conditions.

Resin base plate heat dissipation limit mostly only support under 0.5 W LED, more than 0.5 W above LED packaging mostly use metal system with ceramic system high heat dissipation base plate, the main reason is the base of the heat resistance of LED life and has a direct impact on the performance, so the package base plate become design of micromixer mixing effect LED application products was very important element.

Metal series high heat dissipation base plate and into hard (rigid) and deflection (flexible) system base board two kinds, hard system base plate belongs to traditional metal base plate, the thickness of the base metal is usually greater than 1 mm, widely used in LED lamps and lanterns module and 200W led Flood light module, technically it with aluminum base plate the same level high heat conduction change is outspread, the future will be used in high power LED packaging.

Can deflection system base plate is the emergence of the car in order to meet the navigator and medium-sized LCD backlight module thin shape change, and high power LED three dimensional packaging requirements of the premise, through the aluminum base plate sheet change gives packaging substrates can deflection characteristics, then forms with high heat conductivity and bending property of high power LED packaging base plate.

High efficiency change metal base plate concern

Hard metal series packaging base plate is the use of traditional resin base plate or ceramic substrate, which gives high heat conductivity, processability, electromagnetic shielding property, heat resistant to impact and metal properties, a new generation of high power LED packaging base plate.

High power LED packaging base plate is the use of epoxy resin system then agent will copper foil stick in the surface of the base metal, through of the base metal and the combination of the insulating layer material change, make all sorts of use LED packaging base plate.

High heat resistance is high power LED package with base plate indispensable basic characteristics, so the above metal system LED packaging substrates using aluminum and copper materials, insulation layer are mainly used for heat conductivity inorganic Filler (Filler) epoxy resin. Aluminum base plate is the application of aluminium heat conductivity and lightweight properties to make high density packaging base plate, at present has been used in air conditioning system of converter (Inverter), communication equipment of power supply base plate, etc, also suitable for high power LED packaging.

Generally speaking, metal packaging base plate of the equivalent thermal conductivity standard is about 2 w/mK, to meet customer 4 ~ 6 w/mK high power change needs, companies have launched equivalent and heat conduction rate more than eight w/mK metal series packaging base plate. Because of hard metal series packaging base plate main purpose is to support high power LED packaging, so the package base plate manufacturers are actively development can improve the rate of heat transfer technology.

Hard metal series packaging base plate is chiefly characterized by its high heat resistance. High heat conductivity insulating layer encapsulation base plate, can greatly reduce the temperature of the LED chip. In addition base plate of the thermal design, through the radiator diaphragm and packaging base plate combination, still hope prolong the service life of LED chips.

Metal series packaging substrates are the shortcomings of the base metal thermal expansion coefficient is very large, and low thermal expansion coefficient ceramic system chip components are similar in welding, vulnerable to thermal cycle impact, if high power LED packaging use aluminum nitride, metal series packaging substrates may occur not harmonious, so must try to absorb LED module material coefficient of thermal expansion difference caused by thermal stress, the thermal stress relaxation and improve the reliability of the base board packaging.

Packaging base plate industry actively develop deflection base plate

But the main purpose of the base plate bending mostly concentrated in the wiring with base plate, previous high power transistor and IC contour heating elements hardly used deflection base plate, in recent years, liquid crystal display to meet the demand of micromixer mixing effect degree melts, strong demand can deflection base plate can be high density set high power LED, however, LED by the fever LED loss of life, but a very difficult technical issues, although the use of aluminum plate quality reinforcing plate can improve the heat resistance, but cost and assembly sex limit, cannot fundamentally solve the problem.

High heat conduction deflection base plate in the insulating layer paste metal foil, although the basic structure, and the traditional deflection base plate exactly the same, but the insulating layer using soft epoxy resin filling heat conductivity inorganic filler material, with hard metal series packaging base plate with rank 8 w/mK thermal conductivity, and at the same time, both soft can deflection, high heat transfer characteristics and high reliability. In addition can deflection base plate can also according to the customer demand, the single single panel design into a single double, double double structure.

High heat conduction deflection base plate is the main features of can set high heating elements and three yuan assembly, which can play free bending properties, and obtain high assembly space utilization.

According to the result of the experiment shows that use high heat conduction deflection base board, LED to reduce temperature of about 100 c, the mean temperature causes LED to reduce the service life of the presumed to improve. In fact in addition to high power LED besides, high heat conduction deflection base plate also can set up other high power semiconductor devices, it is suitable for short space or high density packaging requirements for high heat, etc.

The similar 200W led Flood light LED module cooling characteristics, only depending on the packaging substrates are often unable to meet the actual demand, so base plate with surrounding materials become very important, such as cooperate with 3 w/mK thermal conductivity diaphragm, can effectively improve the LED module cooling sex and assembly operation sex.

Ceramic package base slabs thermal skew is very favorable

As mentioned above the white light LED the heat with the increase of input power strength increasing, the LED chip temperature rise will cause light output is reduced, thus LED packaging structure and use material review is very important. In the past LED using low heat conduction rate resin encapsulation, is regarded as one of the reasons for the cooling characteristics influence, so in recent years gradually convert high heat conduction ceramic, or a metal plate resin encapsulation structure. High power LED chip change commonly used way including: LED chip large-scale, improve LED chip luminous efficiency, high light efficiency, and take the package big current change and so on.

Although improve current luminous quantity will increase in proportion, but LED chip calorific value will rise with the. Because in the high input field radiation intensity of illumination present saturation and attenuation phenomenon, this kind of phenomenon is mainly LED chip fever caused by high power LED chip, so change, you must solve the heat dissipation problems.

LED encapsulation in addition to protect the internal LED chip, but also both LED chip and external for electrical connection, the function such as heat. LED packaging requirements of the light from the LED chip can be efficient to take outside, so packaging must have high strength, high insulation, heat conductivity and high reflectivity, surprising is ceramic almost all of the above characteristics, in addition a snare ceramic heat resistance and resistance to light degradation sex than resin outstanding.

The traditional high cooling package is LED chip installed in the substrate

Belong to the substrate and coating resin around, but the encapsulation of metal thermal expansion coefficient and LED chip difference is quite large, when the temperature changes very big or packaging operation not was susceptible to thermal skew, causing chip defects or luminous efficiency lower.

The future LED chip facing large-scale development, thermal skew problems will inevitably become problems cannot be ignored, in view of the above questions, have close to the LED chip of the coefficient of thermal expansion of ceramic, is on the thermal skew countermeasures is very favorable material.

High power accelerated ceramic jig resin material

LED packaging with ceramic material into alumina and aluminum nitride, the thermal conductivity of alumina is epoxy resin 55 times, aluminum nitride is epoxy resin 400 times, so at present high power LED package with base plate are mainly used for heat transfer rate for 200 w/mK aluminum, or heat transfer rate for 400 w/mK copper metal packaging base plate.

Semiconductor IC chip cement separately using epoxy system cement, glass, tin, gold eutectic alloy materials. LED chip with cement in addition to the above heat conductivity, but based on the joint decrease when thermal stress and point of view, it also requires low temperature joint and low young's coefficient, etc., and meet the conditions of the cement were epoxy system cement filling silver epoxy resin, and gold eutectic alloy system of Au - 20% Sn.

Cement coated area and LED chip area are almost the same, so we can not expect horizontal thermal diffusion, can only hope in the vertical direction of the heat conductivity. According to the simulation results show that the temperature difference between the LED copula, thermal conductivity very good Au - Sn ratio low heat resistance silver filling epoxy resin cement is more outstanding.

LED packaging base plate of the thermal design, roughly divided into LED chip to frame body heat conduction, frame body to external thermal convey two big aspects.

The improvement of the heat conduction almost entirely on the evolution of materials, it is generally thought that with the LED chip large-scale, high current is changed, the development of high power change, the future will accelerate metal and ceramic packaging instead of traditional resin encapsulation, moreover LED chip copula is breach of one of the reasons for the heat dissipation, so thin joint technology for the future improvement project.

Improve LED heat emission to external thermal convey characteristics, in the past are mainly used for cooling fan and heat exchanger, due to noise and set up space, and many other restrictions, actually contain consumer, 200W led Flood light lamps and lanterns, manufacturers, do not want to use the above mandatory radiating element, this means that the imposition of thermal design must be much higher frame body and external contact area, and at the same time, improve packaging base plate and frame body heat resistance.

Specific countermeasures such as: high heat conduction copper layer surface coated by far infrared thermal radiation to promote the deflection cooling film, etc., according to the experimental results demonstrate that the use of the deflection cooling film cooling, heating element is almost as close to the cooling area of film cooling fan is same, if the deflection cooling film paste in packaging base plate, frame body, or will be blotted out layer directly coated in packaging base plate, frame body, theoretically can also increase the cooling property.

The high power LED encapsulation structure, want to be able to support the LED chip epitaxial joint subtle wiring technology; The development of relevant material, although aluminum nitride has high heat conduction change, but high heat conduction and reflectivity of the interactive relationship between became another one difficult problem, it is generally thought that the future if can improve the thermal conductivity aluminum nitride, the high power LED encapsulation material has positive help.