2013年01月15日
High Power LED Cooling
Discussion and Prospect: High Power LED Package Cooling Technology
For a long time, the led heat requirements are not very high case, led more than traditional resin substrate and encapsulation. However, with the market expanding applications continuously improve the level of demand, the The traditional resin substrate after the arrival of the high-power led generations, has gradually inadequate. Therefore, to explore and prospect of high power led packaging materials, has become a hot topic of concern to the industry.
LED cooling principle studies have shown that high power led only 20% of the electrical energy into light energy, the rest will be lost in the form of heat. Up to 80% of the heat energy can not be lost, then led the life will be greatly reduced. led the heat exactly how lost it?
LED cooling capacity usually by encapsulation mode, and the thermal conductivity of the material of the package, the thermal path nor outside conduction, convection, and radiation of these three. As the heat led packaging materials accumulate in the conduction loss package material selection becomes particularly important.
Traditional media is unable to meet the high power led heat demand
With the the market growing number of high-power led applications appear, while considering how lost heat, but also on the stability and continuity of led light. If the heat energy of the LEDs can not be lost, as soon as possible so the brightness and lifetime will decrease rapidly. So, for high power led, traditional epoxy resin by its features are limited, no longer meet the cooling needs.
LED low power or power under conditions of use, the epoxy resin thermal conductivity is lower and the disadvantage of poor heat resistance have not yet been fully apparent. But use epoxy resin material as encapsulated high power led, is likely to appear before the led chip life has not been reached, the epoxy resin has been unsustainable.
In addition, not only the cooling phenomenon causes the epoxy resin changes, even the short wavelength also epoxy causing distress. This is because the white LED emission spectrum also includes the short wavelength light, while epoxy resins are susceptible to the short wavelength light in the white led destruction. Even low-power white led epoxy destruction can exacerbate, not to mention the issue of high power white led short-wavelength light more deteriorated naturally more rapid and severe. Thus, finding new material to replace epoxy encapsulated high power led imminent.
LED heat sink substrate type
At present, the common LED type of heat dissipation board comprising: a rigid printed circuit board, a high thermal conductivity aluminum plate, a ceramic substrate, a flexible printed circuit board, metal composites, and the like.
The rigid printed circuit board (printedcircuitboard; PCB) used for various electronic substrate, LED controller but can not afford the dissipated heat out of the high power led, so applications limited to the low power and the general power LED does not have to high-power LED The possibility of extending the application.
The high thermal conductivity aluminum plate (metalcorePCB; mcPCB) is the PCB below the base material instead of aluminum alloy, general, pure aluminum heat coefficient than aluminum, but because of the hardness of pure aluminum is not high cause difficulties in the use so only when making aluminum substrate material.
Ceramic substrate three, al2o3 (alumina), ltcc (low temperature co-fired ceramic), the aln (AIN). Technical standards alone, no doubt to aluminum nitride highest low temperature co-fired ceramic followed. Led substrate, produced by low-temperature co-fired ceramic heat better, and the high temperature, moisture resistance, etc., but its price is higher than the traditional board several times, until today is still not ideal for production of heat-type substrate material. Of course, if you do not consider the price factor, the ceramic substrate or a well-deserved first choice.
Flexible printed circuit board (fpc) has the advantages of light weight, thin, flexible, flexible use of space, and the coefficient of thermal conductivity is superior to the traditional the the PCB substrate and mcPCB substrate and application area larger than the ceramic substrate. However, the technology is still at the experimental stage, the yield is low, and so could not be put into large-scale.
Metal substrate to become the preferred high-power led
Through the above comparison, the most cost-effective due to the metal substrate relative terms, so it has also become the preferred solution led high power conditions. With footsteps led chips, large-scale, high-current, high-power development, to replace the traditional metal package substrate resin package substrate will be faster.
The purpose of the high heat metal substrate material, can be divided into rigid and flexible two. The LED controller structure, the rigid substrate is a conventional metal material, using a metal such as aluminum, copper, high thermal conductivity of the insulating layer portion is mostly populated inorganics. This metal substrate has a high thermal conductivity, high heat resistance, as well as electromagnetic shielding, etc., and its thickness is usually greater than 1 mm, it is widely used in which the LED lighting module and the lighting module, and contribute significantly to the high power LEDs in the lights the promotion and popularization.
Flexible substrate promising
In general, the efficiency of the thermal conductivity of the metal package substrate about 2w / m • k. But because of the higher thermal requirements of high efficiency led, so in order to meet the efficiency of the thermal conductivity of the 4 ~ 6w / m • k, has the efficiency of the thermal conductivity more than 8w / m • k metal package substrate. The rigid metal packaging substrate to meet high power led package each package substrate manufacturers are actively developing the technology can improve the efficiency of the thermal conductivity.
However, the metal package substrate has the same great disadvantage of metal thermal expansion coefficient the the LED controller when welding with low thermal expansion coefficient of the ceramic chip vulnerable to the impact of thermal cycling, so when the aluminum nitride packaging, metal packaging substrate disharmony may occur, and is therefore necessary to overcome the difference of thermal stress between the led in a variety of different thermal expansion coefficient material, and to improve the reliability of the package substrate.
Flexible substrate appears precisely to solve the above problems. The highly thermally conductive flexible substrate, on the insulating layer-adhesive metal foil, Although the basic structure of the conventional flexible substrate are identical, but in the insulating layer, LED controller is the soft epoxy resin filled with thermally conductive inorganic substance and therefore has a high thermal conductivity of 8w / m? k, and also both the advantages of the soft, flexible and high reliability. In addition, the flexible substrate is also in accordance with customer demand, single-sided single-layer board design into a single-sided double-layer, double-sided double-layer board. According to the experimental results show that the use of high thermal conductivity flexible substrate led temperature can be reduced by approximately 100 degrees Celsius, which can greatly improve the service life of the led.
For a long time, the led heat requirements are not very high case, led more than traditional resin substrate and encapsulation. However, with the market expanding applications continuously improve the level of demand, the The traditional resin substrate after the arrival of the high-power led generations, has gradually inadequate. Therefore, to explore and prospect of high power led packaging materials, has become a hot topic of concern to the industry.
LED cooling principle studies have shown that high power led only 20% of the electrical energy into light energy, the rest will be lost in the form of heat. Up to 80% of the heat energy can not be lost, then led the life will be greatly reduced. led the heat exactly how lost it?
LED cooling capacity usually by encapsulation mode, and the thermal conductivity of the material of the package, the thermal path nor outside conduction, convection, and radiation of these three. As the heat led packaging materials accumulate in the conduction loss package material selection becomes particularly important.
Traditional media is unable to meet the high power led heat demand
With the the market growing number of high-power led applications appear, while considering how lost heat, but also on the stability and continuity of led light. If the heat energy of the LEDs can not be lost, as soon as possible so the brightness and lifetime will decrease rapidly. So, for high power led, traditional epoxy resin by its features are limited, no longer meet the cooling needs.
LED low power or power under conditions of use, the epoxy resin thermal conductivity is lower and the disadvantage of poor heat resistance have not yet been fully apparent. But use epoxy resin material as encapsulated high power led, is likely to appear before the led chip life has not been reached, the epoxy resin has been unsustainable.
In addition, not only the cooling phenomenon causes the epoxy resin changes, even the short wavelength also epoxy causing distress. This is because the white LED emission spectrum also includes the short wavelength light, while epoxy resins are susceptible to the short wavelength light in the white led destruction. Even low-power white led epoxy destruction can exacerbate, not to mention the issue of high power white led short-wavelength light more deteriorated naturally more rapid and severe. Thus, finding new material to replace epoxy encapsulated high power led imminent.
LED heat sink substrate type
At present, the common LED type of heat dissipation board comprising: a rigid printed circuit board, a high thermal conductivity aluminum plate, a ceramic substrate, a flexible printed circuit board, metal composites, and the like.
The rigid printed circuit board (printedcircuitboard; PCB) used for various electronic substrate, LED controller but can not afford the dissipated heat out of the high power led, so applications limited to the low power and the general power LED does not have to high-power LED The possibility of extending the application.
The high thermal conductivity aluminum plate (metalcorePCB; mcPCB) is the PCB below the base material instead of aluminum alloy, general, pure aluminum heat coefficient than aluminum, but because of the hardness of pure aluminum is not high cause difficulties in the use so only when making aluminum substrate material.
Ceramic substrate three, al2o3 (alumina), ltcc (low temperature co-fired ceramic), the aln (AIN). Technical standards alone, no doubt to aluminum nitride highest low temperature co-fired ceramic followed. Led substrate, produced by low-temperature co-fired ceramic heat better, and the high temperature, moisture resistance, etc., but its price is higher than the traditional board several times, until today is still not ideal for production of heat-type substrate material. Of course, if you do not consider the price factor, the ceramic substrate or a well-deserved first choice.
Flexible printed circuit board (fpc) has the advantages of light weight, thin, flexible, flexible use of space, and the coefficient of thermal conductivity is superior to the traditional the the PCB substrate and mcPCB substrate and application area larger than the ceramic substrate. However, the technology is still at the experimental stage, the yield is low, and so could not be put into large-scale.
Metal substrate to become the preferred high-power led
Through the above comparison, the most cost-effective due to the metal substrate relative terms, so it has also become the preferred solution led high power conditions. With footsteps led chips, large-scale, high-current, high-power development, to replace the traditional metal package substrate resin package substrate will be faster.
The purpose of the high heat metal substrate material, can be divided into rigid and flexible two. The LED controller structure, the rigid substrate is a conventional metal material, using a metal such as aluminum, copper, high thermal conductivity of the insulating layer portion is mostly populated inorganics. This metal substrate has a high thermal conductivity, high heat resistance, as well as electromagnetic shielding, etc., and its thickness is usually greater than 1 mm, it is widely used in which the LED lighting module and the lighting module, and contribute significantly to the high power LEDs in the lights the promotion and popularization.
Flexible substrate promising
In general, the efficiency of the thermal conductivity of the metal package substrate about 2w / m • k. But because of the higher thermal requirements of high efficiency led, so in order to meet the efficiency of the thermal conductivity of the 4 ~ 6w / m • k, has the efficiency of the thermal conductivity more than 8w / m • k metal package substrate. The rigid metal packaging substrate to meet high power led package each package substrate manufacturers are actively developing the technology can improve the efficiency of the thermal conductivity.
However, the metal package substrate has the same great disadvantage of metal thermal expansion coefficient the the LED controller when welding with low thermal expansion coefficient of the ceramic chip vulnerable to the impact of thermal cycling, so when the aluminum nitride packaging, metal packaging substrate disharmony may occur, and is therefore necessary to overcome the difference of thermal stress between the led in a variety of different thermal expansion coefficient material, and to improve the reliability of the package substrate.
Flexible substrate appears precisely to solve the above problems. The highly thermally conductive flexible substrate, on the insulating layer-adhesive metal foil, Although the basic structure of the conventional flexible substrate are identical, but in the insulating layer, LED controller is the soft epoxy resin filled with thermally conductive inorganic substance and therefore has a high thermal conductivity of 8w / m? k, and also both the advantages of the soft, flexible and high reliability. In addition, the flexible substrate is also in accordance with customer demand, single-sided single-layer board design into a single-sided double-layer, double-sided double-layer board. According to the experimental results show that the use of high thermal conductivity flexible substrate led temperature can be reduced by approximately 100 degrees Celsius, which can greatly improve the service life of the led.
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