JP5681035B2 - LED light source package - Google Patents

Description

The present invention relates to an LED light source package.

An LED light-emitting element (hereinafter referred to as “LED chip”) is an element that emits light when a forward current flows through a pn junction of a semiconductor, and is manufactured using a III-V group semiconductor crystal such as GaAs or GaN. In recent years, with the progress of semiconductor epitaxial growth technology and light emitting device process technology, LED chips with excellent conversion efficiency have been developed and widely used in various fields.

The LED chip is composed of a p-type layer and an n-type layer obtained by epitaxially growing a group III-V semiconductor crystal on a growth substrate, and a photoactive layer sandwiched therebetween. Generally, a group III-V semiconductor crystal is epitaxially grown on a growth substrate such as single crystal sapphire, and then an electrode or the like is formed to form an LED chip.

Since the single crystal sapphire has a thermal conductivity of about 40 W / mK, the heat generated in the III-V group semiconductor element cannot be sufficiently dissipated. In particular, in a high-power LED through which a large current flows, the temperature of the element rises, causing a decrease in luminous efficiency and a decrease in element life. In order to solve this, a method has been proposed in which a III-V semiconductor crystal is epitaxially grown on a growth substrate, a package substrate (holding substrate) is bonded through a metal layer, and then the growth substrate is removed. (Patent Document 1) was not satisfactory. That is, since the metal package substrate (holding substrate) is also conductive, it must have a non-insulating structure for mounting. For example, when soldering to a mounting board such as a circuit board, it is necessary to dispose an insulating layer having a low thermal conductivity such as a resin directly under the joint, but this insulating layer hinders sufficient heat dissipation.

On the other hand, in a high-power LED light emitting device (hereinafter referred to as “LED light source module”) in which two or more LEDs are connected in order to reduce the trouble caused by heat generation of the LED chip, a heat sink, for example, a copper (Cu) plate is used. A method of mounting an LED light source module on a circuit board or the like has been proposed (Patent Document 2). However, since the thermal expansion coefficient of Cu is about 17 × 10 ⁻⁶ / K, which is largely different from about 5 × 10 ⁻⁶ / K of the LED light source module, when a thermal load is applied to the LED light source module, Thermal stress is generated due to the difference in coefficient of thermal expansion between the LED light source module and the metal circuit board, which may cause warpage of the metal circuit board. In addition, there is a problem that cracks are generated in the bonding layer due to thermal stress, and as a result, heat radiation becomes insufficient, causing the LED chip to malfunction or break.

JP 2006-128710 A Special table 2008-544488

Therefore, an aluminum-silicon carbide composite has been proposed as a circuit board having a thermal expansion coefficient close to that of a metal circuit board. The aluminum-silicon carbide composite for the circuit board is manufactured by a forging method in which a silicon carbide porous body is impregnated with a molten aluminum alloy, and a silicon carbide porous body is not pressurized with a molten aluminum alloy. A non-pressure impregnation method infiltrated with the use of is practically used. On the other hand, from the viewpoint of cost, a powder metallurgy method in which aluminum powder and silicon carbide powder are mixed and heat-molded is advantageous, and an aluminum-silicon carbide composite by the same production method has been studied. However, since aluminum-silicon carbide composites of any manufacturing method have a problem in cost, an inexpensive copper circuit board is often used in a field where cost reduction is required. There was a problem in the reliability between circuit boards.

A metal such as copper or aluminum used for a metal circuit board has a large thermal expansion coefficient of about 17 × 10 ⁻⁶ to 23 × 10 ⁻⁶ / K, and an LED having a thermal expansion coefficient of about 5 × 10 ⁻⁶ / K.
Since the difference in thermal expansion coefficient from the chip is large, thermal stress is generated, and warpage of the metal circuit board and cracks occur in the bonding layer.

This invention is made | formed in view of said situation, The objective is by mounting | wearing the stress relaxation board which has a thermal expansion coefficient between a LED light source module and a metal circuit board, and by thermal expansion coefficient difference. It is an object to provide an LED light source package that can relieve the generated stress and achieve improved reliability.

Between the LED light source module in which two or more LED chips are connected to the surface of the insulating ceramic substrate and the metal circuit board, the Young's modulus is 70 GPa or less, and the thermal expansion coefficient at 25 ° C. to 150 ° C. is 5 × 10 ⁻⁶ to 12 × 10 ⁻⁶ / K, a thermal conductivity of 150 W / mK or more, and a stress relaxation plate made of a flat aluminum-graphite composite having a thickness of 0.5 to 3.0 mm is mounted. It is the LED light source package characterized by these.

In the LED light source package of the present invention, (a) the stress relaxation plate is a plate-shaped metal-impregnated ceramic substrate in which a graphite porous body or graphite powder compact and aluminum or an aluminum alloy are combined, It is preferable to have at least one embodiment selected from the fact that the volume fraction of graphite in the aluminum-graphite composite is 60 to 85% by volume.

The present invention also includes: (c) soldering between the aluminum-graphite composite with the plated layer and the LED light source module and the metal circuit board; (d) between the LED light source module and the aluminum-graphite composite; The aluminum-graphite composite and the metal circuit board are brazed, and the brazing material used in (2) contains at least one of tin, copper, silver, zinc, and bismuth. It is preferred to have at least one selected embodiment.

According to the present invention, by optimizing the particle size, type and content of graphite used for the stress relaxation plate, and by optimizing the metal component, the obtained stress relaxation plate is placed between the LED light source module and the metal circuit board. Therefore, it is possible to provide an LED light source package that can achieve good matching with respect to both the LED light source module side and the metal circuit board side, and has significantly improved reliability.

Furthermore, since the thermal conductivity is 150 W / mK or more, the heat from the LED light source module can be transferred well to the metal circuit board, and can be suitably used as an LED light source package.

<LED light source module>
The LED light source module in the present specification includes two or more LED light emitting elements made of III-V group semiconductor crystal and LED chips made of a holding substrate mounted on a circuit board and connected by an electrical connection member, and a resin sealing material The basic structure is to be sealed with.

As the LED light emitting element, a III-V group semiconductor crystal emitting light in the ultraviolet to blue wavelength region is used, and specifically, InGaN, AlGaAs, AlGaInP, or the like. The holding substrate is a growth substrate used for epitaxially growing a group III-V semiconductor crystal, or after a group III-V semiconductor crystal is epitaxially grown on the growth substrate, a high thermal conductivity substrate is bonded via a metal layer. Then, the high thermal conductivity substrate from which the growth substrate has been removed. Examples thereof are sapphire, silicon carbide, silicon, Cu / W, Cu / Mo, and the like. Among these, in the LED chip that requires an output of 0.5 W or more, the holding substrate belonging to the latter is used from the viewpoint of thermal conductivity, and the LED chip has a non-insulating structure. The advantage of the non-insulating LED chip is that high brightness can be obtained in a small area.

The stress relaxation plate used for the LED light source package of the present invention has a plate thickness of 0.5 to 3.0 mm, preferably 0.5 to 2.0 mm. Since the LED light source package is formed by forming a metal layer on the surface of the stress relaxation plate and then soldering or brazing between the LED light source module and the metal circuit board, the heat from the LED light source module is good for the metal circuit board. Thus, an LED light source package having high reliability can be realized.

If the thickness of the stress relaxation plate is less than 0.5 mm, the stress relaxation layer is too thin to relieve stress and reliability is lowered. On the other hand, if it exceeds 3.0 mm, the thermal resistance of the stress relaxation plate increases.

The Young's modulus of the stress relaxation plate is 70 GPa or less, preferably 50 GPa or less. If the Young's modulus of the stress relaxation plate is 70 GPa or more, the stress caused by the difference in thermal expansion of the LED package cannot be relaxed by the stress relaxation plate, and the reliability is lowered. The lower limit of Young's modulus is not particularly limited, but is preferably 10 GPa or more. The Young's modulus can be determined by optimizing the particle size, type, and content of graphite used for the stress relaxation plate. For example, increasing the graphite content decreases the Young's modulus, and decreasing the graphite content increases the Young's modulus. Moreover, it can control by optimization of a metal component.

The thermal conductivity of the stress relaxation plate at a temperature of 25 ° C. is 150 W / mK or more, preferably 200 W / mK or more. If it is less than 150 W / mK, the heat from the LED light source module cannot be sufficiently transferred to the metal circuit board. The semiconductor may malfunction or be damaged.

Moreover, it is preferable that the thermal expansion coefficient of a stress relaxation board is a thermal expansion coefficient between an LED light source module and a metal circuit board.
When the thermal expansion coefficient of the stress relaxation plate is outside the above range, the thermal load during operation of the LED chip may cause damage to the bonding layer (solder layer, etc.) and the LED light source module, resulting in deterioration of heat dissipation characteristics. Moreover, the thermal expansion coefficient of a stress relaxation board can be increased / decreased by increasing / decreasing the content rate of the metal to compound.

The stress relaxation plate made of an aluminum-graphite composite has a graphite volume fraction of 50 to 90% by volume, preferably 60 to 85% by volume, and the balance is made of aluminum or an aluminum alloy, preferably aluminum 80 to 100%. It is a composite of aluminum or aluminum alloy that is mass% and silicon is 0 to 20 mass%.
As a method of combining graphite and aluminum or an aluminum alloy, it is preferable that the graphite is manufactured by a molten forging method impregnated by a method such as the example of Japanese Patent No. 3468358.

Also, instead of the above-mentioned molten metal forging method, a mixed powder of graphite powder and aluminum or aluminum alloy powder is filled into a mold subjected to a release treatment, and heated to a temperature equal to or higher than the melting point of aluminum or aluminum alloy, and then pressed to be combined. Even those produced by the method can be used.

The pressure required for combining graphite powder with aluminum or an aluminum alloy is preferably 30 MPa or more. If the pressure at the time of hot press molding is less than 30 MPa, the adhesion between the graphite powder and aluminum or aluminum alloy is insufficient, and properties such as thermal conductivity and strength are not preferred. Further, the upper limit of the press pressure is not limited in terms of characteristics, but 200 MPa or less is appropriate from the strength of the mold and the strength of the apparatus. The aluminum-graphite composite is depressurized at a temperature below the melting point and then cooled to room temperature. In addition, annealing treatment of the aluminum-graphite composite may be performed for the purpose of removing strain at the time of compounding.

The volume ratio of graphite is preferably 50 to 90% by volume, particularly 60 to 85% by volume.
When the volume fraction of graphite is less than 50% by volume, the thermal expansion coefficient of the aluminum-graphite composite becomes too large. On the other hand, if it exceeds 90% by volume, the metal cannot be sufficiently impregnated and the thermal conductivity may be too small. The graphite filling state is not particularly limited, and a graphite porous body or a graphite powder molded body can be used. The volume ratio of graphite can be adjusted by adjusting the particle size of the graphite component, shaping pressure, sintering conditions, and the like.

The metal component to be combined with graphite is preferably aluminum or aluminum alloy containing 80 to 100% by mass of aluminum and 0 to 20% by mass of silicon. If the silicon component exceeds 20% by mass, the melting point of the alloy increases, and an unimpregnated portion may occur. On the other hand, when the silicon component exceeds 20% by mass, the thermal conductivity of the obtained alloy is lowered, and as a result, the thermal conductivity of the obtained aluminum-graphite composite is lowered, which is not preferable. The component other than the silicon component is not particularly limited as long as it does not affect the properties, but magnesium has an effect of improving the wettability of the obtained alloy and graphite, and if it is within 3% by mass, the production of aluminum carbide adversely affecting the strength and thermal conductivity (Al 4 _{C 3)} may contain can be suppressed.

The graphite powder molded body can be produced by molding only the powder of the graphite component, or can be produced using an inorganic binder such as silica sol or alumina sol. Other ceramic powders such as silicon carbide, silicon nitride, aluminum nitride, and boron nitride may be added to the graphite powder compact as long as the characteristics are not affected. For the molding, a general graphite powder molding method such as press molding or cast molding is employed. Moreover, a graphite porous body can be manufactured by carrying out the sintering process of the said graphite powder molded object, for example. There is no restriction | limiting in the shape of a graphite porous body and a graphite powder molding, It uses by flat form, a column shape, etc.

The graphite porous body or graphite powder molded body impregnated with metal is usually used for an LED package after being subjected to cutting and surface processing. When the shape of the graphite porous body or graphite powder molded body impregnated with metal is a rectangular parallelepiped shape, the outer shape is processed to a predetermined size using a diamond grinding wheel with a surface grinding plate, and then the final shape is obtained with a multi-wire saw, an inner peripheral cutting machine It is preferable to cut to a thickness of about 0.1 to 0.5 mm thicker than the shape. There is no limitation on the cutting method, but a multi-wire saw having a small cutting margin and suitable for mass production is preferable. In the cutting of a multi-wire saw, a wire to which an abrasive such as a loose abrasive type and diamond is attached is used. In the surface processing, a plate thickness is processed to 0.3 to 3 mm using a processing machine such as a double-side grinding machine, a rotary grinding machine, a surface grinding machine, or a lapping machine.

When the shape of the graphite porous body or graphite powder molded body impregnated with metal is plate-like, use a processing machine such as a double-sided grinder, rotary grinder, surface grinder, lapping machine, etc., and the plate thickness is 0.3. Surface processing is performed to ˜3 mm and the surface roughness (Ra) is 1.0 μm or less, and then outer periphery processing is performed into a predetermined shape with a water jet processing machine, an electric discharge processing machine, a laser processing machine, a dicing machine, a cylindrical grinding machine or the like. In this case, surface processing may be performed after the outer periphery processing is performed first.

The aluminum-graphite composite has a thickness of 0. 1 on the surface of at least one metal selected from Ni, Co, Pd, Cu, Ag, Au, Pt and Sn, particularly preferably Ni or Au. It is preferable to have a plating layer of 5 to 20 μm. A particularly preferable plating layer thickness is 2 to 10 μm. By forming the plating layer, the adhesion state of the LED light source module, the stress relaxation plate, and the metal circuit board is improved. If the thickness of the metal layer is less than 0.5 μm, the adhesion state is deteriorated, and if it exceeds 20 μm, there is a risk of peeling due to the difference in thermal expansion between the plating layer and the stress relaxation plate. The plating layer can be formed by washing the stress relaxation plate and then performing electroless plating or electrolytic plating with the above metal species.

The LED light source module, the stress relaxation plate, and the metal circuit board are joined using soldering or brazing. As the solder, cream solder, eutectic solder, lead-free solder or the like may be used. For brazing, it is preferable to use a brazing material containing at least one of tin, copper, silver, zinc, and bismuth.

[Example 1]
A graphite plate (manufactured by Tokai Carbon Co., Ltd .: G250, volume ratio: 78%, dimensions: 185 mm × 135 mm × 5.0 mm) is sandwiched between release plates made of stainless steel plate coated with graphite release material, and iron plates ( (Thickness 12 mm) is arranged and connected with eight bolts to form a single laminate. The laminate is preheated to a temperature of 630 ° C. in an electric furnace, and then stored in a preheated press mold (inner diameter: 400 mm × height: 300 mm), and contains 12% by mass of silicon and 1% by mass of magnesium. A molten aluminum alloy (temperature: 800 ° C.) was poured, and the aluminum alloy was impregnated by applying pressure of 100 MPa for 25 minutes. After cooling to room temperature, cut with a wet band saw along the shape of the release plate, peel off the release plate, and anneal for 3 hours at 500 ° C. to remove strain during impregnation. Aluminum alloy-graphite composite Got the body.

From the composite for evaluation obtained above, a thermal expansion coefficient measurement specimen (diameter 4 mm, length 20 mm), a thermal conductivity measurement specimen (25 mm × 25 mm × 1 mm), a Young's modulus measurement test by grinding. The body (40 mm × 4 mm × 3 mm) was cut out, the thermal expansion coefficient at a temperature of 25 ° C. to 150 ° C. was measured with a thermal dilatometer (Seiko Denshi Kogyo Co., Ltd .; TMA300), and the thermal conductivity at a temperature of 25 ° C. was measured by the laser flash method (ULVAC Young's modulus was measured with a bending strength tester (manufactured by Imada Seisakusho; SV301).

In addition, the aluminum alloy-graphite composite obtained above was cut with a diamond cutter into a plate having a length of 40 mm, a width of 40 mm, and a thickness of 1 mm, and then electroless Ni-P plating was performed to obtain a plating layer (5 μm thick). ) Was formed. Further, an LED light source module and an Al circuit board were joined to the plate-like aluminum alloy-graphite composite with lead-free solder, and then joined to an external lead-out conductive pattern by wire bonding to produce an LED light source package.

<Evaluation of reliability of LED light source package>
After holding the LED light source package in a constant temperature bath at −40 ° C. and 125 ° C. for 30 minutes and performing a heat cycle treatment (500 times), the appearance and bonding state were confirmed by ultrasonic flaw detection. The location was not confirmed.

[Example 2]
An LED light source was obtained in the same manner as in Example 1 except that the aluminum alloy-graphite composite obtained in Example 1 was cut out with a diamond cutter into a plate having a length of 40 mm, a width of 40 mm, and a thickness of 0.5 mm. Packaged.

[Example 3]
An LED light source was obtained in the same manner as in Example 1 except that the aluminum alloy-graphite composite obtained in Example 1 was cut out with a diamond cutter into a plate having a length of 40 mm, a width of 40 mm, and a thickness of 3.0 mm. Packaged.

[Example 4]
An aluminum alloy-graphite composite was produced in the same manner as in Example 1 except that the graphite plate was made by Toyo Tanso Co., Ltd. (MIC25, volume ratio 83%), and LED light source packaging was performed.

[Example 5]
An aluminum alloy-graphite composite was produced in the same manner as in Example 1 except that the graphite plate was made by Toyo Tanso Co., Ltd. (IE252G, volume ratio 60%), and LED light source packaging was performed.

[Example 6]
1000 g of artificial graphite powder (manufactured by Kobayashi Shoji Co., Ltd .: DSC-A, fixed carbon content: 99.25%) and 183 g (10 vol%) of silicon carbide powder (manufactured by Taiyo Random Co., Ltd .: NC2000, average particle size: 7 μm) After mixing, the mixture is filled in a cylindrical (inner diameter 100 mm, height 150 mm) iron container, and the volume ratio is 80% by volume in a state where the upper and lower sides are sandwiched between iron plates with holes for gates, By press molding at a pressure of 80 MPa, a cylindrical (diameter 100 mm, height 90 mm) shaped body was obtained.

In addition, the said iron container and the iron plate arrange | positioned at the upper and lower sides of this container were welded and sealed after shaping | molding. The obtained molded body was held in an iron container, preheated to a temperature of 630 ° C. in an electric furnace, and then stored in a preheated press mold (inner diameter 400 mm × height 300 mm). A molten aluminum alloy (temperature 800 ° C.) containing 12% by mass and 1% by mass of magnesium was poured, and the aluminum alloy was impregnated by applying pressure at 100 MPa for 25 minutes.
The obtained composite was packaged with an LED light source in the same manner as in Example 1.

[Example 7]
An aluminum alloy-graphite composite was produced in the same manner as in Example 5 except that the amount of silicon carbide powder added was 20% by volume, and LED light source packaging was performed.

[Comparative Example 1]
An LED light source was obtained in the same manner as in Example 1 except that the aluminum alloy-graphite composite obtained in Example 1 was cut with a diamond cutter into a plate having a length of 40 mm, a width of 40 mm, and a thickness of 0.3 mm. After packaging and heat cycle treatment (500 times), cracks in the stress relaxation plate were confirmed.

[Comparative Example 2]
An LED light source was obtained in the same manner as in Example 1 except that the aluminum alloy-graphite composite obtained in Example 1 was cut with a diamond cutter into a plate having a length of 40 mm, a width of 40 mm, and a thickness of 5.0 mm. After packaging and heat cycle treatment (500 times), solder cracks were confirmed.

[Comparative Example 3]
An aluminum alloy-graphite composite was prepared in the same manner as in Example 1 except that the graphite plate was G458 (volume ratio: 85%) manufactured by Tokai Carbon Co., Ltd., packaged with an LED light source, and heat cycle treated After performing (500 times), when the external appearance and the bonding state were confirmed by ultrasonic flaw detection, solder cracks were confirmed in the bonding layer.

[Comparative Example 4]
An aluminum alloy-graphite composite was produced in the same manner as in Example 1 except that the graphite plate was G535 (volume ratio: 84%) manufactured by Tokai Carbon Co., Ltd., packaged with an LED light source, and heat cycle treated After performing (500 times), when the external appearance and the bonding state were confirmed by ultrasonic flaw detection, solder cracks were confirmed in the bonding layer.

[Comparative Example 5]
An aluminum alloy-graphite composite was prepared in the same manner as in Example 5 except that the amount of silicon carbide powder added was 30% by volume, packaged with an LED light source, and heat cycled (500 times). After that, when the appearance and bonding state were confirmed by ultrasonic flaw detection, solder cracks were confirmed in the bonding layer.

[Comparative Examples 6 and 7]
A stress relieving plate was produced in the same manner as in Example 1 except that a silicon carbide porous body made of silicon carbide having a volume ratio of 65 and 80% was used as the ceramic porous body instead of the graphite plate, and the LED light source packaged. After performing the heat cycle treatment (500 times) and confirming the appearance and bonding state by ultrasonic flaw detection, solder cracks were confirmed in the bonding layer.

Table 1 shows main conditions and results of Examples and Comparative Examples.

Claims (5)

Between the LED light source module in which two or more LED chips are connected to the surface of the insulating ceramic substrate and the metal circuit board, the Young's modulus is 70 GPa or less, and the thermal expansion coefficient at 25 ° C. to 150 ° C. is 5 × 10 ⁻⁶ to 12 × 10 ⁻⁶ / K, a thermal conductivity of 150 W / mK or more, and a stress relaxation plate made of a flat aluminum-graphite composite having a thickness of 0.5 to 3.0 mm is mounted. LED light source package characterized by the above. 2. The LED light source package according to claim 1, wherein the stress relaxation plate is a plate-like metal-impregnated ceramic substrate in which a graphite porous body or a graphite powder compact and aluminum or an aluminum alloy are combined. 3. The LED light source package according to claim 1, wherein the volume ratio of graphite in the aluminum-graphite composite is 60 to 85% by volume. Aluminum having at least one plating selected from Ni, Co, Pd, Cu, Ag, Au, Pt, and Sn having a thickness of 0.5 to 20 μm formed on both main surfaces of the aluminum-graphite composite The LED light source package according to any one of claims 1 to 3, wherein the graphite composite, the LED light source module, and the metal circuit board are soldered or brazed. The LED light source package according to claim 4, wherein the brazing material contains at least one of tin, copper, silver, zinc, and bismuth.