KR20080061792A - Manufacturing method for ceramic dbc substrate using cold spraying coating process - Google Patents

Abstract

A manufacturing method of a ceramic DBC(Direct Bonded Copper) substrate using a cold spraying coating process is provided to reduce manufacturing time and cost by simply coating a copper layer on ceramic base material through once coating or pre-treatment. A ceramic DBC substrate is manufactured by performing cold spraying coating of copper particles on ceramic base material. The copper particle has a diameter of 5 to 200um. In the cold spraying coating, a temperature of spraying gas is 300 to 450°C, and pressure of the spraying gas is 10 to 27kg/cm^2 just before a nozzle. The spraying gas is nitrogen, helium, air, or a mixture thereof. The ceramic base material is one selected among alumina, aluminum nitride, and beryllium oxide.

Description

MANUFACTURING METHOD FOR CERAMIC DBC SUBSTRATE USING COLD SPRAYING COATING PROCESS

1 is a schematic cross-sectional view showing a structure of a DBC substrate;

2 is a configuration diagram showing a configuration of a low temperature spray coating apparatus;

Figure 3 is a photograph of the appearance of the DBC substrate manufactured by an embodiment of the present invention, and

Figure 4 is an electron micrograph photographing a cross section of the DBC substrate coating layer prepared by the embodiment of the present invention.

The present invention relates to a method of manufacturing a ceramic DBC substrate using a low temperature spray coating process, and more particularly, to a method of manufacturing a ceramic DBC substrate having a strong bonding strength by using a low temperature spray process, which is simplified compared to the prior art. .

Ceramic DBC substrates are used in semiconductor power modules and have higher heat dissipation characteristics than those placed on existing heat dissipating materials. Also, the ceramic DBC substrate does not require inspection process for the adhesion state of heat sinks. It is a substrate having an advantage of providing a semiconductor module with improved consistency. In the case of using the ceramic DBC substrate, the semiconductor can be directly mounted on the circuit, and a semiconductor mounting substrate excellent in heat dissipation can be manufactured. A technique for manufacturing a power transistor module, a high frequency power transistor, a large capacity power transistor, or a power transistor for an igniter using the same has been put to practical use.

The general structure of the ceramic DBC substrate is as shown in Fig. 1 is an alumina ceramic base material, an aluminum nitride layer or a beryllium oxide layer (hereinafter, a ceramic base material), which is an insulating base material 2, and a lower copper layer bonded to the bottom of the ceramic base material ( 3), the upper copper layer (1) is bonded to have a pattern on the upper surface of the ceramic base material.

At this time, the copper layer and the ceramic base material need to be bonded in a special way because it is difficult to provide a bonding force to each other by the normal method due to the characteristics of the metal and ceramic that is not well bonded. Korean Patent Laid-Open Publication No. 2003-0077203 by the method provided therein describes a method of manufacturing a DBC substrate by pressing and heating a copper layer on the bottom and top of an insulating plate (ceramic base material).

However, the method of manufacturing the DBC substrate by pressing the copper layer as in the Republic of Korea Patent Publication No. 2003-0077203 has a disadvantage in that it is difficult to provide sufficient bonding strength between the ceramic base material and the copper layer.

In order to further improve this, Japanese Patent Laid-Open No. 2003-188316 discloses a ceramic DBC substrate in which a copper circuit board is formed on a surface of a ceramic substrate having a metal copper coating layer through the metal copper coating layer. A ceramic DBC substrate and a DBC substrate for manufacturing the DBC substrate, which are formed by adhering to a ceramic substrate through a process of copper oxide formed on a bonding surface of either a metal copper film layer or this copper circuit board and copper of a copper circuit board. A method for producing a ceramic DBC substrate, comprising forming a metal copper film layer on the surface of a ceramic substrate by sputtering or vacuum deposition, and then placing copper oxide on the metal copper film layer and placing a copper circuit board on the substrate. This is described.

That is, the DBC substrate manufacturing method described in Japanese Unexamined Patent Publication No. 2003-188316 is proposed to supplement the problems of the invention described in 2003-0077203, and the copper film layer is formed on the surface of the ceramic substrate by sputtering or vacuum deposition. After forming the copper oxide layer, the copper oxide layer is placed on the copper film layer, and the copper circuit board is mounted and heated. This technique is improved compared to a method of directly placing a copper layer on a ceramic substrate and heating and bonding the copper layer. Although strength can be obtained, it is composed of various complicated manufacturing processes, and there is a problem that manufacturing time and manufacturing cost increase.

The present invention is to solve the above problems, a method of manufacturing a ceramic DBC substrate can provide a sufficient bonding strength between the copper layer and the ceramic base material without causing problems of manufacturing time and manufacturing cost in a simple process Its purpose is to provide a method.

The method of manufacturing a ceramic DBC substrate of the present invention for achieving the above object is characterized in that to produce a DBC substrate by low-temperature spray coating of copper particles on a ceramic base material.

At this time, the copper particles used during the low temperature spray coating preferably has a diameter of 5 ~ 200㎛.

In addition, in the low temperature spray coating, it is preferable to use the temperature of the injection gas heated to 300 ~ 450 ℃.

In addition, during the low temperature spray coating, it is preferable to adjust the pressure of the injection gas just before the nozzle to 10 to 27 kg / cm ² .

In addition, in the low temperature spray coating, the spray gas is effectively nitrogen, helium, air or a mixture thereof.

In addition, the distance between the tip of the nozzle and the ceramic base material used for the low temperature spray coating is preferably 10 ~ 40mm.

And, the ceramic base material is preferably one selected from alumina, aluminum nitride or beryllium oxide.

The advantageous method of the present invention as described above, it is more preferable to perform a pretreatment to increase the surface roughness of the ceramic base material before the low temperature spray coating.

At this time, the pretreatment is effective to perform the blasting method of spraying the alumina powder having a size of 80 ~ 30mesh to the surface of the ceramic base material at a pressure of about 5 ~ 8kg / cm ² .

Hereinafter, the present invention will be described in detail.

The inventors of the present invention have studied in order to solve the above-mentioned problems of the prior art, and have found that when the copper is coated on a ceramic base material through a low temperature spraying process, the object of the present invention can be achieved and leads to the present invention. It became.

The cold spray process is a concept that is distinguished from the thermal spray process. Unlike the thermal spraying method in which the material is heated to a high temperature and sprayed in a molten state, the cold spray process is performed at a high speed to the subject without melting at normal or warm temperature. It is a method of coating the material on the subject surface by spraying.

Conventionally, the thermal spraying method was used for coating a material, but when the thermal spraying method is used to coat copper on a ceramic base material, when the molten copper adheres to the surface of the ceramic base material and solidifies and cools according to heat release, copper and ceramics are used. Due to the large difference in coefficient of thermal expansion between the base materials, there is a big difference between the degree of shrinkage of the copper and the size of the ceramic base material. Therefore, a large stress is applied to the interface between the copper and the ceramic base material. Development occurs and is not suitable for coating.

The inventors of the present invention have found that excellent results can be obtained by using the low temperature spray coating as another coating method.

The cold spray coating may be carried out by a cold spray coater illustrated by way of example in FIG. 2. As can be seen in Figure 2, the low temperature spray coater includes a gas supply device 4, a control panel 5, a gas heating device 6, a powder supply device 7 and a De Laval nozzle (de Laval Nozzle) have. The gas supplied from the gas supply device 4 is controlled by the amount of gas in the control panel 5, and is divided into a gas heating device 6 and a powder supply device 7. The gas heating device 6 heats the gas to a high temperature to induce a speed increase due to the expansion of the gas, and the powder supply device 7 supplies the powder to the gas supplied from the control panel 5 by gas. It serves to ensure that the powder can be fed into the DeLaval nozzle (8). Immediately before the de Laval nozzle 8, the mixture of powder and gas supplied from the powder feeder 7 and the heated high speed gas supplied from the gas heater 6 meet to form a high speed gas / powder mixture. The deLaval nozzle 8 is injected into a high velocity gas / powder jet stream. DeLaval nozzle is a nozzle that is used to increase the speed of the gas to the supersonic speed above the speed of sound as it has a form that the inner diameter of the nozzle is reduced (converge) and then diverged again when viewed in the nozzle length direction. The powder transported by the gas injected at supersonic speed through the de Laval nozzle collides with the subject at a high speed close to the velocity of the gas, and the kinetic energy of the powder is converted into the energy required for the coupling between the subject / powder. Thus, a powder-coated subject can be obtained.

The low temperature spray coating method has a long history than the thermal spraying method, but has been developed and used in the past. However, in order to coat copper on a ceramic base material to produce a DBC substrate, it is not possible to apply the conventional low temperature spray coating conditions alone and it is necessary to satisfy more specific conditions. This is because the following phenomenon occurs when coating the copper particles on the surface of the ceramic base material.

First, when the particles and the base metal collide during the low temperature spray coating, most of the kinetic energy is changed to thermal energy, so that a part of the copper particles coated at the contact point is heated up to a melting point. In the cooling process after the temperature increase, peeling may occur due to a difference in thermal expansion coefficient between the ceramic base material and the copper coating layer.

Second, since the ceramic base material has high brittleness, fine cracks may be generated in the base material due to the impact generated during the collision of the copper particles under process conditions where the speed of flight of the copper particles is high, which may cause breakage of the base material. .

Third, when the collision energy between the copper particles and the copper layer is greater than the bonding energy of the copper layer laminated on the ceramic base material with respect to the ceramic base material, the bonding between the ceramic base material and the copper is broken at the portion where the beads and the beads overlap. Peeling may occur in this portion.

Therefore, in order to form a coating layer having excellent bonding strength when the copper particles are sprayed on the ceramic base material, it is necessary to set appropriate process conditions.

There are various parameters that can be set when cold spray coating the copper particles, but according to the present invention, it is particularly important to set the following preferable conditions. Conditions not specifically mentioned in the present invention are based on the normal low-temperature spraying conditions, and anyone skilled in the art may use the normal low-temperature spraying conditions without great difficulty. Hereinafter, specific conditions of the copper low temperature spray coating method for manufacturing a ceramic DBC substrate will be described in detail.

Temperature of gas

It is preferable that the heating temperature of the gas heated by the gas heater is 300-450 degreeC.

 If the heating temperature is less than 300 ° C., since the kinetic energy of the gas is not sufficient, the copper particles may not collide with the object at a sufficient speed, which is not preferable. In addition, when the heating temperature is higher than 450 ℃ because the thermal expansion coefficient between the copper particles and the ceramic base material is different because the thermal stress is generated and peeling is disadvantageous.

Gas pressure

The pressure of the gas just before the nozzle for injecting the powder having the above preferred conditions is 10 ~ 27kg / cm ² , and when injecting a powder having a particle size of 10 ~ 35㎛ more preferred powder particle size range 17 It is more preferable that it is -21 kg / cm <^2> . The gas pressure is an important factor that allows the injected copper particles to be attached to the ceramic base material with sufficient energy and at the same time maintain the adhesion state even after being attached. If the pressure of the gas is less than 10 kg / cm ² , the copper particles to be injected may not have sufficient speed (lamination continuity) to be laminated and thus may not be attached to the ceramic base material. On the contrary, the pressure of the gas is 27 g. When / cm ² is exceeded, the first bead may be easily attached to the ceramic base material, but in the next bead, the first bead and the second bead at the portion where the second bead overlaps with the first copper particles are copper particles The phenomenon of being peeled off without being able to withstand the repulsive energy due to the impact transmitted from the same may occur. In the low temperature spray coating method, the coating cannot be large at a time, and the coating is performed in a linear shape while moving the spray line sprayed in a point shape using a traveler, and the coating line of the linear shape is formed at a predetermined interval. In the end, the entire surface is coated. The coating line formed by the travel of the traveler is called a bead. Therefore, after the bead (coating line) is formed, another bead (coating line) is formed at the bottom (or the top) by the traveler's movement. It's a second bead.

Diameter of copper particles

The diameter of the copper particles is an important factor in determining the coating property. If the diameter of the copper particles is too small, the kinetic energy of the particles is insufficient to reduce the lamination rate during coating. On the contrary, if the diameter of the copper particles is too large, the gas does not accelerate the particles sufficiently, making the particles difficult to coat. do. Therefore, although it is preferable to use the thing of a fixed range for the diameter of a copper particle, it is preferable that it is 5-200 micrometers for DBC board | substrate manufacture, and it is most preferable that it is 10-35 micrometers especially.

Putting together the more preferable conditions of the present invention, the ceramic DBC substrate manufacturing method of the present invention, as a method for low temperature spray coating of copper particles on a ceramic base material, using copper particles having a diameter of 5 ~ 200㎛, when spraying It is characterized by adjusting the temperature of the gas to 300 ~ 450 ℃, the pressure of the gas immediately before the nozzle to 10 ~ 27 kg / cm ² . Of course, the copper layer to be coated may be coated on a plane, it may be coated in a pattern with a pattern if necessary.

At this time, the type of gas for producing the DBC substrate in the above-described manner is not particularly limited because the reactivity of copper is not high. Nitrogen, helium, air, or a mixed gas thereof may be used, and among them, it is most preferable to use nitrogen in consideration of price and reactivity.

In addition, even if the copper particles are injected from the nozzle at a high speed, if the distance between the nozzle and the ceramic base material is far, the speed of the copper particles is slowed down, so that it is difficult to have sufficient energy during collision, and conversely, the distance between the nozzle and the ceramic base material is too high. If it is close, the flow of the gas for transporting the copper particles is dissipated (bowshock) by the ceramic base material is difficult to have a sufficient speed. Therefore, in consideration of this point, the distance between the nozzle (front end) and the ceramic base material is more preferably 10 to 40 mm.

In addition, a more preferable condition for obtaining a DBC substrate having a uniform surface is the distance between the beads and the center of the beads. That is, when the beads and the beads overlap as described above, the repulsive force may be applied while the impact energy of the beads attached to the second formed beads is applied. Thus, when the beads and the beads overlap excessively (i.e., when the distance between the beads and the center of the beads are too close), the first formed beads may peel off. On the contrary, if the distance between the beads and the center of the beads is too far, not only is it difficult to obtain a uniform surface, but also it is not preferable because the exposed parts appear extremely uncoated. Therefore, the distance between the beads and the center of the beads needs to be maintained in an appropriate range. In the case of manufacturing a ceramic DBC substrate as in the present invention, the distance between the beads and the center of the beads is preferably 0.5 to 4.5 mm.

In addition, when the surface of the ceramic base material is very flat, since the copper particles are hard to adhere, it is more preferable to pretreat the surface of the ceramic base material before the low temperature spray coating to increase the surface roughness. It is preferable to use a blasting method as said pretreatment. The blasting is made by spraying the alumina powder having a size of 30 ~ 80 mesh (177 ~ 595㎛) to the surface of the ceramic base material at a pressure of about 5 ~ 8kg / cm ² . The blasting process can be easily carried out by anyone changing the condition, as long as a person having ordinary knowledge of the present invention teaches that the blasting process can be used as a pretreatment. It does not specifically limit in this invention.

In addition, since the fine ceramic particles or other impurities crushed by blasting may exist on the surface of the blasted ceramic base material, the bonding strength may be inhibited due to these. Therefore, it is preferable that the impurities are removed by a washing process. As a washing method which can be easily used, an ultrasonic washing method may be mentioned.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, it is necessary to note that the following examples are only for illustrating the present invention and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and the matters inferred therefrom.

(Example)

Alumina having a thickness of 1 mm was used as the ceramic base material of the DBC substrate. In order to improve the mechanical bonding between the alumina base material and the coating layer, grit-blasting was performed using alumina powder having a size of 30 to 80 mesh at a pressure of 5.0 kg / cm ^{2 on} the surface of the alumina base material. The surface of the blasted alumina base material was ultrasonically cleaned to remove impurities to complete pretreatment.

Low temperature spray coating of spherical copper powder distributed in the range of 10 ~ 35㎛ diameter on the upper and lower surfaces of the pretreated ceramic base material. The coating equipment was a type of equipment similar to that shown in FIG. 2, and a cold spray coating equipment of CGT, Germany, was used for nitrogen powder spraying. The temperature of the gas used was controlled at 350 ° C. and the pressure was set at 21 kg / cm ² .

In addition, the distance between the nozzle and the substrate was set to 30mm, and the coating was carried out while moving the nozzle at a speed of 200mm / s so that the copper particles could be coated without gaps. During coating, the distance between the beads and the center of the beads was set to 3.5 mm.

The photograph of the DBC substrate manufactured by the above method and the photograph of the cross section of the coating layer of the substrate are shown in FIGS. 3 and 4, respectively. As can be seen in Figure 3 it can be seen that the copper layer is evenly formed on the entire surface of the substrate, as shown in Figure 4 it can be seen that a strong bonding layer is formed on the surface of the copper coating layer and the alumina base material. Thus, it was found that by the method provided by the present invention, a ceramic DBC substrate having good bonding strength can be easily produced.

As described above, in the method of manufacturing the ceramic DBC substrate of the present invention, since the copper layer may be coated on the ceramic base material by a simple method by one coating treatment and pretreatment performed as necessary, the manufacturing time and manufacturing cost may be reduced by a simple process. It is an effective way to provide sufficient bond strength between the copper layer and the ceramic base without causing problems.

Claims (10)

A method for producing a ceramic DBC substrate, characterized in that to produce a DBC substrate by cold spray coating the copper particles on the ceramic base material. The method of claim 1, wherein the copper particles used in the low temperature spray coating have a diameter of 5 μm to 200 μm. The method of manufacturing a ceramic DBC substrate according to claim 1, wherein in the low temperature spray coating, the temperature of the spraying gas is heated to 300 to 450 ° C. The method of manufacturing a ceramic DBC substrate according to claim 1, wherein, during the low temperature spray coating, the pressure of the injection gas just before the nozzle is adjusted to 10 to 27 kg / cm ² . The method of claim 1, wherein in the low temperature spray coating, the injection gas is nitrogen, helium, air, or a mixture thereof. The method of manufacturing a ceramic DBC substrate according to claim 1, wherein the distance between the tip of the nozzle and the ceramic base material used for the low temperature spray coating is 10 to 40 mm. The method of claim 1, wherein the ceramic base material is one selected from alumina, aluminum nitride, and beryllium oxide. The method of claim 1, wherein the distance between the beads and the center of the beads during the cold spray coating is 0.5 ~ 4.5mm. The method for producing a ceramic DBC substrate according to any one of claims 1 to 8, wherein a pretreatment for increasing the surface roughness of the ceramic base material is performed before the low temperature spray coating. The method of claim 9, wherein the pretreatment is performed by a blasting method of spraying alumina powder having a size of 30 to 80mesh on the surface of the ceramic base material at a pressure of about 5 to 8 kg / cm ² .

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