JPH0883701A - Large power resistor - Google Patents

Abstract

PURPOSE: To provide a highly reliable large power resistor, which is hardly deteriorated by aging in heat conductivity, having excellent withstand voltage characteristics. CONSTITUTION: A resitor substrate 30, on which a thick film resistor 35 is printed, and a metal heat radiating plate 10, to be attached to other heat sink, are provided on a tabular ceramic substrate 31. The resistor substrate 30 is bonded and integrally formed with the heat radiating plate 10 by a thermosetting silicon bonding agent 20 containing an excellently heat conducting filler. A silane coupling agent 60 is applied to the resistor substrate 30 which is adhered to the heat radiating plate 10. A case 4, made of resin, is placed on the resistor substrate 30 on which a silane coupling agent 60 is applied and the circumference of the resistor substrate 30 is sealed by filling resin 70 in the case 40.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high power type resistor.

[0002]

2. Description of the Related Art Conventionally, for example, a power source line of an inverter motor is provided with a high power type resistor for the purpose of suppressing the generation of inrush current generated when the motor is driven.

This type of high power type resistor is required to have a good heat dissipation property and a structure resistant to heat. Specifically, a flat resistor substrate is bonded and integrated with a metal-based heat dissipation plate with an epoxy adhesive. Here, this resistor substrate is formed by printing a thick film resistor on a heat-resistant ceramic substrate. Further, the heat sink is attached to another heat sink.

When a lead wire is connected to the thick film resistor on the resistor substrate and a current is passed through the thick film resistor, the thick film resistor generates heat and current is consumed. At this time, the heat is conducted from the resistor substrate to the heat sink via the heat dissipation plate.

[0005]

However, during the repeated energization of the resistor substrate, the heat conduction from the resistor substrate to the heat sink deteriorates over time,
There was a case of breaking the wire.

Therefore, the inventor of the present application conducted various experiments and found the cause as follows. That is, since the heat radiating plate and the resistor substrate are made of different materials and have different thermal expansion coefficients, the amounts of expansion and contraction of the two differ when heat is applied. On the other hand, the epoxy-based adhesive that bonds the two has strong adhesive strength, but has almost no flexibility and hardly stretches due to mechanical tension. For this reason, when the heat sink and the resistor substrate are repeatedly stretched and shrunk, stress is applied to the adhesive each time, and the adhesive state due to the adhesive gradually deteriorates, which results in poor heat conduction at the adhesive portion. This is because

The present invention has been made in view of the above points, and an object of the present invention is to provide a high-power type resistor which is highly reliable and has a high withstand voltage characteristic in which the conduction state of heat is not easily deteriorated with time. To provide.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is to mount a resistor substrate in which a thick film resistor is printed on a flat ceramic substrate, which is made of metal and is attached to another heat sink. In a high-power type resistor having a structure to be mounted on a heat sink, the resistor substrate is bonded and integrated with the heat sink by a heat-curable silicone adhesive containing a filler having good thermal conductivity, and A silane coupling agent is applied to the adhered resistor substrate, and a resistor case is covered on the resistor substrate coated with the silane coupling agent, and the case is filled with a resin material to reduce the resistance. The periphery of the body substrate was sealed with the resin material.

[0009]

This high-power resistor is used so that a desired current is passed through the thick film resistor of the resistor substrate and the current is consumed. The consumed current is converted into heat by the thick film resistor, but this heat is also transferred to the heat through the ceramic substrate with high thermal conductivity and the silicon-based adhesive mixed with the filler to increase the thermal conductivity. Conducted by the heat dissipation plate with high conductivity. At this time, the heated ceramic substrate and the heat sink differ in the amount of expansion and contraction due to the difference in the coefficient of thermal expansion. However, since the silicone-based adhesive that bonds the two is flexible, this amount of expansion / contraction is absorbed by this silicone-based adhesive. Therefore, the adhesion state of the silicon-based adhesive does not deteriorate, and therefore the heat conduction from the resistor substrate to the heat sink does not deteriorate over time.

On the other hand, the main component of silicon in the silicon-based adhesive used to bond the resistor substrate to the heat sink is siloxane. The inventor of the present application, when the resistor substrate is adhered to the heat dissipation plate with the silicon-based adhesive which is essential to the invention of the present application, the low-molecular-weight siloxane component in the silicon exudes from the silicon-based adhesive and the upper surface of the resistor substrate Crawling up to the side and curing, when the resin material is filled with the case covered with the resin in this state, the cured low-molecular siloxane component (which has a property that it is difficult to adhere to general organic substances) It was confirmed that the adhesion with the resin material was hindered and a thin gap was created between the two. In this case, when a high voltage is applied between the thick film resistor of the resistor substrate and the heat sink, creeping discharge is likely to occur in the gap.

To cope with this phenomenon, if a silane coupling agent is applied as a primer on a resistor substrate as in the present invention and a resin material is filled thereon,
Even if the low-molecular-weight siloxane is cured on the resistor substrate, the resin material easily adheres to the cured low-molecular-weight siloxane. Therefore, no air gap is generated between them, and a high-power resistor having better withstand voltage characteristics can be constructed.

[0012]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is an exploded perspective view of a high power resistor according to an embodiment of the present invention. As shown in the figure, in this high power resistor, a resistor substrate 30 is bonded and integrated on a heat dissipation plate 10 with a silicon adhesive 20, and a silane coupling agent 60 is applied on the resistor substrate 30. Further, the case 40 is further covered thereon, and the case 40 is filled with the resin material 70. Two lead wires 50, 50 are connected on the resistor substrate 30. Each component will be described below.

The heat radiating plate 10 is made of a metal plate having high thermal conductivity (aluminum plate in this embodiment), and holes 11 for fixing the heat radiating plate 10 to a heat sink having a larger area are provided at four corners thereof. Has been.

Next, the resistor substrate 30 is formed by printing and firing two silver patterns 33, 33 on a flat ceramic substrate 31 and then connecting the silver patterns 33, 33 with a thick thickness. It is manufactured by printing and firing the film resistor 35.

Here, the ceramic substrate 31 is made of a fired ceramic having a high thermal conductivity, and in this embodiment, one containing alumina as a main component (96%) is used.

Next, the silicon-based adhesive 20 is formed by mixing a heat-curable silicone adhesive with a filler having good thermal conductivity so as to enhance its thermal conductivity. Here, as the filler, it is possible to use various materials such as ceramic powder of aluminum nitride or alumina, metal powder of silver or the like. The point is that the filler has good thermal conductivity.

The silicone adhesive 20 is considerably more flexible than the epoxy adhesive due to the characteristics of its material. In this embodiment, the elongation is 50% [JIS K6.
The calculation formula of elongation in the 301 vulcanized rubber physical test (according to the following formula (1)) is used. In the case of an epoxy adhesive, this elongation is almost 0%.

[0018] E here_B: Elongation (%) L₀: Mark distance (mm) L₁: Length between marked lines when cutting (mm)

Next, the silane coupling agent 60 applied on the resistor substrate 30 has two different kinds of functional groups in the same molecule, and thus it plays the role of an organic resin and an inorganic substance. However, it plays the role of a bond between the organic resins, and has a function of improving the adhesiveness between the two as a primer. Therefore, it has a function of adhering general organic substances to cured silicon.

Next, FIG. 2 is a side sectional view of the case 40 (AA sectional view of FIG. 1). As shown in FIGS. 1 and 2, the case 40 is formed by molding, for example, a highly heat-resistant plastic, and has a substantially rectangular shape with an open lower surface and a lead wire 50 on the upper surface. There are two holes 43, 43 penetrating therethrough and two small holes 45, 45 for filling the resin material 70.

On the other hand, as the resin material 70 to be filled, a silicon-based resin material having good electric insulation, heat resistance and flexibility is used. A heat-curable resin material is used as the resin material.

In order to manufacture this high power resistor, as shown in FIG. 3, a resistor substrate 30 is adhered to the center of the heat dissipation plate 10 with a silicone adhesive 20 (see FIG. 1) and dried and fixed. . The drying conditions for the silicone adhesive 20 according to this example are 150 ° C. and 30 minutes.

Next, the lead wires 50, 50 are inserted into the holes 43, 43 of the case 40, and the tips of the lead wires 50, 50 are respectively inserted into the resistor substrate 3.
Solder on each silver pattern 33, 33 of 0.

Next, as shown in FIG. 4, a silane coupling agent 60 dissolved in a solvent is applied onto the resistor substrate 30 and the heat radiating plate 10 around the resistor substrate 30 completely without gaps and dried. At this time, it is preferable that the thickness of the silane coupling agent 60 is thin (for example, several μm). The drying conditions of the silane coupling agent 60 according to this embodiment are 120 to 130 ° C. and 10
Minutes.

Next, as shown in FIG. 5, the case 40 is covered on the heat sink 10 so as to cover the resistor substrate 30, and the case 4 is removed.
The resin material 70 is filled and cured through the small holes 45, 45 provided in No. 0. As a result, the periphery of the resistor substrate 30 is sealed with the resin material 70.

By the way, silicon is a stable substance (no reactive limbs (eg, OH groups)). Therefore, once the silicone resin is heated and cured, the adhesiveness is poor even if the silicone resin of the same substance is applied or heated.

In the case of the present invention, since the resistor substrate 30 is adhered by the silicon adhesive 20, the low molecular siloxane component in the silicon adhesive 20 exudes and the side surface and the upper surface of the resistor substrate 30 are extruded. The silane coupling agent 60 may be applied as a primer on the resistor substrate 30 as described above, so that the low-molecular-weight siloxane component may not be deposited on the resistor substrate 30. Even if it is cured, the cured low-molecular-weight siloxane component and the resin material 70 can be reliably bonded. Therefore, no gap is created between the resistor substrate 30 and the resin material 70.

As described above, according to the present invention, since the periphery of the resistor substrate 30 is sealed with the resin material 70, the lead wire 5
Discharging from a charging unit such as 0, 50 to the heat sink 10 or the heat sink is prevented, and the withstand voltage characteristic of this high power resistor can be improved as compared with the case where the case 40 and the resin material 70 are not used.

Moreover, the present invention is not limited to simply using the case 40 and the resin material 70, but also the silane coupling agent 60.
Since the resistor substrate 30 and the resin material 70 can be reliably adhered to each other and no void is formed between them, creeping discharge between the resistor substrate and the heat sink, which may occur through the void portion, is surely performed. To be prevented. Therefore, the withstand voltage characteristic is further improved.

Specifically, in a high power type resistor (having a withstand voltage rating of 2500 V) which has the same structure as the above embodiment except that the silane coupling agent 60 is not used,
3 between the thick film resistor 35 of the resistor substrate 30 and the heat sink 10.
When a voltage of 000 V was applied, a creeping discharge occurred between the two, but in the above example using the silane coupling agent 60, a creeping discharge did not occur even at a voltage of 6000 V.

By the way, the high-power type resistor configured as described above is used so that a desired current is passed through the thick film resistor 35 of the resistor substrate 30 through the lead wires 50, 50 to consume the current. .

The consumed current is converted into heat by the thick film resistor 35, and the heat is the ceramic substrate 3 having high thermal conductivity.
1 and a heat-dissipating plate 1 having a large thermal conductivity through a silicone adhesive 20 in which a filler is mixed to increase the thermal conductivity.
Conducted to zero.

At this time, the ceramic substrate 31 and the heat radiating plate 10 which are heated have different amounts of expansion and contraction due to the difference in the coefficient of thermal expansion. However, since the silicone adhesive 20 that bonds the two is flexible, this amount of expansion / contraction is absorbed by the silicone adhesive 20. Therefore, the adhesive state of the silicon-based adhesive 20 does not deteriorate, and therefore the heat conduction from the resistor substrate 30 to the heat sink 10 does not deteriorate over time.

FIG. 6 is a diagram showing a comparison test result of an acceleration test (temperature shock cycle number-thermal resistance) of the high power type resistor according to the above-mentioned embodiment and the high power type resistor of another structure. In the figure, samples A and B are high-power type resistors according to the above-described embodiment (however, the case 40 and the resin material 70 are not attached or filled, and the resistor substrate 30 is exposed).
Samples a and b are comparative examples in which the resistor substrate 30 and the heat radiating plate 10 are bonded with an epoxy adhesive (again, the case and the resin material are not attached / filled).

The specific experimental method is as follows: Samples A, B, a, b
The thermal resistance (° C / W) of each sample was measured for each predetermined number of cycles by repeatedly performing the temperature shock of changing the ambient temperature of -20 ° C for 30 minutes ⇔ + 150 ° C for 30 minutes.

As for the thermal resistance, the thick film resistors of the samples A, B, a, and b consume power of 10 W, and the temperature difference ΔT between the temperature of the resistor substrate and the temperature of the heat sink at that time is measured. Then, the thermal resistance θ (° C./W) is obtained according to the following formula (2).

That is, when the same electric power is consumed, if the thermal conductivity is large (that is, the temperature difference ΔT is small), the thermal resistance θ
Is small, and conversely, if the thermal conductivity is small, the thermal resistance θ becomes large.

As shown in the figure, the samples a and b according to the comparative example using the epoxy-based adhesive showed a rapid increase in thermal resistance due to repeated temperature shock cycles,
This indicates that heat conduction from the resistor substrate to the heat sink deteriorates with time.

On the other hand, in the samples A and B relating to the high power type resistor of the present invention, the thermal resistance hardly increased, which indicates that the thermal conductivity hardly changed with time.

In the above embodiment, the silicon-based resin material is used as the resin material 70 filled in the case 40. However, the present invention is not limited to this, and any heat-curable resin having high heat resistance can be used. Other resin materials such as epoxy resin materials may be used.

[0041]

As described in detail above, the high power resistor according to the present invention has the following excellent effects. Since the silane coupling agent is applied on the resistor substrate and the resin material is filled on the resistor substrate, the silane coupling agent ensures the adhesion between the resistor substrate and the resin material and does not cause a gap between them. Therefore, creeping discharge between the resistor substrate and the heat sink, which may occur through the void portion, is reliably prevented, and the withstand voltage characteristic is improved.

At the same time, since the resistor substrate is adhered and integrated with the heat sink by means of a heat-curing type silicone adhesive mixed with a filler having good thermal conductivity, the resistor plate causes the heat sink to dissipate despite the drastic temperature change. The heat conduction to the metal does not deteriorate over time, and the reliability is dramatically improved.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a high power resistor according to an embodiment of the present invention.

FIG. 2 is a side sectional view of a case 40 (AA sectional view of FIG. 1).
Is.

FIG. 3 is a diagram showing a manufacturing process of the high power resistor according to the present embodiment.

FIG. 4 is a diagram showing a manufacturing process of the high power resistor according to the present embodiment.

FIG. 5 is a diagram showing a manufacturing process of the high power resistor according to the present embodiment.

FIG. 6 is a diagram showing test results of an acceleration test (temperature shock cycle number-thermal resistance) of a high power resistor according to the present example and a high power resistor having another structure.

[Explanation of symbols]

 10 Heat Radiating Plate 20 Silicon Adhesive 30 Resistor Substrate 31 Ceramic Substrate 35 Thick Film Resistor 40 Case 50, 50 Lead Wire 60 Silane Coupling Agent 70 Resin Material

Claims (1)

[Claims] 1. A high-power type resistor having a structure in which a resistor substrate, in which a thick film resistor is printed on a flat ceramic substrate, is mounted on a radiator plate made of metal and attached to another heat sink, The resistor substrate is bonded and integrated with the heat sink by a heat-curable silicone adhesive containing a filler with good thermal conductivity, and a silane coupling agent is applied on the resistor substrate bonded to the heat sink. Further, a resin case is covered on the resistor substrate coated with the silane coupling agent, and a resin material is filled in the case to seal the periphery of the resistor substrate with the resin material. High power type resistor.