JPH11236868A - Igniter - Google Patents

Abstract

(57) [Problem] To provide an igniter capable of suppressing damage caused by generation of thermal stress. An igniter (10) includes a case (11), a heat sink (12) on which a bare-chip type power transistor (22) is disposed, an IC substrate on which a low-current element (20) is disposed, and an insulating layer (2) covering these heat sinks (12).
1 is provided. When forming the insulating layer 21, first, a granular glass filler G is injected into the case 11 in which the heat sink 12, the IC substrate 16, and the like are disposed at predetermined positions, and the filler G is placed on the bottom of the case 11. Accumulate in After the liquid epoxy resin E is injected into the vicinity of the opening of the case 11, the epoxy resin E is heated to a predetermined temperature and cured to form the insulating layer 21. As a result, the glass filler G becomes the power transistor 2 in the insulating layer 21.
The state is more unevenly distributed in the vicinity of 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an igniter in which a built-in component including an IC substrate and a power element is accommodated in a case, and the built-in component is covered with a filler filled in the case.

[0002]

2. Description of the Related Art An ignition system for an internal combustion engine includes a spark plug,
It is composed of an ignition coil, an igniter, and the like. In this ignition system, a high voltage for ignition generated in the ignition coil is supplied to the ignition plug, so that a spark is generated between the electrodes of the ignition plug and the mixture is ignited in the combustion chamber of the internal combustion engine.

In such an ignition system, the igniter has a function of generating a high ignition voltage in the ignition coil by intermittently controlling a primary current flowing through the ignition coil. Generally, the igniter includes an IC board and a power element housed in a case, and has a structure in which these internal components are sealed by a filler filled in the case (for example, see Japanese Unexamined Patent Publication No. No. 1472, “Electronic ignition device for internal combustion engine”).

[0004]

Since the igniter controls the primary current of the ignition coil intermittently as described above, it tends to generate heat and increase in temperature. When the IC substrate, the power element, the filler, and the like thermally expand due to the rise in temperature, these members have locally different thermal expansion coefficients, which cause excessive thermal stress. There is a possibility that the above members may be damaged.

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an igniter capable of suppressing damage caused by generation of thermal stress.

[0006]

According to one aspect of the present invention, there is provided a filler for accommodating a built-in component including an IC substrate and a power element in a case and filling the case. In the igniter in which the built-in components are covered, the filler has a coefficient of thermal expansion that is partially different depending on the difference in the coefficient of thermal expansion of each built-in component.

According to the above construction, the difference in the coefficient of thermal expansion between each built-in component and the filler covering the built-in component can be reduced, and the thermal stress generated in the built-in component and the filler can be reduced. Will be able to do it.

According to a second aspect of the present invention, in the igniter according to the first aspect, the filler is formed such that an additive having a different coefficient of thermal expansion from that of the filler is unevenly distributed therein. .

According to the above configuration, in addition to the operation of the first aspect of the invention, unlike the configuration in which the filler is formed of different materials having different thermal expansion coefficients, for example, the thermal expansion of the filler is different. The rate can be changed continuously.

Further, according to the third aspect of the present invention, in the igniter according to the first aspect, the additive has substantially the same coefficient of thermal expansion as that of the power element and is unevenly distributed around the power element. And

According to the above construction, in addition to the effect of the second aspect of the invention, the coefficient of thermal expansion between the power element and the filler which covers the element is self-heating and the thermal expansion is particularly large. The difference can be reduced, and the thermal stress generated in the power element and the filler in the vicinity of the power element can be reduced.

Further, according to the invention described in claim 4, the IC
The internal components including the board and the power element are housed in the case,
In the igniter in which the built-in component is covered by the filler filled in the same case, the thermal expansion coefficient of the bonding pad provided on the IC substrate and connected to the power element via the bonding wire and the thermal expansion coefficient of the filler are substantially equal. They are set equal.

According to the above configuration, the difference in thermal expansion and the difference in thermal shrinkage between the bonding pad and the filler covering the periphery thereof can be reduced, and the heat generated at the connection between the bonding pad and the bonding wire can be reduced. Stress can be reduced.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] A first embodiment of the present invention will be described below.

FIG. 1 shows an igniter 10 according to this embodiment.
2 shows a cross section of FIG. As shown in FIG.
The zero case 11 is formed in a bottomed rectangular tube shape having an accommodation space 11a. A heat sink 12 made of copper is provided in the accommodation space 11a. An insulating plate 14 made of a thermoplastic resin is provided above the heat sink 12, and a ceramic IC substrate 16 is provided on the insulating plate 14 so as to cover the entire upper surface thereof.

A plurality of low-current elements 20 (one of which is shown in the figure) such as an IC, a capacitor, and a resistor, a bonding pad 27, and the like are provided on the upper surface of the IC substrate 16. Also, on the upper surface of the heat sink 12, the case 11
A power transistor 22 is disposed adjacent to the insulating plate 14 on the bottom side (right side in FIG. 1). The power transistor 22 is a so-called bare-chip type transistor whose elements are not covered with resin or the like. The power transistor 22 is electrically connected to a bonding pad 27 via a bonding wire 26 made of aluminum. An electric circuit for intermittently controlling the primary current of the ignition coil (not shown) is configured by the power transistor 22 and the low current element 20 and the like. This electric circuit is connected to an ignition coil and a control device (both not shown) via a terminal 25 attached to one end of the IC substrate 16.

An insulating layer 21 is formed by filling the housing space 11a with an epoxy resin. The insulating layer 21 allows the heat sink 12 and the insulating plate 1 to be formed.
4. The periphery of the IC substrate 16, the power transistor 22, and the like are covered.

Hereinafter, a schematic process for forming the insulating layer 21 will be described. First, as shown in FIG. 2A, the heat sink 12, the insulating plate 14, the IC substrate 1
6 and the like inject the granular glass filler G into the accommodation space 11 a provided at a predetermined position, and store the glass filler G at the bottom of the case 11. The coefficient of thermal expansion of the glass filler G is smaller than the coefficient of thermal expansion of the epoxy resin. Further, since both the glass filler G and the element of the power transistor 22 are formed of silicon, their thermal expansion coefficients are substantially equal.

Next, as shown in FIGS. 2B and 2C,
The liquid epoxy resin E is poured into the vicinity of the opening of the case 11. By injecting the epoxy resin E in this manner, the glass filler G collected at the bottom of the case 11 is diffused. However, since the viscosity of the epoxy resin E is relatively large, the glass filler G is uniformly dispersed in the epoxy resin E. The glass filler G is dispersed near the power transistor 22. Therefore, the glass filler G is more unevenly distributed near the power transistor 22 in the insulating layer 21.

The epoxy resin E thus injected is
A glass filler (not shown) is also added therein. The amount of the glass filler added is determined by the epoxy resin E after curing.
Is set in advance to be equal to the average value of the coefficients of thermal expansion of the members (such as the IC substrate 16 and the insulating plate 14) except for the power transistor 22 among the members arranged in the accommodation space 11a. ing.

After the glass filler G is injected into the case 11 and filled with the epoxy resin E, the insulating layer 21 is formed by heating and curing the epoxy resin E to a predetermined temperature.

As described above, in the igniter 10 according to the present embodiment, the distribution density of the glass filler G in the vicinity of the power transistor 22 is adjusted so as to be higher than the other parts.

Accordingly, the thermal expansion coefficient of the insulating layer 21 is partially reduced, and the difference in thermal expansion coefficient between the power transistor 22 and the insulating layer 21 covering the power transistor 22 is reduced. Thermal stress generated in the nearby insulating layer 21 is reduced.

As a result, according to the present embodiment, (1) the power transistor 22 and the insulating layer 2
1 or the bonding portion of the wire bonding to the power transistor 22 can be prevented from being damaged due to thermal stress, and the durability and reliability of the igniter 10 can be improved.

In the present embodiment, the thermal expansion coefficient of the insulating layer 21 is partially reduced by unevenly distributing the glass filler G in the insulating layer 21 near the power transistor 22. By increasing the amount of the glass filler added to the resin E in advance and reducing the coefficient of thermal expansion of the epoxy resin E as a whole, it is possible to reduce the thermal stress generated near the power transistor 22. However, the insulating layer 2
In the case where the thermal expansion coefficient of 1 is made smaller as a whole, the difference in thermal expansion coefficient between the insulating layer 21 and the IC substrate 16 or the insulating plate 14 having a larger thermal expansion coefficient than that of the power transistor 22 becomes large. The stress generated in the vicinity of each member may increase.

In this regard, according to the present embodiment, (2) the glass filler G is unevenly distributed in the epoxy resin E to partially change the coefficient of thermal expansion of the epoxy resin E. Therefore, the thermal stress generated in the vicinity of the IC substrate 16 and the like is not increased as described above, and damage to the IC substrate 16 and the like due to the increase in the thermal stress can be avoided. .

Further, in this embodiment, as described above, the insulating layer 2 is formed in order to make the thermal expansion coefficient of the insulating layer 21 partially different.
Since the configuration in which the glass filler G is unevenly distributed in the inside of the insulating layer 21 is adopted, unlike the configuration in which the insulating layer 21 is formed of different materials having different thermal expansion coefficients, for example, The coefficient of thermal expansion can be changed continuously.

Therefore, according to the present embodiment, (3) it is possible to prevent the formation of an interface in which the coefficient of thermal expansion changes greatly inside the insulating layer 21, and the insulation caused by the formation of such an interface can be prevented. It is possible to avoid a decrease in mechanical strength of the layer 21 and a concentration of stress at the interface.

[Second Embodiment] Next, a second embodiment according to the present invention will be described, focusing on differences from the first embodiment. The description of the same configuration as that of the first embodiment will be omitted.

The power transistor 22 of the igniter 10 has an IC for suppressing a rise in temperature during its operation.
It is provided directly on the heat sink 12 instead of the substrate 16. As described above, the power transistor 22 is electrically connected to the bonding pad 27 provided on the IC substrate 16 by wire bonding.

By the way, unlike the first embodiment, in an igniter in which the insulating layer is formed of a gel material, such a bonding pad is usually made of a material having a relatively small coefficient of thermal expansion (42 alloy). , 50
Alloy, etc.). If the insulating layer is formed of a gel material, thermal expansion and contraction of the bonding pad are hardly restricted by the insulating layer. In order to reduce the thermal expansion and contraction, it is necessary to suppress such thermal expansion and thermal contraction by selecting a material for forming the bonding pad.

However, when the insulating layer 21 is formed of an epoxy resin as in the first embodiment, the thermal expansion and thermal contraction of the bonding pad 27 are regulated by the insulating layer 21. Although
A slight difference in thermal expansion (or difference in thermal shrinkage) between the insulating layer 21 and the bonding pad 27 causes an increase in thermal stress generated at the interface between the two, and damage to the above-mentioned joint due to this thermal stress cannot be avoided. Becomes

Therefore, in the present embodiment, the insulating layer 21 and the bonding pad 27 are used in order to avoid such damage.
The following configuration is adopted for First, the insulating layer 21 is formed of an epoxy resin having substantially the same coefficient of thermal expansion as copper, which is a material for forming the heat sink 12 that occupies most of the housing space 11a. Unlike the first embodiment, the present embodiment does not employ a configuration in which the glass filler G is unevenly distributed in the insulating layer 21.
The coefficient of thermal expansion of 1 is substantially uniform in the accommodation space 11a.

The bonding pad 27 is made of copper, which is a material having the same coefficient of thermal expansion as that of the insulating layer 21.
Is connected.

With this configuration, in this embodiment, the difference in thermal expansion (or difference in thermal contraction) between the bonding pad 27 and the insulating layer 21 can be almost eliminated. Therefore, according to the present embodiment, (4) the bonding pad 27 and the bonding wire 2
6 can be prevented from generating an excessive stress at a joint portion with the joint 6, and it is possible to avoid damage to the joint portion or disconnection of the bonding wire 26 due to such excessive stress. The reliability of the igniter 10 can be further improved.

(5) Further, since copper is particularly used as a material for forming the bonding pad 27, the bonding pad is made of an extremely expensive material such as 42 alloy or 50 alloy as described above, for example. Compared to the case where the bonding pad 27 is formed,
And the cost of the igniter 10 can be reduced.

Each of the embodiments described above can be implemented by changing the configuration as described below. In the first embodiment, the granular glass filler G is added to the epoxy resin E, but a fibrous glass filler G may be used. If the fibrous glass filler G is used as described above, the mechanical strength of the epoxy resin E can be increased, and damage to the insulating layer 21 due to thermal stress can be further suppressed.

In the first embodiment, when the insulating layer 21 is formed, the glass filler G is injected into the accommodation space 11a, and then the epoxy resin E is filled into the accommodation space 11a. On the other hand, two types (or plural types) of epoxy resins with different amounts of glass filler added
By preparing and first filling the housing space 11a with the epoxy resin with a large addition amount of the glass filler and then filling with the small addition amount of the epoxy resin, the distribution density of the glass filler in the vicinity of the power transistor 22 is reduced. It may be adjusted so as to be larger.

The timing for injecting the glass filler G may be changed according to the position of the power transistor 22 in the case 11. For example, the power transistor 22 is placed in the housing space 11 in the left-right direction of FIG.
In the case where it is arranged at the center of a, the glass filler is injected after filling the epoxy resin E to the position of the power transistor 22, and then the epoxy resin E is further filled to the vicinity of the opening of the case 11. To

In the second embodiment, copper is used as a material for forming the bonding pad 27. However, the bonding pad 27 may be formed of another material having substantially the same coefficient of thermal expansion as the epoxy resin forming the insulating layer 21. Can also.

While the embodiments embodying the present invention have been described above, technical ideas that can be grasped from the above embodiments will be described together with their effects. -In the igniter according to claim 2 or 3, the additive is made of glass fiber.

With this configuration, the mechanical strength of the filler can be increased, and damage to the filler due to thermal stress can be further suppressed. -The igniter according to any one of claims 1 to 3, wherein
The bonding pad disposed on the substrate and wire-bonded to the power element is characterized in that its coefficient of thermal expansion is set to be substantially the same as the coefficient of thermal expansion of the filler.

With this configuration, it is possible to suppress the occurrence of excessive stress at the joint between the bonding pad and the wire, and the joint is damaged or damaged due to the excessive stress. Breakage of the wire can be avoided, and the reliability of the igniter can be further improved.

[0044]

According to the first to third aspects of the present invention, the coefficient of thermal expansion of the filler covering the built-in component is made to differ partially according to the coefficient of thermal expansion of the built-in component contained in the case. I made it. Therefore, by reducing the difference in the coefficient of thermal expansion between each built-in component and the filler near the built-in component, the thermal stress generated in the built-in component and the filler can be reduced, and the built-in component caused by such thermal stress can be reduced. In addition, damage to the filler can be suppressed.

According to the second or third aspect of the present invention, an additive having a thermal expansion coefficient different from that of the filler is unevenly distributed inside the filler. Unlike the configuration in which the filler is formed of different materials, the coefficient of thermal expansion of the filler can be continuously changed. Therefore, it is possible to prevent the formation of an interface in which the coefficient of thermal expansion changes greatly inside the filler, and to avoid a decrease in the mechanical strength of the filler due to the formation of such an interface and a stress concentration at the interface. Will be able to do it.

In particular, according to the third aspect of the present invention, the additive having substantially the same coefficient of thermal expansion as the power element is unevenly distributed around the power element. Therefore, the thermal stress generated in the power element and the filler near the element is alleviated by reducing the difference in the coefficient of thermal expansion between the power element, which has a particularly large thermal expansion due to self-heating, and the filler covering the element. Thus, damage to the power element and the filler near the element due to such thermal stress can be suppressed.

According to the fourth aspect of the present invention, the IC
The coefficient of thermal expansion of the bonding pad provided on the substrate and connected to the power element via the bonding wire is set substantially equal to the coefficient of thermal expansion of the filler. Therefore, by reducing the difference in thermal expansion and the difference in thermal contraction between the bonding pad and the filler covering the periphery thereof, it is possible to reduce the thermal stress generated at the connection portion between the bonding pad and the bonding wire. As a result, it is possible to avoid damage to the bonding portion caused by such thermal stress and obtain a more reliable igniter.

[Brief description of the drawings]

FIG. 1 is a sectional view of an igniter.

FIG. 2 is a schematic process diagram illustrating a process of forming an insulating layer.

[Explanation of symbols]

10 igniter, 11 case, 11a accommodation space,
12 heat sink, 14 insulating plate, 16 IC
Substrate, 20: low current element, 21: insulating layer, 22: power transistor, 25: terminal, 26: bonding wire, 27: bonding pad, E: epoxy resin, G: glass filler.

Claims (4)

[Claims] 1. An igniter in which a built-in component including an IC substrate and a power element is housed in a case, and the built-in component is covered with a filler filled in the case. An igniter characterized in that the igniter is partially different depending on a difference in thermal expansion coefficient of a built-in component. 2. The igniter according to claim 1, wherein the filler is formed by unevenly distributing an additive having a different coefficient of thermal expansion from that of the filler. 3. The igniter according to claim 2, wherein the additive has a coefficient of thermal expansion substantially equal to that of the power element and is unevenly distributed around the power element. . 4. An igniter in which a built-in component including an IC substrate and a power element is accommodated in a case and the built-in component is covered with a filler filled in the case, wherein the igniter is provided on the IC substrate and bonded to the power element. An igniter characterized in that a coefficient of thermal expansion of a bonding pad connected via a wire and a coefficient of thermal expansion of the filler are set substantially equal.