JP2003068970A - Automotive electronic circuit devices - Google Patents

Abstract

(57) [Abstract] [Problem] Electronic circuit board and its lead frame (base)
When packaging up to molding resin,
An inexpensive automotive electronic circuit that is intended to be produced at low cost, has excellent heat dissipation and waterproofness, and does not cause peeling or cracking between the mold resin, circuit board, and base due to thermal stress. Provide equipment. A circuit board on which an electronic circuit element is mounted and a lead frame on which the circuit board is mounted are provided, and the circuit board and a part except for a part of the lead frame are collectively embedded in a mold resin. An electronic circuit device for an automobile, wherein the lead frame is provided with a first protrusion near a center thereof and a plurality of second protrusions around the protrusion, and the first protrusion is provided with the second protrusion. Lower the height by a predetermined value,
The circuit board is bonded only to the first protrusion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a package structure of an electronic circuit device for an automobile, and more particularly to an electronic circuit device mounted on an automobile engine room, a transmission or the like for controlling an engine, an automatic transmission or the like. The present invention relates to a suitable package structure.

[0002]

2. Description of the Related Art Conventionally, a method of controlling an automatic transmission of an automobile by an electronic circuit has been widely adopted, and there are various mounting structures for the electronic circuit. In the electronic circuit device directly attached to the transmission, the mounting place is selected so that the electronic circuit is not damaged by the intrusion of water, oil, or the like, and the electronic circuit device is structured so that they do not infiltrate.

As an example of the structure, an electronic circuit board is mounted on a metal base, the base and the cover are resistance-welded or laser-welded to hermetically seal the inside of the electronic circuit device, and nitrogen or the like is used. There is known a so-called hermetic seal structure in which an inert gas of

In this structure, the input / output terminals of the electronic circuit are led out through the through holes provided in the base, and the through holes are sealed with glass having a high insulation resistance. Therefore, it is necessary to optimally select the linear expansion coefficient of the base, the glass, and the terminal. That is, several 100 ° C. to 1000
This is because it is necessary to cause residual compressive stress to act between the three parts when the glass is melted at a high temperature of ° C and returned to room temperature. The materials of these materials are limited. For example, when soda barium glass is used as the sealing material, a steel plate is used as the material of the base, and the material of the terminals is an iron-nickel alloy (iron 50% -nickel 50%). %) Is used to form the combination.

Therefore, it is necessary to prevent oxidation at high temperatures,
The base requires nickel plating or the like having a high melting temperature. Further, in the welding, the combination material of the cover is limited, and the same steel plate as the base is used. When there are many heating elements in the electronic circuit, aluminum, copper, etc. are suitable as the base material to facilitate heat dissipation, but as mentioned above, steel plates have to be used and the heat dissipation properties of steel plates Is bad.

Further, in resistance welding, there is a cost-increasing factor such that it is necessary to improve the flatness accuracy of both the base and the cover so that the electrical contact resistance between the base and the cover becomes uniform. In laser welding, variations in the thickness of the nickel plating applied to the base affect the welding, and the beads of the welded portion are exposed. A protective coating is required to prevent rusting due to it.

From the appearance, it is difficult to reliably judge the quality of welding, and in order to confirm the airtightness, a check method using helium gas, or a bubble for checking the presence or absence of bubbles in an inert liquid is used. A leak check method was necessary. In order to improve the above-mentioned various points, a circuit board on which an electronic circuit element is mounted is adhered to a base made of a material having good thermal conductivity, and while exposing one side of the base, the circuit board and the base are made of epoxy resin ( A packaging technology for sealing with a mold resin) has been proposed.

However, in this case, for example, a silicon chip is used as the electronic circuit element, a glass ceramic substrate having a linear expansion coefficient similar to that of the silicon chip is used as the circuit substrate, and these members are sealed with epoxy resin. In the structure to do, there were the following problems.

That is, during the molding process (transfer molding process) of the epoxy resin for embedding the circuit board or base, the molding resin (epoxy resin) is removed from the mold through the curing process, and the epoxy resin is cooled during cooling. Due to the curing shrinkage and the difference in linear expansion coefficient with respect to the substrate or base, peeling or resin cracks occur at the interface between the epoxy resin and the circuit board or base.

This is because the epoxy resin equivalent linear expansion coefficient at the time of molding (the epoxy resin equivalent linear expansion coefficient is
The chemical shrinkage of the resin at the molding temperature until the mold resin is taken out of the mold and cooled to room temperature, and the molding temperature ~
It is a combination of the linear expansion coefficient α1 up to the glass transition temperature Tg and the linear expansion coefficient α2 between the glass transition temperature Tg and room temperature, which is about 4 times the linear expansion coefficient at room temperature). Since the linear expansion coefficient of the circuit board is larger than that of the base, and the linear expansion coefficient of the circuit board is smaller than that of the base, the circuit board and the base warp due to the shrinkage stress of the epoxy resin that adheres to the circuit board, and the epoxy resin portion that is not adhered or adheres Tensile stress acts on the weak part and peeling occurs at the interface.

In order to eliminate this peeling, for example, if a film treatment with good adhesion is formed on the end face portion of the base, there is a problem that cracks occur in the epoxy resin near the boundary surface. As a countermeasure, it is conceivable to use an epoxy resin having a small curing shrinkage and a small linear expansion coefficient, or to apply a flexible resin coating treatment for absorbing the difference in the linear expansion coefficient to the end face of the base. However, in each case, an increase in cost is unavoidable, and an inexpensive structure has been desired.

[0012] In the prior art, as disclosed in, for example, Japanese Patent Laid-Open No. 7-240493, a semiconductor element is mounted on a lead frame and these parts are embedded in a mold resin and packaged. Japanese Patent Laid-Open No. 1-2055
As disclosed in Japanese Patent No. 56, there is a package of an IC chip, its mounting member, and a heat sink. These conventional techniques do not attempt to package the electronic circuit board and even the base thereof with the molding resin. The technique of sealing and mounting an electronic circuit board and a base, which are much larger in area than IC packages and semiconductor elements, with one mold resin is a new attempt.

[0013]

In realizing the new mounting technique, the shrinkage stress of the epoxy resin (mold resin) enclosing the circuit board and the base is large due to the large area of the circuit board and the base as described above. As a result, a new problem has arisen that peeling occurs at the interface between the circuit board and the epoxy resin.

The present invention has been made in view of the above points, and an object of the present invention is to mold a new mounting technique as described above, that is, an electronic circuit board and its lead frame (base). When it is packaged with resin, it is intended to be produced at low cost.
Another object of the present invention is to provide an inexpensive electronic circuit device for an automobile, which has excellent heat dissipation and waterproof properties, and does not cause peeling or cracks between the mold resin, the circuit board, and the base due to thermal stress.

[0015]

In order to achieve the above-mentioned object, an electronic circuit device for an automobile according to the present invention is basically a circuit board on which an electronic circuit element is mounted, and leads for mounting the circuit board. An electronic circuit device for an automobile, comprising: a frame, wherein the circuit board and a portion excluding a part of the lead frame are collectively embedded in a mold resin, wherein the lead frame has a first portion near a center thereof. And a plurality of second protrusions around the protrusions, the height of the first protrusion is lower than the second protrusion by a predetermined value, and the circuit board is bonded only to the first protrusion. It is characterized by doing.

In the automobile electronic circuit device of the present invention configured as described above, the optimum thickness can be secured without the adhesive layer of the first protrusions being neither too thin nor too thick, It is possible to prevent the interface between the substrate and the encapsulation resin from peeling and cracks, and to package the circuit board and its lead frame with mold resin at a low cost, with excellent heat dissipation and waterproof properties. An electronic circuit device for use can be provided.

Further, in a specific aspect of the electronic circuit device for automobiles of the present invention, the plurality of second protrusions are arranged closer to the first protrusion than the outer periphery of the circuit board, The number of the protrusions is one, and the number of the second protrusions is three or four. Further, the lead frame includes a flange portion and leads, and the circuit board and the leads are electrically connected. It is characterized in that the lead and the flange are collectively embedded in the molding resin except for a part thereof.

Further, in another specific aspect of the electronic circuit device for an automobile of the present invention, the first and second protrusions are formed by pressing the lead frame, and the mold resin of the flange portion is formed. The more protruding portion serves as a mounting portion, and the heat of the circuit board is conducted to the outside through the flange portion. The circuit board is made of glass-ceramic or ceramic-based material. It has a feature. Still another specific aspect of the electronic circuit device for automobiles of the present invention is characterized in that the circuit board is a multilayer circuit board.

Furthermore, as an aspect of the mounting structure of the electronic circuit device for an automobile of the present invention, the flange portion of the lead frame is sandwiched between the first bracket and the second bracket on the automobile side, and the bolt or the like. Characterized in that a plurality of tongue pieces provided in a part of the first bracket are inserted into a small hole provided in the second bracket, the tip portion is bent, and both are integrated. There is.

In the structure for mounting the electronic circuit device for an automobile of the present invention constructed as described above, since it is not necessary to provide holes for fixing bolts in the flange portion of the lead frame, the area of the flange portion can be reduced, When many products are taken at once by transfer molding, the number of taken products can be increased. Further, since the flange portion of the lead frame is sandwiched by the first bracket and the second bracket, and the tongue piece is bent to be integrated, it is easy to handle when mounting on the mating member.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, some embodiments of an automobile electronic circuit device of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a plan view of an automobile electronic circuit device (control unit) 1 of the present embodiment, and FIGS. 2 and 3 are partial cross-sectional side views in which the viewing direction is changed. Automotive electronic circuit device (control unit) 1
Includes a lead frame 2 having a flange portion 2c,
An electronic circuit 4 including a circuit element 5 and a circuit board 6 is mounted on the lead frame 2. The electronic circuit 4 is mounted by bonding the circuit board 6 onto the lead frame 2. The bonding mode will be described later.

The lead (terminal) 2a is the lead frame 2
When a part of the lead 2a is formed by being cut off and the lead 2a is electrically connected to an external connection target (not shown),
The lead 2a is a harness connector of an external object, or
It is connected to the harness terminal by welding or the like. The electronic circuit 4 and the lead 2a are electrically connected via the aluminum thin wire 8 by a wire bonding method such as thermocompression bonding or ultrasonic wave.

The electronic circuit 4 is mounted on the lead frame 2, and after connecting the electronic circuit 4 and the lead 2a, these parts (circuit element 5, circuit board 6, lead frame 2, lead 2a) are collectively packaged. Then, a part of the lead 2a and the flange 2 are placed in a molding resin (hereinafter referred to as a sealing resin) 3.
It is buried except for part of c.

The sealing resin 3 is manufactured by transfer molding. Transfer molding is a method that generally uses a thermosetting resin such as epoxy resin as a sealing resin.The tablet-shaped epoxy resin obtained by compression molding powder is melted by applying a predetermined temperature and pressure in the mold. And to solidify. It is widely used as a package for chips such as LSI (Large Scale Integrated Circuit).

The sealing resin 3 is particularly a resin having a low linear expansion coefficient and entirely encloses the internal parts. The encapsulating resin 3 always maintains the adhesive force with the internal parts, and the peeling and the disconnection due to the thermal stress do not occur in the soldering part or the thin wire wire bonding connecting part between the semiconductor chip and the circuit board. Therefore, the optimum physical property value is selected.

In the electronic circuit device 1 for automobiles, due to repeated thermal stresses during use, there is a concern that water, oil, etc. may enter from the closely contacting interfaces between the sealing resin 3 and the leads 2a and the lead frame 2. . With respect to this point, the linear expansion coefficient difference between the lead 2a and the lead frame 2 and the sealing resin 3 is made as small as possible to reduce the thermal stress between these members, and a special surface treatment is applied to the lead 2a and the lead frame 2. This can be solved by a method of performing (for example, aluminum chelate treatment) and covalently bonding at the boundary between the resin and the member. For the leads 2a and the lead frame 2, copper or a copper-based alloy material having good thermal conductivity is selected. For the circuit board 6, an appropriate material such as ceramic, glass-ceramic, epoxy-glass plate, etc. is selected, and a predetermined circuit pattern is formed.

FIG. 4 shows an electronic circuit device 1 according to this embodiment.
FIG. 4 is an enlarged cross-sectional view of an essential part of FIG. 3 and corresponds to FIG. 3.
As shown in FIG. 4, a board supporting structure in which a projection 7 having an area smaller than that of the circuit board 6 is formed on the upper surface near the center of the lead frame 2, and the back surface of the central portion of the circuit board 6 is bonded to the projection 7. Is doing.

A wiring pattern (not shown) is formed on the circuit board 6, and the circuit elements 5 and the bonding pads 9 are soldered on the board 6. The lead frame 2 is provided with a protrusion 7 for adhering and supporting the center of the circuit board 6 with an adhesive 10 in the vicinity of the center, and three protrusions 11 for supporting the end of the circuit board 6 in this embodiment. Four
It is arranged at various places. These protrusions 7 and 11
Is formed by pressing the lead frame 2.

The protrusion 11 has a size, shape, and
An arbitrary number can be selected depending on the layout of the circuit pattern and the like. If this protrusion 11 is not provided, the substrate 6 will be inclined and adhered in the adhesion region only near the center due to the flatness error of the substrate 6 or the parallelism error between the flat surface of the lead frame 2 and the upper surface of the protrusion 7. Sometimes. An aluminum thin wire 8 is connected to the bonding pad 9 and the lead 2a by a wire bonding method such as thermocompression bonding or ultrasonic wave.

To give an example of the specific specifications of the lead frame 2, a phosphor bronze plate having a high thermal conductivity is selected.
After pressing, referring to FIG. 4, the thickness (t) is 0.6
The protrusion 7 has an outer diameter (d) of 5 mm, a height (h) of 1.44 mm, and a linear expansion coefficient of 17.5 ppm / ° C. In addition, the circuit board 6 formed by the presence of the protrusion 7
The gap (g) between the lead frames 2 is 0.8 mm. By the way, the maximum particle diameter of the filler mixed in the sealing resin 3 is 150 μm (0.15 mm). Therefore, a space in which the sealing resin 3 containing the filler can sufficiently flow is secured in this gap.

FIG. 5 shows a two-dimensional numerical model for analysis by the finite element method, which has a structure in which the circuit board 6 is bonded to the lead frame 2 by a conventional method. O is the center position of the circuit board 6 and the lead frame 2. Conventionally, generally, a structure has been adopted in which the entire back surface of the circuit board 6 is adhered to the lead frame 2 using an adhesive 10.
If the entire circuit board 6 is embedded in the sealing resin 3 with this adhesive structure, a large number of minute bubbles remaining when the adhesive 10 is cured expands and collapses due to the heat of the transfer molding process, and the lead frame 2 In addition, the problem of interface peeling was likely to occur in the vicinity of the contact interface between the adhesive portion of the circuit board 6 and the sealing resin 3.

In particular, in the process of removing the package (mold resin) 3 from the mold after cooling the sealing resin 3 and cooling to room temperature, the epoxy resin equivalent linear expansion coefficient is larger than the linear expansion coefficient of the lead frame 2, and Since the linear expansion coefficient of the circuit board 6 is also smaller than that of the lead frame 2,
The contracting stress of the adhered epoxy resin acts on the circuit board 6 and the lead frame 2, which, in combination with the expansion of the bubbles, causes the tensile stress to act on the portion having a weak adhesive force, resulting in separation at the boundary surface.

Particularly, thermal stress (peeling shear stress) concentration due to the difference in linear expansion coefficient between the circuit board 6 and the sealing resin 3 occurs near the four corners of the circuit board 6 where the shape changes abruptly, and peeling occurs at these portions. It is a thing. When peeling occurs in this portion, the peeling progresses further due to the temperature change during use. This peeling eventually leads to cracks in the sealing resin 3 and breaks in the soldering portion and the wire bonding portion, which are the electrical connection portions of the circuit element 5.

Here, the mechanism of interface separation between the circuit board 6 and the sealing resin 3 will be described in more detail. Transfer molding encapsulation resin 3 and lead frame 2
However, the encapsulation resin 3 is warped due to the combination of the physical property values of the electronic circuit element 5, the circuit board 6, the leads 2a, and the like, particularly the difference in the linear expansion coefficient.

In the example shown in FIG. 4, this warpage occurs in a convex direction on the lower side when the sealing resin 3 is taken out from the mold and cooled. The reason is that, in general, the melting temperature of epoxy resin is
150 to 200 ° C., glass transition temperature Tg is around 150 ° C., there is shrinkage during curing in the mold, and linear expansion coefficient between melting temperature and Tg is larger than Tg or less (about 4 times). ), The epoxy resin equivalent linear expansion coefficient is the circuit board 6
This is because it is larger than the linear expansion coefficient of.

For example, the circuit board 6 is made of glass ceramic, its linear expansion coefficient is 5.2 ppm / ° C., the linear expansion coefficient of the lead frame 2 is 17.5 ppm / ° C., and the apparent linear expansion coefficient of the sealing resin 3 ( That is, when the shrinkage ratio, the linear expansion coefficient between the melting temperature and the glass transition temperature Tg, and the linear expansion coefficient of the glass transition temperature Tg to the room temperature are combined to 30 ppm / ° C, A large shrinkage stress is generated in the sealing resin 3 due to the difference in the linear expansion coefficients. Further, since a space for mounting the circuit element 5 is required on the upper surface of the circuit board 6, the position of the circuit board 6 is arranged at the center or below the height direction of the sealing resin 3. Therefore, the thickness of the resin 3 is thicker in the upper part of the substrate than in the lower part, and as a result, the tensile force due to the contraction of the resin 3 is larger in the upper part of the circuit board 6 and the lower side is convex. As a result, the circuit board 6 and the lead frame 2 are protruded downward while being in close contact with each other.

Due to such warpage, thermal stress (peeling shear stress) concentration due to the difference in linear expansion coefficient between the circuit board 6 and the sealing resin 3 occurs near the four corners of the circuit board 6. When the thickness ratio of the sealing resin 3 is different, the size and the shape are different, the warp may be concave downward. Therefore, in this structure, peeling of the adhesive interface occurs,
It is a very important issue to have a structure that does not progress.

The circuit board 6 is preferably made of a material having a linear expansion coefficient close to that of a silicon chip which occupies most of the circuit element 5 and having a small difference in linear expansion coefficient from the sealing resin 3. When the value becomes large, a multilayer circuit board is preferable for miniaturization, and for example, a laminated glass / ceramic board or a ceramic board is suitable. However, with the above-mentioned adhesive structure, it was difficult to prevent partial peeling of the substrate as described above. In this embodiment, since the problem can be dealt with as follows,
The interface peeling prevention mechanism will be described with reference to FIGS. 6 and 19 to 21.

FIGS. 19 to 21 are examples showing specific dimensions of the present embodiment, and FIG. 6 shows a two-dimensional numerical model for analysis by the finite element method for this bonded structure portion. is there. Here, the representative physical property values of each member are shown in Table 1.
It is as follows.

[0041]

[Table 1]

As in FIG. 5, O in FIG. 6 is the center position of the circuit board 6 and the lead frame 2. In the present embodiment, the circuit board 6 and the entire lead frame 2 are covered with the sealing resin 3
However, the lead frame 2 is bonded to only a part of the circuit board 6 near the center where the thermal stress is very small through the projection 7. Therefore, when the adhesive 10 is cured, a large number of minute bubbles remain in the adhesive, and even if the bubbles expand due to the heat of the transfer molding process, they are generated at a portion where the thermal stress is small, so there is no problem. ,Also,
By interposing the sealing resin 3 also between the lead frame 2 and the circuit board 6, the thicknesses of the lower side of the board 6 and the upper side of the board 6 are balanced, whereby the resin near the four corners of the circuit board 6 is formed. The concentration of thermal stress can be relaxed, and in combination, the peeling between the sealing resin 3 and the four corners of the circuit board 6 and the occurrence of cracks in the sealing resin 3 can be prevented.

FIG. 7 is a comparison diagram of the results of a simulation analysis using a finite element method of the peeling shear stress of the adhesive portion of the circuit board 6 in the conventional structure of FIG. 5 and the structure of this embodiment of FIG. Yes, the shear stress distributions at the interfaces AA ′ (FIG. 5) and BB ′ (FIG. 6) between the circuit board 6 and the adhesive 10 are compared.

The origin (y = 0) on the horizontal axis in FIG. 7 corresponds to points A and B. Since these stresses have a distribution that increases as they approach the origin, they have the action of attempting to cause interface debonding starting from points A and B.
It can be seen that the structure of this embodiment is always significantly smaller than the stress of the conventional structure.

In addition to the above effects, the present embodiment can also provide the following effects. That is, although the high heat generating element is used depending on the circuit function, as shown in FIG. 4, the high heat generating element of the circuit elements 5 corresponds to the center of the substrate, that is, the position where the protrusion 7 is present. If it is arranged at a location, the heat radiation effect via the projection 7 can be enhanced.

Incidentally, a part of the heat generated in the electronic circuit 4 is
The surface of the circuit element 5 mounted on the circuit board 6 is radiated to the upper part by the heat conduction of the sealing resin 3, and the other part is radiated to the circuit board 6.
It escapes to the external mating member (mounting position of the electronic circuit device) connected to the flange via the lower sealing resin 3 and the flange portion 2c in the plane direction of the lead frame 2.

Further, as shown in FIG. 18, in addition to disposing the high heat generating element of the circuit element 5 on the upper part of the protrusion 7 through the circuit board 6, the portion on the protrusion 7 of the circuit board 6 is thermally conducted. If the heat generating element 5 and the projection 7 are brought into contact with each other through the thermal via 20 so that the heat is conducted to the lead frame 2, the circuit element 5 of The temperature rise can be reduced.

FIG. 8 shows the details of the first embodiment of the lead frame 2 before the lead 2 is separated, and FIG. 9 shows the details of the second embodiment. Here, in the first and second embodiments, as shown in FIG. 10, the heights of the protrusion 7 and the protrusion 11 are different from each other. The height h1 of the protrusion 7 is set slightly lower than the height h2 of the protrusion 11. Therefore, the difference δ becomes the thickness of the adhesive 10.

When the heights of the protrusions 7 and 11 are the same, when the circuit board 6 is placed, variations occur due to respective height manufacturing errors and flatness errors (warpage) of the circuit board 6.
It is unspecified which part is in contact. In the structures of the first and second examples of the present embodiment, when the adhesive 10 is applied to the protrusions 7 and the circuit board 6 is placed, an adhesive thickness δ within a predetermined range is obtained. This is very important.

It is generally said that the thinner the adhesive thickness δ, the higher the adhesive strength, and the thicker the adhesive thickness, the lower the adhesive strength. However, if it is too thin, in the case of the structure of the example of the present embodiment, the stress strain due to the difference in linear expansion coefficient between the circuit board 6 and the lead frame 2 cannot be absorbed, so that the peeling of the adhesive interface is likely to occur. Therefore, there is an optimum thickness capable of absorbing the strain and obtaining an adhesive force to some extent, and the thickness can be secured.

When the adhesive thickness δ is different for each product, some of them have insufficient adhesive strength, and peeling may occur after transfer molding or under use environment conditions, particularly, temperature change. . When peeling occurs, the thermal resistance at that portion increases, the amount of heat conducted from the lead frame 2 decreases, and the temperature rise of the circuit element 5 increases.
Further, this peeling serves as a starting point, and the circuit board 6 and the sealing resin 3
Affects the vicinity of the adhesion interface with and develops interfacial peeling at that part.

In the case of this kind of adhesive, for example, an epoxy adhesive, an adhesive having a good compatibility with the lead frame 2 and the circuit board 6, particularly, viscosity during work or immediately before curing, tensile strength, linear expansion coefficient, Young's modulus , Physical properties such as thermal conductivity and elongation are taken into consideration. Therefore, the epoxy component contains a predetermined amount of an inorganic filler, a filler such as carbon, and the inorganic filler is generally quartz powder or alumina powder having a maximum particle diameter of several to several tens of μm. Is being used for.

Therefore, in this case, the adhesive thickness δ when the circuit board 6 is mounted is not thinner than this particle size, but as described above, the strain cannot be absorbed and the adhesive thickness becomes too thick. When it occurs, the adhesive strength is reduced. By making this thickness within a predetermined range, it is possible to reduce the variation in the adhesive force and ensure the adhesive reliability.

Here, as the value of the adhesive thickness δ, as shown in Table 1,
In the examples of FIGS. 19 to 21, 30 μm to 200 μm
Was the optimum value. If the adhesive thickness δ is too thick, there is a problem that the above-mentioned adhesive strength is reduced and the thermal resistance at the joint between the circuit board 6 and the lead frame 2 is increased. The adhesive 10 may be made of a material having a high thermal conductivity, for example, a conductive epoxy resin containing silver, but there are problems such as low adhesive strength and high price. Therefore, the adhesive thickness δ described above differs depending on the type of adhesive base material, the type of inclusions, the blending ratio thereof, etc., and therefore it is necessary to determine the optimum value for the selected one.

In order to reduce variations in the thickness δ of the adhesive 10, in the first embodiment shown in FIG. 8, four protrusions 11 are provided as support portions for the circuit board 6. When the circuit board 6 is placed, there may be a case where one portion is not in contact with the lower surface of the circuit board 6 due to manufacturing errors of the heights of the projections 7 and the projections 11 and a flatness error (warpage) of the circuit board 6. The thickness δ of the adhesive 10 can be ensured to have a predetermined value in consideration of the respective errors.

In the second embodiment shown in FIG. 9, the projections 11 are provided at three places as the supporting portions of the circuit board 6. With the three-point support, when the circuit board 6 is placed, the three points always come into contact with the lower surface of the circuit board 6, so that it is not unspecified which portion comes in contact with the four-point support. In this case, the contact states of the protrusion 11 and the circuit board 6 are all the same, and the sealing resin 3, the circuit board 6, and the lead frame 2 in that portion are the same.
There is an advantage that the mutual adhesiveness is balanced and no bias occurs. The lead frame 2 includes the protrusions 7 and 11,
Circuit mounting portion 2 ', lead 2a, bonding portion 2b, flange portion 2c, hole portion 2d, connecting portion 2e, frame portion 2
f and notches 2g, which are formed by pressing.

Next, a method for forming the shapes of the protrusion 7 and the protrusion 11 of FIG. 10 by pressing will be described in detail. Both the protrusion 7 and the protrusion 11 are formed by drawing or overhanging (hereinafter collectively referred to as drawing), but they are formed by so-called double drawing. If the material hardness of the lead frame 2 is low, it can be formed by drawing once, but if the hardness is high, the elongation rate of the material is small, and cracks are likely to occur in the material near the stress concentration portion from the flat surface to the drawing. In the structure of this embodiment, for example, the material is phosphor bronze and the hardness is H.
In the case of v120 (Vickers hardness 120) and the elongation rate of 5%, cracking occurred at one drawing, but it did not occur in the material having the elongation rate of 10%. Further, in the case of drawing twice, cracks did not occur even at an elongation of 5%, and good results were obtained. If the material hardness of the lead frame 2 is low, the strength is also low, and it is preferable that the hardness is high in order to enhance the vibration resistance when mounted on an actual machine.

FIG. 11 shows an example of the shape at the time of one stop before performing the twice stop to obtain the shape of FIG. The heights of the protrusion 7 and the protrusion 11 are h1 ′ and h, respectively.
2'is set slightly higher than h1 and h2 in FIG. Then, the shape of FIG. 10 is obtained by the second stop.

In the shape shown in FIG. 10, the upper surface of the protrusion 10 has a flat area as wide as possible with respect to the outer diameter d. If this shape is obtained by drawing once, the above-mentioned cracks are likely to occur, so that the flat upper surface region cannot be made large. The flat area needs to be widened to some extent in order to increase the adhesive strength of the adhesive 10, and the double drawing is effective.

The upper surface of the protrusion 11 only comes into contact with the circuit board 6 and does not adhere to it. Therefore, the protrusion 11 may be a spherical surface in terms of function, but when the height dimension h2 is measured or when the press die is manufactured with accuracy. From the point, it is better to have a flat surface even in a small area. Further, the recessed portion 11a on the lower surface is formed by crushing a part of the plate thickness t, but it has an effect of reducing residual stress in the vicinity thereof, as compared with the method of forming the plate thickness t to have the same plate thickness. If the residual stress is large, the lead frame 2 is largely deformed by heat during transfer molding, and a local thermal stress displacement occurs at the contact interface with the encapsulating resin 3 to cause easy peeling.

As shown in FIGS. 8 and 9, the surface portion (bonding pad) 2b for connecting the aluminum thin wire 8 by wire bonding is plated with nickel, silver or the like to prevent the surface from being oxidized. Partially applied. The flange portion 2c is for fixing to a mating member, and the hole 2d is provided for positioning a jig during assembly.

The notch 2g determines the directionality,
It is provided for the purpose of reducing the mold alignment error at the time of transfer molding that is caused by manufacturing error. Further, when the sub-assembly shown in FIG. 12 is set in this mold, it also serves the purpose of preventing it from going in the opposite direction. When the lead frame 2 has a symmetrical shape, the notch 2g may be selected to have an arbitrary shape and position that can identify the front and back.

The connecting portion 2e, the frame portion 2f, and the flange portion 2c have a closed loop structure because the epoxy resin is melted in the die by tightening this portion with a transfer mold. This is to prevent the liquid resin from leaking to the outside even when it becomes liquid by the closed loop portion.

Since a gap due to a manufacturing error is formed between the width of the lead 2a to be fitted and the mold, the liquid epoxy resin leaks to the outside at this portion, but due to the closed loop structure, In the loop, after curing, it remains as a thin burr that will be removed in a later step.

FIG. 12 shows a sub-assembly state in which the circuit board 6 constituting the electronic circuit 4 of the present embodiment is placed on the lead frame 2 and the circuit board 6 is bonded to the projection 7. The adhesive 10 is made of a material such as epoxy resin or acrylic resin having good thermal conductivity, and is applied on the upper portion of the protrusion 7 and then the circuit board 6 is mounted. The circuit board 6 has an adhesive 10
When it is liquefied in the heating step of curing, it falls by its own weight, but since the protrusion 11 is set higher than the protrusion 7 in advance, it does not fall more than that amount, and an adhesive layer with a predetermined thickness is formed. . The adhesive 10 is selected to have an optimum viscosity so that the substrate 6 and the protrusion 7 can be bonded to each other with a predetermined layer thickness without a gap.

FIG. 13 is a plan view of the sub-assembly shown in FIG. 12, and FIG. 14 is a cross-sectional view showing a state of a jig for wire bonding work.
After the bonding work is completed, the upper and lower portions of the lead 2a of the lead frame 2 are sandwiched by the upper jig 12 and the lower jig 13, and the lower portion of the substrate 6 is vacuum-sucked by the suction jig 14, so that the sub-assembly does not move. To hold. Then, the aluminum thin wire 8 is electrically connected to the electronic circuit 4 and the lead 2a by a thermocompression bonding or a wire bonding method such as ultrasonic wave.

After the wire bonding work is completed, transfer molding is performed with the sealing resin 3 in the portion shown by the dotted line in FIG. After this molding, the connecting portion 2e and the frame portion 2f of the lead frame 2 are cut to form a plurality of independent leads 2a, and the flange portion 2c is punched and bent into a predetermined shape,
The control unit 1 is completed.

FIG. 15 is a partial plan view showing a structure for mounting the electronic circuit device according to this embodiment on an external mating member, FIG. 16 is a sectional view thereof, and FIG. 17 is a partial sectional view thereof. In the present embodiment, as an example, the electronic circuit device 1 is attached to a transmission of an automobile. When the electronic circuit device 1 is attached, the flange portion 2c is pressed and fixed by the bracket 15 as described below. To do.

The mounting portion comprises a first bracket 15, a second bracket 16, a washer 17, and a bolt 18. Components such as a sensor, a connector, and a wire harness (not shown) are mounted on the first bracket 15.
A plurality of tongue pieces 15a are provided on a part of the first bracket 15,
The second bracket 16 is inserted into the small hole 16a and the tip is bent to integrate the two.

The flange portion 2c is sandwiched between the first and second brackets 15 and 16. The bolt 18 is tightened through the brackets 15 and 16 while avoiding the flange portion 2c. As a result, the flange portion 2c is sandwiched between the brackets 15 and 16, and is fastened together with the washer 17, the second bracket 16, and the first bracket 15 to the mating member, for example, the body of the transmission. With such a mounting structure, the following points can be improved.

That is, in the structure in which the holes for fixing bolts are provided in the flange portion 2c, the area of the flange portion 2c must be increased by that amount, and thus the outside of the lead frame 2 must be increased. However, when a large number of products are taken at one time by transfer molding, there is a drawback that the number taken is small. This defect can be eliminated by using a minimum flange size and fixing it with a bracket as described later.

Further, as described above, the sealing resin 3 may be convex on the lower side due to heat shrinkage stress during molding. When the mating member is in a planar state, for example, when the flange portion 2c of the lead frame 2 is fixed while the lower surface of the encapsulating resin 3 is in direct contact with this surface in a convex state on the lower side, the central portion of the encapsulating resin 3 is opposed. Be restrained by members. As a result, the warping of the sealing resin 3 is corrected, so that excessive stress acts on the bonding interface between the sealing resin 3 and the lead frame 2, and there is a risk of peeling between the two.

According to the above-described structure, the bracket 15 also functions as a spacer, so that a gap is provided between the mating member and the lower surface of the sealing resin 3, and the flange portion provided near the outermost shape of the lead frame 2 is provided. Only 2c can be pressed. Therefore, the excessive stress as described above can be avoided, and the problem of peeling does not occur. Further, the lead frame 2 is formed by the first bracket 15 and the second bracket 16.
Since the flange portion 2c is sandwiched and the tongue piece 15a is bent and integrated, there is also an advantage that it can be easily handled when it is mounted on a mating member.

[0074]

As can be understood from the above description, in the electronic circuit device of the present invention, protrusions are provided in the vicinity of the center of the lead frame and in the area smaller than the outer shape of the electronic circuit board, and the protrusions near the center are Since it has a structure in which the electronic circuit board is bonded only to the protrusions near the center by making it a predetermined value lower than the protrusions, the optimum thickness can be secured without the adhesive layer being too thin and not too thick. It is possible to prevent peeling of the interface with the sealing resin and generation of cracks. Therefore, it is possible to package the electronic circuit board and its lead frame with molding resin at low cost.
It is possible to provide an automobile electronic circuit device having excellent heat dissipation and waterproof properties.

[Brief description of drawings]

FIG. 1 is a partially cutaway plan view of an automobile electronic circuit device according to an embodiment of the present invention.

FIG. 2 is a side view of a part of the automobile electronic circuit device shown in FIG.

FIG. 3 is another side view of a part of the electronic circuit device for automobiles of FIG.

4 is a cross-sectional view of a main part of the automobile electronic circuit device of FIG.

FIG. 5 is a two-dimensional numerical model of a structure in which a conventional substrate is bonded to a lead frame.

FIG. 6 is a two-dimensional numerical model of a structure in which the substrate of the present embodiment is bonded to a lead frame.

FIG. 7 is an explanatory diagram showing the results of a simulation analysis of the peeling shear stress of the substrate bonding portion in the conventional structure and the present embodiment using the finite element method.

FIG. 8 is a plan view showing details of a lead frame that is a first example of the present embodiment.

FIG. 9 is a plan view showing details of a lead frame that is a second example of the embodiment.

FIG. 10 is a CC of the protrusion of the lead frame of FIGS. 8 and 9;
Sectional drawing and DD sectional view.

11 is a cross-sectional view showing a shape of a single press of the press for forming the shape of the protrusion of FIG.

FIG. 12 is a cross-sectional view showing a sub-assembly state in which a substrate that constitutes the electronic circuit of the present embodiment is bonded to a lead frame.

FIG. 13 is a plan view of a subassembly of the electronic circuit device of this embodiment.

FIG. 14 is a view showing a state of performing a wire bonding operation on the subassembly of the electronic circuit device of FIG.

FIG. 15 is a partial plan view showing a structure for mounting the electronic circuit device of FIG. 13 on an external mating member.

16 is a side sectional view of the electronic circuit device of FIG.

17 is a partial cross-sectional view of the electronic circuit device of FIG.

FIG. 18 is a cross-sectional view of essential parts of an electronic circuit device according to another embodiment of the present invention.

FIG. 19 is a cross-sectional view showing an example of specific implementation dimensions of the electronic circuit device of the embodiment of FIG.

FIG. 20 is a partially cutaway plan view showing an example of specific implementation dimensions of the electronic circuit device according to the embodiment of FIG. 1;

21 is a partially cutaway side view of the electronic circuit device according to the embodiment of FIG. 20. FIG.

[Explanation of symbols]

1 ... Control unit (electronic circuit device) 2 ... Lead frame 2a ... lead 2c ... Flange part 3 ... Sealing resin 4 ... Electronic circuit 5 ... Electronic circuit element 6 ... Circuit board 7 ... Protrusion 11 ... Protrusion

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hisashi Yukita             Hitachinaka City, Ibaraki Prefecture 2520 Takaba             Ceremony Company Hitachi Ltd. Automotive equipment group

Claims (10)

[Claims] 1. A circuit board on which an electronic circuit element is mounted and a lead frame on which the circuit board is mounted are provided, and the circuit board and a portion excluding a part of the lead frame are collectively molded resin. An embedded electronic circuit device for an automobile, wherein the lead frame is provided with a first protrusion in the vicinity of the center thereof and a plurality of second protrusions around the protrusion, and the first protrusion is provided with the second protrusion. An electronic circuit device for an automobile, wherein a height of the protrusion is lower than a predetermined value, and the circuit board is bonded only to the first protrusion. 2. The electronic circuit device for an automobile according to claim 1, wherein the plurality of second protrusions are arranged closer to the first protrusion than an outer periphery of the circuit board. 3. The electronic circuit device for an automobile according to claim 1, wherein the first protrusion is one and the second protrusion is three or four. 4. The lead frame includes a flange portion and a lead, the circuit board and the lead are electrically connected to each other, and the lead frame and the flange are partially embedded in a molding resin except for a part thereof. The electronic circuit device for an automobile according to claim 1, wherein the electronic circuit device is for an automobile. 5. The first and second protrusions are formed by pressing the lead frame.
The electronic circuit device for an automobile according to any one of 1. 6. A structure in which a portion of the flange portion protruding from the mold resin is used as a mounting portion, and heat of the circuit board is conducted to the outside through the flange portion. The electronic circuit device for an automobile according to. 7. The electronic circuit device for an automobile according to claim 1, wherein the circuit board is made of glass-ceramic or ceramic-based material. 8. The electronic circuit device for an automobile according to claim 1, wherein the circuit board is a multilayer circuit board. 9. The automobile electronic circuit device mounting structure according to claim 1, wherein the flange of the lead frame is provided between the first bracket and the second bracket on the automobile side. An electronic circuit device mounting structure for an automobile, characterized in that the parts are sandwiched and fastened and fixed by bolts or the like. 10. A plurality of tongue pieces provided in a part of the first bracket are inserted into a small hole provided in the second bracket, and a tip portion is bent to integrate the both. The mounting structure for an automobile electronic circuit device according to claim 9.