JP2014107482A - Electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic device which allows for enhancement of immunity/ESD tolerance without causing the up-sizing, even when an electronic component is housed in a conductive housing.SOLUTION: An insulating adhesive 20 is interposed between a lead frame 14 and the inner surface at the insertion part 11b of a housing 11. In order to protect an electronic component housed in the lead frame 14 from a noise current resulting from electrostatic discharge applied to the lead frame 14, an ESD diode 16 for connection with the lead frame 14 is housed in the housing 11. The lead frame 14 is formed so that the path length Lb of a coating part 14a covered with the insulating adhesive 20, where the noise current flows, is longer than the length La of the insulating adhesive 20 in the insertion direction.

Description

  The present invention relates to an electronic device in which an electronic component is accommodated in a conductive casing.

  2. Description of the Related Art Conventionally, in an electronic apparatus configured by housing one or more electronic components such as a semiconductor device in a casing, current generated due to electrostatic discharge applied to external connection terminals such as lead frames and signal pins ( An electrostatic discharge protection circuit that is electrically connected to the external connection terminal in the housing is provided when it is necessary to protect the electronic component from the noise current (hereinafter referred to as noise current). However, in a conductive housing, for example, a metal housing, if noise current flows into the housing itself via the external connection terminal, a part of the noise current is generated in the housing even when the housing is grounded. In some cases, the electronic component in the housing may be reached via the installation surface. In this case, electrostatic breakdown or malfunction may occur in the electronic component due to noise current.

  As a technique for solving such a problem, a semiconductor device disclosed in Patent Document 1 below is known. This semiconductor device includes a field effect transistor (FET) using gallium arsenide (GaAs), and a spiral coil portion having a spiral coil shape is formed at the end of a lead frame connected to the gate electrode of the GaAsFET. Yes. Since this spiral coil portion has high reactance with respect to high frequency noise, immunity / ESD resistance is improved and noise propagation to the semiconductor device is suppressed.

Japanese Patent No. 3130809

  However, in the configuration for improving the immunity / ESD resistance as described above, it is necessary to provide a spiral portion in the lead frame accommodated in the housing, and the device itself becomes large. In particular, as the noise current to be suppressed increases, the spiral portion needs to be enlarged, which makes it difficult to reduce the size of the device.

  The present invention has been made to solve the above-described problems, and the object of the present invention is to improve immunity / ESD resistance without causing an increase in size even when an electronic component is housed in a conductive casing. It is to provide an electronic device that can be improved.

In order to achieve the above-mentioned object, the invention according to claim 1 of the present invention is an electronic device (10, 10a, 10b) in which electronic components (12a-12d) are accommodated in a conductive casing (11). ), A terminal for electrically connecting the electronic component and an electronic device outside the casing, and the insertion portion (11b) formed in the casing is inserted without contacting the casing. It is caused by the external connection terminal (14) arranged on the dielectric, the dielectric (20) interposed between the external connection terminal and the inner surface of the insertion portion, and electrostatic discharge applied to the external connection terminal. An electrostatic discharge protection circuit (16) housed in the housing and connected to the external connection terminal to protect the electronic component from the noise current. The external connection terminal covers the dielectric. Covered parts (14a, 14 The noise current flows path length of) (Lb) is being formed to be longer than the length of the insertion direction of the dielectric (La).
In addition, the code | symbol in the parenthesis of a claim and the said means shows a corresponding relationship with the specific means as described in embodiment mentioned later.

  In the first aspect of the present invention, a dielectric is interposed between the external connection terminal and the inner surface of the insertion portion of the housing, and the noise current generated due to the electrostatic discharge applied to the external connection terminal In order to protect the electronic components housed in the housing, an electrostatic discharge protection circuit connected to the external connection terminal is housed in the housing. The external connection terminal is formed such that the path length through which the noise current of the covering portion covered with the dielectric flows is longer than the length in the insertion direction of the dielectric.

  As a result, the mutual inductance between the housing and the external connection terminal is larger than that in the conventional configuration in which the length of the path through which the noise current in the covering portion flows is the same as the length in the insertion direction of the dielectric. Therefore, it becomes difficult for noise current to flow into the housing itself via the external connection terminal and the dielectric. For this reason, noise current flows through the external connection terminals in the housing space of the housing, and the electronic components housed in the housing are protected from this noise current by the electrostatic discharge protection circuit. In this way, noise current is less likely to flow into the housing itself, and it is not necessary to provide a spiral coil portion or the like inside the housing, which leads to an increase in size even when electronic components are housed in a conductive housing. Thus, the immunity / ESD resistance of the electronic device can be improved.

It is sectional drawing which shows schematic structure of the electronic device which concerns on 1st Embodiment. It is explanatory drawing which shows arrangement | positioning with an ESD diode and the element of the protection object. It is explanatory drawing for demonstrating the influence of the noise current via the external connection terminal with respect to the electronic component accommodated in a housing | casing. It is a graph which shows the relationship between the mutual inductance for every self-inductance, and an applied voltage ratio. It is sectional drawing which expands and shows the coating | coated part of the lead frame hold | maintained at a housing | casing through a dielectric material. It is sectional drawing which shows the principal part of the electronic device which concerns on the modification of 1st Embodiment. It is sectional drawing which shows the principal part of the electronic device which concerns on 2nd Embodiment. It is sectional drawing which shows the principal part of the electronic device which concerns on the modification of 2nd Embodiment. It is sectional drawing which shows the principal part of the electronic device which concerns on 3rd Embodiment. It is sectional drawing which shows the principal part of the electronic device which concerns on the modification of 3rd Embodiment. It is a graph which shows the frequency dependence of the magnetic permeability when a Ni-Zn type ferrite powder is contained in an insulating adhesive.

[First Embodiment]
Hereinafter, a first embodiment of an electronic device according to the present invention will be described with reference to the drawings.
As shown in FIG. 1, an electronic device 10 according to the present embodiment is configured by housing a plurality of electronic components in a conductive casing 11 made of a metal material or the like. In the present embodiment, for example, four semiconductor devices 12a to 12d are arranged and accommodated on the bottom wall 11a via an insulator 13 such as an adhesive. Examples of the semiconductor devices 12a to 12d include a logic circuit, a sensor, a power device, an SRAM, and a flash memory. In FIG. 1, illustration of other electronic components and the like housed in the housing 11 is omitted for convenience.

  At least a part of each of the semiconductor devices 12a to 12d and other electronic components is bonded to any one of a plurality of lead frames 14 configured as external connection terminals for electrical connection with an electronic device outside the housing 11. It is electrically connected via a wire 15 or the like. Among the semiconductor devices 12a to 12d, an electrostatic discharge protection circuit is provided in a semiconductor device that needs to be protected from noise current generated due to electrostatic discharge applied to the lead frame 14. For example, as shown in FIG. 2, the semiconductor device 12 a is provided on the chip as an electrostatic discharge protection circuit so that the ESD diode 16 is connected to the input terminal 17 connected to the lead frame 14. Further, an element 18 (for example, PolyCapa) that is a protection target of the ESD diode 16 is connected to the input terminal 17 via a predetermined resistor 19.

  A part of each lead frame 14 is exposed to the outside through a through hole 11 b formed as an insertion part on the side wall of the housing 11. Each insertion hole 11b is comprised by combining the recessed parts formed in the upper edge of a lower case, and the lower edge of an upper case, respectively, when the housing | casing 11 is comprised by the assembly | attachment of an upper and lower case, for example.

  Between the intermediate portion of the lead frame 14 and the inner surface (inner peripheral surface) of the insertion hole 11b, insulation is provided to suppress conduction between the lead frame 14 and the housing 11 and to hold the lead frame 14. Insulating adhesives 20 made of an epoxy resin are interposed, and the lead frames 14 and the casing 11 are not in direct contact with each other. The detailed configuration of the insulating adhesive 20 and the intermediate part of the lead frame 14 (hereinafter referred to as the covering part 14a) covered with the insulating adhesive 20 will be described later. The lead frame 14 is not limited to being inserted through the insertion hole 11b having a cylindrical inner peripheral surface with the insulating adhesive 20 interposed therebetween, but to other shapes of insertion portions. Then, the insulating adhesive 20 may be inserted therethrough. The adhesive 20 can correspond to an example of a “dielectric” recited in the claims.

  Next, the influence of the noise current through the external connection terminal 14 on each of the semiconductor devices 12a to 12d accommodated in the housing 11 will be described in detail with reference to FIGS. FIG. 3 is an explanatory diagram for explaining the influence of noise current through the lead frame 14 on the electronic component 12 accommodated in the housing 11. FIG. 4 is a graph showing the relationship between the mutual inductance M for each self-inductance Lk and the device applied voltage ratio.

  Normally, the noise current generated as described above is reduced by the ESD diode 16 when flowing through the current path between the lead frame 14 and the electronic component 12 (see arrow α in FIG. 3). However, since the conductive housing 11 is employed, a part of the noise current is passed through the lead frame 14 and the insulating adhesive 20 due to capacitive coupling between the insulating adhesive 20 and the housing 11. May flow into the housing 11 itself (see arrow β in FIG. 3). The noise current that has flowed into the housing 11 itself as described above is partially lost even when the housing 11 is grounded and the insulator 13 is interposed between the inner surface of the housing 11 and the electronic component 12. The electronic component 12 may be reached through the insulator 13.

Therefore, in the present embodiment, the lead frame 14 is configured to increase the mutual inductance M between the lead frame 14 and the housing 11 in order to reliably suppress the noise current as described above from flowing into the housing 11 itself. Is formed. This is because increasing the mutual inductance M makes it difficult for noise current to flow into the casing 11 itself. This mutual inductance M is expressed by the following equation, where μ ₁ is the magnetic permeability of the lead frame 14, l ₁ is the length of the path through which the noise current flows in the covering portion 14 a of the lead frame 14, and d is the distance between the lead frames 14. The relationship (1) is established.

As shown in FIG. 4, regardless of the self-inductance Lk of the housing 11, the ratio of the voltage applied to the electronic components arranged in the housing 11 (device applied voltage ratio) increases as the mutual inductance M increases. It turns out that it reduces. For example, under the conditions shown in FIG. 4, assuming that the device applied voltage ratio is 0.3 and the electronic component is destroyed, if the self-inductance Lk = 1.0 × 10 ⁻¹² (H), the mutual inductance M is If it exceeds about 6.0 (H), the electronic components are prevented from being destroyed. If the self-inductance Lk = 1.0 × 10 ⁻⁹ (H), the mutual inductance M is about 1.0 (H). If exceeded, destruction of the electronic components is prevented. When the self-inductance Lk = 1.0 × 10 ⁻⁶ (H), the electronic component is prevented from being destroyed regardless of the value of the mutual inductance M.

Next, a specific configuration for increasing the mutual inductance M as described above will be described with reference to FIG. FIG. 5 is an enlarged cross-sectional view showing the covering portion 14 a of the lead frame 14 held by the housing 11 via the insulating adhesive 20.
As shown in FIG. 5, in the covered portion 14 a of the lead frame 14, the path length (see the dashed line in FIG. 5) Lb through which the noise current flows is longer than the length La in the insertion direction of the insulating adhesive 20. Thus, it is formed so as to be folded.

  That is, in the electronic device 10 according to the present embodiment, the insulating adhesive 20 is interposed between the lead frame 14 and the inner surface of the insertion hole 11 b of the housing 11, and electrostatic discharge applied to the lead frame 14 is prevented. An ESD diode 16 connected to the lead frame 14 is housed in the housing 11 in order to protect the electronic components housed in the housing 11 from noise current caused by the noise. The lead frame 14 is formed such that the path length Lb through which the noise current of the covering portion 14 a covered with the insulating adhesive 20 flows is longer than the length La in the insertion direction of the insulating adhesive 20. .

  As a result, the mutual inductance M between the housing 11 and the lead frame 14 is such that the path length Lb through which the noise current of the covering portion 14a flows is the same as the length La of the insulating adhesive 20 in the insertion direction. Since it becomes larger than the configuration, it is difficult for noise current to flow into the housing 11 itself via the lead frame 14 and the insulating adhesive 20. For this reason, noise current flows through the lead frame 14 in the housing space of the housing 11, and the electronic components housed in the housing 11 are protected from the noise current by the ESD diode 16. Thus, it becomes difficult for noise current to flow into the housing 11 itself, and it is not particularly necessary to provide a spiral coil portion or the like inside the housing 11, so that even when an electronic component is accommodated in the conductive housing 11, the size is increased. It is possible to improve the immunity / ESD resistance of the electronic device 10 without incurring any damage.

FIG. 6 is a cross-sectional view illustrating a main part of an electronic device 10 according to a modification of the first embodiment.
As the covering portion of the lead frame 14, a covering portion 14a formed so as to be folded is employed in order to make the path length Lb through which the noise current flows longer than the length La in the insertion direction of the insulating adhesive 20. However, the present invention is not limited to this, and other shapes of covering portions may be employed. Specifically, for example, as shown in FIG. 6, by adopting a mountain-shaped covering portion 14 b, the path length Lb of the covering portion 14 b is made longer than the length La in the insertion direction of the insulating adhesive 20. Can be formed long.

[Second Embodiment]
Next, an electronic device according to a second embodiment of the present invention will be described with reference to FIG. FIG. 7 is a cross-sectional view illustrating a main part of the electronic device 10a according to the second embodiment.
The electronic device 10a according to the second embodiment is different from the electronic device according to the first embodiment in that a high magnetic permeability member 21 is newly employed in order to further improve immunity / ESD resistance. Therefore, substantially the same components as those of the electronic device of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  In the present embodiment, as shown in FIG. 7, a high permeability member 21 having a higher permeability than the insulating adhesive 20 is provided between the insulating adhesive 20 around the covering portion 14 a of the lead frame 14 described above. It is wound and interposed. Here, as the high magnetic permeability member 21, for example, Kovar TM, 42 alloy, Invar core, 42 alloy core, Permalloy B, SUS430, Permalloy C or the like can be employed.

  Even in this case, since the mutual inductance M between the housing 11 and the lead frame 14 is increased, it is difficult for noise current to flow into the housing 11 itself via the lead frame 14 and the insulating adhesive 20. Even when an electronic component is accommodated in the flexible casing 11, the immunity / ESD resistance of the electronic device 10 can be improved without causing an increase in size.

FIG. 8 is a cross-sectional view showing a main part of an electronic device 10a according to a modification of the second embodiment.
As shown in FIG. 8, a high magnetic permeability member 21 is wound around a conventional covering portion 14c in which the path length Lb through which the noise current flows is equal to the length La in the insertion direction of the insulating adhesive 20. A high magnetic permeability member 21 may be interposed between the portion 14 c and the insulating adhesive 20. Even in this case, since the mutual inductance M between the housing 11 and the lead frame 14 is increased, it is difficult for noise current to flow into the housing 11 itself via the lead frame 14 and the insulating adhesive 20. Even when an electronic component is accommodated in the flexible casing 11, the immunity / ESD resistance of the electronic device 10 can be improved without causing an increase in size.

  Further, in order to increase the mutual inductance M, the high permeability member 21 is not limited to being interposed between the covering portion 14a or the covering portion 14c and the insulating adhesive 20, and the covering portion 14b is insulatively bonded. The lead frame 14 may be interposed between the adhesive 20 and the length of the path Lb through which the noise current flows is longer than the length La in the insertion direction of the insulating adhesive 20. It may be interposed between the insulating adhesive 20.

[Third Embodiment]
Next, an electronic device according to a third embodiment of the present invention will be described with reference to FIG. FIG. 9 is a cross-sectional view showing a main part of an electronic device 10b according to the third embodiment.
In the electronic device 10b according to the third embodiment, in order to further improve the immunity / ESD resistance, the electronic device according to the first embodiment is formed such that the housing 11 increases its self-inductance Lk. And different. Therefore, substantially the same components as those of the electronic device of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

In the present embodiment, the housing 11 is formed so as to increase its self-inductance Lk in order to reliably suppress noise current from flowing into the housing 11 itself. This is because increasing the self-inductance Lk makes it difficult for noise current to flow into the housing 11 itself. This self-inductance Lk is shown below when μ ₂ is the magnetic permeability of the casing 11, l ₂ is the length of the casing 11 in the noise current propagation direction, and a is the thickness of the casing 11 in the noise current propagation direction. The relationship of Formula (2) is materialized.

Therefore, in the present embodiment, as shown in FIG. 9, an uneven portion 11 c is formed on the inner surface of the insertion hole 11 b of the housing 11 so as to increase the surface area. As a result, the length l ₂ of the casing 11 in the noise current propagation direction can be increased, and the self-inductance Lk can be increased.

  In the present embodiment, as shown in FIG. 9, a recess 11 d is formed on the bottom wall 11 a where the semiconductor devices 12 a to 12 d are arranged so that the thickness thereof is thinner than the other walls. Yes. Thereby, the thickness a of the housing | casing 11 of a noise current propagation direction can be made small, and the self inductance Lk can be increased.

  Thus, by increasing the self-inductance Lk of the housing 11, it becomes difficult for noise current to flow into the housing 11 itself via the lead frame 14 and the insulating adhesive 20, and the electronic device 10 does not increase in size. Immunity / ESD resistance can be improved.

FIG. 10 is a cross-sectional view showing a main part of an electronic device 10b according to a modification of the third embodiment.
As shown in FIG. 10, when the above-described covering portion 14 c is employed, the uneven portion 11 c may be formed on the inner surface of the insertion hole 11 b of the housing 11. Even in this case, since the self-inductance Lk of the housing 11 is increased, it is difficult for noise current to flow into the housing 11 itself via the lead frame 14 and the insulating adhesive 20, and the electronic device is not increased in size. The immunity / ESD resistance of 10 can be improved.

  In addition, at least any one of the uneven | corrugated | grooved part 11c and the recessed part 11d can be employ | adopted as the structures for improving immunity / ESD tolerance to the housing | casing 11 of other embodiment mentioned above and its modification.

In addition, this invention is not limited to said each embodiment and modification, For example, you may actualize as follows.
(1) FIG. 11 is a graph showing the frequency dependence of the magnetic permeability μi when the insulating adhesive 20 contains Ni—Zn ferrite powder.
In each of the above embodiments and modifications thereof, in order to increase the mutual inductance M, the insulating adhesive 20 may contain a powder having a relatively high magnetic permeability, for example, a Ni—Zn ferrite powder. For example, as illustrated in FIG. 11, when Ni—Zn-based ferrite powder is contained at 80 wt% (mass percentage), 85 wt%, and 88 wt% with respect to the insulating adhesive 20, 88 wt% is obtained. The magnetic permeability μi can be increased most.

(2) The ESD diode 16 is not limited to the ESD protection circuit that is housed in the housing 11 and connected to the lead frame 14 in order to protect the electronic components from noise current. A protection circuit may be employed.

(3) Between the intermediate portion of the lead frame 14 and the inner surface of the insertion portion (11b), not only the insulating epoxy resin is interposed as the insulating adhesive 20, but also another dielectric is interposed. Thus, each lead frame 14 may be held so as not to be in direct contact with the housing 11.

DESCRIPTION OF SYMBOLS 10, 10a, 10b ... Electronic device 11 ... Housing 11a ... Bottom wall 11b ... Insertion hole (insertion part) 11c ... Uneven part 12a-12d ... Semiconductor device (electronic component)
14 ... Lead frame (external connection terminal)
14a, 14b ... Covering part 16 ... ESD diode (electrostatic discharge protection circuit)
20 ... Insulating adhesive (dielectric)
21 ... High permeability member

Claims (4)

In the electronic device (10, 10a, 10b) in which the electronic components (12a to 12d) are accommodated in the conductive casing (11),
It is a terminal for electrically connecting the electronic component and an electronic device outside the casing, and is arranged so as to pass through an insertion portion (11b) formed in the casing without contacting the casing. An external connection terminal (14),
A dielectric (20) interposed between the external connection terminal and the inner surface of the insertion portion;
An electrostatic discharge protection circuit (16) housed in the casing and connected to the external connection terminal to protect the electronic component from noise current caused by electrostatic discharge applied to the external connection terminal; With
In the external connection terminal, the path length (Lb) through which the noise current flows in the covering portions (14a, 14b) covered with the dielectric is longer than the length (La) in the insertion direction of the dielectric. An electronic device formed.   The electronic device according to claim 1, wherein a high permeability member (21) having a permeability higher than that of the dielectric is interposed between at least a part of the covering portion and the dielectric.   The electronic device according to claim 1, wherein an uneven portion (11 c) is formed on an inner surface of the insertion portion that contacts the dielectric.   The wall portion (11a) in which the electronic component is disposed among the wall portions constituting the housing is formed so that the thickness thereof is thinner than other wall portions. 4. The electronic device according to any one of 3.

Images