JP2001332878A - Screw tightening structure of electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent cracking or breaking at the soldered part of a circuit element by suppressing the effect of stress in the vicinity of the screw tightening part between a member being tightened and a housing. SOLUTION: A step screw 3 having an unthreaded part 33 of larger outside diameter than a male screw 31 between the male screw 31 and a screw head 32 is employed. Diameter of a hole part 11a in a circuit board 1 is set larger than the outside diameter of the unthreaded part 33. Under a state where a spring washer 4 and a flat washer 5 are placed between the screw head 32 of the step screw 3 and the circuit board 1, the step screw 3 and the female screw 22a of a housing 2 subjected to burring 22 are screw tightened. The unthreaded part 33 abuts against the housing 2 to ensure a sufficient axial force and the circuit board 1 can be retained with an appropriate force other than the axial force of the screw 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw tightening structure of an electronic device for fixing a member on which an electronic component is mounted to a housing (case).

[0002]

2. Description of the Related Art In recent years, as electronic devices have become smaller and more sophisticated, the mounting density of electronic components on circuit boards has increased. Along with this, the fixing position of the circuit board is also increasingly restricted, and screws are frequently fastened and fixed near the narrow pitch integrated circuit components.

[0003] Electronic devices used in the general public are usually
A circuit element is mounted on a printed circuit board on which a circuit pattern is formed by soldering. Then, in order to protect this circuit board, it is stored in a housing. At this time, as a general method of fixing the circuit board, screw fixing is frequently used.

FIG. 10 shows an example of the structure of a conventional general electronic device. The structure of the conventional electronic device will be described with reference to FIG.

[0005] The printed board J11 is formed by forming a circuit pattern with a copper foil on an epoxy resin containing glass fiber (hereinafter referred to as glass epoxy) plate which is an insulator. The circuit element J12 is mounted on the printed board J11 by soldering to form the circuit board J1.
In general, the circuit element J12 is roughly divided into a power supply unit for operating the circuit and a calculation unit for realizing the function. These are usually provided on the circuit board J1 for convenience in circuit configuration and pattern formation.
It is arranged separately also on the top.

The power supply section is composed of a tall and heavy electrolytic capacitor, coil, power transistor and the like. Therefore, the soldered portion also has a large strength and the terminal length is sufficiently ensured. On the other hand, the arithmetic unit is mounted with an integrated circuit element such as a CPU and a memory having a large area but a short height. These are usually surface-mounted elements and have a large number of terminals and a narrow pitch. Therefore, the strength of the soldered portion of each terminal is low, and the length of the terminal portion is extremely short.

[0007] The circuit board J1 thus configured is housed and fixed in a housing J2 formed by bending an iron sheet metal.

At four corners of the bottom surface of the housing J2, threaded burring portions J22 are provided, and the circuit board J1 is fixed to the burring portions J22. The burring portion J22 has a shape that is drawn inward so that the lower part of the neck of the screw J3 penetrated at the time of screwing does not protrude below the bottom surface of the housing.

On the other hand, four screw holes are provided in the printed circuit board J11 in advance. Specifically, a hole slightly larger than the diameter of the screw J3 is formed so as to absorb the dimensional tolerance between the housing J2 and the printed board J11.

[0010] The circuit board J1 is housed in the housing J2, and four corners of the circuit board J1 and four corners of the bottom surface of the housing J2 are fixed by screws. The screw J3 used at this time has a size in consideration of the size of the circuit board J1 and workability at the time of assembling. For example, 1DIN (normal; W178 × H50 × D165 mm) which is a standard size of a mounting space for audios of a vehicle is used. ), An M3 screw with a metric screw diameter of 3 is used. The M3 screw is tightened with a torque of 0.5 Nm (5 kgf · cm) as a general value for preventing the screw J3 from loosening.

[0011]

When the above-mentioned electronic equipment is mounted on a vehicle, there are the following problems.

In general, electronic equipment mounted on a vehicle is required to have durability against a temperature change between day and night and a rise in internal temperature due to daily startup. As a test simulating this, there is a thermal shock test. This is a test in which an electronic device is repeatedly exposed to a predetermined low and high temperature atmosphere. This is repeated for several hundred cycles, and the above durability is confirmed.

The most likely problem in this test is that
This is a soldering part of the circuit element J12. The reason is that stress is generated in the soldered portion of the circuit element J12 at high and low temperatures due to a difference in thermal expansion between the printed circuit board J11 and the circuit element J12. As a result, cracks occur in the soldered portion, and in the worst case, a break occurs.

This phenomenon is noticeable in the circuit element J12 in which the integrated circuit of the operation section is formed. This is the circuit element J
In addition to the originally low soldering strength of No. 12, the difference in thermal expansion with the printed circuit board J11 is large due to the large area,
In addition, since the terminal is short and the length of the terminal is short and the difference in thermal expansion cannot be sufficiently absorbed in the terminal portion, the stress generated in the soldered portion increases. For this reason, the above-mentioned inconvenience is particularly likely to occur in the arithmetic unit, and it can be said that the design margin (safety coefficient) is small with respect to the stress of the thermal shock test.

With the above in mind, the inventor conducted a thermal shock test on the electronic device shown in FIG. as a result,
Cracks occurred in the soldered portions of some circuit elements J12, leading to disconnection. However, some integrated circuit elements have no crack at all. A comparison of the mounting conditions of the problematic circuit element J12 revealed that the crack occurred in the element mounted near the screwed portion on the circuit board J1, and the disconnection occurred in the screwed portion. It turned out to be the closest terminal.

As a cause of the above problem, other stresses applied to the circuit board J1, especially stress generated near the screwed portion were considered. As a result, there are two types of effects, namely, the influence of the steady stress in the vicinity of the screw portion of the circuit board J1 due to the screw tightening, and the effect of the thermal stress stress in the vicinity of the screw portion of the circuit board J1 due to the difference in thermal expansion between the circuit board J1 and the housing J2. It was found that the stress was assumed to have an adverse effect on the element soldering portion near the screwed portion.

Before describing the influence of the above-mentioned stress, a fundamental problem in ordinary screw tightening will be described.

At present, ordinary screw fastening is performed by simply sandwiching a circuit board J1 as a member to be fastened between the screw head J32 and the screw fastening seat surface J21 as shown in FIG. At this time, a tensile force in the axial direction (hereinafter, referred to as an axial force) is generated in the screw J3 due to the repulsive force compressing the circuit board J1. The axial force fixes the circuit board J1 and generates a frictional force in the rotational direction of the screw J3, thereby preventing the screw J3 from loosening. In other words, the axial force generated when the screw J3 is tightened plays two roles of fixing the circuit board J1 and generating a frictional force for preventing screw loosening.

However, as a practical matter, considering the weight of the circuit board J1 corresponding to the size of the screw J3,
The axial force of 3 is more than expected.

Here, as shown in FIG. 10, an M3 screw J3 for fixing a circuit board J1 of an electronic device mounted on a vehicle.
As an example, consider the above axial force.

In general, if the screw is M3, the tightening torque for preventing the screw J3 from loosening is 0.5 Nm (5 kg).
f · cm). The axial force generated at this time depends on the frictional force of each part, but is about 500 N (50 kgf).
About. On the other hand, the weight of the circuit board J1 of the electronic device is usually about several hundred g. Usually, the circuit board J3 is firmly fixed at some points. From this, the axial force of M3 is one of the forces required for fixing the circuit board J1.
This means that the number of occurrences is 00 times or more. This is an extremely large value for fixing the circuit board J1 even in consideration of the vibration of the vehicle.

Considering such a problem in ordinary screw tightening, the influence of the above-mentioned stress on the electronic apparatus shown in FIG. 10 will be considered.

First, the effect of the stress will be described. As shown in FIG. 10, the circuit board J1 is fixed to the housing J2 by fixing it at four locations using M3 screws J3. As shown in FIG. 11, the screw heads 32 and the screw seat surfaces J are formed by the individual screw tightening portions by the axial force of the screw J3.
21 so as to be sandwiched therebetween. Since the axial force generated at this time is an excessive value of about 500 N (50 kgf), the axial force is somewhat immersed in the glass epoxy which is the material of the circuit board J1.

Normally, the screw head J32 and the screw fastening seat surface J21 of the housing J2 are not always the same area. For this reason,
The areas to be sunk on the front and back of the circuit board differ. That is, the area to which the axial force is applied when sandwiching is different. Here, FIG.
As shown in the figure, a case is considered where the area of the screw fastening seat surface J21 of the housing J2 is larger than the area of the screw head J32. Then, the vertical force is balanced by the portion where the screw head J32 of the front surface of the circuit board J1 applies the axial force and the portion where the screw seat surface J21 on the back applies the axial force. This relationship is shown by the following equation.

F1 + F2 = F3 + F4 + F5 + F6 (1) Here, L1 to L6 indicate distances from the center axis of the screw J3, and F1 to F6 indicate the screw head J32 and the bearing surface J21 at the respective distances L1 to L6. Shows the force applied to

However, considering the moment from the center of the screw hole, since the area of the screw tightening seat surface J21 is large, imbalance occurs as shown by the following equation.

F1 · L1 + F2 · L2 <F3 · L3 + F4 · L4 + F5 · L5 + F6 · L6 (2) Therefore, as shown by the following equation, a moment M that warps the circuit board into a concave shape is generated, and distortion occurs in the circuit board J1.

M = (F3 · L3 + F4 · L4 + F5 · L5 + F6 · L6) − (F1 · L1 + F2 · L2) (3) As shown in FIG. 13, the magnitude of this distortion is greatest near the screwed portion. Naturally, it is proportional to the magnitude of the axial force at the time of screw tightening, and does not change as long as the circuit board J1 is kept fixed to the housing J2.

From the above, a constant stress is always applied to the circuit board J1 near the screwed portion. For this reason, when a thermal shock test is performed, thermal shock stress of the circuit element J12 and the circuit board J1 and steady stress due to screw tightening are simultaneously applied, which adversely affects the element soldering portion near the screwed portion.

Next, the effect of the stress will be described. As shown in FIG. 10, the circuit board J1 is fixed at four places using M3 screws J3, so that the circuit board J1 is made of an iron housing J2.
Fixed to Here, the circuit board J1 uses a glass substrate for the printed circuit board J11 as a base, and has a different thermal expansion coefficient from the iron housing J2. Therefore, when a thermal shock test is performed, the printed circuit board J11
And the housing J2 has a difference in thermal expansion. However, the circuit board J1 is about 500N due to the axial force of the screw J3 of M3.
(50 kgf) and is fixed to the housing J2 with an excessive value. Therefore, it cannot expand and contract freely, and thermal stress is generated.

FIG. 14 shows a case where a difference in thermal expansion from the housing J2 occurs and the circuit board J1 expands and contracts while the circuit board J1 is screwed.
Shown in The broken line in the figure indicates the case where the circuit board J1 expands from the housing J2, and the dashed line indicates the case where the circuit board J1 contracts from the housing J2. As can be seen from FIG. 14, the magnitude of the thermal stress is greatest at the hatched portion near the screwed portion. Naturally, thermal stress occurs only in low-temperature and high-temperature atmospheres such as in a thermal shock test, and there is no problem at normal temperature.

As described above, thermal stress is generated in the circuit board J1 near the screwed portion due to temperature change. Therefore, when the thermal shock test is performed, the circuit element J1
2, the thermal shock stress of the circuit board J1 and the thermal stress of the circuit board J1 and the housing J2 are simultaneously applied, which adversely affects the element soldering portion near the screwed portion.

As described above, the above stress is applied to the vicinity of the screwed portion of the circuit board J1 in FIG. In addition, since the circuit element J12 constituting the integrated circuit, which originally has a small design margin, was mounted near the screwed portion, a crack was generated in the soldered portion, resulting in disconnection.

Generally, when a circuit board is fixed by screws,
Since the axial force is excessive, various stresses are applied around the screwed portion as described above. For this reason, stress is also applied to the soldered portion of the circuit element mounted near the screwed portion. Therefore, when a circuit element constituting an integrated circuit with a small design margin is originally mounted, there is a problem that a soldered portion is destroyed by a durability test.

As a method of avoiding this problem, for example, there is a method of not mounting a circuit component near the screwed portion. However, according to this method, the area of the substrate required for mounting components increases, which leads to an increase in cost. Further, the mounting position of the electronic component is restricted. In particular, restrictions on integrated circuit components having a large chip size increase, making it impossible to optimally arrange circuit boards on wiring. As a result, the processing speed is restricted and the problem of electromagnetic wave noise is caused, and the performance of the electronic device is reduced. Therefore, this method cannot be said to be a very realistic method in consideration of recent miniaturization of electronic devices and high-density mounting of components.

The same applies to the case where a precision device other than a circuit board, for example, a sensor, a hard disk, or a CD / DVD player is screwed and fixed, and a fundamental measure is required.

In view of the foregoing, it is an object of the present invention to suppress the influence of stress in the vicinity of a screwed portion between a member to be fastened and a housing, and to prevent cracks and disconnections in a soldered portion of a circuit element. .

[0038]

In order to achieve the above object, according to the first aspect of the present invention, the holes (11a to 11a) are provided.
d) and the female screw (22)
a) Aligning the female screw of the housing (2) with the configuration, and screwing the screw (3) having the male screw to the female screw through the hole, thereby connecting the member to be fastened to the housing. In a screw tightening structure for an electronic device, the screw is formed by a stepped screw having a screwless portion (33) having an outer diameter larger than the male screw between the screw head of the screw and the male screw. The hole has a diameter larger than the outer diameter of the screwless portion, and an elastic member (4 to 7) is provided between the screw head and the member to be fastened.
Is inserted.

According to such a configuration, a sufficient axial force can be ensured by abutting the screwless portion and the housing, and the member to be fastened can be pressed with an appropriate force different from the axial force of the screw. Can be. For this reason, it is possible to suppress the influence of stress in the vicinity of the screwed portion between the member to be fastened and the housing, and to prevent cracks and disconnections in the soldered portion of the circuit element.

For example, a spring washer (4) and a flat washer (5) can be applied as the elastic member. Further, as described in claim 3, an O-ring (6) arranged so as to surround the outer periphery of the portion without a screw can be applied. Further, as shown in claim 4, an elastic washer (7) made of resin or rubber, which is disposed so as to surround the outer periphery of the portion without a screw, can be applied.

According to the fifth aspect of the present invention, the casing (2) is subjected to burring (23) with the punching direction being the side of the member (1) to be punched. A screw (23a) is formed, and the hole is formed with a diameter larger than the outer periphery of the burring process.
An elastic member (8) is arranged between the seat surface (21) formed by burring and the member to be fastened, or between the screw head (32) of the screw and the member to be fastened. I have.

According to such a configuration, a sufficient axial force can be ensured by abutting the screwless portion and the housing, and the member to be fastened can be pressed with an appropriate force different from the axial force of the screw. Can be. Thereby, the same effect as the first aspect can be obtained.

According to the sixth aspect of the present invention, the housing (2) has a female screw (24a) and a seating surface (24b), and a portion protruding from the seating surface is formed in the hole. A stud (24) configured to be inserted is provided, and the holes (11a to 11d) have a diameter larger than the outer circumference of a portion of the stud inserted into the hole, and are fastened to the seat surface. An elastic member (8) is arranged between the member or between the screw head of the screw and the member to be fastened.

According to such a configuration, a sufficient axial force can be ensured by the contact between the screwless portion and the housing, and the member to be fastened can be pressed with an appropriate force different from the axial force of the screw. Can be. Thereby, the same effect as the first aspect can be obtained.

According to the seventh aspect of the present invention, the member to be fastened and the casing are screwed and fixed at a plurality of positions, and a part of the plurality of positions (S to V) to be screwed and fixed. Only in this case, the screw tightening structure according to any one of claims 1 to 6 is applied.

As described above, the screw tightening structure of the present invention can be applied to only a part of a plurality of screw-fixed portions. This can reduce the number of places to which the special screw tightening structure is applied, thereby reducing costs.

According to the invention described in claim 8, the member to be fastened has an operation section on which a circuit element is arranged, and among a plurality of places to be screwed and fixed, the screw fastening sections (S, T) in the operation section are provided. ), Wherein the screw fastening structure according to any one of claims 1 to 6 is applied.

As described above, it is preferable to apply the screw tightening structure of the present invention particularly to the arithmetic operation section where the soldering section is weakly joined.

As a matter of course, as described in claim 9, the screw tightening structure according to any one of claims 1 to 6 may be applied to all of the plurality of positions (S to V) to be screwed and fixed.

In this case, the positioning member (11) for positioning the member to be fastened with the housing is provided.
By providing e and 11f), it is possible to prevent the displacement between the member to be fastened and the housing.

According to the eleventh aspect, in one of the plurality of locations (U) to be screwed and fixed, the diameter of the hole (11c) is equal to the diameter of the threadless portion, the outer periphery of burring, or the stud. The hole (11d) has a minor axis and a major axis in one (V) of the plurality of places to be screwed and fixed. And the short diameter is made equal to the outer diameter of the screwless portion, the outer periphery of the burring, or the outer diameter of the portion of the stud inserted into the hole. Can be obtained.

The reference numerals in parentheses of the above-mentioned means indicate the correspondence with the concrete means described in the embodiments described later.

[0053]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG.
FIG. 1B shows an overall configuration of an electronic apparatus to which a screw fastening structure according to a first embodiment of the present invention is applied, and FIG. 1B is a cross-sectional view taken along a line AA in FIG. Since the structure of this electronic device is substantially the same as the above-described conventional structure, different parts will be described. In this figure, for the sake of simplicity, only the outer shapes of the circuit board 1 and the housing 2 as members to be fastened are illustrated, and screw heads and the like are omitted. The broken lines in the drawing indicate the magnitude of the stress in each of the screw fastening portions S, T, U, and V. Furthermore, the arrow in the figure indicates the circuit board 1 at high and low temperatures.
This indicates the direction in which the circuit board 1 can slide when there is a difference between the thermal expansion of the housing 2 and the thermal expansion of the housing 2.

Also in this embodiment, the circuit board 1 and the housing 2
Are fixed by screwing at four places. Of these four screw tightening parts, both the screw tightening parts U and V on the power supply part side and the screw tightening parts S and T on the arithmetic unit side are those which are located only at the position where the circuit element 12 is apart (the screw tightening part). For the three points T), a conventional screw tightening structure is adopted. Then, one of the screw tightening portions S and T on the calculation section side where the circuit element 12 is disposed in the vicinity (the screw tightening portion S).
As for the location, the screw fastening structure according to the embodiment of the present invention is adopted.

FIG. 2 shows a cross-sectional configuration of the screw tightening structure according to the present embodiment, and the details of the main screw tightening structure will be described with reference to FIG.

As shown in FIG. 2, a circuit board 1 is screwed to a housing 2 with screws 3. The circuit board 1 has a circuit element 12 mounted on a printed board 11 made of glass epoxy and a hole 11a for screwing.

The housing 2 is made of a cold-rolled steel plate, and a burring process 22 is applied to a drawn seating surface 21 to form a female screw 2.
2a is formed. The screw 3 has a screwless portion 33 having a larger outer diameter than the male screw 31 between the male screw 31 and the screw head 32.
(Hereinafter, this type of screw is referred to as a stepped screw). An iron spring washer 4 and a flat washer 5 are inserted between the screw head 32 and the printed circuit board 11.

Since the length of the threadless portion 33 of the stepped screw 3 is adjusted with respect to the thickness of the printed board 11 and the flat washer 5, the spring washer 4 is fixed by a certain amount based on the adjustment amount. It is designed to be compressed. In addition,
The hole diameter of the screw hole 11 a is larger than the outer diameter of the screwless portion 33. The screw hole 11a is
Screw holes 11b to 11 in other screw fastening portions TV
It is opened larger than d.

Next, a specific operation of the screw tightening structure using the stepped screw as in the present embodiment will be described.

The stepped screw 3 comprises a male screw 31 and a screw head 3
A screwless portion 33 having an outer diameter larger than that of the male screw 31 is provided between the two. For this reason, when the male screw 31 of the stepped screw 3 is screwed into the female screw 22a of the housing 2, the screwless portion 3
3 comes into contact with the seating surface 21. Therefore, when the screw is tightened with a constant torque, an axial force of the screw is generated at the contact portion.

On the other hand, between the screw head 32 and the printed board 11, a spring washer 4 is inserted as an elastic member. These elastic members are compressed by a certain amount due to the length of the threadless portion 33 of the stepped screw 3. That is, the compression repulsive force of these elastic members causes the circuit board 1
Is pressed against the screw seat surface 21.

As described above, in the screw tightening structure of the present embodiment, a sufficient axial force can be secured by the contact between the threadless portion 33 and the seat surface 21. In addition, by adjusting the length of the screwless portion 33, the circuit board 2 can be pressed with a proper force different from the axial force of the screw. Note that the appropriate force is usually several tens of N from the weight of the circuit board 1 even in consideration of vibration when mounted on a vehicle.
(Several kgf).

As described above, in this embodiment, the circuit board 2
Can be held down and fixed with an appropriate force different from the axial force of the screw, so that even if the screw head 32 and the screw seating surface 21 have different areas, no excessive moment is generated to warp the circuit board 1. Further, even when a difference occurs in the thermal expansion between the circuit board 1 and the housing 2 at high and low temperatures, it is possible to slide in the surface direction with a relatively low force obtained by multiplying the force holding the circuit board 1 by the coefficient of friction. Therefore, no excessive thermal stress occurs between the circuit board 1 and the housing 2.

Furthermore, the axial force of the screw 3 is ensured by the contact between the threadless portion 33 and the seating surface 21. For this reason, the axial force does not decrease due to settling of the printed board 11 made of glass epoxy. Therefore, over a long period of time,
An effect of preventing the screw 3 from being loosened can also be expected.

As described above, by employing the screw tightening structure of this embodiment, the influence of stress in the vicinity of the screw tightening portion between the circuit board 1 and the housing 2 can be suppressed, and the circuit element 1
Cracks and breaks in the soldered portion 2 can be prevented.

In this embodiment, the spring washer 4 and the flat washer 5 are both used as elastic members. For this reason, the compression repulsive force of the spring washer 4 becomes
Distributed by the flat washer 5 and evenly printed circuit board 11
Is transmitted to Therefore, the circuit board 1 can be fixed with a more stable force, and the stress on the circuit element 12 can be further reduced.

Further, as the spring washer 4 and the flat washer 5, general-purpose products can be selected and used, and they are very inexpensive. Further, when both are made of iron, if the bit of the driver is magnetized at the time of screw tightening, the screw can be tightened integrally with the stepped screw 3, and workability is improved. The spring washer 4 can be replaced with a washer made of iron and also having elasticity, a coil spring, a disc spring, or the like.

(Second Embodiment) FIG. 3 shows a sectional configuration of a screw tightening structure according to a second embodiment of the present invention. As shown in FIG. 3, the circuit board 1 is screwed to the housing 2 with screws 3. Among these configurations, the configurations of the circuit board 1, the housing 2, and the stepped screw 3 are the same as those in FIG.

In this embodiment, an iron flat washer 5 and an O-ring 6 are inserted between the screw head 32 and the printed circuit board 11. Since the length of the threadless portion 33 of the stepped screw 3 is adjusted with respect to the thickness of the printed board 11 and the flat washer 5, the O-ring 6 is compressed by a fixed amount based on the adjustment amount. It has become. The O-ring 6 has a smaller inner diameter than the outer diameter of the threadless portion 33.

As described above, in this embodiment, the O-ring 6 is used as the elastic member. Usually, the O-ring is made of rubber, has a circular cross section, and has a very high dimensional accuracy because it is used as a sealing material. Therefore, since this compression repulsion is used, the circuit board 1 can be fixed with a very high and stable force. Also, because the cross section is circular,
If necessary, the circuit board 1 can be pressed with a very light force.

Since the inner diameter is smaller than the outer diameter of the threadless portion 33, the O-ring 6 can be prevented from coming off the screw 3. Therefore, the screw can be tightened integrally with the stepped screw 3, and workability can be improved. In addition,
The flat washer 5 is not particularly required as long as the size of the screw head 32 and the length of the screwless portion 33 are sufficient.

(Third Embodiment) FIG. 4 shows a sectional configuration of a screw tightening structure according to a third embodiment of the present invention. As shown in FIG. 4, the circuit board 1 is screwed to the housing 2 with screws 3. Among these configurations, the configurations of the circuit board 1, the housing 2, and the stepped screw 3 are the same as those in FIG.

In this embodiment, an elastic washer 7 made of resin or rubber is inserted between the screw head 32 and the printed board 11. Since the length of the threadless portion 33 of the stepped screw 3 is adjusted with respect to the thickness of the printed circuit board 11, the elastic washer 7 is compressed by a fixed amount based on the adjustment amount. ing. The elastic washer 7 has an inner diameter slightly smaller than the outer diameter of the screwless portion 33.

As described above, in this embodiment, the elastic member washer 7 made of resin or rubber is used as the elastic member. The inner diameter of the elastic washer 7 is smaller than the outer diameter of the threadless portion 33. For this reason,
The elastic washer 7 can be prevented from coming off the stepped screw 3. In addition, if the screw is integrated with the stepped screw 3, it is not necessary to insert the elastic washer 7 into the stepped screw 3 at the time of screw tightening.

(Fourth Embodiment) FIG. 5 shows a sectional configuration of a screw tightening structure according to a fourth embodiment of the present invention. In the present embodiment, the same effect as that of the first embodiment is obtained with a configuration different from that of the stepped screw.

As shown in FIG. 5, a circuit board 1 is screwed to a housing 2 with screws 3. The circuit board 1 has a configuration in which a circuit element 12 is mounted on a printed board 11 made of glass epoxy, and has a hole 11a for screwing.

The housing 2 is made of a cold-rolled steel plate, and a burring process 23 is applied to a drawn seating surface 21 of the housing 2 to form a female screw 23a. However, in the present embodiment, unlike the above-described first to third embodiments, the burring process 23 has the punching direction on the circuit board 1 side.

As the screw 3, a standard screw having a male screw 31 and a screw head 32 is used. The elastic member 8 is inserted between the printed board 11 and the seat 21. By adjusting the height of the burring process 23 with respect to the thickness of the printed circuit board 11, the elastic member 8 is compressed by a certain amount. The diameter of the screw hole 11a is
It is larger than the outer diameter of the burring 23.

As described above, in this embodiment, standard screws are used instead of stepped screws. Then, instead of the threadless portion 33 of the stepped screw 3 shown in FIG. 2, a burring process 23 in which the punching direction is the circuit board 1 side is provided. Therefore, when the male screw 31 of the screw 3 is screwed into the female screw 23 a of the housing 2, the burring 23 comes into contact with the screw head 32. Therefore, when the screw is tightened with a constant torque, an axial force of the screw 3 is generated by a contact portion between the burring 23 and the screw head 32.

On the other hand, an elastic member 8 is inserted between the printed board 11 and the seating surface 21. The elastic member 8 is compressed by a certain amount according to the height of the burring 23. That is, the circuit board 1 is pressed against the screw seat surface 21 by the compression repulsive force of the elastic member 8.

As described above, a sufficient axial force can be ensured by the contact portion between the burring 23 and the screw head 32.
Further, by adjusting the height of the burring 23, the circuit board 1 can be pressed with a proper force different from the axial force of the screw 3. Therefore, the same effect as in the first embodiment can be obtained by the screw fastening structure shown in the present embodiment.

(Fifth Embodiment) FIG. 6 shows a sectional structure of a screw tightening structure according to a fifth embodiment of the present invention. This embodiment also has a configuration different from that of the stepped screw so that the same effects as those of the first embodiment can be obtained.

As shown in FIG. 6, a circuit board 1 is screwed to a housing 2 with screws 3. The circuit board 1 has a configuration in which a circuit element 12 is mounted on a printed board 11 made of glass epoxy, and has a hole 11a for screwing.

The housing 2 is made of a cold-rolled steel plate.
Is press-fitted with a stud 24 made of iron. The stud 24 has a female screw 24a, and further has a seat surface 24b and a stepped portion 24c.

As the screw 3, a standard screw having a male screw 31 and a screw head 32 is used. The elastic member 8 is inserted between the printed board 11 and the seat surface 24b. By adjusting the height of the stepped portion 24c with respect to the thickness of the printed circuit board 11, the elastic member 8 is compressed by a certain amount. The diameter of the screw hole 11a is larger than the outer diameter of the stepped portion 24c.

As described above, in this embodiment, standard screws are used instead of stepped screws. Then, a stepped portion 24c of the stud 24 is provided instead of the threadless portion 33 of the stepped screw 3 shown in FIG. Therefore, when the male screw 31 of the screw 3 is screwed into the female screw 24 a of the housing 2, the stepped portion 24 c comes into contact with the screw head 32. Therefore, when the screw is tightened with a constant torque, the stepped portion 2
An axial force of the screw 3 is generated at a contact portion between the screw 4c and the screw head 32.

On the other hand, the elastic member 8 is inserted between the printed board 11 and the seat surface 24b. This elastic member 8
Depending on the height of the stepped portion 24c, it is compressed by a certain amount.
That is, the circuit board 1 is compressed by the repulsive force of the elastic member 8.
Is pressed against the screw seat surface 21.

As described above, a sufficient axial force can be secured by the contact portion between the stepped portion 24c and the screw head 32. In addition, by adjusting the height of the stepped portion 24c, the circuit board 1 can be pressed with an appropriate force different from the axial force of the screw. Therefore, the same effect as in the first embodiment can be obtained by the screw fastening structure shown in the present embodiment.

(Other Embodiments) In each of the above-described embodiments, as shown in FIG.
2 to 6, the screw fastening structure shown in FIGS. 2 to 6 is employed only in the portion (the screw fastening portion S) where the circuit element 12 is arranged closest to the other components.

This is because the screw tightening structure according to the present invention
Because the structure of the stepped screw 3 and the number of parts of the elastic member increase the cost as compared with general screwing, the present invention is applied only to the screw tightening portion S where the thermal stress is excessively large, and the cost is reduced. This is because

Therefore, as shown in FIG. 7, if the screw tightening structure in each of the above embodiments is adopted for both the screw tightening portions S and T in the calculation section, the influence of stress can be further prevented. .

However, if the screw tightening structure of the present invention is employed only in a part of the plurality of screw tightening portions S to V, the general screw tightening structure is mixed.
In this case, there is a possibility that a wrong assembly will occur,
As shown in FIG. 8, the screw tightening structure in each of the above embodiments may be adopted for all the screw tightening portions S to V. In this case, an effect of stress reduction can be expected in the entire circuit board 1.

As described above, when the screwing of the present invention is used, the circuit board 1 can be fixed with an appropriate force, and can be displaced in the surface direction by a relatively low force obtained by multiplying the circuit board 1 by the friction coefficient. It becomes possible. In order to prevent the displacement of the circuit board 1 due to this, in the application example of FIG. 8, the circuit board 1 is positioned by the positioning holes 11 e and the elongated holes 11 f and the projection of the housing 2. That is, the circuit board 1 is positioned so as not to deviate from a predetermined position by the positioning holes 11e and the projections, and the circuit board 1 is prevented from slipping in the rotational direction by the elongated holes 11f and the projections. The substrate 1 is made to slide.

Further, the configuration shown in FIG. 9 may be adopted. In this configuration, the screw tightening structure shown in each of the above embodiments is adopted for all the screw tightening portions S to V. However, the positioning of the circuit board 1 in the screw tightening portions U and V on the power supply side is performed. It is also possible to do.

That is, the hole diameter of the screw hole 11c of the printed circuit board 11 is set to be the same as the outer diameter of the screwless portion 33 so that the screw hole 11d serves as a positioning hole. An elongated hole having the same outer diameter as 33 serves as an anti-rotation elongated hole. With such a configuration, the same effect as that of the application example shown in FIG. 8 can be obtained.

In the fourth and fifth embodiments, the elastic member 8 is inserted between the printed circuit board 11 and the housing 2, but this is a result in consideration of the assemblability and the like. Even if it is inserted between 11 and the screw head 32, it is functionally equivalent. Further, the elastic member 8 itself includes first to third members.
The spring washer 4 and the O-ring 6 shown in the embodiment,
Any of the configurations to which any of the elastic washer 7 is added may be used.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams showing an electronic device according to a first embodiment of the present invention, wherein FIG. 1A is a diagram showing the entire configuration of the electronic device, and FIG. 1B is a cross-sectional view taken along line AA of FIG. FIG.

FIG. 2 is a cross-sectional view illustrating a screw tightening structure according to the first embodiment of the present invention.

FIG. 3 is a sectional view showing a screw tightening structure according to a second embodiment of the present invention.

FIG. 4 is a sectional view showing a screw fastening structure according to a third embodiment of the present invention.

FIG. 5 is a sectional view showing a screw fastening structure according to a fourth embodiment of the present invention.

FIG. 6 is a sectional view showing a screw fastening structure according to a fifth embodiment of the present invention.

FIG. 7 is a diagram for explaining an application portion of a screw fastening structure.

FIG. 8 is a diagram for explaining an application portion of a screw fastening structure.

FIG. 9 is a diagram for explaining an application portion of a screw fastening structure.

FIG. 10 is a diagram showing a conventional electronic device;
(A) is a figure which shows the whole structure of an electronic device, (b) is a figure which shows the BB sectional drawing of (a).

FIG. 11 is a view showing a conventional screw tightening structure.

FIG. 12 is a diagram showing a force relationship in the screw tightening structure shown in FIG. 11;

13 is a view for explaining a moment generated in the screw tightening structure shown in FIG. 11 and a distortion due to the moment.

FIG. 14 is a diagram illustrating a state of thermal stress in a conventional electronic device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Circuit board, 2 ... Case, 3 ... Screw, 4 ... Spring washer, 5 ... Flat washer, 11 ... Printed circuit board, 11a
11d: hole 12: circuit element, 21: seating surface, 22a: female screw, 31: male screw, 32: screw head, 33: screwless portion, SV: screw tightening portion.

Claims (11)

[Claims] 1. The positioning of the hole of a member to be fastened (1) having holes (11a to 11d) and the female screw of a housing (2) having a female screw (22a). A screw (3) having a male screw screwed to the female screw through the hole to fix the member to be screwed to the housing; Is composed of a stepped screw having a screwless portion having a larger outer diameter than the male screw between the screw head of the screw and the male screw, and the hole is larger than an outer diameter of the screwless portion. An elastic member (4 to 4) is provided between the screw head and the member to be fastened.
(7) A screw tightening structure for an electronic device, wherein the screw is inserted. 2. The screw tightening structure according to claim 1, wherein the elastic member is a spring washer (4) and a flat washer (5). 3. The screw tightening structure for an electronic device according to claim 1, wherein the elastic member is an O-ring disposed so as to surround an outer periphery of the screwless portion. 4. The electronic device according to claim 1, wherein the elastic member is an elastic washer made of resin or rubber and disposed so as to surround an outer periphery of the screwless portion. Equipment screw tightening structure. 5. The positioning of the hole of the member to be fastened (1) having holes (11a to 11d) and the female screw of the housing (2) having the female screw (23a). And a screw (3) having a male screw screwed to the female screw through the hole to fix the member to be screwed to the housing. The body is subjected to a burring process (23) with the punching direction being the side of the member to be fastened, and the female screw is formed by an inner peripheral surface of the burring process. And between the seating surface (21) formed by the burring process and the member to be fastened, or the screw head (3
An elastic member (8) is disposed between the member (2) and the member to be fastened. 6. The positioning of the hole of the member to be fastened (1) having holes (11a to 11d) and the female screw of the housing (2) having the female screw (24a). And a screw (3) having a male screw screwed to the female screw through the hole to fix the member to be screwed to the housing. The body has the female screw and a seating surface (2).
4b), comprising a stud (24) configured to insert a portion protruding from the seating surface into the hole, wherein the hole is inserted into the hole of the stud. An elastic member (8) is arranged between the seat surface and the member to be fastened, or between the screw head of the screw and the member to be fastened. A screw tightening structure for electronic equipment. 7. The fastening member and the housing are screw-fixed at a plurality of positions, and only a part of the plurality of screw-fixed portions (S to V). 6. An electronic device, wherein the screw fastening structure according to any one of 6 is applied. 8. The screw-fastened part (S, T) of the arithmetic part, wherein the member to be fastened includes an arithmetic part on which a circuit element is arranged, and among the plurality of places to be screwed and fixed. An electronic device to which the screw tightening structure according to any one of claims 1 to 6 is applied. 9. The fastening member and the casing are screw-fixed at a plurality of positions, and at all of the screw-fixed positions (S to V). An electronic device, wherein the screw tightening structure according to (1) is applied. 10. The electronic device according to claim 9, wherein the member to be fastened includes positioning portions (11e, 11f) for positioning the member with the housing. 11. One (U) of the plurality of screw-fixed portions may have a diameter of the hole (11c) that is equal to the diameter of the screwless portion, the outer periphery of the burring process, or the stud. One of the plurality of positions (V), which is configured to have the same outer diameter as that of the portion to be inserted into the hole, and is fixed by screwing
The hole (11d) is formed of a long hole having a short diameter and a long diameter, and the short diameter is inserted into the hole of the threadless portion, the outer periphery of the burring, or the stud. The electronic device according to claim 9, wherein the electronic device is configured to have an outer diameter equal to an outer diameter of a portion to be formed.