JPH0654837B2 - Circuit board fixing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] In the method for fixing a circuit board according to the present invention, a spring washer and a flat plate washer made of a brazing material are superposed and screwed on the circuit board, and then the solid phase temperature and liquid phase of the brazing material are fixed. By heat-treating between the temperature and the temperature, the spring washer will bite into the flat plate washer in response to the variation in screwing, and finally the circuit board distortion caused by the variation in screwing will be eliminated. It is the one.

[Industrial application field]

 The present invention relates to a method of fixing a circuit board.

The circuit board is generally made of alumina ceramics, and is used by being fixed on, for example, an aluminum pedestal in consideration of grounding and heat dissipation. Here, it is necessary to fix the circuit board so as not to break it. For this purpose, it is necessary to prevent thermal stress from acting in the surface direction of the circuit board and to prevent mechanical strain from remaining in the thickness direction of the circuit board.

[Conventional technology]

Conventionally, the circuit board is soldered and fixed to the pedestal.

[Problems to be solved by the invention]

Since the coefficient of thermal expansion of the circuit board and that of the pedestal are considerably different, thermal stress is applied in the surface direction of the circuit board due to thermal history, and the circuit board may be cracked.

Further, when the circuit board is fixed on the pedestal by screwing at a plurality of points, variations in tightening force of each screw become a problem. That is, at each screwing point, the force applied to the circuit board in the thickness direction becomes non-uniform, a part of the circuit board is distorted, stress is generated in this part, and there is a problem that the board cracks. .

[Means for solving problems]

The present invention relates to a method of fixing a circuit board on a pedestal by screwing a plurality of points with screws, in which a spring washer is interposed between the circuit board and the pedestal, and the circuit board and the head of the screw. The screw washer and the flat plate washer made of a brazing filler metal, and the screw was tightened with a predetermined torque to compress and deform the spring washer and the washer toothed washer. The step of fixing the circuit board to the pedestal by sandwiching the circuit board between the washers, and the chrysanthemum type toothed washer biting into the flat plate washer in response to the situation of distortion of the circuit board after the fixing step. In order to eliminate the distortion of the circuit board, the heat treatment is performed at a temperature between the solid phase temperature and the liquid phase temperature of the brazing material.

[Action]

The heat treatment step releases the strain in the thickness direction of the circuit board due to the variation in the tightening force of each screw fastening portion.

〔Example〕

FIG. 1 is a process diagram of a method of fixing a circuit board according to an embodiment of the present invention. The fixing method of the present invention comprises a screwing fixing step 1 and a heat treatment step 2 which is a main part of the present invention which follows the step 1.

FIG. 2 shows a circuit device 3 manufactured by the fixing method of the present invention.
Indicates. In the figure, the circuit board 4 is made of alumina ceramic, and the electronic component 5 is mounted on the upper surface. Circuit board 4
Is are a plurality of points is screwed and fixed to the Al or Cu-made base 7 by screws ₆ 1 ～6- _9.

Next, will be described in detail a fixing method, the second drawing screw 6-1 _will be described with taking out the screw cramp portion by _6-2.

First, the screw fixing step 1 will be described. FIG. 3 shows a state during screw fixing, and FIG. 4 shows a state where screw fixing is completed.

As shown in the figures, the through holes 8-1 in a location to be screwed out of the circuit device _3, 8 ₂ Yes formed, the substrate table where the bush 9 _1, 9 ₂ is inserted Soldered to the ground pattern on the back. Bush _9- 1, _9-2
Form a part of a ground circuit that electrically connects the ground pattern to the base 7.

The pedestal 7, in each screwing point, counter bore ₁₀ 1, 1
0- _2, and the internal thread portion ₁₁ 1, 11 ₂ are formed.

As shown in FIG. 3, the spot facing ₁₀ 1, wave washer ₁₂ 1 in 10 _2, fitted with _12-2, placing the circuit board 4 on the base 7, the bushing 9- ₁ overlapping a flat washer 14 ₁ of inner clip washer type toothed washer 13 ₁ and the solder material made on the upper surface,
Overlapping the inner clip washer type toothed washer 13 ₂ and the solder material made flat washer 14 ₂ on the upper surface of the bush 9 _2, screw ₆ 1, 6
₂ is inserted inside of the internal thread ₁₁ 1, 11 ₂
Screw it on.

Figure 5 is chrysanthemum type toothed washer ₁₃ 1, (13 ₂₎ indicates, on the inner peripheral side, the tooth faces obliquely upward 13- _1a (13 _2a)
The teeth 13- _1b (13- _2b) facing obliquely downward and are arranged in the circumferential direction alternately.

Each screw _6-1. Tighten the _6-2 at a predetermined torque T.
Thus, as shown in FIG. 4, wave washer ₁₂ 1,
S 12 ₂ each bush ₉ 1, 9 ₂ and is compressed and deformed between the seat 7, chrysanthemum-type toothed washer ₁₃ 1, 13 ₂
Tooth _{13- 1a, 13- 2a, 13- 1b} , 13- 2b is, bush ₉ 1, 9 ₂ and flat washer ₁₄ 1, 14 ₂ (screw head 6- _1a, 6- _2a) and is compressed and deformed between the circuit board 4 bushes ₉ 1, 9-washer ₁₃ 1 from vertical for point of _2, 12 ₁ and ₁₃ 2, the upper base 7 in a state of being sandwiched by 12- ₂ Fixed to.

Here, the screw ₆ 1, to strictly equalize the clamping force of _6-2 is actually difficult, for example, screws ₆ 1,
Clamping force of each of 6- _{2 T} 1, _{T 2 is} assumed to be _T 1 <T _2.

In this case, the deeper screwed from screw _6-2 screws _6-1, rather than at the same height position the screw head 6 _2b and the screw head 6 _2a, the former dimension g lower position than the latter Becomes Thus, the bush _9-2 parts of the circuit board 4,
Acts downward force F as indicated by an arrow with respect to the bush 9 ₁ part, the bush _9-2 parts distorted downwards,
There is a stress σ directed upward.

Next, the heat treatment step 2 will be described.

Solder components of flat washer 14 ₁ Sn (70) -Pb-
In (18), solid phase temperature is 120 ° C, liquidus temperature is 170
℃.

The heat treatment is performed by heating at a temperature intermediate between the solid phase temperature and the liquid phase temperature, for example, 130 ° C. to 150 ° C. for a predetermined time.

Flat washer ₁₄ 1 This heating 14 ₂ is softened,
As shown in FIG. 6, the teeth _{13-1a, 13-2a} is flat washer ₁₄ 1, bite into 14- _2. Tooth 13- _2a teeth 13
Compared to _1a , the stress σ is cut in more, the strain is reduced, and the stress σ is reduced. By carrying out this heat treatment for a predetermined time, the strain finally becomes zero and the stress σ also becomes zero, and the circuit board 4 has no strain and stress due to variations in screw tightening, as shown in FIG. each bush ₉ 1, 9
- strain and stress in the _two locations is made zero, the stress is fixed to the base 7 in a completely free state.

This is the same for screwing point according to Figure 2 in another thread _6-3 ～6- _9, the circuit board 4 is fixed to the base 7 in a state where strain and stress are zero in the thickness direction Thus, the circuit board 4 will not break due to strain and stress in the thickness direction.

Note the thickness t of the flat washer 14 _1, as the teeth 13 _1a bites, when the thickness of the washer 13 ₁ is 0.5 mm, 0.7 to 1.
It is set to 0 mm.

Also, in order to prevent the mounting state of the electronic component 5 from being affected by the heat treatment, the solder for mounting the component has a melting point of 18
Sn (63%)-Pb, 3 ° C and higher than the above liquidus temperature
I am using solder.

Next, a configuration in which the above-described circuit device 3 is mounted on the device so as not to be affected by the thermal history received when the device is used will be described with reference to FIG.

Due to the change in ambient temperature, the circuit board 4 and the pedestal 7 expand and contract in the surface direction with different thermal expansion coefficients.

However, Bush _9-1, s upper and lower ends of the _9-2 husband washer 1
_{3-1, 13 2,} 12 1, the circuit board 4 in contact with the _12-2 is in a floating state from the base 7, the screw ₆ 1, 6
- _second shaft portion 6- _1a, 6- _2a bush ₉ 1, are loosely fitted into the _9-2, is between them a gap ₁₅ 1, there is 15 _2. Thus, the bush ₉ 1, 9 ₂ and the washer 13
_{1, 13 2,} 12 1, 12 slip laterally between _2, the circuit board 4 and the base 7 and contraction freely stretch without being each other constraints, the surface direction of the stress on the circuit board 4 occurs Absent. Therefore, the accident that the circuit board 4 is cracked due to the heat history can be reliably prevented.

In addition, the fact that the circuit board 4 is not pressed against the pedestal 7 makes the circuit board 4 less likely to be distorted when screwed and fixed.

〔The invention's effect〕

According to the present invention, the strain and stress in the thickness direction of the circuit board caused by the variation in the tightening torque of each screw can be finally eliminated by heat treatment, and the strain in the circuit board in the thickness direction can be eliminated. Also, it can be fixed by screwing to the pedestal without stress remaining, and because it is fixed by screwing, it can be fixed in a state in which the difference in thermal expansion coefficient between the circuit board and the pedestal in the surface direction can be absorbed. .

[Brief description of drawings]

FIG. 1 is a process diagram of an embodiment of a method for fixing a circuit board of the present invention, FIG. 2 is a perspective view of a circuit device in which the circuit board is fixed by the method of the present invention, and FIG. FIG. 4 is a diagram showing a state after completion of the screw fixing process, FIG. 5 is a perspective view of the chrysanthemum type toothed washer, and FIG. 6 is a diagram showing a state after the heat treatment process. In FIG, 1 is screwed step 2 the heat treatment step, 3 circuit device, the circuit board 4, the electronic component 5, _6-1 ～6- ₉ screws, 7 pedestal, _8-1, 8 ₂ through holes, ₉ 1, 9 ₂ Bush, _10-1, 10- ₂ spot facing, _11- 1, 11- ₂ internal thread, _12- 1, 12- ₂ wave washer, 13- _1, 13 ₂ chrysanthemum-type toothed washer, 13 _1a, 13 _1b, 13 _2a, 13 _2b teeth, ₁₄ 1, 14 ₂ is flat washer made of solder material ₁₅ 1, _15-2 is a gap.

Claims (1)

[Claims] 1. A method of fixing screws to the circuit board by screws multiple locations (6-1 _{～6- 9)} (4) on the base (7), the circuit board (4) and the pedestal Between the spring washer (12
- _1, interposed 12- _2), with inner clip washer-type teeth between the head (6 _1a, 6 _2a) of the circuit board (4) and the screw ₍₆ 1 ～6- ₉₎ washer ₍₁₃ 1, 13 ₂₎ and the brazing material made of flat washer ₍₁₄ 1, 14 ₂₎ and the screw in a state of interposing superimposed ₍₆ 1 ～6- ₉₎ a predetermined torque in fastening, the spring washer ₍₁₂ 1, 12 ₂₎ and the inner clip washer type toothed washer ₍₁₃ 1, 13 ₂₎ and to the compressive deformation,
The circuit board (4) to the washer ₍₁₂ 1, ₁₃ 1,
12 2, _{13 2)} and step (1) to be fixed to the base (7) sandwiched between the said chrysanthemum-type toothed washer in response to the distortion condition of the circuit board after the fixing process ₍₁₃ 1, 13 ₂₎ of the flat washer ₍₁₄ 1, 14 ₂₎ cut into the order eliminate distortion of the circuit board (4), the braze solidus temperature and liquidus temperature of A method of fixing a circuit board, comprising the step (2) of heat-treating at a temperature in between.