JPH01100994A - electronic unit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electronic unit in which electronic components are mounted on a printed wiring board, and particularly relates to an electronic unit in which electronic components are mounted on a printed wiring board, and in particular, smoke generation, ignition, and damage to the printed wiring board and adjacent electronic components in the event of a short-circuit mode failure. The present invention relates to an electronic unit suitable for preventing contamination.

[Conventional technology]

Conventionally, in electronic components such as resistors, a large amount of power exceeding the rated power may be applied due to failure propagation due to short-circuit mode of other components making up the circuit. The increase in self-heating causes the surface temperature to rise and the exterior material of the electronic component to generate heat, and depending on the amount of applied power, the heat generated may ignite the gas generated from the exterior material and cause the electronic component to burn. . Furthermore,
There is also a risk of fire spreading to the printed wiring board and adjacent parts that make up the electronic unit.

For example, in the case of a power type resistor with a rated power of 4 watts, when 6 times the rated power, that is, a power of 4 watts, is applied,
The surface temperature rise of the resistor itself reaches approximately 800°C. Further, when this resistor is assembled in a 1 m floating state on a printed wiring board and an overload of 24 watts is applied as above, the surface temperature rise value of the printed wiring board will be about 350°C. The temperature of the printed wiring board is 405° C., which is the sum of this temperature increase value of 350° C. and the average temperature inside the electronic device of 55° C., and if this state continues, the printed wiring board will become burnt. In the above case, the value is when an overload power of 6 times the rated power is applied. However, due to the circuit configuration of the electronic unit, the overload power applied due to the short-circuit mode failure of other parts is the rated power. It often reaches 10 to 50 times. In this state, the printed wiring board emits smoke, which further expands the scope of the damage and poses a major problem in terms of product safety.

Therefore, a resistor with a fusing mechanism, that is, a fuse resistor, has been developed and used in some electronic devices. This fuse resistor is, for example, BI A J RC-267O according to the Japan Electronics Industry Association (EIJ) standards.
It is standardized to A.

Currently commercially available fuse resistors have a fuse that melts within a few minutes when 10 times the rated power is applied, stopping excessive self-heating due to the overload power and preventing further fire. It has the property of preventing danger.

[Problem that the invention seeks to solve]

When an overload power in the range of 4 to 10 times the rated power is applied to the above-mentioned fuse resistor, the fuse does not blow or the fuse finally blows after a very long period of time. There is a risk of fire spreading to adjacent parts.

Furthermore, for electronic components other than fuse resistors, such as semiconductor devices such as capacitors, transistors, and ICs, the fact is that the electronic components themselves are not equipped with the above-mentioned measures to prevent burnout due to increased self-heating and to prevent the spread of fire to other components. It is.

An object of the present invention is to provide an electronic unit that can prevent combustion such as heat generation and ignition caused by excessive self-heating due to short-circuit mode failure spread to other components.

[Means for solving problems]

The above object is achieved by providing a shape memory alloy piece between an electronic component and a printed circuit board on which the electronic component is mounted.

In a preferred embodiment, the operating temperature of the shape memory alloy piece is set to 150° C. or higher.

[Effect]

In the present invention, the temperature of the element of the electronic component increases due to self-heating, and when this reaches the operating temperature of the shape memory alloy,
A shape memory alloy piece placed on the surface of the element is activated to push the electronic component away from the printed wiring board on which it is mounted. On the other hand, since the solder that connects the terminals of electronic components on the printed wiring board is melted by the temperature transmitted from the elements, the terminals of the electronic components that have abnormally heated up are pulled out from the printed wiring board.

Therefore, electronic components that generate abnormal heat are disconnected from the circuit formed within the printed wiring board, and the power supply is cut off, stopping heat generation. It is possible to prevent burning.

〔Example〕

Below, a first example showing an electronic unit which is an embodiment of the present invention will be described.
The diagram will be explained.

As shown in FIG. 1, an electronic component 1 such as a resistor is an element 1
A and a terminal 1b, the tip of the terminal 1b is inserted into a through hole 2a of a printed wiring board 2 and connected with solder 3. Further, a metal piece 4 made of a shape memory alloy is inserted between the element 1a and the printed wiring board 2. The shape of the metal piece 4 does not change up to an operating temperature determined by manufacturing conditions, and one end is fixed to the element 1a. Further, in this embodiment, the metal piece 4 is formed to operate when the temperature reaches 150° C. or higher. The reason is that the solder 3 used in the printed wiring board 2 is generally a eutectic solder, and its melting point is around 180° C., and it becomes liquid when this temperature is exceeded. Since the surface temperature of the electronic component 1 during soldering is about 1500°C, the operating temperature of the metal piece 4 is set to 150°C or higher.
The soldering of the electronic component 1 is made so that it will not operate at temperatures as high as 100 mph.

Since the electronic unit according to the present invention is configured as described above, a large power exceeding the rated power is applied to the electronic component 1 due to the failure propagation of the short circuit mode of other components (not shown) mounted on the printed wiring board 2. Then, the element 1a of the electronic component 1 generates an abnormally high amount of self-heating, which is transmitted to the metal piece 4. After that, when a temperature of 150°C or higher, which is the operating temperature of the metal piece 4, is transmitted from the electronic component 1 to the metal piece 4, the metal piece 4
is expanded as shown in FIG. 2, and a force acts to push the element 1a away from the printed wiring board 2.

On the other hand, when element 1a reaches a temperature of 150°C or higher, terminal 1b
As the heat is transferred from the solder 3 to the solder 3 and turns the solder 3 into a liquid state, the electronic component 1 is lifted up by the metal piece 4,
As a result, the terminal 1b is pulled out from the through hole 2a and disconnected from the circuit, cutting off the power supply to the electronic component 1 and stopping abnormal heat generation.

Therefore, it is possible to prevent the electronic component 1 itself from emitting smoke, catching fire, and spreading fire to other components.

In addition, although the above embodiment shows the case where the electronic component 1 is a resistor, the present invention is not limited to this, and for example, as shown in FIG.
It can also be applied to so-called surface-mounted components, that is, chip components, which are connected to the printed circuit board 2' by solder 3', as well as capacitors, transistors, and ICs.
It can also be applied to semiconductor parts such as. .

〔Effect of the invention〕

According to the present invention, it is possible to separate the electronic component from the circuit and cut off the power supply in the event of abnormal heat generation, so even if there is a fault that causes abnormal heat generation in the electronic component, the electronic component itself will not generate heat or catch fire. This has the effect of preventing contagious fire to other parts.

[Brief explanation of the drawing]

FIG. 1 is a side view showing an electronic unit according to an embodiment of the present invention, FIG. 2 is a side view showing a state in which an electronic component is removed from a printed wiring board due to abnormal heat generation, and FIG. 3 is a side view showing an electronic unit according to an embodiment of the present invention. FIG. 7 is a side view showing an electronic unit that is another example. 1.1'...Electronic components 2.2'...Printed wiring board 3.3'...Solder

Claims (2)

[Claims] 1. 1. An electronic unit comprising an electronic component, a printed wiring board to which terminals of the electronic component are connected by solder, and a shape memory alloy piece inserted between the elements of the electronic component and the printed wiring board. 2. 2. The electronic unit according to claim 1, wherein the shape memory alloy piece is configured to operate at a temperature of 150° C. or higher.