JPH05226115A - Surge absorber - Google Patents

Abstract

PURPOSE:To provide a surge absorber excellent in heat-cycle properties by suppressing cracks and resin deficiency in a resin dripping part stuck to the base of a lead wire, when a surge absorber is mounted on a substrate by an automatic mounting machine, for the surge absorber protecting an electronic equipment from abnormal voltage such as lightning surge voltage. CONSTITUTION:Powder epoxy resin 5a, 5b to supplement insulation resin is applied to resin dripping parts 4a, 4b formed in the base of the lead wires 3a, 3b of insulation resin 2 covering a varistor body part 1 so that supplementary insulation layer is formed. Thus, the resin dripping parts 4a, 4b low in mechanical strength are reinforced and no crack and resin deficiency occur in the resin dripping parts 4a, 4b when the title apparatus is mounted on a substrate by an automatic mounting machine.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surge absorber for protecting semiconductor devices and electronic equipment from abnormal voltage such as lightning surge voltage.

[0002]

2. Description of the Related Art In recent years, along with the multifunctionalization of electronic devices, electronic devices have been promoted in the fields of home electric appliances, information communication equipment, industrial equipment and the like. A large number of semiconductor elements such as ICs and LSIs are used in this electronic device and realize excellent functions. However, when an abnormal voltage such as a lightning surge voltage enters the circuit, the semiconductor element reacts extremely sensitively, which may cause malfunction or destruction of the circuit and may cause the electronic device to stop functioning. Therefore, from the viewpoint of ensuring and improving the reliability of electronic devices, measures against surge voltage of these semiconductor elements are extremely important problems, and surge absorbers are indispensable for electronic devices.

Recently, a large number of electronic devices have been used even in fields where reliability under harsh environmental conditions such as automobile electrical equipment is required, and as a result, surge absorbers are also used as automobile electronic components for automobiles. High reliability that can be used even under severe environmental conditions has been demanded. In particular, surge absorbers are required to have high heat cycle performance, and we are aiming to achieve high heat cycle performance by changing the insulation resin. As described above, the conditions required for the surge absorber tend to become more severe as the application range of electronic devices is expanded.

A conventional surge absorber will be described below. Conventionally, a surge absorber such as a varistor using a semiconductor ceramic element has been used as a countermeasure against surge voltage in electronic devices. 3A and 3B are views showing a conventional surge absorber. FIG. 3A is a front view thereof, FIG. 3B is a front perspective view thereof, and FIG. 3C is a sectional view taken along the line AA. In FIG. 3 (a), 11 is a varistor main body, and 12 is an insulating resin such as an epoxy-modified phenolic resin for the exterior which has excellent heat cycle properties. Reference numerals 13a and 13b are lead wires obtained by solder-plating copper or silver, and reference numerals 14a and 14b are resin hanging portions in which the insulating resin 12 is unnecessarily attached to the lead wires 13a and 13b.

FIG. 3 (b) shows the internal structure of the varistor, and FIG. 3 (c) is a side view of the cross section taken along the line AA of FIG. 3 (b) as seen from the side. Reference numeral 15 is a plate-shaped varistor element, which generally contains zinc oxide, strontium titanate or the like as a main component. 16a and 16b are varistor elements 1
5 is an electrode made of silver paste or the like formed on both surfaces by baking. The lead wires 13a and 13b are soldered to the electrodes 16a and 16b, respectively. The insulating resin 12 covers the varistor element 15, the electrodes 16a and 16b, and the vicinity of the roots of the lead wires 13a and 13b.

The insulating resin 12 generally has a coefficient of thermal expansion of 1.
It is a resin of the order of 0 × 10 ⁻⁶ / ° C. This is because the thermal expansion coefficient of the varistor element 15 made of semiconductor ceramic is 6.
It is about 0 × 10 ⁻⁶ / ° C., and by reducing the difference between the two as much as possible, the object is to suppress the thermal strain of the insulating resin 12 and improve the heat cycle property when a thermal shock is applied. I am trying. As a means for reducing the coefficient of thermal expansion, a method of increasing the content of filler such as silica (SiO ₂ ) in the insulating resin 12 is generally used. However, while this method improves the heat cycle property, the mechanical strength of the insulating resin 12 tends to decrease.

The operation of the surge absorber configured as described above will be described below. Such as lightning surge voltage,
When a momentary overvoltage is applied to both ends of the lead wires 13a and 13b, a momentary overvoltage is also applied between the electrodes 16a and 16b, and a momentary overvoltage is also applied to the varistor element 15.
Then, the resistance value of the varistor element 15 sharply decreases, a current flows, and the surge voltage is absorbed. At this time, an excessive voltage is momentarily generated in the varistor element 15, so if the varistor element 15 is in the atmosphere,
There is a possibility that a creeping discharge phenomenon may occur on the side surface of the varistor element 15 and the varistor element 15 may deteriorate. Therefore, as described above, the varistor element 15 is covered with the insulating resin 12.

The varistor having the above-mentioned functions is connected to the power supply line or the signal line connected to various electric / electronic devices which are protected devices, or between the ground lines, and is connected to the ground, and the static electricity or the electric discharge which invades the line. , Is used for the purpose of absorbing and protecting abnormal voltage such as lightning surge voltage.

The surge absorber configured as described above is
Generally, it is used by mounting it on a board together with other electronic components, but recently, the automatic mounting technology for electronic components has developed, and the mounting of components on an automatic mounting machine has become the mainstream.Surge absorbers are also automatically mounted. Products that comply with are required.

[0010]

However, in the conventional configuration, when the board is mounted by the automatic mounting machine, as shown in FIG.
There is a problem that cracks or defects occur in the resin sloping portions 14a and 14b of (a). This is because when the lead wires 13a and 13b of FIG. 3 (a) are inserted into the defined holes on the board by the mounting machine, the centers of the lead wires 13a and 13b deviate from the centers of the holes to be inserted. Lead wire 13
It is considered that a and 13b come into contact with the substrate, mechanical stress such as distortion and vibration occurs, and stress is applied to the resin droop portions 14a and 14b. The degree of occurrence of defects such as cracks and defects caused by the mounting of the board by such an automatic mounting machine is, for example, 10 mm in diameter of the varistor element, 3.0 mm in the length of the resin hanging portions 14a, 14b, and lead wires 13a, 1
When the diameter of 3b was 0.8 mm, the number was 32 out of 100.

When the resin dripping portions 14a and 14b are cracked or chipped, stress caused by mechanical shock such as thermal shock or vibration due to a change in ambient temperature where the varistor is used is concentrated on the defective portion of the resin. Furthermore, the phenomenon that cracks grow and the defective portion expands was observed. In addition, the moisture entering from the cracks deteriorated the moisture resistance and the insulation resistance.

As described above, when the conventional surge absorber is mounted on a board by an automatic mounting machine, a defect occurs in the resin dripping portion, which lowers the reliability and safety of the product. ..

The present invention solves the above-mentioned problems of the prior art by preventing cracks or defects in the resin sagging portion that occurs when a surge absorber is mounted on a substrate by an automatic mounting machine.
It is an object of the present invention to provide a surge absorber which is excellent in heat cycle property and can secure reliability and safety.

[0014]

In order to achieve this object, a surge absorber according to the present invention is provided with a machine made of epoxy resin or the like on the surface of an insulating resin of a resin dripping portion which is formed at the root of a lead wire of a conventional surge absorber. Has a structure in which a reinforcing insulating resin that is excellent in mechanical strength and can withstand a mechanical load during mounting by an automatic mounting machine is applied, and the resin hanging portion has a double structure to reinforce. ..

[0015]

According to the present invention, the reinforcing insulating resin bears the mechanical load generated at the resin dripping portion generated at the root of the lead wire of the surge absorber when the board is mounted by the automatic mounting machine with the above-mentioned structure. It is possible to reduce the mechanical load applied to the resin hanging portion. Therefore, it is possible to prevent defects such as cracks and defects of the resin dripping portion, and ensure the reliability and safety of the product.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A surge absorber according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a surge absorber composed of a disk type varistor of this embodiment. FIG. 1 (a) is a front view,
The same figure (b) is a side view. In FIG. 1, reference numeral 1 is a varistor main body portion, and 2 is an insulating resin for an exterior made of an epoxy-modified phenol resin having excellent heat cycle property. The insulating resin 2 has a coefficient of thermal expansion of about 4 × 10 ⁻⁶ / ° C. and a coefficient of thermal expansion of a varistor element made of ceramics of about 6 × 10 ⁻⁶ / ° C.
The difference is small and the thermal shock resistance is excellent, but the mechanical strength is weak.

3a and 3b are lead wires made of solder-plated copper, 4a and 4b are resin drip portions, and 5a and 5b are reinforcing powder epoxy resins having excellent mechanical strength. The powdered epoxy resins 5a and 5b are resin drip portions 4a and 4b.
The resin strength is about four times as high as that of the insulating resin 2 made of epoxy-modified phenol resin. The coating thickness of the powdered epoxy resins 5a and 5b is about 0.3 mm. In addition, in FIG. 1, the varistor main body 1, the insulating resin 2, the lead wires 3a and 3b, and the resin sagging portions 4a and 4b are the same as those in the conventional surge absorber.
Varistor body 11, insulating resin 12, lead wire 13
a, 13b, and the resin hanging parts 14a, 14b.

Next, the function and effect of the surge absorber configured as described above will be described. Varistor element diameter 1
0 mm, the length of the resin sagging portions 4a and 4b is 3.0 mm, the diameter of the lead wires 3a and 3b is 0.8 mm, and the powdered epoxy resin 5a and 5
When the thickness of b was 0.3 mm (referred to as Example 1), the number of defects such as cracks and defects that occurred during the substrate mounting by the automatic mounting machine was 0 in 100. Further, when only the thickness of the powdered epoxy resins 5a and 5b is changed under the same conditions as in Example 1, when the thickness is 0.2 mm (referred to as Example 2) and when it is 0.1 mm (Example 3
7) out of 100 and 24 out of 100. The defective rate at the time of automatic mounting of the surge absorber according to the present embodiment and the conventional surge absorber is shown in comparison with (Table 1).

[0020]

[Table 1]

As is clear from this (Table 1), in the surge absorber according to the present embodiment, the resin dripping portions 4a and 4b are coated with the powder epoxy resins 5a and 5b. It is possible to suppress the occurrence of defects such as cracks and defects, and if the powder epoxy resin 5a, 5b has a thickness of 0.3 mm or more, defects do not occur, and the resin dripping part 4a during automatic mounting of the surge absorber, An excellent effect is obtained in that the defect of 4b is eliminated.

Incidentally, reinforcing powder epoxy resins 5a, 5
b is epoxy resin and silica (SiO ₂) Such as inorganic
Easy to apply powdered epoxy resin containing
It is the most suitable and the main of resin strength of powdered epoxy resin
The content of the epoxy resin component is 40 to 60% by weight
A range of% is suitable. This has 40 epoxy resin components
If it is less than wt%, the mechanical strength is weak and it is not practical,
If it exceeds 60% by weight, the drying time will be longer and
It is because the workability deteriorates.

Next, a method of applying the powdered epoxy resin will be described with reference to FIG. FIG. 2A shows the resin dripping part 4.
a, 4b for explaining the heating method, FIG. 7 (b) is a front view for explaining the method of attaching the powdered epoxy resins 5a, 5b, and FIG. 6 (c) is another heating method for the resin dripping portions 4a, 4b. It is an explanatory perspective view of a method. In FIG. 2, 6a and 6b are heating pads made of silicone rubber, 7 is a powdered epoxy resin liquid, 8a,
8b is a nozzle for ejecting hot air 9.

The coating procedure is as shown in FIG.
The resin dripping portions 4a and 4b are sandwiched and heated from both front and rear directions of the varistor main body portion 1 by heating pads 6a and 6b made of silicon rubber and heated to 50 to 200 ° C. Next, as shown in FIG. 2B, the varistor main body 1 is dipped in the powdered epoxy resin liquid 7 and attached to the resin dripping portions 4a and 4b. Then, it hardens in a 150-170 degreeC thermostat. It should be noted that the heating of the resin dripping portions 4a and 4b is 170 to 170% as shown in FIG.
There is also a method of blowing hot air 9 at 220 ° C.

As described above, according to this embodiment, the resin sagging portions 4a and 4b generated when the insulating resin 2 for the exterior of the surge absorber is coated are cracked or cracked when they are automatically mounted on the substrate by the automatic mounting machine. The problem of resin deficiency can be solved by applying the powder epoxy resins 5a, 5b having excellent mechanical strength to the resin dripping portions 4a, 4b. In this example, the example of the powdered epoxy resin is shown as the most preferable example of the reinforcing insulating resin, but if the resin has better mechanical strength than the insulating resin for the exterior, that resin may be used. Good.

[0026]

As described above, the surge absorber of the present invention is
The resin dripping portion that occurs when the insulating resin for exterior is coated, by forming a reinforcing resin layer by applying a reinforcing insulating resin having excellent mechanical strength, even when the mechanical strength of the insulating resin is weak, It is possible to realize board mounting by an automatic mounting machine.

[Brief description of drawings]

FIG. 1A is a front view of a surge absorber according to an embodiment of the present invention, and FIG. 1B is a side view of the surge absorber.

FIG. 2A is a perspective view for explaining a heating method for a resin dripping portion of a surge absorber according to an embodiment of the present invention. FIG. 2B is a view for explaining a method for adhering a powder epoxy resin to the resin dripping portion. The front view (c) is a perspective view for explaining another heating method for the resin dripping part.

3A is a front view of a conventional surge absorber, FIG. 3B is a front perspective view of the same, and FIG. 3C is a cross-sectional view taken along the line AA shown in FIG. 3B.

[Explanation of symbols]

 1 Varistor main body 2 Insulating resin 3a, 3b Lead wire 4a, 4b Resin hanging part 5a, 5b Powder epoxy resin (reinforcing resin layer)

Claims (2)

[Claims] 1. A plate-shaped varistor element, electrodes formed on both surfaces of the varistor element, lead wires led from the electrodes, and an insulating resin covering a part of the varistor element, the electrodes and the lead wires. In the surge absorber, the reinforcing resin layer is formed by applying a reinforcing insulating resin to the surface of the resin sloping portion formed at the root of the lead wire that is led out of the insulating resin. Surge absorber. 2. The surge absorber according to claim 1, wherein the reinforcing insulating resin is a powdered epoxy resin containing an epoxy resin and an inorganic filler as main components and the component ratio of the epoxy resin is 40 to 60% by weight. ..