JPS62162307A - Positive characteristic thermister - 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 The present invention relates to a positive temperature coefficient thermistor used for controlling demagnetizing current and various other uses.

Conventional technology (2) Conventional positive temperature coefficient thermistors generally have a structure as shown in FIG. That is, electrodes 1. An external lead 3.3 is fixed to the electrode 1.1 of a positive temperature coefficient thermistor element (hereinafter simply referred to as the element) 2 formed with the positive temperature coefficient thermistor element 1 with solder 4, 4, and the entire structure is molded with an exterior resin 5. ing.

However, the positive temperature coefficient thermistor having such a structure has the following problems.

However, if the solder 4 and the exterior resin 5 are in close contact with each other as in the thermistor described above, if the element 2 suddenly generates heat due to the application of voltage, the solder 4 with high thermal conductivity will However, the temperature of the exterior resin 5 is low and the temperature cannot be raised quickly following the solder 4 and the exterior resin 5.
This causes problems such as peeling of the solder 4 or cracking of the element 2 or the exterior resin 5.

Such a problem can also occur when the device receives a thermal shock such as a sudden change in the ambient temperature.

One way to solve this problem is to use exterior resin 5.
Although it is conceivable to use a soft resin as a material, such soft resins are generally expensive, have low strength, and have problems such as being easily peeled off, so it is difficult to say that it is a good idea.

Means for Solving the Problems In order to solve the above problems, the present invention provides a positive temperature coefficient thermistor in which external leads are fixed to electrodes on both sides of the element with solder and molded with exterior resin. The gist is that a void is formed between the outer resin and the outer resin.

Effect of the Invention If a gap is formed between the element or solder and the exterior resin in this way, when heat is generated due to voltage application or when a thermal shock is received from the outside, a considerable amount of air will be generated between the solder 4 and the exterior resin 5. Even if a difference in thermal expansion occurs, the stress based on the difference in thermal expansion is largely absorbed and alleviated by the voids.

friend blood Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of a positive temperature coefficient thermistor according to the present invention. In the figure, 2 is an element having electrodes 1.1 formed on both sides, and this element 2 is made of, for example, ceramic or synthetic resin mixed with conductive particles, and has a positive resistance-temperature characteristic. Electrodes 1 on both sides of this element 2.
1, the ends of the external leads 3 and 3 are soldered 4.
．． It is fixed by 4. These are molded with a thermosetting exterior resin 5 such as epoxy resin, and a gap 6 is formed between the solders 4, 4 and the exterior resin 5.

Such a positive temperature coefficient thermistor is manufactured by forming a void 6 in a manner as shown in FIG. That is,
The element 2 having electrodes 1, 1 on both sides as shown in FIG. It is fixed with solder 4, 4, and the solder 4, 4 is covered with wax 7.7. Then, by immersing this in an exterior resin liquid, it is molded with an exterior resin 5 as shown in FIG. When heat-cured in this manner, the exterior resin 5 becomes porous due to volatilization of the solvent in the exterior resin 5, so the internal wax 7゜7 is absorbed into the fine pores of the exterior resin 5, and the cavities 6゜6 are formed. It is formed.

As the means for forming the cavity 6.6, various means can be employed in addition to the above-mentioned means by wax absorption. FIG. 2 shows an example in which the cavity 6.6 is formed by such other means. According to this, a camp 8.
It is molded.

As mentioned above, there is a gap 6 between the solder 4.4 and the exterior resin 5.
, 6, when a voltage is applied, the element 2 suddenly generates heat. In this way element 2
When the element 2 generates heat, the solders 4, 4 having high thermal conductivity follow the element 2 and quickly rise in temperature. However, since the exterior resin 5 has a low thermal conductivity, it cannot quickly expand following the elements 2 and the solders 4, 4, but the stress due to this difference in thermal expansion is caused by the stress between the solders 4, 4 and the exterior resin 5. The air gap 6.6 formed between them absorbs and relaxes the air to a large extent.

Therefore, unlike conventional thermistors, the solders 4, 4 are prevented from peeling off due to large stress, and the element 2 and the exterior resin 5 are prevented from being cracked. In addition, the stress generated when thermal shock is applied from the outside is sufficiently absorbed and alleviated by the void 6.6, so that peeling of the solder 4.4 and cracking of the element 2 and the exterior resin 5 will not occur. There is no. Furthermore, the presence of such voids 6.6 improves the heat insulation to some extent, so there is also the advantage that the element 2 is less susceptible to the effects of outside temperature.

By the way, the gaps 6, 6 between the solder 4, 4 and the exterior resin 5
If it is too large, the strength of the exterior resin 5 may be reduced, so it is preferable that the void 6.6 is not large. Further, as the electrodes 1' and 1, it is preferable to form ohmic electrodes such as nickel electrodes by means such as electroless plating.
It is desirable to form a silver coating on the surface. Therefore, a positive temperature coefficient thermistor according to an embodiment shown in FIG. 3 was constructed to meet these demands.

That is, the positive temperature coefficient thermistor shown in FIG. 3 has ohmic electrodes 1.1 such as nickel electrodes formed on both sides of the element 2, and a silver coating 9.9 formed on a part of the electrodes 1,1. Solder the ends of the external leads 3.3 to the silver coatings 9 and 9.
, mold the whole thing with exterior resin 5, and solder 4.4.
It has a structure in which a gap 6.6 is formed between the outer resin 5 and the outer resin 5. When the silver films 9, 9 are formed on a part of the ohmic electrodes 1, 1 in this way, the solder 4, 4 adheres only to the part of the silver film 9, 9, which has good solder wettability, and the solder 4
, 4 becomes considerably smaller, the voids 6, 6 formed around the solder 4.4 also become considerably smaller,
The mechanical pressure strength of the exterior resin 5 is improved.

As is clear from the above explanation, the positive temperature coefficient thermistor of the present invention has a gap formed between the solder and the exterior resin, so that the PTC thermistor is able to withstand sudden heat generation of the element or thermal shock from the outside. It can sufficiently absorb and alleviate the stress caused by the difference in thermal expansion between the solder, the element, and the exterior resin when exposed to stress, thereby satisfactorily preventing solder aIt m and cracks in the element and exterior resin due to stress. This has the effect of significantly improving reliability.

[Brief explanation of drawings]

1, 2 and 3 are cross-sectional views showing positive temperature coefficient thermistors according to different embodiments of the present invention, and FIGS.
(d) is a sectional view illustrating an example of a positive temperature coefficient thermistor according to the present invention, and FIG. 5 is a sectional view of a conventional positive temperature coefficient thermistor. 1... Electrode, 2... Positive temperature coefficient thermistor element, 3...
・External lead-out lead, 4...Solder, 5...Exterior resin,
6...Void, 9...Silver coating.

Claims (2)

[Claims] (1) A PTC thermistor in which external leads are fixed to electrodes on both sides of a PTC thermistor element with solder and molded with an exterior resin, characterized in that a gap is formed between the solder and the exterior resin. Positive characteristic thermistor. (2) The electrodes on both sides of the positive temperature coefficient thermistor element are ohmic electrodes, a silver coating is formed on a part of the ohmic electrode, and an external lead is fixed to this silver coating with solder. A positive temperature coefficient thermistor according to range (1).