KR20000028640A - NTC thermistor devices - Google Patents

Abstract

PURPOSE: An NTC(Negative Temperature Coefficient) thermistor device is provided to control the generation of Ag3Sn even under a high temperature environment and to prevent a bad influence on ohmic contact of an electrode in a surface of a thermistor element by using a solder material containing Sn as the chief ingredient and Ni of 0.05-1.0 wt percent. CONSTITUTION: A thermistor element have a negative temperature coefficient. An electrode have Ag as the chief ingredient performing ohmic contact with the thermistor element. A conductive terminal is soldered to the electrode by using a solder material. The conductive terminal is made of metal materials not containing Pb, and the solder material contains Sn as the chief ingredient and contains Ni of 0.05¯1.0 wt percent.

Description

Negative-Thermistor Devices {NTC thermistor devices}

The present invention relates to negative temperature coefficient (NTC) thermistor devices. In particular, the present invention relates to an NTC thermistor device having electrically conductive terminals soldered to an electrode on the thermistor body.

An NTC thermistor device of this kind can be described as including a disk-shaped thermistor body of negative temperature coefficient with electrodes on each of the main surfaces in ohmic contact. Each electrode has a soldered lead wire acting as a conductive terminal, and the whole thermistor body is wrapped in a resin material having moisture resistance and heat resistance. An electrode whose main component is silver is usually used. However, when the thermistor device is used for suppressing rush current, a large amount of heat is generated when the thermistor device is used, and thus high heat resistance is required. Solder is usually used.

However, when the device having an electrode whose main component is silver and a solder material whose main component is tin is placed in a high temperature environment for a relatively long time, the tin contained in the solder causes solid phase diffusion toward the electrode, which adversely affects the bonding between the electrode and the thermistor element. The silver contained in allows solid phase diffusion to the solder. As a result, silver in the electrode reacts with tin to form Ag ₃ Sn. This weakens the ohmic contact between the electrode and the thermistor element, so that the resistance of the thermistor device gradually increases.

When the lead wire is soldered to the electrode or using the device, a high temperature condition occurs that causes the formation of Ag ₃ Sn. The rate at which Ag ₃ Sn is formed is increased in the high temperature environment when using the device. This problem is particularly acute at temperatures above 140 ° C.

Therefore, if the thermistor device is for suppressing inrush current, the solder material with increased tin content is used to improve the resistance to high temperature, but the current flows constantly through the thermistor device and the thermistor device always generates heat. The problem is serious because it is under conditions. Similar problems also arise when thermistor devices are used as high temperature sensors.

Accordingly, it is an object of the present invention to provide an NTC thermistor device in which the above problem can be solved.

1 is a cross-sectional view of an auxiliary thermistor device according to an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of a portion of the thermistor device of FIG. 1 showing how diffusion of tin is suppressed. FIG.

3 is an enlarged cross-sectional view showing a conventional thermistor device having a structure as shown in FIG. 1 but using a conventional material, and how tin is diffused toward the electrode.

Briefly described, the present invention relates to the use of an improved solder for attaching a terminal member such as a conductive lead to an electrode of an NTC thermistor, and to the selection of the composition of the material for the terminal member. In detail, the solder used for attaching the terminal member to the electrode contains tin as a main component but also contains 0.05 to 1.0 wt% of nickel, so that tin is diffused toward the silver electrode, that is, Ag. Formation of ₃ Sn is suppressed. In addition, since the addition of nickel excludes lead which adversely affects the effect of suppressing diffusion of tin toward the electrode, the terminal according to the present invention is characterized in that the terminal is made of a metal material containing no lead.

According to a preferred embodiment of the present invention, solder containing tin, silver and nickel is used. The terminal member may be composed of a lead wire or a lead terminal composed of a metal plate or a terminal plate. When lead wire is used, it is preferable to use silver wire, copper wire, tin-plated iron lines, tin-plated stainless wire and tin-plated copper wire as lead wires.

The accompanying drawings, which form a part of this specification, illustrate embodiments of the present invention and also help explain the principles of the present invention. Like or equivalent components in the accompanying drawings are components of different thermistor devices, but are denoted by the same serial number, and need not be repeatedly described to simplify the disclosure.

[Examples]

Fig. 1 shows a negative electrode thermistor device according to an embodiment of the present invention, which includes a disc-shaped negative electrode thermistor element 2 having electrodes 3 formed in ohmic contact on each of the main surfaces facing each other. Lead wires 5 serving as conductive terminals are soldered and attached to electrodes 3 using solder 4, respectively. According to the embodiment shown in Fig. 1, the entire structure is enclosed inside the enclosure 6 made of a material having heat resistance and moisture resistance such as a silicone resin.

The main component of the electrode 3 is silver. The solder material 4 for soldering and attaching the lead wire 5 to the electrode 3 is characterized by containing not only tin as a main component but also 0.05 to 1.0 wt% nickel. For example, solder materials containing tin, silver and nickel can be used.

By using the solder material which added 0.05-1.0 wt% nickel to tin which is a main component, it can suppress that tin enters or diffuses from the solder material 4 to the electrode 3. As shown in Fig. 2, this is composed of a three-element layer, specifically Ag-Sn-Ni layer 7, which is stable when lead wire 5 is soldered to electrode 3, and a solder material 4 and silver mainly composed of tin. It can be considered that the formation of tin between the solder material 4 and the diffusion of the tin of the solder material 4 into the electrode 3 is suppressed. As a result, ohmic contact between the electrode 3 and the surface of the thermistor element 2 is not adversely affected, and the phenomenon of gradually increasing resistance in a high temperature environment can be greatly reduced.

When the content of nickel is less than 0.05 wt%, the above effect of suppressing the intrusion or diffusion of tin into the electrode 3 becomes small. On the contrary, when the nickel content exceeds 1.0 wt%, the effect of suppressing the intrusion or diffusion of tin into the electrode 3 due to the presence of Ni remains large, but it is easy to form cracks on the surface of the solder 4. Therefore, there is little profit to use in practical use.

In addition, the inventors have found that the effect of nickel to inhibit the invasion and diffusion of tin described above is adversely affected by the presence of lead. Therefore, the lead-free metal material is used not only as a base material for making lead 5 but also for surface treatment of lead 5. It is preferable to use a silver wire, a copper wire, an iron wire plated with tin, a stainless wire plated with tin, and a copper wire plated with tin as the lead wire 5 of the present invention.

Next, the present invention will be described through tests and comparative experiments conducted by the inventors. Molded objects containing oxides of Mn, Ni, Cu, Fe, La, Co, and Cr were sintered to obtain the negative characteristic thermistor element 2 shown in FIG. A conductive paste containing silver as a main component was printed on the surface of the thermistor element and baked at 800 to 850 ° C. to form electrode 3.

Next, solder material 4 was prepared containing Ag by 3.5 wt% and Ni by the amounts shown in Table 1, the remainder being Sn. In addition, as shown in Table 1, other types of lead wires were prepared to prepare a sample shown in Table 1.

Sample Number Ni content of solder (wt%) Lead wire % Change in resistance One* 0 Sn / Pb plated Cu wire 51.5 2* 0.05 Sn / Pb plated Cu wire 12.2 3 * 0.15 Sn / Pb plated Cu wire 10.1 4* 0.3 Sn / Pb plated Cu wire 9.6 5 * 0.7 Sn / Pb plated Cu wire 9.1 6 * 1.0 Sn / Pb plated Cu wire 7.8 7 0.15 Ag wire -0.4 8 0.15 Cu wire 0.1 9 0.15 Sn-plated Fe wire -0.3 10 0.15 Sn-plated stainless steel wire 0.1 11 * 0 Sn-plated Cu wire 32.8 12 * 0.03 Sn-plated Cu wire 5.7 13 0.05 Sn-plated Cu wire 1.3 14 0.15 Sn-plated Cu wire 0.5 15 0.3 Sn-plated Cu wire 0.2 16 0.7 Sn-plated Cu wire 0.3 17 1.0 Sn-plated Cu wire 0.2 18 * 1.2 Sn-plated Cu wire 0.2

Solder 4 was attached to lead wire 5 by dipping, and lead 5 was soldered to electrode 3 by a reflow process to make each of the samples. Next, the thermistor element 2 was completely dipped into a resin material having sufficient heat resistance and moisture resistance to form a resin sheath 6 to obtain a specimen of the negative characteristic thermistor device 1. In Table 1, samples not according to the present invention (ie, comparative samples) were separated by an asterisk (*).

Each of the samples was left for 1000 hours in a high temperature environment of 160 ℃, and the resistance value before and after standing. The results are shown in Table 1.

Samples 1 to 6 are comparative samples using lead wires each containing Pb, in which a Cu wire coated with Sn / Pb is used. Among the comparative examples, it can be seen that Samples 2 to 6 containing 0.05 to 1.0 wt% of Ni have a small change in resistance value when compared with Sample 1 containing no Ni. Solid phase diffusion toward the electrode 3 is suppressed.

However, although the effect of Ni is apparent in Samples 1 to 6, the smallest change in resistance value is as large as 7.8% of Sample 6. Samples 7 to 18 have the feature that lead wire 5 does not contain Pb. According to the present invention among the samples 7 to 18 are the samples 7 to 10 and the samples 13 to 17 in which the Ni content is in the range of 0.05 to 1.0 wt%. Table 1 clearly shows that the change in resistance value of the samples containing Ni in the range determined according to the present invention is smaller, which shows an excellent effect of reducing the change in resistance value. Furthermore, comparing Samples 2 to 6 with Samples 7 to 10 and 13 to 17, it can be clearly seen that the presence of Pb seriously affects the suppression of the diffusion of Sn due to the presence of Ni. In addition, Sample 18 exhibited the adverse effect of cracking on the surface of Solder 4 due to the Ni content of more than 1.0wt%.

In summary, the present invention utilizes a solder material containing tin as a main component and containing 0.05 to 1.0 wt% of Ni to attach a conductive terminal member such as a lead wire containing silver as a main component, thereby forming Ag ₃ Sn in a high temperature environment. Can also be suppressed, and adverse effects on ohmic contact of electrodes on the surface of the thermistor body can be prevented. In addition, since the terminal member is formed only of a material containing no Pb, the Sn diffusion suppressing effect of Ni is not adversely affected by the presence of Pb.

The above implementation can be interpreted broadly. Although the tin content of the test sample is greater than 95 wt%, the expression 'main ingredient' can be understood to be at least 50 wt%.

Claims (4)

Thermistor body with negative temperature coefficient; An electrode in ohmic contact with the thermistor body and composed mainly of silver; And Conductive terminals soldered to the electrode using solder material It includes; The conductive terminal is made of a metal material containing no lead, and the solder contains tin as a main component and contains 0.05 to 1.0 wt% of Ni. NTC thermistor device, characterized in that. The negative thermistor device of claim 1, wherein the solder comprises tin, silver, and nickel. The subsidiary thermistor of claim 1 or 2, wherein the terminal comprises a lead wire selected from the group consisting of a silver wire, a copper wire, a tin plated iron wire, a tin plated stainless wire, and a tin plated copper wire. Device. 3. A negative electrode thermistor device according to claim 1 or 2, wherein the solder contains 95 wt% or more of tin.