JPS6041683Y2 - Positive characteristic thermistor - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a positive temperature coefficient thermistor with an improved electrode configuration.

Conventionally, the electrodes of a positive temperature coefficient thermistor have different configurations depending on the connection method of the lead terminal.

That is, when the electrode 2 and the lead terminal 3 are connected by soldering 1 as shown in FIG. An ohmic contact is made, and an electrode 2 is formed by plating copper or tin 6, which is easy to solder, on the nickel film layer, and the electrode 2 and a lead wire 3 are connected with a solder 1.

On the other hand, when connecting the spring terminal fitting 7 and the electrode 2 by pressure welding, a nickel film 5 is coated on the surface of the positive temperature coefficient thermistor porcelain 4 by electroless nickel plating as described above to make ohmic contact, and an inrush current It is generally well known to provide a silver layer 8 that can withstand high temperatures, and to press a spring terminal fitting 7 onto the silver layer 8.

However, the former electrode 2 has a high surface resistance, and there is a risk of electrode burnout due to the initial current.

In addition, the latter is expensive due to the recent rise in the price of silver, and the baking temperature is 600% to obtain ohmic contact.
Below °C, there are drawbacks such as weak tensile strength between the electrode and the terminal, so in Japanese Patent Application Laid-Open No. 11875-1987, a two-layer electrode made of silver and copper was published, and the life characteristics, solderability, and high voltage Although the pulse characteristics have been improved, since copper rapidly oxidizes at temperatures above 200°C, it is necessary to create ohmic contact by processing at as low a temperature as possible, which is extremely difficult. It has low strength, is easily oxidized even at room temperature and humidity, and has very poor solderability.

The present invention has been devised to improve the above-mentioned drawbacks, and will be described with reference to the embodiment shown in FIG.

FIG. 3 shows the electrode 12 of the positive temperature coefficient thermistor porcelain 14 of the present invention.
14 is a PTC thermistor porcelain, 12 is an electrode, 13 is a nickel layer, 15 is a copper layer, and 16 is a tin layer. After activating the PTC thermistor porcelain 14,
After washing with water, a nickel film layer is formed on the surface of the element 14 by electroless plating, heat treatment is performed at 300 to 400°C, then a copper layer is overlaid on the nickel layer by plating, and further tin is plated to form a tin film. Build layers.

Then, the outer periphery of the PTC thermistor porcelain 14 is centerlessly polished to obtain a PTC thermistor element 18 with a triple layer electrode 12 of the nickel layer 13, copper layer 15, and tin layer 16, and the electrode 12 and the lead terminal are soldered. A positive temperature coefficient thermistor was constructed by connecting or pressure-welding the spring terminal fittings.

In addition, for the formation of the electrode 12, each layer is formed by plating, and the heat treatment or immersion time in the plating solution is arbitrarily selected depending on the characteristics to be obtained, and the plating method is also obtained by electroplating or electroless plating. It is something.

The nickel layer 13 of the electrode 12 of the positive temperature coefficient thermistor element 18 formed as described above is for improving ohmic contact with the positive temperature coefficient thermistor ceramic 14, and the copper layer 15 is a metal having the second highest conductivity after silver. On the other hand, the surface of copper has the disadvantage that it is extremely susceptible to oxidation even at room temperature, and if stored for a long period of time, solderability will deteriorate, and in the case of a pressure welding structure, the copper metal at the spring pressure welding part may oxidize. Since this has the disadvantage of causing burnout of the electrode, a tin layer is further applied to compensate for the disadvantage of the silver layer, improving the solderability between the electrode and the lead end, and improving the inrush current resistance of the pressure welding structure. By increasing the amount, the same characteristics as the conventional nickel-silver two-layer electrode were obtained.

The positive temperature coefficient thermistor having three-layer electrodes of the present invention obtained as described above has an electrode structure of nickel-copper-tin layers, which prevents oxidation of copper and improves solderability during long-term storage. It can be used as an electrode with good inrush current capacity by utilizing the electrical conductivity of copper, and with the same electrode configuration, it can be used in soldered structures for connecting electrodes and terminals, as well as positive temperature coefficient thermistors with pressure welding structures. , which simplifies process control, simplifies the process, and can be manufactured at low cost, so it has great industrial value.

[Brief explanation of drawings]

1 and 2 are cross-sectional views of a conventional PTC thermistor, and FIG. 3 is a cross-sectional view of a PTC thermistor element of the present invention. 12: Electrode, 13: Nickel layer, 15: Copper layer, 16: Tin layer, 14: Positive temperature coefficient thermistor porcelain.

Claims (1)

[Scope of utility model registration request] A nickel film is directly deposited on the surface of barium titanate-based positive characteristic thermistor semiconductor porcelain, and a copper film is deposited on top of the nickel film, and a tin film is further deposited to form a three-layer structure electrode. A positive temperature coefficient thermistor consisting of a lead wire soldered to the surface or a spring terminal fitting pressed into contact.