JPH04199801A - Manufacture of positive-characteristic thermistor element - Google Patents

Abstract

PURPOSE:To prevent a decline in mechanical breaking strength of the title element by leaving a partial electrode in each electrode forming area in such a way that the surfaces of no-electrode forming areas are made to protrude from the surfaces of electrode forming areas and, after forming a full-surface electrode on the entire surface of a positive-characteristic(PTC) ceramic chip, part of the full-surface electrode are deleted from the no-electrode forming areas. CONSTITUTION:Protruding sections 2 are formed in areas where no partial electrode is required (no-electrode forming areas) on the surface of PTC ceramic chip 1 by causing the surfaces of the areas to protrude from the areas where partial electrodes are required (electrode forming areas). Then a full-surface electrode 4 is formed on the entire surfaces of six faces of the chip by electroless plating of Ni, etc., and the electrode 4 is deleted from the surfaces of the protruding sections 2 by a grinding method using sandblast, lapping, etc., after masking the electrode forming areas as required. In addition, the chip surface is exposed in the no-electrode forming areas and, at the same time, the partial electrodes 3 are formed by using the electrodes left in the electrode forming areas. Therefore, a decline in the mechanical breaking strength of this positive-characteristic thermistor element can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a chip-type positive temperature coefficient thermistor element.

[Background Art] FIGS. 4(a), 4(b), and 4(c) show a conventional method of manufacturing a positive characteristic (hereinafter referred to as PTC) thermistor element. What is shown in FIG. 4(a) is a PTC ceramic chip 51 fired into a rectangular parallelepiped shape, and the entire surface of this chip 51 is plated with nickel (Ni) or the like as shown in FIG. 4(b). A full surface electrode 52 is formed. Next, a part of the entire surface electrode 52 is covered with a masking material so as to expose the electrode unnecessary region 53, and the portion of the surface electrode 52 exposed from the masking material is ground by sandblasting, as shown in FIG. 4(C). First, the entire surface electrode 52 is divided into two to form a partial electrode 54. Furthermore, a silver paste is applied and baked onto the partial electrode 54 to form the external electrode 55 of the positive temperature coefficient thermistor element 56.

[Problems to be Solved by the Invention]-' However, in the method of sandblasting the entire surface electrode 52 and forming the divided electrodes 54 as described above, the entire surface electrode 52t! - When partially removing by sandblasting, not only the electrode metal but also the underlying PTC ceramic chip 51 is scraped off, creating a step on the chip surface at the boundary between the electrode forming area and the electrode unnecessary area 53. (See Figure 4(C)).

Therefore, stress concentration tends to occur in this stepped portion, and the mechanical bending strength of the PTC thermistor element 56 decreases in this portion.

Furthermore, when this PTC thermistor element 56 is mounted on the surface of the printed wiring board 57, as shown in FIG.
The C ceramic chip 51 does not contact the surface of the printed wiring board 57, and a space 58 is created between the C ceramic chip 51 and the printed wiring board 57. This makes it difficult for the PTC thermistor element 56 to detect the heat and temperature of the printed wiring board 57.
There was a problem in that the sensing ability of the PTC thermistor element 56 was reduced.

The present invention has been made in view of the drawbacks of the conventional examples described above, and its purpose is to provide a method for forming electrodes without causing a decrease in mechanical bending strength or a decrease in sensor performance. An object of the present invention is to provide a method for manufacturing a characteristic thermistor element.

[i1! Means for Solving the Problem: The method of manufacturing a PTC thermistor element of the present invention includes making the surface of the electrode-free region protrude beyond the surface of the electrode formation region at least on the mounting surface and the surface facing the mounting surface of the PTC ceramic chip. The method is characterized in that after a full-scale electrode is formed on the entire surface of the PTC ceramic chip, a part of the full-face electrode is removed in areas where electrodes are not required, and partial electrodes are left in each electrode formation area.

In the present invention, since the surface of the electrode-free region of the PTC ceramic chip is made to protrude from the surface of the electrode-forming region, even if the entire surface electrode is removed in the electrode-free region and the chip surface is exposed, In this case, the chip surface in the area where electrodes are not required is not etched further than the part of the partial electrodes, and a decrease in the mechanical bending strength of the PTC therminuta element can be prevented.

In addition, since the mounting surface of the PTC thermistor element can be made almost uniform, when this PTC thermistor element is mounted on a printed wiring board etc., the chip surface can be brought into contact with or close to the printed wiring board etc. PTC
The sensing ability of the thermistor element can be improved.

[Example] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIGS. 1(a), 1(b), and 1c show a manufacturing method according to an embodiment of the present invention. The one shown in Fig. 1(a) is a PTC ceramic chip 1 of ceramic type exhibiting positive temperature characteristics.
It is a fired product formed into a substantially rectangular shape, and the area on the chip surface where it is not necessary to provide a partial electrode (electrode unnecessary area) is replaced by the area where a partial electrode is required (electrode formation area).
A protrusion 2 is formed in an area where no electrode is required, protruding from the surface of the electrode. In the illustrated example, band-shaped protrusions 2 are provided on four sides of the chip surface along the central portion of the PTC ceramic chip 1, but the protrusions 2 may have an appropriate shape depending on the application. Further, the protrusion height h of the protrusion 2 is larger than the film thickness of the partial electrode 3. Next, Figure 1 (
As shown in b), the six gold surfaces of the PTC ceramic chip 1 are plated with Ni using electroless plating to form electrodes 4 on the entire surface, masking the electrode formation area as necessary, and polishing such as sandblasting or lapping. As shown in FIG. 1(c), the entire surface electrode 4 on the protrusion 2 is removed by this method, and the chip surface is exposed in the area where no electrode is required, and a partial electrode 3 is formed using the electrode left in the electrode formation area. do. Further, the chip surface in the electrode-free region and the partial electrode surface are flush with each other. Thereafter, in order to improve soldering properties, an additional electrode 5 is formed by applying and baking an electrode paste made of Ag or an Ag alloy onto the partial electrode 3 or by electroplating.

Therefore, the PTC ceramic chip 1 does not have a thin portion due to excessive cutting, and a decrease in mechanical bending strength can be prevented. Therefore, the occurrence of cracks due to heat stress during soldering is eliminated, and the reliability of the element is improved.

Furthermore, when this PTC thermistor element 6 is mounted on the surface of the printed wiring board 7, as shown in FIG. The heat of the wiring board 7 is easily transmitted to the PTC ceramic chip 1, and the sensing ability of the PTC thermistor element 6 can be improved. Further, since the surface of the PTC thermistor element 6 is flat without any unevenness, it becomes easy to attach the PTC thermistor element 6 to the printed wiring board 7 using a chip placer, and process defects during element mounting can be reduced.

What is shown in FIG. 3 is a sectional view of a PTC thermistor element 8 manufactured by a manufacturing method according to another embodiment of the present invention. This is because the protrusions 2 are located only in the upper and lower surfaces of the substantially rectangular parallelepiped-shaped PTC ceramic chip 1 in areas where electrodes are not required.
The entire upper and lower surfaces of the PTC ceramic chip 1 are covered with electrodes (
Illustrations are omitted. ), remove the electrodes in areas where electrodes are not needed and provide partial electrodes 3 in the electrode formation areas on the upper and lower surfaces,
Next, the surface of the partial electrode 3 and the PTC ceramic chip 1
Additional electrodes 5 are formed on both end faces of Ag or Ag alloy.

Therefore, this embodiment is suitable for forming electrodes on the entire upper and lower surfaces of a parent substrate (not shown) and cutting the parent substrate into PTC ceramic chips after forming the electrodes on the entire surface.

[Effects of the Invention] According to the present invention, since the PTC ceramic chip is not scraped in areas where electrodes are not required, there are fewer scratches on the chip and the mechanical strength of the element is increased.

This also eliminates the occurrence of cracks due to heat stress during soldering, improving the reliability of the device.

Furthermore, since there are no steps on the mounting surface of the element, the element can be mounted closely to the printed wiring board, and the PT
The sensing ability of the C thermistor element is improved. Furthermore, since there are no irregularities on the surface, mounting of elements using a chip placer can be carried out reliably and easily.

[Brief explanation of the drawing]

Figures 1 (a), (b), and (c) are cross-sectional views showing a method for manufacturing a PTC thermistor element according to an embodiment of the present invention, and Figure 2 is a mounting of the element manufactured by the above method on a printed wiring board. 3 is a sectional view showing another embodiment of the present invention, and FIGS. 4(a) (b) (
c) is a sectional view showing a conventional manufacturing method, and FIG. 5 is a sectional view showing a state in which an element manufactured by the above method is mounted on a printed wiring board. 1... PTC ceramic chip 2... Protrusion 3... Partial electrode 4... Full electrode Patent applicant Murata Manufacturing Co., Ltd. Figure 2

Claims (1)

[Claims] (1) At least on the mounting surface and the surface facing the mounting surface of the PTC ceramic chip, the surface of the area where no electrode is required is made to protrude beyond the surface of the electrode formation area, and an electrode is formed on the entire surface of the PTC ceramic chip. rear,
A method of manufacturing a positive temperature coefficient thermistor element, characterized in that a part of the entire surface electrode is removed in an area where no electrode is required, and a partial electrode is left in each electrode formation area.