JPH09129478A - Mounting structure of ceramic electronic part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration in electric characteristics caused by the cracks generated on a ceramic sintered body when the terminal electrode of an electronic part is mounted on a substrate by soldering and also when cracks are grown when the temperature changes repeatedly. SOLUTION: When the terminal electrode 3 of a ceramic electronic part 1, having a terminal electrode 3 on both edges of a ceramic sintered body 2, is to be mounted on a substrate 4 using solder 6 so that the ratio (l/L) of the length l of one-side terminal electrode forming part in longitudinal direction of the ceramic sintered body 2 against the total length L of the ceramic sintered body 1 may be 0.18 to 0.35, and the ratio (h/H) of the height h of the connection part between the terminal electrode 3 and the solder 6 against the thickness H of the ceramic sintered body may be 0.7 or smaller. Desirably, at least the corner part of the edge face, where the terminal electrode of the ceramic sintered body 2 is formed, is formed in a curved shape.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a structure in which a ceramic sintered body such as a multilayer capacitor has terminal electrodes at both ends, and the terminal electrodes and a wiring layer of a substrate are mounted by soldering.

[0002]

2. Description of the Related Art Conventionally, a ceramic multilayer capacitor, which is one type of ceramic electronic component, has a structure in which internal electrodes are embedded in layers between dielectric ceramics to form a multilayer body, and further internal electrodes at both ends of the multilayer body are formed. Has a structure in which a terminal electrode containing silver or the like as a main component is formed on the exposed surface of.

To mount such a laminated capacitor on a predetermined substrate, as shown in FIG.
The terminal electrode 13 of the multilayer capacitor 12 having internal electrodes (not shown) formed inside 1 and the wiring layer 15 formed on the surface of the substrate 14 are electrically connected by the solder 16 and mounted.

[0004]

However, in general, the substrate 14, the ceramic sintered body 11, and the terminal electrode 13 are generally used.
Since the coefficient of thermal expansion of the solder 16 is different, the contraction of the terminal electrode when forming the terminal electrode, the contraction of the solder when mounting the capacitor on the board by soldering, the contraction difference between the board and the ceramic sintered body, etc. There has been a problem that residual stress is generated in the sintered body and a crack is generated at the electrode end of the ceramic sintered body on the substrate side of the terminal electrode.

Since the occurrence of such cracks is so small that it may not be a problem with the electrical characteristics such as insulation resistance during surface mounting, but when temperature changes are repeatedly applied during use, There is a problem that the electrical characteristics are deteriorated because the crack gradually grows.

As a method for solving such a problem, the applicant of the present invention has previously proposed to control the length of the terminal electrode within a predetermined range with respect to the length of the ceramic sintered body (Japanese Patent Laid-Open Publication No. Hei 4 (1998)). 294512). However, even an electronic component having such a structure is insufficient to prevent deterioration of electric characteristics when used under severe conditions such as mounting on an automobile or the like.

[0007]

The inventors of the present invention have conducted stress analysis on various mounting structures to solve the above problems, and as a result, the length of the terminal electrode is changed to the length of the ceramic sintered body. On the other hand, at the same time when forming so as to satisfy the predetermined relationship, when the connection of the terminal electrode with the solder is performed not on the entire surface of the terminal electrode but on the part of the substrate side, stress concentration is eliminated and cracks It was found that crack initiation and crack growth under severe conditions are prevented.

That is, according to the mounting structure of the ceramic electronic component of the present invention, the total length L of the ceramic sintered body having the length 1 of the terminal electrode forming portion on one side in the length direction of the ceramic sintered body.
Is designed to satisfy 0.18 to 0.35, and the ratio (h) of the height h of the connection portion of the terminal electrode with the solder to the thickness H of the ceramic sintered body is / H) is adjusted to 0.7 or less.

Further, it is desirable that at least a corner portion of the end surface of the ceramic sintered body on which the terminal electrode is formed is formed into a curved surface by processing such as polishing.

[0010]

According to the present invention, the ratio (l / L) of the length l of the terminal electrode forming portion on one side in the length direction of the ceramic sintered body to the total length L of the ceramic sintered body is 0.18 to 0.35.
At the same time, when the terminal electrode and the substrate are connected by solder, the ratio (h / H) of the height h of the connection portion of the terminal electrode to the solder to the thickness H of the ceramic sintered body is 0.7 or less. By adjusting so that the stress caused by the difference in thermal expansion when mounting the ceramic electronic component on the substrate,
It is possible to reduce the stress concentration and also to reduce the occurrence of stress due to the curing shrinkage of the solder.

Further, stress concentration can be further reduced by forming at least the corners of the end surface of the ceramic sintered body on which the terminal electrodes are formed by a curved surface by processing such as polishing.

As a result, cracks do not occur in the ceramic sintered body of the ceramic electronic component at the time of mounting, and even under severe conditions in which temperature changes are repeatedly applied, cracks develop and electrical characteristics do not deteriorate. It is possible to improve yield at the time of mounting electronic components and obtain long-term reliability.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to FIG. 1 by taking a monolithic ceramic capacitor as an example of a ceramic electronic component. In the monolithic ceramic capacitor 1 according to the present invention, terminal electrodes 3 are formed at both ends of a ceramic sintered body 2 in which electrodes (not shown) are arranged. According to the present invention, the ratio (l / L) of the length l of the one-sided terminal electrode forming portion in the length direction of the ceramic sintered body to the total length L of the ceramic sintered body is 0.18 to 0.35, particularly 0. It is important that it is 0.25 to 0.35. This is because if the ratio is less than 0.18, remarkable stress concentration occurs in the ceramic sintered body and cracks are likely to occur. This is because there is a problem that

Ceramic sintered body 2 of this multilayer capacitor
Is a known material containing barium titanate (BaTiO ₃ ) or lead titanate (PbTiO ₃ , PbZrTiO ₃ ) as a main component, and the internal electrodes are made of Ag, Pd,
As the terminal electrode 3, such as Ag-Pd, Ni, and Cu, A
g, Cu, Ni, Ag—Pd, etc. Especially,
The terminal electrode has a laminated structure of a base layer made of Ag, a Ni layer, and a Sn layer, so that wettability with solder and adhesion of the terminal electrode to the ceramic sintered body can be enhanced.

When mounting such a multilayer capacitor 1 on a predetermined substrate 4, a wiring layer 5 formed on the surface of the substrate 4
And the terminal electrode 3 of the multilayer capacitor 1 are connected by solder 6 such as Sn-Pb-based eutectic solder.

At this time, in the connection portion of the terminal electrode 3 with the solder 6 in FIG. 1, the height h of the connection portion and the thickness H of the ceramic sintered body 1 have an h / H ratio of 0.7 or less, In particular, it is important that it is 0.5 or less, and more preferably 0.3 to 0.5. This is because if the h / H ratio exceeds 0.7, the stress caused by the curing shrinkage of the solder increases and cracks are likely to occur in the ceramic sintered body.

Further, according to the present invention, it is desirable that at least the corner portion 7 of the end surface of the ceramic sintered body 2 of the multilayer capacitor 1 on which the terminal electrode 3 is formed is formed by a curved surface. Specifically, the ratio of the radius of curvature R of the corner portion 7 and the thickness H of the ceramic sintered body 3 represented by R / H is 0.1 to 0.
It is desirable that it is 5, especially 0.25 to 0.5.

The end surface of the ceramic sintered body 2 on which the terminal electrode 3 is formed is preferably formed with a curved ridge line in addition to the corners, and these are easily formed by ordinary barrel polishing or the like. be able to.

The mounting structure according to the present invention has the same effect not only on the above-mentioned multilayer capacitor but also on electronic parts having terminal electrodes formed on both end faces of the ceramic sintered body. It can also be applied to LC composite filters and the like.

[0020]

EXAMPLES The present invention will be described below with reference to specific experimental examples. Experimental example 3.2 × 1.6 × 0.6 containing BaTiO ₃ as a main component
Ag inside the dielectric ceramic sintered body in the shape of (mm)
After producing a capacitor body with internal electrodes made of, the terminal electrodes were Ag 80 μm, Ni 3 μm, Sn 4 μm so that 1 / L and h / H were as shown in Table 1.
Sequentially baked with a thickness of m. For some of the samples, the corners and ridges of the end faces of the sintered body were chamfered by barrel polishing before forming the terminal electrodes, and the radii of curvature thereof are shown in Table 1.

This capacitor is 75 × 55 × 0.6 (m
m) to the wiring layer of the alumina substrate, Sn62% -Pd
It was mounted at 230 ° C. using 38% solder.

A thermal shock test was carried out for 200 cycles, each cycle of holding the mounted structure in oil at -55 ° C. and 155 ° C. for 5 minutes. In the test, 40 samples were tested for each sample, and the number of cracked ceramics and those with reduced electrostatic capacity were examined after the test. The results are shown in Table 1. It was

[0023]

[Table 1]

As is clear from the results shown in Table 1, in sample No. 1 having an I / L smaller than 0.18, many cracks and a decrease in capacitance were observed, and the sample N exceeding 0.35 was observed.
At o.6, a short circuit occurred between the electrodes due to migration of Ag. In addition, even if l / L was in the range of 0.18 to 0.35, many cracks and a decrease in capacitance were observed in Sample No. 7 in which h / H of the solder connection portion exceeded 0.7. Was given.

On the other hand, l / L is 0.18 to 0.3
5 and h / H of 0.7 or less, the products of the present invention were all suppressed in the occurrence of cracks and the decrease in capacitance. Further, as the radius of curvature of the curved surface of the end surface of the sintered body was increased, the number of defective products was further reduced.

[0026]

As described in detail above, according to the present invention, in a connection structure of a ceramic electronic component by soldering, cracks and electric characteristics are caused in the ceramic sintered body even under severe conditions such as repeated temperature changes. It is possible to provide a mounting structure which is free from deterioration and has a high yield in mounting electronic components and excellent long-term reliability.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a mounting structure of an electronic component of the present invention.

FIG. 2 is a diagram for explaining a conventional electronic component mounting structure.

[Explanation of symbols]

 1 Multilayer Capacitor (Ceramic Electronic Component) 2 Ceramic Sintered Body 3 Terminal Electrode 4 Board 5 Wiring Layer 6 Solder 7 Corner

Claims (2)

[Claims] 1. A structure in which the terminal electrodes of a ceramic electronic component having terminal electrodes on both ends of a ceramic sintered body are mounted on a wiring layer of a predetermined substrate by soldering, and one side terminal in the longitudinal direction of the ceramic sintered body is provided. The ratio of the length l of the electrode forming portion to the total length L of the ceramic sintered body (l /
L) is 0.18 to 0.35, and the ratio (h / H) of the height h of the connection portion of the terminal electrode with the solder to the thickness H of the ceramic sintered body is 0.7 or less. A mounting structure for a ceramic electronic component, which is characterized in that 2. The mounting structure for a ceramic electronic component according to claim 1, wherein at least a corner portion of an end surface of the ceramic sintered body on which the terminal electrode is formed is formed by a curved surface.