JPH04257212A - Surface mounting type electronic component - Google Patents

Abstract

PURPOSE:To prevent unfavorableness in a device body and in the joint of a device and a circuit board by enabling a sufficient buffer of tensile stress generated by a difference in coefficient of thermal expansion between the circuit board and a device. CONSTITUTION:A U-shaped metal cap 3 of high solder wettability is fitted to the electrode part 2 of a device 1 (ceramic capacitor), so that the cross-sectional structure of this metal cap 3 is doubled by bending. The internal and external layers of this metal cap 3 are so structured as to be not fixed at the part except one side that is a bent part at least; further, the electrode part 2 and the internal layer of the metal cap 3 are connected with a conductive adhesive or solder 4.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to surface-mounted electronic components, and more particularly to technical improvements for improving thermal shock resistance at external connections.

0002

BACKGROUND OF THE INVENTION With remarkable technological developments in recent years, various electronic components mounted on the surface of a substrate are becoming smaller and thinner, and as a result, higher density packaging is progressing. FIG. 3 is a diagram showing a square chip ceramic capacitor as an example of such a surface-mounted electronic component. As shown in FIG. 3, the ends of the ceramic capacitor element 1 are made of Ag or
An external electrode 2 whose main component is Pd is formed. When mounting such a square chip ceramic capacitor on a board, the external electrodes 2 are soldered to the board by flow or reflow.

On the other hand, with the progress of high-density surface mounting, the concentration of heat-generating components has also progressed, and it is necessary to prevent local overheating of various electronic components and circuit boards due to the heat generated by these concentrated heat-generating components, as well as deterioration and damage caused by the heat generation. That is required. As a heat dissipation method for this purpose, it has been considered to provide a dedicated heat dissipation section on the substrate, or to construct the substrate itself from a material with excellent heat dissipation ability. For the latter method, for example, the use of an aluminum substrate is being considered.

0004

[Problems to be Solved by the Invention] However, when a square chip ceramic capacitor with the conventional structure as described above is mounted on an aluminum substrate, the external electrode part, which is the connection part, becomes a fatal weak point against thermal shock. . In other words, since the aluminum substrate and the ceramic constituting the ceramic capacitor have coefficients of thermal expansion that differ by an order of magnitude, the external electrode section that connects the two is subject to large tensile and compressive stresses as they are heated and cooled. Occur. Therefore, when a thermal cycle is applied to the mounting board, problems such as cracks occurring in the ceramic capacitor element and peeling of the solder connection with the board occur. Such defects are mainly caused by tensile stress. It should be noted that the problem of defects due to thermal stress at the connection portions is not limited to ceramic capacitors, but also exists in various other electronic components mounted on a board.

The present invention was proposed in order to solve the problems of the prior art, and its purpose is to prevent the bond between the board and the element when thermal shock is applied during mounting on the board. The object of the present invention is to sufficiently buffer the tensile stress caused by the difference in coefficients of thermal expansion with a simple buffer structure, thereby preventing defects from occurring in the element body or the connection between the element and the substrate. The more general purpose is to have excellent thermal shock resistance when mounted on a board, and to be small and compact.
Our objective is to provide superior surface-mounted electronic components that can contribute to thinner, higher-density packaging. Although the object of the present invention is typically a ceramic capacitor, it is not limited to this, and the present invention can also be applied to various other surface-mounted electronic components having external electrodes. is the object of the purpose of

[0006]

[Means for Solving the Problems] In the surface-mounted electronic component of the present invention, a U-shaped metal cap with good solder wettability is fitted to the electrode portion of the element, and the cross-sectional structure of the metal cap is changed by bending. It has a two-layer structure, an inner layer and an outer layer, and the inner layer and outer layer of the metal cap are not bonded to each other except for at least one side, which is the bent portion, and the electrode portion and the inner layer of the metal cap are bonded with conductive adhesive. It is characterized by being connected with adhesive or solder.

[0007]

[Operation] In the surface-mounted electronic component of the present invention having the above-described configuration, the metal cap connected to the electrode portion of the element has a two-layer structure, the inner and outer layers, most of which are not fixed to each other. Therefore, the layers can be moved relative to each other with a considerable degree of freedom. In addition, since the inner layer of this metal cap is connected to the electrode part of the element, if the remaining outer layer is soldered directly to the board, the tensile stress caused by the difference in thermal expansion coefficients caused by heating and cooling will be absorbed by the metal cap. absorbed by the relative movement between the inner and outer layers of the Therefore, when a thermal shock is applied, there is no problem in the element body and the connection portion between the element and the substrate. Note that the relative movement between the inner layer and the outer layer is usually an opening operation, since the expansion coefficient of the substrate is generally much larger than that of the device.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the surface-mounted electronic component according to the present invention will be described in detail below with reference to FIGS. 1 and 2. The embodiment shown in FIGS. 1 and 2 is an embodiment in which a surface-mounted electronic component according to the present invention is applied to a square chip ceramic capacitor.

That is, as shown in FIG. 1, the external dimensions are 7.5 x 6.3 x 2.5 mm and the capacity rating is 25 V.
/10 μF, ceramic capacitor element 1
prepared. This ceramic capacitor element 1 is shown in FIG.
Similar to the prior art shown in 1, this embodiment has a solderable external electrode 2 whose main component is Ag or Ag/Pb. On the other hand, a sheet-like member made of 42 nickel alloy with silver plating applied to the surface was bent at approximately the center and
The metal cap 3 was formed into a layered structure and further bent at two sides to form a U-shape. Then, solder paste 4 is applied to the surface of the inner layer part of the metal cap 3 (the surface that fits into the external electrode 2), and then the metal cap 3 is
was fitted to the external electrode 2 of the element 1. Subsequently, this fitting portion was heated to a temperature higher than the melting point of the solder to join the metal cap 3 and the external electrode 2.

As shown in FIG. 2, the ceramic capacitor with a metal cap according to the present invention (product of the present invention) produced as described above is attached to an aluminum substrate 5 with a thickness of 1 mm.
It was mounted on top by reflow. In addition, in FIG. 2, 6 is solder that connects the metal cap 3 and the aluminum substrate 5, and 7 is an electrode pattern formed on the aluminum substrate 5. On the other hand, for comparison, we prepared a ceramic capacitor (conventional product) with the same external dimensions and the same capacity rating without the conventional metal cap as shown in Figure 3, and similarly reflowed it on an aluminum substrate with a thickness of 1 mm. Implemented by.

[0011] As described above, 100 samples each of the present invention product and the conventional product mounted on the same substrate were tested at -55°C.
, +125°C for 15 minutes each. Table 1 below shows the results of this test.
It is indicated by the cumulative number of defective products in units of 10 cycles. In this case, the criterion for determining a defective product is the capacity reduction rate due to peeling of the solder joint or cracking of the electrode part, and if the capacity reduction rate is 10% or more, it is determined to be a defective product.

0012

[Table 1] As shown in Table 1, with conventional products, as many as 20 (20%) defective products occur in 10 cycles, and 50
During the cycle, all of the sample products ended up being defective. In contrast, in the product of the present invention, not a single defective product was produced even after 100 heat cycle tests. This result proves that the metal cap, which is a feature of the product of the present invention, can sufficiently absorb the tensile stress caused by the difference in coefficient of thermal expansion between the substrate and the element.

It should be noted that the present invention is not limited to the above-mentioned embodiments; for example, as long as a complete two-layer structure is maintained, such as the inner and outer surfaces of the metal cap are not bonded to each other. In this case, it is also possible to fix the outer periphery of the inner layer and the outer layer of the metal cap. Further, the specific material of the metal cap can be changed freely, and it is also possible to connect the electrode part and the inner layer of the metal cap with a conductive adhesive. Furthermore, the present invention is not limited to ceramic capacitors, but can be similarly applied to various other surface-mounted electronic components having similar external electrodes, and similarly excellent effects can be obtained. be.

[0014]

[Effects of the Invention] As described above, in the present invention,
When a thermal shock is applied by fitting a two-layer metal cap to the electrode part of the element, connecting the inner layer to the electrode part of the element, and connecting the outer layer to the board and mounting the element on the board. In addition, since the tensile stress generated due to the difference in thermal expansion coefficient between the substrate and the element can be sufficiently buffered, there is no problem in the element body or the connection between the element and the substrate. Therefore, it has excellent thermal shock resistance when mounted on a board, and
It is possible to provide excellent surface-mounted electronic components that can contribute to miniaturization, thinness, and high-density packaging.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of a surface-mounted electronic component according to the present invention.

FIG. 2 is a side view showing a state in which the electronic component shown in FIG. 1 is mounted on a board.

FIG. 3 is a perspective view showing an example of a conventional surface-mounted electronic component.

[Explanation of symbols]

1 Ceramic capacitor element 2 External electrode 3 Metal cap 4 Solder 5 Aluminum substrate 6 Solder 7 Electrode pattern

Claims (1)

[Claims] Claim 1: A U-shaped metal cap with good solder wettability is fitted to the electrode part of the element, and the cross-sectional structure of this metal cap is made into a two-layered structure by bending, an inner layer and an inner layer of the metal cap. A surface characterized by having a structure in which the outer layers are not fixed to each other except for at least one side, which is a bent part, and further, the electrode part and the inner layer of the metal cap are connected with a conductive adhesive or solder. Mounted electronic components.