JPH0118566B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to a film that can be used as a chip electronic component that has the solder heat resistance necessary for mounting on a printed wiring board in the same way as chip electronic components such as resistors, coils, and transistors. Regarding chip capacitors.

Traditionally, capacitor chips have been commercialized based on relatively heat-resistant dielectric materials, such as ceramic tantalum and mica. However, in recent years, trends among set users have led to demand for chip parts due to the trend toward thinner, smaller, and lighter equipment through high-density mounting on printed circuit boards, and labor-saving orientation through automatic mounting onto printed circuit boards. With film capacitors using plastic film (polyethylene terephthalate film, hereinafter referred to as PET film) as the dielectric material, when mounting them on a printed circuit board, the soldering conditions are limited due to the low heat resistance of PET film. was considered extremely difficult to satisfy.

Therefore, as a heat-resistant measure, manufacturers use exterior materials with poor thermal conductivity, moisture resistance,
The current situation is that heat resistance is somehow achieved by making the exterior thicker than necessary, which is completely wasteful in terms of insulation.

The heat resistance level of conventional PET film capacitors will be explained below with reference to FIG.

Figure 1 shows a PET film with a thickness of 5 μm as the dielectric.
It is a characteristic diagram showing the relationship between the mold exterior thickness and the heat resistance level of a conventional film capacitor composed of aluminum foil as an electrode material and a thickness of 5 μm.

Even if the exterior thickness is increased, epoxy resin for molding generally has a high thermal conductivity.Thermal conductivity is 3~
5×10 ^-4 / (Cal・sec・℃), and even though the resin thickness is thicker and the capacitor shape is larger than the single coating made of only molding resin, the heat resistance level is extremely low and the heat resistance level is extremely low. It turns out that in order to improve the level, the exterior thickness needs to be 1.6mm or more.

As is well known, this is a very disadvantageous method for reducing the size and weight of the capacitor and further reducing the cost.

Purpose of the invention The present invention comprises a capacitor element main body.
By determining the relative thickness of the PET film capacitor, aluminum foil, and molded exterior, it can be made smaller and lighter, and the heat resistance level has been greatly improved. The purpose is to enable automatic attachment to the board.

Structure of the Invention The present invention provides a dielectric polyethylene terephthalate film that constitutes a capacitor element with a thickness of 1.5 mm.
~ 6.0 μm, the thickness T μm of the aluminum foil that is the electrode material is T = (2x ± 1) μm with respect to the thickness x of the polyethylene terephthalate film, and the capacitor element formed by winding the polyethylene terephthalate film. The device is characterized in that an exterior portion having a minimum thickness of 0.3 mm is provided in close contact with the capacitor element.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 2 to 5.

FIG. 2A shows a sectional view of the structure of the film capacitor of the present invention, and FIG. 2B shows a sectional view of the capacitor element body.

In FIG. 2, 1 is a PET film which is a dielectric, 2 is an aluminum foil which is an electrode material, and 3 is a capacitor element main body composed of 1 and 2. 4 is an electrode comb connected to an aluminum foil serving as an electrode, and 5 is a molded exterior resin part, which is the same as the structure of a conventional film capacitor.

In the film chip capacitor constructed as described above, the thickness relationship and heat resistance of the PET film 1, which is a dielectric material, and the aluminum foil 2, which is an electrode material, will be explained below.

Figure 3 shows the relationship between aluminum foil thickness and heat resistance level when the PET film thickness is 3 μm and the molded resin exterior is constant at 0.3 mm. It can be seen that this improves the most.

Furthermore, Figure 4 shows the relationship between aluminum foil thickness and heat resistance level when the PET film thickness is 4 μm and the molded resin exterior is 0.3 mm. It is clear that this will improve the most.

As a result of conducting experiments on aluminum foil thickness and heat resistance level while changing the PET film thickness and keeping the molded resin exterior part constant at 0.3 mm as described above, the inventors of the present invention came to the following conclusion. I got it.

In other words, to improve the heat resistance level the most,
This means that the thickness of the aluminum foil, which is the electrode material, must always be 2x±1 μm in comparison to the thickness x of the PET film, which is the dielectric material.

In other words, if the thickness of the aluminum foil is less than 2x±1μm compared to the thickness of the PET film, the aluminum foil will be too thin to hold the PET film firmly, and the capacitor element formed will be mechanically damaged. The strength will be very weak. Therefore, in the heat resistance test, when heat is applied, the expansion and contraction of the film cannot be fully covered, resulting in a large change in capacity. In other words, the heat resistance level is greatly reduced.

On the other hand, if the aluminum foil thickness T is more than (2x±1) μm with respect to the PET film thickness x, the aluminum foil is thick and can hold the PET film and form a capacitor element with strong mechanical strength. However, because the aluminum foil is thicker, heat conduction and absorption are greater, and therefore, in heat resistance tests, when heat is applied, the capacitor margin shrinks due to the shrinkage of the PET film, resulting in shoot failure. occur frequently. In the present invention, the margin portion is normally 0.5 to 1.5 mm, but in this example, a capacitor designed to have a margin of 1.0 mm was used. FIG. 3A and FIG. 4A show shot defect rate charts.

Figure 5 shows the dielectric material with the greatest improvement in heat resistance.
This is a diagram showing the relationship between the thickness of PET film and the thickness of aluminum foil, which is an electrode material.
The relationship is 2±1)μm, and the thickness of aluminum foil that improves heat resistance is (2x+1)μm, (2x−1)μm.
It is represented by two straight lines of m. Therefore, in order to improve heat resistance, the thickness of each PET film is
All you have to do is select an aluminum foil whose thickness falls within these two linear ranges.

Figure 6 shows the thickness of the aluminum foil used as the electrode material.
This is a diagram showing the relationship between PET film thickness and heat resistance level when the mold resin exterior thickness is constant at 0.3 mm.When the film thickness is 7 μm or more, the film is thicker and the heat resistance of the film itself improves. By doing so, the aluminum foil thickness Tμm
= (PET film thickness x 2 ± 1 μm) The relationship between PET film and aluminum foil to improve heat resistance is
There is no need to consider it. Therefore, in the film chip capacitor of the present invention, the thickness of the dielectric film is limited to a very thin range of 1.5 to 6.0 .mu.m. FIG. 6A shows a shot defective rate chart.

Furthermore, Figure 7 shows that the thickness of the PET film that is the dielectric material is 3 μm, and the thickness of the aluminum foil that is the electrode material is 6 μm.
It is a diagram showing the relationship between the mold resin exterior thickness and the heat resistance level when the thickness is kept constant, and it is clear that the heat resistance level is significantly improved when the mold resin exterior thickness is 0.3 mm.

Therefore, the feature of the present invention is that it is an invention with a very thin dielectric film thickness in the range of 1.5 to 6.0 μm, which is extremely important for miniaturization and weight reduction of capacitors. The ability to achieve sufficient heat resistance with a thickness of only 0.3 mm will have a significant impact on the capacitor industry.

In the above heat resistance test, the film chip capacitor whose capacitance was measured was exposed to a temperature of 150°C.
After preheating in a hot air circulation oven for 5 minutes at (℃), the temperature
After quickly immersing the capacitor in a solder bath at 230 (°C) for 10 seconds, the capacitor was taken out and in a state where it was in equilibrium with room temperature, the capacitance was measured again and the rate of change before and after the test was calculated.

In addition, in the above example, in the heat resistance test, the capacitance change rate, which is the main characteristic of the capacitor, was ±5 (%).
The goal was to achieve a survival rate of 100% due to shot defects.

As described above, according to the present invention, in a PET film having a thickness of 1.5 to 6 μm, which is a dielectric material forming a capacitor element, the thickness of aluminum foil, which is an electrode material, for each film thickness is: aluminum foil thickness =
(PET film thickness x 2 ± 1) μm allows for a very thin exterior of about 0.3 mm, without making the exterior thicker than necessary, such as the mold exterior thickness of 1.6 mm or more, which is the case with conventional heat-resistant products. Good thickness,
Therefore, the capacitor can be made smaller and lighter.
Moreover, a film chip capacitor with a high level of heat resistance can be obtained.

[Brief explanation of drawings]

Figure 1 is a characteristic diagram showing the relationship between the mold exterior thickness and heat resistance level of a conventional film chip capacitor, Figure 2 A is a sectional view of the structure of the film chip capacitor of the present invention, and Figure B is the capacitor element body. Figures 3 and 4 are characteristic diagrams showing the thickness relationship and heat resistance level of PET film and aluminum foil according to an embodiment of the present invention, Figures 3A and 4A are shot defect rate diagrams, Figure 5 is a diagram showing the range of PET film and aluminum foil where the heat resistance level is improved the most, Figure 6 A and B are characteristic diagrams showing PET film thickness, shot defect rate, and capacity change rate. A characteristic diagram showing the relationship between the mold exterior thickness and the heat resistance level of the inventive film chip capacitor is shown. 1: PET film, 2: Aluminum foil as electrode material, 3: Capacitor element body, 4: Electrode comb,
5: Mold exterior resin part.

Claims (1)

[Claims] 1 The thickness of the dielectric polyethylene terephthalate film constituting the capacitor element is 1.5 to 6.0μ.
m, the thickness T μm of the aluminum foil serving as the electrode material is T = (2x ± 1) μm relative to the thickness x of the polyethylene terephthalate film, and the capacitor element is constituted by winding the polyethylene terephthalate film. A film capacitor characterized in that an exterior portion having a minimum thickness of 0.3 mm is provided in close contact with the capacitor element.