JP2006351830A - Metallized film capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem of thermal cracking between metallized contact layers, by lowering the melting point down to 1,000°C or lower for suppressing corrosion between metallized contact layers, taking into consideration degradation in heat resistance of a film on selecting an aluminum metallized contact metal as an end-face electrode contacting an aluminum vapor deposition film, taking corrosion resistance into account, in obtaining a metallized film capacitor that is compatible with high temperature reflow which uses aluminum vapor deposition. <P>SOLUTION: A metallized contact layer of brass is stacked on an aluminum added, with silica as the end face electrode of a metallized film capacitor with aluminum vapor deposited thereon. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a surface mount type metallized film capacitor in which a metallized film is wound or laminated and a metallized end surface electrode is formed on the end surface by metal spraying. In particular, the present invention relates to a high-temperature reflow-compatible metallized film capacitor on which aluminum is deposited.

Conventionally, this type of surface mount type metallized film capacitor has a metallized end face electrode formed by winding or laminating a metallized film on which zinc or aluminum metal is vapor-deposited on one side of a plastic film and spraying the metal on both end faces. It has a configuration. As the metal sprayed as the end face electrode in contact with the vapor deposition, a copper-based material, for example, an alloy of copper and zinc has been used (for example, Patent Document 1).
When aluminum is used for vapor deposition, it is preferable in terms of corrosion resistance to use an aluminum metallicon end face electrode of the same metal as the vapor deposition on the side in contact with the vapor deposition, in order to reduce the melting point while maintaining corrosion resistance. In particular, silicon was added to suppress thermal deterioration of the film during thermal spraying. However, since the surface of aluminum is difficult to be plated or difficult to wet with low-melting metal for soldering, alloy metallicons composed of lead, tin, silver, copper, etc. have been laminated on the end electrode surface. (For example, patent document 2).
By the way, as lead-free electronic products have been promoted globally, the upper limit of reflow temperature during mounting has been raised to 240-260 ° C. To cope with this high temperature reflow, aluminum is applied to the end face electrode. After spraying, a single metal of copper or nickel having a melting point exceeding 1000 ° C. was sprayed and laminated thereon (for example, Patent Document 3).
JP-A-1-77912 JP-A-4-333209 JP-A-6-151240

In order to obtain a metallized film capacitor compatible with high-temperature reflow using an aluminum vapor deposition film, if an aluminum-based metallicon metal is selected as an end face electrode in contact with the aluminum vapor deposition film from the viewpoint of corrosion resistance, the surface can be easily plated or used for soldering. However, it is necessary to select a metal whose melting point does not exceed 1000 ° C. from the viewpoint of heat resistance deterioration of the film. Moreover, it is necessary to solve the problem of corrosion resistance and thermal cracks between metallicon metal laminates.

In order to solve the above-mentioned problems, the present invention adds zinc to copper to the first metallicon layer in which silicon is added to aluminum as the end face electrode on the side in contact with the vapor deposition of the metallized film capacitor on which aluminum is evaporated. The present invention provides a metallized film capacitor characterized by laminating a second metallicon layer.
In addition, the present invention provides a metallized film capacitor characterized in that the amount of zinc added to the second metallicon layer is 20 wt% or more and less than 40 wt%.

By adding zinc to copper having a melting point (1067 ° C.) that is the second metallicon layer, the melting point can be lowered to 1000 ° C. or less, so that heat resistance deterioration of the film can be suppressed.
By adding silicon to the aluminum of the first metallicon layer, the immersion potential difference between the first metallicon layer and the second metallicon layer is reduced, and corrosion between the metallicon layers can be suppressed.
By adding silicon to the aluminum of the first metallicon layer and adding zinc to the copper of the second metallicon layer, the difference in thermal expansion coefficient between the first metallicon layer and the second metallicon layer is reduced. Can solve the thermal crack problem.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view and a sectional view of a film capacitor according to the present invention.
1 is a stack of two metallized films formed by depositing aluminum on a high heat-resistant film such as polyphenylene sulfide, polyethylene naphthalate, polyether sulfone, polyimide, polyamide, or polyetherimide, shifted from each other. Then, the device is wound and a sealing film is wound around the outermost periphery. Here, the sealing film may be replaced with a portion where the metal of the metallized film is removed by applying a high voltage.
Reference numeral 2 denotes a first metallicon layer formed on the end face of the element 1 and directly connected to a metal thin film, which is made of a metal obtained by adding silicon to aluminum, and contains 80% or more of aluminum and 3% or more of silicon. The film thickness is about 0.05 mm to 0.3 mm, preferably about 0.1 mm to 0.2 mm.
By adding 12.6% of silicon to aluminum, the melting point of aluminum can be lowered from 660 ° C. to about 570 ° C.
Reference numeral 3 denotes a second metallicon layer laminated on the first metallicon layer 2, which is obtained by adding zinc to copper and polishing the surface. The film thickness is about 0.2 mm to 0.6 mm, preferably about 0.3 mm to 0.4 mm.
The interface between the first metallicon layer and the second metallicon layer is an uneven shape rather than a plane because it is a connection between the metallicon layers, and there is a portion where the first metallicon material and the second metallicon material are mixed, and In addition to the alloyed part, the part merely in physical contact is also included.
Reference numeral 4 denotes a first plating layer made of Ni or Cu laminated on the second metallicon layer 3. The film thickness is about 5 μm to 20 μm, preferably about 8 μm to 15 μm.
Reference numeral 5 denotes a second plating layer made of tin laminated on the first plating layer 4. The film thickness is about 2 μm to 20 μm, preferably about 4 μm to 8 μm.
In the implementation, 4, 5 plating layers may be omitted.

In order for the second metallicon layer to cope with high temperature reflow, it is necessary to select a metallicon material having a melting point of 260 ° C. or higher, but in order to suppress thermal deterioration of the film, select a metallicon material having a low melting point as much as possible. Is preferred. Excluding radioactive elements that are problematic in use and rare earth elements that are limited in supply, metals other than aluminum that have a melting point of 260 ° C. or higher include bismuth (271 ° C.), astatine (302 ° C.), Thallium (304 ° C), Cadmium (321 ° C), Lead (328 ° C), Zinc (420 ° C), Tellurium (450 ° C), Antimony (631 ° C), Magnesium (649 ° C), Aluminum (660 ° C), Barium ( 725 ° C), strontium (769 ° C), calcium (839 ° C), germanium (937 ° C), silver (962 ° C), gold (1064 ° C), and copper (1083 ° C).
Astatine is an element that does not exist stably and cannot be used. Bismuth, tellurium, and antimony are brittle materials that cannot be made into wires, and thallium, lead, and cadmium cannot be used due to environmental problems. Tellurium and germanium are semiconductors and cannot be used as electrode materials. Alkaline earth metals such as magnesium, barium, strontium, and calcium are not suitable as thermal spray materials because of their high reactivity with water and oxygen. Zinc is inferior in corrosion resistance and is not suitable for the outer layer electrode.
From the above, the remaining options are silver, gold, and copper. Among these materials, copper is the most promising material in terms of price.
In order to lower the melting point (1067 ° C.) of copper to 1000 ° C. or lower, it is effective to alloy and lower the solidus and liquidus.
In general, the addition of an element that forms a eutectic can reduce the solidus temperature to the eutectic temperature. In addition, when an element that forms a peritectic is added, there may be cases where the peritectic temperature is higher or lower than the melting point, but when the peritectic temperature is lower than the melting point, the solidus is lowered to the peritectic temperature. be able to. In this case, if the alloy element is increased beyond the peritectic composition, the solidus will further decrease, but if the phase that forms the peritectic combination is an intermetallic compound, the material itself becomes hard and difficult to process. There's a problem.
For example, when zinc is added to copper, the solidus line gradually decreases, and the solidus line can be lowered to a peritectic line at 903 ° C. in the range of 32.5 wt% to 37.5 wt%. Therefore, in a copper alloy to which 35% of zinc is added, the solidus can be lowered to 903 ° C. When zinc is added in an amount of 37.5 wt% or more, the solidus can be further lowered. However, when zinc is added in an amount of 40 wt% or more, a two-phase structure is formed with an intermetallic compound phase (β phase) containing more zinc. The phase is not preferred because it significantly reduces corrosion resistance. Therefore, brass with a zinc content of less than 40 wt%, which can lower the liquidus temperature without impairing the corrosion resistance of the copper-zinc alloy, is suitable considering the corrosion resistance and heat resistance. Here, the brass is a copper alloy having a zinc content of 20 wt% to 40 wt%.

  Considering only connectivity with aluminum, which is a deposited metal, when aluminum is used for the first metallicon layer, since the immersion potential of aluminum is as low as −0.8 V vs Ag / AgCl (pH = 7), the immersion potential is − When 0.3VvsAg / AgCl (pH = 7) and a high copper alloy are laminated and combined, a local battery is formed and corrosion of aluminum is promoted. In the present invention, -0.3VvsAg / AgCl (pH = 7) and an aluminum-silicon alloy having a high immersion potential are used as the base of the heat-resistant copper alloy, so that the potential difference when combined with the copper alloy is reduced. Corrosion of the base alloy can be suppressed. This is because the immersion potential of the silicon phase in the aluminum-silicon alloy is as high as -0.2 V vs Ag / AgCl (pH = 7).

Further, since the end face metallicon has a substantially different two-layer structure, generally, the two-layer metallicon functions as a bimetal with heating, and warps the metallicon. Since this is constrained at the interface with the film, cracking occurs at the interface between the metallicon and the film due to repeated heating and cooling, and moisture enters and increases the capacity reduction at the time of moisture resistance load.
FIG. 2 is a model diagram showing bimetal bending, and Equation 1 shows an equation representing bimetal warpage.
Table 1 shows a comparative example of bimetallic bending and tip concentrated load that restrains it when aluminum or an aluminum-12 wt% silicon alloy is used for the first metallicon layer and copper is used for the second metallicon layer. The difference between the thermal expansion coefficient 23.5 × 10 ⁻⁶ K ^{−1 of} aluminum and the thermal expansion coefficient 17.0 × 10 ⁻⁶ K ⁻¹ of copper is large, and as shown in Table 1, a large deflection and a restraining load are generated. . When the material of the first metallicon layer is changed from aluminum to aluminum-12 wt% silicon alloy, the thermal expansion coefficient is reduced to 20.5 × 10 ⁻⁶ K ⁻¹ and the difference in thermal expansion coefficient from copper is reduced. Therefore, the bending and restraint load are halved. In order to further reduce this, it is necessary to increase the thermal expansion coefficient of copper, which is the second metallicon layer, so as to approach the value of the aluminum-12 wt% silicon alloy.
In the alloy in the range of the solid solution, the crystal structure of the base alloy is reflected, and the characteristics of the additive element are affected depending on the addition amount. The thermal expansion coefficient is the same, and as long as it is used as a solid solution, it is desirable to add as much alloy elements having a large thermal expansion coefficient as possible within the range of the solid solution.
FIG. 2 shows the correlation between the thermal expansion coefficient and the melting point of a pure substance. The coefficient of thermal expansion is roughly inversely proportional to the melting point. Among these, the elements having the largest thermal expansion coefficient excluding alkali metals that are difficult to alloy in large quantities are zinc, cadmium, thallium, and lead. Of these, cadmium, thallium, and lead cannot be used due to their toxicity due to environmental problems. Therefore, zinc is the most effective element as an alloy element that improves the thermal expansion coefficient. According to the literature, the coefficient of thermal expansion can be made 20 × 10 ⁻⁶ K ⁻¹ or more by making the amount of zinc 30 wt% or more.
Table 2 shows a comparative example of bimetal bending and a concentrated tip load that restrains the bimetal bending when an aluminum-12 wt% silicon alloy is used for the first metallicon layer and a copper alloy is used for the second metallicon layer. By using brass, it is possible to reduce the bimetallic deflection and the concentrated tip load that restrains it to 1/10.

  Next, examples of the present invention will be described. However, the present invention is not limited to the following examples.

  First, an element is formed by winding a metallized film and winding a sealing film around the outermost periphery. After forming the element, a first metallicon layer having a thickness of 15 μm is formed on the end face of the element by an electric arc spraying method using a 1.2φ alloy wire containing 88% aluminum and 12% silicon. After thermal spraying, a copper-zinc 1.3φ brass wire is used to form a second metallicon layer with a thickness of about 45 μm on the surface of the first metallicon layer. Zinc was added at 15 wt%, 20 wt%, 30 wt%, 35 wt%, and 40 wt%. After forming the second metallicon layer, excess metallicon is removed with a rotating barrel. Next, the element 1 is impregnated with an epoxy resin in a vacuum for 3 hours, and is cured by heating at 170 ° C. for 16 hours. After this operation, the surface of the second metallicon layer is cut with an end mill blade and polished so that the thickness of the second metallicon layer is about 35 μm. After polishing, a first plating layer having a thickness of about 10 μm is formed by Ni electroplating. After forming the first plating layer, the surface is plated with tin having a thickness of about 5 μm to form a second plating layer.

Next, Sn-3 wt% Ag-0.3 wt% Cu solder was prepared by hot air reflow with a reflow profile of preheating 150 to 180 ° C. for 2 minutes or more, main heating 240 ° C. or more for 10 seconds, and peak temperature 250 ° C. Was surface mounted on the substrate. Reflow was repeated three times for each sample. When measuring the reflow temperature, the reflow heat resistance varies depending on the shape of the object to be measured, the temperature measurement position, the thermocouple connection method, the solder connection between the land and the electrode, and the heating method of the reflow furnace even under the same heat load. Care must be taken because it may be evaluated as temperature. In this example, the reflow temperature was measured using a product having the same configuration as the sample, a thermocouple was fixed to the electrode surface with high-temperature solder, and the high-temperature solder was also connected to the land, so that hot air flowed sufficiently. The temperature was measured under the conditions, and the reflow profile was verified.
The reflowed sample was allowed to stand in 20 ° C. and 30% RH for 12 hours. After measuring the capacity at 1 kHz, the tan δ, and the insulation resistance at the rated voltage, the sample was put into a furnace at 85 ° C. and 85% RH. The moisture resistance load test was performed for 250 hours with the rated voltage applied, then taken out again and left in 20 ° C. and 30% RH for 12 hours, and the capacity at 1 kHz, tan δ, and insulation resistance at the rated voltage were measured.
Table 3 shows the result of the characteristic comparison before and after the moisture resistance load test. As a comparative example, the second metallicon layer in Example 1 was changed to copper, bronze (Cu-10 wt% Sn-2 wt% Zn), phosphor bronze (Cu-13.5 wt% Sn-0.33 wt% P). The first metallicon layer was changed to aluminum in Example 1 and the comparative example in which the other processes were performed in the same manner, and the other processes were performed in the same manner.
From this result, it can be said that the optimum amount of zinc added to copper is 20 wt% or more and less than 40 wt% as the second metallicon material formed on the aluminum-12 wt% silicon alloy first metallicon.

It is the perspective view and sectional drawing of the film capacitor which concern on this invention. It is a model figure showing the bimetal bending of the two-layer metallicon which concerns on this invention. The correlation between the thermal expansion coefficient and the melting point of a pure substance is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Element, 2 ... 1st metallicon layer, 3 ... 2nd metallicon layer, 4 ... 1st plating layer, 5 ... 2nd plating layer

Claims (2)

  The metallized film capacitor on which aluminum is vapor-deposited is characterized in that, as an end face electrode on the side in contact with the vapor deposition, a second metallicon layer in which zinc is added to copper is laminated on a first metallicon layer in which silicon is added to aluminum. Metalized film capacitor.   2. The metallized film capacitor according to claim 1, wherein the amount of zinc added to the second metallicon layer is 20 wt% or more and less than 40 wt%.

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