JP2012119375A - Electrostatic protective element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic protective element capable of suppressing deterioration in luminous efficiency of an LED even when mounted together with the LED.SOLUTION: An electrostatic protective element 1 comprises: a varistor 3 comprising a sintered body which contains ZnO as a main component and Co as an accessory component; and a plurality of conductors 5 and 7 arranged to sandwich the varistor 3 therebetween. At least one conductor 7 of the plurality of conductors 5 and 7 comprises a sintered body which contains ZnO as a main component and does not substantially contain Co as an accessory component.

Description

  The present invention relates to an electrostatic protection element.

  A Zener diode is known as an electrostatic protection element that protects an LED from electrostatic discharge (ESD) by being connected in parallel to a light emitting diode (LED) (for example, see Patent Document 1).

JP 2007-251167 A

  However, the electrostatic protection element described in Patent Document 1 has the following problems. Zener diodes are generally made of silicon. Silicon has a light absorption wavelength in the visible light region due to interband transition of electrons. For this reason, when a Zener diode is mounted on a substrate or a lead frame together with an LED, the light emitted from the LED is absorbed. As a result, the light emission efficiency of the LED decreases.

  The objective of this invention is providing the electrostatic protection element which can suppress that the luminous efficiency of LED falls even when it mounts with LED.

  An electrostatic protection element according to the present invention includes a varistor portion made of a sintered body containing ZnO as a main component and Co as a subcomponent, and a plurality of conductor portions arranged with the varistor portion interposed therebetween. The at least one conductor portion of the plurality of conductor portions is made of a sintered body containing ZnO as a main component and substantially not containing Co as a subcomponent.

  In the electrostatic protection element according to the present invention, the varistor portion is made of a sintered body containing ZnO as a main component and Co as a subcomponent. Co is a material for expressing varistor characteristics. For this reason, the varistor part exhibits current-voltage nonlinear characteristics, so-called varistor characteristics. Therefore, when the varistor part of the electrostatic protection element according to the present invention is connected in parallel with the LED, the LED can be protected from ESD.

  In the present invention, at least one of the plurality of conductor portions is made of a sintered body containing ZnO as a main component. ZnO has the property that the light absorption wavelength due to the interband transition of electrons is in the ultraviolet region and transmits visible light. For this reason, even when the electrostatic protection element is mounted together with the LED, at least one conductor portion hardly absorbs the light emitted from the LED and transmits the light.

  In a sintered body mainly composed of ZnO, light incident on the sintered body is scattered at grain boundaries of ZnO crystal grains. In the present invention, since the sintered body constituting at least one conductor part does not substantially contain Co, ZnO grain growth is promoted in at least one conductor part as compared with the varistor part. The crystal grains become larger. For this reason, at least one conductor portion has few grain boundaries of ZnO crystal grains, and scattering at the grain boundaries is suppressed.

  As a result, according to the present invention, even when the electrostatic protection element is mounted together with the LED, it is possible to suppress a decrease in the light emission efficiency of the LED. Since the sintered body constituting at least one conductor part does not substantially contain Co, varistor characteristics are hardly exhibited and the sintered body has relatively high conductivity. Therefore, the function as an electrode is not hindered in at least one conductor portion.

  The conductor part arrange | positioned on both sides of at least 1 conductor part and a varistor layer among several conductor parts may consist of metal. In this case, wire bonding to the conductor portion made of metal is possible.

  The thickness of at least one conductor part may be set larger than the thickness of the varistor part. In this case, when connecting at least one conductor portion to a substrate, a lead frame, or the like using a conductive paste (eg, copper paste), the varistor portion is physically separated from the substrate, the lead frame, or the like. As a result, it becomes difficult for the conductive paste to adhere to the varistor part, and it is possible to prevent the function of the varistor part from being hindered by the adhesion of the conductive paste.

  ADVANTAGE OF THE INVENTION According to this invention, even when it mounts with LED, the electrostatic protection element which can suppress that the luminous efficiency of LED falls can be provided.

It is a perspective view which shows the electrostatic protection element which concerns on this embodiment. It is a figure explaining the cross-sectional structure of the electrostatic protection element which concerns on this embodiment. It is a schematic diagram which shows the mounting structure of the electrostatic protection element which concerns on this embodiment.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description, the same reference numerals are used for the same elements or elements having the same function, and redundant description is omitted.

  First, with reference to FIG.1 and FIG.2, the structure of the electrostatic protection element 1 which concerns on this embodiment is demonstrated. FIG. 1 is a perspective view showing an electrostatic protection element according to this embodiment. FIG. 2 is a diagram illustrating a cross-sectional configuration of the electrostatic protection element according to the present embodiment.

  As shown in FIGS. 1 and 2, the electrostatic protection element 1 includes a varistor portion 3 and a plurality of (in this embodiment, two) conductor portions 5 and 7 arranged with the varistor portion interposed therebetween. I have. The electrostatic protection element 1 has a layer structure in which a varistor part 3 and conductor parts 5 and 7 are laminated. The electrostatic protection element 1 has a substantially rectangular parallelepiped shape. For example, the electrostatic protection element 1 has a length set to about 0.25 mm, a width set to about 0.25 mm, and a height set to about 0.15 mm. In the actual electrostatic protection element 1, the varistor part 3 and the conductor part 7 are integrated so that the boundary between the varistor part 3 and the conductor part 7 cannot be visually recognized.

  The varistor portion 3 is made of a sintered body (semiconductor ceramic) that exhibits varistor characteristics. The varistor portion 3 contains ZnO (zinc oxide) as a main component, and Co, rare earth metal elements, group IIIb elements (B, Al, Ga, In), Si, Cr, Mo, alkali metal elements (K) as subcomponents. Rb, Cs) and alkaline earth metal elements (Mg, Ca, Sr, Ba) and the like, and oxides thereof. In the present embodiment, the varistor portion 3 includes Co, Pr, Cr, Ca, K, Al, and Si as subcomponents. The content of ZnO in the varistor part 3 is not particularly limited, but is usually 99.8 to 69.0% by mass when the total material constituting the varistor part 3 is 100% by mass. The thickness of the varistor part 3 is set to about 5 to 50 μm, for example.

  Co acts as a substance that forms an acceptor level at the grain boundary of ZnO and exhibits varistor characteristics. The ratio of Co to 100 mol of the main component (ZnO) is set in a range of, for example, 0.1 atomic% or more and 20 atomic% or less in terms of Co.

  Pr acts as a substance that increases the diffusion rate of oxygen to the grain boundaries. The ratio of Pr with respect to 100 mol of the main component (ZnO) is set in a range of, for example, 0.05 atomic% or more and 5 atomic% or less in terms of Pr.

  Cr acts as a substance that improves the load characteristics at high temperatures. The ratio of Cr with respect to 100 moles of the main component (ZnO) is set, for example, in the range of 0.01 atomic% to 1 atomic% in terms of Cr.

  Ca acts as a substance that reduces the electrostatic capacity expressed in the varistor part 3. The ratio of Ca to 100 moles of the main component (ZnO) is set in a range of 0.01 atomic% or more and 2 atomic% or less, for example, in terms of Ca.

  K acts as a substance that improves the varistor characteristics. The ratio of K to 100 moles of the main component (ZnO) is set in the range of 0.001 atomic% or more and 1 atomic% or less, for example, in terms of K.

  Al acts as a donor for controlling the amount of electrons to the main component containing ZnO, and acts as a substance that increases the amount of electrons to the main component and makes the composition a semiconductor. The ratio of Al to 100 moles of the main component (ZnO) is set in the range of, for example, 0.0005 atomic% or more and 0.5 atomic% or less in terms of Al.

  Si acts as a donor for controlling the amount of electrons to the main component containing ZnO, increases the amount of electrons to the main component, and acts as a substance that makes the composition a semiconductor, and also controls sintering. The ratio of Si to 100 moles of the main component (ZnO) is set in a range of, for example, 0.001 atomic% or more and 0.5 atomic% or less in terms of Si.

  The conductor portion 5 is disposed so as to cover one main surface of the varistor portion 3. The conductor part 5 has a first conductor layer 5a formed on one main surface of the varistor part 3, and a second conductor layer 5b formed on the first conductor layer 5a. The conductor portion 5 (first and second conductor layers 5a and 5b) is made of metal. The first conductor layer 5a is made of, for example, aluminum (Al) or nickel (Ni) and has a thickness of about 0.5 to 5 μm. The second conductor layer 5b is made of, for example, gold (Au) and has a thickness of about 0.05 to 1 μm. The first and second conductor layers 5a and 5b can be formed, for example, by vapor deposition or sputtering.

  The conductor part 7 is arrange | positioned so that the main surface facing the main surface in which the conductor part 5 is arrange | positioned may be covered. The conductor portion 7 is made of a sintered body containing ZnO as a main component. In addition to ZnO, the conductor portion 7 includes rare earth metal elements, group IIIb elements (B, Al, Ga, In), Si, Cr, Mo, alkali metal elements (K, Rb, Cs) and alkaline earth as subcomponents. It contains simple metals such as metal elements (Mg, Ca, Sr, Ba) and their oxides. Although content of ZnO in the conductor part 7 is not specifically limited, When the whole material which comprises the conductor part 7 is 100 mass%, it is 99.8-69.0 mass% normally.

  In the present embodiment, the conductor portion 7 contains Pr, Cr, Ca, K, Al, and Si as subcomponents and does not substantially contain Co. Here, the “substantially free” state means a state in which Co is not intentionally contained as a raw material when the material constituting the conductor portion 7 is prepared. For example, when these elements are included unintentionally due to diffusion from the varistor portion 3 to the conductor portion 7 or the like, it corresponds to a “substantially not contained” state.

  Unlike the varistor part 3, the conductor part 7 hardly contains varistor characteristics because it does not substantially contain Co. For this reason, the conductor part 7 has a low electrical resistance and a relatively high conductivity. For this reason, the conductor part 7 functions as an electrode similarly to the conductor part 5. The thickness of the conductor part 7 is set larger than the thickness of the varistor part 3. The thickness of the conductor part 7 is set to about 100 to 140 μm, for example.

  The contents of Pr, Cr, Ca, K, Al, and Si in the conductor portion 7 are as follows. The ratio of Pr with respect to 100 mol of the main component (ZnO) is set in a range of, for example, 0.05 atomic% or more and 5 atomic% or less in terms of Pr. The ratio of Cr with respect to 100 moles of the main component (ZnO) is set, for example, in the range of 0.01 atomic% to 1 atomic% in terms of Cr. The ratio of Ca to 100 moles of the main component (ZnO) is set in a range of 0.01 atomic% or more and 2 atomic% or less, for example, in terms of Ca. The ratio of K to 100 moles of the main component (ZnO) is set in the range of 0.001 atomic% or more and 1 atomic% or less, for example, in terms of K. The ratio of Al to 100 moles of the main component (ZnO) is set in the range of, for example, 0.0005 atomic% or more and 0.5 atomic% or less in terms of Al. The ratio of Si to 100 moles of the main component (ZnO) is set in a range of, for example, 0.001 atomic% or more and 0.5 atomic% or less in terms of Si.

  Subsequently, an example of a manufacturing process of the electrostatic protection element 1 having the above-described configuration will be described.

  First, after weighing ZnO, which is the main component constituting the varistor part 3, and trace additives such as Co, Pr, Cr, Ca, K, and Al metals or oxides so as to have a predetermined ratio. The varistor material is prepared by mixing each component. Thereafter, an organic binder, an organic solvent, an organic plasticizer, and the like are added to the varistor material, and mixing and pulverization are performed using a ball mill or the like to obtain a slurry. This slurry is applied onto a film made of, for example, polyethylene terephthalate by a known method such as a doctor blade method, and then dried to form a film having a predetermined thickness (for example, about 30 μm). The film thus obtained is peeled from the film to obtain a first green sheet.

  In addition, after weighing ZnO, which is the main component constituting the conductor portion 7, and a small amount of additives such as Pr, Cr, Ca, K, and Al metals or oxides to a predetermined ratio, The material for the conductor part 7 is adjusted by mixing the components. Thereafter, an organic binder, an organic solvent, an organic plasticizer, and the like are added to the material for the conductor portion 7 and mixed and pulverized using a ball mill or the like to obtain a slurry. This slurry is applied onto a film made of, for example, polyethylene terephthalate by a known method such as a doctor blade method, and then dried to form a film having a predetermined thickness (for example, about 30 μm). The film thus obtained is peeled from the film to obtain a second green sheet.

  Next, a predetermined number of first green sheets and second green sheets are stacked to form a sheet laminate in which a layer made of the first green sheet and a layer made of the second green sheet are laminated. . At this time, the thickness of the layer made of the second green sheet is made larger than the thickness of the layer made of the first green sheet by making the number of the second green sheets larger than the number of the first green sheets. Yes. The number of first green sheets may be at least one.

  Next, the sheet laminate is subjected to heat treatment under predetermined conditions (for example, 180 to 400 ° C. and 0.5 to 24 hours) to perform binder removal, and further, predetermined conditions (for example, 1000). The sintered body is obtained by firing at ˜1400 ° C. and 0.5 to 8 hours. By this firing, the layer made of the first green sheet becomes the varistor part 3, and the layer made of the second green sheet becomes the conductor part 7. Thus, the first green sheet and the second green sheet are fired at the same time in a stacked state.

  Next, a first metal film made of a metal (for example, Al or Ni) is formed on one main surface of the sintered substrate by vapor deposition or sputtering so as to cover the one main surface. To do. Thereafter, a second metal film made of a metal (for example, Au) is formed at a predetermined position on the first metal film by the same vapor deposition method, sputtering method, electroplating method, or the like. The first metal film becomes the first conductor layer 5a, and the second metal film becomes the second conductor layer 5b.

  Next, the sintered body substrate is cut into a desired size. Through these processes, the electrostatic protection element 1 is obtained.

  Subsequently, a mounting structure of the electrostatic protection element 1 according to the present embodiment will be described with reference to FIG. FIG. 3 is a schematic diagram showing a mounting structure of the electrostatic protection element according to the present embodiment. In FIG. 3, illustration of a package, sealing resin, etc. is omitted.

  The LED 11 is mounted on a lead frame 13 having a pair of leads 13a and 13b. Specifically, the LED 11 is placed on one lead 13a and fixed to the one lead 13a with an adhesive or the like. The LED 11 is connected to the pair of leads 13 a and 13 b by the wire 15.

  The electrostatic protection element 1 is also mounted on the lead frame 13. Specifically, the electrostatic protection element 1 is placed on the other lead 13b so that the other lead 13b and the conductor portion 7 face each other, and the conductor portion 7 and the other lead 13b are connected to the conductive paste 17. Connected and fixed by. One lead 13 a and the conductor portion 5 (second conductor layer 5 b) are connected by a wire 19. Therefore, in the mounting structure shown in FIG. 3, the electrostatic protection element 1 (varistor part 3) is connected in parallel to the LED 11 between the pair of leads 13a and 13b.

  As described above, in the present embodiment, since the varistor portion 3 exhibits varistor characteristics, the LED 11 can be protected from ESD.

  In this embodiment, the conductor part 7 consists of a sintered compact which has ZnO as a main component. ZnO has the property that the light absorption wavelength due to the interband transition of electrons is in the ultraviolet region and transmits visible light. For this reason, even when the electrostatic protection element 1 is mounted on the lead frame 13 together with the LED 11, the at least one conductor portion 7 hardly absorbs light emitted from the LED 11 and transmits the light.

  In a sintered body mainly composed of ZnO, light incident on the sintered body is scattered at grain boundaries of ZnO crystal grains. In this embodiment, since the sintered body constituting the conductor portion 7 does not substantially contain Co, ZnO grain growth is promoted in the conductor portion 7 as compared with the varistor portion 3, and the ZnO crystal Grain grows. For this reason, in the conductor part 7, the grain boundary of the crystal grain of ZnO decreases and scattering at a grain boundary is suppressed. By the way, Co contained in the varistor part 3 exists as a solid solution in the crystal grains of ZnO. Thus, since Co is dissolved in the crystal grains of ZnO, even when the first green sheet and the second green sheet are laminated and fired at the same time, Co contained in the first green sheet is contained. Is difficult to diffuse into the second green sheet.

  As a result, according to the present embodiment, even when the electrostatic protection element 1 is mounted on the lead frame 13 together with the LED 11, it is possible to suppress a decrease in the light emission efficiency of the LED 11. Since the sintered body constituting the conductor portion 7 does not substantially contain Co, varistor characteristics are hardly exhibited and electric resistance is low. Therefore, in the conductor part 7, the function as an electrode is not inhibited.

  In the present embodiment, the conductor portion 5 is made of metal. Thereby, the wire bonding to the conductor part 5 is attained.

  In the present embodiment, the thickness of the conductor portion 7 is set larger than the thickness of the varistor portion 3. Thus, the varistor portion 3 is physically separated from the lead frame 13 when the conductor portion 7 is connected to the lead frame 13 (lead 13b) using the conductive paste 17. For this reason, it becomes difficult for the conductive paste 17 to adhere to the varistor part 3, and it is possible to prevent the function of the varistor part 3 from being hindered by the adhesion of the conductive paste 17. As a result, the LED 11 can be reliably protected from ESD.

  In this embodiment, since the first green sheet and the second green sheet are mainly composed of ZnO, the sintered body of the layer made of the first green sheet and the second green sheet are fired when the sheet laminate is fired. The sintered body of the layer made of the green sheet is not peeled off, and a good sintered body substrate can be obtained.

  The preferred embodiments of the present invention have been described above. However, the present invention is not necessarily limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

  In the present embodiment, the conductor portion 5 is made of metal, but like the conductor portion 7, it may be made of a sintered body containing ZnO as a main component and substantially not containing Co as a subcomponent. In this case, it can suppress further that the luminous efficiency of LED11 falls.

  In the present embodiment, the conductor portion 5 is made of metal, but like the conductor portion 7, it may be made of a sintered body containing ZnO as a main component and substantially not containing Co as a subcomponent. In this case, it can suppress further that the luminous efficiency of LED11 falls.

  In the present embodiment, the conductor portion 5 has a two-layer structure of the first conductor layer 5a and the second conductor layer 5b, but is not limited thereto. The conductor portion 5 may have a single layer structure made of metal, or may be a layer structure having three or more layers.

  In the mounting structure of the electrostatic protection element 1 described above, the electrostatic protection element 1 and the LED 11 are mounted on the lead frame 13, but the present invention is not limited to this. The electrostatic protection element 1 and the LED 11 may be mounted on a substrate, or may be mounted on another electronic component.

  DESCRIPTION OF SYMBOLS 1 ... Electrostatic protection element, 3 ... Varistor part, 5, 7 ... Conductor part, 13 ... Lead frame.

Claims (3)

A varistor portion composed of a sintered body containing ZnO as a main component and Co as a subcomponent;
A plurality of conductor portions arranged across the varistor portion, and
The electrostatic protection element, wherein at least one of the plurality of conductor portions is made of a sintered body containing ZnO as a main component and substantially not containing Co as a subcomponent.   2. The electrostatic protection element according to claim 1, wherein among the plurality of conductor portions, the conductor portion arranged with the at least one conductor portion and the varistor layer interposed therebetween is made of metal.   The electrostatic protection element according to claim 1, wherein a thickness of the at least one conductor portion is set to be larger than a thickness of the varistor portion.

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