Temperature detector

Abstract

Provided is a temperature detector in which deterioration of a thermistor chip and / or a connection end portion of a lead due to migration can be prevented even when the detector is subjected to a relatively large temperature change and / or is immersed in water for a relatively long period of time. The temperature detector includes a thermistor chip, a pair of leads connected to the thermistor chip, and an insulating coating layer covering connection ends of the thermistor chip and the leads. The insulating coating layer is configured from an inner layer made of a high-adhesiveness resin and an outer layer made of an epoxy resin.

Description

Technical Field

[0001] The present invention relates to a temperature detector, and more particularly to a temperature detector comprising a thermistor chip, a pair of leads connected to the thermistor chip, and an insulating coating layer covering the connection ends of the thermistor chip and the leads. Background Art

[0002] Patent document 1 below discloses a temperature detector including a thermistor chip, a pair of leads connected to the thermistor chip, and an insulating coating covering the connection ends of the thermistor chip and each lead. The insulating coating includes an ordinary (i.e., non-highly adhesive) inner layer composed of a silicone resin and an outer layer composed of an epoxy resin. The thermistor chip, the connection ends of a pair of leads, and the insulating coating are contained in a cylindrical metal housing with one end closed and the other end open. The housing is filled with a high thermal conductivity epoxy resin.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: WO2019 / 159221 Summary of the invention

[0006] Problem that the invention aims to solve

[0007] The present inventors have found through experience that there are problems with the thermistor chip and / or the connection ends of the leads of the temperature detector described in Patent Document 1. More specifically, the thermistor chip and / or the connection ends tend to deteriorate due to migration (i.e., the occurrence of a short circuit), especially when the temperature detector is subjected to relatively large temperature changes and / or is immersed in water for a relatively long time.

[0008] The present invention has been made in view of the above facts, and its main technical purpose is to provide a new and improved temperature detector that can prevent the connection ends of thermistor chips and / or leads from deteriorating due to migration even when the temperature detector is subjected to relatively large temperature changes and / or is immersed in water for a relatively long time.

[0009] Solutions for solving problems

[0010] As a result of in-depth research and experiments by the inventors, the inventors have recognized the following problems of the above-mentioned conventional temperature detectors: due to insufficient peel strength between the inner layer and the outer layer of the insulating coating layer, when the temperature detector is subjected to relatively large temperature changes and / or immersed in water for a relatively long time, local peeling occurs, especially between the inner layer and the outer layer of the insulating coating layer, and a gap is formed therebetween, thereby deteriorating the connection end of the thermistor chip and / or the lead due to migration. Based on this recognition, the inventors have found that using a high-adhesive resin instead of a common (i.e., non-high-adhesive) silicone resin for the inner layer of the insulating coating layer is the key to achieving the above-mentioned main technical purpose, because the high-adhesive resin has sufficient peel strength not only for the thermistor chip but also for the outer layer of the insulating coating layer, while the common silicone resin has high peel strength only for the thermistor chip and low peel strength (about 0.08 to 0.09 MPa) for the outer layer of the insulating coating layer.

[0011] Therefore, as a temperature detector capable of achieving the above-mentioned main technical purpose, the present invention provides a temperature detector comprising a thermistor chip, a pair of leads connected to the thermistor chip, and an insulating coating layer covering the connection ends of the thermistor chip and each lead. The insulating coating layer comprises an inner layer made of a high-adhesive resin and an outer layer made of an epoxy resin.

[0012] The high adhesive resin is preferably an addition reaction type silicone resin, in particular an addition reaction type silicone resin with a vinyl-containing organopolysiloxane as the main component. The inner layer is suitable to have a thickness of 0.5 μm or more. The peel strength of the inner layer to the thermistor chip and the outer layer is preferably 0.20 MPa or more, in particular 0.30 MPa or more, and in particular 0.50 MPa or more. It is desired that the thermistor chip, the connecting end of a pair of leads, and the insulating coating layer are contained in a cylindrical shell made of metal or synthetic resin with one end closed and the other end open, and the shell is filled with synthetic resin.

[0013] Effects of the Invention

[0014] As can be clearly understood from the embodiments and the like described below, the inner layer of the insulating coating of the temperature detector constructed according to the present invention is made of a high adhesive resin having a high peel strength to the thermistor chip and the outer layer of the insulating coating. Therefore, even when the temperature detector is subjected to a relatively large temperature change and / or is immersed in water for a relatively long time, the inner layer and the outer layer of the insulating coating will not be partially peeled off from each other. As a result, the connection ends of the thermistor chip and the lead wire are reliably insulated to prevent them from deteriorating due to migration. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] [ Figure 1]: A cross-sectional view showing the main parts of a temperature detector in a preferred embodiment constructed according to the present invention. DETAILED DESCRIPTION

[0016] Hereinafter, a temperature detector in a preferred embodiment constructed according to the present invention will be described in more detail with reference to the accompanying drawings.

[0017] refer to Figure 1 The temperature detector generally indicated by reference numeral 2 includes a thermistor chip 4. The thermistor chip 4 may be of a type known per se, for example including a thermistor element as a temperature detection element, a thermistor element formed on both sides of the thermistor element (i.e., Figure 1 The thermistor chip 4 of this type is described in detail in JP-A-2020-21861 and its description is omitted here with reference to the specification.

[0018] On both sides of the thermistor chip 4, a pair of connection ends (i.e., ends without insulation covering) 6a of lead wire 6 are connected respectively. The connection ends 6a of lead wire 6 can be connected to the front surface and the rear surface of thermistor chip 4 respectively with Sn-Cu solder 8, for example. In order to detect the temperature, the other end of lead wire 6 is connected to a power supply (not shown) via a resistance meter (not shown). Thermistor chip 4, the connection ends 6a of lead wire 6, and in the illustrated embodiment, a portion of the lead wire 6 located near the connection ends 6a is covered by an insulating coating 10. The insulating coating 10 includes an inner layer 12 and an outer layer 14 covering the inner layer 12. In the illustrated embodiment, a portion of each connection end 6a of lead wire 6 is not covered by the inner layer 12, but only by the outer layer 14. If necessary, the connection ends 6a of lead wire 6 and the front end of lead wire 6 near the insulation covering of the connection ends 6a can also be covered by the inner layer 12. However, if the inner layer 12 is formed by dip coating to cover the connection end portion 6a of the lead 6 and the insulation-covered front end portion of the lead 6 near the connection end portion 6a, the region of the insulating coating layer 10 corresponding to the front end portion of the insulation-covered portion of the lead 6 partially bulges. This tends to make it difficult to insert the thermistor chip 4 covered with the insulating coating layer 10 into a housing (described later), especially when the inner diameter of the housing is small for use in a small temperature detector.

[0019] It is important for the temperature detector 2 constructed according to the present invention that the inner layer 12 of the insulating coating layer 10 is made of a high-adhesive resin and the outer layer 14 of the insulating coating layer 10 is made of an epoxy resin. The peel strength of the high-adhesive resin of the inner layer 12 of the insulating coating layer 10 to the thermistor chip 4 (for example, the thermistor chip disclosed in JP 2020-A-21861, both surfaces of which include covering electrodes, each covering electrode having an outer layer of Au thin film) and the epoxy resin of the outer layer 14 of the insulating coating layer 10 is preferably 0.20MPa or more, more preferably 0.30MPa or more, and even more preferably 0.50MPa or more. It is desirable that the peel strength of the high-adhesive resin to the thermistor chip 4 is 5.60MPa or less. According to the experience and experiments of the inventors, if the peel strength of the high adhesive resin of the inner layer of the insulating coating layer 10 to the thermistor chip 4 and the outer layer 14 of the insulating coating layer 10 is too low, then especially when the thermistor chip 4 and the insulating coating layer 10 are subjected to relatively large temperature changes and / or immersed in water for a relatively long time, local peeling may occur between the thermistor chip 4 and the inner layer 12 of the insulating coating layer 10 and between the inner layer 12 and the outer layer 14 of the insulating coating layer 10, and the connection end 6a of the thermistor chip 4 and the lead 6 may be deteriorated due to migration. On the other hand, if the peel strength of the high adhesive resin of the inner layer 12 of the insulating coating layer 10 to the thermistor chip 4 is too high, then especially when the thermistor chip 4 and the insulating coating layer 10 are subjected to relatively large temperature changes, the element electrode layer and the cover electrode layer of the thermistor chip 4 tend to move with the inner layer 12 of the insulating coating layer 10 and partially peel off from the thermistor element.

[0020] Preferred examples of the high adhesive resin include addition reaction type silicone-based resins, particularly addition reaction type silicone-based resins having a vinyl group-containing organopolysiloxane as a main component.

[0021] The outer layer 14 of the insulating coating layer 10 may be made of a suitable epoxy resin, but is preferably made of a thixotropic epoxy resin such as a bisphenol A epoxy resin.

[0022] The insulating coating layer 10 can be formed by a so-called dip coating method. Specifically, first, the thermistor chip 4 is immersed in a liquid high-adhesive resin, then pulled out of the liquid high-adhesive resin, and then heated and cured to form the inner layer 12. Next, the thermistor chip 4 covered with the inner layer 12 is immersed in a liquid epoxy resin, then pulled out from the molten epoxy resin, and then heated and cured to form the outer layer 14.

[0023] Still refer to Figure 1In the illustrated embodiment, the thermistor chip 4, the insulating coating layer 10, and a portion of the lead 6 (i.e., the connection end 6a and the front end portion continuous therewith) are housed in a housing 16, and the housing 16 is filled with a synthetic resin 18. More specifically, the housing 16 is cylindrical in shape as a whole, and one end (i.e., Figure 1 The left end in the figure) is closed with a circular end wall and the other end (i.e., Figure 1 The thermistor chip 4, the insulating coating 10 and a portion of the lead 6 (i.e., the connecting end 6a and the front end portion continuous therewith) are inserted into the housing 16 through the open end. Thereafter, the housing 16 is filled with a liquid synthetic resin 18 and then cured. The housing 16 can be made of a suitable metal sheet such as a copper sheet, or a suitable synthetic resin such as polyethylene terephthalate. It is suitable that the synthetic resin 18 used to fill the housing 16 is a flexible epoxy resin.

[0024] Peel strength test A (high adhesive resin)

[0025] A plate-like element with a thickness of 0.5 mm is prepared, and its structure is basically the same as the thermistor chip available from Ohizumi Mfg. Co., Ltd. under the trade name "NBC". One side of the plate-like element is covered with an addition reaction type silicone resin (a high adhesion resin) with a vinyl-containing organopolysiloxane as the main component until the resin thickness is 0.05 mm. Then, the surface of the high adhesion resin is covered with a bisphenol A type epoxy resin with a thickness of 1.0 mm to prepare a test piece. A tensile tester is used to measure the peel strength of the high adhesion resin to the element and to the epoxy resin. The peel strength test is performed twice, and the results are shown in Table 1 below. In Table 1, the "fracture" in the "state" column indicates that the high adhesion resin is broken and separated.

[0026] [Table 1]

[0027]

[0028] Peel strength test B (non-high adhesive resin)

[0029] The peel strength test was performed twice in the same manner as the peel strength test A, except that a condensation reaction type silicone resin as a non-high adhesive resin was used instead of a high adhesive resin to prepare the test piece. The results are shown in Table 2. "Peeled" in the "State" column in Table 2 means that the non-high adhesive resin peeled off at the interface with the epoxy resin without breaking.

[0030] [Table 2]

[0031]

[0032] Peel strength test C (high adhesive resin)

[0033] The same test piece as in the peel strength test A was subjected to a 96-hour pressure cooker test (PCT) and then to two peel strength tests. The results are shown in Table 3. In Table 3, "broken" in the "state" column indicates that the high adhesive resin was broken and separated.

[0034] [Table 3]

[0035]

[0036] Peel strength test D (non-high adhesive resin)

[0037] The peel strength test was performed twice in the same manner as the peel strength test C, except that the test piece used in the peel strength test B was used. The results are shown in Table 4. In Table 4, "Peeled" in the "State" column means that the non-high-adhesion resin peeled off at the interface with the epoxy resin without breaking.

[0038] [Table 4]

[0039]

[0040] Example

[0041] Preparation Figure 1 10 temperature detectors of the form shown. Each temperature detector includes a thermistor chip available from Ohizumi Mfg. Co., Ltd. under the trade name "NBC". The inner layer of the insulating coating is formed by dip-coating an addition reaction type silicone resin (a high adhesion resin) with a vinyl-containing organopolysiloxane as the main component. The thickness of the inner layer of the insulating coating is 0.05 to 0.12 mm (the thickness is measured by X-ray imaging of a temperature detector prepared separately in a similar manner.) The outer layer of the insulating coating is formed by dip-coating a bisphenol A type epoxy resin. The shell is made of a copper sheet with a thickness of 0.3 mm and an outer diameter of 4.0 mm. The shell is filled with a flexible epoxy resin.

[0042] Each of the 10 temperature detectors prepared in this way is subjected to a migration resistance test. In the migration resistance test, a series voltage of 5V is applied to the thermistor chip via a series resistance of 1KΩ, and a pressure cooker test (PCT) of 96 hours is carried out under this state. After this, the resistance value of the thermistor chip measured in an atmosphere of 25°C after the migration resistance test is compared with the resistance value of the thermistor chip measured in an atmosphere of 25°C before the migration resistance test. When the change in resistance value is below 3%, the migration resistance of the temperature detector is considered to be qualified. All 10 temperature detectors are found to be qualified.

[0043] Comparative Example

[0044] Ten temperature detectors were prepared in the same manner as in Example 1, except that the inner layer of the insulating coating layer was formed by dip coating a condensation reaction type silicone resin as a non-high adhesive resin. Then, the migration resistance test was performed in the same manner as in Example 1. None of the temperature detectors was considered qualified.

[0045] Description of Reference Numerals

[0046] 2: Temperature detector

[0047] 4: Thermistor chip

[0048] 6: Lead

[0049] 6a: Connection end of the lead wire

[0050] 8: Solder

[0051] 10: Insulation coating

[0052] 12: Inner layer of insulating coating

[0053] 14: Outer layer of insulating coating

[0054] 16: Shell

[0055] 18: Synthetic resin filling the shell

Claims

1. A temperature detector comprising a thermistor chip, a pair of leads connected to the thermistor chip, and an insulating coating layer covering the connection ends of the thermistor chip and each of the leads, The insulating coating layer includes an inner layer made of a high-adhesive resin and an outer layer made of an epoxy resin. 2 . The temperature detector according to claim 1 , wherein the high-adhesive resin is an addition reaction type silicone-based resin. 3 . The temperature detector according to claim 2 , wherein the addition reaction type silicone-based resin contains a vinyl group-containing organopolysiloxane as a main component. The temperature detector according to claim 1 , wherein the inner layer has a thickness of 0.5 μm or more. 5 . The temperature detector according to claim 1 , wherein the peel strength of the inner layer to the thermistor chip and the outer layer is 0.20 MPa or more. 6 . The temperature detector according to claim 5 , wherein the peel strength of the inner layer to the thermistor chip and the outer layer is 0.30 MPa or more. 7 . The temperature detector according to claim 6 , wherein the peel strength of the inner layer to the thermistor chip and the outer layer is 0.50 MPa or more.

8. A temperature detector according to any one of claims 1 to 4, wherein the thermistor chip, the connecting ends of the pair of leads, and the insulating coating are housed in a cylindrical shell made of metal or synthetic resin which is closed at one end and open at the other end, and the shell is filled with synthetic resin.

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