JP4302713B2 - PTC element - Google Patents

Description

  The present invention relates to a PTC (Positive Temperature Coefficient) element.

A PTC element is known as an element for protecting a circuit element from an overcurrent. A PTC element is an element in which the positive temperature coefficient of resistance value increases abruptly when reaching a specific temperature range. As one of such PTC elements, one described in Patent Document 1 below is known.
Japanese Patent Publication No. 5-9921

  The PTC element described in Patent Document 1 has a rough surface by edging on the surface of an element having a positive resistance temperature characteristic composed of a polymer and a conductive powder dispersed in the polymer. The faced metal plates are joined, and the metal plates are used as terminal electrodes. The reason why the surface in contact with the surface of the element is roughened is to improve the bonding strength between the element and the metal plate.

  However, when the entire surface in contact with the surface of the element is roughened as in the PTC element described in Patent Document 1 above, bonding is performed when a metal plate that has become a terminal electrode is bonded to a connection terminal such as an external terminal by welding or soldering. In some cases, sufficient strength could not be secured.

  Therefore, an object of the present invention is to provide a PTC element capable of improving the bonding strength when a lead terminal extending from an element body is bonded to another terminal.

  In the course of studying PTC elements that can solve the above-mentioned problems, the present inventors have also found the following new problems. When a predetermined time elapses after manufacturing the PTC element, oxygen may enter the element body from the surroundings. Therefore, it is conceivable to provide a protective film so as to cover the element body. However, the present inventors have found that this protective film may be peeled off and some measures are necessary. The present invention has been made from this viewpoint.

  A PTC element according to the present invention is a PTC element that includes an element body in which a conductive filler is dispersed in a crystalline polymer, and a pair of lead terminals that are crimped by sandwiching the element element. The pair of lead terminals further includes a protective film that covers portions not crimped to the pair of lead terminals, and each of the pair of lead terminals has an overlapping region that overlaps the element body and a non-overlapping region that does not overlap the element body. Each overlapping region has anchor protrusions that bite into the element body, and a non-overlapping region adjacent to the element body has a roughened region and at least a non-overlapping region excluding the roughened region In FIG. 2, the anchor protrusion is crushed and flattened.

  According to the present invention, since the non-overlapping region except the roughened region of the lead terminal is flattened, it is possible to improve the bonding strength when bonding with other terminals. In addition, since the roughened region having a substantially increased surface area is formed in the non-overlapping region adjacent to the element body, the contact area between the protective film and the lead terminal can be effectively increased, The peel strength of the protective film can be further improved.

  In the present invention, the roughened region is preferably formed in a region where a pair of lead terminals overlap each other. Since the roughened region is formed in a region where the lead terminals overlap with each other, the lead terminal is sandwiched between the lead terminals, and the peel strength of the protective film can be improved more effectively.

  In the present invention, it is also preferable that the roughened region is formed by roughening by etching. Since the etching can easily roughen the surface of the lead terminal as compared with a mechanical method such as grinding, a roughened region can be easily formed.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to improve the joint strength at the time of joining the lead terminal extended from an element body to another terminal, and can suppress peeling of the protective film which covers an element body. Therefore, it is possible to suppress oxygen from contacting the element body and oxidizing the element body.

  The knowledge of the present invention can be easily understood by considering the following detailed description with reference to the accompanying drawings shown for illustration only. Subsequently, embodiments of the present invention will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals, and redundant description is omitted.

  Example 1 which is an embodiment of the present invention will be described with reference to FIG. FIG. 1A is a plan view of the PTC element 1 according to the first embodiment, and FIG. 1B is a diagram illustrating the vicinity of the center of the PTC element 1 according to the first embodiment (II in FIG. 1A). FIG. The PTC element 1 in Example 1 is a polymer PTC element, and includes a pair of terminal electrodes 12 and 14 (lead terminals), an element body 10, and protective films 16a, 16b, 16c, and 16d.

  The pair of terminal electrodes 12, 14 is Ni or Ni alloy having a thickness of about 0.1 mm. The pair of terminal electrodes 12 and 14 are arranged so that a part of each of them faces each other. Since the element body 10 is disposed between the facing portions, the pair of terminal electrodes 12 and 14 sandwich the element body 10 between their facing surfaces. Accordingly, the pair of terminal electrodes 12 and 14 are formed with overlapping regions 121 and 141 that overlap the element body 10 and non-overlapping regions 122 and 142 that do not overlap the element body 10, respectively.

  The element body 10 is formed to be smaller than a portion where the terminal electrode 12 and the terminal electrode 14 overlap each other. Therefore, around the element body 10, non-overlapping regions 122 and 142, where the terminal electrode 12 and the terminal electrode 14 overlap each other, are formed.

  The element body 10 is formed by dispersing a conductive filler in a crystalline polymer resin. Ni powder is preferably used as the conductive filler, and polyethylene resin, which is a thermoplastic resin, is preferably used as the crystalline polymer resin. The element body 10 is pressure-bonded to the pair of terminal electrodes 12 and 14 by pressure.

  A plurality of anchor protrusions AC and flattening protrusions FC are formed on the surface of each of the terminal electrodes 12 and 14 sandwiching the element body 10, and a region where the anchor protrusions AC and the flattening protrusions FC are not formed is a rough surface. It has become. The anchor protrusion AC is formed in the overlapping regions 121 and 141.

  In the non-overlapping regions 122 and 142 adjacent to the element body 10, roughened regions 122a and 142a are formed, respectively. The roughened regions 122a and 142a are non-overlapping regions 122 and 142, and are formed at least in regions where the terminal electrode 12 and the terminal electrode 14 overlap each other.

  The roughened regions 122a and 142a are regions that are roughened so that the surface areas of the terminal electrodes 12 and 14 in the regions are substantially increased. It is also preferable that the roughened regions 122a and 142a are formed by roughening by etching using hydrochloric acid or the like. The roughened regions 122a and 142a are also preferably formed by machining such as grinding or sand blasting. The roughened regions 122a and 142a are preferably formed to be roughened by forming the anchor projections AC and then crushing them to the extent that protective films 16a, 16b, 16c, and 16d, which will be described later, enter. The roughening region is not limited in the aspect of roughening as long as peeling of protective films 16a, 16b, 16c, and 16d described later can be substantially suppressed.

  The flattening protrusions FC are non-overlapping regions 122 and 142, and are formed in regions excluding the roughened regions 122a and 142a. From another viewpoint, the flattening protrusion FC is formed in the non-overlapping regions 122 and 142 where the terminal electrodes 12 and 14 do not overlap each other.

  In FIG. 1, the anchor protrusion AC and the flattening protrusion FC are drawn relatively large for the sake of explanation. The actual anchor protrusion AC and flattening protrusion FC are minute protrusions and are difficult to visually recognize. Further, the roughened shapes of the roughened regions 122a and 142a are schematically drawn. The same applies to the drawings used in the following description.

  Each of the anchor protrusions AC has a large diameter portion and a small diameter portion. The large-diameter portion is provided on the distal end side in the direction in which the anchor protrusion AC extends from the terminal electrodes 12 and 14, and the outer periphery in that direction is formed to be larger than the outer periphery of the small-diameter portion. The small diameter portion is provided closer to the root side of the anchor protrusion AC than the large diameter portion. The shape of the large diameter part and the small diameter part in each anchor protrusion AC may be uneven. Further, the outer peripheral shape of the large diameter portion and the small diameter portion may not be a regular shape such as a circle or an ellipse, but may be an irregular shape.

  Adjacent anchor projections AC are arranged so as to be separated from each other. Therefore, the element body 10 enters the recesses formed between the anchor protrusions AC (the anchor protrusion AC bites into the element body 10), and the terminal electrodes 12, 14 and the element body 10 are fixed.

  The flattening protrusions FC each have a large diameter portion and a small diameter portion. The large-diameter portion is provided on the distal end side in the direction in which the flattening protrusion FC extends from the terminal electrodes 12 and 14, and is formed so that the outer periphery in that direction is larger than the outer periphery of the small-diameter portion. A flat surface is formed at the tip of the large diameter portion. The small diameter portion is provided closer to the base side of the flattening protrusion FC than the large diameter portion. The shape of the large diameter part and the small diameter part in each flattening protrusion FC may be uneven. Further, the outer peripheral shape of the large diameter portion and the small diameter portion may not be a regular shape such as a circle or an ellipse, but may be an irregular shape.

  Adjacent flattening protrusions FC are arranged in contact with each other. The flat surface of each flattening protrusion FC (the front end surface of the flattening protrusion FC) is continuous to form a substantially flat surface. Therefore, the element body 10 and the protective films 16a, 16b, 16c, and 16d do not substantially enter the recesses formed between the flattening protrusions. However, the flattening protrusions FC are not completely in contact with each other over the entire surface, and the flattening is performed within a range that does not substantially affect the bonding strength when the terminal electrodes 12 and 14 are bonded to other terminals. The protrusions FC may be separated from each other.

  In the present embodiment, the substantially flat surface is formed by forming the flattening protrusions FC in contact with each other. However, if it is possible to form a substantially flat surface, the embodiment is as described above. Not limited. For example, it may be flattened by cutting or grinding.

  The protective films 16a, 16b, 16c, and 16d are arranged so as to cover portions where the element body 10 is not crimped to the terminal electrodes 12 and 14, respectively. There are four surfaces on which the element body 10 is not pressure-bonded to the terminal electrodes 12 and 14, and the protective films 16a, 16b, 16c and 16d are arranged along the four surfaces, respectively.

  The protective films 16a, 16b, 16c, and 16d are in contact with the terminal electrodes 12 and 14 at least in the roughened regions 122a and 142a. Therefore, the area where the protective films 16a, 16b, 16c, and 16d are in contact with the terminal electrodes 12 and 14 is substantially larger than that in the case where the protective films 16a, 16b, 16c, and 16d are in contact with each other in the non-roughened region.

  In the protective films 16a, 16b, 16c and 16d, a filler made of a material having a lower oxygen permeability than the cured product layer is dispersed in a cured product layer formed by reacting an epoxy resin and a thiol-based curing agent. Is formed. The filler is preferably an inorganic filler. Moreover, it is preferable that at least a part of the filler has a plate shape. Moreover, it is preferable that the protective films 16a, 16b, 16c, and 16d contain 5 to 50% by mass of filler based on the mass of the entire protective film.

  The protective films 16a, 16b, 16c, and 16d are formed by, for example, heating an epoxy resin composition containing an epoxy resin, a thiol-based curing agent, and a filler to advance the reaction between the epoxy resin and the thiol-based curing agent. The

  As fillers, inorganic fillers such as mica, silica, talc, clay (natural or synthetic smectite or mixtures thereof), glass, aluminum hydroxide, magnesium hydroxide and ceramic, silver powder, gold powder, copper powder and nickel powder, etc. Metal fillers, organic fillers such as carbon and polyimide are preferably used.

Subsequently, a reference example of the present embodiment will be described with reference to FIG. FIG. 2 is a cross-sectional view of a PTC element 2 as a reference example. The PTC element 2 is a polymer PTC element, and includes a pair of terminal electrodes 22 and 24 (lead terminals), an element body 10a, and protective films 26a, 26b, 26c, and 26d.

  The pair of terminal electrodes 22 and 24 is Ni or Ni alloy having a thickness of about 0.1 mm. The pair of terminal electrodes 22 and 24 are arranged so that a part of each of them is opposed. Since the element body 10a is disposed between the facing portions, the pair of terminal electrodes 22 and 24 sandwich the element body 10a between their facing surfaces. Accordingly, the pair of terminal electrodes 22 and 24 are respectively formed with overlapping regions 221 and 241 that overlap with the element body 10a and non-overlapping regions 222 and 242 that do not overlap with the element body 10a.

  The element body 10a is formed in substantially the same shape as a portion where the terminal electrode 22 and the terminal electrode 24 overlap each other. Since the element body 10a has the same composition as that of the element body 10, the description thereof is omitted. The element body 10a is pressure-bonded to the pair of terminal electrodes 22 and 24 by being pressurized and heated.

  A plurality of anchor protrusions AC and flattening protrusions FC are formed on the surfaces where the terminal electrodes 22 and 24 sandwich the element body 10a. The anchor protrusion AC is formed in the overlapping regions 221 and 241. A region where the anchor protrusion AC and the flattening protrusion FC are not formed is roughened. Accordingly, roughened regions 222a and 242a are formed in the non-overlapping regions 222 and 242 adjacent to the element body 10a, respectively. The aspects of the roughened regions 222a and 242a are the same as those of the roughened regions 122a and 242a, and thus description thereof is omitted.

  The protective films 26a, 26b, 26c, and 26d are arranged so as to cover portions where the element body 10a is not crimped to the terminal electrodes 22 and 24, respectively. The protective film 26d corresponds to the protective film 16d shown in FIG. 1A and is not clearly shown in FIG. There are four surfaces on which the element body 10a is not pressure-bonded to the terminal electrodes 22, 24, and the protective films 26a, 26b, 26c, 26d are arranged along the four surfaces, respectively.

  The protective films 26a, 26b, 26c, and 26d are in contact with the terminal electrodes 22 and 24 at least in the roughened regions 222a and 242a. Therefore, the area where the protective films 26a, 26b, 26c, and 26d are in contact with the terminal electrodes 22 and 24 is substantially larger than the case where they are in contact with each other in a non-roughened region.

  The composition and the like of the protective films 26a, 26b, 26c, and 26d are the same as those of the protective films 16a, 16b, 16c, and 16d already described, and thus the description thereof is omitted.

Subsequently, the peeling prevention effect of the PTC element 1 and the PTC element 2 in the present embodiment will be described. In the description of this effect, the embodiment in which the roughened regions 122a and 142a are formed by etching using the form of the PTC element 1 is referred to as Embodiment 1, and the embodiment in which the anchor protrusion is crushed is referred to as Embodiment 2. Further, a configuration in which the roughened regions 222a and 242a are formed by etching using the form of the PTC element 2 is referred to as Reference Example 1 , and a configuration in which the anchor protrusion is crushed is referred to as Reference Example 2 . As a comparative example, a PTC element 4 shown in FIG. 3 is used.

  The PTC element 4 includes a pair of terminal electrodes 42, 44, an element body 10a, and protective films 46a, 46b, 46c, 46d.

  The pair of terminal electrodes 42 and 44 is Ni or Ni alloy having a thickness of about 0.1 mm. The pair of terminal electrodes 42 and 44 are arranged so that a part of each of them faces each other. Since the element body 10a is disposed between the facing portions, the pair of terminal electrodes 42 and 44 sandwich the element body 10a between their facing surfaces. Therefore, the pair of terminal electrodes 42 and 44 are respectively formed with overlapping regions 421 and 441 that overlap the element body 10a and non-overlapping regions 422 and 442 that do not overlap the element body 10a.

  The element body 10a is formed in substantially the same shape as a portion where the terminal electrode 42 and the terminal electrode 44 overlap each other. The protective films 46a and 46c are arranged so as to cover portions where the element body 10a is not crimped to the terminal electrodes 22 and 24, respectively. Although protective films corresponding to the protective films 26b and 26d shown in FIG. 2 are also formed, they are not explicitly shown in FIG. Since the composition and the like of the protective films 46a and 46c are the same as those of the protective films 16a, 16b, 16c and 16d already described, the description thereof is omitted.

  A plurality of anchor protrusions AC are formed on the surfaces of the terminal electrodes 42 and 44 sandwiching the element body 10a. Anchor protrusion AC is formed only in overlapping regions 421 and 441. The portions where the protective films 46a and 46c are in contact with the terminal electrodes 42 and 44 are smooth and not roughened.

FIG. 4 shows the results of a terminal electrode peel strength test performed on the above-described Example 1, Example 2, Reference Example 1 , Reference Example 2, and Comparative Example. FIG. 4 shows the peel strength of the protective film when the terminal electrodes of Example 1, Example 2, Reference Example 1 , Reference Example 2, and Comparative Example are each separated vertically from the element body.

As shown in FIG. 4, Example 1 and Example 2 according to this embodiment have higher peel strength than Reference Examples 1, 2 and Comparative Examples. Specifically, the peel strength of Example 1 is 5.93N to 9.87N and the average value is 8.74N with 5 samples. The peel strength of Example 2 is 5.65N to 9.33N and the average value is 8.52N with 5 samples. The peel strength of Reference Example 1 is five samples, 3.23N to 5.43N, and the average value is 3.98N. The peel strength of Reference Example 2 is 5.75N to 4.61N, the average value is 3.89N, with 5 samples. The number of samples of the comparative example is 5, 0.98N to 1.55N, and the average value is 1.17N.

As described above, the peel strengths of Examples 1 and 2 increase with respect to Reference Examples 1 and 2 and Comparative Example because the contact area between the protective films 16a to 16d and the terminal electrodes 12 and 14 is a roughened region. This is considered to be due to the substantial increase due to the formation of 122a and 142a . In Examples 1 and 2, since the protective films 16a to 16d are sandwiched between the terminal electrode 12 and the terminal electrode 14, it is considered that the peel strength is further increased.

  Next, a method for manufacturing the above-described PTC elements 1 and 2 will be described. The manufacturing method of the PTC elements 1 and 2 includes an element body preparation step, a terminal preparation step, a roughening step, a flattening step, a thermocompression bonding step, and a protective film forming step.

  In the element body preparation step, an element body material to be the element bodies 10 and 10a is prepared and prepared. First, Ni powder used as a conductive filler and polyethylene used as a base resin are kneaded to form a block. This block is pressed into a disk shape and cut to obtain a base material.

In the subsequent terminal preparation step, a metal plate to be the terminal electrodes 12 and 14 is prepared and prepared. An anchor projection AC is formed on the surface where the terminal electrodes 12 and 14 sandwich the element bodies 10 and 10a. The anchor protrusion AC is formed by continuously forming the above-described nodular protrusions.

In the roughening step, as described above, before the terminal electrodes 12 and 14 and the element body 10 are fixed, the front terminal electrodes 12 and 14 are etched with hydrochloric acid to form roughened regions 122a and 142a .

In another aspect, the roughened regions 122a and 142a may be formed by machining such as grinding or sandblasting. In another aspect, the roughened regions 122a and 142a may be formed by crushing the anchor protrusion AC to such an extent that the uneven shape remains.

  In the flattening step, as described above, the anchor protrusion AC is crushed and flattened in a necessary region to obtain a flattened protrusion FC. In this case, the amount of press movement is 10 to 35 μm, and more preferably 10 to 15 μm. As long as a substantially flat surface can be formed, the embodiments are not limited to those described above. For example, it may be flattened by cutting or grinding.

  As described above, the flattening protrusions FC are in contact with each other and are substantially flattened. When viewed from the thickness of the terminal electrode, the average thickness of the region where the flattening protrusion FC is formed is thinner than the average thickness of the region where the anchor protrusion AC is formed. The average thickness can be determined from the mass and specific gravity of a sample punched out from a predetermined area.

  For example, in the case of the present embodiment, the thickness after planarization is preferably 60 to 140 μm for the overlapping regions 121 and 141 (regions where the anchor protrusions AC are formed) and 50 to 120 μm for the non-overlapping regions 122 and 142. . In this case, the average height of the anchor protrusion AC is 5 to 40 μm. Moreover, as for the thickness after planarization, it is more preferable that the overlapping regions 121 and 141 are 95 to 100 μm, and the non-overlapping regions 122 and 142 are 80 to 90 μm. In this case, the average height of the anchor protrusion AC is 5 to 20 μm.

  When the thickness of the overlapping regions 121 and 141 is greater than 140 μm, the terminal electrodes 12 and 14 become too thick, and the thermocompression bonding between the element body 10 and the terminal electrodes 12 and 14 becomes insufficient, and the element body 10 and the terminal electrode The connection strength with 12 and 14 is weakened. Therefore, the thickness of the non-overlapping regions 122 and 142 is preferably 120 μm or less in consideration of planarization.

  In addition, when the thickness of the non-overlapping regions 122 and 142 is less than 50 μm, the strength of the terminal electrodes 12 and 14 itself is reduced, and the non-overlapping regions 122 and 142 are bent. Become. Therefore, the thickness of the overlapping regions 121 and 141 is preferably 60 μm or more in consideration of the flattening of the non-overlapping regions 122 and 142.

  If the average height of the anchor protrusion AC is lower than 5 μm, the anchor effect between the element body 10 and the terminal electrodes 12 and 14 cannot be sufficiently exhibited, and the connection between the element body 10 and the terminal electrodes 12 and 14 is not possible. The strength is weakened. Further, if the average height of the anchor protrusion AC is higher than 40 μm, the strength of the anchor protrusion AC itself is lowered, and the anchor protrusion AC drops off from the terminal electrodes 12 and 14 during thermocompression bonding with the element body 10.

  In the thermocompression bonding step, the element body material (element body) is sandwiched between the overlapping regions 121 and 141 in the pair of terminal electrodes 12 and 14, respectively, and the pair of terminal electrodes 12 and 14 and the element body 10 are fixed by thermocompression bonding.

  In the protective film forming step, protective films 16a, 16b, 16c, and 16d are formed. The protective films 16a, 16b, 16c, and 16d disperse a filler made of a material having a lower oxygen permeability than the cured product layer in a cured product layer formed by the reaction of the epoxy resin and the thiol curing agent. Form.

  According to the present embodiment, since the non-overlapping regions 122 and 142 except for the roughened regions 122a and 142a of the terminal electrodes 12 and 14 are flattened, it is possible to improve the bonding strength when bonding to other terminals. Can do. Further, since the roughened regions 122a and 142a are formed in the non-overlapping regions 122 and 142 adjacent to the element body 10, peeling of the protective films 16a to 16d covering the element body 10 can be effectively suppressed.

It is the top view and sectional drawing which show the PTC element in this embodiment. It is sectional drawing which shows the PTC element of the reference example of this embodiment. It is sectional drawing which shows the PTC element of the comparative example of this embodiment. It is a figure which shows the result of having compared the PTC element of this embodiment, and the PTC element of a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... PTC element, 12, 14 ... Terminal electrode, 10 ... Element body, 121, 141 ... Overlapping region, 122, 142 ... Non-overlapping region, 122a, 142a ... Roughening region, 16a, 16b, 16c, 16d ... Protection Membrane, AC ... anchor projection, FC ... flattening projection.

Claims (2)

A PTC element comprising an element body in which a conductive filler is dispersed in a crystalline polymer, and a pair of lead terminals that are crimped by sandwiching the element body,
A protective film that covers a portion of the element body that is not crimped to the pair of lead terminals;
Each of the pair of lead terminals has an overlapping region that overlaps the element body and a non-overlapping region that does not overlap the element body,
Anchor protrusions that bite into the element body are formed in the overlapping regions of the pair of lead terminals,
Each non-overlapping region of the pair of lead terminals has a roughened region and a region formed in a region excluding the roughened region and flattened by the anchor protrusion being crushed ,
The roughened region has a surface state different from the overlapping region and is in contact with the protective film,
The PTC element , wherein the roughened region is formed at least in a region adjacent to the element body and the pair of lead terminals overlapping each other . The PTC element according to claim 1 , wherein the roughened region is formed by roughening by etching.

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