JP2001307904A - Polymer ptc element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the possibility of a polymer PTC element causing a characteristic failure due to thermal deterioration and, at the same time, to manufacture the element inexpensively. SOLUTION: The main body section of this polymer PTC element 10 is constituted of a plate-like element main body 12 composed of a polymer and a conductive substance scatteredly contained in the polymer. Paired electrodes 14 for energization are respectively provided on both the upper and lower surfaces of the main body 12 and connected to paired lead terminals 16 formed in narrow and long plate-like shapes through Sn-Bi alloy solder 18.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polymer PTC having a positive temperature coefficient of resistance for protecting batteries and circuits from overcurrent.
The present invention is suitable as an element for protecting a circuit connected to a battery pack of a mobile phone, a video camera, a computer, or the like from overcurrent or overheating.

[0002]

2. Description of the Related Art A polymer PTC element is a PTC (Positi
ve Temperature Coefficient), which is a conventional example of this polymer PTC element.
No. 401 discloses a structure in which an electrode 114 provided on an element body 112 and a lead terminal 116 are connected by soldering by melting a solder plating layer 118 as shown in FIG. ing.

[0003] Japanese Patent Application Laid-Open No. 2-2684, also referred to as a conventional example.
No. 02 discloses not only a structure for connecting an electrode provided on an element body and a lead terminal by welding as a conventional technique, but also, as shown in FIG.
Is disclosed in which the lead terminal 116 and the electrode 114 are welded with the spot welding electrode 120 while being pressed to such an extent that they do not deform, and the periphery thereof is fixed with an adhesive 122.

[0004]

However, particularly in a polymer PTC element operating at a low temperature, when the lead terminal and the electrode are simply connected by general soldering, the melting temperature of the solder is about 200 ° C. or more. So that
The polymer PTC element has a disadvantage that it deteriorates due to heat and causes poor characteristics. In addition, the above-mentioned Japanese Utility Model Laid-open No.
Even in the case where the solder plating layer 118 is melted and connected as in Japanese Patent Application Laid-Open No. 1 (1993), the problem of thermal degradation could not be basically solved because the melting temperature was similarly high.

Further, when the solder is melted to connect between the electrode 114 and the lead terminal 116, various processes other than a general reflow process are used. In this case, the element body 1
12 has been deformed and the yield has been reduced.

On the other hand, general welding disclosed as a conventional technique in Japanese Patent Application Laid-Open No. 2-268402 has a problem that the element body and the electrodes are deformed and the yield is reduced. Therefore, in order to solve this problem, this publication discloses a manufacturing method in which the electrodes 114 and the like are pressed and welded so as not to be deformed, and the periphery thereof is fixed with an adhesive 122 to increase the connection strength of the lead terminals 116. However, this manufacturing method has a drawback in that it requires an adhesive 122 and a special process such as a bonding process using the adhesive 122, which leads to an increase in cost.

In consideration of the above facts, the present invention not only eliminates the possibility of causing characteristic failure due to thermal deterioration, but also increases the connection strength of the lead terminals to eliminate the need for a special process and to improve the yield and reduce the cost. P that can be produced by
An object is to provide a TC element.

[0008]

According to a first aspect of the present invention, there is provided a polymer PTC element including a polymer and a conductive material dispersedly mixed in the polymer, wherein a resistance change occurs in a temperature range of 60 ° C. to 120 ° C. A polymer PTC element having a main body, wherein electrodes are provided on both surfaces of the PTC element main body, and Bi is 47 to 64 as a component.
%, Ag is set to 0 to 3%, and the Sn-Bi-based alloy solder whose remaining is Sn is melted, and lead terminals are connected to these electrodes, respectively.

According to the first aspect of the present invention, a PTC element which includes a polymer and a conductive substance dispersedly mixed in the polymer and has a resistance change in a low temperature range of 60 ° C. to 120 ° C. The main body. For this reason, the PTC element body becomes weak to heat, but the Sn-Bi alloy solder having the above components and having a low melting point of 139 to 160 ° C. is used for the electrode provided on the PTC element body. The lead terminals are connected.

Accordingly, not only the connection between the electrode and the lead terminal can be performed by a general reflow process as a soldering process, but also the solder reflow peak temperature is 160 ° C.
To 180 ° C. As a result, the influence of heat on the PTC element main body of the polymer PTC element is reduced, and there is no possibility of causing characteristic failure due to thermal deterioration. That is, the PTC element body according to the present invention is weak to heat,
In particular, the deterioration of the characteristics becomes remarkable due to the application of heat at 200 ° C. or more, but in the present invention, the characteristics do not deteriorate because the solder reflow peak temperature is as low as 160 ° C. to 180 ° C.

The maximum value of the operating temperature range of the polymer PTC element is also set to about 120 ° C., which is lower than 139 ° C. when Bi, which is the lowest melting point in the melting point range of the solder, is 57%. Also, there is no connection problem such as melting of the solder during use. As described above, when soldering between the electrode and the lead terminal, the soldering process can also be performed by a general reflow treatment, and the connection strength between the electrode and the lead terminal is increased, and the use of an adhesive is required. This eliminates the need for a special process such as a bonding process. Furthermore, since the influence of heat and deformation are small, not only reliability is increased but also yield is high, and as a result, inexpensive polymer PTC is used.
Element.

On the other hand, the Sn—Bi alloy solder used in the present invention contains Sn, Bi, and Ag as components,
Is 47 to 64%, Ag is 0 to 3%, and Sn is the balance. That is, according to the present invention,
Since it is a lead-free solder, there is no lead and its impact on the environment is small. Further, even if Ag is within 0 to 3%, for example, 1%
If it is on the order, the mechanical reliability such as the connection strength by soldering is improved. For this reason, it is desirable to determine the direction of the more detailed components of the solder based on the manufacturing cost, the structure of the polymer PTC element, reliability data, and the like.

Further, for example, the polymer PTC of the present invention
After the PTC element main body in which the resistance change occurs in the temperature range of 60 ° C. to 120 ° C. was manufactured in a state where the electrodes were provided on both surfaces thereof, Sn having the above-described components was used.
It is completed by using a manufacturing method in which a Bi-based alloy solder is melted by a reflow treatment and lead terminals are connected to these electrodes, respectively.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be clarified by describing embodiments of a polymer PTC element according to the present invention with reference to the drawings. FIG. 1 is a perspective view showing a polymer PTC element 10 according to the present embodiment. In the present embodiment, the element body 12 which is a plate-like PTC element body composed of a polymer and a conductive substance dispersedly mixed in the polymer is a polymer PTC element shown in FIG.
The main body of the element 10 is constituted.

The polymer PTC element 1 according to the present embodiment
0 is a polymer synthesized using a metallocene catalyst so that a temperature change at a relatively low temperature can be detected; and
As the element body 12, a substance containing conductive particles having spike-like projections dispersedly mixed in the polymer is used as the element body 12, and the temperature of the resistance change point of the element body 12 is 60 ° C. It is set relatively low at 120 ° C.

Further, current-carrying electrodes 14 are provided on both upper and lower surfaces of the element body 12, respectively, and a space between the pair of electrodes 14 and a pair of lead terminals 16 formed in an elongated plate shape is provided. Sn-Bi alloy solder 18
Are connected to each other. That is, the element body 12
The polymer PTC element 10 is formed by connecting the lead terminals 16 to the upper and lower surfaces via the electrodes 14, respectively.

Next, as the element body 12 according to the present embodiment, a polymer synthesized using a metallocene catalyst and conductive particles having spike-like projections dispersedly mixed in the polymer are formed of a conductive material. The reason for adopting what is included as will be described. The characteristics required as the element body 12 of the polymer PTC element 10 include a sufficiently low room temperature resistance value at the time of non-operation at room temperature and a sufficiently large change rate between the room temperature resistance value and the resistance value at the time of operation. The change in the resistance value due to the repetitive operation is small.

As a thermoplastic crystalline polymer which is a polymer for the element body 12 of the polymer PTC element 10, high-density polyethylene having high crystallinity has been mainly used. The reason for this is that the higher the crystallinity of the polymer, the larger the expansion rate and the greater the rate of change in resistance. On the other hand, the lower the crystallinity of a polymer, the slower the crystallization speed, and when cooled after melting, it cannot return to the original crystalline state and the change in resistance at room temperature becomes large. It was difficult.

However, a drawback of using high-density polyethylene is its high operating temperature. That is, the polymer PTC when used as an overcurrent protection element
The operating temperature of the element is about 130 ° C. of its melting point, and the thermal effect on other electronic components on the circuit board may not be ignored. Also, the operating temperature is still too high for the overheat protection component of the secondary battery.

Accordingly, a linear polymer, which is a polymer polymerized using a metallocene catalyst, can be maintained at an operating temperature of about 100 ° C., which is lower than that of a high-density polyethylene having a high operating temperature, while maintaining good resistance returnability. Low density polyethylene (LLDPE) has been specifically adopted. Polymerization using the metallocene catalyst narrows the molecular weight distribution of the polymer and reduces the low-density and low-molecular-weight components. That is, in the conventional general linear low-density polyethylene, the high-density component is crystallized, and it becomes a crystal nucleus, whereby crystallization proceeds. On the other hand, in a polymer synthesized using a metallocene catalyst, since crystal nuclei are generated and grown uniformly, even if the polymer PTC element operates and the crystal melts, the subsequent change in characteristics becomes small and the room temperature increases. It is considered that the change of the resistance value at the time is small.

As described above, by employing a polymer synthesized using a metallocene catalyst, the conventional polymer P
The operating temperature can be lower than that of the TC element, and an element having a stable operating characteristic at a low operating temperature, which has been conventionally difficult, can be obtained.

Further, the use of conductive particles having spike-like projections makes it possible to achieve both low room temperature resistance and a large resistance change rate. That is, since conductive particles having spike-shaped protrusions are used, a tunnel current easily flows due to the shape thereof, and an element body having a lower room temperature resistance than spherical conductive particles can be obtained. Further, since the distance between the conductive particles is larger than that of the spherical particles, a larger resistance change can be obtained during operation.

FIG. 2 is a graph showing the relationship between resistance and temperature in a first example of a material that can be used as the element body 12 according to the present embodiment, and shows the relationship between resistance and temperature in the second example. The graph is shown in FIG. In the first example shown in FIG. 2 of these figures, there is a hysteresis between heating and cooling, but this is within a range that can be adopted as the element body 12. On the other hand, by mixing a low-molecular organic compound and using the low-molecular organic compound as an operating substance, the transition temperature (operating temperature) at which the resistance increases during heating and the temperature at which the resistance returns to low during cooling can be made almost the same. Thus, a material having the characteristics shown in the graph of FIG. 3 can be obtained.

Next, the polymer PTC according to the present embodiment
The manufacturing process of the element 10 will be described. First, an element body 12 composed of a polymer and a conductive substance dispersedly mixed in the polymer is manufactured with a pair of electrodes 14 arranged on the upper and lower surfaces of the element body 12, and FIG. ), A paste-like Sn—Bi-based alloy solder 18 is applied to the electrode 14 side (only the application to one electrode 14 is shown).
State. However, the Sn-Bi-based alloy solder 18 in paste form may be applied to the lead terminals 16 side.

At this time, the electrode 14 may be formed separately from the element main body 12 by press working or the like and fixed to the element main body 12.
Electrode 14 by electroless plating or thermal spraying.
May be formed. Thereafter, the paste is once melted by a reflow process, so that the electrodes 14 and the lead terminals 16 are soldered and connected by Sn-Bi alloy solder 18 as shown in FIG. The polymer PTC element 10 is completed.

That is, since the temperature of the resistance change point of the element main body 12 is relatively low at 60 ° C. to 120 ° C., it is easily affected by heat during the reflow process, but the melting point of the Sn—Bi alloy solder 18 is also 139. Because the temperature is as low as ~ 160 ° C, with soldering between the electrode 14 and the lead terminal 16,
The thermal effect on the element body 12 is small.

As a specific example of the Sn—Bi-based alloy solder 18 of the present embodiment, Sn—Bi—Ag
It is conceivable to use a lead-free solder having a component of 47 to 64%, a component of Ag of 0 to 3%, and a remaining component of Sn. The reflow by the Sn-Bi alloy solder 18 is considered. The reflow peak temperature at the time of processing is set to about 160 ° C to 180 ° C.

Next, the polymer PTC according to the present embodiment
The operation of the element 10 will be described. In the present embodiment, the element main body 12 includes a polymer and a conductive substance dispersedly mixed in the polymer and changes resistance in a low temperature range of 60 ° C. to 120 ° C. Therefore, the element body 12
Is weak to heat, but has a low melting point of 139 to 160 ° C.
The electrode 14 provided on the element body 12 and the lead terminal 16 were connected by a Bi-based alloy solder 18.

Therefore, not only the connection between the electrode 14 and the lead terminal 16 can be performed by a general reflow process as a soldering process, but also the solder reflow peak temperature is reduced to 160 ° C. to 180 ° C. for connection. It can be processed. As a result, the element body 1 of the polymer PTC element 10
2 is less affected by heat, and there is no risk of causing characteristic failure due to thermal degradation. In other words, the element body 12 according to the present embodiment is weak to heat, and although the characteristics are particularly deteriorated by the heat application of 200 ° C. or more, the solder reflow peak temperature is as low as 160 ° C. to 180 ° C .; No drop occurs.

The maximum value of the operating temperature range of the polymer PTC element 10 is also set to about 120 ° C., which is lower than the melting point of 139 ° C., which is the melting point of 57% Bi having the lowest melting point. There is no connection problem. Incidentally, the melting point of a general eutectic solder of Sn-37Pb is 183 ° C., and the reflow peak temperature at the time of the treatment is about 200 ° C. to 220 ° C., as in the present embodiment. Solder 18
Since the processing temperature is much higher than in the case of using, the element body 12 is not easily used because it is much damaged.

As described above, when soldering between the electrode 14 and the lead terminal 16, the soldering process can be performed by a general reflow process, and the connection strength between the electrode 14 and the lead terminal 16 is high. This eliminates the need for a special process such as a bonding process using an adhesive. Further, since the influence and deformation due to heat are small, not only the reliability is increased but also the yield is high, and as a result, the inexpensive polymer PTC element 10 is reduced.
Becomes

On the other hand, the components of the Sn—Bi alloy solder 18 include Sn, Bi, and Ag, and Bi is 47 to 64.
% And Ag is 0-3%,
Since lead-free solder with Sn as the balance is used, there is no lead and the effect on the environment is small. If Ag is 3% or less, for example, about 1%, and Bi is about 57%, mechanical reliability such as connection strength by soldering is improved. For this reason, it is desirable that the more detailed component directionality of the solder is determined by the manufacturing cost, the structure of the polymer PTC element 10, the reliability data, and the like.

In the above-described embodiment, Bi as bismuth is set in the range of 47 to 64%, Ag as silver is set to 3% or less, and Sn as tin is used as the balance, but tin containing no silver is used. And bismuth alone may be used as an alloy solder, and% representing these components is WT%.

[0034]

According to the polymer PTC element of the present invention,
In addition to eliminating the risk of causing characteristic failure due to thermal degradation, it is possible to manufacture a polymer PTC element at low cost by increasing the connection strength of the lead terminals, eliminating the need for special steps, and improving the yield. .

[Brief description of the drawings]

FIG. 1 is a perspective view showing a polymer PTC element according to one embodiment of the present invention.

FIG. 2 is a graph showing a relationship between resistance and temperature of an element body in a first example of a polymer PTC element according to one embodiment of the present invention.

FIG. 3 is a graph showing a relationship between resistance of an element body and temperature in a second example of the polymer PTC element according to one embodiment of the present invention.

4A and 4B are diagrams showing the production of the polymer PTC element according to one embodiment of the present invention, wherein FIG. 4A is a diagram showing a state before connection of lead terminals, and FIG. It is a figure showing a state after.

FIG. 5 is a perspective view showing a polymer PTC element according to a first related art.

6A and 6B are views showing a polymer PTC element according to a second conventional technique, wherein FIG. 6A is a perspective view of an element body of the polymer PTC element, and FIG. 6B is a state in which a lead terminal is welded to the element body. FIG. 1C is a perspective view showing the appearance of a polymer PTC element to which lead terminals are fixed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Polymer PTC element 12 Element main body 14 Electrode 16 Lead terminal 18 Sn-Bi alloy solder

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Norihiko Shigeta 1-13-1 Nihombashi, Chuo-ku, Tokyo FTD term (reference) 5E034 AA10 AC10 DA02 DC04

Claims (1)

[Claims] 1. A polymer PTC element comprising a polymer and a conductive substance dispersedly mixed in the polymer and having a PTC element main body in which a resistance change occurs in a temperature range of 60 ° C. to 120 ° C., wherein the PTC Electrodes are provided on both sides of the element body. Bi is 47-64% and Ag is 0-3.
%, And the lead terminals are connected to these electrodes by melting Sn-Bi-based alloy solder, the balance being Sn.