JP3039356B2 - Method of fixing magnetic head slider - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for fixing a floating magnetic head slider used in a hard disk drive or the like.

[0002]

2. Description of the Related Art Known techniques for adhering and fixing a floating magnetic head slider to a suspension which is a supporting member thereof include (1) a method using a thermosetting adhesive, and (2) ultraviolet rays. There are a method using a curable (UV) adhesive, (3) a method using both a thermosetting adhesive and a UV adhesive, and (4) a method using semi-reflow or welding.

(1) Method using a thermosetting adhesive An example is a method described in JP-A-6-60346. As shown in FIG. 1, after attaching a magnetic head slider 11 coated with a thermosetting adhesive 12 and a suspension 13 to a positioning jig 10 for bonding, the jig is put into a curing oven and heated. Cures the thermosetting adhesive 12 to bond them. In FIG. 1, 14 is a guide for the slider 11, 15 is a holding member for the suspension 13 and the slider 11, 16 is a holding spring thereof, 17 is a holding member for the suspension 13,
Reference numeral 18 denotes a holding spring, and reference numerals 19a and 19b denote positioning pins inserted into a reference hole of the suspension 13 and a mounting hole of the base portion, respectively.

When bonding is performed using a thermosetting adhesive, sufficient strength can be obtained even when the bonding area is small, but the positioning and bonding jig 10 must be put into an oven during heat curing for processing. Therefore, the use efficiency of the positioning and bonding jig is poor, and a huge number of jigs corresponding to the production amount of the magnetic head are required. For this reason, not only the variation in the positional accuracy between the jigs becomes large, but also the management of the positional accuracy becomes complicated. In addition, the heating in the oven causes the jig to thermally change with time, and the positioning mechanism is disturbed. From this point, it is very difficult to control the positional accuracy. In addition, since not only the magnetic head slider and the entire suspension but also the jig are heated, the heat capacity to be heated increases, the heating time becomes longer, and the overall heating conditions are determined by the heat resistance conditions of the portion having poor heat resistance. Will be done.

(2) Method using UV adhesive For example, a method described in JP-A-5-325460 is used. A UV adhesive is applied to a magnetic head slider and superposed on a predetermined position of a suspension. In this state, ultraviolet rays are irradiated to cure and bond the UV adhesive.

If the bonding is performed using a UV adhesive, it is not necessary to put the bonding jig into the oven, so that the positional accuracy of the jig due to heating can be prevented from being deviated, and there is no thermal restriction described above. However, since the portions that are not exposed to ultraviolet light are not cured, a sufficient adhesive strength cannot be obtained only by ultraviolet irradiation. In particular, since the interface between the slider and the flexure, which requires the most adhesive strength, is not normally irradiated with ultraviolet light, the adhesive strength is insufficient. Further, when the bonding area is small, it is difficult to obtain a satisfactory bonding strength only with the UV adhesive.

Japanese Patent Application Laid-Open No. Hei 5-40927 discloses a technique in which a flexure portion is made of a transparent resin that transmits ultraviolet light in order to reduce the portion not irradiated with ultraviolet light. However, this not only requires a special flexure, but it is difficult to obtain a sufficient adhesive strength only with a UV adhesive when the adhesive area itself is small.

(3) A method using both a thermosetting adhesive and a UV adhesive This is a method described in JP-A-6-60346, and a thermosetting adhesive is used in places where ultraviolet irradiation is difficult. The slider and the flexure are fixed under the respective curing conditions of the two adhesives by simultaneously using the UV adhesive in the portions where the ultraviolet irradiation is possible.

However, the use of two types of adhesives has a problem in terms of improving the productivity, and the UV adhesive basically has a property of inhibiting the curing of the thermosetting adhesive by the epoxy resin. Therefore, both adhesives must be used properly so that they do not come into contact with each other, and the processing becomes complicated in that sense.

(4) Method using semi-reflow or welding For example, a method described in JP-A-59-63058, in which a slider and its suspension are joined using semi-reflow or welding.

[0011] The magnetic head slider and the suspension and the entire jig for positioning them require heat resistance to reflow or welding, and a bonding electrode or welding electrode must be provided on the bonding surface.

A first object of the present invention is to provide a method of fixing a magnetic head slider, which has good thermal efficiency during heat curing and can shorten the curing time.

A second object of the present invention is to solve the above-mentioned problems of the prior art, so that it is not necessary to put the jig for bonding in an oven at the time of heating and curing, and to use only one kind of adhesive. It is an object of the present invention to provide a method of fixing a magnetic head slider that can achieve high bonding strength by performing bonding.

[0014]

According to the present invention, a magnetic head slider and a slider supporting member are positioned and attached to a bonding jig, and a conductive thermosetting adhesive is provided between the magnetic head slider and the slider supporting member. The magnetic head slider is temporarily bonded to the slider support member by intervening, passing a current to the conductive thermosetting adhesive, and curing the conductive thermosetting adhesive by self-heating by Joule heat, and then temporarily bonded. The magnetic head slider and the slider supporting member are detached from the bonding jig, and the conductive thermosetting adhesive is further cured to perform the actual bonding, thereby providing a method of fixing the magnetic head slider.

[0015] Since the adhesive itself is self-heated and cured by Joule heat due to the current of the conductive thermosetting adhesive, only the minimum area required for curing is locally heated, and the heating source is Since the adhesive itself is used, heat required for curing can be applied most efficiently, and the curing treatment can be performed in a very short time and easily.

In the temporary bonding step, the magnetic head slider and the slider supporting member are attached to a bonding jig and self-generated by Joule heat to locally heat the adhesive, thereby gelling the adhesive. And the slider support member are adhered without support. In the main bonding step, the magnetic head slider and the slider supporting member temporarily bonded are removed from the bonding jig, placed in an oven, and further heated and cured. According to this method, it is not necessary to put the bonding jig into the oven and the time required for the temporary bonding is short, so that it is not necessary to prepare a large number of jigs, and the positional accuracy among the jigs greatly varies. In addition, the jig can be completely prevented from being thermally changed with time. In addition, there is no need to consider a non-irradiated portion as in the case of using a UV adhesive, and a sufficient adhesive strength can be obtained because a thermosetting adhesive is used. Furthermore, since only one kind of adhesive is used, it is not necessary to use different adhesives, and the workability is greatly improved.

Preferably, the temperature of the conductive thermosetting adhesive is detected, and the current flowing through the conductive thermosetting adhesive is adjusted according to the detected temperature. As a result, the temperature of the conductive thermosetting adhesive is feedback-controlled accurately.

The conductive thermosetting adhesive is preferably an epoxy resin-based adhesive containing a conductive filler, and more preferably the conductive filler is a silver filler.

The weight ratio of the conductive filler to the epoxy resin of the conductive thermosetting adhesive is 1: 0.3 to 0.9.
It is preferred that By using the conductive thermosetting adhesive having this mixing ratio, higher adhesive strength can be obtained while reducing resin stress.

The current flowing through the conductive thermosetting adhesive may be a continuous direct current or an intermittent pulse current.

When the current flowing through the conductive thermosetting adhesive is a continuous direct current, it is preferable to switch from a constant voltage to a constant current in accordance with the resistance of the adhesive and control it.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 2 is a side view schematically showing a fixing jig for fixing a magnetic head slider to a support member thereof according to an embodiment of the present invention.

In FIG. 1, reference numeral 20 denotes a temporary bonding jig, and reference numeral 21 denotes a magnetic head slider positioned and mounted at a predetermined position on the temporary bonding jig 20. A conductive thermosetting adhesive 22 is applied to an adhesive surface (the side opposite to the ABS surface) of the magnetic head slider 21, and a metal (for example, stainless steel) suspension serving as a slider support member is provided at a predetermined position thereon. 23 are placed. The positioning of the suspension 23 is performed by a conductive pin 24 for positioning which is inserted into contact with the reference hole and an electrically insulating pin 25 for positioning which is inserted into a mounting hole of the base portion. In the figure, reference numeral 26 denotes a conductive stopper pressed against the side surface of the magnetic head slider 21, and 27 denotes a spring which is pivotally attached to a fulcrum 27a thereof.
It is a pressing member of the suspension 23 biased by the.

A DC power supply 29a with a regulator and a switch 29 are provided between the conductive pin 24 and the conductive stopper 26.
b are connected in series. The DC power supply 29a is, for example, a PAD 35-5L manufactured by Kikusui Electronics Co., Ltd., and is a power supply with a regulator that performs constant voltage control when the load resistance is high and switches to constant current control as the load resistance decreases. Note that most of the temporary bonding jig 20 except the conductive pins 24 and the conductive stoppers 26 is made of an electrically insulating material. Also, the magnetic head slider 21
Is a conductor made of conductive AlTiC (Al-TiC), except for the magnetic head element forming portion 21a protected by the insulating protective film. Further, since the suspension 23 is also made of metal, it is naturally a conductor.

Therefore, when the switch 29b is closed, a current flows from the DC power supply 29a in a loop of the conductive stopper 26, the magnetic head slider 21, the conductive thermosetting adhesive 22, the suspension 23 and the conductive pin 24, As a result, the conductive thermosetting adhesive 22 self-heats and hardens due to Joule heat. Strictly speaking, not only self-heating due to the Joule heat of the resin itself, but also a current flowing through the magnetic head slider 21 and the suspension 23, these also slightly generate heat and contribute to the resin curing.

In the present embodiment, as the conductive thermosetting adhesive 22, an epoxy resin recommended for curing at 90 ° C. for one hour is kneaded with a conductive filler. As the conductive filler, a flake-like silver filler (for example, TCG7N manufactured by Tokurika Chemical Co., Ltd.) is used. However, the epoxy resin and the conductive filler are not limited to this example.

Next, the fixing operation of the magnetic head slider using the apparatus of this embodiment will be described. First, the magnetic head slider 21 is placed at a predetermined position on the temporary bonding jig 20, a conductive thermosetting adhesive 22 is applied to the bonding surface of the magnetic head slider 21, and then the suspension 23 is positioned thereon. Put out and place. Next, the switch 29b is closed and a continuous direct current is passed in a direction penetrating the plane of the conductive thermosetting adhesive 22, and the adhesive 22 itself is locally heated to gel the epoxy resin. The magnetic head slider 21 and the suspension 23 are temporarily bonded. The DC current supply time varies depending on the content of the conductive filler, but is about 40 to 50 seconds, and gelation is achieved without exceeding 60 seconds.

The magnetic head slider 21 and the suspension 23 (head gimbal assembly, HGA) temporarily bonded in this way are removed from the temporary bonding jig 20 and placed in a curing oven, for example, heated at 120 ° C. for one hour. Is performed, the epoxy resin 22 described above is further cured, and the actual bonding is performed.

Next, the mixing ratio (weight mixing ratio) of the conductive filler to the epoxy resin will be described. This weight mixing ratio is most preferably the conductive filler “about 0.7” with respect to the epoxy resin “1” with respect to the stress and adhesive strength of the adhesive after curing. It has been experimentally confirmed that, when the conductive filler is in the range of “0.3 to 0.9”, the stress of the adhesive is small and the adhesive strength is large and excellent.

Hereinafter, an experimental method of the weight mixing ratio and the stress and adhesive strength of the conductive thermosetting adhesive after bonding and the results thereof will be described. The stress of the conductive epoxy resin adhesive can be represented by the amount of change in the crown-like deflection of the member fixed by the adhesive in accordance with the temperature. Therefore,
The stress characteristics of the conductive epoxy resin adhesive when the weight mixing ratio of the conductive filler was changed, and the adhesive strength characteristics when the weight mixing ratio of the conductive filler was changed were measured as follows.

A conductive adhesive having a weight mixing ratio of an epoxy resin to a conductive filler, for example, a conductive adhesive having a weight mixing ratio of 1: 0.3, is prepared. With respect to, for example, five samples to which the adhesive was applied, current was applied by the method shown in FIG. 2 and temporary bonding was performed, followed by final bonding. In this example, the curing conditions in the temporary bonding step are as follows.
A constant current control, voltage is controlled by 5.0V limit (it fluctuates by the resistance of the adhesive.
実 3 V), and the current supply time is 40 seconds. The curing conditions in the main bonding step are 120 ° C. and 60 minutes. For the five samples thus bonded, the amount of crown-like deflection at room temperature (25 ° C.) and the low-temperature (5
° C), the result of measuring the crown-like deflection amount, the change in the deflection amount depending on the temperature (difference between both deflection amounts), and the adhesive strength by the peel test, and the average value of the five samples are shown in Table 1 below. Is shown in

[0033]

[Table 1]

The weight ratio of the conductive filler is 0, 0.0
05, 0.025, 0.05, 0.5, 0.7, 0.9
The same measurement was performed for the case of changing, and the average value of the change in the amount of deflection according to the temperature was plotted,
FIG. 3 shows a change characteristic of the amount of bending with respect to the weight mixing ratio of the conductive filler according to the temperature, which shows the stress characteristic of the conductive epoxy resin adhesive with respect to the weight mixing ratio of the conductive filler. In addition, the plot of the average value of the adhesive strength when the weight mixing ratio of the conductive filler is changed is the adhesive strength characteristic of the conductive epoxy resin adhesive with respect to the weight mixing ratio of the conductive filler shown in FIG. . As is apparent from both figures, when the weight mixing ratio is in the range of the conductive filler “0.3 to 0.9” with respect to the epoxy resin “1”, the stress of the adhesive is small and the adhesive strength is large. Preferred.

As described above, according to the present embodiment, the current is directly passed through the conductive epoxy resin, and the resin is self-heated and cured by the Joule heat. Therefore, the resin can be cured very efficiently. Therefore, temporary bonding can be performed in a time shorter than 60 seconds. There is no need to put the temporary bonding jig into the oven, and since the temporary bonding time is short, there is no need to prepare a large number of jigs. Thermal aging can be completely prevented. In addition, since the conductive epoxy resin itself generates heat, a rise in temperature other than this portion can be suppressed to a minimum. In addition, there is no need to consider a non-irradiated portion as in the case of using a UV adhesive, and a sufficient adhesive strength can be obtained because a thermosetting epoxy resin is used. In addition, since only one kind of adhesive is used, it is not necessary to use the adhesive properly and the workability is greatly improved. Further, the conductive thermosetting adhesive 2
2 and the magnetic head slider 21 and the suspension 2
3 is in a conductive state, so that it is not necessary to additionally provide a conductive means between the two after fixing, and the manufacturing process is simplified accordingly.

In the above-described embodiment, the current supplied to the conductive thermosetting adhesive 22 is a continuous DC current. This is, for example, a pulse current having a duty ratio of 50% intermittently. Is also good.

FIG. 5 is a side view schematically showing a fixing jig for fixing a magnetic head slider to its support member as another embodiment of the present invention.

In the same figure, reference numeral 50 denotes a temporary bonding jig, and reference numeral 51 denotes a magnetic head slider positioned and mounted at a predetermined position on the temporary bonding jig 50. A conductive thermosetting adhesive 52 is applied to an adhesive surface (the side opposite to the ABS surface) of the magnetic head slider 51, and a metal (for example, stainless steel) suspension serving as a slider support member is provided at a predetermined position on the conductive thermosetting adhesive 52. 53 are placed. The positioning of the suspension 53 is performed by a conductive pin 54 for positioning which is inserted into contact with the reference hole and an electrically insulating pin 55 for positioning which is inserted into a mounting hole of the base portion. In the drawing, reference numeral 56 denotes a conductive stopper pressed against the side surface of the magnetic head slider 51, and 57 denotes a spring 58
The pressing member of the suspension 53 is urged by the suspension 53.

A DC power supply 59a with a regulator and a switch 59 are provided between the conductive pin 54 and the conductive stopper 56.
b are connected in series. Thermocouple 59c is slider 5
1 and a conductive thermosetting adhesive 52
Is detecting the actual temperature. The controller 59d electrically connected to the thermocouple 59c receives the temperature detection signal from the thermocouple 59c, and
Is controlled according to the temperature detection signal.

The DC power supply 59a is, for example, a PAD 35-5L manufactured by Kikusui Electronics Co., Ltd. The power supply with a regulator performs constant voltage control when the load resistance is high, and switches to constant current control when the load resistance decreases. It is.

Most of the temporary bonding jig 50 except the conductive pins 54 and the conductive stoppers 56 is made of an electrically insulating material. The magnetic head slider 51 is made of conductive AlTiC (Al-TiC), and is a conductor except for the magnetic head element forming portion 51a protected by an insulating protective film. Further, since the suspension 53 is also made of metal, it is naturally a conductor.

Accordingly, when the switch 59b is closed, a current flows from the DC power supply 59a through a loop of the conductive stopper 56, the magnetic head slider 51, the conductive thermosetting adhesive 52, the suspension 53 and the conductive pin 54, As a result, the conductive thermosetting adhesive 52 self-heats and hardens due to Joule heat. Strictly speaking, not only self-heating due to the Joule heat of the resin itself, but also a current flowing through the magnetic head slider 51 and the suspension 53, these also slightly generate heat and contribute to the resin curing. The temperature of the conductive thermosetting adhesive 52 is controlled by a thermocouple 59.
c, and is accurately controlled by a feedback loop composed of a controller 59d and a DC power supply 59a.

As the conductive thermosetting adhesive 52, FIG.
The same conductive epoxy resin as that of the embodiment is used.

Except for performing temperature detection using a thermocouple and performing feedback control, the structure, operation, and effects of the temporary bonding step and the main bonding step in this embodiment are shown in FIG.
Since it is almost the same as that of the embodiment, the description thereof is omitted.

FIG. 6 is a diagram schematically illustrating the configuration of still another embodiment of the fixing method according to the present invention.

In the embodiment shown in FIGS. 2 and 5, a current flows in a direction penetrating the planes of the conductive thermosetting adhesives 22 and 52. In this embodiment, a direct current is applied to the conductive thermosetting adhesive 62. In the direction along the plane. That is, a conductive thermosetting adhesive 62 is applied to the bonding surface (the side opposite to the ABS) of the magnetic head slider 61, and a metal (for example, stainless steel) serving as a slider supporting member is provided at a predetermined position on the conductive thermosetting adhesive. A suspension 63 is mounted. Both ends 62a and 6a of the applied conductive thermosetting adhesive 62
A DC power supply with regulator 69 is connected between 2b. The DC power supply 69 performs a constant voltage control when the load resistance is high, and switches to the constant current control as the load resistance decreases as in the case of FIGS. The power supply may be a power supply with a regulator or a pulsed power supply through which an intermittent pulse current flows. In the case of a pulse power supply, for example, the duty ratio is 50
%, The applied voltage is set to 5V, and the current limit is set to 2A.

Except for the direction in which the direct current is applied to the conductive thermosetting adhesive, the configuration, operation, and effect of the temporary bonding step and the main bonding step in this embodiment are the same as those in the embodiments of FIGS. The description is omitted because it is completely the same.

FIG. 7 is a diagram schematically illustrating the configuration of a reference example of the fixing method.

In the embodiments shown in FIGS. 2, 5, and 6, the conductive thermosetting adhesives 22, 52, and 62 are used, and current is directly applied to the adhesives to generate heat. A resistance pattern 74 is formed in advance on a bonding surface of a suspension 73 serving as a slider support member by using a thermosetting adhesive 72 having no conductivity, and a current is applied to the resistance pattern 74 to locally generate heat. This cures the thermosetting adhesive 72. That is, a thermosetting adhesive 72 is applied to the bonding surface (the side opposite to the ABS surface) of the magnetic head slider 71, and a suspension 73 having a resistance pattern 74 formed in advance on the bonding surface is mounted on a predetermined position thereon. Is placed. Both ends 7 of this resistance pattern 74
A constant current DC power supply 79 is connected between 4a and 74b. The DC power supply 79 may be a power supply for supplying a continuous DC current or a pulse power supply for supplying an intermittent pulse current. Note that the resistance pattern 74 may be provided on the bonding surface on the magnetic head slider 71 side.

As described above, since the adhesive is locally heated and cured by the Joule heat caused by the current flowing through the resistance pattern provided on the surface of the thermosetting adhesive 72, the minimum necessary for curing is obtained. Only the area of is locally heated,
Since heat can be applied most efficiently, curing can be performed in a short time. Except for passing a current through the resistance pattern, the configurations, operations, and effects of the temporary bonding step and the final bonding step in this reference example are almost the same as those in the embodiments of FIGS. 2, 5, and 6, and The description is omitted.

In the above-described embodiment, the magnetic head slider is fixed to the supporting member. However, the fixing method of the present invention is not limited to the magnetic head slider, and electronic components or other members are fixed to other members. Obviously, it can be widely applied in such cases.

The embodiments described above all show the present invention by way of example and not by way of limitation, and the present invention can be embodied in various other modified and modified forms. Therefore, the scope of the present invention is defined only by the appended claims and their equivalents.

[0053]

As described in detail above, according to the present invention, the adhesive itself is self-heated and cured by Joule heat caused by the current of the conductive thermosetting adhesive.
Only the minimum area required for curing is locally heated, and since the heating source is the adhesive itself, the heat required for curing can be applied most efficiently, and it can be done in a very short time and easily. A curing treatment can be performed.

In the temporary bonding step when the magnetic head slider is fixed, the adhesive is gelled by causing self-heating by Joule heat while the magnetic head slider and the slider support member are mounted on the bonding jig. In the bonding step, the magnetic head slider and the slider support member temporarily bonded are removed from the bonding jig, placed in an oven, and further heated and cured. According to this method, the jig does not need to be put into the oven and the temporary bonding time is short, so that it is not necessary to prepare a large number of jigs. It is possible to completely prevent the heat from changing over time. In addition, since the adhesive itself generates heat, the temperature rise in other parts can be minimized. In addition, there is no need to consider a non-irradiated portion as in the case of using a UV adhesive, and a sufficient adhesive strength can be obtained because a thermosetting adhesive is used. In addition, since only one kind of adhesive is used, it is not necessary to use the adhesive properly and the workability is greatly improved. Further, since the magnetic head slider and the suspension are in a conductive state by the conductive thermosetting adhesive, there is no need to additionally provide a conductive means between the magnetic head slider and the suspension after fixing, and the manufacturing process is correspondingly simplified. .

[Brief description of the drawings]

FIG. 1 is a side view showing a state in which a magnetic head slider and a suspension are attached to a jig in a conventional magnetic head slider fixing method.

FIG. 2 is a side view schematically showing a fixing jig for fixing a magnetic head slider to a support member thereof as one embodiment of the present invention.

FIG. 3 is a graph showing stress characteristics of a conductive epoxy resin adhesive with respect to a weight mixing ratio of a conductive filler in the embodiment of FIG. 2;

FIG. 4 is a graph showing an adhesive strength characteristic of a conductive epoxy resin adhesive with respect to a weight mixing ratio of a conductive filler in the embodiment of FIG. 2;

FIG. 5 is a side view schematically showing a fixing jig for fixing a magnetic head slider to a supporting member as another embodiment of the present invention.

FIG. 6 is a diagram schematically illustrating a configuration of still another embodiment of the fixing method according to the present invention.

FIG. 7 is a diagram schematically illustrating a configuration of a reference example of a fixing method.

[Explanation of symbols]

 20, 50 Temporary bonding jig 21, 51, 61, 71 Magnetic head slider 22, 52, 62 Conductive thermosetting adhesive 23, 53, 63, 73 Suspension 24, 54 Conductive pin 25, 55 Electrical insulation Pins 26, 56 Conductive stoppers 27, 57 Holding members 29a, 59a, 69 DC power supply with regulator 29b, 59b Switch 59c Thermocouple 59d Controller 72 Thermosetting adhesive 74 Resistance pattern 79 DC power supply

Claims (8)

(57) [Claims] 1. A magnetic head slider and a slider supporting member are positioned and attached to a bonding jig, and a conductive thermosetting adhesive is interposed between the magnetic head slider and the slider supporting member. Current is passed through the mold adhesive, and the conductive thermosetting adhesive is hardened by self-heating by Joule heat, thereby temporarily bonding the magnetic head slider to the slider support member, and then temporarily bonding the magnetic head slider. And removing the slider support member from the bonding jig, and further hardening the conductive thermosetting adhesive to perform final bonding. 2. The method according to claim 1, wherein a temperature of the conductive thermosetting adhesive is detected, and a current flowing through the conductive thermosetting adhesive is adjusted according to the detected temperature. the method of. 3. The method according to claim 1, wherein the conductive thermosetting adhesive is an epoxy resin-based adhesive containing a conductive filler. 4. The method according to claim 3, wherein said conductive filler is a silver filler. 5. A weight mixing ratio of the conductive filler to the epoxy resin of the conductive thermosetting adhesive is 1: 0.3 to 0.3.
The method according to claim 3 or 4, wherein the value is 0.9. 6. The method according to claim 1, wherein a current flowing through the conductive thermosetting adhesive is DC. 7. The method according to claim 6, wherein a current flowing through the conductive thermosetting adhesive is controlled by switching from a constant voltage to a constant current according to the resistance of the conductive thermosetting adhesive. The method described in. 8. The method according to claim 1, wherein the current flowing through the conductive thermosetting adhesive is an intermittent pulse current.