JP2000113728A - Conductive adhesive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive adhesive having excellent reworkability and large bonding strength at a room temperature. SOLUTION: This conductive adhesive 3 is obtained by mixing an epoxy resin, conductive powder and a polysulfone resin. The content of the polysulfone resin is preferably set in the range of 3-10 wt.%, while the epoxy resin and the polysulfone resin come to 100 wt.% in total. Further, the content of the conductive powder is preferably set in the range of 1-10 vol.%, while the epoxy resin, the polysulfone resin and the conductive powder come to 100 vol.% in total.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a conductive adhesive, and more particularly, to a conductive adhesive used for mounting electronic components on a circuit board or the like.

[0002]

2. Description of the Related Art When electronic components are mounted on a circuit board or the like, solder, which is an alloy of lead and tin, has conventionally been used. However, in recent years, from the viewpoint of voluntary regulation of lead emissions,
Instead of solder, lead-free, so-called Pb-free solder or conductive adhesive has attracted attention. The conductive adhesive is
Although it is more expensive than Pb-free solder, it also has many advantages such as no need for cleaning, low temperature bonding, and high thermal shock resistance due to the flexibility of the adhesive layer. As such a conductive adhesive, a thermosetting type such as an epoxy adhesive has been proposed.

When mounting an electronic component on a circuit board or the like using a conductive adhesive, or when manufacturing a multi-chip module or the like, mounting failure of the electronic component occurs, or after the mounting. Electronic components may fail. In such a case, a so-called rework process in which the problematic electronic component is removed from the circuit board, excess conductive adhesive remaining on the circuit board is removed, and then a non-defective product is connected again with the conductive adhesive. May be performed.

[0004]

However, in the conventional rework process when an electronic component is mounted on a circuit board using an epoxy-based conductive adhesive, it is difficult to perform the rework process using a general-purpose solvent. Need to use a strong solvent. For this reason, the conventional epoxy-based conductive adhesive has a problem in that corrosion or the like occurs in the reconnection portion due to an acid or a halide as a release agent component, and the connection reliability is reduced.

In order to solve such a problem,
An epoxy-based conductive adhesive to which a cyanate ester resin has been added has been proposed (see JP-A-9-279121). Since the cyanate ester resin is soluble or swellable in a general-purpose solvent, the epoxy-based conductive adhesive to which the cyanate ester resin is added has good reworkability. However, when a cyanate ester resin is added to an epoxy resin, a new problem such as a reduction in the curing speed of the conductive adhesive and a decrease in bonding strength at room temperature has occurred, which has hindered practical use.

[0006] An object of the present invention is to provide a conductive adhesive having excellent reworkability and high adhesive strength at room temperature.

[0007]

In order to achieve the above object, a conductive adhesive according to the present invention is characterized in that an epoxy resin, a conductive powder, and a polysulfone resin are mixed. . Here, 3 to 10% by weight of the polysulfone resin is added to 100% by weight of the total of the epoxy resin and the polysulfone resin. Furthermore, the total of epoxy resin, polysulfone resin and conductive powder is 1
The conductive powder is mixed with 1 to 10% by volume with respect to 00% by volume.

[0008] With the above structure, the polysulfone resin is soluble or swellable in a general-purpose solvent. Therefore, the epoxy-based conductive adhesive to which the polysulfone resin is added is:
Has good reworkability. Moreover, while the conventional cyanate ester resin acts to lower the adhesive strength of the conductive adhesive, the polysulfone resin reduces the brittleness of the conductive adhesive and imparts toughness to the conductive adhesive. Therefore, the bonding strength of the conductive adhesive at room temperature is improved.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the conductive adhesive according to the present invention will be described.

The conductive adhesive according to the present invention is obtained by kneading an epoxy resin, a conductive powder, and a polysulfone resin. Polysulfone resin is a thermoplastic resin. When the polysulfone resin is mixed with the epoxy resin and cured, it forms a moderately sized phase-separated structure with the epoxy resin, which is effective for improving the flexibility and toughness of the conductive adhesive. To an appropriate value. In addition, as a thermoplastic resin, there are a phenoxy resin, a polyamide resin, a polyester resin, a polyvinyl butyral resin, and the like, in addition to the polysulfone resin. However, when these resins are mixed and cured with an epoxy resin, the flexibility and toughness of the conductive adhesive are inferior to those of the polysulfone resin.

The total amount of the epoxy resin and the polysulfone resin is preferably 100% by weight, and the content of the polysulfone resin is preferably set in the range of 3 to 10% by weight. When the mixing amount of the polysulfone resin is 2% by weight or less of the whole resin, the effect of lowering the adhesive strength of the conductive adhesive at a high temperature (for example, 220 ° C.) and obtaining excellent reworkability is reduced. is there. Conversely, if the mixing amount of the polysulfone resin is 20% by weight or more of the entire resin, the conductive adhesive after curing becomes too soft, and the adhesive strength at room temperature (25 ° C.) is lower than that of the epoxy resin alone. is there. Furthermore, it is preferable that the total amount of the epoxy resin, the polysulfone resin, and the conductive powder is 100% by volume, and the conductive powder is set in the range of 1 to 10% by volume. When the amount of the conductive powder is less than 1% by volume, the conductivity of the conductive adhesive is deteriorated. This is because an increase in adhesive strength cannot be expected. The amount of the conductive powder (1
In consideration of this, the conductive adhesive is more preferably used as an anisotropic conductive adhesive.

In the conductive adhesive having the above structure, the polysulfone resin is soluble or swellable in a general-purpose solvent. Therefore, the epoxy-based conductive adhesive to which the polysulfone resin is added has good reworkability. Moreover, while the conventional cyanate ester resin acts to lower the adhesive strength of the conductive adhesive, the polysulfone resin reduces the brittleness of the conductive adhesive and imparts toughness to the conductive adhesive. Therefore, the bonding strength of the conductive adhesive at room temperature can be increased.

Next, an example of a method for producing the conductive adhesive having the above-described configuration will be described. (Examples 1 to 3) Epoxy resin (main agent: bisphenol A type epoxy resin, curing agent) as resin of conductive adhesive
A mixed material of microcapsule type imidazole) and polysulfone resin was used. 100% by weight of resin components
The polysulfone resin was adjusted to 7% by weight in Example 1, 4% by weight in Example 2, and 10% by weight in Example 3. The main component and the curing agent of the epoxy resin were blended so that there was no excess or deficiency calculated from the epoxy equivalent. The polysulfone resin was mixed with the epoxy resin in a state of a 20% NMP (N-methylpyrrolidone) solution.
The conductive powder composed of Ag, Cu, Ag-Pd, etc. is a total of 1 for the epoxy resin, the polysulfone resin and the conductive powder.
It was added so as to be 5% by volume based on 00% by volume. For kneading, preliminary kneading was performed using a mortar, and main kneading was performed using a Hoover Mara.

After kneading, as shown in FIG. 1, each of the conductive adhesives 3 is put into a size of 25 mm (width) × 25 mm (height) × 5 m.
The test piece was sandwiched between two alumina test pieces 1 and 2 having a dimension of m (thickness), fixed from both ends with jigs, and cured. The curing conditions were two-stage curing, in which after the initial curing at 120 ° C. (30 minutes), the curing was completed at 210 ° C. (20 minutes).

The reason for adopting this two-stage curing is as follows. The epoxy resin / polysulfone resin composite system is a so-called lower critical so-called LCST (LCST).
It has a phase diagram of the type "lution temperature (lower critical solution temperature)". That is, the lower the temperature of the system, the better the compatibility (the smaller the phase separation structure). Therefore, by setting the initial curing temperature as low as 120 ° C., the phase separation structure can be fixed in a small state.
The fixed fine phase-separated structure is not disturbed by the final curing temperature of 210 ° C. required to complete the curing. This fine phase-separated structure is formed by the conductive adhesive 3
It is possible to efficiently absorb mechanical energy when stress is applied to the substrate. As a result, the conductive adhesive 3
Has flexibility and high toughness, and can obtain high adhesive strength. Actually, when compared with the case where the curing conditions are 210 ° C. and 50 minutes (when the phase separation structure is relatively large), the room temperature (2
(5 ° C.), it was found that 1.5 times the adhesive strength was obtained.

For comparison, seven types of comparative examples were manufactured by the following method. (Comparative Examples 1-4) The total of the resin components of the conductive adhesive was 10
0% by weight of the polysulfone resin,
(Comparative Example 1), 2 (Comparative Example 2), 20 (Comparative Example 3), 4
0 (Comparative Example 4), and the other conditions were the same as in Example 1.

Comparative Example 5 The total of the resin components of the conductive adhesive was 100% by weight, and the cyanate ester resin was 20% by weight instead of the polysulfone resin.
Other conditions were the same as in Example 1.

Comparative Example 6 The total amount of the resin components of the conductive adhesive was 100% by weight, of which 7% by weight of a polysulfone resin and 20% by weight of a cyanate ester resin, and the other conditions were the same as in Example 1. And

Comparative Example 7 The total of the resin component of the conductive adhesive and the conductive powder was 100% by weight, and the conductive powder was blended so as to be 20% by volume. And the same.

The measurement results of the adhesive strengths of Examples 1 to 3 at 25 ° C. and 220 ° C. are shown in Table 1 and FIGS. 2 and 3 together with the measurement results of Comparative Examples 1 to 7.

[0021]

[Table 1]

Table 2 shows the adhesive strength at 25 ° C., the reworkability at 220 ° C., and the overall evaluation of Examples 1 to 3 and Comparative Examples 1 to 7 based on Table 1 and FIGS. 2 and 3. The determination of the presence or absence of reworkability in Table 2 is based on the following definition of reworkability. That is, the reworkability means that the test pieces 1 and 2 bonded to each other with a 10 mm overlap are placed in an oven, reheated at 220 ° C. for 10 minutes, and then moved in the direction indicated by the arrow A in FIG. To 20
The test pieces 1 and 2 can be separated from each other with a force of not more than kgf / cm ² , and the resin components remaining on the bonding surfaces of the test pieces 1 and 2 after removal from the oven are NM.
The property is such that it can be wiped off within one minute with P (N-methylpyrrolidone). Table 2 shows that the conductive adhesives of Examples 1 to 3 have high adhesive strength at room temperature (25 ° C) and excellent reworkability at high temperature (220 ° C).

[0023]

[Table 2]

Examples 1 to 3 and Comparative Examples 1 to 7
Of the conductive adhesive was evaluated by the following measurement method. As shown in FIG. 4, a conductive adhesive 14 is screen-printed on the electrodes 12 and 13 on the glass epoxy substrate 11, and a chip capacitor 15 (having a size of 1.6 m) is placed thereon.
mx 0.8mm, capacitance is 100pF)
The conductive adhesive 14 was cured at 150 ° C. for 30 minutes under pressure. After cooling, the capacitance was measured by the LCR meter 16. In the case where all the conductive adhesives 14 of Examples 1 to 3 and Comparative Examples 1 to 7 were used, the measured value was around 100 pF, and it was found that the conductivity of the conductive adhesive 14 was good. If the conductivity of the conductive adhesive 14 is poor, measurement becomes impossible.

The conductive adhesive according to the present invention is not limited to the above embodiment, but can be variously modified within the scope of the invention.

[0026]

As is apparent from the above description, according to the present invention, an appropriate amount of a polysulfone resin, which is a thermoplastic resin, is mixed with an epoxy resin as a resin component. The flexibility and toughness of the agent are improved. Further, the conductive adhesive is improved to an appropriate elastic modulus, can increase the bonding strength at room temperature, and has a reduced bonding strength at a high temperature, so that excellent rework can be obtained.
As a result, when mounting surface-mounted electronic components on a circuit board, adhesion reliability is obtained, and in addition, since they are excellent in rework, a conductive material that is effective for bonding high-value-added electronic components to the circuit board is effective. Adhesive can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a conductive adhesive according to the present invention and a test piece bonded by the conductive adhesive.

FIG. 2 shows the room temperature of Examples 1 to 3 and Comparative Examples 1 to 7 (25
3C is a graph showing measurement data of adhesive strength at (° C.).

FIG. 3 shows the high temperatures (22) of Examples 1 to 3 and Comparative Examples 1 to 7;
FIG. 5 is a graph showing measurement data of adhesive strength at 0 ° C.).

FIG. 4 is a front view showing a method for evaluating the conductivity of a conductive adhesive.

[Explanation of symbols]

 3,14 ... conductive adhesive

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Koji Kimura, Inventor 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto F-term in Murata Manufacturing Co., Ltd. (Reference) 4J040 EC061 EJ031 EJ032 JB10 KA03 KA32 LA06 LA09 NA20 5G301 DA03 DA06 DA11 DA42 DA57 DD03

Claims (3)

[Claims] 1. A conductive adhesive comprising a mixture of an epoxy resin, a conductive powder, and a polysulfone resin. 2. The conductive adhesive according to claim 1, wherein the total amount of the polysulfone resin is 3 to 10% by weight based on 100% by weight of the total of the epoxy resin and the polysulfone resin. 3. The total of the epoxy resin, the polysulfone resin and the conductive powder is 100% by volume,
3. The conductive adhesive according to claim 1, wherein the conductive powder is 1 to 10% by volume. 4.