JP2001143529A - Conductive bonding agent by cream solder mixing and bonding method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the conventional problem that a conducive bonding agent has bonding deficiency caused by humidity with an inexpensive conductive bonding agent. SOLUTION: This conductive bonding agent is composed by mixing a conductive bonding agent of a conductive filler and a resin binder with a cream solder or a zinc-free cream solder using a resin based flux as the base. It uses at least one kind out of silver, nickel and copper as conductive filler, filler consisting of both or either one of silver filler and a tin alloy filler as the conductive filler, and uses a filler consisting of a tin-bismuth alloy or/and a tin-silver-bismuth alloy as the filler of the zinc-free cream solder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive bonding agent using a conductive adhesive and cream solder, and a bonding method using the same.

[0002]

2. Description of the Related Art At present, in the electronic equipment industry, conductive adhesives are used for assembling semiconductors and other precision electronic parts, and the conductive adhesives exhibit conductivity of silver, gold, nickel, carbon, and the like. As a filler to be used, epoxy resin, phenol resin, polyester resin, acrylic resin, etc. are used as a binder, and these fillers and a binder are appropriately blended with a curing agent and a solvent according to the purpose to obtain a predetermined conductive adhesive. ing. On the other hand, with the recent trend of lead-free electronic devices, attempts have been made to use these conductive adhesives as substitutes for solders in assemblies of general electronic device substrates.

[0003]

The conductive adhesive is produced by kneading a conductive powder filler mainly composed of a metal powder for controlling conductivity and a synthetic resin binder for controlling adhesion.
Generally, as a binder, epoxy resin, polyamide resin, phenol resin, etc. are used, but these synthetic resins generally do not have sufficient moisture resistance, and although there is no problem in packaging like a semiconductor, Components that are built into the device while exposed to the atmosphere, such as general substrates, do not like to cause a decrease in conductivity and a decrease in adhesive strength at the joints of parts due to the influence of moisture in an environment of high temperature and high humidity.

That is, since the structure of these synthetic resins is generally microscopically coarse, moisture penetrates through the gaps of the synthetic resin structures and rapidly oxidizes the surfaces of the electrodes of the substrate and the electrodes of the components. This also oxidizes the surface of the metal filler, causing a decrease in conductivity of the entire connection portion and a deterioration in bonding strength.

Various proposals have been made in the past to improve the problem of moisture resistance. That is, the electrode surface is cleaned by allowing an acid to coexist in the binder to recover the conductivity, or the conductivity or the bonding strength is secured by piercing the electrode portion using a needle-like filler. And a conductive adhesive consisting of a high-melting-point alloy filler, a low-melting-point solder alloy filler, and a binder containing a latent activator that exhibits a flux action, causing a diffusion action between the electrode and the solder alloy during heating. Although it is intended to ensure conductivity and bonding strength, all of these methods are not only complicated but also insufficient.

[0006]

The present invention is not technically complicated as in the above-mentioned various proposals, and is achieved by simply kneading a conductive adhesive and cream solder.
An object of the present invention is to solve the problem of deterioration of conductivity and bonding strength under high humidity conditions by the excellent synergistic effect of the effect of the conductive adhesive and the soldering effect of cream solder. That is,
To a conductive adhesive consisting of a conductive filler and a resin binder, a conductive bonding agent obtained by mixing cream solder based on a resin flux, and to a conductive adhesive consisting of a conductive filler and a resin binder , A tin-bismuth alloy or / and a tin-silver-bismuth alloy filler and a lead-free cream solder based on a resin-based flux, and in particular, a conductive bonding agent comprising silver, nickel, copper The conductive bonding agent is characterized by using at least one kind of filler described above, and a filler comprising both or one of a silver filler and a tin alloy filler. Further, the present invention solves the problem by a bonding method characterized by using these conductive bonding agents.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The following description is for the purpose of facilitating the understanding of the present invention, and does not limit the present invention. The conditions required for the conductive adhesive in the conductive bonding agent of the present invention are that a) the curing temperature is not too low. Desirably, it is about 170 to 220 ° C. b) The conductive filler is a metal or alloy that is easy to solder.
Preferably, metals such as silver, copper, tin and nickel or alloys thereof are desirable.

Further, the conditions required for the cream solder in the conductive bonding agent of the present invention are as follows: a) The solder material must melt at a temperature not higher than the curing temperature of the conductive adhesive used in combination. B) The flux must be of a synthetic resin type and compatible with the synthetic resin of the binder used for the conductive adhesive used in combination. Preferably, the synthetic resin is similar to the synthetic resin of the binder. Hereinafter, a specific description will be given based on examples. The present invention is not limited to the configurations of the examples described below unless departing from the gist.

[0009]

EXAMPLE 1 A thermosetting one-part type conductive adhesive composed of an epoxy resin binder and a silver filler was used.
10 parts by weight (parts) of a rosin-based tin-bismuth eutectic alloy filler cream solder having a melting point of 138 ° C. was mixed with parts by weight (parts) to prepare a conductive bonding agent 1.
The average particle size of the silver filler was 5 μm. The conductive bonding agent 1 was applied to a test substrate and heated at a curing temperature of the conductive adhesive of 150 ° C. for 20 minutes. After cooling, a visual inspection and a destructive inspection were performed. In the appearance inspection, the conductive bonding agent 1 solidified on the test substrate, and sufficient adhesion was confirmed. However, as a result of magnifying observation of the joint in the destructive inspection, it was observed that the solder of the electrode portion of the substrate was insufficiently melted and solder wetting on the substrate electrode was hardly achieved.

Example 2 In view of the results of Example 1, a conductive bonding agent 2 was prepared under the same conditions as in Example 1 except that the curing temperature was increased by 20 ° C. and set to 170 ° C. The same test substrate was heated under a heating time of 20 minutes. Although the bleeding of the fine rosin was observed in the state of the conductive bonding agent on the test substrate, no problematic bleeding of the metal particles was observed, and adhesion without defects in appearance was completed. As a result of destroying this sample and observing the substrate electrode portion in detail, sufficient melting of the solder was observed, and under the heating conditions, the desired bonding state, that is, the solder melted and wetted the electrode surface of the substrate and the component. In addition, there is cooperation between the filler and the part due to partial wetting. As a whole, not only the conductivity due to the contact between the filler and the electrode, but also the complementation of the conductivity due to the wetting of the solder and the bonding with the binder, as well as the solder bonding It has been observed that a bonding state having a complementary relation of the bonding strength with the addition of “” has been completed.

Example 3: 95 parts by weight of a conductive adhesive obtained by mixing 35 parts by weight of silver filler with 40 parts by weight of tin alloy filler and 5 parts by weight of tin filler Then, 5 parts by weight (part) of a rosin-based low-temperature cream solder was added and kneaded to produce a conductive bonding agent 3 as a trial. This is applied to a test substrate and heated at a heating temperature of 170 ° C. for 20 minutes.
After cooling, the appearance of the test substrate was inspected. As a result, it was observed that rosin did not bleed out at the joint, and that bonding without shape defects was completed. Further, the test substrate was broken, and the substrate electrode portion was observed in detail. It was observed that solder wettability was observed on the electrode, partial wettability between the surrounding tin alloy filler and the solder also developed, and aggregation occurred in part.

Example 4: 95 parts by weight of a conductive adhesive obtained by mixing 5 parts by weight of a copper filler with 75 parts by weight of a silver filler, and 5 parts by weight of a rosin-based low-temperature cream solder A part by weight (parts) was added and kneaded to prepare a conductive bonding agent 4 as a trial. This was applied to the test substrate as described above, and a heating temperature of 1
Heated at 70 ° C. for 20 minutes. After cooling, the appearance of the test substrate was inspected. As a result, stable adhesion was observed at about the same level as in Example 3. In addition, as a result of destroying the test substrate and observing the substrate electrode portion in detail, favorable wetting of the solder on the electrode was observed.

Example 5: 95 parts by weight of a conductive adhesive obtained by mixing 5 parts by weight of nickel filler with 75 parts by weight of silver filler, and 5 parts by weight of a rosin-based low-temperature cream solder The conductive bonding agent 5 was prototyped by adding and kneading parts by weight (parts). This was applied to a test substrate and heated at a heating temperature of 1
Heated at 70 ° C. for 20 minutes. After cooling, the appearance of the test substrate was inspected, and the test substrate was broken to observe the electrode portions of the substrate in detail as in the previous example. The electrode surfaces of the substrate and the component were sufficiently wetted by the solder, and the degree of adhesion of the entire joint was good.

Example 6 In order to further reduce the amount of silver filler by adding a copper filler to Example 5,
95 parts by weight of a conductive adhesive obtained by mixing 5 parts by weight of nickel filler, 5 parts by weight of copper filler, 70 parts by weight of silver filler, and rosin-based low-temperature cream 5 parts by weight (parts) of solder were added and kneaded to produce a conductive bonding agent 6 as a trial. This was applied to a test substrate and heated at a heating temperature of 170 ° C. for 20 minutes. After cooling, the appearance of the test substrate was inspected, and the test substrate was destroyed to observe the substrate electrode in detail. Compared to Example 5, no inferiority was observed in the wet state and the adhesion state.

Example 7: The same silver filler as in Example 6 was used in order to further increase the amount of cream solder to be added and to confirm the effect of the amount of cream solder to be the same as the conductive adhesive composition of Example 6. 90 parts by weight of a conductive adhesive obtained by mixing 5 parts by weight of nickel filler and 5 parts by weight of copper filler in 70 parts by weight, and 10 parts by weight of rosin-based low-temperature cream solder A part by weight (parts) was added and kneaded to produce a conductive bonding agent 7 as a trial. This was applied to a test substrate and heated at a heating temperature of 170 ° C. for 20 minutes. After cooling, the appearance of the test substrate was inspected, and the test substrate was destroyed to observe the substrate electrode in detail. The bonding state of the bonding portion and the degree of wetting of the solder on the electrode were substantially the same as in Example 6, and the effect of increasing the amount of cream solder was not particularly observed. It was found that a sufficient synergistic effect can be expected even when the amount of the cream solder is about 5 parts by weight (parts).

Example 8: To confirm the effect when the silver filler was completely removed, 95 parts by weight of a conductive adhesive containing only a tin / silver eutectic alloy filler as a filler and a rosin-based adhesive were used. 5 parts by weight (parts) of low-temperature cream solder was added and kneaded to produce a conductive bonding agent 8 as a trial. This was applied to a test substrate and heated at a heating temperature of 170 ° C. for 20 minutes. After cooling, the appearance of the test substrate was inspected, and the substrate was broken, and detailed observation of the substrate electrode was performed. Compared to the case of all the silver fillers of Example 2, the bonding state of the bonding portion and the wet state of the solder on the electrode are almost unchanged, and the difference in bonding between the silver filler and the tin / silver eutectic alloy filler is as follows. Almost no.

Example 9: In order to compare the effect when the composition of the cream solder to be kneaded was changed with respect to Example 2, 90 parts by weight (part) of the same conductive adhesive as in Example 2 was used.
10 parts by weight of rosin-based low-temperature cream solder containing eutectic tin / silver / bismuth alloy filler
In addition, the mixture was kneaded to produce a conductive bonding agent 9 as a trial. This was applied to a test substrate and heated at a heating temperature of 170 ° C. for 20 minutes. After cooling, the appearance of the test substrate was inspected, and the substrate was broken, and detailed observation of the substrate electrode was performed. Compared to Example 2, the degree of adhesion of the joints was almost the same level, and a slight difference was observed in the wet state of the solder on the electrodes, but this was also judged to be the same level. .

Example 10, Example 11, Example 12 In order to confirm the effect of changing the composition of the tin / bismuth alloy filler of the kneaded cream solder, the mass ratio of tin to bismuth in the alloy was set to 40/60. , 70/30, and 90/10, a rosin-based low-temperature cream solder based on fillers was prepared and kneaded with the conductive adhesive in Example 2 in the same manner as in the conductive bonding agents 10, 11, and 10. 12 were prototyped. In this case, since the melting point of the alloy increases with the decrease in the amount of bismuth, the curing heating conditions after application to the test substrate were 170 ° C. for 20 minutes, 200 ° C. for 20 minutes, and 220 ° C. for 20 minutes. In the same manner as in the above-mentioned example, after cooling, the appearance of the substrate was inspected, and the substrate was broken to observe the electrode portion of the substrate in detail. result,
When the mass ratio of tin to bismuth is in this range, there is almost no significant difference between the adhesion state of the joint and the wet state of the solder on the electrode. Therefore, there is a degree of freedom in selecting the composition of the tin-bismuth alloy in the cream solder.

Comparative Example 1 In order to compare the conductive adhesives of Examples 2 to 12 of the present invention with a conventional conductive adhesive, that is, one to which cream solder was not added, The experimental bonding agent 13 was produced. Except for the conditions involved in kneading the cream solder, the conditions are exactly the same as in Example 2. That is, a thermosetting one-pack type conductive adhesive (average particle size of silver filler: 5 μm) composed of an epoxy resin-based binder and a silver filler is applied to a test substrate. Heated for minutes. After cooling, a visual inspection and a destructive inspection were performed. In the appearance inspection, it was confirmed that the conductive bonding agent 13 was uniformly solidified and adhered on the test substrate. However, the result of magnified observation of the joints in the destructive inspection shows that complete bonding at the electrode portion of the substrate was not obtained, and the effect of wetting on the substrate electrode by cream solder and the effect of solder fusion bonding are extremely preferable. It was confirmed that.

Tables 1 and 2 show the composition contents, curing conditions, and characteristics before and after curing of Examples 1 to 9 and Examples 10 to 13 described above. In addition, the aspect ratio with respect to the average particle diameter of the filler used was set to within 1: 1.5.

[0021]

[Table 1]

[0022]

[Table 2]

Comparative tests were conducted on the fixing strength and contact resistance of the conductive bonding agents in Examples 1 to 12 of the present invention. 212
The five-chip component was bonded to the substrate according to the normal standard operation to form a bonded test piece. Immediately after bonding, the thermal shock test conditions (-55
° C / 15min, + 125 ° C / 15min, room temperature 5 between each
min, 250, 500, 750, 1
After 000 cycles, the adhesive strength (bonding strength: MPa) and the contact resistance (mΩ) were measured. The bonding test piece was placed in a high humidity environment (humidity condition: 85 ° C., 85 parts by weight (parts)).
RH), adhesion strength (MPa) and contact resistance (mΩ) after exposure for 250, 500, 750 and 1000 hours. Tables 3 and 4 show the measured values. FIGS. 1 to 4 show the results displayed on a bar graph in order to easily grasp the attenuation state of the measured values.

[0024]

[Table 3]

[0025]

[Table 4]

The viscosity was measured by a standard kinematic viscometer (Toki Sangyo RB80 type) with a measuring volume of 3 ml and a measuring temperature of 2.
The measurement was performed at 5 ± 0.3 ° C. under a rotation condition of 20 rpm × 3 min. The adhesion strength was measured by applying a metal mask with a thickness of 150 μm to one side of a 100 mm × 40 mm glass epoxy board, mounting a 2125 chip capacitor as standard with a chip mounter, and then heating and curing it under specified conditions. A sample was used. The measurement was performed by applying a pressure at a pressing speed of 23 mm / min using a bonding strength tester, and taking the load MPa at the time of breaking and breaking as the bonding strength.

The contact resistance was measured by using a glass epoxy substrate having the same adhesion strength as described above, applying a sample with a thickness of 4 mmφ × 150 μm over a land at the center of the substrate, and heating and curing it under predetermined conditions. A test sample was used. The contact resistance (mΩ) was measured at a distance of 50 mm between the electrodes using a digital multimeter (Advantest).

As apparent from FIGS. 1 and 3, Comparative Example 1
Compared to (cream solder-free conductive bonding agent), the contact resistance value (mΩ) of any of the examples of the present invention is as low as about 30 to 50 parts by weight (parts). It shows a sufficient value. This is in agreement with the above-mentioned observation result of the bonding state, and it can be seen that the present invention in which cream solder is used and kneaded together has a considerable difference in contact resistance as compared with the conventional conductive adhesive. The difference in the filler composition, the difference in the filler of the cream solder, the difference in the amount of the cream solder to be kneaded with the conductive adhesive and the like in the examples are not significantly different in the range of the present example, and all are suitable for practical use. That is, regardless of the content of the cream solder to be kneaded, the present invention is characterized in that an extremely large effect can be expected by adding cream solder to a certain degree.

On the other hand, the bonding strength is not necessarily superior to the comparative example, but all of the required bonding strength levels are satisfied, so that there is no practical problem. Examples 6 and 7 (conductive fillers: silver filler, copper filler, nickel filler) have a low and stable attenuation rate by a thermal shock test and a humidity resistance test, and thus may be suitable for long-term use.

From the results of Examples 2 to 12, the conductive bonding agent obtained by adding the resin-based cream solder to the conductive adhesive causes good solder wettability to the substrate electrode and the component electrode, and The conductive effect is enhanced by partial wetting with the filler of the conductive adhesive, and the conductive effect is increased. It was confirmed that a remarkable effect on deterioration was exhibited. In addition, due to the synergistic effect with cream solder, the degree of freedom in selecting fillers is extremely large as compared with the case of using a conductive adhesive alone, and it is possible to restrict the use of expensive fillers, which is extremely economical. . Therefore, the conductive bonding agent of the present invention can provide a bonding method that can increase the degree of freedom in a soldering production line.

[0031]

According to the present invention, a defect of a conventional conductive adhesive which is inexpensive, has excellent conductivity, and has a problem due to the influence of humidity, is used as an adhesive for solder replacement to address the problem of global environmental pollution. , And an excellent bonding method using the conductive bonding agent.

[Brief description of the drawings]

FIG. 1 is a diagram showing the results of a contact resistance test according to an example of the present invention.

FIG. 2 is a view showing a result of an adhesive strength test of an example of the present invention.

FIG. 3 is a diagram showing the results of a contact resistance test according to another example of the present invention.

FIG. 4 is a view showing a result of an adhesive strength test of another example of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05K 3/32 H01L 21/92 621A

Claims (6)

[Claims] 1. A conductive bonding agent comprising a conductive adhesive comprising a conductive filler and a resin binder, and a cream solder based on a resin-based flux. 2. A conductive adhesive comprising a conductive filler and a resin binder, and a tin-bismuth alloy or / and a tin-silver-bismuth alloy filler and a lead-free cream solder based on a resin-based flux. Conductive bonding agent. 3. The conductive bonding agent according to claim 1, wherein the conductive filler is a conductive filler made of at least one of silver, nickel, and copper. 4. The conductive bonding agent according to claim 1, wherein the conductive filler comprises a silver filler and / or a tin alloy filler. 5. The cream solder according to claim 1, wherein the filler is tin-bismuth alloy powder, and the mass ratio of tin to bismuth is 9: 1 to 4: 6. Item 2. The conductive bonding agent according to item 1. 6. A bonding method using the conductive bonding agent according to any one of claims 1 to 5.