JP5760170B2 - Solder paste - Google Patents

Description

  The present invention relates to a solder paste.

  In the field of electronic equipment or circuit formation technology for electronic equipment, so-called cream solder in which solder powder and flux are kneaded is used when electronic components are mounted on a substrate. Generally, the flux used for cream solder is composed of rosins, solvents, activators, thixotropic agents and the like. The above-described flux does not participate in the adhesion of the soldered parts after soldering, and solder bonding is achieved only by melt bonding of solder powder, and the bonding strength strongly depends on the solder bonding area.

  However, as electronic devices have become smaller and lighter in recent years, the mounting density of components has increased and the solder joint area is still becoming narrower, making it difficult to cope with conventional means that ensure joint strength only in the solder joint area. It's getting on.

  At present, a tin-bismuth eutectic solder is known as a low melting point solder, which has a melting point of 138 ° C. and a mounting temperature of about 160 ° C., and is a material that can lower the mounting temperature. However, this low melting point solder has poor impact resistance at the joint, and it is necessary to reinforce the joint in order to increase the reliability of the joint.

  Therefore, a method has been devised in which an adhesive component is contained in the flux and the bonding strength is improved by the adhesive. For example, Patent Document 1 is an adhesive-containing solder paste in which an adhesive component composed of a thermosetting resin that is a thermosetting resin and a carboxylic acid is contained in a flux. In this method, after soldering, the bonding portion is reinforced by covering the periphery of the solder with an adhesive.

JP 2001-170797

  However, the adhesive is transparent, and it is difficult to visually recognize the location of the adhesive at the joint. As described above, the reinforcement of the joint portion is achieved by covering the solder joint portion with the adhesive, and therefore it is difficult to confirm the reinforcement effect when the adhesive is low in visibility, as intended. It is impossible to detect the occurrence of a defective product such as whether or not the reinforcing effect is obtained and whether the adhesive flows and the sufficient reinforcing effect cannot be obtained.

  Therefore, a means to improve the visibility of the adhesive by adding colorants such as pigments and dyes in the flux can be considered, but these components are used because they adversely affect the cohesiveness and printability of solder. I can't.

  This invention solves such a conventional subject, and it aims at providing the solder paste which improved the visibility of the reinforcement location of the junction part by an adhesive agent.

In order to achieve the above object, the first present invention provides:
A solder composed of Sn with a Bi content of 15 to 65 wt%,
An adhesive resin which is an epoxy resin;
A curing agent;
A solder paste containing a first activator that is a hydroxycarboxylic acid and a second activator that is an aliphatic dicarboxylic acid that form an unsaturated bond that forms a conjugated system with a carboxyl group at a soldering temperature .

The second aspect of the present invention
When the content of the first activator is A (parts by weight) and the content of the second activator is B (parts by weight), 0.5 ≦ A ≦ 3.0 and 100 parts by weight of the solder The solder paste according to the first aspect of the present invention satisfies 1.0 ≦ B ≦ 3.5 and 1.5 ≦ (A + B) ≦ 4.0.

The third aspect of the present invention
The solder paste of the first or second aspect of the present invention, wherein the first active agent is citric acid and the second active agent is glutaric acid.

The fourth aspect of the present invention is
The solder is 42Sn-58Bi,
The solder paste according to the second or third aspect of the present invention, wherein the epoxy resin is 10 parts by weight and the curing agent is 5 parts by weight with respect to 100 parts by weight of the solder.

  Thereby, the solder paste of the present invention has, for example, a solder composed of Sn and Bi, an epoxy resin and its curing agent as an adhesive in the flux, and a melting point of 2 to 40 ° C. as an activator than the low melting point solder. It is composed of a hydroxycarboxylic acid that generates an unsaturated bond that forms a conjugated system with a carboxyl group by intramolecular dehydration at a soldering temperature, and an aliphatic dicarboxylic acid that similarly has a lower melting point than solder. By this structure, the visibility of the reinforcement location by the adhesive agent of a junction part can be improved, and the detection of inferior goods can be made easy.

  As mentioned above, according to the solder paste of this invention, the visibility of the reinforcement location by the adhesive agent of a junction part can be improved, and the detection of inferior goods can be made easy.

(A)-(c): Sectional drawing which represented typically the process of mounting a chip resistor using the solder paste which concerns on this invention.

  Hereinafter, an embodiment of the solder paste of the present invention and a mounting structure using the same will be described.

  The adhesive-containing solder paste of the present embodiment is composed of a solder composed of tin and bismuth, two activators belonging to the following (a) and (b) having a melting point 2 to 40 ° C. lower than the melting point of the solder, It is comprised by the epoxy resin which is an agent component, and its hardening | curing agent.

  (a) The first activator is a hydroxycarboxylic acid that forms an unsaturated bond that forms a conjugated system with a carboxyl group at the soldering temperature.

  (b) The second activator is an aliphatic dicarboxylic acid.

  Examples of the hydroxycarboxylic acid belonging to the above (a) include citric acid, isocitric acid, malic acid and the like.

  The hydroxycarboxylic acid belonging to the above (a) has a brownish color due to the formation of a conjugated system with an unsaturated bond formed by an intramolecular dehydration reaction at the soldering temperature. Not only a role but also a role as a colorant is expressed. Furthermore, since the affinity with the epoxy resin is also high, the colored carboxylic acid is easily taken into the epoxy resin, and the colored component is easily fixed in the adhesive.

  Examples of the aliphatic dicarboxylic acid belonging to the above (b) include glutaric acid and sebacic acid.

  Aliphatic dicarboxylic acids belonging to (b) above are optimal for supplementing the deficiency in the activity of the hydroxycarboxylic acids belonging to (a) alone, and are effective as coloring effects and cohesiveness, wettability, and solder paste. Necessary for satisfying characteristics such as working time.

As a result obtained from Examples and Comparative Examples described later, the contents of the above two (a) and (b) two activators are based on 100 parts by weight of solder.
(a) The content of the first active agent is 0.5 to 3.0 parts by weight, preferably 0.5 to 1.0 parts by weight,
(b) Content of 2nd active agent is 1.0-3.5 weight part, Preferably, it is 2.0-2.5 weight part.

  However, the total amount ((a) + (b)) of the amount (a) of the first active agent and the amount (b) of the second active agent is 1.5 to 4.0 parts by weight, preferably 2.5 to 3.0. It is characterized by satisfying the weight part.

  Here, if the total amount of the first activator (a) and the second activator (b) is less than 1.5 parts by weight with respect to 100 parts by weight of the solder, the cohesiveness and wettability of the solder will decrease. In addition, the bonding reliability may be reduced. Conversely, if the total amount of the first activator (a) and the second activator (b) exceeds 4.0 parts by weight with respect to 100 parts by weight of solder, the pot life will be shortened, May be restricted.

  Further, if the content of the first activator is less than 0.5 parts by weight with respect to 100 parts by weight of the solder, the coloring effect may not be sufficiently obtained. At the same time, the content of the second activator is relatively lowered, so that the cohesiveness and wettability of the solder are lowered, and the joining reliability may be lowered.

  On the other hand, when the content of the second activator is less than 1.0 part by weight with respect to 100 parts by weight of the solder, the cohesiveness and wettability of the solder are lowered, and the joining reliability may be lowered. On the other hand, if it exceeds 3.5 parts by weight, the pot life is shortened and the usage pattern may be limited.

  Further, the content of Bi in the solder is preferably 15 to 65% by weight, and more preferably 20 to 59% by weight. If the Bi content is 15% by weight, the alloy starts to melt at about 160 ° C. When the Bi content is further increased, the melting start temperature decreases, and when it is 20% by weight or more, the melting start temperature becomes 139 ° C., and at 58% by weight, the eutectic composition is obtained. On the other hand, if the Bi content is less than 15% by weight or exceeds 65% by weight, the effect of lowering the melting point may not be sufficiently obtained.

  The above epoxy resin is mainly a liquid epoxy resin such as bisphenol A type epoxy resin or bisphenol F type epoxy resin, and in order to improve adhesiveness, mechanical strength, heat resistance, etc., biphenyl aralkyl type epoxy resin, Various epoxy resins such as an alicyclic epoxy resin, a dicyclopentadiene type epoxy resin, a naphthalene type epoxy resin, and a polyfunctional epoxy resin can be included.

  In the examples of the present invention, 10 parts by weight of epoxy resin is added to 100 parts by weight of solder powder, but the addition amount can be freely selected as long as the desired viscosity and printed shape can be obtained. Can do.

  As the epoxy resin curing agent, any kind or amount of addition can be used as long as the epoxy resin curing reaction proceeds sufficiently in the soldering process. Examples of the kind include imidazole-based curing agents, amine-based curing agents, and acid curing agents. An anhydride type hardening | curing agent etc. can be illustrated.

  Moreover, the solder paste of this invention may contain the reactive diluent and the thixotropy imparting agent. These are optionally added in order to obtain a desired viscosity and printed shape.

Examples of the present invention and comparative examples are shown below.
Example 1
Here, first, an example of producing an adhesive-containing solder paste, which is an embodiment of the present invention, will be described, and further, an adhesive-containing solder paste will be described with reference to FIGS. 1 (a) to 1 (c). A process of mounting the chip resistor on the substrate will be described.

  I. Spherical particles having a composition of 42Sn-58Bi were used as solder powder. This solder powder has an average particle size of 20 μm and a melting point of 139 ° C.

  Further, as an adhesive component, “E806” manufactured by Japan Epoxy Resin, which is a liquid bisphenol F type epoxy resin, and “EHI-I” manufactured by ADEKA, which is an imidazole-based curing agent, were used.

  The activator is citric acid (melting point: about 100 ° C.) as the above-mentioned first activator hydroxycarboxylic acid, and glutaric acid (melting point: about 99 ° C.) as the aliphatic dicarboxylic acid is the above-mentioned second activator. Was used.

  As a thixotropic agent, “Gelall D” manufactured by Shin Nippon Chemical Co., Ltd. was used.

  The solder paste of the present invention is prepared by preparing a flux and then adding and kneading solder particles therein. Here, the addition amount of the flux component is defined with respect to 100 parts by weight of the solder particles.

  0.1 parts by weight of a thixotropic property-imparting agent was added to 10 parts by weight of the epoxy resin, and the thixotropy-imparting agent was dissolved by heating and stirring at 140 ° C. and allowed to cool to room temperature. Thereto was added 5 parts by weight of an imidazole-based curing agent, 0.5 parts by weight of citric acid, and 2.5 parts by weight of glutaric acid, and kneaded for 20 minutes with a vacuum planetary mixer to obtain a flux.

  100 parts by weight of solder powder was added to the flux and kneaded with a vacuum planetary mixer for 1 hour to obtain an adhesive-containing solder paste.

  II. Next, a process of mounting the chip resistor on the substrate using the adhesive-containing solder paste produced in this way will be described.

  Here, FIG. 1A to FIG. 1C are cross-sectional views schematically showing a process of mounting a chip resistor using an adhesive-containing solder paste.

  This adhesive-containing solder paste 1 is printed on a substrate electrode 3 of a component mounting board 2 through a metal mask (see FIG. 1A), and a 2012 size chip resistor 4 is mounted (FIG. 1B). See), and soldering was performed by passing through a reflow furnace set at 160 ° C. for 6 minutes.

  As a result, the solder particles are melted and integrated into a lump of metal to form a solder joint 6 between the chip resistor 4 and the substrate electrode 3, and the adhesive resin layer 5 that does not contain solder particles is formed around the solder joint 6. A surrounding state was formed. Thereby, the mounting structure represented by the cross-sectional view of FIG. 1C was obtained, and the state where the metal joint was reinforced by the adhesive was observed.

  Furthermore, the adhesive resin layer 5 was colored brown, and the reinforced state could be easily visually confirmed.

  (1) In addition, about the effect of coloration, the mounting structure of a chip resistor is produced as mentioned above, and the joint location is observed visually, and the adhesive resin layer is colored and the presence location is clear. In some cases, ◯ was given, in which the location was unclear, x was given, and ○ was accepted.

  (2) The solder agglomeration test was conducted according to the JIS Z 3284 solder ball test, ranked as follows, and when ◎ and ○ were passed, the adhesive-containing solder paste produced in this example Exhibited class 2 cohesion and met the acceptance criteria.

A: Class 1-2
Y: Class 3
×: Class 4-5
(3) In addition, the solder wettability test was conducted according to the JIS Z 3197 solder spread test, ranked as follows, and when ◎ and ○ were passed, the adhesive-containing solder paste produced in this example Exhibited 88% wettability and satisfied the acceptance criteria.

◎: 85% or more ○: 80% or more and less than 85% ×: Less than 80% (4) Solder working time test is performed by screen printer, squeegee speed 40mm / sec, squeegee moving distance 200mm, every reciprocation In a cycle of minutes, the adhesive-containing solder paste is continuously rolled for 24 hours on a blinded metal mask, and JIS Z 3284 printability test is performed on the material that was initially rolled for 4 hours, 8 hours, and 24 hours. Conducted according to the flow property test, ranked as follows, and ◎, ○ passed, the adhesive-containing solder paste prepared in this example was 24 hours from the beginning in both the printability test and the flow property test There was no change in the evaluation results across the board, which satisfied the acceptance criteria.

A: Initial evaluation result is maintained for 24 hours. O: Initial evaluation result is maintained for 8 hours. X: Initial evaluation result cannot be maintained for 8 hours. Next, other examples will be described.
(Examples 2 to 10)
As in Example 1, citric acid was used as the hydroxycarboxylic acid as the first activator and glutaric acid was used as the aliphatic dicarboxylic acid as the second activator, and the blending ratio (weight ratio) is shown in Table 1. By changing as shown, an adhesive-containing solder paste was prepared and evaluated in the same procedure as in Example 1, and the results are shown in Table 1.

（実施例１１〜１８）
ここでは、実施例１〜８で用いた第１の活性剤のヒドロキシカルボン酸であるクエン酸を、イソクエン酸（融点約105℃）に置き換えたフラックスおよび接着剤含有はんだペーストを作製した。

(Examples 11 to 18)
Here, a flux and adhesive-containing solder paste was prepared by replacing citric acid, which is the hydroxycarboxylic acid of the first activator used in Examples 1 to 8, with isocitric acid (melting point: about 105 ° C.).

  An adhesive-containing solder paste was prepared in the same procedure as in Example 1 and evaluated. The results are shown in Table 2.

（比較例１〜１３）
ここでは、比較例を説明する。

(Comparative Examples 1 to 13)
Here, a comparative example will be described.

  As in Example 1, citric acid was used as the hydroxycarboxylic acid as the first activator and glutaric acid was used as the aliphatic dicarboxylic acid as the second activator, and the blending ratio (weight ratio) is shown in Table 3. The comparative examples 1-13 changed as shown are shown.

  In these comparative examples, an adhesive-containing solder paste was prepared and evaluated in the same procedure as in Example 1, and the results are shown in Table 3.

次に、上記の実施例および比較例の結果について考察する。

Next, the results of the above examples and comparative examples will be considered.

  (1) When focusing on the effect of coloration and comparing Examples 1 to 10 and Comparative Examples 1 to 13, the material having a citric acid amount (a) of 0.5 to 3.2 parts by weight satisfies the acceptance criteria, while 0.3 to It was found that 0.4 weight part (Comparative Examples 1 to 3) could not satisfy the acceptance criteria.

  Further, when Examples 6, 9, 10 and Comparative Example 2 are compared, it is considered that the coloration effect depends only on the citric acid amount (a) regardless of the glutaric acid amount (b).

  From the above, it was found that the amount of citric acid (a) is required to be 0.5 parts by weight or more in order for the coloring effect to satisfy the acceptance criteria.

  (2) Focusing on cohesion and wettability, comparing Examples 1 to 10 with Comparative Examples 1 to 13, the material having a glutaric acid content (b) of 1.0 to 3.7 parts by weight satisfies the acceptance criteria, while 0.8 It was found that in the parts by weight (Comparative Examples 4, 6, 8, 9, 12), it was not possible to satisfy the acceptance criteria of either or both of cohesiveness and wettability.

  Further, from Examples 1, 6, 8 and Comparative Examples 4, 6, 8, 9, 12, the contribution of citric acid amount (a) to the cohesiveness and wettability of solder is small, and the contribution of glutaric acid amount (b). Is considered large.

  From the above, it was found that the amount of glutaric acid (b) is required to be 1.0 part by weight or more in order to meet the acceptance criteria for solder cohesion and wettability. Further, if the amount of glutaric acid (b) is 2.0 parts by weight or more, except for Comparative Example 1 in which the amount of citric acid (a) is less than 0.5 parts by weight, both the wettability and the cohesiveness satisfy the criterion ◎. It has been found that more favorable results can be obtained.

  (3) Focusing on the pot life, when comparing Examples 1 to 10 and Comparative Examples 1 to 13, the total amount (a) + (b) of the citric acid amount (a) and the glutaric acid amount (b) is 1.3 to While 4.0 parts by weight of the material satisfied the acceptance criterion, it was found that 4.2 parts by weight of the material (Comparative Examples 5, 7, 10, 11, 13) could not satisfy the acceptance criterion.

  This is thought to be due to the change in characteristics caused by the reaction of citric acid and glutaric acid with solder particles and epoxy resin.

  When Examples 2 to 4 and Comparative Examples 5, 7, 10, 11, and 13 were compared, the total amount (a) + (b) was found regardless of the ratio of the amount of citric acid (a) to the amount of glutaric acid (b). If it is 4.0 parts by weight, it will meet the acceptance criteria for pot life, but if it is 4.2 parts by weight or more, it will be understood that the acceptance criteria for pot life cannot be satisfied.

  From the above, in order to satisfy the acceptance criteria for pot life, the total amount (a) + (b) of the citric acid amount (a) and the glutaric acid amount (b) needs to be 4.0 parts by weight or less. I understood it. Furthermore, it was found that if it is 3.0 parts by weight or less, the criteria for determining the pot life is satisfied, and more preferable results are obtained.

  (4) Further, from Examples 11 to 18, even when citric acid, which is the hydroxycarboxylic acid of the first activator, is replaced with isocitric acid, the same coloring effect as when citric acid is used, cohesion, Results showing wettability and pot life were obtained. From this, malic acid (melting point: about 100 ° C.), which is a hydroxycarboxylic acid that generates an unsaturated bond that forms a conjugated system with a carboxyl group by intramolecular dehydration at the soldering temperature, is used as the first activator. It can be assumed that the same effect can be obtained.

  The above results are summarized as follows.

That is, for 100 parts by weight of solder particles, 1) the amount of the first activator (a) is 0.5 parts by weight or more in order for the coloration effect to satisfy the acceptance criteria,
2) The amount of the second active agent (b) is 1.0 part by weight or more in order that the cohesiveness and wettability satisfy the acceptance criteria,
3) The total amount (a) + (b) of the first activator and the second activator is 4.0 parts by weight or less in order to satisfy the pass standard.

  In the adhesive-containing solder paste that satisfies the following three conditions, that is, 0.5 ≦ (a) ≦ 3.0 and 1.0 ≦ (b) ≦ 3.5 and 1.5 ≦ (a) + (b) ≦ 4.0, coloring effect, wettability It has been found that all the acceptance criteria for cohesiveness and pot life are satisfied. Furthermore, when 0.5 ≦ (a) ≦ 1.0 and 2.0 ≦ (b) ≦ 2.5 and 2.5 ≦ (a) + (b) ≦ 3.0, the wettability, cohesiveness, and pot life may be more preferable. all right.

  In addition, although the case where Sn58Bi was used as a solder was demonstrated in the said embodiment, even if it is not only this but a solder of Sn57Bi1Ag composition, the same effect as the above is exhibited.

  Moreover, although the case where the 1st and 2nd activator was used was demonstrated in the said embodiment, it is not restricted to this, For example, you may add levulinic acid, a succinic acid, etc. as an auxiliary activator.

  Moreover, although the case where aliphatic dicarboxylic acid was used as a 2nd active agent was demonstrated in the said embodiment, it is not restricted to this, For example, even if it uses a rosin (abietic acid derivative) as a 2nd active agent. good.

  Moreover, in the said embodiment, although the case where an epoxy resin was used was demonstrated as an example of resin for adhesive agents, it is not restricted to this, For example, thermosetting resins, such as a phenol resin, a polyimide resin, a polyurethane resin, or a melamine resin May be used.

  The solder paste of the present invention has an effect that the visibility of the reinforced part by the adhesive at the joint can be enhanced and the detection of defective products can be facilitated, and is useful as a solder paste for component mounting. is there.

DESCRIPTION OF SYMBOLS 1 Adhesive-containing solder paste 2 Component mounting board 3 Board electrode 4 Chip resistor 5 Adhesive resin layer 6 Solder joint

Claims (4)

A solder composed of Sn with a Bi content of 15 to 65 wt%,
An adhesive resin which is an epoxy resin;
A curing agent;
A solder paste comprising a first activator that is a hydroxycarboxylic acid and a second activator that is an aliphatic dicarboxylic acid that form an unsaturated bond that forms a conjugated system with a carboxyl group at a soldering temperature . When the content of the first activator is A (parts by weight) and the content of the second activator is B (parts by weight), 0.5 ≦ A ≦ 3.0 and 100 parts by weight of the solder 1.0 ≦ B ≦ 3.5 and 1.5 ≦ (A + B)
The solder paste according to claim 1, wherein ≦ 4.0 is satisfied.   The solder paste according to claim 1 or 2, wherein the first activator is citric acid and the second activator is glutaric acid. The solder is 42Sn-58Bi,
The solder paste according to claim 2 or 3, wherein the epoxy resin is 10 parts by weight and the curing agent is 5 parts by weight with respect to 100 parts by weight of the solder.

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