JP5198157B2 - Scale-like silver powder for conductive thermosetting paste - Google Patents

Description

  The present invention relates to a scaly silver powder suitable for a conductive paste used for forming a circuit by mounting electronic components, screen printing, or the like, and a method for producing the same.

  Conductive pastes used to form circuits by mounting electronic parts, screen printing, etc. are broadly classified into high-temperature firing types and heat-curing types depending on their applications. Since silver is added, the silver particles are fused to each other, and the resistance is as low as that of bulk silver. The silver powder used for this application is often a spherical silver powder, whereas the heat-curing type cures the resin at a relatively low temperature of about room temperature to 200 ° C., and the resulting silver particles contact each other to provide conductivity. To express. The heat-curing type has higher resistance than the high-temperature firing type, and is expected to have a lower resistance. Therefore, the silver powder used for this purpose is often scaly silver powder. This is because, in the case of scaly silver powder, surface contact can be expected due to its shape, and conduction is easily obtained.

  Until now, heat-curing type pastes have often been used for circuit formation and electrical continuity with materials having poor heat resistance. In addition to these applications, recently, from the viewpoint of reducing environmental impact, there is a trend in the industry from a high temperature firing type that consumes a lot of energy to a heat curing type. In addition, the abolition of lead in solder has been discussed against the background of environmental pollution problems, but conductive adhesives are considered to be a promising candidate as one of the solutions.

Conventionally, the scaly silver powder used in the heat-curing type conductive paste is mechanically pulverized by, for example, a ball mill, a vibration mill, or the like of a spherical silver powder generated by reducing an ammonia complex of silver salt or silver oxide. Have been manufactured. At this time, in order to prevent coarsening of silver particles due to aggregation, substances having the purpose of imparting lubricity, such as fatty acids and metal soaps, have been added to the silver powder that is to be ground.
JP-A-10-183209 JP-A-10-050142 JP 09-096552 A Japanese Patent Laid-Open No. 61-276902

  However, in the above-described conventional technology, the fatty acid added before and / or during pulverization adheres and remains firmly on the surface of the silver powder and is difficult to remove. It has already been known that voids are formed in the coating film as an outgas component at the time of curing, which causes the resistance value to increase, and that the familiarity with the paste resin greatly deteriorates and the paste cannot be kneaded. Further, in the case of metal soap, ion impurity becomes a problem, and it cannot be used as a conductive paste used around ICs that dislike ion contamination.

  One of the uses, conductive adhesives, is a one-pack type pot life (usable time) to improve workability while maintaining basic properties such as low resistance, high adhesive strength, and dimensional stability. There is a need for conductive pastes that are long, preferably storable at room temperature.

  As a result of intensive studies to meet these demands, it has become clear that there is a system in which the reaction between the paste resin and the additive adhering to the surface of the silver powder becomes a problem.

  For example, certain epoxy resin systems and additive fatty acids cause cure inhibition. This is considered to be a reaction between the carboxyl group of the fatty acid and the epoxy group in the epoxy resin. Similarly, it is newly apparent that there are problems with thermosetting resins with certain types of condensation polymerization even when using salts of fatty acids, amines, acid amides, and various coupling agents as additives. It has become.

  It is preferable to deal with this type of problem on the side of the silver powder used as the conductive filler in order to maintain the degree of freedom in paste design.

  As a countermeasure for this, it is ideal that there is no organic deposit on the surface of the silver powder, but there is a problem that the scaling treatment cannot be performed substantially unless a grinding aid is added.

  Accordingly, an object of the present invention is to provide a method for producing a scaly silver powder and a silver powder that have an effect of a grinding aid, do not react with a thermosetting resin, and use an additive having a small amount of ion impurities.

  The scaly silver powder referred to here is, for example, silver powder produced by mechanically pulverizing spherical silver powder produced by reducing a silver salt ammonia complex or silver oxide with a ball mill, vibration mill or the like, and scanning. The shape observed by a scanning electron microscope (SEM) means a dominant silver powder that is processed into a non-spherical shape (for example, a shape that is described as a scale shape, a plate shape, or a flake shape).

  As a result of intensive studies to achieve the above object, the present inventors have added a nonionic surfactant to silver powder, and wet pulverized it in a pulverizing solvent by a pulverizer such as a ball mill, an attritor mill, or a bead mill. If there is no organic substance having a functional group that reacts with the thermosetting resin on the surface and inside of the resulting flaky silver powder, and there is no ion-dissociating organic substance on the surface and inside of the produced flaky silver powder. It has been found that scaly silver powder can be produced and scaly silver powder suitable for a conductive paste is obtained, and the present invention has been achieved. The impregnated component that reacts with the thermosetting resin such as fatty acid remains in the silver powder before pulverization used here, but this is not a problem in the case of a nonionic surfactant. If it says further, it is preferable that surface treatment is not performed at the time of spherical powder reduction | restoration production | generation.

  That is, the present invention firstly has a nonionic surfactant on the surface of the silver powder, and is a flaky silver powder for conductive heat-curing paste; secondly, a nonionic surfactant on the surface of the silver powder. Scale for conductive thermosetting paste, characterized in that there is no organic substance having a functional group that reacts with the thermosetting resin on the surface and inside, and no organic substance that ionically dissociates on the surface and inside. Thirdly, the nonionic surfactant is at least one of polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid ester, polyoxyethylene sorbitan fatty acid ester, and sorbitan fatty acid ester. The scaly silver powder for conductive thermosetting pastes according to the first or second aspect is provided.

  According to the method of the present invention, when a flaky silver powder is produced by pulverizing silver powder, a predetermined amount of a nonionic surfactant is added, and the pulverization treatment is performed by wet pulverization. A scale-like silver powder suitable for a conductive paste used for forming a circuit by mounting an electronic component, screen printing, or the like can be produced without causing curing inhibition with the cured resin.

  In the present invention, by adding a nonionic surfactant to the silver powder, and pulverizing in a wet atmosphere in a pulverizing solvent by a pulverizer such as a ball mill, an attritor mill, a bead mill, etc. It is possible to produce a flaky silver powder that does not contain an organic substance having a functional group that reacts with the resin and that does not have an organic substance that ionically dissociates on the surface and inside of the flaky silver powder that is generated. The silver powder before pulverization used here becomes impossible when an additive that reacts with a thermosetting resin such as a fatty acid remains, but this is not a problem in the case of a nonionic surfactant. If it says further, it is preferable that surface treatment is not performed at the time of spherical powder reduction | restoration production | generation.

  Embodiments of the present invention will be described below.

  The nonionic surfactant used in the present invention is preferably at least one of polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene fatty acid ester, polyoxyethylene sorbitan fatty acid ester, and sorbitan fatty acid ester. .

  The nonionic surfactant used in the present invention does not have a functional group that reacts with the thermosetting resin, and consequently does not inhibit the curing of the resin. The term “curing inhibition” here refers to all phenomena that are contrary to the intended use of the paste. Specifically, 1) Curing starts when the paste is kneaded, viscosity rises and cannot be made into a paste, 2) Unexpected curing when the pot life is very short and curing starts during storage. And 3) includes any case where the material does not cure even when heated. Moreover, since it does not have a functional group capable of ion dissociation, it cannot be a cause of ion impurity.

  There are other additives that do not have a functional group that reacts with the thermosetting resin, and that do not have a functional group that ionically dissociates. In view of ease of removal, nonionic surfactants are most effective. For example, hydrocarbons such as ethylene wax and liquid paraffin are very difficult to control at the time of scaling.

  The pulverization may be performed in a solvent and a wet atmosphere using a ball mill, an attritor mill, a bead mill or the like. As the grinding solvent, water or an organic solvent can be used, and in particular, water, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 3 -At least one of pentanol, dimethyl ketone, diethyl ketone, diethyl ether, dimethyl ether, diphenyl ether, toluene and xylene is preferred.

  In general, it is specified that nonionic surfactants are present between HLB values 0 to 20, which indicate the hydrophilic lipophilic balance of the surfactant. In the present invention, those having an HLB value of 0.1 to 20 can be arbitrarily used according to the characteristics of the grinding solvent. That is, when the grinding solvent is water, the HLB value is preferably 6 to 20, more preferably 8 to 20. If it is less than 6, it is not suitable for water and is not suitable. On the other hand, when the grinding solvent is an organic solvent such as alcohol, those having an HLB value of preferably 0.1 to 6, more preferably 0.1 to 4 can be used. When no hydrophilic group is possessed, the HLB value is 0, which is unsuitable as an additive during the sizing process of silver powder (for example, hydrocarbons such as ethylene wax and liquid paraffin). On the other hand, when the ratio is larger than 6, aggregation is likely to occur during the scaly treatment, which is not suitable.

  The nonionic surfactant is added to the silver powder and / or the grinding solvent during the production of the scaly silver powder, before the grinding and / or during the grinding. The addition may be performed only once or twice or more. When the addition is performed twice or more, the kind of the nonionic surfactant may be the same or different, but it is added to the silver powder in advance before pulverization. Is particularly preferred. This is because if the pulverization is started without adding in advance, the silver particles aggregate and are easily coarsened. Further, the silver powder before pulverization is preferably not subjected to a surface treatment at the time of reducing the spherical powder, but in the case of the nonionic surfactant, it can be used without any problem.

  The addition amount of the nonionic surfactant is 0.1% by weight to 50% by weight, preferably 0.1% by weight to 25% by weight, based on the weight of the silver powder before pulverization. This is because when the amount is less than 0.1% by weight, the particles tend to aggregate, and even when the amount is more than 50% by weight, no significant difference is observed.

  In the present invention, there is no organic substance having a functional group that reacts with the thermosetting resin on the surface and inside of the generated flaky silver powder, and there is no organic substance ion-dissociated on the surface and inside of the generated flaky silver powder. not exist.

  As described above in detail, the flaky silver powder of the present invention increases the degree of freedom of resin selection during paste preparation because there is no reaction with the thermosetting resin, and in particular, the paste pot caused by the additive Solve the problem of shortening life.

  Further, it can be used around ICs in which ion impurities are small and ion contamination is a problem. Furthermore, the conductivity was also good.

  Hereinafter, although an example and a comparative example explain concretely, the range of the present invention is not limited by these.

[Example 1]
Add 1% by weight of Neugen ET190 (Daiichi Kogyo Seiyaku Co., Ltd. nonionic surfactant HLB value = 19) to 600 g of additive-free spherical silver powder. After premixing, add 400 ml of pure water. The pulverization was performed with an 5.25 kg SUS ball in an attritor mill for 40 minutes. The pulverized slurry was separated from SUS balls, and solid-liquid separation was performed by suction filtration, followed by vacuum drying at 70 ° C. for 20 hours. The obtained dried product was crushed with a small pulverizer. The scaly silver powder thus obtained did not cause curing inhibition with the thermosetting resin and had good conductivity.

[Example 2]
Grinding was performed under the same conditions as in Example 1 except that the addition amount was 20% by weight.

  The scaly silver powder thus obtained did not cause curing inhibition with the thermosetting resin and had good conductivity.

Example 3
Grinding was carried out under the same conditions as in Example 1 except that Neugen EA120 (Daiichi Kogyo Seiyaku Co., Ltd. nonionic surfactant HLB value = 12) was used as the additive. The scaly silver powder thus obtained did not cause curing inhibition with the thermosetting resin and had good conductivity.

Example 4
Grinding was performed under the same conditions as in Example 3 except that the amount added was 10 wt%.

  The scaly silver powder thus obtained did not cause curing inhibition with the thermosetting resin and had good conductivity.

Example 5
Grinding was performed under the same conditions as in Example 1 except that Neugen ES99 (Daiichi Kogyo Seiyaku Co., Ltd., nonionic surfactant, HLB value = 9) was used as the additive. The scaly silver powder thus obtained did not cause curing inhibition with the thermosetting resin and had good conductivity.

Example 6
Grinding was carried out under the same conditions as in Example 1 except that the additive was Neugen ET80E (Daiichi Kogyo Seiyaku Co., Ltd., nonionic surfactant, HLB value = 8). The scaly silver powder thus obtained did not cause curing inhibition with the thermosetting resin and had good conductivity.

Example 7
5% by weight of Neugen EA33 (Daiichi Kogyo Seiyaku Co., Ltd. nonionic surfactant HLB value = 4) is added to 600 g of additive-free spherical silver powder. After pre-mixing, 400 ml of ethanol (Wako Pure) In the reagent grade 1), pulverization was performed for 60 minutes with an 5.25 kg SUS ball in an attritor mill. The pulverized slurry was separated from SUS balls, and solid-liquid separation was performed by suction filtration, followed by vacuum drying at 70 ° C. for 20 hours. The obtained dried product was crushed with a small pulverizer. The scaly silver powder thus obtained did not cause curing inhibition with the thermosetting resin and had good conductivity.

Example 8
Grinding was carried out under the same conditions as in Example 7 except that Neugen ET60E (Daiichi Kogyo Seiyaku Co., Ltd., nonionic surfactant HLB value = 6) was used as the additive. The scaly silver powder thus obtained did not cause curing inhibition with the thermosetting resin and had good conductivity.

Example 9
Grinding was performed under the same conditions as in Example 7, except that the additive was Sorgen 30 (Daiichi Kogyo Seiyaku Co., Ltd., nonionic surfactant, HLB value = 3.7). The scaly silver powder thus obtained did not cause curing inhibition with the thermosetting resin and had good conductivity.

[Comparative Example 1]
Grinding was carried out under the same conditions as in Example 1 except that spherical silver powder with oleic acid attached to the surface was used and the grinding solvent was changed to ethanol (Wako Pure Chemicals Reagent Grade 1). The scaly silver powder thus obtained caused curing inhibition with the thermosetting resin.

[Comparative Example 2]
Grinding was carried out under the same conditions as in Example 7 except that the additive was changed to oleic acid (Wako Pure Chemicals Reagent Special Grade). The scaly silver powder thus obtained caused curing inhibition with the thermosetting resin.

[Comparative Example 3]
Grinding was carried out under the same conditions as in Example 7 except that the additive was changed to stearic acid (Wako Pure Chemicals reagent special grade). The scaly silver powder thus obtained caused curing inhibition with the thermosetting resin.

Claims (2)

  Nonionic surfactant adheres to the surface of silver powder, there is no organic substance with functional groups that react with thermosetting resin on the surface and inside, and there is no organic substance that ionically dissociates on the surface and inside A scaly silver powder for conductive heat-curing paste. The conductive material according to claim 1 , wherein the nonionic surfactant is at least one of polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene fatty acid ester, polyoxyethylene sorbitan fatty acid ester, and sorbitan fatty acid ester. Scaly silver powder for heat-resistant heat-curing paste.