JPH0368553B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention involves forming a conductive circuit on an insulating substrate using a conductive paste that can be soldered, and curing the coating film of the circuit by heating. Related to a method of forming a printed circuit with improved heat resistance, moisture resistance, and conductivity by applying flux to a coating film and directly bonding with tin or solder (prior art) Recently, IC, MSI, LSI, etc. Various methods have been proposed for forming conductive circuits that implement . This method can be roughly divided into the following two methods. In other words, in the etched oil method, after each reactive resin is applied onto a copper clad laminate, a mask is applied and a prescribed conductive circuit is formed by light irradiation, the unreacted resin is removed, and then the copper foil is etched. This is a method of removing layers. This method is suitable for mass production of printed circuits on insulating substrates, but the process is complicated and takes a long time.
In addition, the equipment costs are large and side etching occurs during the chemical etching process for circuit formation, which poses a problem in forming fine and precise printed circuits. In the additive method, an adhesive containing active species that form plating nuclei is applied onto an insulating substrate, a mask is placed on top of the coating, and light is irradiated at a predetermined position, and the irradiated area is exposed to the metal that will form the plating nucleus. to break out,
Then, the unreacted portion is removed, and an electroless copper plating layer is formed on the deposited metal to form a predetermined conductive circuit. Although this method allows the formation of thin wire circuits, it is difficult to uniformly disperse the active species in the adhesive, making it impossible to form uniform metal plating nuclei, which may cause trouble in the next plating process. There are also problems such as impurities mixed into the adhesive causing abnormalities in the radical reactions that occur upon irradiation with light. On the other hand, a method of forming a printed circuit using a conductive paste containing metal powder such as silver or copper and resin has been used. This is because it is simpler and more cost-effective than the method of forming a printed circuit by chemically etching excess copper foil from the etched foil copper clad laminate. For example, there is a method of forming a conductive circuit on an insulating substrate by screen printing a silver paste with a specific resistance of 10 ^-4 Ω·cm, which is made of silver powder and phenolic resin.
However, this silver paste is used as a material for forming a conductive circuit, and the soldering necessary for fixing electronic components cannot be directly applied to the conductive circuit obtained. In addition, silver paste is expensive, and when a DC voltage is applied to a printed circuit in a humid atmosphere, silver migration occurs, causing an accident that shorts the circuit, so it is used in specific locations. That is the reality. Next, a conductive copper paste made of copper powder and a thermosetting resin is used to form a conductive circuit on an insulating substrate using a screen printing method, etc., and the coating film is heated and cured. Therefore, oxygen contained in the air and in the binder resin combines with the copper powder, forming an oxide film on its surface and significantly inhibiting conductivity, or completely losing conductivity over time. For this reason, various studies have been conducted on copper pastes that have stable conductivity, and because the conductivity can be approximately 10 ^-3 Ω·cm, they are used as materials for forming conductive circuits. However, there is a problem in that soldering cannot be directly applied to the coating film on the resulting conductive circuit. (Problems to be Solved by the Invention) Soldering on a copper foil on which a printed circuit is formed from a copper-clad laminate by the etched foil method is carried out in the following steps. In other words, the surface of the copper-clad laminate that forms the printed circuit is contaminated with various foreign substances during the manufacturing process and the shipping process, so after surface treatment is performed in advance, electroless copper plating is applied to the copper foil. Then electrolytic copper plating is applied to the printed circuit process, and flux is applied and soldered in the solder leveler process. Next, since soldering cannot be directly applied to conductive circuits formed using known conductive pastes as described above, the coating film of the circuit must be activated and then electroless copper plated or painted. After electrolytic copper plating is performed in a plating solution using the film as a cathode, soldering is performed on the copper surface. After that, electronic components and lead frames to be mounted are soldered. In such case,
Needless to say, it cannot be put to practical use unless the bond between the coating film and the copper plating is reliable. In order to form a soldering base for printed circuits manufactured by either method, a chemical plating method and/or an electroplating method is employed. Therefore, if a solderable conductive paint that does not require electroless copper plating or/and electrolytic copper plating is developed, the manufacturing process will be greatly shortened and the economic benefits will be significant. . The problems that a solderable conductive paint should have are that it can be applied by screen printing, intaglio printing, brushing and spray painting, it can form fine line circuits, and it has good adhesion of the paint film to the insulating substrate. , it has electrical conductivity equivalent to that of silver paste, it has excellent solderability on a coating film, and the electrical conductivity of the conductive circuit of the solder coat can be maintained over a long period of time. SUMMARY OF THE INVENTION The present invention aims to solve these problems and provides a method for forming a printed circuit using a solderable conductive paint that has the above-mentioned problems. (Means for Solving the Problems) As a result of intensive studies to impart solderability to a conductive paint containing metallic copper powder, the present inventors discovered that a conductive paint that has excellent conductivity and can be soldered. Patent Application No. 61-75302 (Patent Publication No. 2-48184), Japanese Patent Application No. 75303 (Patent Publication No. 2-48185), and Japanese Patent Application No. 95809 (Patent Publication No. 2-48186) The present invention was completed based on the application. The present invention provides () metallic copper powder, () resin mixture (resin mixture consisting of P-tert-butylphenol resin, metal surface activated resin, and thermosetting resin), () saturated fatty acid or unsaturated fatty acid. or a metal salt thereof, () a metal chelate forming agent, or () a metallic copper powder, () a thermosetting resin, () a saturated fatty acid or an unsaturated fatty acid or a metal salt thereof, () a metal chelate forming agent, () Soldering accelerator, or () metallic copper powder, () resin mixture (resin mixture consisting of metal surface activated resin and thermosetting resin), () saturated fatty acid or unsaturated fatty acid or their metal salt, A solderable conductive paint containing specific amounts of () a metal chelate forming agent and () a soldering accelerator as described below is printed on an insulating substrate, and then the resulting conductive circuit coating is cured by heating. After that, a printed circuit is formed by applying flux to the coating film and directly applying tin or soldering. Next, the types and blending ratios of the metallic copper powder, resin, additives, etc. used in the present invention will be explained below. Here, the metallic copper powder used in the present invention may have any shape such as flake, dendritic, spherical, or irregular shape, and its particle size is preferably 100 μm or less, particularly 1 to 30 μm. preferable. The P-tert-butylphenol resin used in the present invention is obtained by heating and polymerizing P-tert-butylphenol and formalin in the presence of an alkaline catalyst, and the resin used has a degree of polymerization of 50 or less. It is preferable. For example, if a polymer with a degree of polymerization exceeding 50 is used and the resulting coating film is cured by heating, the formation of a three-dimensional network structure of the thermosetting resin as a binder will be inhibited, resulting in a decrease in electrical conductivity. The metal surface-activated resin used in the present invention is selected from activated rosin, or modified rosin such as partially hydrogenated rosin, fully hydrogenated rosin, esterified rosin, maleated rosin, disproportionated rosin, and polymerized rosin. Use at least one type. Preferred rosins are active rosins or maleated rosins. The thermosetting resin used in the present invention binds the metallic copper powder and other components in the conductive paint according to the present invention, and is a polymeric substance that is liquid at room temperature and hardens by heating. Any molecular substance may be used, such as phenol, acrylic, epoxy, polyester, xylene resin, etc., but is not limited thereto. Among them, resol type phenolic resins are preferably used. The saturated fatty acids, unsaturated fatty acids, or metal salts thereof used in the present invention are saturated resin acids such as palmitic acid, stearic acid, arachidic acid, etc. having 16 to 20 carbon atoms, or unsaturated fatty acids such as palmitic acid, stearic acid, arachidic acid, etc. Zomarinic acid, olenic acid, linolenic acid, etc. having 16 to 18 carbon atoms, and their metal salts include salts with metals such as potassium, copper, and aluminum. The use of a dispersant of these saturated fatty acids, unsaturated fatty acids, or metal salts thereof is preferable because it promotes fine dispersion of the metallic copper powder into the thermosetting fat and forms a coating film with good electrical conductivity. The metal chelate forming agent used in the present invention is at least one selected from aliphatic amines such as monoethanolamine, diethanolamine, triethanolamine, ethylenediamine, triethylenediamine, and triethylenetetramine. The metal chelate forming agent added prevents oxidation of the metal copper powder, contributes to maintaining conductivity, and exhibits a synergistic effect with the metal surface activating resin to further improve solderability. The soldering accelerator used in the present invention is oxydicarboxylic acid, aminodicarboxylic acid, or a metal salt thereof. For example, at least one selected from tartaric acid, malic acid, glutamic acid, aspartic acid, or a metal salt thereof is used. do. The added soldering promoter exhibits a synergistic effect with the metal chelate forming agent to further improve solderability. In other words, by disposing a metal surface activating resin, a metal chelate forming agent, and a soldering accelerator, it is possible to exhibit a synergistic effect and make the soldering surface of the coating film smoother and with a metallic luster. can. In the conductive paint according to the present invention, a conventional organic solvent can be appropriately used to adjust the viscosity. For example, known solvents such as butyl carbitol, butyl carbitol acetate, butyl cellolsolve, methyl isobutyl ketone, toluene, xylene and the like are preferred. The insulating substrates used in the present invention include glass/epoxy resin substrates, paper/phenol resin substrates, ceramic substrates, polycarbonate resin substrates, polyethylene terephthalate resin substrates, polyimide resin substrates, polyolefin resin substrates, vinyl chloride resin substrates, and polyester. Resin substrate, ABS
Resin substrate, polymethyl methacrylate resin substrate,
Examples include, but are not limited to, melamine resin substrates, phenol resin substrates, epoxy resin substrates, glass substrates, and the like. The method of forming a conductive circuit on an insulating substrate using the solderable conductive paint according to the present invention is to apply it by screen printing, intaglio printing, spraying, or brushing, and then heat and harden it, and there are no particular limitations. Not done. The atmosphere in which the coating film of the conductive circuit formed in the present invention is cured may be in the atmosphere or in an inert gas, and is not restricted. In the present invention, the method of applying tin or solder to the heat-cured conductive circuit coating is the usual dipping method in which a commercially available organic acid-based flux agent is applied onto the coating and soldering is performed on the copper surface. Alternatively, it may be performed using a soldering iron, and is not particularly limited. The proportions of the components constituting the solderable conductive paint according to the present invention are () 85 to 95% by weight of metallic copper powder and () 15 to 5% by weight of resin mixture (2 to 30% by weight of P-tert-butylphenol resin). % by weight, a resin mixture consisting of 2 to 30% by weight of a metal surface activated resin and the remainder a thermosetting resin) for a total of 100 parts by weight,
() 1 to 8 parts by weight of a saturated fatty acid or unsaturated fatty acid or a metal salt thereof; () 1 to 50 parts by weight of a metal chelate forming agent; or () metallic copper powder.
85-95% by weight and () thermosetting resin 15-5% by weight
() 1 to 8 parts by weight of a saturated fatty acid or unsaturated fatty acid or a metal salt thereof, () 1 to 50 parts by weight of a metal chelate forming agent, and () 0.1 to 2.5 parts by weight of a soldering accelerator. Parts by weight, or () 85-95% by weight of metallic copper powder and () 15-5% by weight of resin mixture (resin mixture consisting of 2-30% by weight of metal surface activated resin and the remainder of thermosetting resin)
() 1 to 8 parts by weight of a saturated fatty acid or unsaturated fatty acid or a metal salt thereof, () 1 to 50 parts by weight of a metal chelate forming agent, and () 0.1 to 2.5 parts by weight of a soldering accelerator. Parts by weight. Here, the preferred blending amount of metallic copper powder is:
87 in blends with resin admixtures or thermosetting resins
~93% by weight. The preferred blending amounts of P-tert-butylphenol resin and metal surface activating resin are 5 to 5, respectively.
It is 10% by weight. The preferred amount of the saturated fatty acid or unsaturated fatty acid or metal salt thereof is 2 to 6 parts by weight, the preferred amount of the metal chelate forming agent is 5 to 30 parts by weight, and the preferred amount of the soldering accelerator is 0.5 to 6 parts by weight. It is 2.0 parts by weight. (Function) As explained above, the conductivity of the cured coating film of the conductive circuit formed by the solderable conductive paint used in the present invention is in the 10 ^-4 Ω・cm class, which is an extremely good value. The conductivity is similar to that of the coating film obtained with conventional silver paste. When an organic acid-based flux is applied to the cured coating film of the conductive circuit formed according to the present invention, it is immersed in a molten solder bath and pulled out, good soldering is achieved over the entire surface of the conductive circuit, and its conductivity is This can be improved to the 10 ^-5 Ω・cm class, allowing even larger currents to flow through conductive circuits. Furthermore, when the coating film of the conductive circuit is coated with solder, the heat resistance and heat resistance of the coating film are improved. In addition, in the etched oil method, additive method, and known methods for forming printed circuits using copper paste, the conductive circuit is subjected to electroless copper plating and/or electrolytic copper plating and soldering is performed on the copper surface. In the method of the invention, a conductive circuit is formed on an insulating substrate by screen printing using a solderable conductive paint, and after being heated and cured, flux is applied onto the paint film and soldering is performed directly. This greatly shortens the manufacturing process and has great economic merit. (Examples) Hereinafter, the present invention will be explained in more detail based on Examples and Comparative Examples, but the present invention is not limited only to these Examples. Using dendritic metal copper powder with a particle size of 5 to 10 μm, the first
The materials were mixed in the proportions shown in the table (parts by weight), a small amount of butyl carbitol was added as a solvent, and the mixture was kneaded with a triaxial roll for 20 minutes to prepare a conductive paint. This was printed onto a glass/epoxy resin substrate with a width of 0.4 mm and a thickness of 30 ± 5 μ by screen printing.
m, forming an S-shaped conductive circuit with a length of 520 mm, 150 ~
The coating film was cured by heating at 160°C for 30 minutes. In order to apply soldering on the conductive circuit that was subsequently formed,
The board was passed through a solder leveler machine used in the actual process, immersed in an organic acid flux bath for 4 seconds, and then heated to a 250°C molten solder bath (Pb/Sn=40/
60) Dip it in for 5 seconds and pull it out at the same time.
After blowing hot air at 6 atm and 220 to 230°C, a printed circuit board was prepared by cleaning and soldering the entire conductive circuit. In order to mount electronic components on this circuit board, leaving only the connection circuit parts required for soldering, the other circuit parts are overcoated using thermosetting or ultraviolet curing solder resist ink using a screen printing method. protect printed circuits by
Electronic components were soldered directly or through through-holes to the connected circuit parts. Table 1 shows the results of examining various characteristics of the conductive circuit according to the present invention obtained through the above process. Here, the electrical conductivity of a coating film is a value obtained by measuring the volume resistivity of a heat-cured coating film. The adhesion of the coating film refers to the conductive coating composition shown in Table 1, which is printed onto a glass/epoxy resin substrate using a screen printing method to a thickness of 5cm x 5cm and a thickness of 30±5μ.
After forming a coating film of m and curing the coating film by heating,
According to the grid test method of JIS K5400 (1979),
Draw 11 parallel lines perpendicular to each other on the paint film.
Make cuts in a grid pattern with 100 squares in 1 ^cm2 at intervals of mm, and remove the coating film from above with cellophane tape.The coating film that remains on the insulating substrate. The number of pieces on the grid is calculated. Solderability was evaluated by observing the soldered state on the paint film using a low-magnification stereoscopic microscope and using the following criteria. ◎ mark: Smooth surface with metallic luster and solder adheres to the entire surface ○ mark: The surface is uneven but solder adheres to the entire surface △ mark: Partially exposed coating film Heat resistance and The resistance change rate refers to the soldered coating.
It was heated at 80°C for 1000 hours and the rate of change in resistance relative to the initial resistance was determined. Moisture resistance and resistance change rate refer to the solder coating film at 55℃
It was left in a temperature atmosphere of 95% RH for 1000 hours, and the rate of change in resistance with respect to the initial resistance was determined. Printability refers to the ability to form a conductive circuit using the obtained conductive paint by screen printing.
The printability was observed and evaluated according to the following criteria. ○ mark: Good conductive circuit formation △ mark: Slightly difficult conductive circuit formation As can be seen from the results in Table 1, Comparative Examples 1 to 3
However, Examples 1 to 3 show that none of the characteristics Although it is not shown in Table 1, the thickness of the solder soldered to the coating film is approximately 10 μm, so the conductivity of the soldered printed circuit is on the order of 10 ^-5 Ω cm. improve,
A larger current can be passed through the printed circuit. In addition, the solder strength between the paint film and solder is 3.3 kg or more (3.
mmφ runt, soldering strength of 0.6mmφ solder plated wire in a hole diameter of 0.8mmφ), which ensures that the coating film and solder interface are firmly soldered, and connects circuit parts of electronic components. Soldering to the copper clad laminate is the same as soldering to a copper clad laminate, and both are reliable in practical use. (Effects) In the method for forming a printed circuit according to the present invention, since a conductive circuit is formed on an insulating substrate by screen printing using a solderable conductive paint, a thin wire circuit can be formed, and the resulting conductive circuit can be It is possible to solder directly onto the cured coating, and electronic components can also be soldered onto the soldered printed circuit.
There is no need to perform electroless copper plating and/or electrolytic copper plating on the coating film of copper foil printed circuits or conductive circuits as in the past, and these manufacturing steps can be largely omitted, and it has a significant economic effect. and contribute to industry. 【table】

Claims (1)

[Claims] 1 () 85-95% by weight of metallic copper powder and () 15-5% by weight of resin mixture (2-30% by weight of P-tert-butylphenol resin, 2-30% by weight of metal surface activated resin) 1 to 100 parts by weight of (resin mixture consisting of thermosetting resin and thermosetting resin),
8 parts by weight and () 1 to 50 parts by weight of metal chelate forming agent, or () 85 to 95 weight % of metallic copper powder and () 15 to 5 weight % of thermosetting resin for a total of 100 parts by weight. hand,
() 1 to 8 parts by weight of saturated fatty acids or unsaturated fatty acids or metal salts thereof; () 1 to 50 parts by weight of metal chelate forming agent; and () 0.1 part by weight of soldering accelerator.
~2.5 parts by weight, or () 85-95% by weight of metallic copper powder and () 15-5% by weight of resin mixture (resin mixture consisting of 2-30% by weight of metal surface activated resin and the remainder of thermosetting resin) thing)
() 1 to 8 parts by weight of saturated fatty acids or their metal salts, () 1 to 50 parts by weight of metal chelate forming agent, and () 0.1 to 2.5 parts by weight of soldering accelerator. The solderable conductive paint is printed on an insulating substrate, the resulting conductive circuit coating is heated and cured, and then flux is applied to the coating and soldering is performed directly with tin or solder. Characteristic printed circuit formation method.