JPH0280194A - Solder paste - Google Patents

Abstract

PURPOSE:To keep delicate printability of the title paste for a long time without changing its viscosity by mixing solder powder and a liq. thermosetting resin oligomer or a liq. thermoplastic resin in a specified weight ratio to obtain the solder paste. CONSTITUTION:One hundred pts.wt. of solder powder and 5-20 pts.wt. of the liq. thermosetting resin oligomer or liq. thermoplastic resin are mixed to obtain solder paste. The viscosity of the solder paste is not changed while the paste is printed on the conductor of a printed wiring board, and the delicate printability can be kept for a long time. When an electronic circuit is formed using the paste, mounting can be smoothly performed, since the stickiness on the printed solder is not changed.

Description

[Detailed Description of the Invention] [Industrial Field of Application] [Prior Art] In recent years, the number of chip-shaped electronic components installed in electronic circuits without lead wires has been increasing.

Surface mounting (Surrac) is the mounting method for these electronic components.
e Mount). In surface mounting,
Terminals of chip-shaped electronic components are connected to conductor portions of printed wiring boards using paste-like solder. Solder paste is known in the form of a paste made by kneading solder alloy powder and a solution obtained by dissolving rosin in an organic solvent to give it a viscosity that provides suitable printability.

This paste contains organic amine hydrochloride, imidazole,
It is known that so-called activators such as carboxylic acids and viscosity modifiers are added (Japanese Patent Laid-Open No. 60-149
Publication No. 193, Publication No. 61-95797, Special Publication No. 1983
-224491 Publication, JP-A-62-214895 Publication, Electronic Packaging
Technology Sat No. 4.33.
(198B)).

Solder paste is printed on the conductor of a printed wiring board using a silk screen method or a metal mask method, but since conventional solder paste contains a large amount of volatile organic solvent during printing, it may deteriorate over time on the printing plate. The disadvantage was that the viscosity changed and fine printability could not be maintained for a long time. Further, even after printing, the surface of the solder dries over time, making it impossible to obtain good adhesion to the terminals of electronic components.

[Problems to be Solved by the Invention] The present invention provides a circuit that can be smoothly surface-mounted with a solder paste that does not change its viscosity during printing on the conductor of a printed wiring board and does not change the adhesiveness of the printed solder. The purpose is to provide a method for forming.

[Means to solve the problem]

The above-mentioned drawbacks are due to the volatile organic solvent used to dissolve the rosin, and when various liquid, solvent-free thermoplastics were investigated in place of rosin, it was found that liquid thermosetting resins with low curability were found. It has been found that oligomeric or liquid thermoplastic resins are effective.

That is, the present invention provides a solder paste made by kneading 5 to 20 parts by weight of liquid thermosetting resin oligomer or liquid thermoplastic resin with 100 parts by weight of solder alloy powder.

In order to adjust the viscosity of the solder paste of the present invention,
Alternatively, 5 parts by weight or less of an organic solvent may be added to 100 parts by weight of the resin in order to dissolve other additives. Since the organic solvent hardly evaporates due to the affinity between the organic solvent and the resin at room temperature, there is no particular problem even if it is added to this extent.

As the liquid thermosetting resin oligomer used in the present invention, unsaturated polyester resin, epoxy resin, masked polyisocyanate, etc. are preferably used. As the liquid thermoplastic resin, polyols and polyamines are preferably used. These additives are added in an amount of 5 to 20 parts by weight, preferably 8 to 12 parts by weight, per 100 parts by weight of the solder alloy. If it is less than 5 parts by weight, there will be no fluidity and printing will be difficult, and if it exceeds 20 parts by weight, the amount of solder will be small and connection reliability will be poor. A spherical solder alloy of about 200 mesh size is usually used, and the above-mentioned resin is added to this and kneaded using a laikai machine or the like to form a paste. The viscosity of the paste is 1,000 to 10,00
It is determined based on suitability for printing with a silk screen or metal mask between 0 cpsO. Usually 2.000~5
It is preferably between 0.000 cpsO. If necessary, an activator is added to this paste for the molten alloying reaction between the solder and the conductor part (W4 or solder alloy) of the printed wiring board. Various activators are known, but amine hydrochloride, imidazole hydrochloride, carboxylic acid, phosphoric acid, ZnC1zNH, CI, etc. are particularly preferred, and this is 3 parts by weight per 100 parts by weight of the solder alloy. The following amounts are added:

In addition, chicken agents such as hydrogenated castor oil and organic bentonite are also added as paste viscosity modifiers.

[Effect]

Since the paste of the present invention does not contain volatile solvents, the viscosity does not change over time, the surface dries after printing, and electronic components do not come off due to non-adhesion, allowing for smooth mounting work. be. The synthetic resin used in the present invention is one that has not conventionally attracted attention for soldering or was not thought to be useful for soldering, and was selected from among a large number of resins studied.

〔Example〕

Hereinafter, the present invention will be explained in detail based on Examples, but the present invention is not limited thereto.

(Parts in the following examples represent parts by weight) Example 1 Epicote 828 10 parts (Yuka Shell Co., Ltd. bisphenol A type epoxy resin) Imidazole hydrochloride 0.3 parts Solder powder (300 mesh or less) 87.7 parts ( Pb37%
5n63%) Hardened castor oil 1 part Example 2 Adekal resin BP-6060 (manufactured by Asahi Denka Kogyo ■, polyol) Monomethylamine hydrochloride solder powder (300 mesh or less) (Pb37% 5n63%) Hardened castor oil 10 parts 0.5 part 89.5 parts 1 part Example 3 Hitachi Polyset Resin PS-5110 parts (manufactured by Hitachi Chemical Co., Ltd., unsaturated polyester resin) ZnClx ・NHa
C11 parts Solder powder (300 mesh or less) (Pb 37% 5N63%) Hardened castor oil 88 parts 1 part Comparative example 1 Polymerized rosin 4.7 parts Butyl calpitol 4.3 parts Jetanolamine/HB r 0.04 parts hydrogenated castor oil
0.96 parts powder solder
Cream solder with a composition of 90 parts or more in 4 cases was produced using a Raikai machine and silk screen printed, and the viscosity of Examples 1 to 3 did not change even after being exposed to the atmosphere for 8 hours or more. Although printing and properties were maintained, in the comparative example, printing became impossible after about 30 minutes.

[Effects of the Invention] The solder paste of the present invention does not cause viscosity change during printing on conductors of printed wiring boards, and can maintain fine printability for a long time. Once the circuit is formed, the adhesiveness on the printed solder does not change, allowing for smooth mounting work.

Claims (2)

[Claims] 1. A solder paste made by kneading 5 to 20 parts by weight of a liquid thermosetting resin oligomer or a liquid thermoplastic resin to 100 parts by weight of solder alloy powder. 2. Based on 100 parts by weight of solder alloy powder, 5 to 20 parts by weight of liquid thermosetting resin oligomer or liquid thermoplastic resin and 5 parts by weight or less of amine hydrochloride, imidazole, carboxylic acid, and phosphoric acid selected from A solder paste made by kneading at least one type of compound.