JPH06182586A - Flux for cream solder - Google Patents

Abstract

PURPOSE:To provide a flux for a cream solder not requiring cleaning after soldering in the case of the cream solder (solder paste) used for surface mounting of production of electronic equipment, particularly electronic parts. CONSTITUTION:In the flux for a cream solder containing a rosin and activator, it has a composition constituting of, by a ratio of the activator to total flux quantity, 2.0-20.0wt% diphenyl acetic acid and diethyl amine salt, 1.0-15.0wt.% sebacic acid and 2. 0-20.0wt.% diphenyl acetic acid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a "cream solder (solder paste)" used for manufacturing electronic devices, particularly for surface mounting of electronic parts, and more particularly to a flux for cream solder which enables non-cleaning.

[0002]

2. Description of the Related Art Cream solder is prepared by mixing (kneading) solder fine powder and flux into a cream form, and there are various types (for example, Nobuo Kageyama:
"Current status and usage of cream solder in SMT", Electronic Technology, December 1988 Supplement, pp. 47-53, Takao Ohno: "Fine solder paste and present status", Electronic Technology, December 1988 Supplement, pp. 33-38). Sn / Pb, Sn / Pb / A for solder alloy
g, Sn-based alloys such as Sn / Pb / Bi, In-based alloys such as In / Pb, and Pb-based alloys such as Pb / Ag.
It is pulverized by a gas atomization method or a centrifugal atomization method. Flux is composed of rosin (pine resin) that removes the oxide film on the surface of the base material, a viscous agent that suppresses the separation of solder powder and flux, an activator that promotes solderability, and a solvent that is involved in printability. There is. When using cream solder, since it is applied on the substrate by screen printing or a dispenser, flow characteristics in the cream state, especially,
The viscosity is properly adjusted and maintained so that it has an appropriate coating property.

In order to ensure good solderability,
At the time of soldering, it is necessary to remove the solder powder and the oxide on the surface of the metal to be bonded to prevent reoxidation, and conventionally a flux composed of rosin and an activator has been used. And this activator has the printability of cream solder,
It affects solderability and insulation after soldering, and various activators and fluxes or cream solders containing them have been proposed in consideration of improving these characteristics. For example, in JP-A-63-278695, an activator of diphenylacetic acid or triphenylacetic acid improves solderability and detergency with an organic solvent, and an amine such as triethanolamine or monoethylamine hydrobromide is used. The combined use of a system activator further improves solderability and cleanability. Japanese Patent Laid-Open No. 1-1548
In JP 97, a flux derived from a salt derived from a carboxylic acid and an amine is added to the resulting cream solder, which is not corrosive, has a long sticking duration, does not easily change over time, and has very few solder balls. I am supposed to.

In general, when the flux residue absorbs water after soldering, it may cause deterioration of insulation and corrosion. Therefore, it is removed by washing with an organic solvent (for example, washing with chlorothane). .

[0005]

On the other hand, the cleaning after soldering has a problem of depleting the ozone layer when the Freon cleaning which has been widely used in the past is carried out, and the water cleaning which is being put into practical use as a substitute therefor. Even if it is performed, there is a concern that the disposal of the cleaning liquid may have an adverse effect on the environment. Therefore, development of flux that does not require cleaning is in progress. In this case, many involve shutting down the soldering atmosphere from the atmosphere to a nitrogen (N ₂ ) protective atmosphere. If the atmosphere control is perfect, it is possible to carry out soldering with a small amount of low-activity flux, but the equipment and soldering time therefor cause a significant cost problem.

Further, Japanese Patent Laid-Open No. 3-221295 proposes a flux for cream solder which is soldered in the air and has improved corrosiveness of the residual flux. In this case, although cleaning can be omitted, it is good for removing the oxide film such as solder powder due to the too strong activation force of the flux, but a chemical reaction between the powder and the flux occurs even at room temperature, and the flux is generated. It deteriorates in a short time. As a result, the storage stability of the cream solder is deteriorated.

[0007] In the conventional cream solder, if no cleaning is performed, a flux residue remains after soldering. However, this residue causes corrosion on the circuit board or the soldered portion, or depending on the adhesion state of the residue. In some cases, the quality of insulation deteriorated, and cracks and cracks occurred in the residue, which caused other quality problems. The object of the present invention is to ensure long-term use of electronic equipment while ensuring printability and solderability, without causing corrosion and deterioration of insulation even in the state where flux residue is attached without cleaning after soldering. The purpose is to provide a flux for cream solder that improves the reliability of time.

[0008]

In the flux for cream solder containing rosin and an activator, the above-mentioned object is a ratio of the activator to the entire flux, and a salt of diphenylacetic acid and diethylamine: 2.0 to 2
0.0wt% sebacic acid: 1.0 to 1
5.0 wt% and diphenylacetic acid: 2.0-2
Achieved by a flux for cream solder, which is characterized by comprising 0.0 wt%.

It is preferable to add 8.0 wt% or less of phthalic acid and / or 12.0 wt% or less of benzoic acid to the above-mentioned flux.

[0010]

According to the present invention, (1) in order to secure solderability, the activator exhibits an activation force in the soldering temperature range, and (2) in order to secure insulation after soldering,
An activator with a solubility in water of 1.0% or less does not evaporate during soldering and remains as a residue. (3) During storage before coating, the activator reacts with solder powder during printing and changes over time. An activator satisfying the conditions of not causing it and (4) maintaining good printability is selected in combination.

The physical properties of each component of the activator in the flux used in the present invention and the physical properties of the compounds used for the other activators are as shown in Table 1.

[0012]

[Table 1]

Further, the activation temperature range of the activator used in the present invention is as shown in FIG. Thus, the activator that enhances the flux action of rosin as the primary flux is active in the soldering temperature range, while it is inactive up to at least 50 ° C. The reasons for limiting the components of the activator composition in the present invention are as follows.

Sebacic acid has a carboxyl group and exhibits an activity over a wide temperature range over the entire soldering temperature range. However, if it is less than 1.0 wt%, the solderability becomes poor. Reacts with time to cause a change over time, and the printability deteriorates. Diphenylacetic acid also has a carboxyl group, and if it is less than 2.0 wt%, the solderability is poor, while if it exceeds 20 wt%, the insulation of the residual flux after soldering is poor.

The salt of diphenylacetic acid and diethylamine is
It decomposes at the soldering temperature to become a water-soluble amine having an OH group, and if it is less than 2.0 wt%, the solderability becomes poor, while if it exceeds 20 wt%, the insulation of the residual flux after soldering Becomes worse. Both phthalic acid and benzoic acid have a carboxyl group and have a function of improving solderability and printability. However, phthalic acid is 8 wt%
If the benzoic acid content exceeds 12% by weight, the printability is deteriorated. When these are added at the same time, solderability and printability can be further improved.

[0016]

The present invention will be described in detail below with reference to embodiments of the present invention and comparative examples. First, the following materials were prepared as raw materials for cream solder. Solder powder: Sn63-Pb37 eutectic solder alloy Rosin: Polymerized rosin Solvent: Ethanol solvent Viscosity agent: Hardened castor oil, castor oil Activator: Salt of diphenylacetic acid and diethylamine Sebacic acid Diphenylacetic acid Phthalic acid Benzoic acid And shown in Table 2. Flux sample Nos. 1 to 1 of composition ratio
As No. 5, each flux (10 wt%) and solder powder (90 wt%) were sufficiently kneaded to obtain a cream solder. Sample Nos. 1 to 4, 11, 13 and 15 are the flux according to the present invention, and sample Nos. 5 to 10, 12 and 14 are the flux of the comparative example.

The printability, solderability and insulation of the cream solder thus produced were investigated, and the results are shown in Table 2.

[0018]

[Table 2]

The printability is a general term for workability when transferring solder to a substrate through a metal mask, low occurrence of defects, and the like. “X” means that the solder cream does not rotate during printing and cannot be transferred (poor rolling property), or that the solder shape collapses after printing and leads to an adjacent land (defective defect).

The solderability means that the solder powder and the metal surface of the substrate are cleaned during heating, the solder powders are melted and coalesced, and well wetted with the metal surface for soldering. 90 ° at the wetting angle (contact angle) when the molten solder is placed on the Cu) -based metal layer (substrate to be joined)
When it was smaller, it was designated as "○". "X" has a wetting angle of 9
This is the case of 0 ° or more.

The insulation is insulation of the flux residue after soldering, and the insulation (electric resistance) is measured after soldering on the comb-teeth electrode substrate specified by JISC3197, and there is no decrease. In some cases, the case where it decreased only slightly was marked as "○". The case where the insulating property was remarkably lowered was designated as "x". When the insulation is not deteriorated and is good, the soldering can be completed without the need to clean the flux residue, and the cleaning can be eliminated.

As can be seen from Table 2, when the amount of sebacic acid is larger than the specified amount as in Sample 5, the printability is deteriorated. Solderability is reduced in Sample 6 (diphenylacetic acid and diethylamine salt less than specified amount), Sample 7 (sebacic acid less than specified amount) and Sample 7 (diphenylacetic acid less than specified amount). Then, the insulating properties are lowered in Sample 9 (the salt of diphenylacetic acid and diethylamine is more than the specified amount) and Sample 10 (the amount of diphenylacetic acid is more than the specified amount).

When the amount of phthalic acid is more than the specified amount, the printability is slightly lowered as in Sample 12, and the printability is slightly lowered as in Sample 14 even if the amount of benzoic acid is increased. Further, as a comparative example, adipic acid or triethanolamine was used as an activator, and a cream solder was manufactured as described above as a flux having a composition ratio shown in Table 3.

[0024]

[Table 3]

Adipic acid has a large solubility in water, and the cream solder of Sample 16 has poor insulation (NG) and requires cleaning after soldering. In addition, triethanolamine has a high melting point and a high boiling point, and the cream solder of Sample 17 remains in the residue and has poor insulation (NG), and cleaning is necessary in this case as well. As another example, instead of the eutectic solder powder of the above example, Sn61-In as another alloy component
When the solder powder consisting of the rest of 1.0-Sb0.5-Ag1.0-Pb and the flux of the present invention were kneaded and used, similarly excellent results were obtained. Needless to say, the present invention can be applied to various solder powders within the scope of the present invention.

[0026]

As described above, in the cream solder with the flux using the predetermined activator according to the present invention, the printing property, the solderability and the insulating property are ensured, and the cleaning after the soldering is omitted. be able to. At the time of soldering, soldering can be performed in the air without providing a protective atmosphere of nitrogen, and the equipment and cost can be reduced or reduced. Further, there is no need for a cleaning device, which is also preferable in terms of equipment and cost.

[Brief description of drawings]

FIG. 1 is a graph showing the activation temperature range of an activator.

Front Page Continuation (72) Inventor Mitsuo Nakamura 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation (72) Inventor Hisao Shirai 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation (72) Invention Kenichi Kawai 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Hideki Ishida 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Yasuhisa Tanaka Midorigaoka, Toyota City, Aichi Prefecture 3-65, Otoyo Kogyo Co., Ltd. (72) Inventor Eiji Asada, Midorigaoka, Toyota City, Aichi Prefecture 3-65, Otoyo Kogyo Co., Ltd. (72) Inventor, Takehiko Narita 75 Nagata, Narumi-cho, Midori-ku, Aichi Prefecture 1 Solder Court Co., Ltd. (72) Inventor Hiromitsu Kojima 75 Solder Court Co., Ltd. Nagata, Narumi-cho, Midori-ku, Nagoya, Aichi Prefecture

Claims (2)

[Claims] 1. A flux for cream solder containing rosin and an activator, wherein the activator is a ratio of diphenylacetic acid and diethylamine in a proportion of the whole flux: 2.0-2.
0.0wt% sebacic acid: 1.0 to 1
5.0 wt% and diphenylacetic acid: 2.0-2
Flux for cream solder, characterized by comprising 0.0 wt%. 2. The flux for cream solder according to claim 1, further comprising phthalic acid in an amount of 8.0 wt% or less and / or benzoic acid in an amount of 12.0 wt% or less. Flux for cream solder.