JPH11179589A - Flux - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a soldering flux capable of obtaining a flexible residue without causing cracks. SOLUTION: Terminal (meth)acrylated atactic 1,2-polybutadiene or hydrogenated atactic 1,2-polybutadiene is added to the soldering flux. In this atactic 1,2- polybutadiene, the acrylic group or the methacrylic group is connected, as necessary, to the repeating unit at the molecular end of atactic 1,2-polybutadiene or its hydrogenated compound through appropriate connection group.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flux for soldering, and more particularly to a cream solder, a solder, and a liquid flux mainly used for mounting an electronic component on a printed circuit board.

[0002]

2. Description of the Related Art When electronic components are mounted on a printed circuit board, soldering is performed. For soldering, print cream solder consisting of flux and solder powder,
A method of mounting electronic components by heating and bonding, and mounting (reflow soldering), a method of soldering wire solder (flux-cored solder) with a flux in the core with a soldering iron, and a method of applying liquid flux to lead wires And a method of applying the solder to the electrode and then contacting it with the molten solder for soldering (flow soldering). The flux for cream solder consists of rosin-based resin, activator, solvent, etc., and further contains a thixotropic agent to improve printability.
It is a viscous liquid. The flux of the cored solder is generally a resinous flux composed of a rosin-based resin and an activator. The liquid flux is a liquid in which a rosin-based resin, a synthetic resin, an activator, and the like are dissolved in a solvent (organic solvent, water). When an electronic component is soldered to a printed circuit board using such a flux, a part or most of the flux component remains on the printed circuit board after the soldering is completed.
This is called flux residue. Conventional flux residue
In order to secure the electrical reliability of the printed circuit board, the printed circuit board has been washed and removed with a solvent such as chlorofluorocarbon. However, after the use of chlorofluorocarbons was regulated, a method that does not remove and remove flux residues has become common. Since no cleaning is performed, the residue remains on the substrate. Even if there is a residue on the printed circuit board, electrical reliability must be ensured. In other words, the electrical reliability of the flux residue is important. It is necessary to ensure the electrical reliability of the residue regardless of whether it is placed under high temperature and high humidity or under a drastic temperature change.

However, in the conventional soldering using a flux, the flux residue cannot cope with a drastic temperature change and is easily cracked. When a crack occurs, moisture in the air invades from the crack, ionizing the activator, causing migration, and the electrical reliability may be significantly reduced. In addition, since the residue is fragile and inflexible, the residue may be broken at the time of pin contact in the in-circuit test, and the fragments may adhere to the tip of the tester, making it impossible to carry out the test smoothly. Furthermore, since it has no flexibility, it has been difficult to use it for a flexible electronic substrate.

[0004]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned disadvantages of the conventional flux. That is, an object of the present invention is to provide a flux that does not generate cracks even when abrupt temperature changes and gives a flexible residue.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above-mentioned object, and as a result, have found that the flux contains terminally acrylic or methacrylic modified atactic 1,2-polybutadiene or terminally acrylic or methacrylic modified hydrogen. It has been found that the object is achieved by including an added atactic 1,2-polybutadiene. The present invention relates, firstly, to a soldering flux characterized in that it contains a terminal acrylic or methacryl-modified atactic 1,2-polybutadiene or a terminal acrylic or methacryl-modified hydrogenated atactic 1,2-polybutadiene. The present invention is the second
And a cream solder comprising the above-mentioned flux and solder powder. Third, the present invention relates to a cored solder containing the above flux.

[0006] The terminal acrylic or methacryl-modified atactic 1,2-polybutadiene and the terminal acrylic or methacryl-modified hydrogenated atactic 1,2-polybutadiene used in the present invention are the repetition of molecular terminals of atactic 1,2-polybutadiene or its hydride. An acrylic or methacrylic group is bonded to the unit via an appropriate linking group if necessary. The degree of hydrogenation in the hydride, the type of the linking group when bonding the acryl group or the methacryl group, the amount of the acryl group or the methacryl group bonded per polymer molecule are not particularly limited. Can be indicated by

[0007] A typical example of the terminal acrylic or methacryl-modified atactic 1,2-polybutadiene can be represented by the general formula (1).

[0008]

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A typical example of a hydrogenated atactic 1,2-polybutadiene modified with an acrylic terminal or methacrylic group can be represented by the general formula (2).

[0010]

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The terminal acrylic or methacryl-modified atactic 1,2-polybutadiene and the terminal acrylic or methacryl-modified hydrogenated atactic 1,2-polybutadiene are viscous liquids. Its viscosity is determined by its chemical structure, average molecular weight, molecular weight distribution and the like. In the present invention, 10 to 5000 poise (1 to 50 poise) at 45 ° C.
Those having a viscosity in the range of 0 Pa · s) are preferably used.

As described above, the flux for cream solder is usually a viscous liquid containing a rosin-based resin, an activator, and a solvent, and further contains a thixotropic agent to further improve printability. The flux of the cored solder is generally a resinous flux composed of a rosin-based resin and an activator. The liquid flux is a liquid in which a rosin-based resin, a synthetic resin, an activator, and the like are usually dissolved in a solvent (organic solvent, water). Here, examples of the rosin-based resin include polymerized rosin, hydrogenated rosin, and modified rosin. Typical activators include amine hydrohalides and organic acids. Examples of the solvent include diethylene glycol monohexyl ether, diethylene glycol dibutyl ether, α-terpineol, and the like. As the thixotropic agent, hardened castor oil, higher fatty acid amide, and the like are often used.

The rosin resin usually has a softening point of 70-1.
A relatively brittle resin at 50 ° C. When the solder flux contains these rosin-based resins, the residue after soldering is brittle. At a low temperature of 0 ° C. or lower, distortion due to a difference in thermal shrinkage from the printed circuit board cannot be absorbed, and cracks are generated in the residue. The moisture in the air enters there, and the electrical reliability of the residue is impaired.

The present invention is characterized in that a flux comprising the above-mentioned components contains terminally acrylic or methacrylic modified atactic 1,2-polybutadiene or terminally acrylic or methacrylic modified hydrogenated atactic 1,2-polybutadiene. . These contents vary depending on the type of flux, but are desirably 1 to 70% of the solid content contained in the flux,
More preferably, it is 3 to 40%. The terminal acrylic or methacryl-modified atactic 1,2-polybutadiene and the terminal acrylic or methacryl-modified hydrogenated atactic 1,2-polybutadiene are well mixed with the above-mentioned flux. In the case of cream solder, it does not adversely affect printability and the like, and does not impair solderability. The cream solder is printed on a printed circuit board through a stencil, etc., and electronic components are mounted on it,
Next, soldering is performed in a hot air oven, an infrared heating oven, or the like. It remains on and around the flux solder after soldering. Since the residue is highly flexible, there is no crack, and at the same time, high electrical reliability is provided.

As a prior art similar to the present invention, there is JP-A-9-24488. The purpose of this prior art is to prevent the generation of cracks in the flux residue and to improve the electrical reliability as in the present invention. To a solder cream (solder paste), hydrogen is added to an atactic 1,2-polybutadiene having an molecular weight of 1,000 to 3,000 or an unsaturated bond part thereof to form a saturated bond, or to one or two of their terminals. It is characterized by adding a compound having a hydroxyl group (-OH) or a carboxyl group (-COOH).

More specifically, in this prior art,
(1) atactic 1,2-polybutadiene (homopolymer); (2) hydrogenated atactic 1,2-polybutadiene (homopolymer); (3) atactic 1,2-polybutadiene having a hydroxyl group at a terminal or hydrogenated atactic 1 , 2-polybutadiene, (4) an atactic 1,2-polybutadiene having a carboxyl group at the terminal or a hydrogenated atactic 1,2-polybutadiene. The flux residue according to the prior art has a disadvantage of copper corrosion as shown in a comparative example described later. However, the flux residue according to the invention does not. Although the cause of the presence or absence of copper corrosion has not been studied in detail, it is considered to be due to the difference in the chemical structure of the added polymer component.

[0017]

Next, the present invention will be described with reference to examples and comparative examples. The basic chemical structure of the additives used in these satisfies the formula (1) or (2).

Examples 1 to 5, Comparative Example 1 The components shown in Table 1 were mixed and heated to form a uniform solution, and then cooled to prepare a paste-like flux for cream solder.

[0019]

[Table 1]

Next, 10 parts of the thus obtained flux and solder powder (Sn / Pb: 63/37, spherical 2
(50-325 mesh) and 90 parts were mixed well to obtain a cream solder. The cream solder was printed on a printed circuit board through a stencil. Next, the printed printed circuit board is preheated at 150 ° C. for 30 seconds, and further,
Heat reflow was performed at 230 ° C. for 45 seconds. Both print,
It was judged that there was no problem with respect to reflow, or that no ball was generated, and that it was sufficiently practical. Further, the following test was conducted to check the electrical reliability and the properties of the flux residue.

(Insulation Resistance Test) A test was performed under the following two conditions in accordance with JIS Z 3284. Condition A: temperature 40 ° C, relative humidity 90%, 168 hours Condition B: temperature 85 ° C, relative humidity 85%, 168 hours

(Migration test) JIS Z 3
284.

(Thermal shock test) The printed circuit board after the reflow was put in air in which one cycle was performed at 125 ° C. for 30 minutes, exposure for 10 minutes, and exposure to −55 ° C. for 30 minutes for 10 minutes. The residue was observed.

(Pin Contact Cracking Test)
After leaving the printed board at room temperature for 24 hours, the flux residue remaining on the surface of the solder on the land was pierced with a needle to determine whether the flux residue had cracks.

(Residual Flexibility Test) A cream solder was printed on a copper plate, preheated under the same conditions, and then reflowed. The flux residue was present on and around the solder, and the flexibility was observed by bending the copper plate at about 45 degrees. Without flexibility, the residue will crack and possibly crack down.

The above-mentioned insulation resistance test was performed on the residue after the reflow of the solder paste containing the flux of Examples 1 to 5 and Comparative Example 1. In each case, the insulation resistance value (condition A) was 1 × 10 ¹¹ Ω or more, and the insulation resistance (condition B) was 1 × 10 ⁸ or more, which was a pass level. In the migration test, no occurrence of migration was observed in Examples 1 to 5. However, migration was observed in Comparative Example 1. Further, when a thermal shock test, a pin contact test, and a residue flexibility test were performed, cracks and cracks did not occur in the residues of Examples 1 to 5, but cracks and cracks occurred in the residue of Comparative Example 1. Occurred. The properties of these flux residues are shown in Table 3. Thus, the addition of the terminal acrylic-modified hydrogenated atactic 1,2-polybutadiene is effective in preventing migration, cracks and cracks.

Examples 6 to 11 Next, the basic composition was kept constant, and the type and viscosity of the additives of the present invention were determined.
Is shown in Table 2. these
Mix the flux with the same composition as the solder powder
I made cream solder. Printing and riffing of cream solder
Law confirmed that he could do without problems. In addition,
For the residue after the flow,
Was conducted. In any case, the insulation resistance value under condition A is
1 × 10 ¹¹Ω or more, and the insulation resistance value under the B condition is 1 × 1
0⁸Ω or more, which was a pass level. Also Maigret
No migration has been observed in the
won. In addition, abnormalities were found on the comb-shaped substrate after measuring the insulation resistance.
It did not fit. The properties of flux residue are summarized in Table 3.
Shown.

[0028]

[Table 2]

Comparative Examples 2 to 4 On the other hand, experiments relating to the prior art were conducted and compared with the present invention.
A flux for cream solder was prepared by adding a polymer belonging to the prior art. The composition is shown in Table 4. That is, three kinds of polymers different from those of the present invention were selected, and the other compositions were added in the same manner. The polymers targeted are atactic 1,2-polybutadiene with a carboxyl end, hydrogenated atactic 1,2-polybutadiene with a hydroxyl end and atactic 1,2-polybutadiene with a hydroxyl end. The flux having such a composition was similarly mixed with a solder powder to prepare a cream solder. It was confirmed that printing and reflow of cream solder could be performed without any problem. Further, the above-mentioned insulation resistance test and migration test were performed on the residue after the reflow. As shown in Table 3, the insulation resistance under the condition A was 1 × 10 ¹¹ Ω or more, and the insulation resistance under the condition B was 1 × 1.
0 ⁸ Ω or more, which was a pass level. No migration was observed in the migration test. However, when the insulation resistance under the condition B was measured and the comb-shaped substrate was taken out after 168 hours, a corrosion product of green copper was observed around the conductor in each case. Such copper corrosion indicates a potential defect in electrical reliability.

[0030]

[Table 3]

[0031]

[Table 4]

Embodiment 12 Next, an example in which the present invention is applied to a cored solder will be described. 40 parts of polymerized rosin, 40 parts of hydrogenated rosin, and hydrogenated atactic 1,2-polybutadiene (3500
(Poise / 45 ° C.) 20 parts were heated and melted. 1.5 parts of cyclohexylamine hydrobromide were added thereto.
After the cyclohexylamine hydrobromide had dissolved, it was removed and cooled. The obtained flux was put into a core portion of a wire solder having an outer diameter of 1.0 mm by a conventional method, and was used as a fluxed solder. Here, the amount of the flux of the core component is 3% of the whole. Using the obtained solder, soldering was performed on a copper plate. The flux residue formed around the solder was flexible, and no crack occurred even when the copper plate was bent at about 45 degrees. On the other hand, JIS Z319
The electrical reliability test shown in No. 7 was performed, but no problems were found.

Comparative Example 6 On the other hand, in the same manner, a flux cored solder containing no additive of the present invention was prepared. That is, the polymerized rosin 50
Parts and 50 parts of hydrogenated rosin were heated and melted. In the molten rosin, cyclohexylamine hydrobromide 1.5
Parts were added. After the cyclohexylamine hydrobromide was dissolved, it was taken out and cooled to obtain a flux. In the same manner as in Example 12, a solder was prepared. Soldering was performed on a copper plate. The flux residue formed around the solder was brittle and easily cracked off.

Example 13 An example in which the present invention is applied to a liquid flux will be described.
That is, 15 parts of polymerized rosin, 5 parts of terminally acrylic-modified hydrogenated atactic 1,2-polybutadiene (3500 poise / 45 ° C.), 1 part of triethanolamine hydrochloride,
79 parts of isopropyl alcohol was mixed to obtain a liquid flux. Using this flux, soldering was performed on a copper plate. When the copper plate was bent at 45 degrees, the flux residue formed around the solder was flexible and no cracks occurred.

Comparative Example 7 On the other hand, a liquid flux containing no additive of the present invention was prepared. That is, 20 parts of polymerized rosin, 1 part of triethanolamine hydrochloride, and 79 parts of isopropyl alcohol were mixed to obtain a liquid flux. Using this flux, soldering was performed on a copper plate. Bending the copper plate 45 degrees,
The flux residue formed around the solder was easily broken down.

[0036]

The flux obtained by the present invention is:
After soldering, it gives a flexible residue. The residue is resistant to severe temperature changes and has no cracks. Therefore, no migration occurs. That is,
High electrical reliability. Further, there is no crack in the pin contact test or the bending test of the substrate. Furthermore, there is no concern about corrosion under high temperature and high humidity. Thus, the flux of the present invention is widely used for soldering electronic components and the like.

Claims (3)

[Claims] 1. Acrylic or methacrylic modified atactic 1,2-polybutadiene or acrylic or methacrylic modified hydrogenated atactic 1,2-polybutadiene.
A soldering flux comprising polybutadiene. 2. A cream solder comprising the flux of claim 1 and a solder powder. 3. A flux cored solder containing the flux of claim 1.