JPH10328882A - Cream solder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effect high accurate printing and to prevent the development of a defective solder bridge even after reflowing by obtaining a cream solder composed of powdery solder and liquid or pasty flux and adding a glycol base solvent and a hydroxystearic amide base compound in the flux. SOLUTION: In the flux of the cream solder in which the powdery solder and the liquid or basty flux are mixed, the hydroxystearic amide base compound N,N'-orefinebis (12-hydroxystearic amide) is incorporated as thixo-agent and further, glycol base solvent is incorporated. The amide base compound is one component base and stable compound and the material characteristic of viscosity, thixotropy index, etc., can be uniformized. Further, since the glycol base solvent has low viscosity, the vol. of the flux accepted in the cream solder is reduced and restrains the slump of the cream solder at the time of preheating and has such action as to prevent the solder bridge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cream solder used for soldering electronic equipment.

[0002]

2. Description of the Related Art A cream solder is obtained by uniformly mixing a solder powder and a liquid or paste-like flux. The flux is mainly composed of rosin, which gives fluidity and tackiness, as a main component, and is composed of an activator, a thixotropic agent for maintaining a shape, a solvent, a thickener added as necessary. This is supplied to the soldering joint on the substrate by screen printing, discharge from a dispenser, or the like, and the soldering of the electronic component is performed.

In recent years, as electronic devices have become smaller and higher in density,
Electronic components mounted on substrates are also being miniaturized. For example, in the QFP component of the IC package component, the pitch between leads, which has been conventionally 0.5 mm or more, is reduced to 0.4 mm, and further to 0.3 mm. In order to solder such a small electronic component to an electronic circuit board, a reflow soldering method suitable for high-density mounting is mainly used. With the practical use of such narrow-pitch QFP components, a bridge is formed by soldering during mounting.
The problem of frequent occurrence of solder bridge defects has been increasing. The cause of this defect is, firstly, a variation in the printed shape of the solder during printing. Due to this variation,
Solder shorts occur, thereby resulting in a bridge after mounting. Secondly, it is considered that the viscosity of the flux decreases during preheating, so that the cream solder drops and the solder is connected between adjacent lands, resulting in a bridge failure.

[0004]

Various studies have been made on this problem. One of them has been to improve the precision of the printed shape of the solder. Specifically, it is a method of increasing the amount of a thixotropic agent such as caster oil to have a high thixotropic index. However, in this method, although a predetermined print shape can be obtained, continuous printability is a problem, and there has been an inconvenience that the viscosity increases in a few hours and adheres to the squeegee, thereby causing a state where printing cannot be performed.

Second, with respect to reflow, a measure was taken to replace the solvent with one having a lower boiling point than before. This measure makes it easier for the solvent in the flux to evaporate at the time of preheating, so that the cream solder is less likely to droop and bridge failure is less likely to occur. However, in this method, since the cream solder is easily dried, a new problem arises in that the adhesive strength is reduced, and a defect that the component is shifted or dropped at the time of component mounting is apt to occur. The present invention solves the above problems and enables high-precision printing.
An object of the present invention is to provide a cream solder in which a solder bridge defect does not occur even after reflow.

[0006]

In order to solve this problem, the present invention has focused on printing and reflow, and has found a solution from the viewpoint of flux composition. In other words, regarding printing, in order to improve the thixotropy index of cream solder and stabilize continuous printability, the unstableness of multi-component systems extracted from natural fats and oils such as castor oil and caster wax as thixotropic agents Instead of a thixotropic agent, a one-component stable hydroxystearidamide compound N, N'-olefinbis (12-hydroxystearidamide) is used. This is a one-component system, and can make the physical properties such as viscosity and thixotropy index uniform.

Second, with respect to reflow, a structure is employed in which the flux contains a glycol-based solvent such as propylene glycol monophenyl ether. Propylene glycol monophenyl ether has a large specific gravity of 1.06, so that the volume of the solvent occupied in the flux decreases. Also, since the viscosity is as low as 23 cP, the volume of the flux occupied in the cream solder can be reduced. For this reason, the change in the viscosity of the cream solder during preheating can be reduced. As a result, the cream solder is less likely to drop during preheating, and a cream solder free of solder bridge defects is obtained.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a cream solder in which a powder solder and a liquid or paste-like flux are mixed, and in the flux, a hydroxythearamide compound N, N'-olefinbis (12-hydroxystea) is used as a thixo agent. Lamide) and further contains a glycol-based solvent. The amide-based compound is a one-component, stable compound, and can have uniform properties such as viscosity and thixotropy index. Further, since the viscosity of the glycol-based solvent is low, the glycol solvent has an effect of reducing the volume of the flux occupying in the cream solder, suppressing dripping of the cream solder during preheating, and preventing a bridge failure.

The hydroxystearamide compound is N,
N′-olefin bis (12-hydroxystearamide), and the glycol solvent is preferably propylene glycol monophenyl ether. N,
N'-olefin bis (12-hydroxystearamide) has a large intramolecular interaction that gives a thixotropy index, and thus acts to increase the thixotropy index with a single component. Also, propylene glycol monophenyl ether has an effect of reducing the volume of the solvent in the flux due to its large specific gravity, suppressing the dripping of the cream solder during preheating, and preventing bridge failure. Here, the thixotropic index is obtained from the viscosity-shear rate curve diagram from the slope (expressed in common logarithm) of the change in viscosity due to the change in shear rate. The higher this value, the better the shape retention of the cream solder after printing.

The flux contains propylene glycol monophenyl ether, 2-ethyl-1,3-hexanediol, and 2,2-dimethyl-1,3-propanediol, and the thixotropic agent N , N'-
N, N'-ethylenebis (12-hydroxystearamide), N, N'-hexamethylenebis (12-
(Hydroxystearamide) and N, N'-xylylenebis (12-hydroxystearamide). The thixotropic agent gives the cream solder a higher thixotropy index. 2-ethyl-1,3-hexanediol having a high viscosity;
By adding -dimethyl-1,3-propanediol, a sufficient adhesive strength can be obtained. Hereinafter, embodiments of the present invention will be described.

Embodiment 1 Generally, the flux contains 40 to 70 wt% of an alcoholic solvent. In this, thixotropic agent such as caster oil is 6w
t%, and the thixotropic index of the flux is about 0.55. On the other hand, by including 6 wt% of olefin-based hydroxystearylamide,
The thixotropy index of the flux can be about 0.65. This can prevent solder shorts during printing. Next, 30 of alcoholic solvent
When 〜70 wt% is a glycol-based solvent having a viscosity of 10-30 cP, the viscosity of the flux decreases from 210 Pa · s to 160 Pa · s. For this reason, the flux compounding ratio can be reduced, for example, from 9.5 wt% to 9.0 wt%, whereby a decrease in the viscosity of the cream solder during preheating can be suppressed and a solder bridge defect can be prevented.

<< Embodiment 2 >> The following equation (1) is expressed by n-
The molecular formula of propylene glycol monophenyl ether is shown. Formula (2) is N, N'-ethylenebis (12-hydroxystearamide), formula (3) is N, N'-hexamethylenebis (12-hydroxystearamide), and formula (4) is N , N′-xylylenebis (12-hydroxystearamide).

[0013]

Embedded image

Since the specific gravity of propylene glycol monophenyl ether, which is a glycol solvent, is as large as 1.06, when used as a solvent, the volume ratio of the solvent in the flux can be reduced. N, N′-olefin-based bis 1,2-formulas represented by formulas (2), (3) and (4)
Hydroxystearyl amide is not a multi-component unstable thixotropic agent extracted from natural fats and oils such as castor oil and castor wax, but a one-component stable amide compound. The flux is the above-mentioned amide compound, propylene glycol monophenyl ether, n-propylene glycol monophenyl ether, 2,2-dimethyl-1,3-propanediol, rosin, diphenylguanidine hydrobromide (hydrogen bromide) The salt is represented by HBr).

<< Embodiment 3 >> The glycol solvent is 2
-Ethyl-1,3-hexanediol;
Ethyl-1,3-hexanediol has a viscosity of 23 cP of n-propylene glycol monophenyl ether.
Since it is higher than 320 cP, sufficient viscosity can be given to the flux to improve the adhesive strength. The flux is n-propylene glycol monophenyl ether,
2-ethyl-1,3-hexanediol, 2,2-dimethyl-1,3-propanediol, rosin, N, N'-
It is composed of ethylene bis (12-hydroxystearamide) and diphenylguanidine HBr.

[0016]

Next, specific examples of the present invention will be described.

Example 1 Using a flux having the composition shown in Table 1, high-precision printing is possible, short-circuit does not occur, cream solder viscosity during preheating is suppressed, and solder bridge defects are prevented. can do.

[0018]

[Table 1]

Example 2 The fluxes shown in Table 2 were obtained by using N, N′-hexamethylenebis (12-hydroxystealamide) as the N, N′-olefinbis (12-hydroxystealamide) of Example 1. In this case, n-propylene glycol monophenyl ether was used as a glycol solvent. By improving the thixotropy index, high-precision printing is possible, no short circuit occurs, and a decrease in cream solder viscosity at the time of preheating can be suppressed to prevent a solder bridge defect. In the above example, the content of propylene glycol monophenyl ether is 45 wt%, but it can be carried out in the range of 25 to 50 wt%.

[0020]

[Table 2]

Example 3 The flux shown in Table 3 was obtained by using N, N'-ethylenebis (12-hydroxystearamide) of Example 2 as N, N'-olefinbis (12-hydroxystearamide).
-Hydroxystearamide) and 2-ethyl-1,3-hexanediol as a glycol solvent. By improving the thixotropy index, high-precision printing is possible, no short circuit occurs, and a decrease in cream solder viscosity at the time of preheating can be suppressed to prevent a solder bridge defect. Further, according to this composition, a sufficient adhesive strength can be ensured, and therefore, there is no occurrence of a defect such as a shift or a missing part.

[0022]

[Table 3]

In the above example, the ratio of propylene glycol monophenyl ether, 2-ethyl-1,3-hexanediol and 2,2-dimethyl-1,3-propanediol is 25:20:20, 35:10:20 if more emphasis is placed on preventing bridge failure
Alternatively, it can be performed with a ratio of 35:15:15. If the emphasis is on securing adhesive strength,
Implementations with a ratio of 5:30:20 or 20:25:20 are also possible.

Example 4 The flux shown in Table 4 was changed from the N, N'-olefin bis (12-hydroxystealamide) of Example 2 to N, N'-ethylenebis (12-hydroxystearal). Amide) and N, N '
-Xylylenebis (12-hydroxystearamide)
And further added 2-ethyl- as a glycol-based solvent.
1,3-hexanediol is added. According to this configuration, by further improving the thixotropic index,
High-precision printing is possible and no short circuit occurs. Further, since sufficient adhesive strength can be ensured for the flux, defects such as misalignment or missing parts do not occur.

[0025]

[Table 4]

In the above example, the ratio of propylene glycol monophenyl ether, 2-ethyl-1,3-hexanediol and 2,2-dimethyl-1,3-propanediol is 25:20:20, 35:10:20 if more emphasis is placed on preventing bridge failure
Alternatively, it can be performed with a ratio of 35:15:15. If the emphasis is on securing adhesive strength,
Implementations with a ratio of 5:30:20 or 20:25:20 are also possible.

[0027]

As described above, according to the present invention, as a thixotropic agent, a hydroxystearamide compound N, N'-olefinbis (12-hydroxystearamide) which is stable in one component system is used. Physical properties such as a thixotropic index can be made uniform, thereby enabling high-precision printing. As a result, it has become possible to reduce the occurrence of short-circuiting from zero to several percent in the conventional printing of QFP parts having 0.3 pitch lead terminals. In addition, the transfer rate at the time of solder printing was conventionally about 60% to 70% as compared with the transfer in an ideal state, but 85%.
That's all. In addition, by using a low viscosity, high specific gravity glycol solvent such as propylene glycol monophenyl ether in the flux, it is possible to suppress a decrease in the viscosity of the flux at the time of preheating. It became possible to suppress. Further, by blending 2-ethyl-1,3-hexanediol, an advantageous effect that a sufficient adhesive strength can be secured can be obtained.

Claims (3)

[Claims] 1. A cream solder comprising a powdered solder and a liquid or paste-like flux, wherein the flux contains a glycol-based solvent and a hydroxystearamide-based compound. 2. The glycol-based solvent is propylene glycol monophenyl ether, and the hydroxystearamide-based compound is N, N′-olefin bis (12-
2. The cream solder according to claim 1, which is hydroxystearylamide). 3. A flux containing propylene glycol monophenyl ether, 2-ethyl-1,3-hexanediol, and 2,2-dimethyl-1,3-propanediol, and comprising N, N′-olefin bis (12-
Hydroxystearamide), N, N′-ethylenebis (12-hydroxystearamide), N, N′-hexamethylenebis (12-hydroxystearamide), and N, N′-xylylenebis (12-hydroxystearamide) 3. The cream solder according to claim 2, comprising at least one member selected from the group consisting of (hydroxystearamide).