JPS6192781A - Vapor phase soldering method - Google Patents

Abstract

PURPOSE:To improve the reliability and efficiency of soldering by passing a work through the inside of the 1st vapor vessel for an inert liquid having a specific b.p. then through the 2nd vapor vessel for an inert liquid having the b.p. above the m.p. of solder. CONSTITUTION:The 1st vapor vessel 5 for the inert liquid 8 having the b.p. lower than the m.p. of the cream solder 2, i.e., 110-170 deg.C b.p. is provided and the 2nd vapor vessel 10 for the inert liquid 11 having the b.p. above the m.p. of the solder 2 is disposed. The work 4 carrying electronic parts 3 on a substrate 1 is charged into the vessel 5 and the flux in the solder 2 is melted by satd. vapor 9 to activate and dry the joint surfaces. The solder 2 is then melted by the satd. vapor 12 of the vessel 10 to join the substrate 1 and the parts 3. The soldering with high reliability without balls, etc. is executed in a short period and the soldering efficiency is improved by the above-mentioned method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to beam flow soldering methods, particularly vapor phase soldering methods.

[Prior art]

Japanese Patent Publication No. 53-40934 describes a so-called vapor phase soldering method and apparatus that utilizes the latent heat of vaporization of an inert liquid vapor to supply heat in a glue flow soldering process for electronic components. This inert liquid vapor has low reactivity, is thermally and chemically stable, does not corrode or dissolve in solvents, and has the characteristics of high density, high insulation, nonflammability, non-toxicity and odor. It is. The vapor phase soldering method is (1
) Since the entire surface of the processed product is surrounded by inert liquid vapor, it is heated uniformly regardless of the size or shape of the processed product, (2
) The heating temperature is determined by the boiling point of the inert liquid and is maintained at a constant temperature; and (3) there is no room for air to enter due to the saturated inert vapor, so oxidation is less likely to occur during heating. However, because the heat transfer due to the latent heat of vaporization released when steam condenses is extremely rapid,
There have been problems in that solder balls are generated due to bumping of the cream solder and voids are generated in the soldered area. As a countermeasure against this problem, the conventional method has been to preheat the cream solder in air in an oven or the like after supplying it to remove water, flux, and solvent in the cream solder.

However, such a preheating method oxidizes the solder, making it unsuitable for highly reliable, high-density soldering. In addition, it was difficult to set conditions such as preheating temperature and time, and there was a problem that productivity was poor in terms of process.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the conventional methods described above and to provide a continuous production vapor phase soldering method suitable for highly reliable and high-density glue flow soldering.

〔Example〕

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram for explaining the vapor phase soldering method according to the present invention, in which 1 is a board, 2 is cream solder, and 6
4 is an electronic component, and 4 is a processed product consisting of a substrate 1, cream solder 2, and electronic component 6. 5 is a first steam tank, 8 is a first inert liquid whose boiling point does not exceed the melting point of cream solder 2, and 9 is its saturated vapor layer. 10 is a second steam tank, 11 is a second inert liquid having a boiling point higher than the melting point of cream solder, and 12 is its saturated vapor layer.

Also, 6 is a heater for heating an inert liquid.

7 is a condensing coil that condenses and liquefies the saturated vapor layer and prevents it from escaping, and the same coil can be used in the first steam tank and the second steam tank.

Next, a method according to an embodiment will be explained. First, cream solder 2 is supplied to the substrate 1 by means such as printing, and the processed product 4 on which the electronic component 6 is mounted is placed in the first steam tank 5. In the first steam tank 5, a first inert liquid 8 having a boiling point not exceeding the melting point of the cream solder 2 is heated by a heater 6 to form a saturated steam layer 9. Therefore, the cream solder 2 does not melt, but the flux melts and the joint interface is activated, and the water and solvent in the cream solder evaporate, causing the cream solder to dry. After that, when the processed product 4 is put into the second steam tank 10, the cream solder 2 dried in the first steam tank 5 is melted, and the solder paste 2 is transferred to the substrate 1 and the electronic components 6.
are joined.

By the way, the boiling point of the first inert liquid must be lower than the melting point of the cream solder because the cream solder must not melt. Furthermore, since the flux needs to melt and the cream solder needs to dry, the boiling point of the first inert liquid must be above a certain temperature. However, when the material of the electronic component is a molding resin that is relatively heat-resistant, it may be possible to lower the temperature to a lower temperature, but this requires exposure to heat for a longer period of time and production efficiency is also poor. Furthermore, if there is a significant temperature difference between the first vapor phase and the second vapor phase, the cream solder will be difficult to melt, and the high heat treatment time in the second vapor tank will be undesirably long. From this point of view, the boiling point of the first inert liquid is 10
0°C to 170°C is desirable.

According to experiments, 63Sn 37p was used in cream solder.
When using the eutectic solder of b.
Using Fluorinert FC-70 (trade name, 3M Company) at 5°C, the first inert liquid 8 does not exceed the melting point of the solder, 183°C.
FC-40 (trade name Florinar) with a boiling point of 155℃
(3M Company) was effective.

FIG. 2 is a diagram showing the temperature profile of each part in FIG. 1.

〔Effect of the invention〕

As explained above, according to the present invention, after drying the cream solder with the latent heat of vaporization of saturated steam whose boiling point does not exceed the melting point of the cream solder, the cream solder is continuously dried with the latent heat of vaporization of saturated steam whose boiling point is higher than the melting point of the cream solder. Since it melts solder, cream solder can be dried and melted in a short time without oxidizing the solder, and it is also possible to efficiently perform highly reliable and high-density soldering without solder balls or voids.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the vapor phase soldering method according to the embodiment of the present invention, and FIG. 2 is a diagram showing the temperature profile of each part in FIG. ...Cream solder 6...Electronic component 4...Processed product 5...First steam tank 6...Heater 7...Condensing coil 8...First inert liquid 9...No. 1 saturated steam 10...Second steam tank 11...Second inert liquid 12...Second saturated steam Patent ratio if 1 person Canon Co., Ltd. Figure 1 Figure 2

Claims (2)

[Claims] (1) The first type has a boiling point that does not exceed the melting point of cream solder.
A vapor phase soldering method, which comprises passing through a vapor bath of an inert liquid, and then passing through a vapor bath of a second inert liquid having a boiling point higher than the melting point of the cream solder. (2) The boiling point of the first inert liquid is 100°C or higher17
The vapor phase soldering method according to claim 1, characterized in that the temperature is 0° C. or lower.