JPH0829430B2 - Soldering method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a soldering method, in particular, a technique for joining materials using solder such as surface mounting of a printed circuit board.

[Prior Art] In the conventional soldering method, the oxide film formed on the surface of the material to be joined is removed as shown in "Electronic Technology" Vol. In order to form a stable alloy layer with the material, an inorganic flux such as an inorganic halide or an inorganic acid, or an activated rosin obtained by adding an organic halogen activator to a rosin is used as a flux.

As an example of the soldering method, FIGS. 4A and 4B schematically show the appearance of the lead portion in the surface mounting of the flat package. After the cream solder (1) is printed on the pattern (2) and the leads (3) of the component (4) are mounted on it, the cream solder (1) is melted in a batch in an infrared furnace or the like, and soldering is performed. To do.

[Problems to be Solved by the Invention]

The conventional soldering method is as described above. Here, the cream solder (1) uses water white (WW) rosin or polymerized rosin as the main component, dissolves this in an organic solvent, and then mixes the flux and powder solder. A liquid flux with a thixotropic agent effective for suppressing separation and an activator for improving solderability, and a powdered solder metal were kneaded to form a cream with an appropriate viscosity. is there. Of these, aluminum hydrochloride and organic acids are commonly used as activators, but they are corrosive (that is, they have an etching effect on the metal that constitutes the materials to be joined) After the attaching process is completed, the flux residue attached to the joint, that is, the soldered part (Fig. 2,
In order to remove (6)), washing with chlorocene or the like is inevitable.

The present invention has been made in order to solve the above problems, and provides a highly reliable soldered portion that is free from deterioration due to corrosion, thereby omitting cleaning as a post process. is there.

[Means for solving the problem]

A soldering method according to the present invention has a step of supplying a solder metal to a joint portion, having no etching action on a metal forming the joint portion, and having a reducing action on an oxide of the metal, And a step of supplying only an organic compound of a phenol or an alcohol having a boiling point in the range of the melting point of the solder metal minus 30 ° C. to the melting point plus 100 ° C. to the joint, and heating and melting the solder metal, At the time, a step of heating the organic compound to about the melting temperature of the solder metal to join the joints is performed.

[Action]

In the soldering method of the present invention, the surface of the material to be joined and the solder are cleaned by the reducing action of organic compounds such as alcohols and phenols, instead of the activator used conventionally, The alloy layer is stably formed. The phenols or alcohols have no etching effect on the metal forming the joint. Further, the organic compound also has a function of lowering the surface tension of the solder, and it becomes possible to secure a sufficient spread area. Here, since the organic compound basically evaporates during soldering, only the metal component remains during soldering. Even if a part of the solder remains due to soldering conditions, it does not have corrosive properties and does not deteriorate the soldered part due to corrosion. Therefore, it is not necessary to wash after soldering.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

1 (a), (b) and (c) are schematic side views each schematically showing a soldering process according to an embodiment of the present invention. First, the eutectic solder metal (1) is placed on the pattern to be joined, the component lead (3) is placed on this (Fig. 1 (a)), and then the alcohol has an OH group. Then, it is supplied to the joint by spraying ethylene glycol, which has a boiling point of 198 ° C, etc. (Fig. 1 (b). In this state, it is heated and melted with an infrared soldering device or vapor phase soldering device. , Soldering is performed (Fig. 1 (c)). Fig. 2 shows the temperature profile during vapor phase soldering, where a is the melting point of the solder and b is the boiling point of ethylene glycol as an example. Although the solder is molten for the period indicated by A, the temperature rises to the boiling point B of ethylene glycol immediately after the melting, and the pattern (2), leads (3) and solder (1) Reduction for surface oxide film The effect is strongest and good soldering is performed.Incidentally, C in the figure is a fluorine-based solvent which is a heating medium in vapor phase soldering.

Although ethylene glycol has been described as an example here, propylene glycol or heptyl alcohol may be used. Fig. 3 shows a comparison of the solderability of organic compounds due to the difference in boiling points in terms of the spread area of eutectic solder (melting point 183 ° C) on a copper plate. The boiling point around 200 ° C (the boiling point of ethylene glycol is 198 ° C), where the activation effect is strongest when the solder is melted, is set to 1, but a spread state that can be practically used is obtained in the range of the solder melting point minus 30 ° C to the melting point plus 100 ° C. For high melting point or low melting point solders other than eutectic, the same effect can be obtained by selecting an organic compound within the above range based on the melting point.

In addition, here, the method of spraying the organic compound on the solder that has been plated and simultaneously heating is given as an example. However, other methods such as dropping with a dispenser or supplying the organic compound to the joint portion when the solder metal is melted However, at this time, the organic compound may be heated to about the melting temperature of the solder metal to perform the bonding, or the particle-like solder metal and the organic compound may be kneaded in a cream form from the beginning and supplied to the bonding portion. May be used.

By using the above organic compounds, oxides are effectively removed and soldering is performed with high reliability. Furthermore, since this organic compound does not have an etching effect on the metal forming the joint and does not leave a corrosive residue, the cleaning step is unnecessary. That is, when soldering is performed by the conventional method, the ion concentration on the surface of the substrate after cleaning is measured, and ions of at least about 0.3 μg NaCl / cm ^{3 in} terms of NaCl amount are detected.

On the other hand, when the method of the present invention is used, no ions are detected even in the state where cleaning is not performed immediately after soldering, which proves that there is no corrosiveness.

〔The invention's effect〕

As described above, according to the present invention, the step of supplying the solder metal to the joint has no etching action on the metal forming the joint and has a reducing action on the oxide of the metal. And a step of supplying an organic compound having a boiling point in the range of the melting point of the solder metal minus 30 degrees Celsius to the melting point plus 100 degrees Celsius to the joint, and heating and melting the solder metal while soldering the organic compound at this time. Since the step of joining the above-mentioned joints by heating to the metal melting temperature is performed, the oxides of the metal forming the joints are not affected by the activator such as inorganic acid or organic halogen during soldering. It is possible to effectively remove and form an alloy layer stably at the interface, and since no corrosive residue is left, reliability is improved and the cleaning process becomes unnecessary, leading to simplification of the process.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (a), (b) and (c) are schematic side views schematically showing a soldering process according to an embodiment of the present invention, and FIG. 2 is an embodiment of the present invention. A curve diagram showing a temperature profile of soldering according to an example, FIG. 3 is a characteristic diagram showing a spread area ratio of solder to an organic compound according to an embodiment of the present invention, and FIGS. 4 (a) and 4 (b) are respectively. It is a schematic side view which shows the conventional soldering process typically. In the figure, (1) is a solder metal, (2) is a pattern,
(3) is a component lead, and (5) is an organic compound. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A step of supplying a solder metal to a joint portion, which has a reducing action on an oxide of a metal forming the joint portion, and has a melting point of the solder metal minus 30 ° C. to the melting point plus 100 ° C. Supplying only the organic compound of phenols or alcohols having a boiling point in the range to the joint, and heating and melting the solder metal, and heating the organic compound to a solder metal melting temperature at this time to bond A soldering method that performs a step of joining parts.