JP3362079B2 - Solder powder fixing method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit of uniform and high-definition solder powder on a metal surface of a wiring circuit portion of electronic parts (for example, in order to mount an electronic part on a printed circuit board, the pad surface of the metal circuit is previously attached. And a method of efficiently mounting other electronic components on the electronic component on which the solder powder has been fixed.

[0002]

2. Description of the Related Art In recent years, electronic components such as plastic substrates (including films), ceramic substrates, or insulating substrates such as metal substrates coated with plastic have been used.
A printed wiring board (also referred to as a printed circuit board or a printed wiring board) on which an electronic circuit is formed by an appropriate method has been developed, and an IC element, a semiconductor chip, a resistor,
A means for forming electronic devices by soldering electronic parts such as capacitors has been widely adopted.

By the way, in the manufacture of the above-mentioned mounted circuit device, in order to solder a lead terminal of an electronic component to a predetermined pad, a so-called solder cream containing flux is printed on the pad surface in advance, and the required electronic component is obtained. After locating and locating the solder, the solder cream is usually reflowed for soldering. On the other hand, there is an increasing demand for forming a thin solder layer on the pad surface in advance as the mounting density improves. The reason is that the solder cream cannot avoid defects such as solder bridges.

In order to form a solder circuit (thin solder layer) in an electronic component or the like, a plating method, a solder bath dipping method (immersion method) and the like have been carried out, but they are required as the mounting density is improved. Solder circuit patterns are becoming finer and finer, and due to the demand for improved work efficiency and on-spec ratio as well as reduction of circuit patterns, it is becoming difficult to use these methods.

Among these conventional solder circuit forming methods, a plating method is applicable to a solder circuit having a high-definition pattern. However, a target portion to be a solder circuit portion of electronic parts exists as an independent pattern. In many cases, application of electrolytic plating is difficult in terms of electrical conduction. On the other hand, the electroless plating solves the problem of electrical conduction in the above electroplating, but has a technical problem that it is difficult to obtain the required thickness of the solder thin layer.

Further, a method of applying solder powder whose surface is coated with flux to a circuit portion by an electrostatic coating method (Japanese Patent Laid-Open No. 3-50853), printing and applying flux onto the circuit portion, and depositing the solder powder on it After that, a number of proposals have been made, such as a method for forming a solder circuit by heating the solder to a temperature equal to or higher than the melting point to melt it, blowing gas onto the solder melting surface to perform leveling (JP-A-4-10694). However, there is a problem in forming a solder circuit having a high-definition pattern.

The present inventors have succeeded in solving these problems by making the exposed metal part sticky and accurately adhering the solder powder only to that part.
No. 6 was filed earlier. With this method, it is easy to obtain a high-definition solder pattern. However, it is necessary to use solder powder with a small particle size, and this solder powder with a small particle size has a very large surface area and the surface is easily oxidized, and flux must be applied for smooth solder melting. . For this reason, the solder powder accurately attached to the high-definition pattern may be disturbed by the flux application, and the finer the pattern, the more likely it is to cause the formation of a solder bridge or the variation in the solder film thickness.

[0008]

SUMMARY OF THE INVENTION According to the present invention, solder powder is adhered only to a metal exposed portion which requires solder coating of an electronic component having an extremely fine pattern, and the solder powder is applied by flux or the position of the electronic component is adjusted. Solder powder adhering to exposed metal parts is disturbed even in the processes of matching and placement,
As a result, we have developed a solder powder fixing method that can perform flux processing, a high-definition solder circuit forming method, and a mounting method for other electronic components, while maintaining a solder pattern that does not cause variations in solder bridges and solder film thickness. To aim.

[0009]

Means for Solving the Problems The present invention provides [1] to the metal circuit exposed portion of the electronic component such acts and metal
A tackifier compound that exhibits tackiness (hereinafter simply referred to as "tackiness"
"Giving compound". (2) a composition containing at least one of the above (1 ) to impart tackiness, and after applying solder powder to the tackiness imparting portion, heating and fixing are performed, [2] ] The exposed metal circuit of electronic parts is treated with a composition containing at least one tackifying compound to give tackiness, solder powder is attached, and this is heat-fixed, and then the solder powder is fixed. A solder circuit forming method, characterized in that flux is applied to the parts and then the solder powder is reflowed, and [3] a composition containing at least one tackifying compound in the exposed parts of the metal circuits of electronic parts. After processing to give tackiness, attach solder powder, then heat fix,
Corresponding to the solder powder fixing unit, an electronic component aligning place other mounting parts such, the flux was applied before or after the placement of the other mounting parts such, and performing reflow The above-mentioned object was achieved by developing a method of mounting.

The electronic parts to which the present invention is applied include
For example, there are printed wiring boards and various mounting components. Examples of printed wiring boards include a plastic substrate, a plastic film substrate, a glass cloth substrate, a paper-based epoxy resin substrate, a substrate on which a metal plate is laminated on a ceramic substrate, or the like. The present invention can be applied to single-sided electronic components, a double-sided printed wiring board, a multilayer printed wiring board or a flexible printed wiring board in which a circuit is formed by an appropriate method on an insulating substrate in which a metal base material is covered with plastic or ceramics. Examples of various mounting parts include IC elements (bare chips, various packages), resistors, capacitors, and the like.

In most cases, copper is mainly used as a metal forming a circuit of electronic parts, and it is the most preferable metal material for the tackifying compound of the present invention, but other metals may be used. good. The adhesion of other metals tends to be weaker than that of copper.

The tackifying compound used in the present invention is not particularly limited as long as it is a compound that acts on a metal to develop tackiness, and for example, a benzotriazole derivative represented by the general formula (1),

[Chemical 1] A naphthotriazole derivative represented by the general formula (2),

[Chemical 2] An imidazole derivative represented by the general formula (3),

[Chemical 3] A benzimidazole derivative represented by the general formula (4),

[Chemical 4] A mercaptobenzothiazole derivative represented by the general formula (5),

[Chemical 5] Organic compounds having an element such as N, S, O, or P such as a benzothiazolethio fatty acid derivative represented by the general formula (6) are particularly preferable.

[Chemical 6]

When a dipping or spraying method in the form of an aqueous solution is applied as a method for treating these tackifying compounds, at least one of the tackifying compounds is acidic, preferably pH 3 to A composition adjusted to have a slightly acidity of about 5 is used. In the case of applying the coating method, it is easy to use by adding a thickening agent such as a carboxymethyl cellulose derivative to the composition used in the dipping or spraying method to form an ink. At this time, the concentration of the solution is preferably about 0.05 to 20% by weight as a whole, which is easy to use.

When the treatment temperature is slightly higher than room temperature, the rate and amount of formation of the adhesive film are better, and it is not limited, depending on the concentration of the tackifying compound, the type of metal, etc.
Generally, the range of about 30 ° C to 60 ° C is suitable. Although the immersion time is not limited, it is preferable to adjust other conditions so as to be in the range of about 5 seconds to 5 minutes from the work efficiency.

In this case, it is preferable to coexist 100 to 1000 ppm of copper ions in the composition for forming a solder circuit, because the production rate and production efficiency of the adhesive film are increased.

The electronic parts to be treated are treated with the composition for forming a solder circuit after leaving other metal circuit portions covered with a resist or resin so that only the metal circuits in the solder circuit portion are exposed.

The composition containing the above-mentioned tackifying compound used here is dipped, sprayed or applied, and washed with a solvent and dried appropriately to impart tackiness only to the exposed metal surface. Next, sprinkle solder powder on these electronic parts, attach them to the adhesive surface, remove excess solder powder,
Heat treatment. After that, flux is applied and then reflow is performed to form a solder circuit. Further, after the fixing process of the solder powder, other electronic components are positioned and aligned according to the solder powder pattern, and the flux is applied before or after the other electronic components are disposed. By reflowing, other electronic parts can be mounted efficiently and precisely. The material of the solder used at this time can be arbitrarily selected depending on the application such as eutectic, containing silver, and containing bismuth.

The heat treatment temperature for fixing the solder is
The temperature is preferably set to 50 to 250 ° C., but when the heat fixing temperature is low, it is necessary to set the time long, and when the heat fixing temperature is high, it is necessary to shorten the time, so that the solder powder does not melt and flow out. It is necessary to choose. The flux to be used may be a flux suitable for the solder powder to be used, and a chlorine-free rosin-based flux or the like is preferable.

After applying the flux, the solder powder can be melted by using a reflow oven or the like to form a solder circuit having a fine and uniform thickness on the exposed metal surface of the electronic component circuit. In addition, other electronic components can be mounted with high mounting density without fear of solder bridges.

[0020]

According to the present invention, when a solder circuit for electronic parts is formed, the exposed metal part forming the circuit is treated with a composition containing a tackifying compound to thereby form a gap between the metal and the tackifying compound. It is presumed that a coordination bond or a complex is formed and an adhesive substance is generated on the surface, and by attaching the solder powder there, a precise fine solder powder pattern is formed, and the solder powder is removed before reflowing. By fixing by heating and reflowing after applying flux, a solder circuit with less variation in solder bridge and solder film thickness is obtained. Also,
By fixing the solder powder, other electronic components can be properly mounted without causing a solder bridge.

Although the reaction mechanism of heat fixing has not been completely clarified, the solder powder adhered on the exposed metal surface to which tackiness has been imparted by the tackifying compound treatment has an adhesive force with the adhesive layer. It is presumed that the solder powder does not move even when the flux is applied, the initial high-definition pattern can be maintained, and the solder bridge and the variation in the solder film thickness can be prevented.

This heat fixing is effective not only during the flux treatment but also when the excess solder powder is removed by a physical means such as brushing. When performing the flux treatment, there is an effect that the solder can be smoothly melted even if an oxide film is present. That is, since strong bonding is possible, it is possible to use a solder powder whose surface area is increased by using fine powder, which facilitates formation of a highly precise solder pattern. Further, this enables a fine pattern even when other electronic components are mounted.

[0023]

Example 1 In order to connect a TAB component having a 0.25 mm pitch, a printed wiring board in which copper of a corresponding 0.25 mm pitch copper pad part was exposed was exposed to acetic acid.
1% by weight of 2-dodecylimidazole with H adjusted to about 4
Immerse in an aqueous solution at 40 ° C for 30 seconds, wash with water, dry,
An adhesive layer was selectively formed on the surface of the copper pad.
A eutectic solder powder having an average particle size of about 50 μm was sprinkled on the printed wiring board, and excess solder powder was blown off with air to selectively adhere to the adhesive substance portion to obtain a high-definition solder pattern.

After the electronic parts are heated and fixed at 170 ° C. for 30 seconds, a slight amount of unnecessary portion of the solder powder is removed by brushing, and commercially available rosin flux is applied, and then 230 ° C.
Place in a reflow furnace for 1 minute to melt the solder powder to form a solder circuit, and to form a uniform and high-definition thickness on the copper pad surface
A 0 μm solder-coated printed wiring board was obtained. When 50 soldered wiring boards thus obtained were randomly sampled and inspected for solder bridges, no problems were found.

(Comparative Example 1) The same operation as in Example 1 was carried out except that the reflow was performed without performing the heat fixing. Since the heat fixing was not performed, a part of the solder powder in the necessary part fell off when the solder powder in the minute part was removed. Furthermore, the solder powder pattern that was accurate was probably because the solder powder moved due to flux application. Random sampling was performed on the solder-coated printed wiring board that reflowed the solder powder, and the solder bridge was inspected. A bridge was recognized on the printed wiring board. In addition, the solder thickness also varied greatly.

(Example 2) In the same manner as in Example 1, the rosin-based flux of the solder powder fixing portion was applied to the solder powder fixing printed wiring board after heat fixing, and then the pattern of 0. The 25 mm pitch TAB parts were aligned and placed. Thereafter, the solder powder was melted by pressure bonding with a hot bar heated to 250 ° C., and the TAB component was mounted on the printed wiring board. This product had no solder bridge and could be mounted accurately.

Comparative Example 2 When the same procedure as in Example 2 was carried out except that the heat fixing was not carried out, a part of the solder powder adhered during the flux application was moved. Furthermore, in the inspection after mounting and joining the TAB parts, solder bridges were found in about 10% of the products.

Example 3 A 0.3 mm pitch QFP part was placed in a stainless steel mesh container, and the container was placed in a 1% by weight aqueous solution of 2-peptadecyl-4-methylimidazole whose pH was adjusted to about 4 with acetic acid. After dipping in 40 ° C. for 1 minute, it was washed with water and dried. QFP exhibited adhesiveness only in the lead portion, which is the metal exposed portion. Solder powder having an average particle size of 30 μm is attached to the adhesive portion of the QFP,
It was fixed by heating at ℃ for 1 minute. After fixing the solder powder, a rosin-based flux was applied and reflow was performed at 250 ° C. for 1 minute.
A good solder film having a thickness of μm and no bridge was formed.

(Comparative Example 3) Reflow was carried out in the same manner as in Example 3 except that heating and fixing were not carried out. As a result, an exposed metal surface without a solder film was observed on a part of the lead portion, and the solder film The film thickness also varied greatly. It is considered that this cause occurred because the solder powder moved during the flux application.

[0030]

When thin solder powder is used for forming a solder circuit of electronic parts, a fine pattern can be formed, but on the other hand, there is a problem that the oxidized powder surface area increases.

When solder powder containing a large amount of oxide is used, flux can be used to eliminate the influence of the oxide film and strengthen the solder joint strength, but the flux is applied to the solder pattern. In this case, since an extremely fine solder powder pattern is easily destroyed, a solder bridge of the fine pattern of the obtained solder-coated wiring board is likely to occur, or it may cause variation in the uneven film thickness.

According to the present invention, the solder powder pattern adhered to the surface of the adhesive material is heated and fixed to fix the solder powder pattern, and flux can be applied without breaking the solder pattern.

For this reason, it is possible to suppress a phenomenon in which a solder bridge does not occur or to significantly affect it, and it is possible to suppress variations in the solder film thickness because the movement of the solder powder during flux application can be suppressed. It was possible to form a solder circuit that can fully exert the adhesive force of.

Further, after heating and fixing, the solder powder does not easily move due to external factors such as flux application, so that electronic parts can be directly mounted and bonded on the fixed solder powder circuit, resulting in omission of steps and productivity. It has become possible to improve.

Continuation of front page (56) Reference JP-A-4-230095 (JP, A) JP-A-1-227491 (JP, A) JP-A-3-116994 (JP, A) JP-A-6-61636 (JP , A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H05K 3/34 B23K 3/06

Claims (3)

(57) [Claims] To 1. A metal circuit exposed portion of the electronic component include, metal
To impart tackiness by treating with a composition containing at least one tackifying compound that acts and develops tackiness, and after applying solder powder to the tackiness imparting portion, heating and fixing A method for fixing a solder powder, characterized by: To 2. A metal circuit exposed portion of the electronic component include, metal
The composition is treated with a composition containing at least one tackifying compound that acts to develop tackiness to impart tackiness, and solder powder is attached to the solder powder, which is then heat-fixed and then fluxed to the solder powder fixing portion. And then reflowing the solder powder. To 3. A metal circuit exposed portion of the electronic component include, metal
After applying a tackiness by treating with a composition containing at least one tackifying compound that acts and develops tackiness, solder powder is adhered, and after heat fixing, the solder powder fixing portion is provided in correspondence. A method for mounting an electronic component, characterized in that another mounting component is aligned and arranged, a flux is applied before or after the other mounting component is arranged, and reflow is performed.