JP2020131219A - Joining material - Google Patents

Abstract

To solve a major problem that has arisen in recent years along with a trend of increase in mounting density on the printed circuit board owing to downsizing of printed circuit board and miniaturization of electronic components, resulting in occurrence of significant conduction failure caused by attachment of fine solder balls or fine flux particles onto contacts of electronic components and the like.SOLUTION: A joining material comprises a gum-containing solder wire having openings or slits arranged at a predetermined interval and coated with flux. The flux contained in a core part of the solder wire may account for 0.2% or more and less than 6.3% with respect to a whole weight. The flux coated over a whole of the solder wire may account for 0.3% or more and 5.0% or less with respect to the whole weight.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method of joining various electronic components using a solder wire when electrically joining various electronic components to a printed wiring board or the like.

Conventionally, solder has been used to mount various electronic components on a printed wiring board. Such solders are used by adding various metals, mainly tin, to melt and alloy them. Of these, solder often contains a resin composition called flux. The flux is used for removing the oxide film at the soldered portion, preventing the oxidation of the soldered portion and the molten solder, and improving the wettability of the solder.

In general, solder that contains flux in the center of the solder wire (JIS Z 3283 or solder). At the time of soldering, the flux in the central part of this solder wire acts to remove the oxide film on the soldering surface and prevent the molten solder metal from oxidizing, so that the soldering is completed stably. The electrical connection between the electronic component and the printed wiring board is completed.

A soldering iron is generally used as a heat source for melting the solder. A soldering iron is applied to the solder wire, and the heat of the soldering iron is conducted to the solder wire to melt the solder wire, and the flux contained in the center is also melted for soldering. carry out.

Due to the heat conduction from the soldering iron, the temperature rises from the metal part of the solder, and the heat of the solder itself rises. From the constituent materials, the melting point (softening point) of the flux is about 60 ° C. to 80 ° C., and the melting point of the metal is 217 ° C. for Sn-3.0% Ag-0.5Cu.

When the solder is heated from the outside using a soldering iron, a small amount of flux is dissolved from the end face of the solder wire due to the difference in melting point described above. After that, the metal starts melting from the point where the melting point of the metal is exceeded, and the flux contained in the central portion is rapidly released accordingly. When this flux is released, it may exceed the melting point of the flux and further exceed the boiling point of the content component of the flux. With the force gasified beyond the boiling point, the molten solder metal and molten flux that exist around it are blown off, creating fine solder metal balls or fine particles of flux on the printed wiring board. The phenomenon occurs.

In recent years, the mounting density on the printed wiring board tends to increase due to the miniaturization of the printed wiring board and the miniaturization of electronic components. There is a big problem that such fine solder balls or fine flux particles adhere to the contacts of electronic parts and the like, resulting in a large conduction failure.

Conventionally, it has been devised to change the positions where the solder metal and the flux exist in order to eliminate the particles of the solder balls and the flux generated when the solder balls and the flux are electrically bonded by using the solder.

In addition, when the solder wire is heated, the flux exceeds the boiling point and gasifies, and the pressure rises. Therefore, the solder wire is cut in the length direction or holes are made in the solder wire at regular intervals. It has also been devised.

Published Patent Gazette No. 55-54298

The method of coating the solder wire described in Patent Document 1 with flux is very effective in generating solder balls and flux particles in that the flux and the solder wire are melted in ascending order of melting point. In addition, the method of cutting into the solder wire or making holes at regular intervals is also effective for removing the gas component of the dissolved and vaporized flux.

However, in the technique of applying flux to the surface of the solder wire, the flux must contain a special resin in order to ensure the flexibility of the solder wire. Flux containing this special resin remains at the tip of the soldering iron used for soldering, and it is carbonized by the heat of the soldering iron, causing the drawback that the heat of the soldering iron cannot be conducted to the solder wire, which is practical. Cannot be converted.

In addition, in the method of cutting into the solder wire or making holes at regular intervals, moisture in the atmosphere is mixed into the flux from the notch or holes, reducing the effect of the flux and boiling the contained moisture. Therefore, it cannot be put into practical use because the number of solder balls and flux particles increases.

The present invention has a configuration in which a notch for degassing when the flux is vaporized is made in the solder wire, and a flux adjusted so that moisture in the atmosphere is not mixed into the flux is applied to the surface thereof. It is a thing. Also, in order to prevent the applied flexible flux from adhering to the soldering iron and carbonizing and hindering heat conduction, a better content ratio between the flux in the central part and the flux applied to the surface is set. It was discovered and commercialized.

That is, the bonding material according to claim 1 is characterized in that notches or openings are provided at regular intervals and the solder wire is coated with flux.

In the bonding material according to claim 2, the flux contained in the central portion of the solder wire is 0.2% or more and less than 6.3% based on the total weight, and the flux to be coated is based on the total weight. It is characterized by being 0.3% or more and 5.0% or less.

According to the present invention having the above-described configuration, the flux on the surface does not allow moisture to permeate and can also block air, so that oxidation of the solder metal during storage can be prevented, and the solder wettability can be prevented. It has the effect of improving.

It is sectional drawing of the bonding material which concerns on this invention.

Hereinafter, the bonding material to which the present invention is applied will be described in detail with reference to the drawings. The bonding material to which the present invention is applied is a solder wire coated with flux, which is provided with notches or openings at regular intervals.

In the present invention, a notch is provided so that the solder wire can reach the flux in the length direction. Further, the notched solder wire is impregnated with the molten coating flux, and a coating flux having a certain thickness is applied to the surface.

At this time, the flux applied to the surface does not have to be impregnated with an activator that contributes to soldering. The coating flux to be applied should maintain the flexibility of the solder wire without impairing the flexibility of the solder wire. Furthermore, it is important not to allow water to penetrate the central flux.

Further, since the purpose of the notch is to remove the gas component of the flux at high temperature, it may be a release hole at regular intervals.

According to the above-mentioned product design, the flux is coated on the surface of the solder wire, and the flux is further contained in the central portion.

When a solder wire with a notch coated with flux is heated by applying a soldering iron, the coating flux on the surface melts and is weak, but the action of heating the temperature of the joint and the soldering surface It exerts a coating action and prevents the surface participation of the solder wire due to the heating of the joint.

Next, when the solder metal reaches the melting point and melts, the flux in the central part also melts and spreads wet, and the solder metal wets and spreads in the soldered part where the clean surface is exposed by the flux in the central part, and the electrical bonding is completed. To do.

At the same time, the coating flux adhering to the soldering iron is washed away by the flux in the central part, and the cleanliness of the soldering iron is maintained.

Since the flux in the central portion is designed mainly for solderability, it has the characteristics of being hard, brittle, and hygroscopic because it is mainly composed of rosin or the like.

The flux applied to the surface must have flexible physical properties without cracking or chipping that does not impair the flexibility of the solder wire. However, the flux retained by this effect is carbonized at a high temperature of the soldering iron and retains the property of hindering heat conduction.

It can be confirmed that the effect of the present invention is exhibited by retaining and supplementing these two characteristics with two types of flux, and further carbonization can be prevented by adjusting the content ratio.

Further, since the flux on the surface does not allow moisture to permeate and can block air, it is possible to prevent oxidation of the solder metal during storage, which has the effect of improving the solder wettability.

The flux contained in the center of the solder wire is 0.2% or more and less than 6.3% with respect to the total weight. If it is less than the lower limit of 0.2%, the soldering performance is inferior, and if it exceeds the upper limit of 6.3%, it deviates from the JIS standard and processing becomes difficult. However, in future technological development, it will be possible to further increase the content.

Further, the flux to be coated is 0.3% or more and 5.0% or less with respect to the total weight. If it is less than the lower limit of 0.3%, the uniformity of the coating layer becomes unstable, moisture in the atmosphere is mixed with the contained flux, and the soldering performance deteriorates. If the upper limit of 5.0% is exceeded, carbides will adhere to the soldering iron.

Flux component / contained flux Hydrogenated rosin 96.0% by weight
2 Ethylhexylamine hydrochloride 1.5% by weight
Palmitic acid 2.5% by weight
-Coating flux Ethylene-vinyl acetate copolymer 54.0% by weight
Super flame rosin 25.0% by weight
Fatty acid amide 21.0% by weight

The above-mentioned flux components containing flux and coating flux were compared and evaluated by changing their respective contents. The solder alloy used is Sn-3.0Ag-0.5Cu.

As shown in FIG. 1, a notch was made in the solder wire, and the surface was coated to prepare a test piece. As shown in FIG. 1, the slightly intruded solder wire (bonding material) contains a flux 4 contained in the solder wire 3, and a notch 2 is introduced in the solder wire 3. The surface of the solder wire 3 is coated with a coating flux 1.

The carbides adhering to the soldering iron were soldered at the iron tip temperature of 380 ° C., and the carbonization level was visually observed. Further, in order to evaluate the content of the coating flux, the test piece was placed in a high temperature and high humidity bath of 40 ° C.-90% for 96 hours, and then soldered at a soldering tip temperature of 320 ° C. to remove the solder balls and the flux. We also observed the occurrence of grain scattering. The scattering test of solder balls and flux particles complied with JIS-Z-3197: 2012 flux scattering test.

The generation of carbides was visually confirmed. The coating flux is carbonized at the soldering temperature due to the characteristics of the raw material. This utilizes the phenomenon that the rosin-based flux in the central portion melts and mixes with the coating flux to prevent carbonization of the coating flux.

As in Examples 1, 4 and 7, the characteristics of the coating flux are superior to the characteristics of the flux contained in the central portion, and carbides are generated in the soldering iron.
On the contrary, in Examples 2, 3, 5 and 6, the characteristics of the flux contained in the central portion are superior to the characteristics of the coating flux, and carbides are prevented on the soldering iron.

Example 1 is a result in which the uniformity of the coating layer is not stable, so that the slacks contained in the central portion absorb moisture, a large amount of gas is generated, and scattering can be confirmed.

1 Coating flux 2 Notch 3 Solder wire 4 Containing flux

That is, the bonding material according to claim 1 has notches or openings at regular intervals, and the solder wire is coated with flux, and the flux contained in the center of the solder wire is relative to the total weight. The flux to be coated, which is 0.2% or more and less than 6.3%, and which can block air without permeation of moisture, is 0.3% or more and 5.0% or less based on the total weight. It is characterized by.

In the invention according to claim 1 , the bonding material according to claim 2 contains ethylene-vinyl acetate copolymer: 54.0% by weight, rosin: 25.0% by weight, and fatty acid amide: 21.0% by weight. When coated with the flux to be coated, it is characterized in that it is 0.3% or more and 5.0% or less with respect to the total weight of the flux to be coated .

Flux component / contained flux Hydrogenated rosin 96.0% by weight
2 Ethylhexylamine hydrochloride 1.5% by weight
Palmitic acid 2.5% by weight
-Coating flux Ethylene-vinyl acetate copolymer 54.0% by weight
Rosin 25.0% by weight
Fatty acid amide 21.0% by weight

Claims (2)

A bonding material characterized in that a flux is coated on a solder wire that is notched or has openings at regular intervals. The flux contained in the center of the solder wire is 0.2% or more and less than 6.3% with respect to the total weight, and the flux to be coated is 0.3% or more and 5.0 with respect to the total weight. The bonding material according to claim 1, wherein the content is% or less.

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