JPS61199598A - Flux for soldering and cream solder - Google Patents

Abstract

PURPOSE:To obviate the decrease in insulation resistance after soldering, to decrease the deterioration of the insulation resistance with lapse of time and to improve reliability by using a rosin resin as an essential component for a flux for soldering and adding methacrylate or acrylate as flux thereto. CONSTITUTION:The methacrylate such as ethyl methacrylate or methacryl n-butyl or the acrylate such as ethyl acrylate or n-butyl acrylate is used as the flux. These methacrylate and acrylate themselves have the extremely high insulation resistance and therefore even if such are incorporated into the residual flux, the decrease in the insulation resistance is obviated. These fluxes may be used alone or may be mixed with other fluxes. There are natural rosin, water white rosin refined from natural rosin, synthetic rosin, etc. as the rosin resin. The cream solder is obtd. by mixing the above-mentioned flux for soldering and the pulverous particles of solder.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to soldering flux and cream solder used for soldering printed circuit boards, etc., and more specifically, to a soldering flux and cream solder that is mainly composed of rosin resin. This paper relates to the improvement of solvents in flux.

[Conventional technology]

Conventionally, soldering is often used when mounting T-elements on printed circuit boards.

In order to achieve highly reliable soldering, the above soldering method involves cleaning the surface of the metal to be joined with liquid flux or high-adhesive flux before soldering, or using a method that uses a mixture of solder particles and 7lux. This is done using methods such as cream solder.

Here, the above 7 luxes include product quality and reliability.
(a) High insulation, (b) non-corrosion, (C) long-term stability,
(d) It is required that the material does not change in other parts, and from the viewpoint of soldering work, (a) it does not generate toxic gas, (b) it has good solderability (oxidation on the metal surface). It has the effect of removing objects by melting and wrapping the metal surface,
Furthermore, it lowers the surface tension of molten solder),
(C) It must be easy to clean, and (d) it must not be sticky.

In general, in the field of electronics industry, so-called rosin-based soldering flux, which is prepared by adding activators, molten hydrogen, etc. to a rosin-based resin as a main component, is often used as a flux that meets the above requirements. has been done.

The above-mentioned solvent is used for the purpose of uniformly applying rosin, and alcohol, which dissolves rosin well, has usually been used. As the above-mentioned alcohol, for example, methyl alcohol or isopropyl alcohol is used in liquid flux for automatic soldering of printed circuit boards, and high-grade alcohols such as glycols such as 1,3-butanediol are used in flux in cream solder. alcohol is used.

However, when alcohol is used as a solvent in this way, the insulation resistance of these alcohols is low, so if the heating during soldering is insufficient, alcohol may be contained in the residual flux after soldering. , which causes a decrease in insulation resistance between circuits.

The alcohol in the residual flux will gradually volatilize over time, increasing the insulation resistance, but if the residual flux film is thick, the degree of alcohol volatilization will be slow.
Insulation resistance also does not increase easily, which causes a decrease in the reliability of electronic equipment.

In addition, even though this type of flux sufficiently volatilizes the alcohol in the residual flux and has high insulation properties, when exposed to a high humidity atmosphere, it absorbs moisture in the air.
There is a drawback that the insulation resistance decreases again and the product becomes defective in the market.

In particular, this tendency is strong in high-tack fluxes used for temporary fixing of flat package ICs and fluxes contained in cream solders, so there is a strong desire to improve this tendency.

[Problem that the invention seeks to solve]

In this way, when alcohol is added as a solvent for rosin-based solder elbow fixing, the residual alcohol etc. in the residual flux decreases during soldering, the insulation resistance of this residual flux decreases, and this change over time decreases. There is a problem in that the soldering condition is largely unreliable.

Therefore, the present invention has been proposed to solve the above-mentioned problems, and includes a flux for solder elbows that has a small decrease in insulation resistance even if the residual 7 lac contains a solvent, and has little change over time. The purpose is to provide cream solder.

[Failure to solve the problem]

In order to achieve the above object, the present inventors conducted intensive research and found that methacrylic acid ester or acrylic acid ester itself has high insulation resistance and good solubility in rosin resin. This is what we have come to complete.

That is, the flux for soldering elbows, which is the first invention of the present invention, is characterized by having a rosin resin as a main component and adding a methacrylic acid ester or an acrylic acid ester as a solvent. The cream solder, which is the second invention, is made by mixing 7lacs for soldering, which is mainly composed of rosin resin and with the addition of methacrylic acid ester or acrylic acid ester as a solvent, and solder fine particles. be.

Here, the above-mentioned solvent includes ethyl methacrylate, n-butyl methacrylate, glycyl methacrylate, methacrylic esters such as diethylamine ethyl methacrylate, cyclohexyl methacrylate, and tetrahydrofurfuryl methacrylate, or ethyl acrylate, n-butyl acrylate, glycidyl acrylate,
Examples include acrylic esters such as diethylaminoethyl acrylate, cyclohexyl acrylate, and tetrahydrofurfuryl acrylate. These methacrylic esters and acrylic esters themselves have extremely high insulation resistance, so even if they are contained in the residual flux, the insulation resistance will not decrease. Note that these solvents may be used alone or in combination with other solvents.

Further, examples of the rosin-based resin include natural rosin extracted from pine trees, water-based white rosin made from this natural rosin, and resins synthesized chemically from rosin.

In particular, when a highly active flux is required to actively remove oxides and dirt from the surface of the metal to be joined,
An activator may be added to the rosin resin. As this activator, a compound is used, such as amine hydrochloride, which reacts with heat, decomposes at high temperature to liberate hydrochloric acid, and decomposes surface oxides and dirt.

On the other hand, the cream solder according to the present invention is a mixture of a highly viscous cream component containing the above-mentioned solder elbow flux and fine solder particles, and can be used to solder electronic components and the like through a single reflow operation. The viscosity and metal content of this cream solder, the size and shape of the solder particles, etc. may be within normal ranges.

[Effect]

Therefore, the 7LAX and cream solder for soldering of the present invention have a high insulation resistance as a solvent, and contain methacrylic ester or acrylic ester that sufficiently dissolves the rosin resin. Even if these solvents are included in the flux, the insulation resistance is high and the change over time is small.

〔Example〕

Specific examples of the present invention will be shown below, but it goes without saying that the invention is not limited thereto.

Example 1 Water white rosin (hereinafter abbreviated as WW rosin) 30% by weight, cyclohexalamine hydrochloride 0.5% by weight as an activator, ethyl methacrylate 69 as a solvent
．． A liquid flux was prepared by mixing 5''M of the mixture.

Example 2 A cream solder was prepared by mixing 88% by weight of solder powder and 12% by weight of 7lux.

The composition of the above flux is 65% by weight of ww rosin, 0.5% by weight of diethylguanidine hydrobromide as an activator and 3% by weight of hydrogenated castor oil, and 31.5% by weight of ethyl methacrylate as a solvent. did.

Example 3 70% by weight of ww rosin, 10% by weight of hydrogenated castor oil and 1% by weight of cyclohexalamine hydrochloride as activators.
A highly adhesive 7 lac was prepared by mixing 19% by weight of ethyl methacrylate as a solvent.

Example 4 I-form Fusix was prepared in the same manner as in Example 1 except that the solvent was changed to tetrahydrofurfuryl methacrylate.

Example 5 A cream solder was prepared in the same manner as in Example 2 except that the solvent in the flux was changed to tetrahydrofurfuryl methacrylate.

Example 6 A high tack flux was prepared in the same manner as in Example 3 except that the solvent was changed to tetrahydrofurfuryl methacrylate.

Comparative Example 1 A liquid flux was prepared in the same manner as in Example 1 except that the solvent was changed to inpropyl alcohol.

Comparative Example 2 Shifreem solder was prepared in the same manner as in Example 2, except that the solvent in the flux was changed to 1.3-butanediol.

Comparative Example 3 A high tack flux was prepared in the same manner as in Example 3 except that the solvent was changed to inpropyl alcohol.

Soldering was performed using the liquid fluxes, high adhesive slacks, or cream solders prepared in Examples 1 to 6 and Comparative Examples 1 to 3, and each residual flux after soldering was evaluated according to JIS- Z-3197
According to the insulation resistance test method shown in -4, 10, the initial insulation resistance and the temperature of 40℃ and the relative humidity of 90℃ were tested at 72℃.
The insulation resistance after time exposure was measured. In addition, the thickness of the residual flux was measured to be 300 to 500 μm. The results are shown in Table 1.

Table 1 As is clear from Table 1, the insulation resistance of 7LAX (Comparative Examples 1 to 3) using alcohol as a solvent is low, whereas methacrylic acid as a solvent as in this example shows low insulation resistance. When soldering is carried out using flux or cream solder containing ester, it exhibits extremely high insulation resistance and can maintain high insulation resistance even when exposed to a high humidity atmosphere for a long time.

〔Effect of the invention〕

As explained above, the flux for soldering elbows of the present invention has methacrylic ester or acrylic ester added as a solvent, so even if the residual flux after soldering contains a solvent, the insulation resistance is low. The insulation resistance does not deteriorate, the change in insulation resistance over time is small, and it has excellent long-term stability, making it possible to perform highly reliable soldering.

In addition, in the cream solder of the present invention, since the soldering flux using methacrylic ester or acrylic ester as a solvent is used as the flux component, this flux component oozes out during the process. However, there is no decrease in insulation resistance, and there is almost no decrease in insulation resistance due to changes over time.

Claims (2)

[Claims] (1) A soldering flux characterized by containing a rosin resin as a main component and adding a methacrylic ester or an acrylic ester as a solvent. (2) A cream solder made by mixing solder fine particles with a soldering flux made of a rosin-based resin as a main component and to which a methacrylic ester or an acrylic ester is added as a solvent.