JPH04393A - Method for washing flux after soldering - Google Patents

Abstract

PURPOSE:To safely and satisfactorily wash a flux used for soldering by washing the flux with N-methylpyrrolidone as a solvent. CONSTITUTION:Chips, etc., are soldered to ceramic substrates, etc., with a flux to obtain electronic parts, etc. The flux is then removed by washing with a solvent and N-methylpyrrolidone is used as the solvent. N-methylpyrrolidone is safe to the human body and environment and has 95 deg.C flash point, 202 deg.C b.p., 346 deg.C ignition point and superior solvent power to the flux. When N- methylpyrrolidone is used at about 60 deg.C, the flux can be safely and satisfactorily washed.

Description

[Detailed Description of the Invention] [Summary] The purpose of the present invention is to provide a method for cleaning soldering flux that is safe and sufficiently good, and for cleaning flux after soldering. The structure uses N-methylpyrrolidone as a solvent.

[Industrial application field]

The present invention relates to a method for cleaning soldering flux.

2. Description of the Related Art In recent electronic circuit devices, various components have been miniaturized, and various soldering techniques are used to reliably join a large number of miniaturized microcomponents. In particular, in thin film multilayer substrates that constitute electronic circuits, the thickness is 3μ through an insulating layer.
Which conductor layers are laminated, and paper phase soldering (VPS) is used to join such thin conductor layers.
) will be adopted. Flux is usually used for soldering. Flux is made of, for example, pine resin mixed with an activator, and has the effect of preventing the formation of an oxide film on the surface of the base material and the surface of the molten solder, thereby ensuring good soldering. When soldering work is completed, the surface of the soldered part is often cleaned to remove flux. That is, after soldering, the activator contained in the flux often has a negative effect on the soldered part, contrary to what it does during soldering, so it is desirable to thoroughly clean the flux. In particular, the surface conductor layer of thin-film multilayer substrates that make up electronic circuits is extremely thin.
If even a small amount of flux remains, the conductor layer on the surface will corrode and the durability will decrease, so it is necessary to thoroughly wash away the flux after soldering. but,
After soldering, the flux hardens and becomes difficult to remove, making it difficult to clean it well enough so that even minute portions of flux do not remain.

[Conventional technology]

For this reason, conventionally, a solvent has been used to clean the flux after soldering. However, the types of solvents that can sufficiently clean flux after soldering are limited; for example, the solvents that have been used until now are trichlorethylene (
trichloroethane), trichloroethane, or Freon. Recently, a fruit oil-based solvent, which is a mixture of alcohol and fruit oil extracted from fruit peels (orange beer, etc.), has begun to be used as a solvent for cleaning flux after soldering.

[Problem to be solved by the invention]

The above-mentioned trichlorethylene, trichloroethane, freon, etc. are relatively good solvents for cleaning flux after soldering, but even if these solvents are used, some fluxes may not be removed well depending on the type of flux. In addition, the use of these solvents has recently been restricted due to their adverse effects on the human body and the environment, and therefore they must be excluded from the scope of use.

Therefore, fruit oil-based solvents have recently been attracting attention. However, although fruit oil-based solvents are harmless, their cleaning power is relatively low. Therefore, in order to clean the flux that solidifies and becomes difficult to remove, it is necessary to raise the temperature of the solvent, but fruit oil-based solvents emit a strange odor when the temperature is raised. There is a problem in that it deteriorates the surrounding environment and therefore cannot raise the cleaning temperature. For this reason, in cases where it is required to clean even minute parts, such as in the case of thin-film multilayer substrates, it cannot be said that fruit oil-based solvents can sufficiently clean soldering flux.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for cleaning soldering flux that is highly safe and can perform sufficiently good cleaning.

[Means to solve the problem]

The method for cleaning soldering flux according to the present invention is characterized in that N-methylpyrrolidone is used as a solvent to clean the flux used for soldering after soldering.

[For production]

N-Methylpyrrolidone is harmless to the human body and the environment, dissolves most types of flux well, and has a relatively high flash point, so it can be cleaned at high temperatures and is used as a soldering flux. It was found to be suitable for cleaning. Furthermore, since N-methylpyrrolidone has a high affinity with water, washing with water can be performed after washing with N-methylpyrrolidone, and ionic residues can be completely eliminated.

〔Example〕

FIG. 1 shows an embodiment of the present invention, and is a diagram showing an electronic component 12 being cleaned in a tank 10 filled with N-methylpyrrolidone (NMP). The electronic component work 2 is, for example, a thin film multilayer board for forming an electronic circuit, and this is made by forming a thin conductor layer 16 on the surface of a ceramic substrate 14, and
An insulating layer 18 made of polyimide resin is formed on 6,
Further, a thin conductive layer 20 is formed on the surface of the insulating layer 18. The conductor layers 16, 20 of each layer can be connected to each other by via holes (not shown) provided in the ceramic substrate 14 or the insulating layer 18, and the top conductor layer 20 can be connected to a lead or other layer by soldering. Connected to electrical elements. In FIG. 1, an example is shown in which a chip component 22 is placed on a conductor layer 20 and soldered at a soldering portion 24. For example, solder is made of tin and lead (Sn/
It is a Pb)-based flux, and a flux made by mixing pine resin with an activator is used.

In the present invention, N-methylpyrrolidone (NMP) is used as a flux solvent. N-methylpyrrolidone (NMP) has the structure shown below.

the -CH.

The following table shows the results of a comparative test between the prior art cleaning process and the cleaning process of the present invention.

CH3 N-methylpyrrolidone (NMP) is safe for the human body and the environment, has excellent flux solubility, and has a flash point of 95°C, a boiling point of 202°C, and an ignition point of 346°C. Since the flash point is relatively high, cleaning can be performed at high temperatures. In the example, cleaning was performed using N-methylpyrrolidone (NMP) at 60°C, and good results were obtained.

As shown in Figure 2, N-methylpyrrolidone (NMP)
has excellent affinity with water, so after cleaning with N-methylpyrrolidone (NMP), the electronic component 12 can be cleaned with pure water or a mixture of pure water and alcohol. Therefore, even if ion residues remain after washing with N-methylpyrrolidone (NMP), the ion residues can be completely removed by subsequent washing with water.

○Very good △Good Good The results were also determined by inspecting the soldered parts under a microscope and visually determining the presence of flux residue.

Conventional processing A uses a trichloroethane-based solvent, and first, for example, the electronic component 12 having the soldering part 24 is soldered.
It was placed in a trichloroethane-based solvent at 0°C and washed for 10 minutes. Next, ultrasonic cleaning was performed for 5 minutes in the same trichloroethane solvent at 60° C., and finally it was blown with nitrogen gas. The results are shown in the table above, and it can be said that some types of fluxes (for example, organic acid fluxes) are well cleaned, while other fluxes are not cleaned well.

In the conventional processing port, a fruit oil-based solvent was used, and the electronic component 12 having the soldered portion 24 was first placed in the fruit oil-based solvent at room temperature and washed for 10 minutes.

Furthermore, after the electronic component 12 was taken out, it was again placed in a fruit oil-based solvent at room temperature and washed for 2 minutes. Next, 60°C
After washing with pure water at 60°C for 2 minutes, washing again with pure water at 60°C for 2 minutes, and finally blowing with nitrogen gas.

The results of this treatment show that most of the fluxes do not fall down sufficiently. One of the reasons for this is that the cleaning temperature cannot be increased because fruit oil-based solvents emit a strange odor when the temperature is increased.

In the process of the present invention, the electronic component 12 having the soldered portion 24 is first heated at 60°C using N-methylpyrrolidone (NMP).
) and washed for 10 minutes. Furthermore, electronic parts 1
After taking out 2, add N-methylpyrrolidone (
NMP) and washed for 2 minutes. Next, it was washed with pure water at room temperature for 2 minutes, washed again with pure water at room temperature for 2 minutes, and finally blown with nitrogen gas.

As a result of this treatment, it was found that the solvent N-methylpyrrolidone (NMP) effectively removed most of the flux. Microscopic examination of the soldered joints revealed that a small flux residue was found after cleaning with N-methylpyrrolidone (NMP); however, N-methylpyrrolidone (NMP)
By washing with water after washing with water, the flux residue was further removed, and even when a minute residue was observed, the ion residue of the flux was almost zero.

In addition, although the above explanation is based on the case where N-methylpyrrolidone (NMP) is pure, N-methylpyrrolidone (NM
P) may be used by adding several percent of other organic solvents, such as alcohol dimethylamide, dimethyl formaldehyde, etc.

In short, it has been known for a long time to use N-methylpyrrolidone (NMP) as a solvent; It wasn't something. For example, N-methylpyrrolidone (NMP) has conventionally been used as a solvent for a precursor of a polyimide resin forming the insulating layer 18 of a thin film multilayer substrate, or as a stripping agent for a positive resist. We came up with the idea of using N-methylpyrrolidone (NMP), which is only used in special cases, to clean soldering flux, and after repeated tests, we found that it is suitable for cleaning soldering flux. This has been confirmed.

〔Effect of the invention〕

As explained above, according to the present invention, by using N-methylpyrrolidone as a solvent for cleaning the flux used for soldering after soldering, the soldering flux can be cleaned safely and sufficiently. Became.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the flux of the soldered parts in the embodiment of the present invention being cleaned with NMP, and Fig. 2 is a diagram showing the soldering parts of Fig. 1 washed with water after being cleaned with NMP. . 10... Tank, 12... Electronic component, 16
, 20... Conductor layer, 22... Chip component, 2
4...Soldering part.

Claims (1)

[Claims] A method for cleaning soldering flux, characterized in that N-methylpyrrolidone is used as a solvent to clean the flux used for soldering after soldering.