JPH04335595A - Water cleaning method of soldered printed-circuit board - Google Patents

Abstract

PURPOSE:To provide the water cleaning method, of a soldered printed-circuit board, which eliminates any trouble by bubbles and which can remove corrosive salts and impurities completely. CONSTITUTION:The water cleaning method of a printed-circuit board which has been soldered by using a rosin-based flux and a creamy solder uses cleaning water which contains a defoaming agent. It is proper that the content of the defoaming agent is at 0.001 to 1%.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for washing printed circuit boards soldered using rosin flux and cream solder.

0002

2. Description of the Related Art Currently, rosin-based flux and cream solder containing pine resin as a paste are generally used for electronic devices, and after soldering, they are cleaned with an organic solvent such as chlorofluorocarbon.

However, in recent years, regulations on various organic solvents have become stricter from the standpoint of environmental destruction and occupational health, such as the problem of ozone layer depletion due to fluorocarbons and the suspicion of carcinogenicity of trichlorethylene, and countermeasures have been required. As a countermeasure to this problem, water-soluble cleaning water in which all components are water-soluble has been attracting attention. A simple explanation of the composition of conventional water-soluble cleaning water is water/
Composed of alcohol/surfactant. Water is the best solvent for salts and impurities, and because the amount of amine salt dissolved in water is 300 mg/cc, about 300 times that of alcohol, it is also the most effective solvent for diluting alcohol.

[0004] Water does not have the power to remove impurities adhering to the surface of a printed circuit board, but alcohol dissolves specific impurities and dramatically increases the degree of dryness and significantly shortens the drying time.

Since surfactants can lower the surface energy (surface tension) of water and alcohol at low concentrations, they penetrate into narrow gaps between electronic components and remove salts remaining after soldering.

[0006]

[Problems to be Solved by the Invention] The above-mentioned conventional water-soluble cleaning water contains surfactants, so the surface tension is lowered to the extent that it can penetrate between electronic components, but foaming occurs. The surface tension has not decreased to such an extent. In other words, conventional water-soluble cleaning water or heated water still has a large surface tension (surface tension of water: 73 dynes/
cm 25° C.), it foams, and the foam becomes a hindrance, making it impossible to remove salts and impurities satisfactorily.

In particular, since rosin-based flux has poor water solubility, there is a problem in that salts and impurities cannot be sufficiently removed by washing with water.

[0008] Rosin flux and cream solder are
It contains an activator to remove metal surface oxides and alcohols to adjust flux flow. The activator is a mixture of organic acids, organic amines, organic amine hydrochlorides, hydrobromides, zinc chloride, etc., and the alcohols are monovalent, divalent and/or trivalent fatty alcohols (polymerized alcohols). glycol), etc. Since the activator is acidic, it remains on the surface of the component after soldering.

[0009] In such rosin-based flux and cream solder, when using conventional water-soluble cleaning water, bubbles during cleaning become an obstacle, and the above-mentioned salts and impurities in the flux are removed.
Copper chloride and copper abietic acid often remained on the surfaces or gaps of electronic parts, corroding metal parts and deteriorating insulation. Furthermore, there is also the problem that migration grows in the circuit pattern, resulting in circuit defects.

The purpose of the present invention is to solve the above-mentioned problems, and to provide a method for cleaning soldered printed circuit boards with water, which eliminates problems caused by bubbles and removes corrosive salts and impurities without leaving any residue. It is about providing.

[0011]

Means for Solving the Problems In order to achieve the above object, the water washing method of the present invention is characterized in that washing water containing an antifoaming agent is used.

0012

EXAMPLE There are currently 100 types of antifoaming agents on the market that can be used in the water washing method of the present invention. When classified, there are mineral oil-based, oil-based, fatty acid-based, fatty acid ester-based, lower alcohol, higher alcohol, polyoxyalkylene-based, amide-based, phosphoric acid ester-based, metal soap-based, and silicon-based. Furthermore, to explain the specific types, isopropanol, butanol, amyl alcohol, oleic acid, tall oil, metal soap, polypropylene glycol, polypropylene glycol derivatives, silicone resin,
There are products containing silicone resin with surfactants, and products containing silicone resin with inorganic powder.

[0013] Among these antifoaming agents, in this example,
We selected a compact type of silicon that has low solubility, low surface tension and interfacial tension, good dispersibility and diffusivity, low specific gravity, and is relatively resistant to alkali and heat. According to the test according to the test method described below, the antifoaming agent content was 0.000.
When it was less than 1%, no effect was observed, and when it was more than 1%, stable foam was generated, making it ineffective.

[0014] Next, a test will be described in which cleaning was performed using cleaning water containing 0.1% silicone as an antifoaming agent.

FIG. 1 is a plan view of the test printed circuit board, and FIG.
3 is a diagram showing the amount of ion residue, and FIG. 3 is a diagram showing the results of the insulation resistance value.

As shown in FIG. 1, a comb-shaped copper strip electrode pattern P with a pattern width W=1.0 mm and a spacing L=0.2 mm is made on a printed circuit board, and ICs,
A test printed circuit board was created on which electronic components such as capacitors and IC sockets could be mounted. Electronic components are mounted on this printed circuit board, and rosin-based flux (Tamura Kaken's CF
-330VS) at room temperature for 2 seconds to foam and apply.
After preheating at 00°C, electronic components were soldered using an automatic soldering device. As an example, the water washing process for this substrate is as follows: 60°C warm pure water prewash for 1 minute → water/60% alcohol/1% surfactant/0.1% antifoaming agent (Toray Silicon Co., Ltd. SH-29PA, Toshiba Silicon Co., Ltd.T
Washing was carried out by washing with mixed water of SA730 for 2 minutes and then rinsing with warm pure water for 1 minute. This antifoaming agent, silicone, has excellent chemical stability and thermal stability, and had no effect on the electronic components, plastics, and rubber mounted on it. Silicon-based SH-29PA and silicon-based TSA730 are both water-based types, but SH-29PA can also be used as a solvent.

FIG. 2 shows the results of measuring the ion residue on the printed circuit board that had been cleaned and dried with hot air using an omega meter (manufactured by Nippon Alpha Metals, static method, 6008MD). The principle of this omega meter is to extract the residual ions of the sample into a certain amount of extraction solution (1PA 75%, pure water), measure the electrical resistance of this solution, and use the microprocessor to calculate the electrical resistance value of the same amount. NaC
It is converted into l ions. The unit of the amount of ion residue obtained is mgNaCl/Sq-in. Figure 2
Among them, A is a comparative example based on the prior art, and B and C are examples according to the present invention. B is alcohol/surfactant/SH-
29PA,C is alcohol/surfactant/TSA730
In both cases, the amount of ion residue is smaller than that of Comparative Example A because there is clearly less cleaning interference due to bubbles.

Next, FIG. 3 will be explained. The insulation resistance of the comb-shaped electrode of the comb-shaped copper foil board shown in Fig. 1 was measured, and then in an atmosphere with a temperature of 40°C and a relative humidity of 90 to 95%.
D, C, 30V was applied for 300 hours, and the insulation resistance value was measured. As a result, as shown in B and C in FIG. 3, insulation deterioration was extremely small even after 300 hours. In addition, other silicone antifoaming agents, SH-7PA, SH-28PA, SH-3
Similar results were obtained with 0PA and TSA720. Of course, the silicon used in the present invention is permitted as a food additive under the Food Sanitation Act, so there is no damage to humans or the environment. Furthermore, this water cleaning method is effective for rosin-based flux and cream solder, and is also excellent for water-soluble flux and water-soluble cream solder.

[0019] In addition, the test results according to the above test method are as follows:
It has been confirmed that it is desirable that the content of the antifoaming agent be 0.0001% to 1%, but any content of 1 ppm or less or 1% or more is included in the present invention as long as it does not impair the effects of the present invention. Furthermore, all antifoaming agents other than silicone are also included in the present invention.

[0020]

According to the present invention, by using cleaning water containing an antifoaming agent, the rosin flux and cream solder remaining on the printed circuit board after soldering are completely washed away, preventing electrolytic corrosion and deterioration of insulation. A mounted printed circuit board for electronic equipment with extremely high reliability without any problems can be obtained. Furthermore, the water washing method of the present invention does not reduce workability, productivity, increase drainage volume, or cause drainage troubles, and does not require treatment based on the Water Pollution Control Law or the Sewerage Law, making it extremely useful in terms of resource and energy conservation.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a test printed circuit board of the present invention.

FIG. 2 is a diagram showing the amount of ion residue.

FIG. 3 is a diagram showing insulation resistance values.

Claims (2)

[Claims] Claim 1. A method for water cleaning a printed circuit board soldered using rosin-based flux and cream solder, the method comprising using cleaning water containing an antifoaming agent. Method. 2. The content of the antifoaming agent is 0.0001 to 0.0001.
2. The method of washing a soldered printed circuit board with water according to claim 1, wherein the water washing amount is 1%.