JPH05327183A - Method for managing electrodeposition bath - Google Patents

Abstract

PURPOSE:To refine a negative electrodeposition bath without impairing economy and productivity by ultrafiltering the bath, sensing deterioration of the bath according to a measured value of conductivity of obtained filtrate, and purifying the deteriorated bath. CONSTITUTION:A negative electrodeposited resist bath contains polymer with carboxyl group as a constituent unit. Thus, in the case of an anionic negative electrodeposition resist bath, the carboxyl group exists in a state suspended in a main chain in acrylic polymer formed of acrylic acid and its derivatives, and hence dissociation of the carboxylic group to proton is suppressed. Accordingly, even if organic acid having large dissociation constant is generated in the bath, one type of ion exchange between the acid and carboxylate in the polymer, and ions in the bath are not increased. On the other hand, partial neutralized product of the polymer does not exist in the ultrafiltrate, and salt of the impurity affect influence to conductivity. Therefore, deterioration degree of the bath can be easily sensed according to the measured value of the conductivity of the ultrafiltrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for managing a negative electrodeposition resist bath used in the manufacturing process of printed wiring boards.

[0002]

2. Description of the Related Art In an electrodeposition resist method for forming a resist film by an electrodeposition coating method, management of an electrodeposition bath is extremely important. Usually, the wiring board is manufactured by the electrodeposition resist method by the following process.

Degreasing of substrate → washing → pickling → washing → electrodeposition →
Washing → drying → exposure → development → etching → resist film peeling Then, in order to increase the utilization rate of the solid content of the electrodeposition bath, a part of the electrodeposition bath is subjected to ultrafiltration, and the high solid content electrodeposition solution is electroplated. The filtrate (hereinafter referred to as "ultrafiltrate") returned to the electrodeposition tank is used as a cleaning liquid for collecting the solid component of the electrodeposition bath adhering to the electrodeposition substrate. Further, in order to keep the solid content concentration of the electrodeposition bath constant, the amount of the electrodeposition bath consumed by the electrodeposition is replenished. Water balance is maintained by purging the ultrafiltrate.

However, when long-term continuous electrodeposition is carried out, the acid component of the pickling solution or the hydrolysis product of the resist component, especially the organic acid, accumulates in the electrodeposition bath. As a result, the elution of copper from the copper-clad substrate is promoted, the properties of the electrodeposition coating film deteriorate, and in the worst case, the resist film develops poorly.

In order to avoid such troubles, in the past, 1) when an abnormal coating film such as poor development occurs, a large amount of the ultrafiltrate in the electrodeposition bath is discarded, and a considerable amount of the simulated filtrate is transferred to the electrodeposition bath. Supply. 2) A part of the ultrafiltrate of the electrodeposition bath is always discarded, and a considerable amount of the simulated filtrate is supplied to the electrodeposition bath. Such a bath management method was adopted. However, these methods are insufficient in terms of economical efficiency or productivity.

[0006]

In the conventional bath control method, the concentration of impurities in the electrodeposition bath, which adversely affects the properties of the electrodeposition coating film, is not clearly understood. Or, there is a tendency that inconvenience may occur such that it is too late to respond. This is because the concentration of impurities in the electrodeposition bath, which is an indicator of bath deterioration, or the amount having a primary relationship with the concentration is not known.

The impurity concentration in the electrodeposition bath can be determined by analyzing the ultrafiltrate by liquid chromatography. However, this method has the limitation that it takes a long time to stabilize the equipment or that the column must be maintained and managed with great care.Therefore, this method is not suitable as a process analysis method that requires swiftness. Hard to say. If there is a simpler method to detect the impurity concentration in the electrodeposition bath,
Bath management will be easier and more economical to implement.

[0008]

[Means for Solving the Problems] Generally, the management of the electrodeposition bath is
It is carried out by measuring characteristic values such as the electric conductivity or pH of the bath. However, the electrodeposition bath consists of an aqueous solution or suspension of a partially neutralized product of a weakly acidic or weakly alkaline polymer, and changes in the above characteristic values due to an increase in the impurity concentration are reduced by the partially neutralized product of the polymer. Therefore, it is quite difficult to detect the deterioration degree of the bath by measuring these characteristic values. Therefore, in reality, it is the current situation that the deterioration of the bath is known only after the deterioration of the coating film properties occurs.

As a result of various investigations by the present inventors on means for early detection of bath deterioration, the conductivity of the ultrafiltrate in the electrodeposition bath has a nearly linear relationship with the concentration of impurities in the electrodeposition bath. The present invention has been completed and the present invention has been completed.

That is, according to the present invention, the negative type electrodeposition resist bath is subjected to ultrafiltration, the degree of deterioration of the obtained filtrate is detected from the measured value of the electric conductivity of the filtrate, and a part or the whole of the deteriorated bath is detected. It is a method of controlling an electrodeposition bath characterized by refining.

Ultrafiltration is usually performed in order to increase the utilization rate of the solid content of the electrodeposition bath, as described above, and to return the high-solid content electrodeposition solution from the electrolytic bath diluted with water to the electrodeposition tank. In the present invention, the electric conductivity of the filtrate thus obtained is measured. The method for measuring the conductivity may be a commonly used method.

The degree of electric conductivity at which the bath is to be purified or discarded depends on the properties of the intended electrodeposition coating film and the type of bath and cannot be generally stated. Normally,
Once the conductivity of the ultrafiltrate is measured and the evaluation substrate is continuously created, the allowable conductivity is determined from the properties of the electrodeposition coating film on the obtained substrate, and the conductivity is used as a guide from the next time onward. A method of bath management is taken.

As a method of purifying the bath, a method of passing it through an ion exchange resin column is generally used. In this case, there are a method of passing the electrodeposition bath itself and a method of passing the limiting filtrate, but the latter is preferable from the viewpoint of easy regeneration of the ion exchange resin in the column. As another method for purifying the bath, there is a method of discarding a part of the electrodeposition liquid or a part or all of the limiting filtrate and supplying a new electrodeposition liquid or a simulated filtrate to the electrodeposition tank.

[0014]

[Function] There is no clear correlation between the conductivity of the electrodeposition bath itself and the concentration of impurities, and there is a significant correlation between the conductivity of the ultrafiltrate and the concentration of impurities as follows. It is estimated that this is due to some reason.

The negative electrodeposition resist bath contains an acrylic polymer composed of acrylic acid and its derivative, that is, a polymer having a carboxyl group as a constituent unit. Taking an anionic negative electrodeposition resist bath as an example, in an acrylic polymer consisting of acrylic acid and its derivatives, the carboxyl group exists in the state of being suspended in the main chain. Is suppressed for electrostatic reasons. That is, the carboxyl group in the acrylic polymer has a smaller dissociation constant than the carboxyl group of the acrylic acid monomer. Therefore, during the electrodeposition bath,
Even if an organic acid with a larger dissociation constant is generated (by hydrolysis of the polyfunctional acrylic monomer used as a cross-linking agent), a kind of ion exchange occurs with the carboxylate in the acrylic polymer, and Does not increase the number of ions in the electrodeposition bath.

This can be expressed by the following equation. Here, RCOOH is an organic acid (impurity) having a large dissociation constant. _{^{R-COO - + CH 2 CHCOOH}} → RCOOH + CH
₂ CHCOO ^-

It is presumed that due to this effect, the accumulation of impurities in the bath does not directly appear as an increase in the electric conductivity of the bath.
On the other hand, the partially neutralized product of the acrylic polymer is substantially absent in the ultrafiltrate, and it is the salt of the low molecular weight polymer component and impurities produced during the synthesis of the acrylic polymer that affect the conductivity of the filtrate. Of these, impurities largely contribute to the conductivity of the filtrate.

[0018]

EXAMPLES The present invention will be described in more detail below with reference to examples. (Preparation of electrodeposition bath) 45 parts by weight of methyl methacrylate (parts by weight. The same applies hereinafter), 20 parts of isobutyl acrylate, 15 parts of hydroxyethyl methacrylate, 20 parts of acrylic acid.
Part and 2 parts of azobisisobutyronitrile were added dropwise to 110 parts of isopropyl alcohol maintained at a temperature of 80 ° C. over 5 hours under a nitrogen atmosphere. Aged for 1 hour and then 0.5 of azobisisobutyronitrile
Parts and 10 parts of isopropyl alcohol were added and aged for 2 hours to synthesize a high acid value acrylic resin solution.

While blowing air into this high acid value acrylic resin solution, 20 parts of glycidyl methacrylate, 0.7 part of dimethylbenzylamine as a catalyst and 0.15 part of phenothiazine were added and reacted at a temperature of 80 ° C. for 12 hours to give a high temperature. An acid value photosensitive resin solution was obtained. The nonvolatile component in this high acid value photosensitive resin solution was 50% by weight, the acid value was 74, the number average molecular weight of the high acid value photosensitive resin was 38,000, and the unsaturated equivalent was 1 mol / kg.

To 138 parts of the high acid value photosensitive resin solution, 33 parts of trimethylolpropane triacrylate and 5 parts of Irgacure 907 (manufactured by Ciba-Geigy: α-aminoacetophenone) as a photoinitiator were added and mixed well, then 6 parts of triethylamine to neutralize
Deionized water was added so that the solid content was 15% to obtain a negative type anionic electrodeposition coating (pH 7.1).

(Preparation of Test Substrate) A copper clad laminate (40 × 150 ×) for printed wiring board was prepared by using the above electrodeposition paint.
1.6 mm) as an anode and a SUS304 plate as a cathode, the coating temperature was set at 25 ° C., the current value was set to a current density of 60 mA / dm ^2, and current was applied for 3 minutes to perform electrodeposition coating. After electrodeposition, the copper clad laminate having the coating film deposited thereon is washed with water, air-dried with an air knife, and then heated and dried at a temperature of 100 ° C. for 5 minutes,
A smooth, non-tacky photoresist film having a thickness of 18 μm was obtained.

Next, a wiring pattern film having various intervals is adhered on the photoresist film by a vacuum device, and an irradiation dose of 100 is applied by using an ultrahigh pressure mercury lamp of 3 kW.
Exposure was performed at mJ / cm ² . Subsequently, after developing with a 1% sodium carbonate aqueous solution, etching was performed with a ferric chloride aqueous solution, and the remaining resist film was removed with a 3% sodium hydroxide aqueous solution to obtain a printed wiring board (test board) having a wiring pattern. .

(Example 1) An electrodeposition bath equipped with an ultrafiltration device was filled with an electrodeposition bath, the bath temperature was maintained at 25 ° C, and the electrical conductivity of the electrodeposition bath and the electrodeposition bath were maintained at regular intervals. The pH and the electric conductivity of the ultrafiltrate were measured, and an evaluation substrate was prepared to examine the performance of the electrodeposition bath. The ultrafiltration module uses UFD-10-MPL-LT manufactured by Yuasa Battery Co., Ltd., the module inlet pressure is 1.9 kg / cm ² , and the outlet pressure is 1.
It was operated under the condition of 0 kg / cm ² .

Then, the deterioration bath was purified by an anion exchange resin. The anion exchange resin is a strong base anion exchange resin DIAION SA-10AP manufactured by Mitsubishi Kasei.
Was used to pass the electrodeposition bath through the column with SV10 ^-1 . The results are shown in Table 1. Incidentally, the pattern formability is what was evaluated by a scanning electron microscope of the test substrate, which is how much the wiring pattern of the interval is developed,
The line indicates the portion where the resist film remains, and the space indicates the portion where the resist film does not exist.

[0025]

[Table 1] (Unit) Conductivity: μS / cm Pattern formability: Line (μm) / Space (μm)

(Example 2) An electrodeposition bath equipped with an ultrafiltration device was filled with an electrodeposition bath, the bath temperature was maintained at 25 ° C, and the electrical conductivity of the electrodeposition bath and the electrodeposition bath were maintained at regular intervals. The pH and the electric conductivity of the ultrafiltrate were measured, and an evaluation substrate was prepared to examine the performance of the electrodeposition bath. And the conductivity of the ultrafiltrate is 600
At the time of reaching μS / cm, the electrodeposition bath was passed through an anion exchange resin column for purification. As a result of repeating this operation, the pattern formability of 50 μm / 50 μm could be maintained for at least 3 months.

(Example 3) An electrodeposition bath equipped with an ultrafiltration device was filled with an electrodeposition bath, the bath temperature was maintained at 25 ° C, and the electrical conductivity of the electrodeposition bath and the electrodeposition bath were maintained at regular intervals. The pH and the electric conductivity of the ultrafiltrate were measured, and an evaluation substrate was prepared to examine the performance of the electrodeposition bath. And the conductivity of the ultrafiltrate is 600
While the simulated filtrate was supplied to the electrodeposition tank at the time of μS / cm, the ultrafiltrate was discarded and the bath was purified. As a result of repeating this operation, pattern formability 50 μm / 50 μ
m could be maintained for at least 3 months.

(Embodiment 4) An electrodeposition bath equipped with an ultrafiltration device was filled with an electrodeposition bath, the bath temperature was kept at 25 ° C., and the conductivity of the electrodeposition bath and the electrodeposition bath were maintained at regular intervals. The pH and the electric conductivity of the ultrafiltrate were measured, and an evaluation substrate was prepared to examine the performance of the electrodeposition bath. And the conductivity of the ultrafiltrate is 600
At the time point of μS / cm, the bath was purified by passing the ultrafiltrate through an anion exchange resin column equipped with a branch of the ultrafiltrate outlet pipe. As a result of repeating this operation, the pattern formability of 50 μm / 50 μm could be maintained for at least 3 months.

[0029]

The method for controlling the electrodeposition bath of the present invention is capable of easily detecting the degree of deterioration of the electrodeposition bath without introducing a new analytical instrument and effectively purifying the bath. Therefore, according to the present invention, the purification of the bath can be carried out economically and without impairing the productivity, so that it has a great advantage in practical use.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location C25D 13/24 303 G03F 7/16

Claims (1)

[Claims] 1. A method for purifying a part or all of a deteriorated bath by ultrafiltration of a negative electrodeposition resist bath, detecting the degree of deterioration of the bath from the measured value of the electric conductivity of the obtained filtrate. A characteristic method of managing the electrodeposition bath.