JP4531777B2 - Pre-plating method for printed wiring boards - Google Patents

Description

  The present invention relates to a method for manufacturing a printed wiring board, and more particularly to a pretreatment method for a plating process.

  Normally, the surface of the material to be treated is contaminated with organic matter or oxide, and normal plating treatment cannot be performed as it is. Therefore, it is necessary to remove these contaminations by pretreatment prior to the plating treatment. Depending on the contaminant to be removed, the treatment is separated from degreasing and / or pickling. The methods are roughly classified into a method of immersion in a chemical and a method of electrolytic treatment.

  Among these, the method of immersing in a chemical | medical agent should just contact a to-be-processed material with a chemical | medical solution, and an apparatus structure is simple. However, since the effect of the treatment depends on the chemical reaction, it is necessary to strictly control the drug concentration and the additive concentration, and the drug to be used is more expensive than the electrolytic treatment. Further, because of the chemical reaction, the effect of finishing and pretreatment differs depending on the variation of processing temperature and processing time, and the quality may not be stable.

  Furthermore, due to changes over time, not only the active ingredients of the drug used are consumed, but also reaction products or altered substances accumulate, so even if the drug concentration is simply controlled, a sufficient treatment effect cannot be obtained. Sometimes. In such a case, it is necessary to periodically update expensive drugs, which is a factor in increasing costs.

  On the other hand, the method using electrolytic treatment is simple and may be inexpensive. In addition, the influence on the product finish due to changes in the chemical concentration and processing temperature is small, and stable processing can be performed only by managing the current value and processing time.

In this electrolytic treatment, the structure of the apparatus and the material to be treated are configured to energize the material to be treated. In order to energize the material to be processed, it is necessary to bring the material to be processed into contact with the electrode. Therefore, the electrode is processed into a brush shape, a ring shape, or a roll shape to provide a power feeding portion so that it can contact a specific portion or the entire surface of the material to be processed (see Patent Document 1).
JP 2000-199096 A JP 2006-291244 JP

  However, the contact between the material to be processed and the power feeding unit causes some damage to the material to be processed, such as scratches and hammering. In addition, in order to reduce the degree of this damage, there is a method of reducing the load that the material to be treated and the power feeding unit contact, but on the other hand, there is also a problem that the material to be treated is damaged by sparks due to energization failure. is there.

  Thus, it is desired to employ electrolytic treatment because of the ease of processing and management. However, it is necessary to prevent problems caused by bringing the power feeding unit and the material to be processed into contact for the purpose of energization.

  The material to be treated also needs to be devised for power supply. In order to supply power to the processing site in the material to be processed, an additional wiring pattern is formed on the material to be processed. However, the formation of an additional wiring pattern causes an increase in cost, and the complicated wiring reduces the yield of products.

  Furthermore, with the miniaturization of the wiring pattern, provision of a current-carrying wiring pattern to secure a space for the circuit wiring pattern is also avoided, and as a result, the plating process is becoming an electroless specification. In this case, as a matter of course, there is a problem that the electrolytic treatment method by contact energization cannot be applied to the pretreatment (see Patent Document 2).

  The present invention has been made in consideration of the above-described points, and a plating pretreatment method capable of supplying power to a material to be processed without bringing the material to be processed into contact with a power feeding portion when performing plating pretreatment by electrolytic treatment. The purpose is to provide.

In order to achieve the above object, in the present invention,
In the pre-plating processing method of continuously processing using a pair of electrodes having an anode and a cathode while conveying a material to be processed horizontally or vertically in a manufacturing process of a printed wiring board,
In the processing tank , along the transport direction of the material to be processed, and symmetrically disposed on the front and back of the material to be processed, one or more pairs of the electrodes,
The distance between the electrode and the material to be treated is ¼ or less of the distance between the cathode and the anode in the electrode pair ,
A plating pretreatment method characterized by subjecting the material to be treated to electrolytic treatment without direct contact of the electrode with the material to be treated by passing a direct current between the electrodes in the electrode pair,
Is to provide.

  According to the present invention, when performing electrolytic treatment continuously, power can be supplied without bringing the material to be processed into contact with a jig for power supply, so the problem of surface flaws can be avoided. In addition, since power supply to the material to be treated is not required, the presence or absence of the current-carrying wiring pattern of the material to be treated does not matter, and electrolytic treatment is possible even with a material to be treated without electrolysis.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

Embodiment 1

  FIG. 1 shows a cross-sectional configuration example of a pretreatment layer to which the present invention is applied. As shown in FIG. 1, the electrodes 1 and 2 are installed so as to form a pair of a positive electrode and a negative electrode on one surface (front surface or back surface) of the material 3 to be processed. In FIG. 1, the pretreatment layer 4 is shown as a cross section cut in the vertical direction, and the treated material 3 is passed between two pairs of electrodes 1, 2 arranged above and below, and both ends of the pretreatment tank 4. The to-be-processed material 3 is conveyed in the electrolyte solution 6 between the dam rolls 5 arranged in the.

  And in order to process both surfaces of the to-be-processed material 3 simultaneously, it installs so that it may become a pair of the electrodes 1 and 2 in each surface. At this time, the polarities of the electrodes facing the corresponding positions on the front and back surfaces of the material to be processed 3 must be the same, so that the material to be processed 3 is sandwiched between the electrodes 1, 1 or 2, 2 having the same polarity. In addition, electrodes 1 and 2 are arranged.

FIG. 2 shows a current flow when a voltage is applied in a state where the electrodes 1 and 2 are arranged as described above. Current from the + pole 1 - flows to the electrode 2, the electrolyte path flowing path does not flow (not shown) only as workpiece 3 A and (broken line shown) through the material to be treated 3 B ( It is divided into a solid line) .

  The current distribution ratios in both paths A and B differ depending on the distance between the electrodes 1 and 2, the distance between the electrodes 1 and 2 and the workpiece 3, and the like. What is effective as the electrolytic treatment of the workpiece 3 is the current flowing through the path B, and the smaller the value of the current flowing through the path A, the better the efficiency.

As shown in FIG. 3, when the electrical resistance between the electrodes and R1, R2, _{R M,} the electrical resistance of the path A is R1, 2 × the path B R2 + _{R M} It becomes. Here, since the electric resistance of the metal is sufficiently small compared with the electric resistance of the solution and can be ignored, the electric resistance of the path B may be 2 × R2.

  Since the resistances R1 and R2 are both electric resistance values when the current flows through the same electrolyte solution, these values are proportional to the distance between the electrodes. Since the value of the flowing current is proportional to the reciprocal of the electrical resistance, the current distribution ratio is route A: route B = 2 × R2: R1.

  That is, by reducing the distance between the electrodes 1 and 2 and the material to be processed 3 and increasing the distance between the anode 1 and the cathode 2, the distribution ratio of the current flowing through the material to be processed 3 can be increased. This indicates that the current distribution ratio is determined simply by the arrangement of the electrodes 1 and 2 regardless of the type of the electrolytic solution.

  Usually, since it is desired to use 2/3 of the flowing current for the electrolytic treatment, the distance between the electrodes 1 and 2 and the workpiece 3 is set to 1/4 or less of the distance between the anode 1 and the cathode 2. Although 1/3 of the current flows through the electrolytic solution and the electrolytic solution itself generates heat due to the resistance of the electrolytic solution, this heat can be used to keep the electrolytic solution warm and is not wasted.

  However, when the value of the current flowing through the electrolytic solution increases, a cooling device may be required due to the temperature rise of the electrolytic solution, depending on the processing temperature and characteristics of the electrolytic solution. For this reason, it is desirable that the distance between the electrodes 1 and 2 and the material 3 to be processed is 1/5 or less of the distance between the anode 1 and the cathode 2. If these distances cannot be achieved due to the arrangement of the apparatus, a baffle plate (not shown) may be installed between the anode 1 and the cathode 2.

  A direct current is used as a current flowing between the pair of electrodes 1 and 2. Of course, alternating waves such as alternating current and pulse waves can be used, but in the present invention, only direct current is used in order to clearly separate anodizing and cathodic treatment. This is because the pretreatment for plating according to the present invention is mainly due to the treatment effect by oxygen or hydrogen generated by the anodic reaction or the cathodic reaction rather than the reaction with the chemical.

  By the method described above, the material to be treated 3 can be subjected to electrolytic treatment without directly supplying power to the material to be treated 3.

  When degreasing is mainly performed as a pretreatment, caustic soda, carbonate or silicate, or a mixed agent thereof is used as an electrolytic solution. Basically, this is a technique for oxidizing and decomposing organic substances adhering to the surface of the material to be treated 3 by oxygen generated by the anodic reaction, and the electrolyte is made basic. That is, the concentration of the hydroxyl group in the solution is increased and oxygen is easily generated.

  However, the reaction between the chemical to be used and the material to be treated 3 must be avoided. Therefore, caustic soda, carbonate or silicate or a mixture of these agents is used, but other agents can be used in the same way.

  When it is desired to remove surface oxide as a pretreatment, an electrolytic solution mainly composed of sulfuric acid is selected. In the printed wiring board, the metal species of the material to be plated is copper. Therefore, nitrate-based drugs cannot be used. In the present invention, since a chemical agent based on hydrochloric acid occurs in a pair of anodizing and cathodic treatment, the chlorine gas due to the anodic reaction causes problems such as discoloration of the material to be treated 3 and corrosion of the apparatus.

  The treatment according to the invention is based on reduction by hydrogen generated by the cathodic reaction. Moreover, copper produces | generates an oxide on the surface by an anodic reaction. Accordingly, the electrode arrangement and polarity are determined so that the material 3 to be processed becomes the cathode 2 in the final stage of the processing. This is the reason why the polarities of the electrodes on the front and back surfaces are the same when performing both-side processing.

  If the to-be-processed material 3 is a reel shape, it can process with the method of this invention without a problem. Further, if the sheet can be conveyed even if it is in the form of a sheet, a power supply roll, a power supply brush, or the like is not required, and therefore, the processing according to the present invention can be performed.

Other embodiments

  In the present invention, a constant current is used. However, since the current distribution ratio is determined by the tank structure, processing can be performed even if constant voltage control is performed.

  The present invention relates to a pretreatment for plating, and the kind of plating treatment in the next step is not limited. In addition to the embodiments, the present invention can be applied to, for example, electrolytic solder plating, electrolytic tin-copper plating, electrolytic silver plating, electroless silver plating, and copper plating. Furthermore, the present invention can be applied to other processing, for example, preprocessing such as patterning by etching and blackening processing.

Processing example of workpiece

  Next, the results of pre-processing the material to be processed 3 by applying the above-described embodiment of the present invention are shown as Processing Examples 1 to 3 below.

Processing example 1

  When electrolytic tin plating was performed on the sheet-like printed wiring board in the plating process of the single-sided printed wiring board by the method of the present invention, pretreatment by electrolytic degreasing was performed. As the electrolytic solution, a mixed solution of caustic soda: 4 g / L, sodium carbonate 4 g / L, and orthosilicate sodium 2 g / L was used. The temperature of the electrolyte was set to 45 ± 3 ° C.

  Ti electrodes plated with platinum were used for both the anode and cathode, the distance between the anode 1 and the cathode 2 was 250 mm, and the distance between the electrodes 1 and 2 and the workpiece 3 was 50 mm. The length of each electrode 1 and 2 was 300 mm. The conveyance speed was adjusted so that the processing time was 30 seconds (time for passing through each electrode) for both the anode and the cathode 2. A direct current of 32 A was passed between both electrodes 1 and 2.

  In the process in which the material to be treated 3 passes under the electrodes 1 and 2, gas generation was observed from the copper surface. Moreover, the wettability of the surface of the to-be-processed material 3 after a process was good, and the "plating non-stickiness" by degreasing | defatting defect was not observed after the electrolytic tin plating of the next process.

Processing example 2

  In performing continuous electrolytic gold plating as the surface treatment of the reel-shaped double-sided printed wiring board, electrolytic pickling was performed by the method of the present invention. A 5% sulfuric acid solution was used as the electrolytic solution. The temperature of the electrolyte was set to 25 ± 5 ° C. The treatment was performed in an electrolytic cell having the same tank structure as that in Treatment Example 1. The conveying speed was adjusted so that the treatment time was 30 seconds (time for passing through each electrode) for both the cathode and the anode. The current value per side was 53 A, and a direct current of 106 A was passed on the front and back.

  The copper on the surface of the printed wiring board after passing through the pretreatment tank exhibits a metallic luster, indicating that sufficient electrolytic pickling has been performed. Moreover, after electrolytic gold plating, there were no problems such as gold clouding and surface unevenness. Moreover, there was no problem in plating adhesion. In addition, there was no defect in appearance due to wrinkles and the product yield was improved.

Processing example 3

  In electroless gold plating on the sheet-like printed wiring board, as a pretreatment, electrolytic degreasing by the method of the present invention and subsequent electrolytic pickling were performed. In electrolytic degreasing, a mixed solution of caustic soda: 2 g / L and orthosilicate sodium 5 g / L was used and controlled at a temperature of 45 ± 3 ° C. The treatment was performed in an electrolytic cell having the same tank structure as that in Treatment Example 1.

  Similarly to the processing example 1, the conveying speed was adjusted so that both the cathode and the anode were 30 seconds (time for passing through each electrode). A direct current of 32 A was passed between the electrodes. In the electrolytic pickling, a 5% sulfuric acid solution was used in the same manner as in Treatment Example 2, and the temperature of the electrolytic solution was set to 25 ± 5 ° C. The treatment was performed in an electrolytic cell having the same tank structure as that of Treatment Example 1. The conveying speed was adjusted so that the treatment time was 30 seconds (time for passing through each electrode) for both the cathode and the anode. The electrolysis current was 32A.

  The finish of electroless gold plating was good and there was no cloudiness or other problems. Moreover, there was no problem of poor appearance due to wrinkles.

Sectional drawing of the pretreatment tank by one Example of this invention. FIG. 2 is an explanatory diagram of how current flows in the pretreatment tank shown in FIG. Explanatory drawing of the electrical resistance of each part in the pretreatment tank shown in FIG.

Explanation of symbols

1: Anode 2: Cathode 3: Material to be treated 4: Pretreatment tank 5: Dam roll 6: Electrolytic solution A: Current flowing in the electrolytic solution B: Current flowing through the material to be treated 3 R1: Anode 1 and cathode 2 R2: Electrical resistance between the electrodes 1 and 2 and the workpiece 3 _RM : Metal electrical resistance

Claims (5)

In the pre-plating processing method of continuously processing using a pair of electrodes having an anode and a cathode while conveying a material to be processed horizontally or vertically in a manufacturing process of a printed wiring board,
In the processing tank , along the transport direction of the material to be processed, and symmetrically disposed on the front and back of the material to be processed, one or more pairs of the electrodes,
The distance between the electrode and the material to be treated is ¼ or less of the distance between the cathode and the anode in the electrode pair ,
A plating pretreatment method characterized in that the material to be treated is electrolytically treated by causing a direct current to flow between the electrodes in the electrode pair without directly contacting the electrode to the material to be treated.   The plating pretreatment method according to claim 1, wherein a distance between the electrode and the material to be processed is set to 1/5 or less of a distance between the cathode and the anode.   The plating pretreatment method according to claim 1, wherein the electrolytic solution used is composed of a component mainly composed of caustic soda, carbonate, silicate, or a mixed agent thereof.   The plating pretreatment method according to claim 1, wherein the electrolytic solution used is composed of a component mainly composed of sulfuric acid, and the material to be treated is brought into a reduced state at the final stage of the treatment.   The plating pretreatment method according to claim 1, wherein the material to be treated is in a reel shape or a sheet shape, and the material to be treated is continuously treated.

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