JPS59229499A - Plating method - Google Patents

Abstract

PURPOSE:To form a plating film always having a uniform thickness on a material to be plated in the stage of copper plating by incorporating a stage for removing the copper deposited on a rack for suspending the material to be plated into a plating line. CONSTITUTION:A stage for removing the copper deposited on a rack for suspending a printed wiring board is incorporated in a plating line and the rack from which the deposited copper is thoroughly removed in always used in the stage of electroplating copper on the printed wiring board, etc. The rack from which the wiring board completed of plating is removed is subjected to an electrolytic treatment in an electrolytic stripping liquid contg. >=0.3mol/l oxidixing agent such as HNO3, >=0.3mol/l halogenic acid such as HCl or the salt thereof and >=0.3mol/l short chain carboxylic acid or oxycarboxylic acid such as formic acid as an anode and is further dipped in a dipping and stripping soln. contg. 150ml/l concd. HNO3 to strip and remove thoroughly the deposited copper sticking on the rack. Such rack is used for the succeeding plating. The less number of the racks are required and the plating film of always a uniform thickness is formed on the wiring board to be plated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plating method that is particularly suitable for plating printed wiring boards. The present invention relates to a method of continuously performing plating using a regenerated rack from which unnecessary precipitates have been peeled off and removed, by completely and continuously peeling off unnecessary precipitates in a short period of time.

Conventionally, the method for plating printed wiring boards is to drill the required part of a copper-clad laminate to form a through hole, make the through hole conductive by chemical copper plating, and then apply electricity to the entire copper-clad laminate. A widely used method is to apply copper plating or, after chemical copper plating, to mask the required portions of the copper-clad laminate using a resist, and to apply electrolytic copper plating to the unmasked portions. In this case, it is desirable that the thickness of the copper plating film be uniform in each part, and for this reason, it is necessary to use an auxiliary tool such as a sacrificial plate, or to adjust the position, number, and position of the anode plates. Various improvements have been made to the shape, the shape of the plating rack that suspends the printed wiring board, the way to make contact with the printed wiring board, etc. In other words, in electroplating, there are inevitably high current density areas and low current density areas on the object to be plated, which results in thicker and thinner areas of the plating film, but the difference in thickness is too large. If the desired plating film thickness cannot be obtained even after plating for a certain period of time, especially in low current density areas, problems may arise in the quality of the printed wiring board. Since problems of insufficient etching and overetching occur, it has been desired to make the thickness of the electrolytic copper plating film as uniform as possible in each part of the printed wiring board.

Furthermore, it is not desirable for the plating film thickness to vary from plating to plating, and for this reason, it has been required to maintain a constant quality of printed wiring boards by always plating to a constant film thickness. .

When plating a printed wiring board, the inventor of the present invention aims to make the plating film thickness as uniform as possible in each part of the printed wiring board, and to prevent the film thickness from varying from plating to plating.
As a result of intensive study on plating to a nearly constant thickness at all times, we found that it was necessary to consider factors such as the placement of the anode plate, the shape of the plating rack that suspends the printed wiring board, and how to make contact with the printed wiring board. Of course, the present inventors found that precipitates deposited on the plating rack have a great influence on making the plating film thickness uniform and constant.

In other words, the rack holds the printed wiring board in the plating solution and serves as an intermediary for transmitting electricity from the cathode busbar to the printed wiring board, so it is made of metal, but most of its surface is made of plastic. It is coated with an insulator such as sol to prevent plating from depositing. However, the metal material is exposed in the portions -4- of the rack that hold the printed wiring boards, and plating is deposited on these exposed metal portions. If the rack with this plating deposited on it is used again and again without peeling off the deposits, there may be large differences in the plating film thickness on each part of the printed wiring board, and conditions such as current density and plating time may be changed. It has been found that even if the thickness is kept constant, problems such as considerable differences in the plating film thickness between platings are likely to occur.

For this reason, it was desirable to use racks free of plating precipitates for each plating process, but the conventional method of removing plating precipitates from racks was not efficient, and the efficiency of plating work was reduced. It was recognized that this would result in a loss of quality. To explain this point in more detail, various plating stripping solutions have been proposed in the past. However, these stripping solutions have relatively high stripping speeds when they are new;
It tends to age quickly, and aging causes a decrease in peeling speed. In addition, in the past, peeling and removal of precipitates deposited on racks was usually done by setting up a peeling tank separate from the plating line.
Regardless of the plating process, the racks are left in the stripping solution for a long time after finishing the plating job or after using the rack several times, but this stripping method is not efficient. This was bad and required a large number of racks.

The present inventor has incorporated a peeling and removal process for the precipitates deposited on the rack into the plating line, and by using a rack in which the precipitates are removed and re-stopped after each plating, the thickness of the plating film can be made uniform and constant. As a result of intensive study on how to remove the plating material after the final plating process, the plating rack was immersed in an electrolytic stripping solution to electrolytically remove some of the precipitate deposited on the rack. It has been found that by dissolving and removing the precipitates remaining on the rack with an immersion stripping solution, the load on the stripping solution is reduced, the precipitates on the rack are efficiently and reliably removed in a short time, and the above objectives are successfully achieved. However, the present invention has been completed.

The present invention will be explained in more detail below. In the present invention, after the final plating step, the rack from which the plated material has been removed is immersed in an electrolytic stripping solution to electrolytically peel off a portion of the precipitate deposited on the rack, and -6- further immersed. The remaining precipitates are completely dissolved and removed by immersion in a stripping solution.

Here, the present invention is particularly suitably adopted for plating printed wiring boards, and is particularly effectively applied when birophosphoric acid phase plating or copper sulfate plating is performed as the final plating step.

Further, the material of the rack is not necessarily limited, but stainless steel is preferably used.

In the present invention, various conventionally known electrolytic stripping solutions can be used, but particularly include an oxidizing agent, a halogen acid or a salt thereof, and a short-chain carboxylic acid or hydroxycarboxylic acid or a salt thereof, - is preferably adjusted to about 6 to 8. In this case, examples of the oxidizing agent include nitric acid, nitrates such as sodium nitrate and ammonium nitrate, hydrogen peroxide, and manganese dioxide, all of which contain 0.25 mol/j! or more, preferably 0.3 to 0
．． 7 mol/I! It can be used in certain concentrations. Further, examples of the halogen acid or its salt include hydrochloric acid and ammonium chloride, and these have a rate of 0.3 mol/-7-1 or more, preferably 0.4 to 1 mol/l! It can be used in certain concentrations. Further, examples of short-chain carboxylic acids, oxycarboxylic acids, and salts thereof include formic acid, acetic acid, hydroxyacetic acid, sodium salts and ammonium salts thereof, and 0.3 mol/p or more, preferably 0.3 to 1 mole/
It can be used in concentrations as low as p. Note that a complexing agent such as EDTA or lactic acid can be added to this electrolytic solution.

When electrolytically stripping rack deposits using this electrolytic stripping solution, electrolysis is carried out using the rack as an anode. In this case, the anode current density is 5 to 40 A/d, especially 30 to 4 OA.
/dn. In addition, the liquid temperature is room temperature to 60℃
, in particular 40 to 50°C. Furthermore, it is preferable to perform air agitation during peeling.

Furthermore, it is preferable to use this electrolytic stripping solution while removing precipitates through continuous circulation filtration and replenishing consumable chemicals, so that the electrolytic stripping solution can be used without being discarded.

In other words, conventionally, this type of electrolytic stripper was discarded as it aged, but by adopting the above method, it can be used without being discarded, and therefore it can be used in automatic plating lines. This electrolytic stripping solution can be incorporated.

In this case, the circulation speed of the electrolytic stripping solution is preferably such that the stripping solution in the electrolytic stripping tank is replaced 1 to 3 times per hour. Although filtration can be carried out using a normal filter, it is preferable to introduce the electrolytic stripping solution into a sedimentation tank and allow the precipitate to settle there naturally. There is no inconvenience such as clogging, and the precipitate can be continuously removed by natural settling, and the stripping solution from which the precipitate has been removed can be returned to the electrolytic stripping tank.

When performing electrolytic stripping using the above electrolytic stripping solution under the above conditions, the stripping time will vary depending on the type and thickness of the deposits on the rack, but electrolytic copper plating of about 35 μm is applied to the printed wiring board. If necessary, the peeling time can be about 15 to 30 minutes. In this case, it is not necessary that the precipitates on the rack be completely peeled off and removed in this electrolytic stripping step 1111. It is sufficient that 90 to 98% of the precipitates are removed, and the remaining precipitates are removed. is to be removed in the next immersion stripping process.

In the present invention, immersion stripping is performed after electrolytic stripping of rack deposits, and the immersion stripping solution may be a nitric acid solution, a hydrogen peroxide solution, dichloromethane solution, especially when the rack deposits are copper. ! A solution or the like is used. Among these, nitric acid solution is preferable, but when using nitric acid solution, its concentration is 150 w/J or more of concentrated nitric acid, especially 200 to 400 w
It is preferable to set it to 1/j. In this way, when nitric acid is used as the immersion stripping solution and the above-mentioned stripping solution is used as the electrolytic stripping solution, the nitric acid solution used as the immersion stripping solution can be added to the electrolytic stripping solution. This is convenient because it eliminates the need to dispose of the stripping solution (nitric acid solution) and at least reduces the need for disposal.

The treatment temperature of this immersion stripping solution can be room temperature, and the immersion time can be about 3 to 15 minutes.

Ratu 1 with precipitates peeled off and removed as described above
〇 - After being neutralized with caustic alkali etc. if necessary and washed with water, the object to be plated such as a printed wiring board is suspended and used for plating again.

According to the plating method of the present invention, after the final plating process, the rack from which the plating and plating have been removed is immersed in an electrolytic stripping solution to electrolytically peel off a portion of the precipitate deposited on the rack. ,
Next, the rack is immersed in a stripping solution to completely dissolve and remove the remaining precipitates, so that the negative 1n of the stripping solution is reduced and the precipitates on the rack are reliably removed in a relatively short time. In other words, if you try to completely remove the deposits on the rack by electrolytic stripping alone, it will take more than one hour, and in this case, the thickness of the deposits on the rack is not uniform and varies depending on the location. Even after most of the lac deposits have been electrolytically removed, a thick part of the deposits remains without being completely removed, and it takes a considerable amount of time to remove it (usually up to 90-98%). It is relatively easy to peel off, but it takes a lot of time to completely remove the rest).

In addition, most of the precipitates were removed, and only a small amount of -11
Since electrolysis is performed to remove a single precipitate of about 2 to 10%, the electrolytic stripping solution is in a state similar to being subjected to dry electrolysis for a long time, and the current density in this case is also high. In addition to wasting chemicals, electricity is also wasted.

Furthermore, it takes a long time to completely remove lac deposits using only an immersion stripping solution, and the solution ages rapidly.
The removal speed is significantly reduced. In contrast, in the present invention, it is not necessary for the electrolytic stripping solution to completely remove the deposits on the rack, and most of the deposits, preferably 90 to 98
Since it is only necessary to remove about %, the processing time with this electrolytic stripper is shortened, and wasteful consumption of chemicals is reduced.
The load on the electrolytic stripper is reduced, and only a small amount of remaining deposits are removed by the immersion stripper.
The burden on the immersion stripping solution is reduced, the immersion stripping solution does not age rapidly and the removal speed decreases, and the remaining precipitates are reliably removed in a short time.

In particular, the above-mentioned effects can be obtained by using an electrolytic stripping solution containing an oxidizing agent, halogen acids, short-chain carboxylic acids, or hydroxycarboxylic acids, and continuously removing the precipitates generated in this stripping solution. Temperature 40-50℃,
This is effectively achieved when electrolytic stripping is performed under conditions of an anode current density of 30 to 40 A/dm and air agitation. 90% of copper electrodeposit
~98% was removed and this was made into a chain 211150ν! /1
By immersing the rack in the above-mentioned immersion stripping solution, the copper electrodeposit on the rack can be completely removed in about 3 to 15 minutes.

Therefore, the process for stripping off rack deposits as described above can be incorporated into an automatic plating line, and a recycled rack with precipitates removed can be used for each plating process, making the present invention particularly useful for printed wiring boards. It can be suitably used for plating, and it is possible to effectively make the plating film thickness uniform and constant.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples.

-13- (Example) Ammonium nitrate with the following composition 20111/i) Ammonium chloride 15Q/1 Ammonium formate
150 /12EDTA 1
Electrolytic copper plating of a printed wiring board was carried out using an electrolytic stripping solution of 00/II and maintaining -6 to 8 at a temperature of 45°C, anode current density surface of 35 A/d, and air agitation (approximately 35
The stainless steel racks used in the test were continuously immersed to remove the electrodeposited copper attached to the racks.

In this case, the electrolytic stripping solution is introduced into a sedimentation tank whose internal volume is approximately twice that of the electrolytic stripping tank at a circulation rate such that the electrolytic stripping solution in the electrolytic stripping tank is replaced twice per hour. The cake is separated by sedimentation, the supernatant liquid is returned to the stripping tank, the precipitate in the sedimentation tank is appropriately extracted, and the water in the cake is extruded out by squeezing out the air. The electrolytic stripping solution was supplemented with nitric acid, ammonium oxide, and caustic soda.

Next, after the electrolytic stripping, the rack was washed with concentrated nitric acid 350ν! /!
It was immersed in the immersion stripping solution. In this case, the immersion stripping solution is appropriately supplemented with nitric acid, and its concentration is 200xl/! I kept it above that.

The time for the electrolytic stripping was 20 minutes and the time for immersion stripping was 5 minutes, and the results showed that the copper electrodeposit on the rack was completely peeled off. During this period, the electrolytic stripping solution was not disposed of and a good stripping process was carried out, and the copper electrodeposit on the rack was completely peeled off even after 12 months.

Applicant Sanwa Rust Prevention Co., Ltd. Company Representative Patent Attorney Takashi Kojima-15-515-

Claims (1)

[Claims] 1. After the final plating step, the plating rack from which the plating object has been removed is immersed in an electrolytic stripping solution to electrolytically strip off a portion of the deposits deposited on the rack. A plating method characterized in that the rack is then immersed in an immersion stripping solution to dissolve and remove the remaining precipitates, and plating is performed using the rack from which the precipitates have been completely removed. 2. Oxidizing agent, halogen acid or its salt as electrolytic stripper,
and a short-chain carboxylic acid or oxycarboxylic acid or a salt thereof, and while continuously removing the precipitates generated in this stripping solution, the temperature is 40 to 50 ° C., the anode current density is 30 to 40 A / dm, The copper electrodeposit deposited on the rack after performing electrolytic copper plating under air agitation conditions was 15 to 3
Electrolytic stripping is performed for 0 minutes, and electrolytic stripping machine immersion stripping solution is used.
1- And concentrated salt 121501! 2. The method according to claim 1, wherein the remaining copper electrodeposit is dissolved and removed by using an immersion stripping solution containing at least /j and immersing the rack in this solution for 3 to 15 minutes.