JPH0448873B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a method of depositing particles on the surface of the object to be plated while changing every moment when plating the object in an electroless plating solution. This invention relates to an electroless plating method in which the plating conditions are controlled while continuously measuring the thickness of the plating layer.

(Prior Art) Conventionally, the following method has been used to measure the electroless plating thickness in order to control the plating conditions. That is, first, a predetermined amount of plating liquid is taken out as a sample from the plating liquid tank during the plating process to a location different from the plating liquid tank, and the sensor electrode is plated in this sampled plating liquid. Then, this sensor electrode is moved into an electrolytic film thickness measurement tank, and by passing current between the sensor electrodes, the plating layer deposited on the sensor electrode is dissolved by electrolysis. The thickness of the plating layer deposited on the sensor electrode is calculated from the time and current required for this electrolysis, and this calculated value is indirectly measured as the plating thickness of the object to be plated in the plating liquid tank. It was. The reason for doing this is that the objects to be plated are normally conveyed continuously through the electroless plating bath by assembly line operations, so the thickness of the plating layer applied to each object to be plated can be directly measured. This is because it is difficult and must be done by some indirect method.

However, this measurement method has various problems as follows. In other words, since it is necessary to sample the plating liquid, the plating liquid tank requires various types of piping, pumps, and other attached equipment for sampling. Therefore, this method for measuring plating thickness requires considerable equipment costs.

The amount of plating of electroless plating liquid changes slightly due to changes in its composition, temperature, etc., but as the plating liquid passes through the various attached equipment mentioned above, its temperature decreases. Not only that, but small amounts of plating metal can also be deposited in pipes and pumps. Therefore, the condition of the sampled plating liquid is different from the state in the plating liquid tank, and it is not appropriate to directly use the result as the thickness of the plating layer of the object to be plated.

If the above-mentioned situation is to be avoided, maintenance of the sampling equipment must be performed frequently or the equipment must be made even more complex. In particular, metal precipitates in the piping through which the plating solution flows, causing clogging in the piping, which necessitates frequent replacement of the piping.

The biggest problem is that the object to be plated is usually continuously plated in the plating tank, and the plating thickness of the object to be plated needs to be measured in real time.
If the plating liquid is sampled and then measured indirectly as described above, there will be a considerable time lag, and the results will be obtained after the state of the plating liquid in the plating liquid tank has changed. However, there are doubts about the plating thickness of the object to be plated that is currently in the plating tank.

In any case, in the conventional method of measuring plating thickness, the degree of indirection is quite high, so
Not only is it difficult to measure the plating thickness of the object to be plated in real time, but it is also not appropriate to control the conveyance speed of the object to be plated based on the measurement results.

(Problems to be Solved by the Invention) The present invention has been made in view of the above-mentioned circumstances, and the problems to be solved are those that cannot be achieved by the conventional electroless plating thickness measuring method. The reliability of the results obtained is low.

The purpose of the present invention is to be able to obtain measurement results in real time, and also to be able to reliably control the plating device from the obtained results, and to simplify the device when implementing this. The purpose of the present invention is to propose an electroless plating method that can achieve

(Means for Solving the Problems) The means taken by the present invention to solve the above problems are as follows: ``A gold or platinum material is placed in an electroless plating liquid tank in which the object to be plated is immersed while being conveyed. A pair of electrodes is arranged, and the electrodes are plated at the same time as the object to be plated. After the electrodes have been plated for a certain period of time, electricity is applied to these electrodes to remove the plating layer formed on the electrodes. Dissolve it by electrolysis in an electroless plating liquid tank, measure the time and current value required for this electrolysis, calculate the integrated current, calculate the thickness of the plating layer of the electrode, and calculate the thickness of the plating layer of the electrode. An electroless plating method in which the residence time of the object to be plated in an electroless plating liquid tank is controlled by comparing the thickness of the plating layer to be formed on the surface of the object to be plated.

The method will now be explained in more detail with reference to the drawings.

In this method, first, a pair of electrodes is placed in an electroless plating liquid tank in which the object to be plated is immersed.
It is necessary to plate this electrode at the same time as the object to be plated. In other words, by placing a pair of electrodes for measuring the plating thickness in the electroless plating bath where the plating process is currently being performed, it is possible to measure the plating thickness by placing the pair of electrodes in the electroless plating bath where the plating process is currently being performed. A plating layer is formed and its thickness is measured. The reason for doing this is that when sampling the plating solution, the plating state of the actual object to be plated is far from the actual plating condition, but the electrodes are placed in the electroless plating liquid bath where the object to be plated is being plated. This is because such problems will disappear.

After plating these electrodes for a certain period of time, the plating layer formed on the electrodes is dissolved by electrolysis in an electroless plating liquid tank by applying electricity to these electrodes, and the time and current value required for this electrolysis are The integrated current is determined by measuring the In this case, the reason why the electrodes are plated at regular intervals is to continuously plate the object to be plated. In other words, by plating the electrode for a certain period of time, electrolyzing it to return it to its original state, and plating the electrode again, the electrode is always returned to its initial state and the plating thickness is increased. This is to enable continuous measurement of strength. For example, when plating a printed wiring board, it is preferable that this certain period of time is about one minute. The reason for this is that if the plating time for this electrode is too long, it will not be possible to measure in real time, and even if this time is shortened, it will not be of much use. In this way, the time and current value required for electrolysis are measured, and the integrated current can be obtained by using a number of methods that have already been proposed.

Next, the thickness of the plating layer of the electrode is calculated from this integrated current, and from this calculated value, the thickness of the plating layer formed on the surface of the object to be plated is calculated, that is, compared. This comparison is performed by setting in advance the cumulative current between the thickness of plating required on the object to be plated and the time required to perform that amount of plating. This is done by calculating the difference between the calculated value and the actually obtained value. By comparing the thickness of the plating layer of the object to be plated, if the time during which the object to be plated is placed in the electroless plating bath is the same as the above-mentioned fixed time, plating may be continued.

On the other hand, if the time that the object to be plated is placed in the plating liquid tank is longer than the fixed time for plating the electrodes, conversion is performed according to that time. In other words, if the plating layer thickness at the electrode increases faster than the set value mentioned above, it means that the residence time of the object to be plated in the electroless plating bath is too long. The conveyance speed is increased, or the electroless plating solution is pulled out of the tank as soon as possible. Of course, in the opposite case, the conversion can be done in the opposite way.

(Function of the Invention) As described above, the method of the present invention is more effective than conventional measuring methods by inserting the measuring electrode into the plating liquid tank containing the object to be plated. It is now possible to perform measurements directly.

In addition, an electrode is placed in a plating liquid tank containing the object to be plated, and plating to this electrode and electrolysis of the plating layer deposited by this plating are performed alternately at fixed time intervals, and at the same time. Therefore, the thickness of the plating tank formed on the object to be plated is measured in real time.

Not only that, when carrying out the method of the present invention, the various auxiliary equipment required in conventional measurement methods are significantly reduced.
It can be applied to plating equipment currently in use without making any major changes.

(Example) Next, the present invention will be explained together with the equipment shown in the drawings.

FIG. 1 shows an electroless plating thickness measuring device 10 used in carrying out the present invention, a plating liquid tank 20 into which a pair of electrodes 11 of the electroless plating thickness measuring device 10 are inserted, and This plating liquid tank 2
Objects W to be plated that are sequentially conveyed within 0 are schematically shown. Each electrode 11 is a platinum plate connected to an electrode lead wire 11a, and the electrode lead wire 11a is covered with a glass tube 11b to protect it, as shown in FIG. Overall, it has a simple configuration. When performing measurement, each electrode 11 made of at least a platinum plate is immersed in the plating liquid tank 20, and a controller 12 for obtaining measurement results is used.
It is connected to. As this electrode 11, any metal can be used as long as it does not dissolve at the oxygen generation potential V2, which will be described later, and in addition to the above-mentioned platinum, gold etc. can be used. Note that, as shown in FIG. 1, each electrode 11 is integrated by being fixed to an auxiliary plate 11c.

The controller 12 includes a voltage comparison circuit 12d and a rectifier switching circuit 12e connected to one electrode 11 via an electrode lead line 11a, and a voltage comparison circuit 12d and a rectifier switching circuit 12.
It consists of a microcomputer 12a that receives electrical signals from e and performs predetermined calculations, a rectifier circuit 12c for the rectifier switching circuit 12e, and an oscillation circuit 12b for the microcomputer 12a, and each of these circuits A known one was used. Further, one electrode 11 is grounded.

On the other hand, in this embodiment, the plating liquid tank 20 is filled with an electroless copper plating liquid, and this plating liquid is applied by a device (not shown) using the same method and device as in the case of normal plating processing. Health care has come to be provided by In this embodiment, an electroless copper plating liquid was used as the plating liquid in the plating liquid tank 20, but it is not limited to this, and examples include electroless nickel plating liquid, electroless tin plating liquid, and electroless solder plating liquid. It may also be carried out using

A plating liquid tank 20 filled with such plating liquid
The objects to be plated W are carried into the plating liquid tank 20 at a predetermined speed that can be changed sequentially, and each electrode 11 is immersed together with its auxiliary plate 11c in the plating liquid tank 20 to perform measurements. Specifically, first, each electrode 11
Apply electroless copper plating for 1 minute. After 1 minute,
The rectifier switching circuit 12e is connected to the rectifier circuit 12c, and a weak current of 300 mA is passed between each electrode 11. Then, the copper plating film (layer) is gradually peeled off (electrolyzed) from the electrode 11 on the anode side, and when the peeling is completed, the voltage between the electrodes 11 increases, and the voltage comparison circuit 12d causes the microcomputer 12 to
a to stop the oscillation circuit 12b.
Thereafter, the microcomputer 12a reads the data using the oscillation circuit 12b, converts it into plating thickness, and displays it if necessary.

The state during this time will be explained with reference to the graph shown in FIG. The graph in FIG. 3 is a graph of voltage versus _time between the anode and cathode when electrolytic film thickness measurement was performed in an electroless plating solution. This is the time during which electroless plating is performed without applying a potential. this time t ₁
When this happens, a constant current is applied to both electrodes 11. Then, the interelectrode voltage rises to Metsuki's electrolytic potential V ₁ , continues to rise gradually as time progresses from t ₁ to t ₂ , and finally reaches the oxygen evolution potential V ₂
becomes. The integrated current is calculated from the time period t ₁ to _{t 2} and the current value, and is converted into the plating thickness for the object W to be plated. Also, electrode 1 at time t ₃
The plating layer formed by the electroless plating in No. 1 is completely electrolyzed by the above electrolytic treatment, making it possible to perform the next measurement anew.

By repeating the above cycle, it is possible to continuously measure the electroless plating thickness.

Next, the thickness of the plating layer of the electrode is calculated from this integrated current, and from this calculated value, the thickness of the plating layer formed on the surface of the object to be plated is calculated, that is, compared. This comparison is made by setting in advance the time required to plate the thickness of the plating required on the object to be plated and the cumulative current during that time, and then comparing this set value with the actual value. This is done by calculating the difference between the calculated value obtained in
By comparing the plating layer thickness of the object to be plated,
If the time during which the object to be plated is placed in the electroless plating liquid tank is the same as the above-mentioned fixed time, plating may be continued as is.

On the other hand, if the time that the object to be plated is placed in the plating liquid tank is longer than the fixed time for plating the electrodes, conversion is performed according to that time. In other words, if the plating layer thickness at the electrode increases faster than the set value mentioned above, it means that the residence time of the object to be plated in the electroless plating bath is too long. The conveyance speed is increased, or the electroless plating solution is pulled out of the tank as soon as possible. Of course, in the opposite case, the conversion can be done in the opposite way.

(Effects of the Invention) As detailed above, in the present invention, ``a pair of electrodes made of gold or platinum is arranged in an electroless plating liquid tank in which the object to be plated is immersed while being conveyed; The electrodes are plated at the same time as the object to be plated, and after plating the electrodes for a certain period of time, electricity is applied to these electrodes to dissolve the plating layer formed on the electrodes by electrolysis in the electroless plating liquid tank. The time required for this electrolysis and the current value are measured to obtain the integrated current, and then the thickness of the plating layer of the electrode is calculated, and this calculated value and the thickness of the plating layer to be formed on the surface of the object to be plated are calculated. The residence time of the object to be plated in the electroless plating tank is controlled in comparison with the layer thickness. It becomes possible to measure the thickness of the plating layer formed on the surface of the object W to be plated in real time, and the configuration of the entire apparatus to be used in carrying out this method can also be simplified. It is something.

As described above, since the overall configuration of the equipment used when implementing this method can be simplified, various types of maintenance that are necessary with conventional methods can be omitted, and the product The cost increase can be suppressed.

Further, the result obtained by the electrode 11 is used as the plating thickness of the object W currently flowing in the plating liquid tank 20, and this result is used as the plating thickness of the object W to be plated that is currently flowing in the plating liquid tank 20.
Since the conveyance speed of the object W to be plated can be immediately changed by sending it to the control mechanism of the conveyance device, there is also the advantage that the yield of the object W to be plated can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an apparatus used in carrying out the present invention, FIG. 2 is an enlarged perspective view of an electrode section, and FIG. 3 is a graph illustrating one measurement cycle. Explanation of symbols, 10... Electroless plating thickness measuring device, 11... Electrode, 12... Controller, 20
...Plating liquid tank, W...Object to be plated.

Claims (1)

[Scope of Claims] 1. A pair of electrodes made of gold or platinum is arranged in an electroless plating liquid tank in which the object to be plated is immersed while being conveyed, and the object to be plated is simultaneously plated with respect to the electrodes. After plating these electrodes for a certain period of time, electricity is applied to these electrodes to dissolve the plating layer formed on the electrodes by electrolysis in the electroless plating bath, and the time and current required for this electrolysis are determined. The thickness of the plating layer of the electrode is calculated by measuring the current value and calculating the integrated current, and then comparing this calculated value with the thickness of the plating layer to be formed on the surface of the object to be plated. An electroless plating method that controls the residence time of objects in an electroless plating liquid tank. 2. The electroless plating method according to claim 1, wherein a plating solution of electroless copper, electroless nickel, electroless tin, or electroless solder is used as the electroless plating solution. 3. The electroless plating method according to claim 1 or 2, wherein the plating time for the electrode is one minute or less, and this is repeated a predetermined number of times.