JPS602669A - Device and method for controlling electroless plating liquid - Google Patents

Abstract

PURPOSE:To control automatically an electroless plating bath by partitioning an electroless plating cell for Cu, etc. to three chambers by means of a cation exchange membrane and an anion exchange membrane, performing electroless plating in the central plating bath chamber and impressing an AC voltage on the electrodes in the metallic ion bath chamber and pH adjusting bath chamber on both sides. CONSTITUTION:An electroless plating cell 1 for, for example, Cu, is segmented to three chambers A, B, C by means of a cation exchange membrane 2 and an anion exchange membrane 3 of said cell. An electroless plating bath of Cu is put into the chamber B, a Cu ion-contg. bath in the chamber A and an aq. NaOH soln. as a pH adjusting agent in the chamber C. A Cu plate electrode 4 and a platinum electrode 5 are installed and the pulse voltage of AC constant current is impressed on said electrodes. Electroless Cu plating is performed in the chamber B; at the same time, the Cu ion and OH ion necessary for the plating are replenished into the chamber B from both chambers and the unnecessary Na ion, SO4 ion, etc. are removed therefrom by changing over the positive and negative poles of both electrodes 4, 5, by which the electroless plating bath is automatically controlled.

Description

[Detailed Description of the Invention] [Technical Field] The present invention provides a tube for keeping the composition of an electroless plating solution constant at all times. ! It relates to devices and methods of managing them.

[Prior art]

In general, electroless plating solutions contain metal cations, complexing agents for metal cations, reducing agents for metal cations, pH adjusters, etc. as main components, and electroless copper, which is particularly versatile, Taking a plating solution as an example, a typical plating solution has the following composition.

Cu so4 + 5)-120 (copper ion supply agent) E
DTA-4Na 4H20 (copper ion supply agent) IC
l-10 (transition agent) Na OH (PI-1 regulator) α-α' dipyridyl (stabilizer) Polyethylene glycol (surfactant) In an electroless copper plating solution with such a composition, the following occurs during plating. It is thought that main and side reactions are occurring.

Main reaction Cu Y +2HCHO+40H-→Ct+ ' 10Y
'-+2HCOO-+2H20+H2 Side reaction 2 HCHO+Ol-1-→CH301-10FI C
O0-2CU”+HCHO+508-)Cu20-1-
HCOO-+3820 CIJ20+H20→Cu'+Cu"+208-C
u y2-+1-1coo-+301-1-→Cu'
+Y'-+ Go, -+ 2820 Here, Y is EDTΔ<ethylenediaminetetraacetic acid>, C
u6 represents an adsorbed copper atom.

In order to continuously maintain the plating reaction in a stable state, it is desirable that all components constituting the plating solution remain constant. However, it is very difficult to keep the composition of the plating solution constant while allowing the plating reaction to proceed. That is, in the plating reaction, Cu is a reaction consumable component.

HcHo, 01-1- are Cll5○4 and 5+-12, respectively
0°HCHO,Na can be replenished as 0f-1, but it is not consumed by the reaction and increases with the reaction <SO2°N
a”, and HCO which is the oxidation product of l-I CHO
O, l-IC0O- oxidation product co\ (depending on the dissolution of CO2 gas in the air) is accumulated as accumulated ions as the plating reaction progresses, and the increase in accumulated ions is It is generally known that it adversely affects plating quality. Therefore, as the plating reaction progresses, the composition of the plating solution changes from the beginning of its preparation, and as a result, the plating ability of the plating solution decreases in a relatively short period of time. The disadvantage was that the plating quality also deteriorated.

3- To address this drawback, conventional methods have been to use the plating solution for a certain period of time and then discard it and rebuild it, or to control the specific gravity of the plating solution so as not to increase the amount of accumulated ions in the plating solution beyond a certain level. The method involved replenishing a considerable amount of new fluid. However, the former method requires frequent reconstitution of the plating solution in order to maintain the original composition of the plating solution, leading to high costs and poor workability; The new liquid is also replenished with the reactive consumable component cu”, f-(CHO, 0f-
1- and equivalent SO'+-1l-I CO0-1N a
In order to maintain these compositions as they were when the plating solution was initially prepared, an extremely large amount of new solution must be replenished, and in the end, even with this method, costs and
It was not practical in terms of workability.

(Object of the Invention) The object of the present invention is to improve the above-mentioned conventional drawbacks, and to maintain the composition of an electroless plating solution always the same as the composition at the time of preparation of the plating solution, regardless of the progress of the plating reaction. In other words, it is an object of the present invention to provide a management device and a management method that can supply an electroless plating solution with good plating quality over a long period of time.

[Structure of the invention]

Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 1 shows a sectional view of an electrolytic cell 1, which is divided into three chambers A, B, and C by a cation exchange membrane 2 and an anion exchange membrane 3. The chamber is filled with a metal salt solution that dissociates metal cations used in plating, such as copper ions, cobalt ions, nickel ions, palladium ions, platinum ions, silver ions, and gold ions. In addition, in chamber B, the metal salt, a complexing agent for metal cations from the metal salt, a 9-element agent for metal cations, an alkali metal hydroxide as a PI-1 regulator, and the stability of the plating solution. It is filled with an electroless plating solution containing additives used to improve the mechanical properties of the packed film and increase the plating speed, etc. The complexing agent is ethylenediamine,
Diethylenetriamine, triethylenetetraamine, ethylenediaminetetraacetic acid, N,N, N-N-tetrakis-2-(2-hydroxypropyl)ethylenediamine, citric acid, tartaric L1.3-propanediamine, ammonia, Rochelle hydrochloric acid, N- Sodium salts of hydroxyethylethylenediaminetriacetic acid (mono-, di-,
and trichlorotriacetic acid salts), nitrilotriacetic acid and its alkali salts, glyconic acid, gluconate, triethanolamine, and the like. As the reducing agent, formaldehyde and its early curing agents or derivatives, such as glycolaldehyde, paraformaldehyde, trioxane, dimethylhydantoin, glyoxal and their analogs, other alkali metal borohydrides, and borane can be used. As the pH adjuster, alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide are used. Furthermore, additives include α-α′ dipyridyl, polyethylene glycol, cyanide, ethoxy surfactant, sulfur compound,
Examples include rare earth elements. Further, chamber C is filled with the alkali metal hydroxide solution to adjust the pH of the electroless plating solution filled in chamber B.

Electrodes 4 and 5 are immersed in each of the solutions in the chambers C and C, respectively, and a constant current square wave alternating current pulse as shown in FIG. 2 can be applied between the electrodes 4 and 5.

The duty of this waveform is determined by the plating conditions as described below.

(Example) Next, an example of the present invention will be described in detail by taking an electroless copper plating solution as an example.

In this embodiment, each chamber Δ, B, and C of the electrolytic cell 1 is filled with a solution having the following composition.

Room A CuSO+・51-120 1.0tvl/ノ1-12
sO40,1M/J Na2SO40,5M/J2 Chamber B CuSO+ ・5H200,04M//7! EDTA・
4. Na ・4H200,10M/,/1-I CH0
5m12/! m where NaOHPI-1 is 12.3 7- α-α' dipyridyl 20 mg/2 polyethylene glycol 5 (1/J Chamber C Na01-I IM/, g A constant current pulse is applied to the copper plate electrode 4 and platinum plate electrode 5 immersed in C (
The ions in each solution move through the anion exchange membranes 2 and 3. Referring to FIGS. 3 and 4, the movement state of each ion is as follows: (1) When the copper plate electrode 4 is positive and the platinum plate electrode 5 is negative, (2) When the copper plate electrode 4 is negative and the platinum plate electrode We will explain two cases when 5 becomes positive.

(1) When the copper plate electrode 4 becomes positive and the platinum plate N pole 5 becomes negative.

As shown in FIG.
Move to room B via. Also, in room C, et OH
, so, , , HCO○, COJ, 8- CIJ Y"', Y'- moves to chamber B via the anion exchange membrane 3 because the electrode 5 is negative, but 01- in chamber C The concentration of 1 is higher than other ions SO4, Hco
Since the cJ degree is much higher than that of o-, couni CIJ Y'-1 arm, almost only OH- moves to chamber B via the anion exchange membrane 2. At this time, in chamber B, CII t+ reacts with Y from EDTΔ originally contained in the electroless copper plating solution to form a complex, and is captured as a CIIY complex ion. Also, 01”
- and H+ react with each other and are consumed.

(2) When the copper plate electrode 4 becomes negative and the platinum plate electrode 5 becomes positive.

At this time, Na+ is transferred from chamber B to chamber A via the cation exchange membrane 2, but the cations in chamber B are Na+
Therefore, in the case of (1) described above, Na + moves from chamber △ to chamber B via the cation exchange membrane 2!'JI RJ:
As a result, Na'' is selectively removed from chamber B to chamber Δ.As a result, while an AC constant current pulse is being applied between the copper plate electrode 4 and the platinum plate electrode 5, The degree of N a ” tQ in chamber B is FEDT△-4
Nf1 ・Even if Na0 is generated in excess from old-120, it is kept almost constant. In addition, the permeability of ions to the ion exchange membrane generally increases as the valence of the ion increases, and as ions become bulkier and smaller, CuY and Y among the anions in chamber B are ”-,C
It is much more difficult to permeate the anion exchange membrane than O3, and furthermore, it moves from chamber B to chamber C.
The movement of COO-, CO'3- is larger than the movement when moving from chamber C to chamber B in the case (1) above, so SO+, 1-HCoo-1CO knee is 4.5 By passing an alternating current constant pulse between them, it is selectively removed from chamber B via the anion exchange membrane 3. On the other hand, in chamber B, 0f-1- is consumed in the plating reaction and reaction with H+ as described above, so the concentration of 01-de in chamber B is much higher than the concentration of so4'-1HCO〇-1cony. low, therefore OH- is from chamber B to chamber C.
It is rarely rhythmic.

As explained above in two cases, according to this embodiment, by applying an AC constant current pulse between the copper plate electrode 4 and the platinum plate electrode 5, the , Cu, Ol'' necessary for the plating reaction are selectively replenished into chamber B1!7, and l'4a, which is unnecessary for the plating reaction, increases as the plating reaction progresses.
, SO+ , HCOO-1CO sub- are selectively removed from chamber B. From this, 1-1cHo and EDTA-4Na-4l are consumed along with the plating reaction.
-1sO,! [By replenishing the required amount, the composition of the electroless copper plating solution in chamber B can be kept the same as the initial composition of the plating solution regardless of the progress of the plating reaction. Note that the duty of the AC constant current pulse is set based on the concentration of each component.

An electroless copper plating solution management device constituted by the electrolytic cell 1 is used by being incorporated into a plating device as shown in FIG. In the figure, a pampering liquid whose composition is controlled to be constant in chamber B is sent to an electroless steel plating bath 7 through a circulation pipe 11-6. Plating bath 7
After plating is performed inside, the plating solution is transferred to a storage tank 9 by a pump 8, and from the storage tank 9 is sent again into the chamber B, where the composition is controlled to be constant. Further, the liquid in the chamber A is transferred from the storage tank 11 to the storage tank 13 via the pump 12 by the circulation pipe 10, and then returned to the chamber again.

While being circulated in this way, the liquid in chamber A is stirred and the concentration of Na'' moving from chamber B through the cation exchange membrane 2 is diluted and suppressed to a low concentration. In addition, the liquid in the chamber C is also transferred from the storage tank 15 to the storage tank 17 via the pump 16 by the circulation pipe 14, and is then circulated back to the chamber C. At this time, the liquid in the chamber C is stirred. At the same time, the concentration of 5oS-1HC00- and C03 moving from chamber B via the anion exchange membrane 3 is diluted and suppressed to a low concentration.

When plating was carried out under the following conditions using a plating apparatus constructed as described above, the results shown in the table were obtained.

12- Kumetsuki conditions〉 Plating bath operating time: 1 hour Plating load 1lm2/f Plating speed: 2μ/hr.

Plating bath volume 501 Effective membrane area 8.24 dm2 Plating bath temperature 75°C Room B temperature 500C According to the table, the 5OW-1zcoo-, coS-1N a + concentration, which is unnecessary for plating in conventional plating equipment, is 1 It can be seen that after weeks of plating operation, the overall concentration is extremely high. On the other hand, according to the plating apparatus of this embodiment, so'□-1l-ICOO-, C0E-1Na+
The concentration does not change at all even after one week, and is maintained at the concentration at the start of plating. In addition, in conventional plating equipment, after one week of operation, CLI804・51-120
and Na01-1 at 28.56 mol and 150.
Although it is necessary to replenish only OOmol, there is no need to replenish C'l 804 .5 H20z Na 01-1 over one week of operation ItlJr7M in the plating apparatus of this example. Furthermore, when comparing the mechanical strength of plated copper foil, the tensile strength of the copper foil and the copper The elongation rate of the foil also decreases. On the other hand, in the plating apparatus of this example, the concentrations of 804, HCOO, Cow, and Na can be maintained at the concentrations at the start of plating, so that the tensile strength of the copper foil and the elongation rate of the copper foil do not decrease. , the quality at the start of plating can be maintained.

Note that the AC constant current pulse applied between the copper plate electrode 4 and the platinum plate electrode 5 in the control device used in the plating apparatus of this embodiment has a pulse width ratio a/b of 1.8 as shown in FIG.
Thirteen pulse currents were used.

As explained in detail above, the management device of this embodiment is the electrolytic cell 1.
A, B by cation exchange membrane 2 and anion exchange membrane 3
, C, and each chamber is filled with the predetermined liquid,
By passing an AC constant current pulse between the copper plate electrode 4 and the platinum plate electrode 5 arranged in each of chambers A and C, CU2+ and OH- necessary for plating are selected via both ion exchange membranes 2 and 3. In addition to replenishing chamber B from time to time, remove unnecessary SO for plating.
:”, HCOO-, co-1Na+ were selectively removed from chamber B, so a predetermined amount of HCHO and EDT
The composition of each component of the electroless copper plating solution in chamber B can be kept constant by simply replenishing A.4Na.4H20. Therefore, if such a control device-16= is used, a plating film of constant quality can always be obtained, and the plating cost can be significantly lowered compared to the conventional method.

〔Effect of the invention〕

As explained above, the present invention provides a management device that can maintain the composition of the electroless plating solution constant at all times and adjust the electroless plating solution so that a good plated film can be obtained over a long period of time. The effect is great.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, and FIG. 1 is a cross-sectional view of an electrolytic cell, FIG. 2 is a waveform diagram of an AC constant current pulse, and FIGS. 3 and 4 are AC constant current pulses between electrodes. An explanatory diagram showing the movement state of each ion when a pulse is applied. Figure 5 is a schematic diagram of a tampering device using the control device of this example. Figure 6 is an AC constant current used in this example. It is a waveform diagram of a pulse. In the figure, 1 is an electrolytic cell, 2 is a cation exchange membrane, 3 is an anion exchange membrane, 4 is a copper plate electrode, and 5 is a platinum plate electrode. Figure 1 Figure 2 Figure 6 Figure 3 Figure 4

Claims (1)

[Claims] 1. An ion exchange membrane is provided between the electrodes, and a metal cation, a complexing agent for the metal cation, a reducing agent for the metal cation, and P)-1 alkali metal water as a regulator. Equipped with an electroless F+7 bath filled with an electroless plating solution containing oxides as a main component, by passing an alternating current through the electrode, metal cations are mainly removed from the components of the electroless plating solution through the ion exchange membrane. An electroless plating solution management device characterized in that it selectively allows hydroxide ions, counteranions of metal cations, and oxidation product ions of a reducing agent to permeate therethrough. 2. In an electrolytic cell equipped with an ion exchange membrane between the electrodes, the main components are metal cations, a complexing agent for metal cations, a reducing agent for metal cations, and an alkali metal hydroxide as a pH adjuster. By filling an electroless plating solution and passing an alternating current through the electrode, the components of the electroless plating solution, mainly metal cations, hydroxide ions, and counteranions of metal cations, are reduced through the ion exchange membrane. 1. A method for managing an electroless plating solution, characterized by selectively allowing ions of oxidation products of the agent to pass therethrough.