JP2007131940A - Electroless copper plating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroless copper plating method where, in a horizontal carrier type electroless copper plating method, after a substratea is dipped in plating liquid, plating reaction can be smoothly started. <P>SOLUTION: In the horizontal carrier type electroless copper plating method where a copper clad laminate 12 is carried to a horizontal direction A, before the copper clad laminate 12 is dipped into a plating liquid stored in a plating tank 14, the reaction potential of the electroless copper plating is applied to the copper clad laminate 12. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electroless copper plating method.

Standard electroless copper plating methods are (1) degreasing / hydrophilization treatment and water washing, (2) roughening treatment with sodium persulfate and water washing, (3) pre-dip, (4) plating catalyst (palladium) application Generally, it includes steps of treatment and washing, (5) adhesion promoting treatment and washing, (6) electroless copper plating treatment and washing. A general electroless copper plating method is described in Patent Document 1, for example. The process of the horizontal conveyance type electroless copper plating method is based on this (see FIG. 4).
Japanese Patent Laid-Open No. 5-156459

  However, in the horizontal transfer type electroless copper plating method, it is generally difficult to start the electroless copper plating reaction smoothly (in a short time), increasing the activity of the plating solution itself and increasing the reactivity. For this reason, the activity of the electroless copper plating solution becomes too high, and copper is often abnormally deposited on the tank wall and the transport roll.

  The horizontal transfer method has various advantages such as better workability of the thin plate and better flowability of the processing liquid to the blind via hole as compared with the conventional vertical plating method such as the cage method or the rack method. However, the following disadvantages are mentioned in that the electroless copper plating reaction proceeds smoothly and reliably.

  The first point is as follows. In the case of the horizontal conveyance method, due to the squeezing effect of the conveyance roll, the treatment liquid and washing water hardly remain on the surface of the copper clad laminate, and the copper foil on the substrate surface is easily exposed to air and easily oxidized. This also oxidizes the copper foil and produces cuprous oxide or copper oxide, thereby inhibiting the plating reaction and making it difficult to proceed smoothly.

  The second point is as follows. In the case of a cage method or a rack method that is not a horizontal conveyance method, a plurality of substrates are generally put into the plating solution at the same time, so when any one of the substrates starts the plating reaction, The substrate receives a potential from the substrate that has started the plating reaction and starts the plating reaction together. On the other hand, in the case of the horizontal transfer method, each of the plurality of substrates is independent from each other, and each must have a certain reactivity.

  The third point is as follows. In the horizontal conveyance method, the plating time is set short in order to make the apparatus compact. For this reason, when the substrate is immersed in the plating solution and the time until the start of the plating reaction is long, a sufficient plating thickness cannot be obtained.

  The present invention provides an electroless copper plating method capable of smoothly starting a plating reaction after a substrate is immersed in a plating solution in an electroless copper plating method of a horizontal conveyance system.

  In order to solve the above-mentioned problem, the electroless copper plating method of the present invention is an electroless copper plating method of a horizontal conveyance method, and before the substrate is immersed in a plating solution, the reaction potential of the electroless copper plating is Including a step of applying to the substrate.

  Here, “electroless copper plating reaction potential” means the potential of the substrate during the electroless copper plating reaction when electroless copper plating is performed by immersing the substrate in a plating solution. Say. In order to measure the potential of the substrate, for example, an oxidation-reduction potentiometer (ORP electrometer) can be used.

  According to the electroless copper plating method of the present invention, by applying a reaction potential of electroless copper plating to the substrate, the potential of the substrate can be preliminarily made lower than the standard electrode potential (oxidation reduction potential) of the substrate. it can. Therefore, the plating reaction can be smoothly started after the substrate is immersed in the plating solution by horizontal conveyance.

  Moreover, it is preferable that the said board | substrate is conveyed horizontally using a metal roll, and the said reaction potential is provided to the said board | substrate via the said metal roll.

  In this case, it is not necessary to separately provide a mechanism for applying a reaction potential to the substrate, so that the reaction potential can be easily applied.

  Further, the reaction potential is applied to the substrate by immersing another substrate in the plating solution to perform electroless copper plating on the other substrate and electrically connecting the other substrate and the substrate. It is preferable to do.

  In this case, a reaction potential can be easily applied to the substrate.

The following potential application method is also preferable.
1. In the horizontal transfer electroless copper plating step, a potential applying method in which a natural reaction potential of electroless copper plating is automatically applied when a substrate enters the electroless copper plating solution.
2. Item 2. The potential applying method according to Item 1, wherein the natural reaction potential of the electroless copper plating solution is applied to the substrate by a metal roll.
3. The natural reaction potential is a reduction potential when a board with copper foil or a copper clad laminate is immersed in an electroless copper plating solution, and the board with copper foil or copper clad laminate undergoes a plating reaction. And the electric potential provision method of claim | item 1 which connects a board with a copper foil in a plating solution, and a metal roll, in order to give this electric potential to the board | substrate which wants to plate.

  ADVANTAGE OF THE INVENTION According to this invention, in the electroless copper plating method of a horizontal conveyance system, after a board | substrate is immersed in a plating solution, the electroless copper plating method which can start a plating reaction smoothly is provided.

  Hereinafter, embodiments of the present invention will be described in detail. In the description of the drawings, the same reference numerals are used for the same or equivalent elements, and duplicate descriptions are omitted.

  FIG.1 and FIG.2 is a figure which shows typically the electroless copper plating apparatus of a horizontal conveyance system. An electroless copper plating apparatus 10 shown in FIG. 1 includes a plating tank 14 for containing an electroless copper plating solution, and a plurality of SUS rolls 16 (metals) that convey a copper-clad laminate 12 (substrate) in the horizontal direction A. Roll). The copper clad laminate 12 is sandwiched between a plurality of pairs of SUS rolls 16. By rotating the SUS roll 16, the copper clad laminate 12 can be conveyed and immersed in the plating solution.

  The plating solution preferably contains a copper salt, a complexing agent, and a reducing agent as main components. The plating solution may contain an additive and a stabilizer.

  A board 18 with copper foil (another substrate) is immersed in the plating solution. The board 18 with copper foil and the rotating shaft of the SUS roll 16 are electrically connected by a connection 20. The electroless copper plating apparatus shown in FIG. 2 has the same configuration as the electroless copper plating apparatus 10.

  The electroless copper plating method according to the embodiment is suitably implemented using the electroless copper plating apparatus 10. The electroless copper plating method according to the present embodiment is a horizontal conveyance type electroless copper plating method. In this method, a reaction potential of electroless copper plating is applied to the copper clad laminate 12 before the copper clad laminate 12 is immersed (contacted) in the plating solution. The reaction potential of electroless copper plating is preferably −800 mV or more and −500 mV or less, for example, −650 mV.

  By applying a reaction potential of electroless copper plating to the copper-clad laminate 12, the potential of the copper-clad laminate 12 can be preliminarily made lower than the standard electrode potential of the copper-clad laminate 12. Therefore, after the copper-clad laminate 12 is conveyed in the horizontal direction A and immersed in the plating solution, the plating reaction can be started smoothly in a short time. Therefore, if a printed wiring board is manufactured using the electroless copper plating method described above, the production efficiency of the printed wiring board can be improved.

  In the present embodiment, the copper clad laminate 12 is horizontally conveyed using the SUS roll 16, and a reaction potential for electroless copper plating is applied to the copper clad laminate 12 via the SUS roll 16. For this reason, it is not necessary to separately provide a mechanism for applying a reaction potential to the copper clad laminate 12. Therefore, a reaction potential can be easily applied to the copper clad laminate 12.

  Moreover, the board 18 with a copper foil is immersed in a plating solution, electroless copper plating of the board 18 with a copper foil is performed, and the board 18 with a copper foil and the copper-clad laminate 12 are electrically connected to each other. It is preferable to apply a reaction potential to the laminate 12. In this case, a reaction potential can be easily applied to the copper clad laminate 12.

  When the electroless copper plating reaction proceeds on the board 18 with copper foil, for example, the potential of the board 18 with copper foil becomes lower than the standard electrode potential due to the cathode current due to the reducing action of a reducing agent such as formalin. ing. Further, when the substrate on which the plating reaction is proceeding (board 18 with copper foil) and the substrate (copper-clad laminate 12) newly introduced into the same electroless copper plating solution are connected, a new substrate (copper-clad laminate) is obtained. The surface potential of the plate 12) is lower than the standard electrode potential due to the cathode current of the reacting substrate (board 18 with copper foil). As a result, the electroless copper plating reaction on the copper foil surface of the copper clad laminate 12 proceeds smoothly.

  In the case of horizontal transfer electroless copper plating, a board 18 with copper foil is immersed in an electroless copper plating tank (plating tank 14) in advance, and the board 18 with copper foil and the plating tank in which this plating reaction proceeds. 14 By connecting the metal roll (SUS roll 16) installed immediately before, the potential of the board 18 with copper foil is applied to the substrate (copper-clad laminate 12) to be plated through the metal roll (SUS roll 16). The plating reaction starts immediately. This is because copper oxide and cuprous oxide on the surface of the copper clad laminate 12 are reduced by a reduction potential (reaction potential of electroless copper plating) to become metallic copper, and reduction of the reducing agent (formalin) in the electroless copper plating solution. It is thought that the principle is to work as a catalyst for the reaction.

  FIG. 3 is a diagram schematically showing another horizontal conveyance type electroless copper plating apparatus. The electroless copper plating apparatus 10a shown in FIG. 3 has the same configuration as the electroless copper plating apparatus 10 except that a rectifier 22 is provided instead of the board 18 with copper foil. The rectifier 22 is disposed outside the plating tank 14. The rectifier 22 and the rotating shaft of the SUS roll 16 are electrically connected by a connection 20. The rectifier 22 can apply a reaction potential of electroless copper plating to the copper clad laminate 12. Therefore, the same effect as the electroless copper plating apparatus 10 can be obtained even in the electroless copper plating apparatus 10a.

  In the present embodiment, in the horizontal conveyance type electroless copper plating process, the substrate (copper-clad laminate 12) is applied to the plating solution by applying a reaction potential of electroless copper plating to the substrate (copper-clad laminate 12). When entering, the electroless copper plating reaction proceeds smoothly. The potential can be applied by the rectifier 22 shown in FIG. 3 or the like. However, when the potential (voltage) is high, the adhesion between the underlying copper foil and the electroless copper plating film may be lowered. . In contrast, the occurrence of such a problem can be avoided by applying the potential of the electroless copper plating reaction itself (reaction potential of the electroless copper plating).

  As mentioned above, although preferred embodiment of this invention was described in detail, this invention is not limited to the said embodiment.

  For example, instead of the board 18 with copper foil, a copper-clad laminate, a substrate having a copper layer on the surface, or a copper substrate may be used. Further, instead of the copper clad laminate 12, a substrate having a copper layer on the surface or a copper substrate may be used. Further, a roll that is not made of metal may be used instead of the SUS roll 16. In this case, it is preferable to electrically connect the connection wire 20 to the copper clad laminate 12.

  Hereinafter, the present invention will be described in detail using examples. However, the present invention is not limited to the following examples.

Example 1
For copper-clad laminates (made by Hitachi Chemical Co., Ltd., product name MCL-E-67, plate thickness 0.5t) with little Pd adsorption and slow initiation of plating reaction and without holes. Copper plating was performed according to the procedure shown in Table 1. In Example 1, as shown in FIG. 2, the roll immediately before the electroless copper plating tank is set to SUS, and a board with copper foil (product name: MCL-E, manufactured by Hitachi Chemical Co., Ltd.) in advance in the electroless copper plating tank. -67, plate thickness 1.6t, 300 mm x 300 mm) is immersed, and the board with copper foil and the SUS roll are connected. In the board with copper foil, it is checked beforehand with an ORP electrometer whether the electroless copper plating reaction is proceeding. The substrate (copper-clad laminate) was subjected to the following copper plating step (Table 1), and the time from when the substrate was immersed (contacted) in the plating solution until the start of the plating reaction was measured. The potential of the copper clad laminate surface was measured with an ORP electrometer, and the time when the potential difference between the measured potential and the standard electrode potential became −600 mV or less was defined as the time when the electroless copper plating reaction was started. The number of samples was 10. The results are shown in Table 2.

  As a result, all the substrates started the plating reaction within 3 seconds.

(Examples 2 to 6)
In the same manner as in Example 1, a copper-clad laminate (manufactured by Hitachi Chemical Co., Ltd., product name MCL-E-67, plate thickness 0.5 t) with no holes was subjected to the procedure shown in Table 3 below. Plating was performed. As in Example 1, as shown in FIG. 2, the roll immediately before the electroless copper plating tank is set to SUS, and the board with copper foil (product name: MCL, manufactured by Hitachi Chemical Co., Ltd.) in advance in the electroless copper plating tank. -E-67, plate thickness 1.6 t, 300 mm x 300 mm) was immersed, and the board with copper foil and the SUS roll were connected. In Examples 2 to 6, the copper concentration, pH, and temperature of the electroless copper plating solution were changed, and the conveyor speed was also examined at the standard (0.5 m / min) and twice or three times the speed. There were five types of conditions. The pH was adjusted by appropriately adding dilute sulfuric acid and NaOH to the electroless copper plating solution. Moreover, temperature was adjusted using the heat conversion by flowing cooling water through the piping passed through the electroless copper plating solution. Moreover, the plating thickness of each condition was measured as the plating thickness of the etched copper clad laminate surface. In the board with copper foil, it is checked with an ORP electrometer whether the electroless copper plating reaction is proceeding. The substrate (copper-clad laminate) was subjected to the following copper plating step (Table 3), and the time from when the substrate entered the plating solution (when the substrate contacted the plating solution) to the start of the plating reaction was measured. . The results are shown in Table 4.

  As a result, when the copper concentration, pH, and temperature of the plating solution are lowered, the plating activity is lowered, and when the conveyor speed is increased, the plating thickness is greatly reduced compared to the standard. The time is proceeding smoothly within 3 seconds. In addition, about Example 1-6, as a result of conducting experiment of 10 samples, respectively, time until the plating reaction start was all within 3 seconds.

(Comparative Example 1)
Copper-clad laminate with little Pd adsorption and slow initiation of plating reaction, with no holes (Hitachi Chemical Industry Co., Ltd., product name MCL-E-67, plate thickness 0.5t, 300mm x 300mm) On the other hand, copper plating was performed according to the procedure shown in Table 5 below. At this time, the time from when the copper clad laminate was immersed in the plating solution until the reaction was started was measured. The potential of the copper clad laminate surface was measured with an ORP electrometer, and the time when the potential difference between the measured potential and the standard electrode potential became −600 mV or less was defined as the time when the electroless copper plating reaction was started. The results are shown in Table 6.

  As a result, there are some substrates that start the plating reaction within 3 seconds, but there are also substrates that require about 1 minute to start the plating reaction.

It is a figure which shows typically the electroless copper plating apparatus of a horizontal conveyance system. It is a figure which shows typically the electroless copper plating apparatus of a horizontal conveyance system. It is a figure which shows typically the electroless copper plating apparatus of another horizontal conveyance system. It is a perspective view which shows the conventional electroless copper plating apparatus of a horizontal conveyance system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Degreasing and hydrophilization processing part 2 Water washing part 3 Roughening processing part 4 Pre-dip processing part 5 Catalyst provision processing part 6 Adhesion promotion processing part 7 Horizontal conveyance electroless copper plating line part 8 Electroless copper plating processing part 10, 10a None Electrolytic copper plating equipment 12 Copper-clad laminate (substrate)
14 Plating tank 16 SUS roll (metal roll)
18 Board with copper foil (another board)
20 Connection 22 Rectifier

Claims (3)

A horizontal transfer type electroless copper plating method,
An electroless copper plating method comprising a step of applying a reaction potential of electroless copper plating to the substrate before the substrate is immersed in a plating solution. Use a metal roll to transport the substrate horizontally,
The electroless copper plating method according to claim 1, wherein the reaction potential is applied to the substrate through the metal roll. Dipping another substrate in the plating solution to perform electroless copper plating on the other substrate,
The electroless copper plating method according to claim 1 or 2, wherein the reaction potential is applied to the substrate by electrically connecting the another substrate and the substrate.

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