JP3129596B2 - Method for removing plating resist from printed wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing a plating resist from a printed wiring board.

[0002]

2. Description of the Related Art Conventionally, a wiring pattern of a printed wiring board is formed by, for example, the following process.

[0003] First, after a hole for forming a through hole is formed in a copper clad laminate, electroless copper plating is performed (panel plating). Next, the photosensitive dry film is pressed and exposed and developed to form a plating resist. Next, electrolytic copper plating is performed on a portion where the plating resist is not formed (pattern plating). Next, a metal etching resist is formed by performing solder plating on the electrolytic copper plating. Next, the plating resist is peeled off using an organic solvent such as trichlene. Next, after unnecessary copper is removed by etching, the metal etching resist is further etched. Thereafter, by performing overcoating or terminal plating, a desired wiring board is obtained.

[0004]

Incidentally, in recent years, as part of measures to reduce the use of fluorocarbons, regulations on the use of the above-mentioned organic solvents have become stricter.
For this reason, conversion from a conventional dry film soluble in an organic solvent to a dry film soluble in an alkaline aqueous solution is desired.

However, when a dry film soluble in an alkaline aqueous solution is used, the following problems occur. That is, when the alkaline aqueous solution is treated to remove the dry film, the tin in the metal etching resist is dissolved, so that the wiring pattern is easily broken in the subsequent copper etching step. Therefore, conventionally, measures have been taken to add an inhibitor to an alkaline aqueous solution.

However, there is a problem that the dissolution of tin cannot be completely suppressed even if such an inhibitor is added. In addition, when an inhibitor is added, problems such as an increase in stripping cost and troublesome wastewater treatment also occur.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a printed wiring capable of suppressing dissolution of a metal etching resist without using an inhibitor, thereby preventing disconnection of a wiring pattern. An object of the present invention is to provide a method of removing a plating resist on a plate.

[0008]

In order to solve the above-mentioned problems, according to the first aspect of the present invention, when forming a metal etching resist containing at least tin by plating, the plating resist is removed using an alkaline aqueous solution. In the method of removing the plating resist of the printed wiring board,
The treatment temperature of the alkaline aqueous solution is 30 ° C to 60 ° C.
Anodes on both sides of the printed circuit board
Placed at approximately the same distance from the printed circuit board
In addition, a gist of the present invention is a method for removing a plating resist on a printed wiring board, wherein the plating resist is removed while a weak cathode current is applied to the metal etching resist. According to a second aspect of the present invention, in the first aspect, the wiring board potential is set to-
1.60V --1.20V [SCE = Saturatedcalomelelec
trode, saturated calomel reference electrode (the same applies hereinafter)]. In the invention according to claim 3,
In the invention according to claim 1 or 2, the gist is that the metal etching resist is a solder plating film.

[0009]

According to the first and third aspects of the present invention, the wiring board potential when the resist is removed shifts from the active dissolution potential region of tin or lead to a lower potential direction. Therefore, only the plating resist can be removed without causing active dissolution of tin or lead by the alkaline aqueous solution. According to the second and third aspects of the present invention, since the wiring board potential is within the above range, it is possible to suppress the generation of hydrogen and power consumption, and to reliably suppress the dissolution of tin or lead.

[0010]

【Example】

[Embodiment 1] Hereinafter, Embodiment 1 in which the present invention is embodied in a method of removing a plating resist at the time of manufacturing a printed wiring board.
Will be described in detail with reference to FIGS.

As shown in FIG. 1, through holes 2 are formed in a printed wiring board (hereinafter, referred to as a six-layer wiring board) 1 having six conductor layers. next,
After providing a Pd catalyst nucleus serving as a core when electroless copper plating is deposited on the six-layer wiring board 1, the catalyst nucleus is activated.

Next, the six-layer wiring board 1 is immersed in an electroless copper plating bath for a predetermined time. Then, as shown in FIG.
Copper foil 3 on both sides of layer wiring board 1 and through hole forming hole 2
An electroless copper plating film 4 is formed on the inner wall surface of the substrate (panel plating). Next, after a photosensitive dry film (manufactured by Hitachi Chemical Co., Ltd., trade name: Photec) is pressed on both surfaces of the six-layer wiring board 1, exposure and development are performed. Through this step, a plating resist 5 is formed on the six-layer wiring board 1 as shown in FIG.

Next, pattern plating is performed according to the following procedure. First, by dipping the six-layer wiring board 1 in an electrolytic copper sulfate plating bath, an electrolytic copper plating film 6 having a thickness of 20 μm is formed on a portion where the plating resist 5 is not formed. Next, after washing with water, the six-layer wiring board 1 is immersed in an electrolytic boric acid solder bath. Then, as shown in FIG. 4, an electrolytic solder plating film 7 having a thickness of 3 μm as a metal etching resist is formed on the electrolytic copper plating film 6.

Next, the plating resist 5 is removed by the following method. As shown in FIG. 6, the stripping tank 8 is filled with an alkaline aqueous solution 9 for stripping the plating resist 5. As the alkaline aqueous solution 9, for example, a 10 g / l to 40 g / l NaOH aqueous solution is used. If this concentration is lower than 10 g / l, the plating resist 5 cannot be sufficiently removed. On the other hand, if this concentration is higher than 40 g / l, the cost becomes high.
No inhibitor was added to the NaOH aqueous solution.

The six-layer wiring board 1 is immersed substantially in the center of the peeling tank 8 while being held by the fixing jig 10. In this state, the fixing jig 10 side and the six-layer wiring board 1
The conductor portion on the side is electrically connected. In the immersion tank 8, a pair of stainless steel plates (SUS304 stainless steel plate in this embodiment) 11 as an anode is immersed. These stainless steel plates 11
The six-layer wiring board 1 is arranged so as to be almost equally spaced from both surfaces. Then, a weak cathode current flows through the six-layer wiring board 1.

In this case, the cathode current density is 0.005
A / dm^Two~ 0.5A / dm^Two, And 0.01 A /
dm^Two~ 0.3A / dm^Two, Especially 0.02 A / dm^Two
~ 0.1 A / dm^TwoIt is preferred that Cathode electricity
Flow density is 0.005 A / dm ^TwoSmaller than the wiring board
The potential can be sufficiently shifted to the lower potential direction
And the dissolution inhibiting effect may be reduced. On the other hand,
Sword current density is 0.5 A / dm^TwoLarger than
The wire plate potential is shifted too much in the negative potential direction. That
As a result, the amount of generated hydrogen gas increases, and the working environment deteriorates.
May be affected. In addition, the amount of electricity consumed increases,
Will be done.

Further, the wiring board potential is −1.60V-−
It is preferably 1.20 V, more preferably -1.50 V to -1.30 V, and particularly preferably -1.45 V to -1.35 V. If the wiring board potential is higher than −1.20 V, the dissolution suppressing effect is significantly reduced. On the other hand, the wiring board potential is -1.60.
If it is lower than V, the amount of generated hydrogen gas increases, and the working environment may be deteriorated. In addition, the amount of electricity consumed increases, which is uneconomical.

The treatment temperature of the aqueous alkali solution is 30 ° C. to 60 ° C.
C. and the treatment time are preferably 1 minute to 10 minutes. If the processing temperature is lower than 30 ° C., the plating resist 5 may not be completely stripped in a short time. When the processing temperature exceeds 60 ° C., energy waste increases. If the processing time is less than 1 minute, the plating resist 5 may not be able to be completely removed at a low solution temperature. If the processing time exceeds 10 minutes, it is disadvantageous to shorten the time of the process.

In view of the above, in this embodiment, 50
The six-layer wiring board 1 was immersed for 2 minutes in a 30 g / l NaOH aqueous solution adjusted to ° C. At this time, a current was applied to the six-layer wiring board 1 at a cathode current density of 0.05 A / dm ² . Then, as shown in FIG. 5, the plating resist 5 is dissolved in the NaOH aqueous solution 9, and as a result, only the plating resist 5 is removed.

Next, unnecessary copper foil 3 and electroless copper plating film 4 are etched using an etchant capable of dissolving copper, and an electrolytic solder plating film which is a metal etching resist is further etched using an etchant capable of dissolving solder. 7 is etched. Thereafter, overcoating, terminal plating, and the like are performed according to a conventionally known method. Through the above series of steps, a six-layer wiring board 1 having desired wiring patterns formed on both surfaces is obtained.

The operation and effect of the method for removing the plating resist 5 of this embodiment will now be described. This method is characterized in that the plating resist 5 is peeled off while applying a weak cathode current to the electrolytic solder plating film 7. In this case, the value of the potential of the electrolytic solder plating film 7 shifts from its active dissolution potential range (range of -1.15 V to -0.6 V) to a lower potential range, that is, to a lower potential range. Therefore, even when the six-layer wiring board 1 is immersed in the NaOH aqueous solution 9, only the plating resist 5 can be dissolved without causing active dissolution of the solder. Therefore, disconnection of the wiring pattern due to dissolution of the electrolytic solder plating film 7 which is a metal etching resist is reliably prevented.

In this method, it is not necessary to add an inhibitor to the aqueous NaOH solution 9. Therefore, the stripping cost is lower than before, and the wastewater treatment becomes easier. Further, in this embodiment, the wiring board potential is set to-
Since the voltage is set within the range of 1.60 V to −1.20 V, it is possible to suppress the generation of hydrogen and power consumption, and to reliably suppress the dissolution of tin or lead. Therefore, unlike the related art, the working environment does not deteriorate with the stripping work, and the cost does not increase.

Further, according to this method, since the electrolytic solder plating film 7 does not dissolve, the thickness of the electrolytic solder plating film 7 can be reduced to less than half of the conventional thickness. Therefore, the formation cost of the electrolytic solder plating film 7 is reduced, and the formation time is also reduced. In addition, plating resist 5
When the inspection was performed after the peeling of the electrolytic solder plating film 7
No discoloration or change in film thickness was observed. When the inspection was performed after the etching of the copper foil 3, the electroless copper plating film 4, and the electrolytic solder plating film 7, no defect such as disconnection of the wiring pattern occurred. Embodiment 2 Next, a method of removing a plating resist from a printed wiring board according to Embodiment 2 will be described. Here, differences from the method of the first embodiment will be mainly described.

In this embodiment, a printed wiring board having four conductor layers (hereinafter referred to as a four-layer wiring board) is used. Then, according to the above-described embodiment, the formation of the through-holes, the provision and activation of Pd catalyst nuclei, the formation of an electroless copper plating film (panel plating), and the formation of a plating resist are performed according to the above-described embodiment.

Next, pattern plating is performed according to the following procedure. First, by dipping the four-layer wiring board in an electrolytic copper sulfate plating bath, an electrolytic copper plating film having a thickness of 30 μm is formed on a portion where no plating resist is formed. Next, after rinsing with water, the four-layer wiring board is immersed in an electrolytic tin plating bath to obtain a metal etching resist having a thickness of 5 μm.
m of electrolytic tin plating film is formed.

In the second embodiment, the plating resist is peeled off by spraying an alkaline aqueous solution (30 g / l NaOH aqueous solution) using a roll conveyor peeling machine. In this embodiment, the processing temperature is set to 50 ° C., the spray pressure is set to 1.4 kg / mm ² , the spray time is set to 1.5 minutes, and the cathode current is set to 0.10 A / dm ² . Needless to say, no inhibitor was added to the aqueous NaOH solution as in Example 1. Then, the plating resist is NaO
The plating resist is removed by the H aqueous solution, and as a result, only the plating resist is removed.

Thereafter, a copper foil,
Etching the electroless copper plating film and electrolytic tin plating film,
Further, overcoating and terminal plating are performed. Through the above series of steps, a four-layer wiring board having a desired wiring pattern formed on both surfaces is obtained.

Even with the above-described method of removing the plating resist of the second embodiment, the same operation and effect as those of the first embodiment can be obtained. When the inspection was performed after the plating resist was stripped, no discoloration, no change in film thickness, and the like were observed in the electrolytic tin plating film. When the inspection was performed after etching the copper foil, the electrolytic copper plating film, and the electrolytic tin plating film, no defect such as disconnection of the wiring pattern occurred.

The present invention is not limited to the first and second embodiments, but can be modified as follows. For example, (a) the plating resist 5 stripped by the alkaline aqueous solution 9 is not limited to a photosensitive dry film.
For example, it may be a photosensitive or thermosetting liquid resist.

(B) Stainless steel plate 11 as anode
For example, a titanium plate or a carbon plate or the like may be used instead of the first and second embodiments in which is used. That is, any good conductor that is insoluble in the alkaline aqueous solution may be used.
However, it is preferable to use the stainless steel plate 11 as in the first and second embodiments in terms of cost, workability, and the like.

(C) The metal etching resist is not limited to one formed by an electrolytic plating bath, but may be one formed by an electroless plating bath. (D) The alkaline aqueous solution is not limited to the NaOH aqueous solution used in Examples 1 and 2, for example, KOH, Na ₂ CO 3
₃ , an aqueous solution of NH ₄ OH or the like, or an organic alkali aqueous solution or the like may be used.

Here, in addition to the technical ideas described in the claims, the technical ideas grasped by the above-described embodiments and other examples are listed below together with their effects. (1) In any one of claims 1 to 3, the material of the anode is a stainless steel plate. This is convenient for cost reduction.

[0033]

[0034] (2) according to claim 1 to 3, in Izu <br/> Re of the technical idea 1, the alkaline aqueous solution is an aqueous solution of NaOH 10 g / 40 g / l, the treatment temperature is 30 ° C. to 60 ° C, the processing time shall be 1 minute to 10 minutes. This way,
The plating resist can be peeled off reliably and at low cost.

The technical terms used in this specification are defined as follows. "Metal etching resist containing tin: Various metal plating films formed by electrolytic plating or electroless plating, such as tin plating film, solder (tin-lead alloy) plating film, tin-nickel alloy plating film, tin- Cobalt alloy plating film, copper-tin-zinc alloy plating film, tin-nickel-
It refers to a copper alloy plating film, a tin-zinc alloy plating film, or the like. "

[0036]

As described above in detail, according to the method for removing the plating resist of the printed wiring board according to the first and third aspects, the dissolution of tin or solder in the metal etching resist is suppressed, so that the wiring Disconnection of the pattern can be prevented. According to the second and third aspects of the present invention, tin or solder dissolution is reliably suppressed and hydrogen generation and power consumption can be suppressed, so that cost performance and work environment can be improved.

[Brief description of the drawings]

FIG. 1 is a partial schematic cross-sectional view showing a state in which a through-hole forming hole is provided in Example 1;

FIG. 2 is a partial schematic cross-sectional view showing a state where an electroless copper plating film is formed by panel plating.

FIG. 3 is a partial schematic cross-sectional view showing a state where a plating resist is formed.

FIG. 4 is a partial schematic sectional view showing a state in which an electrolytic copper plating film and an electrolytic solder plating film are formed by pattern plating.

FIG. 5 is a partial schematic cross-sectional view showing a state where a plating resist is peeled off.

FIG. 6 is a schematic diagram showing a peeling tank for immersing a six-layer wiring board when peeling a plating resist.

[Explanation of symbols]

Reference numeral 1 denotes a six-layer wiring board as a printed wiring board, 5 denotes a plating resist, and 7 denotes an electrolytic solder plating film as a metal etching resist.

Claims (3)

(57) [Claims] 1. A method for removing a plating resist from a printed wiring board, wherein the plating resist is removed using an alkaline aqueous solution when a metal etching resist containing at least tin is formed by plating. At 60 ° C
Anodes on both sides of the printed circuit board
Placed at approximately the same distance from the printed circuit board
And removing the plating resist from the printed wiring board by applying a weak cathode current to the metal etching resist. 2. A wiring board potential of −1.60V to −1.20V.
2. The method for removing a plating resist from a printed wiring board according to claim 1, wherein the plating resist is (SCE, saturated calomel reference electrode). 3. The method according to claim 1, wherein the metal etching resist is a solder plating film.