JP2017152492A - Plating method and plating apparatus for printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plating method for a printed wiring board and an electrolytic plating apparatus capable of easily controlling variations in plating thickness of a printed wiring board due to a plating method of a printed wiring board by a direct current plating method and an electrolytic plating apparatus to obtain a uniform plating thickness.SOLUTION: A plating method for electrolytically plating a printed wiring board includes: respectively applying a current to the front and back surfaces of the printed wiring board; alternately jetting a plating solution from a jet device; and applying a current of 5 to 20% of one surface from the other surface as well in a state where a current is applied from the one surface.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a plating method and a plating apparatus for a printed wiring board.

  Conventionally, when electrolytic plating is performed on a substrate (printed wiring board), a known electrolytic plating apparatus is used. In this electrolytic plating apparatus, a substrate is immersed in a plating tank in which a plating solution (for example, a copper sulfate solution) is stored, and both surfaces of the substrate and electrodes disposed on both sides of the front and back surfaces of the substrate are energized. Plating is performed. Such a method is called a direct current plating method.

In recent years, the throwing power of through-hole plating has decreased with the increase in the thickness of the substrate and the increase in the aspect ratio due to the reduction in the diameter of the through-hole. The plating thickness is secured.
However, this high aspect ratio (the ratio of the plate thickness to the through hole diameter is high) not only reduces the fluidity of the plating solution in the through hole, but also reduces the current density in the through hole. There is a problem. Further, since the plating thickness of the surface layer of the substrate is also increased, it is necessary to polish thinly and uniformly in order to form a fine circuit, which makes circuit formation difficult. In addition, variations and unevenness in the plating thickness after polishing occur, or the thickness of the plating is partially reduced, resulting in a decrease in circuit connection reliability.

  Although the above-described problems can be improved by the pulse plating method, the cost of facilities and the like is increased as compared with the direct current plating method.

In order to solve such a problem, for example, in Patent Document 1, a positive current is applied in a copper sulfate plating solution to perform electroplating, and in the same plating solution as the electroplating, a negative polarity opposite to conductor formation is applied. There is a pattern forming method in which a predetermined pattern is formed by applying an electric current to perform local electrolytic etching. In Patent Document 1, electroplating with a copper sulfate plating solution is performed so that the pattern plating thickness and the through-hole plating thickness are uniform.
However, in Patent Document 1, plating is performed by a periodic reversal current application method in which a positive current and a negative current are applied alternately at different times, so that the work becomes complicated and variations in plating thickness are eliminated. Not. Further, even if the application time of the positive current and the negative current is different, the plating thickness does not become uniform on the front and back surfaces.

JP 2006-203013 A

  The present invention relates to a plating method for a printed wiring board by a direct current plating method and a plating method for a printed wiring board capable of easily controlling a variation in the plating thickness of the printed wiring board caused by an electrolytic plating apparatus and obtaining a uniform plating thickness. It is another object of the present invention to provide an electrolytic plating apparatus.

The present invention has been completed in order to solve the above problems, and has the following configuration.
(1) A plating method for electrolytic plating of a printed wiring board, wherein current is applied to the front and back surfaces of the printed wiring board, and a plating solution is jetted from a jet device alternately. Plating method for printed wiring board.
(2) The method for plating a printed wiring board according to (1), wherein a current of 5 to 20% of one surface is applied also from the other surface in a state where a current is applied from one surface.
(3) The method for plating a printed wiring board according to (1) or (2), wherein the printed wiring board has a through hole, and the inside of the through hole is electrolytically plated.
(4) A plating tank in which a plating solution is stored, a printed wiring board that is a plating object that is immersed in the plating solution and whose front and back surfaces are electrically connected to a cathode of an external power source, respectively, and a surface of the printed wiring board Two electrodes respectively disposed opposite to the back surface and electrically connected to the anode of the external power source; and a plating solution jetting device disposed between the printed wiring board and the electrode so as to face the printed wiring board The electroplating apparatus is characterized in that a current is alternately supplied from the external power supply to the front and back surfaces of the printed wiring board and a plating solution is jetted from the jetting apparatus.
(5) The electroplating apparatus according to (4), wherein an upper portion of the printed wiring board is sandwiched and fixed by a jig, and the jig has separate bus bars on the front and back sides.
(6) The electrolytic plating apparatus according to (4) or (5), wherein the printed wiring board has a through hole, and the inside of the through hole is electrolytically plated.

  According to the present invention, the application of current and the jet of plating solution are alternately performed from the front and back surfaces of the printed wiring board, so that variations in the plating thickness of the printed wiring board can be easily controlled and the existing plating apparatus is utilized. Thus, a uniform plating thickness can be obtained at a low cost.

It is explanatory drawing which shows one Embodiment of the electroplating apparatus which concerns on this invention. (A) is a front view which shows one Embodiment of the printed wiring board in the electroplating apparatus which concerns on this invention, (b) is a side view of (a). (A)-(c) is process explanatory drawing which shows one Embodiment of the plating method of the printed wiring board based on this invention. It is a graph which shows the application of each electric current to the front side and back side of the printed wiring board which concerns on this invention.

  As shown in FIG. 1, the electroplating apparatus 100 according to this embodiment includes a plating tank 1, a plating solution 2 stored in the plating tank 1, and an external power source (rectifier) 3. A jetting device 4 provided with at least one nozzle 40 that sucks a plating solution into the plating tank 1 and jets it to the printed wiring board 10 is disposed opposite to both sides of the printed wiring board 10. Two anodes of the external power source 3 are electrically connected to a pair of electrodes (anodes) 5, and a cathode of the external power source 3 is connected to a jig 7 via a bus bar 6. The jig 7 fixes the printed wiring board 10 and electrically connects the external power source 3 and the printed wiring board 10. The printed wiring board 10 is fixed to the jig 7 and immersed in the plating solution 2. In addition, the arrow in a figure shows the direction through which an electron flows.

Examples of the plating solution 2 include a copper sulfate solution and a copper cyanide plating solution.
The printed wiring board 10 before electrolytic plating is subjected to chemical plating (electroless plating) so that the printed wiring board 10 can be used as an electrode for electrolytic plating.

The external power source 3 is used for electrolytic plating of a printed wiring board in a general electrolytic plating apparatus, and is installed so as to face the front and back surfaces of the printed wiring board 10, and a pair of two electrodes 5 are connected to an anode. The printed wiring board 10 is connected to the cathode. Current is applied from the external power source 3 between the front and back surfaces of the printed wiring board 10 and the pair of electrodes 5 to perform electrolytic plating. A separate external power source 3 is used for the front electrode 5 and the back electrode 5, respectively, and the current value is controlled separately, and current is applied alternately to the front and back surfaces. Even when the plating areas on the front and back surfaces of the printed wiring board 10 are different, the current values may be controlled separately by using different external power sources 3 on the front and back surfaces.
The electrolytic plating apparatus 100 is provided with a stirring device (not shown) for eliminating the non-uniformity of metal ions in the plating solution 2.

The jet device 4 is a device having at least one nozzle 40 for jetting the plating solution 2, and is installed in the plating solution 2 of the plating tank 1. The jet device 4 may move on the front and back surfaces of the printed wiring board 10, but a hole of a nozzle 40 such as an eductor nozzle is formed between the printed wiring board 10 and the electrode 5. It is preferable to install a pair so as to face each other. In the pair, the nozzles 40 do not necessarily face each other, and there may be some deviation.
The jet device 4 jets the plating solution 2 from the nozzle 40 alternately on the front and back surfaces of the printed wiring board 10.

  As described above, the electrodes (anodes) 5 are connected to the anode of the external power source 3 and are installed in a pair so as to face the front and back surfaces of the printed wiring board 10.

  As shown in FIGS. 2A and 2B, the jig 7 is for installing the printed wiring board 10 in the plating tank 1 and electrically connecting the printed wiring board 10 to the cathode of the external power source 3. And a pair of bus bars 6 for applying a current from the external power supply 3 to the front and back surfaces of the printed wiring board 10, respectively. As shown in FIG. 2A, the jig 7 can hold a plurality of printed wiring boards 10 at the same time.

A method for plating a printed wiring board according to the present invention will be described.
In order to perform the plating process on the printed wiring board 10 using the electrolytic plating apparatus 100, first, the upper portions of the front and back surfaces of the printed wiring board 10 on which chemical copper plating has been performed in advance are fixed with the clamps 70 of the jig 7. These are connected to the cathode of the external power source 3 by bus bars 6 provided on the front and back sides.
Next, the plating tank in which the plating solution 2 is stored so that the printed wiring board 10 is located between the pair of electrodes 5 connected to the anode of the external power source 3 and between the jet device 4 provided with the nozzle 40. Immerse into 1.
At this time, the front and back surfaces of the printed wiring board 10 face the jet device 4 and the electrode 5, respectively.
Next, a current is alternately applied to the front and back surfaces of the printed wiring board 10 from different external power sources 3 connected to the front electrode 5 and the back electrode 5. At this time, the plating solution 2 is sprayed onto the surface of the printed wiring board 10 from the nozzle 40 of the jet device 4 on the side to which the current of the printed wiring board 10 is applied, and plating is formed on the surface layer. By repeating this alternately from the front and back directions, plating with a uniform thickness is formed on the surface layer of the printed wiring board 10.

Even when the plating areas on the front and back sides of the printed wiring board 10 are different, if the current values are controlled separately by using different external power sources 3 on the front and back sides, the plating thicknesses on the front and back sides can be made uniform.
Further, when there is a difference in density between the front and back surfaces, the plating resist (dry film) is weakly adhered in the dense part and the plating solution is likely to penetrate. Therefore, if the jet flow of the plating solution is adjusted, the plating thickness of the front and back surfaces can be made uniform without causing the plating solution to permeate into the dense portion where the plating resist is formed.

  The printed wiring board 10 may have through-holes 9 penetrating the front and back surfaces. The electrolytic plating apparatus 100 is highly effective in ensuring a uniform plating thickness in the through hole 9.

Next, a method for plating the printed wiring board 10 on the through hole 9 will be described. In addition, the description same as the plating method to the surface of the printed wiring board 10 mentioned above is abbreviate | omitted.
When plating in the through hole 9 of the printed wiring board 10 using the electrolytic plating apparatus 100, first, chemical copper plating is performed. At this time, the printed wiring board 10 and the through hole 9 are also plated.
Next, the chemical copper plating on the side surface of the end portion of the printed wiring board 10 is removed by polishing or the like, and the conduction on the front and back surfaces of the printed wiring board 10 is limited to the through hole 9 only. In this way, the conduction on the front and back surfaces of the printed wiring board 10 is limited to the through hole 9 only, so that current is prevented from flowing from the end side surface of the printed wiring board 10 to the opposite side. Concentrate.
Next, upper portions of the front and back surfaces of the printed wiring board 10 are fixed with clamps 70 of the jig 7 and connected to the cathode of the external power source 3 by the bus bar 6 provided on the front and back surfaces of the jig 7. It is immersed in the plating tank 1 in which the plating solution 2 is stored so as to be between the connected pair of electrodes 5 and between the jet device 4 provided with the nozzle 40.
Next, a current is alternately applied to the front and back surfaces of the printed wiring board 10 from different external power sources 3 connected to the front electrode 5 and the back electrode 5. At this time, the plating solution 2 is sprayed into the through hole 9 from the jet device 4 on the side to which the current of the printed wiring board 10 is applied, and plating is formed in the through hole 9. By repeating this alternately from the front and back directions, plating with a uniform thickness is formed in the through hole 9. In this way, by alternately applying current from the front and back surfaces of the printed wiring board 10, it is possible to prevent the current from being concentrated on both surfaces, and to suppress the plating thickness on the surface of the printed wiring board 10. Furthermore, by alternately spraying the plating solution 2 from the front and back surfaces of the printed wiring board 10, the plating solution 2 circulates in the through hole 9 without stagnation and promotes the formation of plating in the through hole 9.

The formation of plating in the through hole 9 will be described with reference to FIGS.
FIG. 3A shows a case where a current is applied and a plating solution is jetted from the front side of the printed wiring board 10. At this time, the plating 8 in the through hole 9 has a triangular cross section, and the plating is dense in the vicinity of the opening on the front side of the through hole 9, but the plating is sparse toward the back side.
Next, current is applied and a plating solution is jetted from the back side of the printed wiring board 10. At this time, as shown in FIG. 3B, the plating 8 in the through hole 9 has a triangular cross section, and the plating is dense in the vicinity of the opening on the back side of the through hole 9, but the plating is applied to the front side. It becomes sparse.
When the current application and the plating solution jet shown in FIGS. 3 (a) and 3 (b) are alternately repeated, plating 8 having a uniform thickness can be obtained as shown in FIG. 3 (c).

The application of current and the jet of the plating solution to the front and back surfaces of the printed wiring board 10 are preferably performed by alternately switching the front and back at regular intervals, and the switching time is preferably about 5 to 30 minutes, for example.
When the switching time is shorter than 5 minutes, the frequency of switching between the current and the jet increases, so that the plating thickness in the through hole 9 becomes uniform, but the variation in the plating thickness on the front and back surfaces of the printed wiring board 10 increases. On the other hand, when the switching time is longer than 30 minutes, the variation in the plating thickness of the surface layer on the front and back surfaces of the printed wiring board 10 decreases, but the variation in the plating thickness in the through hole 9 increases.

  As a countermeasure against a bipolar phenomenon that may occur on a surface to which no current is applied during the plating process, a current is applied to one surface with a bus bar 6 with respect to the front and back surfaces of the printed wiring board 10 as shown in FIG. In the applied state, a current of 5 to 20% of one surface may be applied to the bus bar 6 on the other surface. At this time, the current may be the same as the current density range used in normal DC plating, and is preferably 0.8 to 3.0 ASD, for example.

  As described above, according to the plating method of this printed wiring board, since it can be manufactured by the direct current plating method utilizing the existing plating apparatus, it is not necessary to introduce new equipment corresponding to the pulse plating method, and the cost increase can be suppressed. .

1 Plating tank 2 Plating solution 3 External power supply (rectifier)
DESCRIPTION OF SYMBOLS 4 Jet apparatus 5 Electrode 6 Bus bar 7 Jig 8 Plating 9 Through hole 10 Printed wiring board 40 Nozzle 70 Clamp 100 Electrolytic plating apparatus

Claims (6)

  A plating method for electrolytically plating a printed wiring board, wherein a current is applied to each of the front and back surfaces of the printed wiring board and a plating solution is jetted from a jetting device alternately. Plating method.   The method for plating a printed wiring board according to claim 1, wherein a current of 5 to 20% of one surface is applied also from the other surface in a state where a current is applied from one surface.   The method for plating a printed wiring board according to claim 1 or 2, wherein the printed wiring board has a through hole, and the inside of the through hole is electrolytically plated. A plating tank in which a plating solution is stored;
A printed wiring board, which is an object to be plated, immersed in the plating solution and whose front and back surfaces are electrically connected to the cathode of the external power source, respectively, and opposed to the front and back surfaces of the printed wiring board and to the anode of the external power source Two electrically connected electrodes;
Between the printed wiring board and the electrode, comprising a plating solution jetting device disposed opposite to the printed wiring board,
An electroplating apparatus, wherein current is alternately supplied from the external power source to the front and back surfaces of the printed wiring board, and a plating solution is jetted from the jet device.   The upper part of the said printed wiring board is clamped and fixed with a jig | tool, This jig | tool has a separate bus bar in the front and back, The electroplating apparatus of Claim 4.   The electrolytic plating apparatus according to claim 4 or 5, wherein the printed wiring board has a through hole, and the inside of the through hole is subjected to electrolytic plating.

Images