Electroplating processing method for through hole with ultrahigh thickness-diameter ratio

Abstract

The invention discloses an electroplating machining method for a through hole with the ultrahigh thickness-diameter ratio. The electroplating machining method comprises the following steps that S1, an electroplating cylinder is prepared; two spray pipes are arranged in the electroplating cylinder; s2, two anodes in one-to-one correspondence with the two spraying pipes are placed in the electroplating cylinder, a PCB is placed between the two spraying pipes, and the spraying pipes are located between the corresponding anodes and the PCB; s3, electroplating liquid medicine is sprayed to the PCB through the spraying pipes, then direct current is provided for the PCB and the anode, pulse current is provided for the PCB and the anode, pulse electroplating is conducted on the through hole of the PCB, and the positive pulse time ratio and the negative pulse time ratio of the pulse current are 15: 1; in the pulse electroplating process, the spraying pipe is driven by the spraying pipe driving mechanism to move left and right, and the PCB is driven by the PCB transverse driving mechanism to move left and right. According to the invention, the thickness of electroplated copper in the through hole can be ensured, and the electroplating capability of the through hole with the ultrahigh thickness-diameter ratio is improved.

Description

Technical Field

[0001] The present invention relates to a method for electroplating through - holes with an ultra - high aspect ratio of thickness to diameter. Background Art

[0002] Through - hole electroplating is one of the important processes in the manufacturing process of PCB (Printed Circuit Board). It uses the principle of electrolytic cell to deposit a certain thickness of metallic copper (according to IPC standards, the minimum copper thickness in the hole is 18um) in the through - hole to achieve electrical interconnection between PCB layers.

[0003] Currently, the conventional through - hole electroplating ability in the industry has an aspect ratio of thickness to diameter of 30:1, where the aspect ratio is the ratio of the PCB thickness to the through - hole diameter. However, with the development trend of miniaturization, thinness, lightness, and portability of electronic products, the integration degree of printed circuit boards is getting higher and higher, specifically manifested as dense circuits, multiple layers, and small apertures, that is, the aspect ratio is getting larger. But the larger the aspect ratio, the higher the difficulty of through - hole electroplating.

[0004] For an ultra - high aspect ratio of thickness to diameter (i.e., the aspect ratio is 60:1, for example, the PCB thickness is 7.8mm and the minimum through - hole diameter is 0.13mm), it is easy to cause the electroplated copper thickness in the through - hole to seriously not meet the IPC standards, that is, the throwing power (TP) is poor, which will affect the production of fine circuits in the outer - layer pattern after through - hole electroplating (the thicker and more uneven the surface copper plating). In addition, it will also increase the production cost of PCB manufacturing factories and reduce the production efficiency of PCB manufacturing factories, thus unable to meet industry requirements. Summary of the Invention

[0005] In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a method for electroplating through - holes with an ultra - high aspect ratio of thickness to diameter, which can improve the electroplating ability of through - holes with an ultra - high aspect ratio of thickness to diameter.

[0006] The purpose of the present invention is achieved by the following technical solutions:

[0007] A method for electroplating through - holes with an ultra - high aspect ratio of thickness to diameter, comprising the following steps:

[0008] Step S1: Equip an electroplating tank; two spray pipes are arranged in the electroplating tank;

[0009] Step S2: Place two anodes corresponding to the two spray pipes respectively in the electroplating tank and place a PCB board between the two spray pipes, so that the spray pipes are located between the corresponding anodes and the PCB board; through - holes are provided on the PCB board, and the ratio of the thickness of the PCB board to the diameter of the through - hole is 60:1;

[0010] Step S3: Spray electroplating solution onto the PCB board using each nozzle, then apply a direct current to the PCB board and the anode to perform direct current electroplating on the vias of the PCB board, and then apply a pulsed current to the PCB board and the anode to perform pulsed electroplating on the vias of the PCB board. The positive and negative pulse time ratio of the pulsed current is 15:1. During the direct current electroplating and pulsed electroplating processes, drive the nozzle to move left and right through the nozzle drive mechanism, and drive the PCB board to move left and right through the PCB board horizontal drive mechanism and drive the PCB board to move forward and backward through the PCB board longitudinal drive mechanism.

[0011] The nozzle includes a plurality of tubes arranged in sequence along the vertical direction and horizontally arranged. A plurality of spray holes are arranged on the tube in sequence along its extending direction.

[0012] The electroplating solution includes an organic additive, copper sulfate, sulfuric acid, and chloride ions.

[0013] The organic additive includes a brightening agent and an inhibitor.

[0014] The pulsed electroplating is divided into a first stage, a second stage, a third stage, and a fourth stage; from the second stage to the fourth stage, the positive and negative current ratio of the pulsed electroplating gradually decreases.

[0015] In the first stage, second stage, third stage, and fourth stage, the positive pulse time of the pulsed electroplating is 120 ms, and the negative pulse time is 8 ms.

[0016] The electroplating tank is supplied with gas through a gas supply device.

[0017] In each stage from the first stage to the fourth stage, the number of times the PCB board moves left and right is the same.

[0018] In each stage from the first stage to the fourth stage, the number of times the PCB board moves forward and backward is the same.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] A method for electroplating through-holes with an ultra-high aspect ratio provided by the present invention. During the pulse electroplating process, a nozzle driving mechanism is used to drive the nozzle to move left and right, and a PCB board horizontal driving mechanism is used to drive the PCB board to move left and right, and a PCB board vertical driving mechanism is used to drive the PCB board to move forward and backward. This can press electroplating solution into the through-holes of the PCB, promote the exchange of electroplating solution in the through-holes, improve the electroplating effect and ability of through-holes with an ultra-high aspect ratio. Moreover, by setting the positive and negative pulse time ratio of the pulse current to 15:1, on the one hand, the reverse etching amount of pulse electroplating is increased by extending the reverse pulse time, avoiding excessive copper deposition at the through-hole opening at the beginning, which is not conducive to the exchange of solution in the through-hole. On the other hand, the copper ions in the through-hole can be replenished, thereby increasing the concentration of copper ions and reducing concentration polarization. Description of the Drawings

[0021] Figure 1 It is an internal schematic diagram of the electroplating tank of the present invention;

[0022] Figure 2 It is a schematic diagram of the structure of the nozzle;

[0023] Figure 3 It is a schematic diagram of the structure of the nozzle driving mechanism;

[0024] Figure 4 It is a schematic diagram of the structures of the PCB board horizontal driving mechanism and the PCB board vertical driving mechanism;

[0025] Among them, 10, electroplating tank; 20, nozzle; 21, pipe body; 22, pipe seat; 30, anode; 40, PCB board; 50, nozzle driving mechanism; 51, first support seat; 52, first lead screw; 53, first lead screw nut; 54, first driving motor; 55, first guide rail; 56, second guide rail; 60, PCB board horizontal driving mechanism; 70, PCB board vertical driving mechanism; 71, second support seat; 72, second lead screw; 73, second lead screw nut; 74, second driving motor; 75, third support seat; 76, third lead screw; 77, third lead screw nut; 78, third driving motor; 79, cathode rod. Detailed Embodiments

[0026] Next, in combination with the drawings and specific embodiments, the present invention will be further described. It should be noted that, on the premise of no conflict, any combination of the following-described embodiments or technical features can form a new embodiment.

[0027] A method for electroplating through-holes with an ultra-high aspect ratio includes the following steps:

[0028] Step S1: Prepare an electroplating tank 10; two nozzles 20 are arranged in the electroplating tank 10;

[0029] Step S2: Two anodes 30 corresponding to the two spray nozzles 20 respectively are placed in the electroplating tank 10, and a PCB board 40 is placed between the two spray nozzles 20, so that the spray nozzles 20 are located between the corresponding anodes 30 and the PCB board 40; through holes are provided on the PCB board 40, and the ratio of the board thickness of the PCB board 40 to the hole diameter of the through holes is 60:1;

[0030] Step S3: Use each spray nozzle 20 to spray electroplating solution towards the PCB board 40, and then perform direct current electroplating on the through holes of the PCB board 40 by providing direct current to the PCB board 40 and the anodes 30, and then perform pulse electroplating on the through holes of the PCB board 40 by providing pulsed current to the PCB board 40 and the anodes 30. The positive and negative pulse time ratio of the pulsed current is 15:1; during the direct current electroplating and pulse electroplating processes, the spray nozzle driving mechanism 50 drives the spray nozzles 20 to move left and right, and the PCB board horizontal driving mechanism 60 drives the PCB board 40 to move left and right, and the PCB board longitudinal driving mechanism 70 drives the PCB board 40 to move back and forth (as Figures 1-4 shown).

[0031] The present invention combines steps S1 - S3, and in step S3, direct current electroplating is performed on the through holes of the PCB board 40 by providing direct current to the PCB board 40 and the anodes 30, and then pulsed current is provided to the PCB board 40 and the anodes 30 to perform pulse electroplating on the through holes of the PCB board 40. The positive and negative pulse time ratio of the pulsed current is 15:1, shortening the positive pulse time and prolonging the negative pulse time. On the one hand, it increases the reverse etching amount of pulse electroplating, avoiding the deposition of too much copper at the hole mouth of the through hole, resulting in hole sealing and being unfavorable for the exchange of electroplating solution in the through hole. On the other hand, it replenishes the copper ions in the through hole, makes the exchange of the solution in the through hole more sufficient, reduces concentration polarization, ensures the thickness of the electroplated copper in the through hole, and can improve the electroplating ability of through holes with an ultra-high aspect ratio. Moreover, during the pulse electroplating process, the spray nozzle driving mechanism 50 drives the spray nozzles 20 to move left and right, and the PCB board horizontal driving mechanism 60 drives the PCB board 40 to move left and right, and the PCB board longitudinal driving mechanism 70 drives the PCB board 40 to move back and forth, which can press the electroplating solution into the through holes of the PCB, promote the exchange of the electroplating solution in the through holes, and further improve the electroplating effect of through holes with an ultra-high aspect ratio, so as to further improve the electroplating ability of through holes with an ultra-high aspect ratio.

[0032] Preferably, as Figures 1-4As shown, the nozzle 20 includes a plurality of pipe bodies 21 arranged in sequence along the vertical direction and horizontally disposed. A plurality of spray holes are provided on the pipe body 21 in sequence along its extending direction. By adopting the above arrangement, the through holes at various positions of the PCB board 40 can be pressed into the electroplating solution through the plurality of pipe bodies 21, enabling the through holes at various positions of the PCB board 40 to be in full contact with the electroplating solution, and promoting the exchange of the electroplating solution in each through hole. Specifically, the nozzle 20 includes a pipe base 22, and the plurality of pipe bodies 21 are installed on the pipe base 22.

[0033] The nozzle driving mechanism 50 includes a first support seat 51, a first lead screw 52 rotatably installed on the first support seat 51, a first lead screw nut 53 sleeved on the first lead screw 52 in a matching manner, and a first driving motor 54 for driving the first lead screw 52 to rotate; a first guide rail 55 and a second guide rail 56 are provided on the first support seat 51. The pipe base 22 of one nozzle 20 is movably installed on the first guide rail 55, and the pipe base 22 of the other nozzle 20 is movably installed on the second guide rail 56. The first lead screw nut 53 is respectively connected to the pipe bases 22 of the two nozzles 20. During pulse electroplating, the pipe bases 22 of the two nozzles 20 are located in the middle of the electroplating tank 10 to spray and press the solution into the through holes in the middle of the PCB through the two nozzles 20. By driving the first lead screw 52 to rotate forward by the first driving motor 54, the pipe bases 22 of the two nozzles 20 are synchronously moved to the left (in the P1 direction), so as to spray and press the solution into the through holes on the left side of the PCB through the two nozzles 20. Then, by driving the first lead screw 52 to rotate reversely by the first driving motor 54, the pipe bases 22 of the two nozzles 20 are synchronously moved to the right (in the P2 direction), so as to spray and press the solution into the through holes on the right side of the PCB through the two nozzles 20. Then, by continuously operating the nozzle driving mechanism 50 to drive the nozzle 20 to continuously move in a cycle in the above manner, the through holes in each area of the PCB board 40 can be in full contact with the electroplating solution, promoting the exchange of the solution in each through hole and improving the pulse electroplating effect. During DC electroplating, the moving mode of the pipe base 22 is similar to that of the pipe base 22 during pulse electroplating to improve the DC electroplating effect.

[0034] The PCB board transverse driving mechanism 60 includes a second support seat 71, a second screw rod 72 rotatably mounted on the second support seat 71, a second screw rod nut 73 matched with the second screw rod 72, and a second driving motor 74 for driving the second screw rod 72 to rotate; the PCB board longitudinal driving mechanism 70 includes a third support seat 75, a third screw rod 76 rotatably mounted on the third support seat 75, a third screw rod nut 77 matched with the third screw rod 76, and a third driving motor 78 mounted on the third support seat 75 and used to drive the third screw rod 76 to rotate, and a cathode rod 79; the cathode rod 79 is movably mounted on the third support seat 75 and connected to the third screw rod nut 77; the third support seat 75 is movably mounted on the second support seat 71 and connected to the second screw rod nut 73; the PCB board 40 is connected to the cathode rod 79. During the pulse electroplating process, the PCB board 40 is located in the middle of the electroplating cylinder 10, and the second drive motor 74 drives the second screw rod 72 to rotate forward, prompting the third support seat 75 to move to the left together with the PCB board 40. At the same time, the third drive motor 78 drives the third screw rod 76 to rotate. At this time, the cathode rod 79 moves backward together with the PCB board 40, causing the PCB board 40 to move to the left rear (i.e., move to M1), and then the second drive motor 74 drives the second screw rod 72 to rotate in the opposite direction, prompting the third support seat 75 to move to the right together with the PCB board 40. At the same time, the third drive motor 78 drives the third screw rod 76 to rotate. At this time, the cathode rod 79 moves forward together with the PCB board, causing the PCB board 40 to move to the right front (i.e., move to M2), and then through The PCB board transverse driving mechanism 60 and the PCB board longitudinal driving mechanism 70 continuously work to drive the PCB board 40 to move in a continuous cycle in the above manner. In this way, in the pulse electroplating process, on the basis of the nozzle driving mechanism 50 driving the nozzle 20 to move in a continuous cycle, the PCB board transverse driving mechanism 60 and the PCB board longitudinal driving mechanism 70 drive the PCB board 40 to move in the above manner, so that the PCB board 40 always moves back and forth between the nozzles 20 on both sides, weakening the influence of the distance from the anode on the primary current distribution. At the same time, when the PCB board 40 moves not in the middle of the two nozzles 20, the flow rate of the liquid medicine on the front and rear sides of the through hole is different. According to the Bernoulli principle, it is known that the electroplating liquid medicine is further pressed into the through hole, and the exchange of the electroplating liquid medicine inside the through hole is promoted. In the DC electroplating process, the movement mode of the PCB board 40 is similar to the movement mode of the PCB board 40 in the pulse electroplating process, so as to improve the DC electroplating effect.

[0035] The electroplating solution includes organic additives, copper sulfate, sulfuric acid and chloride ions. The organic additives include brighteners and inhibitors to improve the electroplating effect.

[0036] Preferably, the concentration of copper sulfate is 41.9 g / L, the concentration of sulfuric acid is 248.7 g / L, the concentration of chloride ions is 49.3 ppm, the concentration of brightener is 0.47 g / L, and the concentration of inhibitor is 36.73 g / L. By reasonably setting the concentration of each component, the secondary current distribution is more uniform, and the pulse plating effect is further improved. The brightener and inhibitor can be selected from Rohm and Haas.

[0037] Among them, the concentrations of copper sulfate, sulfuric acid, chloride ions, brighteners and inhibitors can be set according to actual needs, but setting the concentration of copper sulfate to 41.9 g / L, the concentration of sulfuric acid to 248.7 g / L, the concentration of chloride ions to 49.3 ppm, and the concentration of brightener to 0.47 g / L is the most preferred embodiment of the present invention, which can improve the electroplating effect.

[0038] The pulse electroplating is divided into the first stage, the second stage, the third stage and the fourth stage; from the second stage to the fourth stage, the forward and reverse current ratio of the pulse electroplating gradually decreases. Wherein, the forward and reverse current ratio refers to the ratio of the reverse current to the forward current. Since there is a reverse current in pulse electroplating, copper will be corroded, and since the current density at the through-hole opening is greater than that at the through-hole center, the dissolution rate of copper at the through-hole opening is faster than that at the through-hole center. Since the greater the forward and reverse current ratio, the more serious the reverse corrosion of copper, by reducing the forward and reverse current ratio with the increase of the number of segments, the center of the hole can be plated first, and then the through-hole opening can be plated. In the early stage, the forward and reverse currents are relatively large. Due to the overall effect of the reverse corrosion, the copper deposited in the through-hole center is more than the copper deposited at the through-hole opening. At this time, the aperture of the through-hole opening is larger than the aperture of the through-hole center, which is also conducive to the electroplating solution entering the hole. The reduction of the forward and reverse current ratio is based on the gradual completion of copper plating in the hole center, and the effect of reverse corrosion of copper is gradually reduced accordingly.

[0039] The forward and reverse current ratio of the first stage and the second stage is 4, the forward and reverse current ratio of the third stage is 3.5, and the forward and reverse current ratio of the fourth stage is 3. On the basis of gradually reducing the forward and reverse current ratio of the pulse electroplating, the forward and reverse current ratio of the first stage and the second stage is set to 4, the forward and reverse current ratio of the third stage is set to 3.5, and the forward and reverse current ratio of the second stage is set to 3, which can increase the reverse corrosion amount of pulse electroplating, so that the copper deposited at the through-hole mouth in the first stage and the second stage is less than the copper deposited in the center of the through-hole, so as to avoid the copper deposited at the through-hole mouth being greater than the copper deposited in the center of the through-hole, which makes the hole mouth smaller and is not conducive to the copper ions entering the center of the through-hole for deposition, and further improves the pulse electroplating ability and effect.

[0040] Specifically, in the first stage, second stage, third stage, and fourth stage, the forward pulse time of the pulse electroplating is 120 ms, and the reverse pulse time is 8 ms. By optimizing the forward pulse time and reverse pulse time in the first stage, second stage, third stage, and fourth stage, the reverse etching amount of the pulse electroplating can be further increased, and at the same time, the electroplating solution exchange in the through-hole is more sufficient, which is more conducive to the electroplating solution exchange in the through-hole.

[0041] The forward current density in the first stage is 10 ASF, and the forward current density in the second stage, third stage, and fourth stage is 6.5 ASF to further optimize the deposition rate of copper at the center of the through-hole in each stage.

[0042] In each stage from the first stage to the fourth stage, the number of times the PCB board 40 moves left and right is the same. In each stage from the first stage to the fourth stage, the number of times the PCB board 40 moves back and forth is the same. By adopting the above settings, the electroplating solution can be promoted to fully enter the through-hole, so as to further promote the exchange of the electroplating solution in the through-hole. In each stage (i.e., the first stage, second stage, third stage, and fourth stage), the number of times the PCB board 40 moves left and right is 4 - 6 times / min, the number of times the PCB board 40 moves back and forth is 4 - 6 times / min, and the number of times the spray pipe 20 moves left and right is 4 - 6 times / min.

[0043] The left and right movement amplitude of the spray pipe 20 is ±100 mm, and the left and right movement amplitude of the PCB board 40 is ±70 mm, with an angle of 30°.

[0044] From the first stage to the fourth stage, the spray flow rate of the spray pipe 20 is 250 ± 10 L / min.

[0045] The electroplating tank 10 is supplied with gas through a gas supply device. The electrolytic solution in the electroplating tank 10 is filtered by a filter pump, and the pressure of the filter pump is 1.5 ± 0.5 kg / cm 2 。

[0046] This electroplating processing method for through-holes with an ultra-high aspect ratio further includes step S4: after the pulse electroplating is completed, the PCB board 40 is sliced and analyzed, the copper thickness of multiple through-holes and the copper thickness of the surface are measured, and the average value of the through-hole copper and the average value of the surface copper are calculated, and the actual TP value is calculated using the average value of the through-hole copper and the average value of the surface copper; if the actual TP value is greater than the reference TP value, the PCB board 40 is qualified, otherwise, the PCB board 40 is unqualified; wherein, the actual TP value is the ratio of the average value of the through-hole copper to the average value of the surface copper.

[0047] The above embodiments are only preferred embodiments of the present invention, and the scope of protection of the present invention cannot be limited thereby. Any non-substantive changes and substitutions made by those skilled in the art based on the present invention fall within the scope of protection required by the present invention.

Claims

1. A method for electroplating a through hole with an ultra-high aspect ratio, characterized in that: The following steps are involved: Step S1: equip an electroplating cylinder; the electroplating cylinder is provided with two spray pipes; Step S2: two anodes corresponding to the two nozzles are placed in the electroplating cylinder, and a PCB board is placed between the two nozzles, so that the nozzles are located between the corresponding anodes and the PCB board; the PCB board is provided with a through hole, and the ratio of the thickness of the PCB board to the aperture of the through hole is 60:1; Step S3: using each nozzle to spray electroplating solution toward the PCB board, and then providing a DC current to the PCB board and the anode to perform DC electroplating on the through holes of the PCB board, and then providing a pulse current to the PCB board and the anode to perform pulse electroplating on the through holes of the PCB board, wherein the positive and reverse pulse time ratio of the pulse current is 15:1; during the DC electroplating and pulse electroplating processes, the nozzle is driven to move left and right by the nozzle driving mechanism, and the PCB board is driven to move left and right by the PCB board transverse driving mechanism, and the PCB board is driven to move forward and backward by the PCB board longitudinal driving mechanism.

2. The ultra-high aspect ratio through-hole electroplating processing method according to claim 1, characterized in that: The nozzle comprises a plurality of tube bodies which are arranged in sequence along a vertical direction and are arranged horizontally, and a plurality of spray holes which are arranged in sequence along an extending direction of the tube bodies are arranged on the tube bodies.

3. The ultra-high aspect ratio through-hole electroplating processing method according to claim 1, characterized in that: The electroplating solution comprises organic additives, copper sulfate, sulfuric acid and chloride ions.

4. The ultra-high aspect ratio through-hole electroplating processing method according to claim 3, characterized in that: The organic additives include brighteners and inhibitors.

5. The ultra-high aspect ratio through-hole electroplating processing method according to claim 1, characterized in that: The pulse electroplating is divided into a first stage, a second stage, a third stage and a fourth stage; from the second stage to the fourth stage, the forward and reverse current ratio of the pulse electroplating gradually decreases.

6. The ultra-high aspect ratio through-hole electroplating processing method according to claim 5, characterized in that: In the first stage, the second stage, the third stage and the fourth stage, the forward pulse time of the pulse electroplating is 120 ms, and the reverse pulse time is 8 ms.

7. The ultra-high aspect ratio through-hole electroplating processing method according to claim 5, characterized in that: The electroplating cylinder is supplied with gas through a gas supply device.

8. The ultra-high aspect ratio through-hole electroplating processing method according to claim 5, characterized in that: In each stage from the first stage to the fourth stage, the number of times the PCB moves left and right is the same.

9. The ultra-high aspect ratio through-hole electroplating processing method according to claim 5, characterized in that: In each stage from the first stage to the fourth stage, the number of times the PCB moves back and forth is the same.

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