Plating method for through holes and circuit board

Abstract

To provide a plating method to a penetration hole, capable of filling a conductive metal to the penetration hole in a high aspect ratio of an insulation base material, and embedding a cavity part of the penetration hole without generating a void in a short time.SOLUTION: A plating method to a penetration hole, includes: step 1 of forming a conductive metal layer A covering at least circumference of the penetration hole and the penetration hole in a front surface of one surface A of an insulation base material; and step 2 of depositing a conductive metal layer B in a direction of a surface B of the insulation base material that is different from the surface A using the conductive metal layer A as a conductive layer by using an electrolytic plating method to embed the penetration hole. In the electrolytic plating method in step 2, an electrolytic plating liquid used for the electrolytic plating method starts a current density from a low current density while scattering with a strong jet flow so as to be circulated in the penetration hole, and uses a method for increasing the current density step by step in accordance with a deposition of the conductive metal layer B.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This application relates to a plating method for through holes in an insulating substrate, in which metal is filled into the through holes to fill the cavities of the through holes, and to a circuit board using an insulating substrate in which the cavities of the through holes have been filled with metal by this plating method. [Background technology]

[0002] In recent years, multilayer substrates have been used in electronic circuit boards to improve mounting density. To electrically connect these multiple stacked insulating substrates, through-holes are provided in each substrate, penetrating from top to bottom. A technique has been used to deposit a conductive metal, such as copper, on the surface of these through-holes using techniques such as conformal plating. However, because conformal plating deposits a conductive metal on the surface of the through-holes, voids remain in these holes. If voids remain in the through-holes, during thermal processes such as solder reflow to connect electronic components to the circuit board, the air in these voids expands after conformal plating, leading to defects such as cracks in the plating film or damage to the circuit board, resulting in a decrease in product quality. Therefore, a technique has been adopted to fill the voids in the through-holes after conformal plating with resin or other materials to eliminate these voids.

[0003] However, in order to further improve the mounting density of electronic circuit boards, the miniaturization of electronic components and the reduction of wiring width and spacing on electronic circuit boards are leading to a trend towards higher aspect ratios in through-holes, where the diameter of the through-hole is smaller relative to its length. Consequently, it is becoming increasingly difficult to fill these high-aspect-ratio through-holes with resin without any voids.

[0004] Therefore, Patent Documents 1 and 2 disclose a method for forming through-holes by depositing and layering conductive metal to fill the through-holes using an electroplating method in which an electrode provided on one side of the through-hole is used as a power supply layer. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2017-126865 [Patent Document 2] Japanese Patent Publication No. 2006-210369 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, when depositing and layering conductive metal into high aspect ratio through holes using the general electroplating methods disclosed in Patent Documents 1 and 2, in order to deposit and layer the conductive metal while suppressing the generation of voids (gaps remaining that could not be filled by the deposited conductive metal), it is necessary to perform electroplating at a low current for a long time, which leads to the problem of a long process time.

[0007] The present invention has been made in view of these circumstances. The present invention aims to provide a plating method for through holes in an insulating substrate that can fill high aspect ratio through holes with a conductive metal in a short time, thereby filling the void portion of the through hole without generating voids. [Means for solving the problem]

[0008] In order to solve the aforementioned problems, we conducted intensive research and came up with the following plating method for through holes.

[0009] The present invention relates to a plating method for through holes, which involves filling a through hole provided in an insulating substrate with metal to fill the cavity portion of the through hole, wherein the aspect ratio of the through hole is such that when the diameter of the through hole is 1, the thickness of the insulating substrate is 10 or more, and the method includes: step 1 forming a conductive metal layer A on the surface of one side A of the insulating substrate that covers at least the periphery of the through hole and the through hole itself; and step 2 using an electroplating method to deposit a conductive metal layer B in the direction of a surface B of the insulating substrate different from surface A, using the conductive metal layer A as a current-carrying layer, thereby filling the through hole, wherein the electroplating method in step 2 employs a method in which the electroplating solution used in the electroplating method is stirred by a powerful jet so that it circulates within the through hole, and the current density is started at a low current density and gradually increased as the deposition of the conductive metal layer B progresses.

[0010] The circuit board according to the present invention employs an insulating substrate in which metal is filled into the cavity of the through-hole by the plating method described above. [Effects of the Invention]

[0011] By adopting the plating method for through holes of the present invention, it becomes possible to fill high aspect ratio through holes in an insulating substrate with conductive metal in a short time, thereby filling the void portion of the through hole without generating voids. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram showing an enlarged cross-sectional view of the through-hole portion provided in the insulating substrate at each stage of the manufacturing process. [Modes for carrying out the invention]

[0013] The following describes the plating method for through holes and embodiments of the circuit board according to the present invention. It should be noted that the following description merely illustrates one aspect and should not be interpreted as limiting the scope of the description below.

[0014] 1. Embodiment of the plating method for through-holes The plating method for through-holes according to the present invention is a plating method for filling a through-hole provided in an insulating substrate with a metal to fill the cavity portion of the through-hole. At this time, when the aspect ratio of the through-hole is set to 1 with respect to the diameter of the through-hole, the thickness of the insulating substrate is 10 or more. And the plating method for the through-hole includes a step 1 of forming a conductive metal layer A covering at least the periphery of the through-hole and the through-hole on the surface of one surface A of the insulating substrate, and a step 2 of using an electrolytic plating method to deposit a conductive metal layer B in the direction of surface B of the insulating substrate different from surface A with the conductive metal layer A as the energized layer to fill the through-hole.

[0015] And, in the electrolytic plating method in step 2, while stirring is performed by a strong jet flow so that the electrolytic plating solution used in the electrolytic plating method circulates in the through-hole, the current density is started from a low current density, and as the deposition of the conductive metal layer B proceeds, the current density is increased step by step. By starting the current density of the electrolytic plating method from a low current density in this way, the conductive metal layer B can be deposited without generating voids in the deep part of the through-hole with a high aspect ratio. And by increasing the current density step by step as the deposition of the conductive metal layer B proceeds and the through-hole gradually becomes shallower, the deposition of the conductive metal layer B can be accelerated, and the plating of the through-hole can be completed in a short time. The step-by-step increase in the current density is performed as the deposition of the conductive metal layer B proceeds and the through-hole gradually becomes shallower. That is, at the timing of the step-by-step increase in the current density, the aspect ratio in the portion where the deposition of the conductive metal layer B is performed is smaller than that at the time when the electrolytic plating method is started. Therefore, even if the current density is increased to accelerate the deposition of the conductive metal layer B, the generation of voids can be suppressed.

[0016] In this way, the plating method for through-holes according to the present invention can fill the through-holes with a high aspect ratio in the insulating substrate with a conductive metal and fill the cavity portion of the through-hole without generating voids in a short time. This plating method for through-holes will be described in detail below.

[0017] Figure 1 shows an enlarged schematic view of the cross-sectional state of the through-hole portion provided in the insulating substrate at each process point in the plating method for the through-hole according to the present invention. In Figure 1, an enlarged schematic view of the cross-sectional state of the through-hole portion when the process progresses from No1 to No4 is shown. Note that in Figure 1, the states other than those shown from No1 to No4 are not precluded from being included between No1 and No4.

[0018] The state of No1 in Figure 1 shows a state where a through-hole 11 is provided in the insulating substrate 10. And the lower side of the cross-section of No1 is surface A12, and the upper side of the cross-section of No1 is surface B13. The material of the insulating substrate 10 can be used as long as it has insulation properties. For example, resin substrates such as glass epoxy and phenolic resin, substrates such as glass and ceramic, etc. can be used. Also, a substrate obtained by electrically insulating the surface of a conductive substrate such as aluminum and the surface of the through-hole provided in the conductive substrate using a method such as anodizing can be used as the insulating substrate 10. The method for forming the through-hole 11 can be used as long as it can form the through-hole 11. For example, a laser method, drilling by a drill, a method by etching, etc. can be used. And although the through-hole 11 in Figure 1 is cylindrical, the shape of the through-hole in the plating method for the through-hole according to the present invention is not limited to a cylindrical shape, and it may be, for example, a quadrangular column shape or a polygonal column shape. And each shape may have a tapered shape.

[0019] And the aspect ratio of the through-hole targets a thickness of the insulating substrate of 10 or more when the diameter of the through-hole is 1. In particular, when the diameter of the through-hole is 10 μm or less, the plating method for the through-hole according to the present invention can be preferably adopted. And when the diameter of the through-hole is 1, the upper limit of the thickness of the insulating substrate is not particularly limited. For example, the thickness of the insulating substrate can target a through-hole with a high aspect ratio such as 250.

[0020] 〔Process 1〕 Next, we will describe step 1. Step 1 is the process of forming a conductive metal layer A that covers at least the periphery of the through hole and the through hole itself on the surface of one side A of the insulating substrate. Figure 1, No. 2 shows the state in which, in step 1, a conductive metal layer A20 has been formed that covers at least the periphery of the through hole 11 and the through hole 11 itself on the surface of side A12 of the insulating substrate 10.

[0021] Step 1 can be any method that can form a conductive metal layer A20 that covers at least the periphery of the through hole 11 and the through hole 11 on the surface A12 of the insulating substrate 10. For example, one embodiment of Step 1 is a method for forming a conductive metal layer A20 consisting of conductive metal layer Aa and conductive metal layer Ab, which includes Step 1a of forming a conductive metal layer Aa at least around the through hole 11 on the surface A12 and Step 1b of forming a conductive metal layer Ab that covers the surface of conductive metal layer Aa and the hole in conductive metal layer Aa (i.e., the through hole 11).

[0022] Step 1a described above can be carried out, for example, as follows: A metal complex containing TiO2 and copper is coated onto surface A12, heated at 200-300°C, and then the coating surface is reduced using a reducing agent or the like. After that, a palladium catalyst is applied to the coating surface, and electroless nickel plating is performed to form a conductive metal layer Aa. Alternatively, after activating the coating surface, electroless copper plating is performed to form a conductive metal layer Aa. Next, as step 1b, for example, a conductive metal layer Ab can be formed by applying a thick layer of electrolytic copper plating to cover the surface of conductive metal layer Aa and the pores of conductive metal layer Aa. In this way, a conductive metal layer A20 consisting of conductive metal layer Aa and conductive metal layer Ab can be formed.

[0023] Furthermore, in a second embodiment of step 1, a conductive metal layer A20 can also be formed by laminating a metal foil film onto surface A12. For example, a conductive metal layer A20 can be formed by thermocompressing a copper foil with a thickness of 5-30 μm onto surface A12.

[0024] Furthermore, as a third embodiment of step 1, a conductive metal layer A20 can be formed on surface A12 using a sputtering method. For example, after activating surface A12 in a vacuum using the ion-Bambard method, a conductive metal layer A20 can be formed on the surface of surface A12 by sputtering titanium or copper. Here, the ion-Bambard method is a method of cleaning and activating the surface of the insulating substrate 10 by degassing a container containing the insulating substrate 10 to 0.1 Pa or less, filling the container with argon gas to 20-30 Pa, and plasma-generating the argon gas.

[0025] [Process 2] Next, step 2 will be explained. Step 2 is a process in which conductive metal layer B is deposited in the direction of surface B of an insulating substrate, which is different from surface A, using an electroplating method, with conductive metal layer A as the current-carrying layer, thereby filling the through-holes. This electroplating method uses a method in which the electroplating solution used in the electroplating method is stirred by a strong jet so that it circulates within the through-holes, and the current density is started at a low current density and gradually increased as the deposition of conductive metal layer B progresses. Figure 1, No. 3 shows the state in which the through-hole 11 has been filled by depositing conductive metal layer B21 in the direction of surface B13 of the insulating substrate 10, which is different from surface A12, in step 2.

[0026] Step 2 can be carried out as follows: First, the conductive metal layer A20 is activated. Then, the insulating substrate 10 on which the conductive metal layer A20 is formed is immersed in an electroplating solution, and with the conductive metal layer A20 as the current-carrying layer, the electroplating solution is stirred by a powerful jet so that it circulates within the through-holes 11, starting with a low current density and gradually increasing the current density as the deposition of the conductive metal layer B21 progresses.

[0027] In this way, by starting the electroplating process with a low current density, the conductive metal layer B21 can be deposited in the depths of high-aspect-ratio through-holes 11, such as when the diameter of the through-hole 11 is 1 and the thickness of the insulating substrate 10 is 10 or more, without generating voids. Then, by gradually increasing the current density as the deposition of the conductive metal layer B21 progresses and the through-hole 11 gradually becomes shallower, the deposition of the conductive metal layer B21 can be accelerated, and the plating of the through-hole 11 can be completed in a short time. That is, at the timing of the gradual increase in current density, the aspect ratio in the area where the conductive metal layer B21 is deposited is smaller than at the start of the electroplating process. Therefore, even if the deposition of the conductive metal layer B21 is accelerated by increasing the current density, the generation of voids can be suppressed.

[0028] In electroplating, the current density can be continuously increased from low to high. However, it is preferable to increase the current density in steps according to the amount of conductive metal layer B21 deposited, as this is relatively easier to control. In this case, although there is no upper limit to the number of steps in which the current density is increased in steps, two steps are preferred, and three steps are more preferred.

[0029] In the two-stage method, the first stage involves depositing the conductive metal layer B21 deep within the high-aspect-ratio through-hole 11. This makes circulation of the electroplating solution difficult and prone to void formation. Therefore, a low current density is used to suppress the deposition rate of the conductive metal layer B21 and prevent void formation. The amount deposited in the first stage is not particularly limited, but can be limited to about 1 / 10 of the length of the through-hole 11. In the second stage of the two-stage method, although not particularly limited, the conductive metal layer B21 is deposited until the through-hole 11 is completely filled using a current density increased to 5-50 times that of the first stage. In this way, in the second stage, because the aspect ratio is small in the area where the conductive metal layer B21 is deposited, void formation does not occur even when the current density is increased, and the deposition of the conductive metal layer B21 can be performed at high speed.

[0030] In the first stage of the three-stage method, the conductive metal layer B21 is deposited in the depths of the high-aspect-ratio through-hole 11, making it difficult to circulate the electroplating solution and prone to void formation. Therefore, a low current density is used to suppress the deposition rate of the conductive metal layer B21 to prevent void formation. The amount deposited in the first stage is not particularly limited, but can be limited to about 1 / 10 of the length of the through-hole 11. In the second stage of the three-stage method, the current density is increased to about 50 times that of the first stage, and the amount of conductive metal layer B21 deposited can be limited to about 5 / 10 to 6 / 10 of the length of the through-hole 11. In the third stage of the three-stage method, the current density is increased to 80 to 150 times that of the first stage, and the conductive metal layer B21 is deposited until the through-hole 11 is completely filled. Thus, in the second and third stages, the aspect ratio in the area where the conductive metal layer B21 is deposited is small, so even if the current density is increased, no voids are generated, and the deposition of the conductive metal layer B21 can be performed at high speed. Furthermore, since the current density in the third stage of the three-stage method can be made higher than that of the second stage of the two-stage method, the three-stage method can complete the plating of the through-hole 11 in a shorter time than the two-stage method.

[0031] Furthermore, the stepwise increase in current density, the number of increases, and the timing of increases are not limited, and it is possible to have four or more steps in increasing the current density stepwise. Depending on the shape and aspect ratio of the through-hole 11 and the progress of deposition of the conductive metal layer B21, an appropriate method can be used to suppress void formation and accelerate deposition, and the above is merely one example.

[0032] Furthermore, any method that allows the electroplating solution to circulate within the through-holes by a powerful jet can be used. For example, in the electroplating solution bath, while oscillating the insulating substrate 10 vertically and horizontally at a constant speed, the electroplating solution can be sprayed from a nozzle having a drain structure near the spraying part toward the deposition surface of the conductive metal layer B21 in the through-holes 11, thereby stirring the electroplating solution in a high-speed jet-like stream at a flow rate of 4 L / min or so, so that the electroplating solution circulates within the through-holes 11.

[0033] [Electrolytic plating solution] Next, the electroplating solution used in electroplating in step 2 will be described. The electroplating solution used in electroplating in step 2 is not particularly limited as long as it can be used in the plating method for through holes according to the present invention. For example, if copper is used as the constituent metal of the conductive metal layer B21, an electroplating copper solution with the following composition can be used. In this case, for example, a phosphorus-containing copper anode can be used, and electroplating can be performed at a bath temperature of 25±5℃, although this is not particularly limited. Here, if the bath temperature is high, the decomposition of the electroplating copper solution is promoted and the bath stability decreases. Although a higher bath temperature promotes copper deposition, it is necessary to add more additives to ensure bath stability, which increases the cost of step 2. Therefore, it is sufficient to select an appropriate bath temperature.

[0034] Copper sulfate pentahydrate: 200-300g / L. Sulfuric acid: 50-100g / L. Cl - :50 ppm. Additives.

[0035] Here, it is preferable to pre-add at least one of polyethylene glycol (PEG) with a degree of polymerization of 2000-20000, disodium dithiobis(1-propanesulfonic acid) (SPS), and Janus Green B (JGB) to the electrolytic copper plating solution as an additive. Nonionic surfactants such as PEG are added to eliminate variations in the amount of conductive metal layer B21 deposited at the through-holes 11 in the insulating substrate 10. The amount to be added should be selected according to the size of the insulating substrate 10, but when PEG is used in the electrolytic copper plating solution, it is preferable to add it with a PEG content of 10 ppm or less. Sulfur-based organic compounds such as SPS are generally used when the current density in the electrolytic plating method is, for example, 200 A / dm 2 This additive is intended to be used in cases of high currents such as those mentioned above, to smooth the surface of the plated film. However, in this electrolytic copper plating solution, 200 A / dm 2 Even at the following low current densities, it is preferable to use SPS, and it is preferable to add SPS at a concentration of 50 ppm or more. This is because the quality of the copper in the conductive metal layer B21 is good, and it becomes smooth and glossy. There is no particular upper limit to the SPS content, but it is preferable to add it at a concentration of 100 ppm or less. Dyes such as JGB are used to provide effects such as smoothing the surface of the plating film, but excessive addition will make the plating film brittle, so it is best to select an appropriate amount, but when using JGB in this electrolytic copper plating solution, it is preferable to add it at a concentration of 30 ppm or less.

[0036] [Electrolytic copper plating method] Using the electrolytic copper plating solution described above, an example of the electrolytic plating method in step 2 will be explained for the case where, for example, the diameter of the through-hole 11 is 10 μm and the thickness of the insulating substrate 10 is 100 μm, that is, when the diameter of the through-hole is 1, the thickness of the insulating substrate is 10 or more. In this case, for example, phosphorus-containing copper can be used as the anode. At this time, to prevent deposition from progressing in the direction opposite to the side of the conductive metal layer A20 that is in contact with surface A12, for example, an insulating resin or the like is applied to the side of the conductive metal layer A20 that is in contact with surface A12. Next, the side of the conductive metal layer A20 that is in contact with surface B13 is activated using dilute sulfuric acid. Then, the conductive metal layer A20 is used as the current-carrying layer, and the current density depends on the aspect ratio of the through-hole 11, but the current density of the electrolytic plating is set to, for example, 1 A / dm 2 The process begins by depositing a conductive metal layer B21 (copper in this case) to a thickness of, for example, 10 μm. Then, the current density is increased to, for example, 50 A / dm². 2 The current density is then increased to, for example, 45 μm, to deposit a conductive metal layer B21 (copper in this case). Subsequently, the current density is increased to, for example, 100 A / dm². 2 The conductive metal layer B21 (copper in this case) is further deposited to a thickness of, for example, 45 μm. In this way, a conductive metal layer B21 of 100 μm in the thickness direction of the insulating substrate can be formed inside the through hole 11.

[0037] The example of the electroplating method in step 2 described above is just one example, and the starting current density for electroplating, the amount and timing of the gradual increase in current density, and the additives can be appropriately selected depending on the aspect ratio and shape of the through-hole. In this way, by adopting the plating method for through-holes according to the present invention, it becomes possible to fill high aspect ratio through-holes of an insulating substrate with conductive metal in a short time, thereby filling the void portion of the through-hole without generating voids.

[0038] [Degassing process] It is preferable to have a degassing step between step 1 and step 2 described above to remove air from inside the through-hole 11. The insulating substrate 10 that has gone through step 1 has a conductive metal layer A20 formed on the surface A12 of the insulating substrate 10 that covers at least the area around the through-hole 11 and the through-hole 11 itself. In other words, the through-hole 11 is blocked on the surface A12 side, and the air inside the through-hole 11 cannot easily escape. Therefore, by performing a degassing step to remove the air inside the through-hole 11, the electroplating solution used in electroplating can be circulated inside the through-hole 11.

[0039] Any method that can remove air from inside the through-hole 11 can be used. For example, one method is to immerse the insulating substrate 10 that has gone through step 1 in water and apply ultrasonic vibration to the insulating substrate 10 or the water to remove air from inside the through-hole 11. Another method is to raise or lower the water temperature while the insulating substrate 10 that has gone through step 1 is immersed in water, thereby removing air from inside the through-hole 11 by causing the air inside to expand. Yet another method is to immerse the insulating substrate 10 that has gone through step 1 in water and create a vacuum in the container of water to remove air from inside the through-hole 11.

[0040] [Etching process] It is preferable to have an etching step after step 2 described above to remove the unnecessary portion of the conductive metal layer B21 deposited in the direction of surface B13 of the insulating substrate 10. Figure 1, No. 3 shows the state in which the conductive metal layer B21 has been deposited in the direction of surface B13 of the insulating substrate 10, which is different from surface A12, to fill the through hole 11, but the conductive metal layer B21 is raised on the upper part of surface B13. If such a raised portion of the conductive metal layer B21 is unnecessary, it can be removed in the etching step. Figure 1, No. 4 shows the state in which the raised portion on the upper part of surface B13 of the conductive metal layer B21 has been removed in the etching step.

[0041] Any etching method that can remove unwanted portions of the conductive metal layer B21 can be used. For example, if electrolytic copper plating is performed in step 2 as described above, the conductive metal layer B21 is copper, so unwanted portions of the conductive metal layer B21 can be removed using an etching solution with the following composition. In this case, the bath temperature can be set to 20-30°C, and etching can be performed while rotating the insulating substrate 10 to be etched at 200-1200 rpm.

[0042] Sulfuric acid: 5g / L. H2O2: 50-150 g / L. Polyethylene glycol (stabilizer): 5-15 g / L.

[0043] 2. Embodiment of a circuit board The circuit board according to the present invention employs an insulating substrate in which the void portion of the through-hole is filled with metal by the above-described plating method for through-holes. Furthermore, a circuit pattern made of a conductive metal layer can be formed on the surface of the insulating substrate before, during, or after the above-described plating method for through-holes. By employing the above-described plating method for through-holes, the circuit board according to the present invention can employ through-holes with a high aspect ratio, and the void portion of the through-hole can be filled with conductive metal in a short time without the generation of voids.

[0044] Furthermore, the circuit board according to the present invention may use a single insulating substrate 10 as shown in Figure 1, or it may be a multilayer circuit board made by laminating and bonding multiple insulating substrates 10 produced using the plating method for through holes according to the present invention.

[0045] The embodiments of the present invention described above are one aspect of the present invention and can be modified as appropriate without departing from the spirit of the present invention. Furthermore, the present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples. [Examples]

[0046] In Example 1, an insulating glass substrate 10 with a thickness of 100 μm provided with through-holes 11 having a diameter of 10 μm was used. After degreasing the insulating glass substrate 10, as the above-described step 1a, a metal complex containing TiO2 and copper was coated on the surface A12, heated at 200 - 300 °C, and then the coated surface was reduced using a reducing agent. Thereafter, a palladium catalyst was applied to the coated surface, and electroless nickel plating was performed to form a conductive metal layer Aa. Next, as the step 1b described above, using the following electrolytic copper plating solution, copper containing phosphorus was used as the anode, and the electrolytic current density was 150 A / dm 2 By performing electrolytic copper plating to increase the thickness, a conductive metal layer Ab having a film thickness of about 10 μm covering the surface of the conductive metal layer Aa and the holes of the conductive metal layer Aa was formed. In this way, a conductive metal layer A20 composed of the conductive metal layer Aa and the conductive metal layer Ab was formed.

[0047] Copper sulfate pentahydrate: 250 g / L. Sulfuric acid: 50 g / L. PEG: 0 ppm. SPS: 50 ppm. JGB: 30 ppm. Cl - : 50 ppm. Bath temperature: 25 ± 5 °C. Stirring method: High-speed jet stirring.

[0048] Next, as step 2, using the following electrolytic copper plating solution, copper containing phosphorus was used as the anode, and electrolytic copper plating was performed. At this time, the number of steps for gradually increasing the current density was a two-step method. The current density in the first step was 1 A / dm 2 and the deposition amount in the first step was 10 μm. Next, the current density in the second step was 5 A / dm 2 and the deposition amount in the second step was 90 μm.

[0049] Copper sulfate pentahydrate: 250 g / L. Sulfuric acid: 50 g / L. PEG: 0 ppm. SPS: 50 ppm. JGB: 30 ppm. Cl - :50 ppm. Bath temperature: 25±5℃. Agitation method: Oscillating and high-speed jet agitation (flow rate 4 L / min). [Examples]

[0050] Example 2 used the same insulating substrate 10 as in Example 1 and carried out the same step 1 as in Example 1.

[0051] Next, in step 2, electrolytic copper plating was performed using the same electrolytic copper plating solution as in Example 1, with phosphorus-containing copper used as the anode. In this case, a two-step method was used to gradually increase the current density, with the current density of the first step being 1 A / dm 2 The deposition amount in the first stage was set to 10 μm. Next, the current density in the second stage was set to 50 A / dm 2 The amount of precipitation in the second stage was set to 90 μm. [Examples]

[0052] Example 3 used the same insulating substrate 10 as in Example 1 and carried out the same step 1 as in Example 1.

[0053] Next, in step 2, electrolytic copper plating was performed using the same electrolytic copper plating solution as in Example 1, with phosphorus-containing copper used as the anode. In this case, a method was used to gradually increase the current density in three stages, with the current density of the first stage being 1 A / dm 2 The deposition amount in the first stage was set to 10 μm. Next, the current density in the second stage was set to 50 A / dm 2 The deposition amount in the second stage was set to 45 μm. Next, the current density in the third stage was set to 80 A / dm 2 The amount of precipitate in the third stage was set to 45 μm. [Examples]

[0054] Example 4 used the same insulating substrate 10 as in Example 1 and carried out the same step 1 as in Example 1.

[0055] Next, in step 2, electrolytic copper plating was performed using the same electrolytic copper plating solution as in Example 1, with phosphorus-containing copper used as the anode. In this case, a method was used to gradually increase the current density in three stages, with the current density of the first stage being 1 A / dm 2 The deposition amount in the first stage was set to 10 μm. Next, the current density in the second stage was set to 50 A / dm 2 The deposition amount in the second stage was set to 45 μm. Next, the current density in the third stage was set to 150 A / dm 2 The amount of precipitate in the third stage was set to 45 μm. Comparative Example

[0056] [Comparative Example 1] Comparative Example 1 used the same insulating substrate 10 as Example 1 and underwent the same process 1 as Example 1.

[0057] Next, in Comparative Example 1, electrolytic copper plating was performed using a general conformal electrolytic copper plating method with the electrolytic copper plating solution shown below, with phosphorus-containing copper used as the anode. At this time, the current density was 1 A / dm². 2 A constant value was used.

[0058] Copper sulfate pentahydrate: 65g / L. Sulfuric acid: 200g / L. PEG: 1000 ppm. SPS: 6 ppm. JGB: 10 ppm. Cl - :50 ppm. Bath temperature: 25±5℃. Agitation method: Agitation using air bubbles

[0059] [Comparative Example 2] Comparative Example 2 used the same insulating substrate 10 as in Example 1 and performed the same step 1 as in Example 1.

[0060] Next, in Comparative Example 2, electrolytic copper plating was performed using the same electrolytic copper plating solution as in Comparative Example 1, but with phosphorus-containing copper used as the anode. At this time, the current density was 80 A / dm². 2 A constant value was used.

[0061] 〔evaluation〕 X-ray imaging was performed on the insulating substrates 10 prepared in Examples 1-5 and Comparative Examples 1-2. This confirmed that in Examples 1-4 and Comparative Example 1, copper was deposited in the through-holes 11 and there were no voids. In particular, Example 5 demonstrated successful copper deposition in the through-holes 11 without voids, despite its high aspect ratio of 1:250. On the other hand, Comparative Example 2 showed insufficient copper deposition in the through-holes 11 and the presence of voids.

[0062] Table 1 shows the time required for electrolytic copper plating in step 2 for Examples 1-5 and Comparative Example 1-2. The "aspect ratio" in Table 1 indicates the aspect ratio of the through-holes 11 provided in the insulating substrate 10 used in each example and comparative example. The "completion time" in Table 1 indicates the time required for electrolytic copper plating in step 2 on the through-holes 11. The "void" in Table 1 indicates the presence or absence of voids (air spaces) in the through-holes 11 where copper has not been deposited after the electrolytic copper plating in step 2 has been completed. The "-" in Table 1 indicates that the current density has not been changed and that the current density prior to the "-" has been maintained until the electrolytic copper plating is completed. From Table 1, it is clear that the plating method for through-holes according to the present invention can deposit copper and fill the void portion of the through-hole 11 in a shorter time compared to the conventional conformal electrolytic copper plating method shown in Comparative Example 1, without generating voids. Furthermore, Comparative Example 2 revealed that even when the current density is increased and the time required for electrolytic copper plating is shortened in the conventional conformal electrolytic copper plating method, voids still occur within the through-holes.

[0063] [Table 1] [Industrial applicability]

[0064] The plating method for through holes according to the present invention allows for the filling of high aspect ratio through holes in an insulating substrate with a conductive metal, thereby filling the void portion of the through hole without generating voids in a short time. Therefore, it can be suitably used as a plating method for through holes in an insulating substrate by filling the void portion of the through hole with metal. [Explanation of Symbols]

[0065] 10 Insulating substrate 11 Through hole 12 side A 13 Side B 20 Conductive metal layer A 21 Conductive metal layer B

Claims

1. A plating method for a through-hole provided in an insulating substrate, wherein metal is filled into the through-hole to fill the cavity portion of the through-hole, The diameter of the through-hole is 10 μm or less, and the aspect ratio of the through-hole is such that, when the diameter of the through-hole is 1, the thickness of the insulating substrate is 10 or more. Step 1: Forming a conductive metal layer A on one surface A of the insulating substrate that covers at least the periphery of the through hole and the through hole itself. The process includes a step 2 in which, using an electroplating method, the conductive metal layer A is used as a current-carrying layer, and the conductive metal layer B is deposited from the side of surface A through the through hole toward the side of the insulating substrate which is the opposite side of surface A, thereby filling the through hole. The electroplating method in step 2 is characterized in that, while stirring the electroplating solution used in the electroplating method with a powerful jet so that it circulates within the through hole, the current density is started at a low current density and gradually increased as the deposition of the conductive metal layer B progresses, and the low current density is a current density that suppresses the deposition rate of the conductive metal layer B so as not to generate voids in the through hole.

2. The method for plating through holes according to claim 1, wherein the electrolytic plating solution is an electrolytic copper plating solution containing copper sulfate pentahydrate and sulfuric acid, and the electrolytic copper plating solution contains dithiobis(1-propanesulfonic acid) disodium as an additive, and the content of dithiobis(1-propanesulfonic acid) disodium is 50 ppm or more.

3. The aforementioned step 1 is, Step 1a involves forming a conductive metal layer Aa on the surface of the surface A, at least around the through hole. The step 1b includes forming a conductive metal layer Ab that covers the surface of the conductive metal layer Aa and the pores of the conductive metal layer Aa, The method for plating a through hole according to claim 1, wherein the conductive metal layer A is formed by the conductive metal layer Aa and the conductive metal layer Ab.

4. The aforementioned step 1 is, The method for plating a through hole according to claim 1, wherein the conductive metal layer A is formed by bonding a metal foil film to the surface of the surface A.

5. The method for plating a through hole according to claim 1, further comprising a step of degassing the air in the through hole between step 1 and step 2.

6. The method for plating a through hole according to claim 1, further comprising an etching step after step 2 to remove unwanted portions of the conductive metal layer B deposited in the direction of surface B.

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