Thick palladium electroplating solution and electroplating method for advanced packaging bump process

Abstract

The embodiment of the present application provides a plating thick palladium solution and an electroplating method for advanced packaging bump process. The plating thick palladium solution includes the following mass concentration components: palladium ion 2-20g / L, complexing agent 5-100g / L, conductive salt 2-50g / L, low stress additive 1-5g / L, wetting agent 10-500mg / L, surface adjuster 20-200mg / L, solvent is water, and the low stress additive includes a polyol with a ratio of carbon atoms to hydroxyl groups ≤ 1.25. By adding low stress additives to reduce the stress of the palladium plating layer during the electroplating process, it is helpful to form a high-quality palladium plating layer with a thickness of more than 1μm, and then gold is plated on the surface of the palladium plating layer in a conventional manner to obtain an advanced packaging bump with good performance, thereby realizing a low-cost and advanced packaging bump process with good bonding performance.

Description

Technical Field

[0001] The present application relates to the technical field of advanced packaging bump electroplating, and in particular to a thick palladium electroplating solution and an electroplating method applied to an advanced packaging bump process. Background Art

[0002] In electronic components, copper is widely used due to its excellent electrical and thermal conductivity. However, copper is easily oxidized, and copper easily forms IMC layers or Kirkendall voids with solder, gold wire, aluminum wire, etc., which makes welding and binding difficult, affects the connection strength and electrical and thermal conductivity, and thus reduces the reliability and stability of electronic components. To solve these problems, the copper surface is usually electroplated, such as nickel-gold, nickel-palladium-gold, etc. The traditional nickel-gold layer is composed of nickel and gold. The nickel layer acts as a barrier layer to prevent copper diffusion, and the gold layer acts as a bonding layer for bonding connections. However, in applications with high reliability requirements, the nickel layer is not enough to prevent copper diffusion, so a 0.1-0.5μm palladium layer is added between nickel and gold to enhance the effect of blocking copper diffusion and improve welding and bonding performance, thereby improving overall interconnection performance.

[0003] In the bump packaging process of display driver IC, the bump needs to be smaller in size to meet the higher density of I / O numbers, and lower signal delay is also required. Therefore, the gold bump process is generally used to achieve interconnection, and the thickness of the gold bump is generally between 10-20μm to meet the needs of low-latency signal transmission. However, the production cost of gold bumps is relatively high. The use of electroplated palladium instead of part of the electroplated gold process to synthesize palladium-gold bumps can reduce the production cost of packaged bumps. In addition, since the gold-plated layer is irreplaceable as a bonding interface, it is necessary to increase the thickness of the palladium-plated layer in the bump without affecting the subsequent bonding process in order to significantly reduce costs. For example, when the bump thickness is required to be around 10μm, palladium can be electroplated for 5-8μm first, and then gold can be electroplated for 2-5μm to thicken it to achieve a bump process with a thickness of 10μm.

[0004] However, traditional palladium electroplating solutions and methods are usually only suitable for palladium layers with a thickness of 0.1-0.5μm. When the palladium thickness exceeds 1μm, many problems will arise, such as excessive plating stress causing cracks in the palladium layer or abnormal glue extrusion, excessive palladium surface roughness, irregular shape of palladium bumps, and long electroplating time causing cracks and falling off of the photoresist.

[0005] Therefore, there is an urgent need for an electroplating solution formulation and an electroplating method that can achieve a thick and defect-free palladium plating layer to meet the demand for reducing costs by plating thick palladium to replace part of the gold bumps. Summary of the invention

[0006] Based on this, an embodiment of the present application provides a thick palladium electroplating solution for use in an advanced packaging bump process. The thick palladium electroplating solution uses a low-stress additive to reduce the stress of the palladium plated layer during the electroplating process, prepares a thick, high-quality palladium plated layer, and then gold is plated on the surface of the palladium plated layer to obtain an advanced packaging bump, thereby realizing a low-cost advanced packaging bump process with good bonding performance.

[0007] The specific embodiments of the present application are:

[0008] In the first aspect, an embodiment of the present application provides a thick palladium electroplating solution for use in an advanced packaging bump process, wherein the thick palladium electroplating solution comprises the following components in mass concentration: 2-20 g / L of palladium ions, 5-100 g / L of a complexing agent, 2-50 g / L of a conductive salt, 1-5 g / L of a low stress additive, 10-500 mg / L of a wetting agent, and 20-200 mg / L of a surface adjuster. The solvent is water, and the low stress additive comprises a polyol having a ratio of the number of carbon atoms to the number of hydroxyl groups ≤1.25.

[0009] In some embodiments, the low stress additive includes one or more of glycerol, pentaerythritol, sorbitol, mannitol, xylitol, and isomalt.

[0010] In some embodiments, the mass concentration of the low stress additive is 2-4 g / L.

[0011] In some embodiments, the surface conditioning agent includes 2,6-pyridinedicarboxylic acid, and the mass concentration of the 2,6-pyridinedicarboxylic acid is 50-150 mg / L.

[0012] In some embodiments, the wetting agent includes a cationic surfactant, and the mass concentration of the cationic surfactant is 50-300 mg / L.

[0013] In some embodiments, the cationic surfactant includes dodecyldimethylbenzylammonium chloride and / or dodecyltrimethylammonium chloride.

[0014] In some embodiments, the complexing agent includes nitrilotriacetic acid and / or hydroxyethylidene diphosphonic acid, and the mass concentration of the complexing agent is 20-60 g / L.

[0015] In some embodiments, the palladium ions are derived from one or more of dichlorodiamminepalladium, dichlorotetramminepalladium, palladium sulfate and palladium chloride, and the mass concentration of the palladium ions in the thick palladium electroplating solution is 5-15 g / L.

[0016] In some embodiments, the conductive salt includes sodium salt, potassium salt, ammonium salt or magnesium salt corresponding to phosphoric acid, sulfuric acid, boric acid or carbonate, and the mass concentration of the conductive salt is 10-20 g / L.

[0017] In the second aspect, an embodiment of the present application provides an electroplating method applied to an advanced packaging bump process, using the thick palladium electroplating solution described in any of the aforementioned items, adjusting the temperature and pH value of the thick palladium electroplating solution and then energizing the thick palladium electroplating solution, the temperature being 40-60°C; the pH value being 5.5-7.5.

[0018] Compared with the prior art, this application has the following advantages:

[0019] (1) In the embodiment of the present application, a polyol with a ratio of carbon atoms to hydroxyl groups of ≤1.25 is selected. The hydroxyl functional groups in the polyol can form coordination bonds with palladium ions in the thick palladium electroplating solution, thereby improving the stability and crystallinity of palladium ions in the thick palladium electroplating solution. The formed electroplating layer has good structural tightness and uniform stress distribution, thereby improving the mechanical properties of the electroplating layer. Experiments have confirmed that the palladium-plated layer above 5μm does not have cracks due to excessive tensile stress or glue squeezing due to excessive tensile stress, and has the characteristics of low surface roughness and good conformality. On the one hand, the thick palladium electroplating solution system provided in the embodiment of the present application is friendly to photoresist, has no obvious corrosiveness, and does not affect subsequent processes; on the other hand, the use of a thick palladium-plated layer instead of a gold-plated layer can significantly reduce the cost of advanced packaging bumps and improve economic benefits.

[0020] Specifically, the polyol contained in the low-stress additive can be selected from one or more compounds selected from propylene glycol, pentaerythritol, sorbitol, mannitol, xylitol and isomalt, in which the ratio of the number of carbon atoms to the number of hydroxyl groups is ≤1.25. The polyol is used to coordinate and complex palladium ions to adjust the tension and stress of the palladium plated layer and improve the uniformity of stress distribution of the electroplated layer.

[0021] (2) The embodiment of the present application uses 2,6-pyridinedicarboxylic acid as a surface conditioner to significantly reduce the roughness of the palladium-plated layer, making the surface of the palladium-plated layer smoother and flatter, which is beneficial to the subsequent gold plating and bonding processes. The advanced packaging bumps finally formed have better overall mechanical properties and better welding and bonding performance.

[0022] (3) The embodiments of the present application use cationic surfactants such as dodecyldimethylbenzylammonium chloride and dodecyltrimethylammonium chloride, which can effectively reduce the surface tension of the thick palladium electroplating solution, so that the thick palladium electroplating solution can smoothly infiltrate the blind hole cavity and complete the palladium layer deposition; in addition, the cationic surfactant can also synergistically act with 2,6-pyridinedicarboxylic acid to improve the conformality of the palladium plating layer and obtain advanced packaging bumps with regular shapes.

[0023] (4) The thick palladium electroplating solution formula provided in the embodiment of the present application adjusts the pH value of the plating solution system to work in an environment of 5.5-7.5 during electroplating to avoid the acidic system causing the complexing agent to be unable to stably complex palladium ions, and the alkaline system to corrode the substrate photoresist. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solution of the present application, the drawings required for use in the description of the present application are briefly introduced below.

[0025] Figure 1 This is a surface microscopic image of the palladium-plated layer obtained in Example 1 magnified 1500 times.

[0026] Figure 2 This is an electron microscope image of the three-dimensional angle of the palladium-plated layer obtained in Example 1 after being magnified 2000 times.

[0027] Figure 3 The microscopic morphology images of the advanced packaging bumps of Example 6 and Example 7 after the palladium layer is plated with gold according to the conventional method are magnified 1500 times.

[0028] Figure 4 The electron microscope images of the longitudinal sections of the advanced packaging bumps of Example 6 and Example 7, which were gold-plated according to a conventional method after the palladium layer was plated, were magnified 3000 times.

[0029] Figure 5 This is a surface microscopic image of the palladium-plated layer obtained in Comparative Example 1, magnified 1500 times.

[0030] Figure 6 This is a surface microscopic image of the palladium-plated layer obtained in Comparative Example 2, magnified 2000 times.

[0031] Figure 7 This is a surface microscopic image of the palladium-plated layer obtained in Comparative Example 3, magnified 1500 times.

[0032] Figure 8 This is a surface microscopic image of the palladium-plated layer obtained in Comparative Example 4, magnified 1500 times.

[0033] Fig. 9 This is a surface microscopic image of the palladium-plated layer obtained in Comparative Example 5, magnified 1500 times. DETAILED DESCRIPTION

[0034] Examples of the present embodiment are described in detail below. The examples are only used to explain the present embodiment and are not to be construed as limiting the present embodiment.

[0035] In the description of the present application embodiment, it should be noted that all ranges disclosed in the present application will be understood as covering any and all sub-ranges included therein. For example, the stated range "2 to 20g / L" should be deemed to include any and all following sub-ranges: it starts with a minimum value of 2g / L or greater, and ends with a maximum value of 20g / L or less, for example, 2 to 5g / L or 7 to 11g / L or 13 to 17g / L. At the same time, all ranges disclosed in the present application are also deemed to include the endpoints of the scope, unless otherwise explicitly stated. For example, the range "between 5.5 and 7.5" or "5.5 to 7.5" or "5.5-7.5" should generally be deemed to include endpoints 5.5 and 7.5.

[0036] Herein, unless otherwise specified, ratio refers to mass ratio and percentage refers to mass percentage.

[0037] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0038] The "thick palladium" proposed in the present application refers to a palladium plating layer with a thickness of more than 1 μm. The electroplating thick palladium solution is an electroplating solution that can be used to electroplating to form a high-quality palladium plating layer with a thickness of more than 1 μm. The present application selects low-stress additives to compound an electroplating thick palladium solution system that can reduce the stress of the palladium plating layer, and the formed palladium plating layer has good structural tightness and uniform stress distribution, which is convenient for subsequent gold plating and bonding operations and improves the mechanical properties of the electroplated layer; at the same time, surface adjusters and wetting agents that can synergize with each other are also selected. For blind hole palladium plating scenarios, dodecyl dimethyl benzyl ammonium chloride and dodecyl trimethyl ammonium chloride are selected as wetting agents to reduce the surface tension of the electroplating thick palladium solution system and efficiently wet the inner wall of the blind hole cavity. 2,6-pyridine dicarboxylic acid is selected as a surface adjuster, the carboxylic acid group of which can form a coordination bond with the surface of the palladium plating layer, enhance the interaction between the molecule and the surface, reduce the irregular palladium deposition on the surface, help to smooth the surface and reduce the roughness, which is beneficial to subsequent gold plating and bonding processes.

[0039] In general, the inventors of the present application provide a thick palladium electroplating solution system capable of preparing thick palladium. By selecting suitable low-stress additives, surface adjusters and wetting agents, the system can avoid the occurrence of cracks caused by excessive tensile stress or glue squeezing caused by excessive tensile stress during the formation of the palladium plating layer, thereby maintaining the growth of the plating layer in a specified shape. In addition, the synergistic effect of the three further reduces the surface roughness of the palladium plating layer, providing good surface bonding force for subsequent gold plating and bonding processes, thereby improving the processing quality.

[0040] In some embodiments, the low stress additive may include a polyol having a ratio of carbon atoms to hydroxyl groups of ≤1.25, and the polyol contains a large number of hydroxyl groups, and the hydroxyl functional groups can form coordination bonds with palladium ions in the thick palladium electroplating solution, thereby improving the stability and crystallinity of palladium ions in the thick palladium electroplating solution. It has been verified experimentally that under the present thick palladium electroplating solution system, even if the palladium plating layer formed by electroplating is above 5 μm, there is no cracking of the palladium plating layer due to excessive tensile stress, or the situation of extrusion of the palladium plating layer due to excessive tensile stress, and it also has the characteristics of low surface roughness and good conformality. It is understandable that during the electroplating process, as the thickness of the electroplating increases, the uniformity and conformality of the coating are more difficult to guarantee. Therefore, when the experiment verifies that the present thick palladium electroplating solution system can electroplate a high-quality palladium plating layer of more than 5 μm, the present thick palladium electroplating solution system can also electroplate a palladium plating layer of a smaller thickness, such as 4 μm, 2.5 μm or 1 μm.

[0041] Furthermore, the low stress additive includes one or more of glycerol, pentaerythritol, sorbitol, mannitol, xylitol and isomalt, and correspondingly, the concentration of the low stress additive is 1-5g / L. In the specific implementation process, the concentration of the low stress additive can also be 2-4g / L. It should be noted that if the concentration of the low stress additive is too low, the effect of reducing tensile stress and improving cracks in the palladium plating layer is not obvious; and if the concentration is too high, the electroplating thick palladium solution will have obvious tensile stress, resulting in the extrusion of the palladium plating layer.

[0042] In some embodiments, the surface adjuster includes 2,6-pyridinedicarboxylic acid, and the added concentration is 20-200 mg / L, for example, 50-150 mg / L. 2,6-pyridinedicarboxylic acid contains two carboxylic acid groups, which can form chelates with palladium ions to reduce the free concentration of palladium ions and adjust the uniformity of palladium ion concentration in the thick palladium electroplating solution system, and can also form coordination bonds with the metal surface to enhance the interaction between molecules and surfaces, thereby improving the spreadability of the thick palladium electroplating solution on the surface of the substrate. On the one hand, the thick palladium electroplating solution has good dispersion uniformity on the surface of the substrate, and on the other hand, the palladium ions have good dispersion uniformity in the thick palladium electroplating solution, thereby achieving uniform deposition of palladium ions on the surface of the substrate, reducing the irregularity and roughness of the surface of the palladium plating layer, and improving the surface quality of the plating layer. It should be further explained that the acceptable range of the surface roughness of the palladium plating layer is 20-60nm. If the concentration of the surface adjuster is too low, the effect on reducing the roughness is not obvious, and if the concentration is too high, the palladium plating layer will have color difference, which will have an adverse effect on the uniformity of the appearance.

[0043] In some embodiments, a cationic surfactant is used as a wetting agent. The cationic surfactant can reduce the surface tension of the thick palladium electroplating solution system, can be used for blind hole palladium plating, and the thick palladium electroplating solution is easier to infiltrate the blind hole and the cavity. Specifically, the cationic surfactant includes dodecyl dimethyl benzyl ammonium chloride and / or dodecyl trimethyl ammonium chloride. Further, the concentration of the wetting agent is 10-500 mg / L, for example, 50-300 mg / L. It should be noted that cationic surfactants are less likely to foam than anionic surfactants, which reduces the risk of forming bubbles in the blind hole cavity and avoids leakage plating due to bubbles; in addition, if the concentration of cationic surfactant is too high, it will increase the amount of foam in the thick palladium electroplating solution to a certain extent, resulting in abnormal bonding between the photoresist and the seed layer, resulting in palladium infiltration; if the concentration is too low, it is not conducive to the conformality of the palladium plating layer.

[0044] In some embodiments, the complexing agent includes nitrilotriacetic acid and / or hydroxyethylidene diphosphonic acid, and the mass concentration of the complexing agent is 5-100 g / L, and the added concentration in the specific implementation process can also be 20-60 g / L. When the added concentration of the complexing agent is too low, the complexing agent cannot completely complex the palladium ions, resulting in palladium precipitation and poor stability of the electroplating thick palladium solution system; when the added concentration of the complexing agent is too high, the specific gravity of the electroplating thick palladium solution increases, the viscosity increases, and the amount of the bath solution carried out is increased, resulting in increased costs.

[0045] In some embodiments, the palladium ions are derived from one or more of dichlorodiamine palladium, dichlorotetraamine palladium, palladium sulfate and palladium chloride, and the mass concentration of the palladium ions in the thick palladium electroplating solution is 2-20 g / L, and can also be 5-15 g / L during the specific implementation process. It is understandable that when the thickness of the palladium plating layer is required to be low, the ions can be used at a lower concentration, such as 2-5 g / L, and at the same time, a lower current density can be adapted to reduce the amount of bath liquid taken out and save production costs; if the material cost requirements are high and the production efficiency requirements are low, the palladium ion concentration can be lower, such as 0.5 g / L or 1 g / L, and the palladium plating with a thickness of more than 1 μm can be achieved by appropriately extending the electroplating time; when the thickness of the palladium plating layer is required to be high, the palladium ion concentration can be increased, such as more than 5 g / L, and a relatively high current density can be adapted to improve production efficiency.

[0046] In some embodiments, the conductive salt includes a sodium salt, potassium salt, ammonium salt or magnesium salt corresponding to phosphoric acid, sulfuric acid, boric acid or carbonate, and the mass concentration of the conductive salt is 2-50 g / L, for example, 10-20 g / L. The conductive salt can play a role in transmitting electrons in the plating solution, reducing the resistance of the thick palladium solution during electroplating, and the above-mentioned conductive salt has an obvious pH buffering function, which can assist the thick palladium solution system to maintain a relatively constant pH value, avoiding excessive pH fluctuations and causing other side effects. In addition, if the concentration of the conductive salt is too low, the conductivity and pH buffering capacity will decrease, and if the concentration is too high, the viscosity of the thick palladium solution will increase, resulting in an increase in the amount of carry-out and an increase in cost.

[0047] On the other hand, the present application also provides an electroplating method, wherein the electroplating thick palladium solution is first prepared according to the electroplating thick palladium solution formula described in any of the above items, injected into the electroplating equipment, the temperature and pH value of the electroplating thick palladium solution are adjusted, the substrate is placed in the electroplating equipment, powered on, and the electroplating operation is performed. Among them, the temperature of the electroplating thick palladium solution should be adjusted to 40-60°C, specifically, it can also be 45-55°C; the pH value of the electroplating thick palladium solution should be adjusted to 5.5-7.5, specifically, it can also be 6.0-7.0. It should be noted that too low a temperature will reduce the diffusion rate of palladium ions, which can easily cause problems such as burning of the palladium plating layer; too high a temperature will cause the liquid level to evaporate too quickly, and the solution will increase the dissolution trend of the photoresist, resulting in a shortened life of the palladium plating solution. In addition, when the pH value of the electroplating thick palladium solution system is less than 5.5, the system is too acidic, which will cause the complexing agent to be unable to stably complex palladium ions. When the pH value of the electroplating thick palladium solution system is greater than 7.5, the system is alkaline, which will corrode the photoresist on the substrate and destroy the functional structure on the substrate.

[0048] In some embodiments, during the electroplating process, the current density J is 0.1 ASD -3 ASD, the electroplating time is tmin, the electroplating thickness is d μm, and the relationship is satisfied: d=0.22*J*t. It is understood that, according to the relationship, under the conditions of determining the current density to be used and the target electroplating thickness, the electroplating time value can be obtained. For example, the electroplating thickness is 8 μm, and the electroplating current density is: 1ASD. According to the formula, the electroplating time can be calculated to be about 36 minutes. At the same time, the formula can also be used to balance the current density and production efficiency. According to the conditions of electroplating thick palladium solution, the optimal current density is matched to achieve the most efficient production efficiency.

[0049] In the specific implementation process, the underlying metal of palladium electroplating generally includes iron-nickel alloy, copper, nickel, gold, platinum and other metals. Palladium is electroplated on these metals. The platinum-titanium mesh is used as the anode, and the substrates with the above-mentioned underlying metals such as wafers, ceramics, tube shells, and pins are used as the cathode. After a certain current is applied according to the area of ​​the metal to be plated, under the condition of heating and a certain internal circulation flow of the thick palladium electroplating solution, the palladium ions in the thick palladium electroplating solution are deposited and grown on the plated surface to complete the palladium electroplating.

[0050] In the specific implementation process, the thickness of the palladium-plated layer and the gold-plated layer can be determined respectively according to the thickness requirements of the advanced packaging bump. Generally, under the condition that the bonding performance of the advanced packaging bump can be guaranteed, the thickness of the palladium-plated layer can be increased to the maximum extent to reduce the amount of gold to achieve the purpose of reducing costs; then the above-mentioned thick palladium electroplating solution is used, and the corresponding electroplating parameters are set according to the aforementioned electroplating method to electroplate a palladium-plated layer of a predetermined thickness on the surface of the bottom metal of the substrate; further, a conventional gold plating process is used to transfer the substrate to the gold plating equipment, so that a gold-plated layer of a predetermined thickness can be formed on the surface of the palladium-plated layer, and finally an advanced packaging bump is obtained. Among them, the palladium-plated layer can further block the copper diffusion of the substrate on the one hand, and on the other hand, it can ensure the overall structural strength of the advanced packaging bump and enhance the bonding, welding, binding and other performances of the advanced packaging bump; the gold-plated layer, as a bonding interface, has good process compatibility and strong connection reliability, and can adapt to various subsequent processes.

[0051] It is understandable that in order to meet the surface bonding requirements of subsequent gold plating, the surface roughness Ra of the palladium-plated layer should be between 20-60 nm.

[0052] The present application is further explained below with reference to embodiments.

[0053] The reagents and raw materials used in the examples and comparative examples of the present application are all commercially available.

[0054] The following examples are used for electroplating experiments with a palladium plating layer thickness of 5 μm-8 μm.

[0055] The electroplating thick palladium solution of the following embodiments is prepared to 1L, and the solvent is deionized water. First, add about 600mL of deionized water, add the required complexing agent, palladium ions, conductive salts in sequence, and then add the required low stress additives, wetting agents, and surface adjusters. Measure the pH value. If the pH value is high, use an acidic solution such as sulfuric acid and phosphoric acid to reduce the pH value. The acidic solution can be an aqueous solution of acidic compounds such as sulfuric acid and phosphoric acid in a suitable proportion; if the pH value is low, use an aqueous solution of alkaline compounds such as sodium hydroxide, potassium hydroxide, and ammonia to increase the pH value. When the pH value is adjusted to the required range, replenish the liquid level to 1L, heat the electroplating thick palladium solution to 40-60°C, start stirring, and determine the required current density according to the relationship: d=0.22*J*t, turn on the power, and complete the electroplating operation of d μm electroplating thickness within the predetermined electroplating time t min.

[0056] The judgment of electroplating effect mainly considers five dimensions: 1. Appearance: the palladium-plated layer cannot be blackened or cracked; 2. Glue extrusion: the palladium-plated layer cannot squeeze and deform the photoresist; 3. Plating conformality: the palladium-plated layer has a regular shape and good conformality; 4. Roughness: the roughness Ra is between 20-60nm; 5. Plating penetration: the surface of the substrate cannot have penetration caused by corrosion of the photoresist. If the palladium-plated layer meets the judgment requirements, it will be recorded as "OK" or "None" will be filled in the defect column; otherwise, it will be recorded as "NG" or "Yes" will be filled in the defect column or the specific defects will be recorded.

[0057] project Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Palladium ion (g / L) 10 15 20 5 5 8 Nitrilotriacetic acid (g / L) 20 0 50 5 5 5 Hydroxyethylidene diphosphonic acid (g / L) 40 60 50 0 10 55 Conductive salt (g / L) 2 10 20 30 30 5 Sorbitol or mannitol (g / L) 2 2 4 4 3 3 Dodecyl dimethyl benzyl ammonium chloride (mg / L) 0 500 100 10 0 250 Dodecyltrimethylammonium chloride (mg / L) 500 0 100 0 10 250 2,6-pyridinedicarboxylic acid (mg / L) 20 200 100 50 150 100 pH 5.5 7.5 6.5 6.2 6.8 6.5 Temperature (℃) 40 60 50 55 45 48 Current density (ASD) 1 1.5 3 0.5 0.8 1 Time (min) 36 24 12 72 45 32 Plating thickness (μm) 8 8 8 8 8 7.5 Appearance OK OK OK OK OK OK Glue Extrusion none none none none none none Conformal coating OK OK OK OK OK OK Coating roughness (nm) 46 26 32 38 32 26 Plating none none none none none none project Example 7 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Palladium ion (g / L) 12 10 10 10 10 10 Nitrilotriacetic acid (g / L) 50 20 20 20 20 20 Hydroxyethylidene diphosphonic acid (g / L) 50 40 40 40 40 40 Conductive salt (g / L) 50 20 20 20 20 20 Sorbitol or mannitol (g / L) 2 0 0 4 6 3 Dodecyl dimethyl benzyl ammonium chloride (mg / L) 120 120 0 100 100 500 Dodecyltrimethylammonium chloride (mg / L) 240 240 0 100 100 500 2,6-pyridinedicarboxylic acid (mg / L) 100 200 100 0 150 150 pH 6.5 6.5 6.5 6.5 6.5 6.5 Temperature (℃) 52 50 50 50 55 50 Current density (ASD) 1 1 1 1 1 1 Time (min) 32 22 36 36 36 36 Plating thickness (μm) 7.5 5 8 8 8 8 Appearance OK crack crack Black OK OK Glue Extrusion none none none none have none Conformal coating OK OK NG OK OK OK Coating roughness (nm) 27 22 55 110 33 31 Plating none none none none none have

[0058] In Example 1, the plating thick palladium solution formula and the electroplating method parameters in the above table are used, and the obtained coating has a normal appearance, such as Figure 1 As shown in Figure 1, there is no photoresist squeeze around the palladium-plated layer, and the palladium-plated layer has a regular shape and good conformality. Figure 2 As shown, the surface roughness of the palladium-plated layer is also within an appropriate range, and no penetration occurs.

[0059] In Example 2 and Example 3, the palladium ion concentration in the thick palladium electroplating solution system is higher than that in Example 1 by using the electroplating thick palladium solution formula and electroplating method parameters in the above table, so a larger current density can be used for operation, the electroplating time is relatively short, and the efficiency is high. The palladium plating layer obtained has a normal appearance, the photoresist around the palladium plating layer has no glue squeeze, the palladium plating layer has a regular shape, good conformality, and the surface roughness of the palladium plating layer is also within a suitable range, and no infiltration occurs.

[0060] In Example 4 and Example 5, the palladium ion concentration in the thick palladium electroplating solution system is relatively low, so only a lower current density can be used, the electroplating time is relatively long, and the efficiency is low. However, due to the low palladium ion concentration, the cost of opening the cylinder can be reduced from the material point of view. The palladium plating layer obtained has a normal appearance, the photoresist around the palladium plating layer has no glue squeeze, the palladium plating layer has a regular shape, good conformality, and the surface roughness of the palladium plating layer is also within a suitable range, and no infiltration occurs.

[0061] In Example 6 and Example 7, the electroplating thick palladium solution formula and electroplating method parameters in the above table are used, the electroplating thickness is set to about 7.5 μm, and the appropriate current density and electroplating time are adapted. The palladium-plated layer obtained has a normal appearance, the surrounding photoresist has no glue squeeze, the palladium-plated layer has a regular shape, good conformality, and the surface roughness of the palladium-plated layer is also within a suitable range, and no infiltration occurs. On this basis, a conventional method is used to electroplate a gold-plated layer with a thickness of about 2.5 μm to obtain a palladium-plated layer as shown in FIG. Figure 3 The advanced packaging bump with a combination of a palladium-plated layer and a gold-plated layer shown in the figure has a good appearance, a stable structure, good welding and binding performance, and can be well applied to bonding processing scenarios. Figure 4 As shown, it can be seen that the palladium-plated layer is 7.406μm, the gold-plated layer is 2.531μm, the plating layers are tightly bonded, without defects such as gaps, voids, IMC layers, and underlying metal diffusion, and the mechanical properties are guaranteed.

[0062] See also Figure 5 The difference between Comparative Example 1 and each embodiment is that when the low-stress additive is not added and the electroplating thickness requirement of Comparative Example 1 is reduced to 5 μm, cracks still appear in the palladium-plated layer obtained by electroplating.

[0063] See also Figure 6 The difference between Comparative Example 2 and each embodiment is that: when no low-stress additive is added and no wetting agent is added, and the electroplating thickness requirement of Comparative Example 2 is reduced to 5 μm, cracks still appear in the palladium-plated layer obtained by electroplating, and the photoresist at the edge of the palladium-plated layer shrinks, and the surface of the palladium-plated layer is relatively rough, which affects the subsequent gold plating process and the structural strength of the formed bump.

[0064] See also Figure 7 The difference between Comparative Example 3 and each embodiment is that: without adding a surface conditioning agent, the obtained palladium plating layer has a rough surface and a blackened plating layer under a microscopic image.

[0065] See also Figure 8 The difference between Comparative Example 4 and each embodiment is that due to the addition of a high concentration of low-stress additive beyond the range, the obtained palladium-plated layer tends to expand, causing the photoresist layer at its edge to deform.

[0066] See also Fig. 9 The difference between Comparative Example 5 and each embodiment is that when a high-concentration wetting agent exceeding the range is added and a relatively dense small-sized palladium plating layer is required to be electroplated, a seepage plating phenomenon will occur between each palladium plating layer.

[0067] In summary, the present application adopts polyol as a low-stress additive, which works synergistically with a surface adjuster and a wetting agent to form a thick palladium electroplating solution system that can be suitable for blind hole palladium plating scenarios where a palladium plating layer with a thickness of more than 1 μm needs to be formed. In the process of forming the palladium plating layer, there is no cracking due to excessive tensile stress or glue squeezing due to excessive tensile stress, and it is easy to keep the plating layer growing in a specified shape; at the same time, the synergistic effect of the three can also reduce the surface roughness of the palladium plating layer, and the formed palladium plating layer has good structural tightness and uniformity of stress distribution. In the subsequent gold plating and bonding processes, the surface bonding ability is better, thereby improving the processing quality of advanced packaging bumps.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A thick palladium electroplating solution for advanced packaging bumping process, characterized in that: The thick palladium electroplating solution includes the following mass concentration components: palladium ions 2-20g / L, complexing agent 5-100g / L, conductive salt 2-50g / L, low stress additive 1-5g / L, wetting agent 10-500mg / L, surface adjuster 20-200mg / L, the solvent is water, the low stress additive includes a polyol with a ratio of carbon atoms to hydroxyl groups of ≤1.25, the surface adjuster is 2,6-pyridinedicarboxylic acid, the wetting agent is a cationic surfactant, the complexing agent is nitrilotriacetic acid and / or hydroxyethylenediphosphonic acid, and the pH value of the thick palladium electroplating solution is 5.5-7.

5.

2. The thick palladium electroplating solution according to claim 1, characterized in that The low stress additive includes one or more of glycerol, pentaerythritol, sorbitol, mannitol and xylitol.

3. The thick palladium electroplating solution according to claim 1, characterized in that The mass concentration of the low stress additive is 2-4 g / L.

4. The thick palladium electroplating solution according to claim 1, characterized in that The mass concentration of the 2,6-pyridinedicarboxylic acid is 50-150 mg / L.

5. The thick palladium electroplating solution according to claim 1, characterized in that The mass concentration of the cationic surfactant is 50-300 mg / L.

6. The thick palladium electroplating solution according to claim 5, characterized in that: The cationic surfactant includes dodecyldimethylbenzyl ammonium chloride and / or dodecyltrimethylammonium chloride.

7. The thick palladium electroplating solution according to claim 1, characterized in that: The mass concentration of the complexing agent is 20-60 g / L.

8. The thick palladium electroplating solution according to claim 1, characterized in that: The palladium ions are derived from one or more of dichlorodiamminepalladium, dichlorotetramminepalladium, palladium sulfate and palladium chloride, and the mass concentration of the palladium ions is 5-15 g / L.

9. The thick palladium electroplating solution according to claim 1, characterized in that: The conductive salt includes sodium salt, potassium salt, ammonium salt or magnesium salt corresponding to phosphoric acid, sulfuric acid, boric acid or carbonate, and the mass concentration of the conductive salt is 10-20 g / L.

10. An electroplating method for advanced packaging bump process, characterized in that: The following steps are involved: The thick palladium electroplating solution according to any one of claims 1 to 9 is used, and the temperature and pH value of the thick palladium electroplating solution are adjusted before energizing the thick palladium electroplating solution, wherein the temperature is 40-60° C. and the pH value is 5.5-7.5.

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