Anti-corrosion process for forming gold wrapping layer through secondary gold plating of silver-plated bump

Abstract

Aiming at the limitation of the existing metal bump corrosion prevention technology, the invention provides an innovative process: pure silver electroplating is adopted to form a bump main body, a complete gold wrapping structure is formed on all exposed surfaces of the bump main body through secondary electroplating of pure gold, and the process can be used for accurately regulating and controlling the parameters of the secondary electroplating and the size of a secondary photoetching pattern. The exposed surface of the silver bump is uniformly wrapped by the thin gold layer, so that the problem that metal interconnection is easy to corrode in a severe environment in the traditional technology is effectively solved, and comprehensive breakthrough in corrosion resistance, electrical properties and cost effectiveness is realized through innovative silver core and gold shell layered structure design and precise process control.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of semiconductor packaging technology in electronic manufacturing process, and particularly relates to a silver-plated bump secondary gold plating forming gold wrapping layer anti-corrosion process. BACKGROUND

[0002] In the semiconductor packaging technology, the anti-corrosion performance directly affects the long-term reliability and use efficiency of the chip. Since the packaged chip needs to work in harsh environments such as high temperature, high humidity and chemical corrosion, the corrosion of the metal interconnection structure may cause the resistance to rise, the signal transmission to deteriorate, and even the device to fail. Therefore, optimizing the anti-corrosion process of the metal bump becomes the key to improving the packaging reliability.

[0003] Currently, the anti-corrosion of the metal bump in semiconductor packaging mainly relies on the following technologies:

[0004] A bump structure is formed by photolithography and electroplating, but only relies on the corrosion resistance of the single metal itself, without introducing a noble metal protective layer. Pure copper bumps are prone to oxidation and electrochemical corrosion, and pure tin bumps are prone to whisker growth and sulfidation corrosion. The contact resistance increases significantly after long-term use;

[0005] Silver or copper bumps with high electrical conductivity are formed by electroplating, but no anti-corrosion layer is added to the key exposed surface. Silver bumps quickly sulfide and turn black in a sulfur-containing environment, and copper bumps oxidize in a humid environment, resulting in signal integrity deterioration;

[0006] Solder based on tin is electroplated on the copper pillar and reflowed to form a spherical bump, but the solder itself is not resistant to high temperature and high humidity corrosion. The solder and copper interface are prone to form brittle intermetallic compounds, which may cause cracks in thermal cycling. The solder body dissolves in the corrosion medium;

[0007] The common problem of these technologies is that all exposed surfaces are not provided with complete anti-corrosion protection, and the use of noble metals is costly. SUMMARY

[0008] In view of the above defects, an innovative process is proposed in this paper: through the synergistic control of two independent patterning and pure metal electroplating, a gold wrapping layer is formed on all exposed surfaces of the silver-plated bump, which takes into account high electrical conductivity, strong corrosion resistance and cost controllability.

[0009] A silver-plated bump secondary gold plating forming gold wrapping layer anti-corrosion process, the process comprising the following steps:

[0010] S1, bump surface pretreatment: remove oil stains and impurities on the surface of the bump, clean with an acidic solution to remove the oxide layer and activate the surface of the bump. This step ensures that the plating layer is dense and adheres, provides a clean substrate for silver bump electroplating, avoids interface defects, and ensures the integrity of the anti-corrosion gold layer;

[0011] S2, first patterning process: install a first mask, the size of the first mask is smaller than the size of the bottom of the silver plated bump, and the silver plated bump area is formed after installation, this step defines the plating area through the first small size mask, restricts the silver deposition range, ensures the accuracy of the bump bottom profile, and reserves the side covering space for the subsequent gold wrapping layer;

[0012] S3, first plating: using pure silver plating solution for plating in the area defined in S2, to form a silver plated bump, this step constructs a high-conductive bump core structure by plating pure silver in the precise area defined by the mask, optimizes the density and height uniformity of the plating layer through pulse current, provides a geometric basis for the subsequent gold wrapping, and the high conductivity of silver guarantees the chip interconnection performance;

[0013] S4, second patterning process: perform glue coating, exposure, development and other processes on the surface of the packaging substrate with the silver plated bump, install a second mask, the opening size of the second mask is larger than the peripheral size of the silver plated bump, and a gold wrapping layer plating area is formed after development, which covers the top surface, four side surfaces and the surrounding part of the base of the silver plated bump, this step accurately defines the gold layer deposition area, ensures that the pure gold completely covers the five exposed surfaces of the bump, covers the side wall to solve the corrosion dead angle problem that cannot be protected by traditional planar gold plating, the photoresist window is slightly larger than the bump, compatible with the flow demand of the plating solution, and avoids edge plating deficiency;

[0014] S5, second plating: using pure gold plating solution for plating in the area defined in S4, to deposit a pure gold layer on the top surface, four side surfaces and exposed base of the silver plated bump, this step forms a gold layer of 1-5 μm on the top surface and four side surfaces of the silver plated bump, completely isolates the corrosion medium, pulse reverse plating makes gold and silver form metallurgical bonding to avoid delamination, the gold layer deposited on the base serves as a process transition structure, and only the bump wrapping body is reserved after etching removal after post-processing, which takes into account corrosion prevention and conductivity;

[0015] S6, post-processing: remove the photoresist defining the gold wrapping area and the excess gold layer deposited on the base to obtain a composite structure bump with a silver plated bump and a gold wrapping layer formed by secondary gold plating, this step removes the base gold layer to avoid electrical connection between adjacent bumps, makes the silver plated bump and the gold wrapping layer work together, and provides a clean surface for contact resistance and salt spray test to verify the performance.

[0016] Further, in step S3, the following plating parameters are used to form the silver plated bump:

[0017] Bump height: 5-12 μm;

[0018] Current density: 0.5-1 ASD;

[0019] Plating time: 480-4800 seconds;

[0020] Plating solution flow rate: 8-20 L / min;

[0021] Plating tank shaking frequency: 10-30 Hz;

[0022] The electroplating process adopts a pulse current mode with a duty cycle of 30%-50% and a frequency of 50-100 Hz to optimize the density of the plated layer;

[0023] Further, in step S4, the following steps are specifically included:

[0024] S4.1 Gluing: spin coating photoresist on the substrate surface with silver-plated bumps to uniformly cover the complex topography of the bumps, preparing for exposure;

[0025] S4.2 Glueing: spin coating at a certain speed to ensure uniform coverage;

[0026] S4.3 Exposure: UV exposure using a second mask;

[0027] S4.4 Development: dissolving the photoresist in the unexposed and exposed areas to form a gold-coated layer of electroplating area covering the top and side surfaces of the silver-plated bumps and the surrounding part of the substrate, which precisely forms a sidewall protection window;

[0028] S4.5 Baking: baking at a certain temperature to solidify the remaining photoresist and enhance the photoresist's resistance to plating solution erosion, ensuring sharp boundaries of the gold layer deposition.

[0029] Further, the size of the second mask in step S4 is designed to ensure that the final pure gold layer completely and continuously wraps the five exposed surfaces of the silver-plated bumps.

[0030] Further, in step S5, the following electroplating parameters are used to form the pure gold coating layer:

[0031] Current density: 0.5-1 ASD;

[0032] Electroplating time: 1800-3600 seconds;

[0033] Forming a pure gold coating layer with a thickness of 1-5 μm on the five exposed surfaces of the silver-plated bumps;

[0034] The purity of the pure gold layer is ≥99.99%;

[0035] The coating layer completely covers the five exposed surfaces of the cubic bumps without any plating leakage area.

[0036] Further, in step S4.1, the photoresist is an epoxy-based photoresist with a thickness of 5-15 μm;

[0037] Further, in step S4.2, the glueing speed is 1000-3000 rpm;

[0038] Further, the exposure energy in step S4.3 is 150-250 mJ / cm 2 ;

[0039] Further, a 2.38% tetramethylammonium hydroxide solution is used for development in step S4.4 for 45-90 seconds.

[0040] Further, the baking condition in step S4.5 is hot plate baking at 100-120°C for 60-120 seconds.

[0041] Further, in step S5, the second plating process uses a pulse reverse plating process, with a forward power-on time of 10 ms, a reverse power-off time of 2 ms, a forward current density of 0.5-1 ASD, and a reverse current density of 0.1-0.3 ASD.

[0042] Further, the acid solution in step S1 is a 10% sulfuric acid or 5% nitric acid solution, and the activation treatment time is 30-60 seconds.

[0043] Beneficial effects:

[0044] The process forms a continuous gold wrapping layer on all exposed surfaces of the pure silver bump through an innovative silver core and gold shell layered structure and precise process control. The core breakthrough is:

[0045] The gold layer completely isolates the corrosion medium, preventing silver oxidation and sulfidation.

[0046] The silver main body ensures high electrical conductivity and thermal conductivity.

[0047] The design of gold plating only on the exposed surface significantly reduces the use of precious metals.

[0048] The combination of the three achieves a comprehensive breakthrough in corrosion resistance, electrical properties, and cost-effectiveness, effectively solving the corrosion problem of traditional metal bumps in harsh environments. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 Figure 1 is a first mask positioning for a silver-plated bump secondary gold plating process to form a gold wrapping layer of a corrosion-resistant process,

[0050] Figure 2 Figure 2 is a second mask positioning for a silver-plated bump secondary gold plating process to form a gold wrapping layer of a corrosion-resistant process,

[0051] Figure 3 Figure 3 is a cross-sectional view of a composite structure bump of a silver-plated bump secondary gold plating process to form a gold wrapping layer of a corrosion-resistant process,

[0052] Figure 4 Figure 4 is a process flow diagram of a silver-plated bump secondary gold plating process to form a gold wrapping layer of a corrosion-resistant process,

[0053] Figure: 1, mask No. 1, 2, bump, 3, silver plating, 4, packaging substrate, 5, mask No. 2, 6, silver-plated bump, 7, photoresist coating, 8, gold plating. DETAILED DESCRIPTION

[0054] In order to deepen the understanding of the present application, the present application will be further described below in conjunction with examples and drawings, which are only used to explain the present application and do not constitute a limitation on the scope of protection of the present application.

[0055] Mask No. 1 1, bump 2, silver plating 3, packaging substrate 4, mask No. 2 5, silver-plated bump 6,

[0056] Photoresist coating 7, gold plating 8.

[0057] As shown in Figure 1 , 2 , 3, 4:

[0058] A kind of silver-plated bump 6 secondary gold plating forms gold wrapping layer's anticorrosion process, bump 2 shape is cuboid structure, include five exposed surfaces and one top surface and four side surfaces, the process includes the following steps:

[0059] S1, bump 2 surface pretreatment: remove the oil dirt and impurities on the surface of bump 2, use acid solution to clean to remove oxide layer and activate the surface of bump 2;

[0060] S2, first patterning process: install mask No. 1, the size of the mask No. 1 is less than the size of the bottom of silver-plated bump 6, after installation, silver bump 2 plating area is formed;

[0061] S3, first plating: in the area defined in S2, use pure silver plating solution for plating, form silver-plated bump 6;

[0062] S4, second patterning process: on the surface of the packaging substrate 4 formed with silver-plated bump 6, carry out glue coating, exposure, development and other procedures, install mask No. 5, the opening size of the mask No. 5 is greater than the peripheral size of the silver-plated bump 6, after development, gold wrapping layer plating area is formed, which covers the top surface, four side surfaces and surrounding part of the base of the silver-plated bump 6;

[0063] S5, second plating: in the area defined in S4, use pure gold plating solution for plating, deposit pure gold layer on the top surface, four side surfaces and exposed base of silver-plated bump 6;

[0064] S6, post-processing: remove the photoresist defining the gold wrapping area and the excess gold layer deposited on the base, to obtain the composite structure bump 2 of silver-plated bump 6 secondary gold plating forming gold wrapping layer.

[0065] Further, in step S3, the following plating parameters are used to form silver-plated bump 6:

[0066] Bump 2 height: 5-12 μm;

[0067] Current density: 0.5-1 ASD;

[0068] Plating time: 480-4800 seconds;

[0069] Plating solution flow rate: 8-20 L / min;

[0070] Plating tank shaking frequency: 10-30 Hz;

[0071] The plating process uses a pulse current mode, with a duty cycle of 30%-50% and a frequency of 50-100 Hz, to optimize the density of the plating layer.

[0072] Further, in step S4, the following steps are specifically included:

[0073] S4.1 Gluing: spin coating photoresist on the surface of the substrate with the silver-plated bumps 6;

[0074] S4.2 Leveling: spin coating at a certain speed to ensure uniform coverage;

[0075] S4.3 Exposure: UV exposure using the second mask 5;

[0076] S4.4 Development: dissolving the photoresist in the unexposed and exposed areas to form a gold-coated layer plating area covering the top and side surfaces of the silver-plated bumps 6 and the surrounding part of the substrate;

[0077] S4.5 Baking: hot plate baking at a certain temperature to solidify the remaining photoresist.

[0078] Further, the size of the second mask 5 in step S4 is designed to ensure that the final pure gold layer completely and continuously wraps the five exposed surfaces of the silver-plated bumps 6.

[0079] Further, in step S5, the following plating parameters are used to form the pure gold coating layer:

[0080] Current density: 0.5-1 ASD;

[0081] Plating time: 1800-3600 seconds;

[0082] Forming a pure gold coating layer with a thickness of 1-5 μm on the five exposed surfaces of the silver-plated bumps 6;

[0083] The purity of the pure gold layer is ≥99.99%;

[0084] The coating layer completely covers the five exposed surfaces of the cubic bumps 2 without any plating leakage area.

[0085] Further, the photoresist in step S4.1 is an epoxy resin-based photoresist, and the thickness of the photoresist is 5-15 μm;

[0086] Further, the rotation speed of the photoresist in step S4.2 is 1000-3000 rpm;

[0087] Further, the exposure energy in step S4.3 is 150-250 mJ / cm 2 ;

[0088] Further, the developing solution in step S4.4 is 2.38% tetramethylammonium hydroxide solution, and the developing time is 45-90 seconds;

[0089] Further, the baking condition in step S4.5 is hot plate baking at 100-120 °C for 60-120 seconds.

[0090] Further, the second plating process in step S5 adopts pulse reverse plating process, and the positive current is 10 ms, the reverse current is 2 ms, the positive current density is 0.5-1 ASD, and the reverse current density is 0.1-0.3 ASD.

[0091] Further, the acid solution in step S1 is 10% sulfuric acid or 5% nitric acid solution, and the activation treatment time is 30-60 seconds.

[0092] Embodiment

[0093] Firstly, surface pretreatment is performed: the oil stains and impurities on the bump surface are removed, and the surface is activated by cleaning with an acid solution to remove the oxide layer;

[0094] Secondly, first patterning and pure silver bump plating are performed: a first mask is installed, the plating solution is filled, and then pulse plating is started;

[0095] Thirdly, second patterning is performed: secondary photoresist coating, exposure of key positions, development and curing are performed;

[0096] Fourthly, pure gold coating and post-treatment are performed: a second mask is installed, pure gold plating solution is filled, pulse reverse plating is performed, and then the excess photoresist is cleaned;

[0097] Fifthly, performance verification is performed: contact resistance test, salt spray corrosion resistance test, and high temperature and humidity resistance test are performed.

[0098] The above only describes the preferred embodiments of the present application and should not be used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. An anti-corrosion process for forming a gold wrapping layer by secondary gold plating of a silver-plated bump, wherein the bump is in a cubic structure, comprising five exposed surfaces, a top surface, and four side surfaces, characterized in that: The process includes the following steps: S1. Bump surface pretreatment: remove oil and impurities on the bump surface, use acidic solution to clean to remove the oxide layer and activate the bump surface; S2, first patterning process: installing a first photomask, wherein the size of the first photomask is smaller than the size of the bottom of the silver-plated bump, and forming a silver bump electroplating area after installation; S3, first electroplating: in the area defined in S2, use pure silver electroplating solution to electroplating to form silver-plated bumps; S4, Second Patterning Process: Glue coating, exposure, and development are performed on the surface of the package substrate with the silver-plated bumps formed thereon. A second photomask is installed, wherein the opening size of the second photomask is larger than the outer size of the silver-plated bumps. After development, a gold wrapping layer electroplating area is formed, which covers the top surface, four side surfaces, and surrounding portion of the base of the silver-plated bumps. S5, second electroplating: in the area defined in S4, use pure gold electroplating solution to electroplating, and deposit a pure gold layer on the top surface, four side surfaces and exposed substrate of the silver-plated bump; S6. Post-processing: stripping, removing the photoresist defining the gold-wrapped area and the excess gold layer deposited on the substrate, to obtain a composite structure bump in which the silver-plated bump is plated with gold twice to form a gold-wrapped layer.

2. The anti-corrosion process for forming a gold wrapping layer by secondary gold plating of a silver-plated bump according to claim 1, characterized in that: In step S3, the following electroplating parameters are used to form the silver-plated bumps: Bump height: 5-12μm; Current density: 0.5-1ASD; Plating time: 480-4800 seconds; Plating solution flow rate: 8-20L / min; Plating tank shaking frequency: 10-30Hz; The electroplating process adopts a pulse current mode with a duty cycle of 30%-50% and a frequency of 50-100 Hz to optimize the density of the coating.

3. The anti-corrosion process for forming a gold wrapping layer by secondary gold plating of a silver-plated bump according to claim 1 or 2, characterized in that: The step S4 specifically includes the following steps: S4.1 Glue coating: Spin-coat photoresist on the surface of the substrate with the silver-plated bumps formed thereon; S4.2 Spin coating: Spin coating at a certain speed to ensure uniform coverage of photoresist; S4.3 Exposure: Use mask No. 2 for UV exposure; S4.4 Development: dissolving the photoresist in the unexposed and exposed areas to form a gold wrap electroplated area covering the top surface, side surfaces, and surrounding portion of the base of the silver-plated bump; S4.5 Baking: Baking on a hot plate at a certain temperature to cure the remaining photoresist.

4. The anti-corrosion process for forming a gold wrapping layer by secondary gold plating of a silver-plated bump according to claim 1 or 3, characterized in that: The size design of the second photomask in step S4 ensures that the final pure gold layer completely and continuously covers the five exposed surfaces of the silver-plated bumps.

5. The anti-corrosion process for forming a gold wrapping layer by secondary gold plating of a silver-plated bump according to claim 1, characterized in that: In step S5, the following electroplating parameters are used to form a pure gold wrapping layer: Current density: 0.5-1ASD; Electroplating time: 1800-3600 seconds; Forming a pure gold wrapping layer with a thickness of 1-5 μm on the five exposed surfaces of the silver-plated bump; The purity of the pure gold layer is ≥99.99%; The wrapping layer completely covers the five exposed surfaces of the cubic bump without any missing plating areas.

6. The anti-corrosion process for forming a gold wrapping layer by secondary gold plating of a silver-plated bump according to claim 3, characterized in that: In step S4.1, the photoresist is an epoxy resin-based photoresist with a thickness of 5-15 μm; In step S4.2, the speed of the coating is 1000-3000 rpm; The exposure energy in step S4.3 is 150-250 mJ / cm 2 ; In step S4.4, 2.38% tetramethylammonium hydroxide solution is used for development for 45-90 seconds; The baking condition in step S4.5 is baking on a hot plate at 100-120° C. for 60-120 seconds.

7. The anti-corrosion process for forming a gold wrapping layer by secondary gold plating of a silver-plated bump according to claim 5, characterized in that In the step S5, the second electroplating process adopts a pulse reverse electroplating process, with forward power on for 10ms, reverse power off for 2ms, forward current density of 0.5-1ASD, and reverse current density of 0.1-0.3ASD.

8. The anti-corrosion process for forming a gold wrapping layer by secondary gold plating of a silver-plated bump according to claim 1, characterized in that In step S1, the acidic solution is 10% sulfuric acid or 5% nitric acid solution, and the activation treatment time is 30-60 seconds.

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