Micro bump construction method for forming intermetallic compound with orientation tending to be consistent
Fabrication is carried out using direct current electrodeposition during the 3D packaging process. <111> Preferred-oriented nanotwinned Ni-xCo, combined with annealing and lead-free solder ball bonding, forms an intermetallic compound with consistent orientation, solving the orientation control problem in microbump fabrication technology and improving the reliability and performance of 3D packaging.
Patent Information
- Application Number
- CN202510879267.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-27
- Publication Date
- 2025-11-14
AI Technical Summary
Existing microbump fabrication techniques have difficulty precisely controlling the orientation of intermetallic compounds, leading to unstable electrical connections, increased thermal resistance, and decreased reliability during 3D packaging.
Fabrication on metal pads using direct current electrodeposition <111> Preferred-oriented nanotwins Ni-xCo are used as the under-bump metallization layer, and through annealing and lead-free solder ball placement, intermetallic compounds Ni3Sn4 or CoSn3 with consistent orientation are formed.
Stable connection of micro-bumps is achieved, improving mechanical properties such as thermal cycling, thermal shock, and fatigue resistance, enhancing electrical performance and thermal management efficiency, and improving packaging reliability and service reliability.
Smart Images
Figure CN120954981A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for constructing microbumps in intermetallic compounds with uniform orientation. Background Technology
[0002] In the microelectronics industry, with the rapid development of chip manufacturing technology, electronic devices are rapidly evolving towards miniaturization, high performance, and high integration. Three-dimensional packaging technology (3D packaging) has become one of the key technologies for improving chip performance. 3D packaging is an advanced packaging method that stacks and interconnects multiple chips or electronic components in three-dimensional space, utilizing vertical interconnect technologies (such as through-silicon vias, TSVs) to achieve electrical connections. 3D packaging achieves higher packaging density and shorter signal transmission paths, thus significantly improving the overall performance of the system. However, during the 3D packaging process, the continuous reduction in the size of microbumps (exceeding the 10μm threshold) will lead to an increase in the proportion of intermetallic compounds (IMCs) at the solder joint interface, even forming single-grain all-IMC solder joints. IMCs exhibit strong anisotropy in electrical, thermal, and mechanical properties, which will seriously affect the service performance of packaged devices. Therefore, the performance of intermetallic compounds (IMCs) is a crucial factor affecting the reliability of electronic devices.
[0003] However, existing microbump fabrication techniques often struggle to precisely control the orientation of intermetallic compounds, leading to a series of problems in 3D packaging processes, such as unstable electrical connections, increased thermal resistance, and decreased reliability. Therefore, developing a method to effectively control the orientation of intermetallic compounds in microbumps is crucial for improving the overall level of 3D packaging technology. Summary of the Invention
[0004] Purpose of the invention: The purpose of this invention is to provide a method for constructing microbumps of intermetallic compounds with consistent orientation during the 3D packaging process.
[0005] Technical solution: The method for constructing microbumps for 3D packaging according to the present invention includes the following steps:
[0006] (1) At least one metal pad is prepared at each of the two connection sites by electroplating, and then a metallization layer under the bump is prepared on the metal pad by direct current electrodeposition; wherein, the metallization layer under the bump is... <111> Preferred orientation nanotwins Ni-xCo, where x represents the atomic percentage of cobalt in the nickel-cobalt alloy, and x is 13 at.%, 30 at.%, 50 at.%, or 70 at.%.
[0007] (2) Anneal the metallization layer under the bump of one of the connection sites. After annealing, Sn-based lead-free solder balls are planted on the metallization layer under the bump using a ball-planting machine. Before the ball-planting, a small amount of flux may be applied to the pad to enhance wettability and reduce oxidation, but the amount should be controlled to avoid residues affecting reliability. After the ball-planting is completed, brazing reflow is performed to prepare lead-free solder bumps. Intermetallic compounds Ni3Sn4 or CoSn3 with consistent orientation are formed at the interface between the lead-free solder bumps and the metallization layer under the bump.
[0008] (3) Align the lead-free solder bump and the metallization layer under the bump on another site to be connected, and place them in contact to form an assembly; heat the assembly to perform brazing reflow, the lead-free solder bump melts and a brazing reaction occurs, and at the interface between the metallization layer under the bump on another site to be connected and the lead-free solder bump, an intermetallic compound Ni3Sn4 or CoSn3 with a consistent orientation is also formed.
[0009] In step (1), DC electrodeposition is used to deposit metal pads on the two sites to be connected to prepare... <111> The preferred orientation of the nanotwinned Ni-xCo is as follows:
[0010] (1.1) Preparation of electrolyte solution: Add nickel sulfate hexahydrate, sodium citrate dihydrate, cobalt sulfate heptahydrate, sodium dodecyl sulfate, sodium saccharin, 1,4-butynediol and glacial acetic acid to deionized water, stir to dissolve, filter with filter paper, and then adjust the pH value to 5.2-6.7 with 10wt% NaOH solution and sulfuric acid solution to obtain electrolyte solution; The concentration of each compound in the electrolyte solution is: nickel sulfate hexahydrate 80-150 g / L, sodium citrate dihydrate 60-65 g / L, cobalt sulfate heptahydrate 5-45 g / L, sodium dodecyl sulfate 0.05-0.06 g / L, sodium saccharin 1.0-1.5 g / L, 1,4-butynediol 0.64-0.65 g / L, glacial acetic acid 0.04-0.05 g / L;
[0011] (1.2) Constant current electrochemical deposition was performed at a current density of 60 mA / cm². 2 The electrodeposition time is 1-2 hours, and electrodeposition is performed on the metal pads to obtain... <111> Preferred orientation of nanotwins Ni-xCo.
[0012] In step (1), the thickness of the metallization layer under the bump is 30-50 μm, preferably 50 μm.
[0013] During electrodeposition, the electrolyte solution temperature was 64±1℃, the cathode / anode area ratio was 1:50, the cathode-anode distance was 60mm, and the electrolyte solution was magnetically stirred at a speed of 1500 rpm. The high temperature (64℃) and high stirring speed (1500 rpm) jointly promoted the formation of high-density dislocations and stacking faults (twin precursors), while the uniform current (cathode / anode area ratio 1:50) and electrode distance (60mm) ensured a uniform stress field, ultimately leading to the formation of... <111> Oriented nanotwin structure; furthermore, stable temperature and mass transfer conditions (stirring) allow for controllable Ni / Co co-deposition ratio, and <111> The preference for orientation stems from the minimum strain energy of the crystal plane during electrodeposition. These parameters collectively regulate ion transport, crystallization kinetics, and stress state, achieving... <111> Preferred orientation and nanotwin structure.
[0014] In step (2), the Sn-based lead-free solder is SnAgCu3O5 or SnAgCu3O5; the Sn content in the Sn-based lead-free solder is greater than 50 wt.%.
[0015] In step (2), the ball-mounting machine plants Sn-based lead-free solder balls. Before the balls are planted, a small amount of flux is applied to the metal pads to enhance wettability and reduce oxidation. The ball-mounting machine uses a vision positioning system to precisely align the wafer with the ball-mounting template, ensuring that each pad and template opening are completely overlapped. Vacuum adsorption or vibration feeding is used to distribute the pre-selected spherical lead-free solder into the template openings. At this time, the distance between the template and the wafer is controlled at 10-20μm to avoid ball displacement. After all the openings are filled with solder balls, the balls are initially contacted with the pads through brief negative pressure adsorption or mechanical vibration. Then the template is removed to complete the ball-mounting.
[0016] In steps (2) and (3), the reflow temperature for brazing reflow is 250–270°C.
[0017] In step (2), the diameter of the lead-free solder bump is 20-80 μm.
[0018] This invention utilizes <111> Preferred-oriented nanotwinned Ni-xCo (x = 13 at.%, 30 at.%, 50 at.%, 70 at.%) were chosen as UBMs because the nanotwinned structure possesses high density and excellent mechanical properties, effectively resisting various mechanical stresses and thus ensuring stable connection of microbumps under complex working environments. Furthermore, <111> Preferred orientation of nanotwinned Ni-xCo materials can significantly improve the service reliability of microbumps under long-term high temperature and high current density conditions. This invention utilizes... <111> Preferred orientation of nanotwins Ni-xCo (x = 0, 13 at.%, 30 at.%, 50 at.%, 70 at.%) enables control of the interface IMC orientation in electronic packaging microbumps. The resulting microbumps have a more consistent IMC orientation, which helps to improve the electrical performance and thermal management efficiency of the microbumps and enhance the overall packaging reliability.
[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The present invention utilizes <111> Preferred-oriented nanotwinned Ni-xCo (x = 13 at.%, 30 at.%, 50 at.%, 70 at.%) UBMs replace the cumbersome and expensive single-crystal Cu UBMs, thus ensuring the formation of a uniformly oriented intermetallic compound at the interface of the metallization layer under the bumps during the brazing reaction. This results in uniformly oriented microbumps (IMCs), which effectively improve the mechanical properties of the microbumps, such as thermal cycling, thermal shock, and fatigue resistance, as well as their resistance to electromigration and thermal migration. They also exhibit good thermal stability and can operate reliably for extended periods above 150°C. Attached Figure Description
[0020] Figure 1 This is a schematic diagram of the assembly before reflow soldering;
[0021] Figure 2 This is a schematic diagram of the assembly after reflow soldering;
[0022] Figure 3 Electron backscatter diffraction (EBSD) image of Ni3Sn4 type intermetallic compounds with uniform orientation formed under the conditions of Example 1;
[0023] Figure 4 Electron backscatter diffraction (EBSD) images of CoSn3-type intermetallic compounds with uniform orientation formed under the conditions of Example 2;
[0024] Figures 1-2 In the middle: 10, first substrate; 20, first metal pad; 30, first bump under-metallization layer; 42, lead-free solder bump; 40, second substrate; 50, second metal pad; 60, second bump under-metallization layer; 70 and 80 are IMC with consistent orientation. Detailed Implementation
[0025] Example 1
[0026] The present invention provides a method for constructing microbumps for 3D packaging, comprising the following steps:
[0027] (1) Using the first substrate 10 as one of the connection sites, an electroplating method is used on the first substrate 10 to prepare a first metal pad (Cu pad) 20. Specifically, the substrate surface is ultrasonically cleaned with acetone, ethanol and deionized water in sequence, and dried with nitrogen; a Ti / Cu seed layer is deposited by evaporation; positive photoresist is then spin-coated and pre-baked, and developed to form a pad pattern; the photoresist is reinforced by post-baking, and the seed layer surface is treated with dilute acid or activator; the substrate is connected to the electroplating system as a cathode, and the current density, temperature and time parameters are set to deposit Cu to the target thickness in copper sulfate electroplating solution; the photoresist is removed after rinsing with deionized water, the exposed seed layer is removed by wet etching, and finally cleaned and dried to complete the preparation of the Cu pad. Then, a high-density 50μm thick pad is prepared on the first metal pad 20 by direct current electrodeposition. <111> Preferred-oriented nanotwins Ni-xCo (x = 13 at.%) are used as the under-bump metallization layer, i.e., the first under-bump metallization layer 30. After annealing (annealing temperature is 250℃), SnAgCu305 solder balls are implanted on it. After brazing and reflow, lead-free solder bumps 42 with a diameter of 80μm are formed. An intermetallic compound 70 with a consistent orientation is formed between the first under-bump metallization layer 30 and the lead-free solder bumps 42. The reflow temperature here is 260℃.
[0028] (2) Using the second substrate 20 as another bonding site, a second metal pad (Cu pad) 50 is fabricated on the second substrate 20 in the same manner as the first substrate. Then, a high-density substrate with a thickness of 50 μm is fabricated on the second metal pad 50 using the same method, namely, DC electrodeposition. <111> Preferred-oriented nanotwins Ni-xCo (x = 13 at.%) are used as the under-bump metallization layer, i.e., the second under-bump metallization layer 60, so that the array patterns of the first under-bump metallization layer 30 and the second under-bump metallization layer 60 are the same.
[0029] (3) Align the lead-free solder bumps 42 and the metallization layer 60 under the second bump one by one, and place them in contact to form an assembly; such as Figure 1 As shown;
[0030] (4) The assembly is heated to 260°C for brazing reflow. The lead-free brazing filler metal bumps 42 melt and undergo a brazing reaction, transforming into intermetallic compounds Ni3Sn4 (70, 80) with a more uniform orientation, resulting in micro-bumps (IMC) with a more uniform orientation. Figure 3As shown, the formed intermetallic compound Ni3Sn4 (70, 80) is oriented as follows: <010> .
[0031] In steps (1) and (2), direct current electrodeposition is used to prepare the first metal pad 20 and the second metal pad 50, respectively. <111> The preferred orientation of the nanotwinned Ni-xCo is as follows:
[0032] (1.1) Preparation of electrolyte solution: Add nickel sulfate hexahydrate, sodium citrate dihydrate, cobalt sulfate heptahydrate, sodium dodecyl sulfate, sodium saccharin, 1,4-butynediol and glacial acetic acid to deionized water, stir to dissolve, filter with filter paper, and then adjust the pH value to 5.4 with 10wt% NaOH solution and sulfuric acid solution to obtain electrolyte solution; The concentration of each compound in electrolyte solution is: nickel sulfate hexahydrate 150g / L, cobalt sulfate heptahydrate 5g / L, sodium citrate dihydrate 60g / L, sodium dodecyl sulfate 0.05g / L, sodium saccharin 1.0g / L, 1,4-butynediol 0.64g / L, glacial acetic acid 0.04g / L;
[0033] (1.2) Constant current electrochemical deposition was performed at a current density of 60 mA / cm². 2 The electrodeposition time was 1 hour, and electrodeposition was performed on the metal pads to obtain... <111> Preferred orientation of nanotwinned Ni-xCo (x = 13 at.%); during electrodeposition, the temperature of the electrolyte solution was 64 ± 1 °C, the ratio of cathode to anode area was 1:50, the distance between cathode and anode was 60 mm, and the electrolyte solution was magnetically stirred at a speed of 1500 r / min.
[0034] Example 2
[0035] The present invention provides a method for constructing microbumps for 3D packaging, comprising the following steps:
[0036] (1) Using the first substrate 10 as one of the connection sites, a first metal pad (Cu pad) 20 is prepared on the first substrate 10 by electroplating (same as in Example 1). Then, a high-density substrate with a thickness of 50 μm is prepared on the first metal pad 20 by direct current electrodeposition. <111> Preferred-oriented nanotwins Ni-xCo (x = 50 at.%) are used as the under-bump metallization layer, i.e., the first under-bump metallization layer 30. After annealing (annealing temperature is 300℃), SnAgCu305 solder balls are implanted on it. After brazing and reflow, lead-free solder bumps 42 with a diameter of 20μm are formed. An intermetallic compound 70 with a consistent orientation is formed between the first under-bump metallization layer 30 and the lead-free solder bumps 42. The reflow temperature here is 260℃.
[0037] (2) Using the second substrate 20 as another bonding site, a second metal pad (Cu pad) 50 is fabricated on the second substrate 20 in the same manner as the first substrate. Then, a high-density substrate with a thickness of 50 μm is fabricated on the second metal pad 50 using the same method, namely, DC electrodeposition. <111> Preferred-oriented nanotwins Ni-xCo (x = 50 at%) are used as the under-bump metallization layer, i.e., the second under-bump metallization layer 60, so that the array patterns of the first under-bump metallization layer 30 and the second under-bump metallization layer 60 are the same.
[0038] (3) Align the lead-free solder bumps 42 and the metallization layer 60 under the second bump one by one and place them in contact to form an assembly;
[0039] (4) The assembly is heated to 260°C for brazing reflow. The lead-free brazing filler bump 42 melts and undergoes a brazing reaction, transforming into an intermetallic compound CoSn3(70, 80) with a more uniform orientation, resulting in micro-bumps (IMC) with a more uniform orientation. Figure 4 As shown, the formed CoSn3 intermetallic compounds (70, 80) are oriented as follows: <100> direction.
[0040] In steps (1) and (2), direct current electrodeposition is used to prepare the first metal pad 20 and the second metal pad 50, respectively. <111> The preferred orientation of the nanotwinned Ni-xCo is as follows:
[0041] (1.1) Preparation of electrolyte solution: Add nickel sulfate hexahydrate, sodium citrate dihydrate, cobalt sulfate heptahydrate, sodium dodecyl sulfate, sodium saccharin, 1,4-butynediol and glacial acetic acid to deionized water, stir to dissolve, filter with filter paper, and then adjust the pH value to 6.7 with 10wt% NaOH solution and sulfuric acid solution to obtain electrolyte solution; The concentration of each compound in electrolyte solution is: nickel sulfate hexahydrate 80g / L, cobalt sulfate heptahydrate 45g / L, sodium citrate dihydrate 60g / L, sodium dodecyl sulfate 0.05g / L, sodium saccharin 1.0g / L, 1,4-butynediol 0.64g / L, glacial acetic acid 0.04g / L;
[0042] (1.2) Constant current electrochemical deposition was performed at a current density of 60 mA / cm². 2 The electrodeposition time was 1.5 hours, and electrodeposition was performed on the metal pads to obtain... <111> Preferred orientation of nanotwinned Ni-xCo (x=50at%); during electrodeposition, the temperature of the electrolyte solution was 64±1℃, the ratio of cathode to anode area was 1:50, the distance between cathode and anode was 60mm, and the electrolyte solution was magnetically stirred at a speed of 1500r / min.
Claims
1. A method for constructing microbumps in intermetallic compounds with uniform orientation, characterized in that, Includes the following steps: (1) At least one metal pad is prepared at the two connection sites by electroplating, and then a metallization layer under the bump is prepared on the metal pad by direct current electrodeposition; wherein, the metallization layer under the bump is... <111> Preferred orientation of nanotwinned Ni-xCo; (2) Anneal the metallization layer under the bump of one of the connection sites. After annealing, Sn-based lead-free solder balls are planted on the metallization layer under the bump. After the balls are planted, brazing reflow is performed to prepare lead-free solder bumps. Intermetallic compounds Ni3Sn4 or CoSn3 with consistent orientation are formed at the interface between the lead-free solder bumps and the metallization layer under the bumps. (3) Align the lead-free solder bump and the metallization layer under the bump on another site to be connected, and place them in contact to form an assembly; heat the assembly for brazing reflow, and an intermetallic compound Ni3Sn4 or CoSn3 with consistent orientation is also formed at the interface between the metallization layer under the bump on another site to be connected and the lead-free solder bump.
2. The microbump construction method according to claim 1, characterized in that: In step (1), x represents the atomic percentage of cobalt in the nickel-cobalt alloy, and x is 13 at.%, 30 at.%, 50 at.%, or 70 at.%.
3. The microbump construction method according to claim 2, characterized in that: In step (1), the thickness of the metallization layer under the bump is 30-50 μm.
4. The microbump construction method according to claim 3, characterized in that: In step (1), DC electrodeposition is used to deposit metal pads on the two sites to be connected to prepare... <111> The preferred orientation of Ni-xCo nanotwins is achieved through the following steps: (1.1) Preparation of electrolyte solution: Add nickel sulfate hexahydrate, sodium citrate dihydrate, cobalt sulfate heptahydrate, sodium dodecyl sulfate, sodium saccharin, 1,4-butynediol and glacial acetic acid to deionized water, and adjust the pH of the solution to 6.7-7 to obtain the electrolyte solution; the concentrations of each compound in the electrolyte solution are: nickel sulfate hexahydrate 80-150 g / L, sodium citrate dihydrate 60-65 g / L, cobalt sulfate heptahydrate 5-45 g / L, sodium dodecyl sulfate 0.05-0.06 g / L, sodium saccharin 1.0-1.5 g / L, 1,4-butynediol 0.64-0.65 g / L, glacial acetic acid 0.04-0.05 g / L; (1.2) Perform constant current electrochemical deposition at a current density of 60–65 mA / cm². 2 The electrodeposition time is 1-2 hours, and electrodeposition is performed on the metal pads to obtain... <111> Preferred orientation of nanotwins Ni-xCo.
5. The microbump construction method according to claim 4, characterized in that: During electrodeposition, the ratio of cathode to anode area is 1:50, and the distance between cathode and anode is 60 mm. The temperature of the electrolyte solution is 64±1℃, and the electrolyte solution is stirred magnetically at a speed of 1500 r / min.
6. The microbump construction method according to claim 1, characterized in that: In step (2), when x is 13 at.%, the annealing temperature is 250°C; when x is 50 at.%, the annealing temperature is 300°C.
7. The microbump construction method according to claim 1, characterized in that: In step (2), the Sn-based lead-free solder is SnAgCu3O5 or SnAgCu3O5; the Sn content in the Sn-based lead-free solder is greater than 50 wt.%.
8. The microbump construction method according to claim 1, characterized in that: In step (2), the reflow temperature for brazing reflow is 250-270℃.
9. The microbump construction method according to claim 1, characterized in that: In step (3), the reflow temperature for brazing reflow is 250-270℃.
10. The microbump construction method according to claim 1, characterized in that: In step (2), the diameter of the lead-free solder bump is 20-80 μm.