CN114453694A - Method for realizing self-healing of inter-metal compound internal Cokendall holes in welding spots - Google Patents

Method for realizing self-healing of inter-metal compound internal Cokendall holes in welding spots Download PDF

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Publication number
CN114453694A
CN114453694A CN202210151986.7A CN202210151986A CN114453694A CN 114453694 A CN114453694 A CN 114453694A CN 202210151986 A CN202210151986 A CN 202210151986A CN 114453694 A CN114453694 A CN 114453694A
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healing
welding spot
self
inter
holes
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刘志权
周士祺
薛森明
孙蓉
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Shenzhen Institute of Advanced Electronic Materials
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Shenzhen Institute of Advanced Electronic Materials
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K1/00—Soldering, e.g. brazing, or unsoldering
    • B23K1/012—Soldering with the use of hot gas
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K1/00—Soldering, e.g. brazing, or unsoldering
    • B23K1/20—Preliminary treatment of work or areas to be soldered, e.g. in respect of a galvanic coating

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  • Mechanical Engineering (AREA)
  • Electroplating Methods And Accessories (AREA)

Abstract

The invention discloses a method capable of realizing self-healing of inter-metal compound inner kirkendall holes in welding spots, and belongs to the technical field of three-dimensional packaging interconnection welding spots. The method adopts tin-based solder, takes (111) oriented nano twin crystal copper as a substrate metallization layer (UBM) material, and carries out constant temperature placement treatment after reflow soldering, thereby realizing the self-healing of the Kirkinjal holes in the intermetallic compounds in the soldering point. After constant temperature aging, Cu in welding spot3The average thickness of Sn is not more than 2 mu m, and more than 85% of Cokendall holes in the obtained welding spot can achieve self-healing. The invention reduces the defects caused by the generation of holes in the IMC layer, thereby improving the service reliability of the welding spots.

Description

Method for realizing self-healing of inter-metal compound internal Cokendall holes in welding spots
Technical Field
The invention relates to the technical field of three-dimensional packaging interconnection welding spots, in particular to a method capable of realizing self-healing of inter-metal compound internal kirkendall holes in welding spots.
Background
In the manufacturing process of microelectronic products, the realization of interconnection between a chip and a package carrier or between a package carrier and a printed circuit board through a solder reflow process is one of the most important technologies of electronic packages. At present, the size of electronic components is continuously reduced, and the performance requirement is continuously improved, so the reliability requirement of advanced packaging on welding spots is also continuously improved.
In the sandwich structure of the welding spot, copper (Cu) has good electric conduction, heat conduction, electromigration resistance and low costIs often chosen as the substrate metallization (UBM) material. In addition, the solder is generally selected from tin (Sn) -based solder because Sn has excellent wettability on Cu and Sn can generate Cu with Cu in the reflow soldering process6Sn5And Cu3And the Sn two-metal compound layer (IMC layer) forms a reliable metal interconnection structure. In addition, the solder formed by combining Sn and other elements has a wider melting point range, and different solders can accord with different application scenes. Commonly used Sn-based solders include SAC305, SnIn, eutectic SnBi, SnBiAg, and SnPb, among others.
With the progress of miniaturization in recent years, some new and troublesome problems and development limitations have come to be raised. Firstly, controlling the growth thickness and crystal orientation of the IMC layer inside the solder joint and suppressing the generation of kirkendall pores are the latest issues in the scientific research community. Secondly, the small-sized welding spots have higher requirements on the electromigration resistance, the heat conduction, the electric conduction and the mechanical property of the UBM material. This requires researchers to develop new UBM materials to replace the conventional Cu.
There are a number of reports that during the service life of the device, due to the difference of relative diffusion rates of Cu and Sn, kirkendall pores are distributed sporadically at the Sn/Cu interface first, and then, the sporadically pores are gradually enlarged. Particularly in a tiny welding spot, the heat conduction, the electric conduction and the mechanical property of the welding spot can be greatly influenced. If the kirkendall holes continue to grow and grow, a fracture layer is finally formed, and therefore the welding spot can completely fail. Currently, there are several methods for inhibiting the formation of kirkendall pores. For example, a secondary plating process such as nickel (Ni) plating is performed on the Cu UBM surface; or adding a new phase, such as zinc (Zn), to the solder. The measures can achieve the purpose of adjusting the element composition of the interface IMC layer or inhibiting the growth of the interface IMC layer, thereby indirectly inhibiting the generation and growth of the kirkendall holes. However, both the surface treatment of UBMs and the development of new composition solders require additional research and processing costs.
In view of the above, the growth of kirkendall pores in current advanced packages can only be inhibited. How to achieve the self healing of the kirkendall hole is not an effective method at present.
Disclosure of Invention
In order to solve the problems of generation and growth of Kirkdale holes in the Sn/Cu interface in the later service process in the prior art, the invention aims to provide a method for realizing the self-healing of the Kirkdale holes in the intermetallic compound in a welding spot, wherein tin-based solder and a specific (111) oriented nano twin crystal copper base material (adopting (111) nt-Cu as UBM) are adopted in the method, and the self-healing of the Kirkdale holes in the intermetallic compound in the welding spot is realized through a post-treatment process after reflow soldering. At the same time, Cu3The growth of the Sn IMC layer is fully inhibited, and the service reliability of the welding spot using (111) nt-Cu as the UBM is improved.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a method for realizing self-healing of Kirkdall holes in intermetallic compounds in a welding spot adopts tin-based solder, takes (111) oriented nano twin crystal copper as a substrate metallization layer (UBM) material, and carries out constant temperature placement treatment after reflow soldering, thereby realizing self-healing of the Kirkdall holes in the intermetallic compounds in the welding spot.
The method specifically comprises the following steps:
(1) preparing a Cu substrate: providing a silicon (Si) wafer with a Cu seed layer, and electroplating a Cu film on the Si wafer with the Cu seed layer through an electroplating process to obtain a Cu substrate; the Cu thin film is (111) oriented nano twin crystal copper;
(2) reflow soldering: coating Sn-based solder on the Cu substrate prepared in the step (1), and placing the formed sandwich structure in a reflow furnace for reflow soldering;
(3) placing at constant temperature: and (3) placing the welding spot prepared after reflow soldering in the step (2) into a constant-temperature oil bath, and performing constant-temperature aging for a certain time at a certain temperature to realize the self-welding spot of the Kerkadal hole in the intermetallic compound in the welding spot.
Further, in the step (1), the Cu seed layer completely and uniformly covers the Si wafer surface.
Further, in the step (1), the thickness of the electroplated Cu film is 5-100 μm, and the texture coefficient of (111) crystal orientation of Cu on the surface of the Cu film is 70-100%.
Further, in the step (2), the maximum temperature of the reflow soldering is 280-300 ℃, the maintaining time under the maximum temperature condition is 30-60 s, the atmosphere is a nitrogen atmosphere, and the cooling rate in the cooling stage is 5-10 ℃/min, so that the welding point is finally formed.
Further, in the step (3), the temperature of the constant temperature aging is 150-.
Further, in the step (3), the temperature of the constant temperature aging is preferably 160-.
After the constant temperature aging of the step (3), Cu in the welding spot3The Sn thickness is not more than 2 μm.
After the constant temperature aging in the step (3), more than 85% of the Kenkard holes in the obtained welding spot can be self-healed.
The invention has the following advantages and beneficial effects:
1. the invention provides a method for self-healing of a kirkendall hole in an IMC layer in a welding spot, which has the advantages of simple steps, compatibility with the traditional packaging process, low requirement on packaging equipment and convenience for mass production.
2. The UBM material is (111) nt-Cu, and is matched with a specific aging process, so that the UBM material has a tendency of replacing commercial Cu in future advanced packages.
3. According to the invention, (111) nt-Cu is used as a UBM material, and then a welding spot is treated by a specific process, so that most of grown Cokendall holes can be self-healed. And after prolonged aging time, the kirkendall pores do not regrow. The defects caused by holes in the IMC layer are reduced, and therefore the service reliability of the welding spots is improved.
4. In the process of self-healing of the kirkendall hole, the Cu is added3The thickness of the Sn layer also decreases, so the overall IMC layer thickness does not go any further over the extended aging timeThe service reliability of the welding spot is improved due to the increase of the steps.
Drawings
Fig. 1 shows a solder joint structure in examples 1 to 2.
FIG. 2 shows the distribution of IMC and Cokendall pores at Sn/(111) nt-Cu interface in example 1; the self-healing phenomenon of the kirkendall holes is obvious; wherein: (a) aging for 96 hours; (b) aging for 288 hours.
FIG. 3 shows Cu after reflow soldering of a conventional pure Cu substrate3Sn layer and Cu after the process of the invention3A Sn layer; wherein: (a) carrying out conventional pure Cu substrate and reflow soldering; (b) the invention relates to (111) nt-Cu + reflow soldering + aging.
In the figure: 1-solder, 2-electroplated (111) nt-Cu layer, 3-Cu seed layer and 4-Si substrate.
Detailed Description
For a further understanding of the present invention, the following description is given in conjunction with the examples which are set forth to illustrate, but are not to be construed to limit the present invention, features and advantages.
In the following examples, reference is made to the patent for the process of electroplating a Cu film on a Si wafer (ZL201910956876.6, a method for preparing a copper film material with a full nano twin structure; ZL201410709245.1, a directionally grown copper pillar bump interconnection structure and a method for preparing the same).
Examples example 1
The process for preparing the solder joint structure in this embodiment is as follows:
1. preparing a Cu substrate: providing a silicon (Si) wafer with a Cu seed layer, and electroplating a Cu film, namely a (111) nt-Cu layer 2 on the Si wafer (Si substrate 4) with the Cu seed layer 3 through an electroplating process, wherein the texture coefficient of the Si wafer is 99%, and the thickness of the Si wafer is 20 μm.
2. Brazing: pure Sn solder 1 was applied to the Cu substrate manufactured in step 1, as shown in fig. 1, and the sandwich structure was placed in a reflow furnace for reflow soldering without setting a preheating time and maintained at 300 ℃ for 60 seconds in a nitrogen atmosphere.
3. Placing at constant temperature: placing the welding spots prepared after reflow soldering in the step 2And (4) aging for 288h at 170 ℃ in a constant-temperature oil bath. As shown in fig. 2(b), after aging for 288h, over 90% of the kirkendall holes were self-healed. Cu at the spot of soldering, as shown in FIG. 3(b)3The Sn thickness was 2 microns.
Comparative example 1:
the difference from the embodiment 1 is that: in the step (3), the aging time is 96h, as shown in fig. 2(a), after aging for 96h, the kirkendall pores are obvious and densely distributed.
Comparative example 2:
the difference from the embodiment 1 is that: in the step (3), the aging temperature is 130 ℃, and the aging time is 96h, and the Kerkadal holes are obvious through testing; after the aging time is adjusted to 288h, the Kerkadal holes are still more obvious through testing.
Comparative example 3:
the difference from the embodiment 1 is that: when a Cu substrate is prepared, a conventional pure Cu film is plated on a Cu seed layer, then reflow soldering and aging at 170 ℃ are carried out for 288h according to the process of example 1, and then the Cu at a welding point is tested3The Sn thickness was 4 microns, as in fig. 3(a), significantly thicker than example 1.
Example 2:
the process for preparing the solder joint structure in this embodiment is as follows:
1. preparing a Cu substrate: providing two silicon (Si) wafers with Cu seed layers, and electroplating a Cu film on the Si wafers with the Cu seed layers through an electroplating process, wherein the texture coefficient of the Cu film is 70%, and the thickness of the Cu film is 40 mu m.
2. Brazing: pure Sn solder is used and coated on the Cu substrate manufactured in the step 1, as shown in figure 1, the sandwich structure is placed in a reflow furnace for reflow soldering, the preheating temperature is set to be 100 ℃, the time is set to be 60 seconds, and the preheating temperature is maintained for 30 seconds at 300 ℃ in a nitrogen atmosphere.
3. Placing at constant temperature: and (3) placing the welding spot prepared after reflow soldering in the step (2) into a constant-temperature oil bath, and aging for 264 hours at 170 ℃. After 264 hours of aging, testing, and completing self-healing of more than 90% of Kenkard holes.

Claims (9)

1. A method for realizing self-healing of a kirkendall hole in an intermetallic compound in a welding spot is characterized in that: the method adopts tin-based solder, takes (111) oriented nano twin crystal copper as a substrate metallization layer (UBM) material, and carries out constant temperature placement treatment after reflow soldering, thereby realizing the self-healing of the Kirkinjal holes in the intermetallic compounds in the soldering point.
2. The method for realizing self-healing of the inter-metal compound intracukendal hole in the welding spot according to claim 1, wherein the method comprises the following steps: the method comprises the following steps:
(1) preparing a Cu substrate: providing a silicon (Si) wafer with a Cu seed layer, and electroplating a Cu film on the Si wafer with the Cu seed layer through an electroplating process to obtain a Cu substrate; the Cu thin film is (111) oriented nano twin crystal copper;
(2) reflow soldering: coating Sn-based solder on the Cu substrate prepared in the step (1), and placing the formed sandwich structure in a reflow furnace for reflow soldering;
(3) placing at constant temperature: and (3) placing the welding spot prepared after reflow soldering in the step (2) into a constant-temperature oil bath, and aging at constant temperature for a certain time to obtain the welding spot with the self-healing function of the Kerkatier hole in the intermetallic compound in the welding spot.
3. The method for realizing self-healing of the inter-metal compound intracrkinjal hole in the welding spot according to claim 2, wherein: in the step (1), the Cu seed layer completely and uniformly covers the surface of the Si wafer.
4. The method capable of realizing self-healing of intermetallic inter-metal compound pores in welding spots according to claim 2, characterized in that: in the step (1), the thickness of the electroplated Cu film is 5-100 μm, and the texture coefficient of (111) crystal orientation of Cu on the surface of the Cu film is 70-100%.
5. The method for realizing self-healing of the inter-metal compound intracrkinjal hole in the welding spot according to claim 2, wherein: in the step (2), the maximum temperature of the reflow soldering is 280-300 ℃, the maintaining time under the condition of the maximum temperature is 30-60 s, the atmosphere is a nitrogen atmosphere, and the cooling rate in the cooling stage is 5-10 ℃/min, so that the welding spot is finally formed.
6. The method for realizing self-healing of the inter-metal compound intracrkinjal hole in the welding spot according to claim 2, wherein: in the step (3), the temperature of the constant temperature aging is 150-200 ℃ (130℃)
The holes can not completely disappear even if the time is long), and the constant-temperature time is 100-300 h.
7. The method for realizing self-healing of the inter-metal compound intracrkinjal hole in the welding spot according to claim 2, wherein: in the step (3), the temperature of the constant temperature aging is 185 ℃, and the time of the constant temperature aging is 200-300 h.
8. The method capable of realizing self-healing of intermetallic inter-metal compound pores in welding spots according to claim 2, characterized in that: after the constant temperature aging of the step (3), Cu in the welding spot3The average thickness of Sn is not more than 2 μm.
9. The method capable of realizing self-healing of intermetallic inter-metal compound pores in welding spots according to claim 2, characterized in that: after the constant temperature aging in the step (3), more than 85% of the Kenkard holes in the obtained welding spot can be self-healed.
CN202210151986.7A 2022-02-18 2022-02-18 Method for realizing self-healing of inter-metal compound internal Cokendall holes in welding spots Pending CN114453694A (en)

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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
TW201323131A (en) * 2011-12-14 2013-06-16 Univ Yuan Ze Method for suppressing kirkendall voids formation at the interface between solder and Cu pad
JP2014036966A (en) * 2012-08-11 2014-02-27 Senju Metal Ind Co Ltd Solder for electric power
CN105097746A (en) * 2015-07-07 2015-11-25 中国科学院上海微系统与信息技术研究所 Nano twin copper-based under bump metal layer and preparation method thereof
CN107195605A (en) * 2017-05-18 2017-09-22 上海交通大学 Cuprum-nickel-stannum micro bump using thin nickel dam as barrier layer and preparation method thereof
CN110707069A (en) * 2019-10-10 2020-01-17 深圳先进电子材料国际创新研究院 Copper pillar bump interconnection structure and preparation method thereof
CN111607811A (en) * 2020-07-06 2020-09-01 苏州清飙科技有限公司 Preparation method and application of copper-copper bonding material

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
TW201323131A (en) * 2011-12-14 2013-06-16 Univ Yuan Ze Method for suppressing kirkendall voids formation at the interface between solder and Cu pad
JP2014036966A (en) * 2012-08-11 2014-02-27 Senju Metal Ind Co Ltd Solder for electric power
CN105097746A (en) * 2015-07-07 2015-11-25 中国科学院上海微系统与信息技术研究所 Nano twin copper-based under bump metal layer and preparation method thereof
CN107195605A (en) * 2017-05-18 2017-09-22 上海交通大学 Cuprum-nickel-stannum micro bump using thin nickel dam as barrier layer and preparation method thereof
CN110707069A (en) * 2019-10-10 2020-01-17 深圳先进电子材料国际创新研究院 Copper pillar bump interconnection structure and preparation method thereof
CN111607811A (en) * 2020-07-06 2020-09-01 苏州清飙科技有限公司 Preparation method and application of copper-copper bonding material

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