CN114211068B - Method for forming welding spots of full IMCs structure through prefabricated IMCs welding pads - Google Patents

Method for forming welding spots of full IMCs structure through prefabricated IMCs welding pads Download PDF

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Publication number
CN114211068B
CN114211068B CN202111660949.0A CN202111660949A CN114211068B CN 114211068 B CN114211068 B CN 114211068B CN 202111660949 A CN202111660949 A CN 202111660949A CN 114211068 B CN114211068 B CN 114211068B
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imcs
solder
full
remelting
welding
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CN114211068A (en
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汉晶
孟洲
郭福
马立民
晋学轮
李子萱
陈玉章
贾强
周炜
王乙舒
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Beijing University of Technology
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Beijing University of Technology
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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
    • B23K1/0008—Soldering, e.g. brazing, or unsoldering specially adapted for particular articles or work
    • B23K1/0016—Brazing of electronic components
    • 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
    • B23K1/203—Fluxing, i.e. applying flux onto surfaces
    • 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
    • B23K1/206—Cleaning
    • 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
    • B23K3/00—Tools, devices, or special appurtenances for soldering, e.g. brazing, or unsoldering, not specially adapted for particular methods
    • B23K3/08—Auxiliary devices therefor
    • B23K3/085—Cooling, heat sink or heat shielding means
    • 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
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
    • B23K35/0222—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape for use in soldering, brazing
    • 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
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
    • B23K35/24—Selection of soldering or welding materials proper
    • B23K35/28—Selection of soldering or welding materials proper with the principal constituent melting at less than 950 degrees C
    • B23K35/282—Zn as the principal constituent

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Electric Connection Of Electric Components To Printed Circuits (AREA)

Abstract

The invention discloses a method for forming a welding spot of a full IMCs structure through a prefabricated IMCs welding spot, which belongs to the field of material preparation and connection, is suitable for preparing a miniature brazing butt joint of the full IMCs, is applied to the study of the mechanical, thermal and electrical reliability of microelectronic connection, and is realized through the following steps: solder printing; heating and remelting the solder to form a solder ball; selecting solder balls according to the size requirement; placing the solder balls on the copper sheets on the surface of the printed circuit board, and heating, remelting and combining to form a bump structure; corroding the bump structure; two IMCs bonding pads are manufactured; heating and remelting to bond the IMCs bonding pads; and grinding and finely polishing the welding spots of the IMCs welding spots to finally obtain the full IMCs welding spots. The invention can avoid the condition that the Sn anisotropy in the Sn-based solder reduces the reliability of the welding spot; simple process and low cost. The key step of the invention is that solder is coated on the prefabricated IMCs bonding pad for remelting and cooling, and the welding spot component is determined to be IMCs by EDS technology.

Description

Method for forming welding spots of full IMCs structure through prefabricated IMCs welding pads
Technical Field
The invention relates to the field of material preparation and connection, in particular to a method for forming a welding spot with a full IMCs structure through a prefabricated IMCs welding spot.
Background
The welding spots play roles in mechanical connection and electric signal transmission in the microelectronic interconnection, so that the microelectronic packaging space is reduced, the number of components is increased, and the heat generation of the components is increased; and the current density born by the welding spot is increased, and under the drive of thermodynamic and kinetic factors, IMCs formed in the welding flux can grow or dissolve, so that the welding spot is invalid, and the service life and the reliability of the electronic product are influenced.
The solder used in the microelectronic interconnection is mainly Sn-based solder (the Sn content is more than 80%), and studies have shown that the Sn-based lead-free interconnection solder joint prepared by melting tends to have a single crystal or twin crystal structure, while the BCT crystal structure of β -Sn has anisotropy (a=b=0.5832, c=0.3182, c/a=0.546), the diffusion of atoms such as Cu in the solder joint can have strong anisotropy due to the different grain orientations of β -Sn, for example, at 25 ℃, the diffusion rate of Cu along the c-axis of the β -Sn lattice is 2 x 10 "6 cm2/s which is 500 times the diffusion rate along the a-b axis, the oriented diffusion behavior will have a serious influence on the electromigration behavior of the solder joint, the Sn-based solder single crystal solder joint with the c-axis parallel to the current direction tends to fail in advance, and the growth rate of interfacial IMCs is about 10 times that of the single crystal solder joint or twin crystal solder joint with the c-axis perpendicular to the current direction. Therefore, avoiding the effect of the beta-Sn anisotropy in the solder joint is a difficult problem. After the interconnection is completed, each welding spot has unique crystal orientation, so that some welding spots inevitably fail in advance in the use process of the electronic product due to the adverse orientation of beta-Sn crystal grains, and the service life of the electronic product is further reduced. It follows that the grain orientation of the solder joint can seriously affect its service reliability.
Disclosure of Invention
The invention aims to provide a method for forming a welding spot of a full IMCs structure through prefabricating an IMCs welding spot, so as to solve the problems existing in the prior art, obtain the welding spot of the full IMCs structure, avoid the influence of beta-Sn anisotropy, and simultaneously ensure that lower-temperature bonding and higher-temperature service are realized in microelectronic interconnection.
In order to achieve the above object, the present invention provides the following solutions: the invention provides a method for forming a welding spot with a full IMCs structure through a prefabricated IMCs welding spot, which is realized through the following steps:
step S1: solder printing;
step S2: heating and remelting the solder subjected to the stencil printing to form a solder ball, and performing cooling treatment;
step S3: ultrasonic cleaning the solder balls;
step S4: selecting the solder balls according to the size requirement;
step S5: ultrasonic cleaning treatment of the printed circuit board;
step S6: placing the solder balls on the copper sheets on the surface of the printed circuit board, heating, remelting, combining and forming a bump structure, and performing cooling treatment;
step S7: corroding the bump structure to ensure that only IMCs bonding pads are left on the copper sheet of the printed circuit board;
step S8: forming two IMCs bonding pads from the step S1 to the step S7;
step S9: heating and remelting to bond the two IMCs bonding pads, and cooling;
step S10: grinding welding spots of the two IMCs bonding pads, and finely polishing a designated interface to finally obtain a full IMCs welding spot;
step S11: EDS data of the finish polishing section are obtained, and whether the welding spot is a welding spot composed of IMCs or not is determined.
Preferably, the solder is Sn-Ag-Bi-In series lead-free solder.
Preferably, in the step S2, the step S6 and the step S9, a hot air welding device is used for performing a heating remelting treatment, and the remelting temperature is 220 ℃ to 280 ℃.
Preferably, in the step S2, the step S6, and the step S9, the cooling treatment is performed by any one of furnace cooling, air cooling, and water cooling.
Preferably, in the step S3, acetone and ethanol are used to clean the solder balls in an ultrasonic cleaner.
Preferably, in the step S5, the surface of the printed circuit board is cleaned with ethanol in an ultrasonic cleaner.
Preferably, in the step S7, the bump structure is corroded by using a nitric acid-ethanol-water solution after welding, and all Sn is ensured to be corroded through observation of a metallographic microscope, so that IMCs at the Cu-Sn interface are retained.
Preferably, a layer of flux is coated on the printed circuit board between the step S5 and the step S6.
Preferably, in the step S9, any one of the IMCs pads is inverted and placed in parallel and perfect alignment with the other IMCs pad, and the two IMCs pads are bonded by heat reflow.
Preferably, in step S8, the surfaces of the two manufactured IMCs pads are coated with the combustion improver and the solder in sequence.
The invention discloses the following technical effects: by using the method, the welding spots with the full IMCs structure can be obtained, and the influence of beta-Sn anisotropy can be avoided. In addition, as the melting point of the IMCs is higher than that of the Sn-based solder, the bonding at a lower temperature and the service at a higher temperature in microelectronic interconnection can be ensured, and the situation that the reliability of the solder joint is reduced due to the anisotropy of Sn in the Sn-based solder joint can be avoided by predicting the solder joint with a full IMCs structure. The method has the advantages of low cost and low process flow.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings that are needed in the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a photograph of a screen with different apertures during the screen printing process of the present invention;
FIG. 2 is a SEM photograph of a solder joint according to the present invention;
FIG. 3 is a photograph of an EDS analysis of a weld of the present invention of a full IMCs structure;
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
The invention provides a method for forming a welding spot with a full IMCs structure through a prefabricated IMCs welding spot, belongs to the field of material preparation and connection, is suitable for welding spots with low-temperature combined high-temperature service characteristics in microelectronic interconnection, and is applied to the study of the reliability of mechanics, thermal and electricity of microelectronic connection. The invention aims to avoid the influence of Sn anisotropy on the reliability and service life of a welding spot in microelectronic interconnection and manufacture the welding spot with the full IMCs structure. Meanwhile, the characterization can be carried out through the tests of the full IMCs welding spots such as mechanics, heat and electricity, so that the knowledge level of how the full IMCs structure affects the reliability and the service life of the welding spots is improved, and the purpose of evaluating the reliability of the welding spots is achieved. Referring to fig. 1-3, in order to achieve the above-mentioned object, the present invention provides a method for forming a solder joint of a full IMCs structure by prefabricating an IMCs solder pad, which is implemented by the following steps:
step S1: solder printing, namely, carrying out screen printing on Sn-Ag-Bi-In solder on a glass plate;
step S2: heating and remelting the solder subjected to the screen printing through hot air welding equipment to form a solder ball, and performing cooling treatment;
step S3: ultrasonic cleaning the solder balls, and cleaning the solder balls in an ultrasonic cleaner by using acetone and ethanol in sequence;
step S4: selecting solder balls according to the size requirement, and selecting the solder balls meeting the size requirement for standby under a stereoscopic microscope;
step S5: ultrasonic cleaning the printed circuit board, namely cleaning the surface of the printed circuit board (Printed circuit board, also called as PCB) by using ethanol in an ultrasonic cleaner, and coating a layer of soldering flux on the printed circuit board;
step S6: placing the prefabricated Sn-Ag-Bi-In solder balls on the copper sheets on the surface of the printed circuit board, heating the solder balls by using hot air welding equipment to remelt the solder balls and combining the solder balls with the copper sheets on the printed circuit board, and performing cooling treatment;
step S7: corroding the bump structure, corroding the welded bump structure by using a nitric acid-ethanol-water solution (volume ratio is 1:1:8), ensuring that all Sn is corroded through a metallographic microscope, and retaining intermetallic compounds (Intermetallic compound, hereinafter called IMC) at a Cu-Sn interface;
step S8: two IMCs bonding pads are manufactured by the steps S1 to S7;
step S9: heating and remelting to bond the two IMCs bonding pads, and cooling;
step S10: grinding welding spots of the two IMCs bonding pads, and finely polishing a designated interface to finally obtain a full IMCs welding spot;
step S11: EDS data of the finish polishing section are obtained, and whether the welding spot is a welding spot composed of IMCs or not is determined.
The invention has the advantage that the condition that the reliability of the welding spot is reduced due to the anisotropy of Sn in the welding spot of the Sn-based solder can be avoided by predicting the welding spot with the full IMCs structure. Simple process and low cost.
Further optimizing scheme, the solder is Sn-Ag-Bi-In series lead-free solder.
In a further optimization scheme, in the step S2, the step S6 and the step S9, hot air welding equipment is adopted for heating remelting treatment, and the remelting temperature is 220-280 ℃.
In a further optimized scheme, in the step S2, the step S6 and the step S9, the cooling treatment mode is any one of furnace-following cooling, air cooling and water cooling.
In a further optimized scheme, in step S7, the welded bump structure is corroded by using a nitric acid-ethanol-water solution, all Sn is guaranteed to be corroded through observation of a metallographic microscope, and IMCs at a Cu-Sn interface are reserved.
In a further optimization scheme, in step S8, combustion improver and solder are respectively coated on the surfaces of two manufactured IMCs bonding pads In sequence, before the solder is coated, sn-Ag-Bi-In solder is subjected to screen leakage printing on a glass plate, and a flat head toothpick is used for scraping the solder on the glass plate and coating the solder on the IMCs bonding pads.
In a further optimization scheme, in step S9, any IMCs bonding pad is inverted and placed in parallel and completely aligned with the other IMCs bonding pad, the solder in the middle of the two side IMCs bonding pads is remelted by using hot air welding equipment, the bonding of the two side IMCs bonding pads and the solder is ensured, and cooling treatment is carried out.
The method can obtain the welding spots with the full IMCs structure, and can avoid the influence of beta-Sn anisotropy. In addition, the melting point of the IMCs is higher than that of the Sn-based solder, so that the bonding at a lower temperature and the service at a higher temperature in microelectronic interconnection can be ensured.
Example 1
Referring to fig. 1-3, the present embodiment provides a method for forming a solder joint of a full IMCs structure by prefabricating an IMCs solder joint, the method being implemented by:
step S1: the Sn-Ag-Bi-In solder is screen printed on a glass plate through a screen, and the screen size is 700 mu m;
step S2: heating the solder after the screen printing to form a solder ball with the size of 700 mu m by a hot air welding device (PACE ST325, the same applies below), wherein the remelting temperature is 245 ℃, the remelting time is 30s, and cooling for 30s along with a furnace;
step S3: sequentially using acetone and ethanol to clean the solder balls in an ultrasonic cleaner;
step S4: selecting solder balls meeting the size requirement under a stereoscopic microscope for standby;
step S5: cleaning the surface of the printed circuit board by using ethanol in an ultrasonic cleaner, and coating a layer of soldering flux on the printed circuit board;
step S6: placing the prefabricated Sn-Ag-Bi-In solder balls on the copper sheets on the surface of the printed circuit board, and heating the solder balls by using hot air welding equipment to remelt the solder balls and combine the solder balls with the copper sheets on the printed circuit board, wherein the remelting temperature is 245 ℃, the remelting time is 30s, and cooling the solder balls with a furnace for 30s;
step S7: corroding the welded bump structure by using a nitric acid-ethanol-water solution (volume ratio is 1:1:8), and observing through a metallographic microscope to ensure that all Sn is corroded and remain IMCs at a Cu-Sn interface;
step S8: coating soldering flux on the surface of a bonding pad (hereinafter referred to as an IMC bonding pad) of the IMC;
step S9: the Sn-Ag-Bi-In solder is subjected to screen printing on a glass plate through a screen, wherein the screen size is 250 mu m;
step S10: scraping and coating the solder on the glass plate on the IMC bonding pad by using a flat head toothpick;
step S11: placing any IMC bonding pad structure upside down in parallel and completely aligned with another IMCs bonding pad;
step S12: and (3) heating the structure completed in the step S11 by using hot air welding equipment to reflow the solder in the middle of the IMCs bonding pads on the two sides, ensuring the bonding of the IMCs bonding pads on the two sides and the solder, and cooling. Remelting at 245 ℃ for 30s, and cooling the equipment for 30s;
step S13: grinding the welding spots, and finely polishing the appointed interface to finally obtain the full IMCs welding spots;
step S14: EDS data of the polished section are obtained, and the micro-interconnection welding spots composed of IMCs with preferred orientation are determined.
Example 2
Referring to fig. 1-3, the present embodiment provides a method for forming a solder joint of a full IMCs structure by prefabricating an IMCs solder joint, the method being implemented by:
step S1: the Sn-Ag-Bi-In solder is screen printed on the glass plate through a screen, and the screen size is 650 mu m;
step S2: heating the solder after the screen printing to form a solder ball with the size of 650 mu m by a hot air welding device (PACE ST325, the same applies below), wherein the remelting temperature is 245 ℃, the remelting time is 30s, and cooling for 30s along with a furnace;
step S3: sequentially using acetone and ethanol to clean the solder balls in an ultrasonic cleaner;
step S4: selecting solder balls meeting the size requirement under a stereoscopic microscope for standby;
step S5: cleaning the surface of the printed circuit board by using ethanol in an ultrasonic cleaner, and coating a layer of soldering flux on the printed circuit board;
step S6: placing the prefabricated Sn-Ag-Bi-In solder balls on the copper sheets on the surface of the printed circuit board, and heating the solder balls by using hot air welding equipment to remelt the solder balls and combine the solder balls with the copper sheets on the printed circuit board, wherein the remelting temperature is 245 ℃, the remelting time is 30s, and cooling the solder balls with a furnace for 30s;
step S7: corroding the welded bump structure by using a nitric acid-ethanol-water solution (volume ratio is 1:1:8), and observing through a metallographic microscope to ensure that all Sn is corroded and remain IMCs at a Cu-Sn interface;
step S8: coating soldering flux on the surface of a bonding pad (hereinafter referred to as an IMC bonding pad) of the IMC;
step S9: the Sn-Ag-Bi-In solder is subjected to screen printing on a glass plate through a screen, wherein the screen size is 200 mu m;
step S10: scraping and coating the solder on the glass plate on the IMC bonding pad by using a flat head toothpick;
step S11: placing any IMC bonding pad structure upside down in parallel and completely aligned with another IMCs bonding pad;
step S12: and (3) heating the structure completed in the step S11 by using hot air welding equipment to reflow the solder in the middle of the IMCs bonding pads on the two sides, ensuring the bonding of the IMCs bonding pads on the two sides and the solder, and cooling. Remelting at 245 ℃ for 30s, and cooling the equipment for 30s;
step S13: grinding the welding spots, and finely polishing the appointed interface to finally obtain the full IMCs welding spots;
step S14: EDS data of the polished section are obtained, and the micro-interconnection welding spots composed of IMCs with preferred orientation are determined.
Example 3
Referring to fig. 1-3, the present embodiment provides a method for forming a solder joint of a full IMCs structure by prefabricating an IMCs solder joint, the method being implemented by:
step S1: the Sn-Ag-Bi-In solder is screen printed on a glass plate through a screen, and the screen size is 700 mu m;
step S2: heating the solder after the screen printing to form solder balls with the size of 700 mu m by a hot air welding device (PACE ST325, the same applies below), wherein the remelting temperature is 220 ℃, the remelting time is 40s, and the solder balls are cooled for 40s along with a furnace;
step S3: sequentially using acetone and ethanol to clean the solder balls in an ultrasonic cleaner;
step S4: selecting solder balls meeting the size requirement under a stereoscopic microscope for standby;
step S5: cleaning the surface of the printed circuit board by using ethanol in an ultrasonic cleaner, and coating a layer of soldering flux on the printed circuit board;
step S6: placing the prefabricated Sn-Ag-Bi-In solder balls on the copper sheets on the surface of the printed circuit board, and heating the solder balls by using hot air welding equipment to remelt the solder balls and combine the solder balls with the copper sheets on the printed circuit board, wherein the remelting temperature is 220 ℃, the remelting time is 40s, and cooling the solder balls with a furnace for 40s;
step S7: corroding the welded bump structure by using a nitric acid-ethanol-water solution (volume ratio is 1:1:8), and observing through a metallographic microscope to ensure that all Sn is corroded and remain IMCs at a Cu-Sn interface;
step S8: coating soldering flux on the surface of a bonding pad (hereinafter referred to as an IMC bonding pad) of the IMC;
step S9: the Sn-Ag-Bi-In solder is subjected to screen printing on a glass plate through a screen, wherein the screen size is 250 mu m;
step S10: scraping and coating the solder on the glass plate on the IMC bonding pad by using a flat head toothpick;
step S11: placing any IMC bonding pad structure upside down in parallel and completely aligned with another IMCs bonding pad;
step S12: and (3) heating the structure completed in the step S11 by using hot air welding equipment to reflow the solder in the middle of the IMCs bonding pads on the two sides, ensuring the bonding of the IMCs bonding pads on the two sides and the solder, and cooling. Remelting at 220 ℃ for 40s, and cooling the equipment for 40s;
step S13: grinding the welding spots, and finely polishing the appointed interface to finally obtain the full IMCs welding spots;
step S14: EDS data of the polished section are obtained, and the micro-interconnection welding spots composed of IMCs with preferred orientation are determined.
Example 4
Referring to fig. 1-3, the present embodiment provides a method for forming a solder joint of a full IMCs structure by prefabricating an IMCs solder joint, the method being implemented by:
step S1: the Sn-Ag-Bi-In solder is screen printed on a glass plate through a screen, and the screen size is 700 mu m;
step S2: heating the solder after the screen printing by a hot air welding device (PACE ST325, the same applies below) to form solder balls with the size of 700 mu m, wherein the remelting temperature is 280 ℃, the remelting time is 20s, and the solder balls are cooled for 20s along with a furnace;
step S3: sequentially using acetone and ethanol to clean the solder balls in an ultrasonic cleaner;
step S4: selecting solder balls meeting the size requirement under a stereoscopic microscope for standby;
step S5: cleaning the surface of the printed circuit board by using ethanol in an ultrasonic cleaner, and coating a layer of soldering flux on the printed circuit board;
step S6: placing the prefabricated Sn-Ag-Bi-In solder balls on the copper sheets on the surface of the printed circuit board, and heating the solder balls by using hot air welding equipment to remelt the solder balls and combine the solder balls with the copper sheets on the printed circuit board, wherein the remelting temperature is 280 ℃, the remelting time is 20s, and cooling the solder balls along with a furnace for 20s;
step S7: corroding the welded bump structure by using a nitric acid-ethanol-water solution (volume ratio is 1:1:8), and observing through a metallographic microscope to ensure that all Sn is corroded and remain IMCs at a Cu-Sn interface;
step S8: coating soldering flux on the surface of a bonding pad (hereinafter referred to as an IMC bonding pad) of the IMC;
step S9: the Sn-Ag-Bi-In solder is subjected to screen printing on a glass plate through a screen, wherein the screen size is 250 mu m;
step S10: scraping and coating the solder on the glass plate on the IMC bonding pad by using a flat head toothpick;
step S11: placing any IMC bonding pad structure upside down in parallel and completely aligned with another IMCs bonding pad;
step S12: and (3) heating the structure completed in the step S11 by using hot air welding equipment to reflow the solder in the middle of the IMCs bonding pads on the two sides, ensuring the bonding of the IMCs bonding pads on the two sides and the solder, and cooling. Remelting at 280 ℃ for 20s, and cooling the equipment for 20s;
step S13: grinding the welding spots, and finely polishing the appointed interface to finally obtain the full IMCs welding spots;
step S14: EDS data of the polished section are obtained, and the micro-interconnection welding spots composed of IMCs with preferred orientation are determined.
Example 5
The difference from the above-described embodiment 1 is only that the cooling by air cooling is selected for 20s.
Example 6
The difference from the above-mentioned example 1 is only that the cooling mode of water cooling was selected for 20s.
In the description of the present invention, it should be understood that the terms "longitudinal," "transverse," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like indicate or are based on the orientation or positional relationship shown in the drawings, merely to facilitate description of the present invention, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the present invention.
The above embodiments are only illustrative of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention, and various modifications and improvements made by those skilled in the art to the technical solutions of the present invention should fall within the protection scope defined by the claims of the present invention without departing from the design spirit of the present invention.

Claims (7)

1. A method for forming a welding spot of a full IMCs structure through a prefabricated IMCs welding spot is characterized by comprising the following steps:
step S1: solder printing;
step S2: heating and remelting the solder subjected to the stencil printing to form a solder ball, and performing cooling treatment;
step S3: ultrasonic cleaning the solder balls;
step S4: selecting the solder balls according to the size requirement;
step S5: ultrasonic cleaning treatment of the printed circuit board;
step S6: placing the solder balls on the copper sheets on the surface of the printed circuit board, heating, remelting, combining and forming a bump structure, and performing cooling treatment;
step S7: corroding the bump structure to ensure that only IMCs bonding pads are left on the copper sheet of the printed circuit board;
step S8: forming two IMCs bonding pads from the step S1 to the step S7;
step S9: heating and remelting to bond the two IMCs bonding pads, and cooling;
step S10: grinding welding spots of the two IMCs bonding pads, and finely polishing a designated interface to finally obtain a full IMCs welding spot;
step S11: EDS data of the finish polishing section are obtained, and whether the welding spots are the welding spots formed by IMCs or not is determined;
in the step S7, the welded bump structure is corroded by using a nitric acid-ethanol-water solution, all Sn is guaranteed to be corroded through observation of a metallographic microscope, and IMCs at a Cu-Sn interface are reserved;
in the step S9, any one of the IMCs pads is inverted and placed in parallel and complete alignment with the other IMCs pad, and the two IMCs pads are bonded by heating and remelting;
in the step S8, the surfaces of the two manufactured IMCs pads are respectively coated with flux and solder in sequence.
2. The method of forming a bond pad of a full IMCs structure from a prefabricated IMCs bond pad of claim 1, wherein: the solder is Sn-Ag-Bi-In series lead-free solder.
3. The method of forming a bond pad of a full IMCs structure from a prefabricated IMCs bond pad of claim 1, wherein: in the step S2, the step S6 and the step S9, hot air welding equipment is adopted for heating remelting treatment, and the remelting temperature is 220-280 ℃.
4. The method of forming a bond pad of a full IMCs structure from a prefabricated IMCs bond pad of claim 1, wherein: in the step S2, the step S6, and the step S9, the cooling treatment is performed by any one of furnace-mounted cooling, air cooling, and water cooling.
5. The method of forming a bond pad of a full IMCs structure from a prefabricated IMCs bond pad of claim 1, wherein: in the step S3, acetone and ethanol are used to clean the solder balls in an ultrasonic cleaner.
6. The method of forming a bond pad of a full IMCs structure from a prefabricated IMCs bond pad of claim 1, wherein: in the step S5, the surface of the printed circuit board is cleaned by ethanol in an ultrasonic cleaner.
7. The method of forming a bond pad of a full IMCs structure from a prefabricated IMCs bond pad of claim 1, wherein: and coating a layer of soldering flux on the printed circuit board between the step S5 and the step S6.
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