CN111584377A - Ultrasonic welding method - Google Patents
Ultrasonic welding method Download PDFInfo
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- CN111584377A CN111584377A CN201910121942.8A CN201910121942A CN111584377A CN 111584377 A CN111584377 A CN 111584377A CN 201910121942 A CN201910121942 A CN 201910121942A CN 111584377 A CN111584377 A CN 111584377A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
- H01L24/80—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected
- H01L24/81—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a bump connector
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
- H01L2224/80—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected
- H01L2224/81—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a bump connector
- H01L2224/81009—Pre-treatment of the bump connector or the bonding area
- H01L2224/8103—Reshaping the bump connector in the bonding apparatus, e.g. flattening the bump connector
- H01L2224/81031—Reshaping the bump connector in the bonding apparatus, e.g. flattening the bump connector by chemical means, e.g. etching, anodisation
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
- H01L2224/80—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected
- H01L2224/81—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a bump connector
- H01L2224/81009—Pre-treatment of the bump connector or the bonding area
- H01L2224/81051—Forming additional members
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
- H01L2224/80—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected
- H01L2224/81—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a bump connector
- H01L2224/81053—Bonding environment
- H01L2224/81054—Composition of the atmosphere
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
- H01L2224/80—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected
- H01L2224/81—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a bump connector
- H01L2224/812—Applying energy for connecting
- H01L2224/81201—Compression bonding
- H01L2224/81205—Ultrasonic bonding
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- Microelectronics & Electronic Packaging (AREA)
- Power Engineering (AREA)
- Pressure Welding/Diffusion-Bonding (AREA)
Abstract
The invention provides an ultrasonic welding method, which comprises the following steps: a) carrying out oxidation treatment on the bonding pad on the substrate to form a metal oxide layer on the surface of the bonding pad; b) and (b) ultrasonically welding the bonding pad on the substrate obtained in the step a) and the solder ball on the chip under the gas condition containing the reducing formic acid and under the condition of pressurizing the welding surface to obtain a welding part. According to the invention, before ultrasonic welding, oxidation treatment is carried out on the welding disc, a layer of metal oxide is pre-oxidized on the surface of the metal to be welded, during ultrasonic welding, formic acid gas continuously introduced is utilized to reduce the oxide on the surface of the metal, so that a large amount of metal micro-nano particles are reduced from the surface metal oxide layer in the reduction process, the particles are beneficial to contact with the surface to be welded in the ultrasonic welding process, and meanwhile, the metal particles are easy to generate plastic flow under the action of ultrasonic energy, so that the surface deformation of the surface to be welded is facilitated, and the welding and welding reliability is effectively improved.
Description
Technical Field
The invention relates to the technical field of electronic packaging, in particular to an ultrasonic welding method.
Background
The wire bonding (also called pressure welding or wire welding) technology is the most common method for circuit interconnection between an integrated circuit chip and a packaging structure, and the wire bonding technology mainly comprises three types of ultrasonic bonding, hot-press bonding and thermosonic pen bonding, and thin metal wires or metal bands are sequentially punched on the chip and a lead frame or a bonding pad (pad) of a packaging substrate through the bonding technology to form circuit interconnection.
With the continuous development and progress of the integrated circuit industry, the monolithic integration degree of a chip is higher and higher, the power consumption is higher and higher, and the requirement on the packaging technology is higher and higher, so that the packaging technology is rapidly developed towards the trend of miniaturization, high density, high integration and multi-pin. The single chip packaging technology has also undergone a series of development processes such as dual in-line package, small square plane package, ball grid array package, flip chip package, etc. In the process of continuous development and progress of packaging technology, ultrasonic bonding is increasingly used in the fields of wire bonding, flip chip interconnection and the like as a bonding method which can be performed at a lower temperature and has less damage to a chip. In the bonding process of the flip chip, the flip chip bonding assisted by the ultrasonic welding technology realizes the flip chip bonding at a lower temperature.
Ultrasonic welding means that low-frequency current is converted into high-frequency electric energy by an ultrasonic generator, the converted high-frequency electric energy is converted into mechanical motion with the same frequency again by a transducer, then the high-frequency mechanical motion is transmitted to a welding head by a set of amplitude changing device capable of changing amplitude, the welding head transmits received vibration energy to a joint part of a workpiece to be welded, in the area, on one hand, the temperature of metal is increased by heat generated by friction, on the other hand, the contacted workpiece to be welded generates strong plastic flow under the action of friction force, conditions are created for contact between pure metal surfaces, and the temperature rise and high-frequency vibration of the joint area further cause the excited state of atoms on metal lattices, so that when metal atoms with covalent bond properties are close to the distance of nanometers, an interatomic electronic bridge can be formed by common electrons, i.e. a so-called metal bonding process is achieved.
At present, in an ultrasonic-assisted flip chip bonding process using an ultrasonic bonding technology, solder bumps (or "solder balls") are generally fabricated on pads of a chip, and the pads are fabricated on a surface of a substrate, where the solder balls on the chip correspond to the pads of the substrate one to one, as shown in fig. 1, and fig. 1 is a schematic structural diagram of the chip and the substrate in the prior art. Then putting the substrate into a solution of hydrochloric acid absolute ethyl alcohol for cleaning for 5s, and then putting the substrate and the chip into a solution of absolute ethyl alcohol and acetone solution in equal volume ratio for ultrasonic cleaning for 30s so as to clean the solder bumps, oxides and organic impurities on the metal pads; and then, the positions of the substrate, the chip and the welding head are well placed and adjusted, and technological parameters are well adjusted for welding.
However, in the prior art, the chip and the substrate are pretreated before the welding process by adopting a solution cleaning mode, so that on one hand, time and materials are wasted, and a subsequent waste liquid treatment device is required to be added during industrial use, thereby increasing the manufacturing cost; on the other hand, the waste liquid may leave a certain amount of residue on the solder balls and the pads, which may affect the reliability of bonding. On the basis, some improved processes introduce reducing gas in the welding process, and utilize the reducing gas to reduce the metal oxide on the surfaces of the solder balls and the bonding pads, so that the content of the metal oxide in the whole welding process is kept in a lower range, the influence of the metal oxide on the welding surface is reduced, and the welding reliability is improved. However, the improvement effect of this method is not good enough, and the welding reliability and welding efficiency cannot be effectively improved.
Disclosure of Invention
In view of the above, the present invention provides an ultrasonic welding method, and the preparation method provided by the present invention can effectively improve welding reliability and welding efficiency.
The invention provides an ultrasonic welding method, which comprises the following steps:
a) carrying out oxidation treatment on the bonding pad on the substrate to form a metal oxide layer on the surface of the bonding pad;
b) and (b) ultrasonically welding the bonding pad on the substrate obtained in the step a) and the solder ball on the chip under the gas condition containing the reducing formic acid and under the condition of pressurizing the welding surface to obtain a welding part.
Preferably, the metal oxide layer in step a) is obtained by:
a1) arranging a protective material on the other parts except the bonding pad on the substrate;
a2) heating the substrate obtained in the step a1) to more than 250 ℃ in an oxygen-containing gas atmosphere, oxidizing for 4-8 hours, and forming a metal oxide layer on the surface of the bonding pad.
Preferably, the oxygen content of the oxygen-containing gas is 95% or more, and the oxygen-containing gas does not contain a reducing gas component.
Preferably, in the step b), the flow rate of the formic acid in the gas containing the reduced formic acid is 38sccm or more.
Preferably, in the step b), the vibration frequency of ultrasonic welding is 15-25 KHz, the amplitude is 8-12 μm, the welding power is 650-750W, and the welding time is 1-5 s.
Preferably, in the step b), the ultrasonic welding is performed at a temperature of 180-210 ℃.
Preferably, in the step b), the pressurizing conditions are as follows: the pressure intensity of the welding surface is more than or equal to 0.2 MPa.
Preferably, the step b) further includes a heat-preserving and pressure-maintaining treatment after the ultrasonic welding.
Preferably, the gas containing reducing formic acid is formic acid gas, or formic acid and hydrogen;
the bonding pad is a copper bonding pad; the solder balls are lead-free solder.
Preferably, in the gas containing reducing formic acid, the formic acid gas is a formic acid gas catalyzed by Pt.
The invention provides an ultrasonic welding method, which comprises the following steps: a) carrying out oxidation treatment on the bonding pad on the substrate to form a metal oxide layer on the surface of the bonding pad; b) and (b) ultrasonically welding the bonding pad on the substrate obtained in the step a) and the solder ball on the chip under the gas condition containing the reducing formic acid and under the condition of pressurizing the welding surface to obtain a welding part. According to the invention, before ultrasonic welding, oxidation treatment is carried out on the welding disc, a layer of metal oxide is pre-oxidized on the surface of the metal to be welded, and during ultrasonic welding, formic acid gas continuously introduced is utilized to reduce the oxide on the surface of the metal, so that a large amount of metal micro-nano particles are reduced from the surface metal oxide layer in the reduction process, and the particles are beneficial to the contact of the surface to be welded in the ultrasonic welding process, and meanwhile, the metal particles are easy to generate plastic flow under the action of ultrasonic energy, and are beneficial to the surface deformation of the surface to be welded, so that the welding efficiency can be effectively improved, and the welding reliability is improved. Meanwhile, the method effectively utilizes the original oxide on the metal surface, avoids the influence of the original metal oxide on the metal surface on the welding reliability, and avoids the treatment on the oxide on the metal surface before welding.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
FIG. 1 is a schematic diagram of a chip and a substrate in the prior art;
FIG. 2 is a schematic flow diagram of the oxidation stage of the present invention;
FIG. 3 is a schematic diagram of the present invention prior to the die being pressed to the bond pad during a pre-bonding operation;
FIG. 4 is a schematic view of a die pressed onto a bonding pad during a pre-bonding operation in accordance with the present invention;
FIG. 5 is a schematic illustration of an ultrasonic welding stage of the present invention;
FIG. 6 is a schematic diagram of the heat and pressure maintaining stage of the ultrasonic welding post-treatment according to the present invention;
FIG. 7 is a schematic representation of the pressure relief stage of the post-ultrasonic welding process of the present invention.
Detailed Description
The invention provides an ultrasonic welding method, which comprises the following steps:
a) carrying out oxidation treatment on the bonding pad on the substrate to form a metal oxide layer on the surface of the bonding pad;
b) and (b) ultrasonically welding the bonding pad on the substrate obtained in the step a) and the solder ball on the chip under the gas condition containing the reducing formic acid and under the condition of pressurizing the welding surface to obtain a welding part.
Before ultrasonic welding, a metal oxide thin layer is oxidized on the surface to be welded in advance, and then the metal oxide thin layer is reduced into metal particles by formic acid gas, so that the deformation of the surfaces to be welded which are in contact with each other under the action of ultrasonic waves is increased, and the welding speed and the welding reliability are improved.
According to the present invention, a pad on a substrate is first subjected to oxidation treatment to form a metal oxide layer on the surface of the pad.
In the present invention, before the oxidation treatment, the chip and the substrate are preferably pretreated in advance so that the surfaces to be welded are free from impurities other than metals and metal oxides. The pretreatment mode is not particularly limited in the invention, and the pretreatment mode is an impurity removal mode known to those skilled in the art, such as cleaning treatment and the like.
The present invention is not particularly limited in the kind of the chip, and may be a conventional bonding chip well known to those skilled in the art. In the present invention, solder balls (i.e., solder bumps) are mounted on the chip, and the structure is shown in fig. 1. The invention is not limited to the mounting and connecting method of the chip and the solder balls, and the mounting and connecting method is a mounting and connecting method in the chip packaging solder ball connection known by those skilled in the art.
The solder ball is not particularly limited in kind, and may be a conventional solder ball for soldering known to those skilled in the art, and for improving environmental protection, a lead-free solder is preferred, and a lead-free alloy solder is more preferred, including but not limited to one of silver-tin alloy, tin-copper alloy and the like.
In the present invention, the kind of the substrate is not particularly limited, and may be a conventional soldering substrate known to those skilled in the art. In the present invention, the pad is preferably a copper pad. The present invention is not limited to any particular mounting and connecting method for the substrate and the bonding pad, and may be any mounting and connecting method for the substrate and the bonding pad in the solder ball connection of the chip package known to those skilled in the art.
The invention forms a metal oxide layer on the surface of the bonding pad by oxidizing the bonding pad, and particularly preferably obtains the following steps:
a1) arranging a protective material on the other parts except the bonding pad on the substrate;
a2) heating the substrate obtained in the step a1) to more than 250 ℃ in an oxygen-containing gas atmosphere, oxidizing for 4-8 hours, and forming a metal oxide layer on the surface of the bonding pad.
In the step a1), the protection material is provided in a manner not particularly limited, and the protection material can cover the other region except the pad and protect the other region from oxidation. In some embodiments, the other portion is covered with a film or sheet. In some embodiments, the other portion is coated with an adhesive; the kind of the adhesive is not particularly limited, and may be an adhesive known to those skilled in the art, such as a photoresist. The thickness of the viscose glue is not specially limited, and is preferably more than or equal to 2mm for convenient operation and protection effect.
In the step a2), the oxygen content of the oxygen-containing gas is preferably 95% or more, and the oxygen-containing gas does not contain a reducing gas component. That is, the oxygen-containing gas is substantially high-purity oxygen gas, and the oxidation treatment is performed in this high-purity oxygen atmosphere. In the present invention, the ratio of the oxygen contents refers to a volume ratio, that is, a volume ratio of oxygen to the total amount of the oxygen-containing gas. In the present invention, the flow rate of the oxygen-containing gas is preferably not less than 40sccm, and more preferably 40 to 80 sccm. The pressure of the oxygen-containing gas is not particularly limited, and may be normal pressure. In the present invention, the oxidation treatment is preferably carried out at a temperature of 250 ℃ or higher, and if the temperature is lower than 250 ℃, oxidation is difficult; the temperature of the oxidation treatment is more preferably 250 to 300 ℃, and most preferably 275 ℃. In the oxidation treatment, the oxidation time is preferably 4-8 hours, if the oxidation time is too short, the oxidation effect is poor, and if the oxidation time is too long, the formed oxidation layer is thick, so that the subsequent reduction takes longer, and the reduced particle layer is thick, so that the welding effect is influenced.
In the present invention, the oxidation process can be performed in a reaction chamber, and in some embodiments of the present invention, the specific flow is shown in fig. 2, and fig. 2 is a schematic flow chart of the oxidation stage of the present invention; the method specifically comprises the following steps: placing the substrate with the bonding pad in a reaction chamber, vacuumizing the reaction chamber, filling the oxygen-containing gas, repeating the steps for several times, filling the oxygen-containing gas into the chamber, heating the chamber to a temperature of more than 250 ℃, continuously performing oxidation reaction for 4 to 8 hours, continuously filling the oxygen-containing gas in the process, continuously discharging the gas after the reaction, and oxidizing the surface of the bonding pad to form a layer of metal oxide.
After the above oxidation treatment, the following post-treatment is preferably further performed: and reducing the temperature of the reaction cavity, discharging oxygen-containing gas in the reaction cavity, taking out the substrate, and removing the protective material preset on the substrate to obtain the part to be welded. The method of discharging the oxygen-containing gas is not particularly limited in the present invention, and may be a method known to those skilled in the art, and in some embodiments, may be implemented by: and vacuumizing the reaction chamber, introducing inert gas, repeating the steps for many times, and exhausting the oxygen-containing gas.
According to the invention, after the welding piece is obtained through the oxidation treatment, the welding piece is obtained by carrying out ultrasonic welding on the bonding pad on the substrate obtained in the step a) and the welding ball on the chip under the condition of gas containing reducing formic acid and under the condition of pressurizing the welding surface.
In the present invention, the gas containing reducing formic acid is preferably formic acid gas, or formic acid and hydrogen; more preferably formic acid gas. In the present invention, the flow rate of the formic acid in the reducing formic acid-containing gas is preferably 38sccm or more, and more preferably 38 to 60 sccm. In the invention, when the gas containing the reducing formic acid is formic acid and hydrogen, the flow rate of the hydrogen is preferably 30-90 sccm. In the present invention, the gas pressure of the reducing formic acid-containing gas is not particularly limited, and may be normal pressure. The invention reduces the metal oxide layer on the surface to be welded by formic acid, so that the oxide on the metal surface is fully and effectively utilized, and the requirement on the welding pretreatment of the welding surface is reduced.
In the present invention, the formic acid gas is preferably a formic acid gas catalyzed by Pt. The formic acid gas catalyzed by Pt can improve the reduction efficiency and accelerate bonding. The method for the catalytic treatment of Pt is not particularly limited, and the Pt can be treated in a catalytic gas manner well known to those skilled in the art, for example, formic acid gas can be catalyzed by flowing through a heated Pt sheet, and the heating temperature is preferably 150-200 ℃; in some embodiments, the formic acid gas used is one catalyzed by a Pt sheet at 150 ℃.
In the present invention, it is preferable to further perform a heating treatment before the ultrasonic welding and perform the subsequent welding under a heating condition. In the invention, the welding temperature is preferably 180-210 ℃.
In the present invention, before ultrasonic welding, the welding surface is pressurized in advance, and subsequent welding is performed under the pressurized condition. In the invention, the welding surface is the contact surface of the solder ball and the welding disc. The present invention is not limited to the above-mentioned pressing method, and the method may be a method well known to those skilled in the art for pressing the bonding surface, for example, the bonding head may apply pressure to the chip to press the solder balls on the chip to the surface of the bonding pads of the substrate, so as to generate pressure on the contact surface (i.e., bonding surface) between the solder balls and the bonding pads. In the pressing process, parameters such as pressure, position and the like of the welding head can be adjusted. In the present invention, the pressurizing conditions are preferably: the pressure intensity of the welding surface is more than or equal to 0.1MPa, and more preferably 0.2-0.6 MPa.
In some embodiments of the present invention, the specific flow of the pre-bonding operation is shown in fig. 3 and 4, fig. 3 is a schematic diagram of the pre-bonding operation of the present invention before the chip is pressed onto the bonding pad, and fig. 4 is a schematic diagram of the pre-bonding operation of the present invention before the chip is pressed onto the bonding pad; the method specifically comprises the following steps: and introducing gas containing reducing formic acid into the reaction chamber, starting heating, and applying pressure to the chip through the welding head to enable the solder balls to gradually press the surface of the bonding pad.
In the invention, after the operation before welding is finished and the proper gas environment, pressurizing condition and welding temperature are provided, the welding ball on the chip and the welding pad on the substrate are welded by ultrasonic waves, thereby obtaining the welding piece. In the ultrasonic welding process, the welding head drives the chip and the basic interconnection assembly to start high-frequency transverse vibration, energy carried by ultrasonic waves is transmitted to the chip through the welding head, relative friction occurs between a welding ball of the chip and a bonding pad of the substrate, and the welding between the welding ball and the bonding pad is completed by utilizing the energy of the ultrasonic waves, wherein the process is shown in fig. 5, and fig. 5 is a schematic diagram of the ultrasonic welding stage of the invention. The welding is carried out under the above-mentioned gaseous condition that contains reducing formic acid, and the in-process, the little nano-particle of a large amount of metals is constantly reduced out to the metal oxide layer that forms in advance, and under ultrasonic energy, these metal particles easily take place the plastic flow, increase the surface deformation of face of weld to improve welding efficiency and welding reliability effectively.
In the invention, the vibration frequency of the ultrasonic welding is preferably 15-25 KHz, and more preferably 18-22 KHz. The amplitude of the ultrasonic welding is preferably 8-12 μm, and more preferably 10 μm. The welding power of the ultrasonic welding is preferably 650-750W, and more preferably 680-720W. The welding time of the ultrasonic welding is preferably 1-5 s, and more preferably 1-4 s; after the ultrasonic wave acts for a period of time, the ultrasonic wave generating device is closed, and the action of the ultrasonic wave energy is stopped. Under the welding conditions, the welding strength is improved, and the welding reliability is improved.
In the present invention, it is preferable that the ultrasonic welding is followed by heat and pressure maintaining treatment of the welded material. The pressure maintaining means that the pressure applied to the welding surface by the welding head is continued for a period of time, and the welding strength can be further enhanced by the pressure maintaining, so that the welding reliability is further improved. In the present invention, it is preferable that the gas containing the reducing formic acid in the reaction chamber is discharged during the heat and pressure maintaining; the mode of the reducing formic acid-containing gas is not particularly limited in the present invention, and may be a venting mode well known to those skilled in the art, and in some embodiments, may be achieved by: replacing the reducing formic acid-containing gas with a protective gas to purge the reducing formic acid-containing gas; the protective gas used in the present invention is not particularly limited, and may be an inert gas known to those skilled in the art, such as nitrogen, helium, argon, or the like. In the present invention, it is preferable to stop the heat-retention until the gas containing the reducing formic acid is exhausted; and stopping introducing the protective gas after the cavity is cooled. In the present invention, the pressure maintaining time is preferably 1min or more; more preferably, after the protective gas is stopped to be introduced, the pressure is relieved; after the pressure is relieved, the welding part can be taken out. Fig. 6 and 7 show the post-treatment such as heat preservation, pressure holding, and exhaust pressure relief, fig. 6 is a schematic diagram of a heat preservation and pressure holding stage in the ultrasonic welding post-treatment of the present invention, and fig. 7 is a schematic diagram of a pressure relief stage in the ultrasonic welding post-treatment of the present invention.
The invention provides an ultrasonic welding method, before ultrasonic welding, firstly carrying out oxidation treatment on a welding disc, pre-oxidizing a layer of metal oxide on the surface of a metal to be welded, reducing the oxide on the surface of the metal by using continuously introduced formic acid gas during ultrasonic welding, so that a large amount of metal micro-nano particles are reduced from the surface metal oxide layer in the reduction process, the particles are beneficial to the contact of the surface to be welded in the ultrasonic welding process, and meanwhile, the metal particles are easy to generate plastic flow under the action of ultrasonic energy and are beneficial to the surface deformation of the surface to be welded, thereby effectively improving the welding efficiency and improving the welding reliability. Meanwhile, the method effectively utilizes the original oxide on the metal surface, avoids the influence of the original metal oxide on the metal surface on the welding reliability, and avoids the treatment on the oxide on the metal surface before welding.
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims. In the following examples, the chip used was a ceramic ball grid array chip, and the substrate was an FR4 resin substrate; the chip and the substrate are 17.04mm long, 17.04mm wide and 1mm thick. On the chip, the solder balls are arranged at equal intervals, 16 rows by 16 are totally arranged, and the diameter of the solder ball is 0.5 mm. On the substrate, the pads are arranged at equal intervals, and 16 rows by 16 in total; the bonding pad is the copper bonding pad, and the bonding pad diameter is 25mm, thickness 25 mm. The oxygen content of the high-purity oxygen is more than 95 percent.
Example 1
S1: cleaning the surfaces of the chip and the substrate to remove other impurities except metal and metal oxide on the surfaces of the solder ball and the bonding pad; a 2mm thick photoresist was coated on the substrate and the photoresist on the surface of the pad was removed.
S2: placing the substrate in a reaction chamber, vacuumizing the reaction chamber, then filling high-purity oxygen, repeating the vacuumizing step for three times, and then filling the high-purity oxygen into the reaction chamber to ensure that the chamber is filled with the high-purity oxygen, wherein the air pressure is 1 atmosphere; heating the cavity to 275 ℃, continuously introducing high-purity oxygen (the gas flow rate is 40sccm) during the heating, continuously discharging the reacted gas, continuously reacting for 6 hours, and oxidizing a layer of metal oxide on the surface of the bonding pad; as shown in fig. 2.
S3: and reducing the temperature of the reaction cavity, discharging oxygen in the cavity, taking out the part to be welded, and removing the photoresist on the surface of the substrate.
S4: placing the substrate and the chip on a fixture of a welding chamber, aligning a welding head of the mounted ultrasonic vibration module, the chip and the substrate, and setting process parameters of the ultrasonic vibration module; then, vacuumizing the cavity, introducing argon, repeating for multiple times, exhausting residual oxygen in the cavity, introducing formic acid gas (the flow is 38sccm, and the pressure in the cavity is kept at 1 atmosphere), and heating (at 200 ℃); as shown in fig. 3.
S5: after the positions of the interconnection components are confirmed to be accurate, under the control of a mechanical device, a welding head applies certain preset pressure to the chip to enable a welding ball (a silver-tin alloy welding ball, the material grade is Sn3.5Ag) on the chip to be in contact with a welding pad, and the pressure of a welding surface is 0.3 MPa; as shown in fig. 4.
S6: starting ultrasonic vibration, wherein the vibration frequency is 20 KHz, the amplitude is 10 mu m, the power is 700W, and welding for 4 s; as shown in fig. 5.
S7: after welding, closing the ultrasonic generating device, and continuing to keep the temperature and the pressure for a period of time; in the process, pure nitrogen is introduced into the cavity, and residual formic acid gas in the cavity is discharged by the pure nitrogen; as shown in fig. 6.
S8: stopping heat preservation after formic acid gas is exhausted, stopping introducing nitrogen after the cavity is cooled, removing pressure applied on a welding head, opening the cavity, moving away the welding head, and taking out a welded part after welding; as shown in fig. 7.
Example 2
S1: cleaning the surfaces of the chip and the substrate to remove other impurities except metal and metal oxide on the surfaces of the solder ball and the bonding pad; a 3mm thick photoresist was coated on the substrate and the photoresist on the surface of the pad was removed.
S2: placing the substrate in a reaction chamber, vacuumizing the reaction chamber, then filling high-purity oxygen, repeating the vacuumizing step for three times, and then filling the high-purity oxygen into the reaction chamber to ensure that the chamber is filled with the high-purity oxygen, wherein the air pressure is 1 atmosphere; and heating the cavity to 270 ℃, continuously introducing high-purity oxygen (the gas flow rate is 45sccm) during the period, continuously discharging the reacted gas, continuously reacting for 6 hours, and oxidizing a layer of metal oxide on the surface of the bonding pad.
S3: and reducing the temperature of the reaction cavity, discharging oxygen in the cavity, taking out the part to be welded, and removing the photoresist on the surface of the substrate.
S4: placing the substrate and the chip on a fixture of a welding chamber, aligning a welding head of the mounted ultrasonic vibration module, the chip and the substrate, and setting process parameters of the ultrasonic vibration module; then, the chamber is firstly vacuumized and then filled with argon, the process is repeated for a plurality of times, residual oxygen in the chamber is exhausted, formic acid gas is filled (the flow is 40sccm, the air pressure in the chamber is kept at 1 atmospheric pressure), and heating is started (200 ℃).
S5: after the positions of the interconnection components are confirmed to be accurate, the welding head applies certain preset pressure to the chip under the control of a mechanical device, so that a welding ball (a silver-tin alloy welding ball, the material grade is Sn3.5Ag) on the chip is in contact with the welding pad, and the pressure of the welding surface is 0.2 MPa.
S6: starting ultrasonic vibration, wherein the vibration frequency is 20 KHz, the amplitude is 10 mu m, the power is 680W, and welding is carried out for 3 s.
S7: after welding, closing the ultrasonic generating device, and continuing to keep the temperature and the pressure for a period of time; in the process, pure nitrogen is introduced into the cavity, and residual formic acid gas in the cavity is discharged by the pure nitrogen.
S8: and after formic acid gas is exhausted, stopping heat preservation, after the cavity is cooled, stopping introducing nitrogen, removing the pressure applied on the welding head, opening the cavity, moving away the welding head, and taking out the welded part after welding.
Example 3
S1: cleaning the surfaces of the chip and the substrate to remove other impurities except metal and metal oxide on the surfaces of the solder ball and the bonding pad; a 3mm thick photoresist was coated on the substrate and the photoresist on the surface of the pad was removed.
S2: placing the substrate in a reaction chamber, vacuumizing the reaction chamber, then filling high-purity oxygen, repeating the vacuumizing step for three times, and then filling the high-purity oxygen into the reaction chamber to ensure that the chamber is filled with the high-purity oxygen, wherein the air pressure is 1 atmosphere; and heating the cavity to 280 ℃, continuously introducing high-purity oxygen (the gas flow rate is 43sccm) during the period, continuously discharging the reacted gas, continuously reacting for 8 hours, and oxidizing a layer of metal oxide on the surface of the bonding pad.
S3: and reducing the temperature of the reaction cavity, discharging oxygen in the cavity, taking out the part to be welded, and removing the photoresist on the surface of the substrate.
S4: placing the substrate and the chip on a fixture of a welding chamber, aligning a welding head of the mounted ultrasonic vibration module, the chip and the substrate, and setting process parameters of the ultrasonic vibration module; then, the chamber is firstly vacuumized and then filled with argon, the process is repeated for a plurality of times, residual oxygen in the chamber is exhausted, formic acid gas is filled (the flow rate is 45sccm, the air pressure in the chamber is kept at 1 atmospheric pressure), and heating is started (200 ℃).
S5: after the positions of the interconnection components are confirmed to be accurate, the welding head applies certain preset pressure to the chip under the control of a mechanical device, so that a welding ball (a silver-tin alloy welding ball, the material grade is Sn3.5Ag) on the chip is in contact with the welding pad, and the pressure of the welding surface is 0.4 MPa.
S6: starting ultrasonic vibration, wherein the vibration frequency is 22KHz, the amplitude is 12 mu m, the power is 710W, and welding is carried out for 3 s.
S7: after welding, closing the ultrasonic generating device, and continuing to keep the temperature and the pressure for a period of time; in the process, pure nitrogen is introduced into the cavity, and residual formic acid gas in the cavity is discharged by the pure nitrogen.
S8: and after formic acid gas is exhausted, stopping heat preservation, after the cavity is cooled, stopping introducing nitrogen, removing the pressure applied on the welding head, opening the cavity, moving away the welding head, and taking out the welded part after welding.
Comparative example 1
The bonding process was performed as in example 1, except that the pad was not subjected to the oxidation treatment, that is, steps S1 to S3 (except for the surface cleaning treatment).
Example 4
And testing the welding reliability and the welding yield of the welding parts obtained in the embodiments 1-3 and the comparative example 1, wherein the welding reliability is as follows: cutting the whole welding chip into 16 parts, wherein each part comprises 1 multiplied by 16 welding points, and then testing the shearing strength of each part by using a micro-shearing instrument to obtain the average welding strength of each welding point; the yield is obtained by counting the yield by observing the condition that each welding contact surface is obtained by the fractured welding interface after shearing. The test results are shown in Table 1.
TABLE 1 reliability test results of examples 1-3 and comparative example 1
| Average single spot weld strength range | Yield of good products | |
| Example 1 | 32～55MPa | 88％ |
| Example 2 | 33～58MPa | 84％ |
| Example 3 | 35～60MPa | 93％ |
| Comparative example 1 | 6～30MPa | 80％ |
As can be seen from the test results in table 1, the welding method provided by the present invention significantly improves the welding reliability and welding efficiency compared to comparative example 1.
The foregoing examples are provided to facilitate an understanding of the principles of the invention and their core concepts, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention. The scope of the invention is defined by the claims and may include other embodiments that occur to those skilled in the art. Such other embodiments are intended to be within the scope of the claims if they have structural elements that approximate the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
Claims (10)
1. An ultrasonic welding method, comprising the steps of:
a) carrying out oxidation treatment on the bonding pad on the substrate to form a metal oxide layer on the surface of the bonding pad;
b) and (b) ultrasonically welding the bonding pad on the substrate obtained in the step a) and the solder ball on the chip under the gas condition containing the reducing formic acid and under the condition of pressurizing the welding surface to obtain a welding part.
2. Welding method according to claim 1, wherein the metal oxide layer in step a) is obtained by:
a1) arranging a protective material on the other parts except the bonding pad on the substrate;
a2) heating the substrate obtained in the step a1) to more than 250 ℃ in an oxygen-containing gas atmosphere, oxidizing for 4-8 hours, and forming a metal oxide layer on the surface of the bonding pad.
3. The welding method according to claim 2, wherein an oxygen content of the oxygen-containing gas is 95% or more, and the oxygen-containing gas does not contain a reducing gas component.
4. The welding method according to claim 1, wherein in the step b), the flow rate of the formic acid in the gas containing the reduced formic acid is 38sccm or more.
5. The welding method according to claim 1, wherein in the step b), the vibration frequency of the ultrasonic welding is 15 to 25KHz, the amplitude is 8 to 12 μm, the welding power is 650 to 750W, and the welding time is 1 to 5 s.
6. The welding method according to claim 1, wherein the ultrasonic welding is performed at a temperature of 180 to 210 ℃ in the step b).
7. Welding method according to claim 1 or 6, characterized in that in step b) the pressing conditions are: the pressure intensity of the welding surface is more than or equal to 0.2 MPa.
8. The welding method according to claim 1 or 5, characterized in that, in the step b), after the ultrasonic welding, a heat and pressure maintaining treatment is further included.
9. The welding method according to claim 1, wherein the gas containing reducing formic acid is formic acid gas, or formic acid and hydrogen gas;
the bonding pad is a copper bonding pad; the solder balls are lead-free solder.
10. The welding method according to claim 1, wherein formic acid gas in the reducing formic acid-containing gas is Pt-catalyzed formic acid gas.
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| CN113380636A (en) * | 2021-04-29 | 2021-09-10 | 苏州通富超威半导体有限公司 | Welding method and chip packaging method |
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|---|---|---|---|---|
| JPH0574874A (en) * | 1991-09-11 | 1993-03-26 | Hitachi Ltd | Ultrasonic connection method of metallic fine wiring and device |
| CN104157605A (en) * | 2014-08-23 | 2014-11-19 | 中国电子科技集团公司第五十八研究所 | Salient point interconnection welding method |
| CN105355566A (en) * | 2014-08-21 | 2016-02-24 | 中芯国际集成电路制造(上海)有限公司 | Surface treatment method of bonding pad and manufacturing method of bonding pad |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0574874A (en) * | 1991-09-11 | 1993-03-26 | Hitachi Ltd | Ultrasonic connection method of metallic fine wiring and device |
| CN105355566A (en) * | 2014-08-21 | 2016-02-24 | 中芯国际集成电路制造(上海)有限公司 | Surface treatment method of bonding pad and manufacturing method of bonding pad |
| CN104157605A (en) * | 2014-08-23 | 2014-11-19 | 中国电子科技集团公司第五十八研究所 | Salient point interconnection welding method |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113380636A (en) * | 2021-04-29 | 2021-09-10 | 苏州通富超威半导体有限公司 | Welding method and chip packaging method |
| CN113380636B (en) * | 2021-04-29 | 2024-03-26 | 苏州通富超威半导体有限公司 | Welding method and chip packaging method |
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