Bonding structure for chip packaging bonding

Abstract

The utility model provides a bonding structure for chip packaging bonding, which comprises a bonding pad, a welding ball and a welding wire, the bonding pad is connected with the welding wire through the welding ball, the welding ball is configured to be formed by applying instantaneous high pressure to the tail end of the metal welding wire, and the bottom of the welding ball welded with the bonding pad is configured to be in a downward bending state, aluminum extrusion is formed around the solder ball on the bonding pad, and a gap between the solder ball and the aluminum extrusion is smaller than 1 micron.

Description

Technical Field

[0001] The present disclosure relates to the technical field of semiconductor packaging, and in particular to a bonding structure for chip packaging bonding for improving chip packaging reliability. Background Art

[0002] With the rapid development of the electronics and semiconductor industries, the application environment of electronic equipment is becoming more and more extensive, the functions are becoming more and more complex, and the integration is becoming higher and higher. This puts higher requirements on semiconductor packaging technology, which not only needs a robust process window to ensure a high production yield, but also needs to have high reliability so that it can operate better in different environments.

[0003] The bonding process, also known as the wire bonding process, is a relatively common process in packaging technology. The main method is to use a wire bonding machine to use metal welding wire to connect the aluminum pad on the chip and the chip carrier to achieve the connection between the chip and the carrier, thereby leading the functions inside the chip to the outside.

[0004] Generally speaking, the main material of the chip pad is aluminum, and the main material of the welding wire is copper. The welding process is that the instantaneous high voltage generated by the wire bonding machine burns the tail of the welding wire into a ball shape. The copper ball will be firmly embedded in the tip of the splitter, and then the splitter drives the copper ball to move and quickly press the copper ball onto the aluminum pad. The copper ball is harder than the aluminum pad, and the copper ball will squeeze and deform the aluminum pad to form aluminum extrusion. At the same time, intermetallic compounds are formed in the area where the aluminum pad contacts the bottom of the copper ball, thereby achieving the welding effect. The quality of bonding directly affects the reliability of the product.

[0005] However, in the traditional bonding process, the solder ball is not embedded deep enough in the aluminum pad, resulting in a large gap between the aluminum extrusion and the solder ball. The aluminum extrusion does not wrap the solder ball well, and the bottom of the solder ball is bent upward. In addition, impurities such as water vapor can easily enter the bottom of the solder ball through the gap between the solder ball and the aluminum extrusion, causing an electrochemical reaction at the bottom of the solder ball, causing the intermetallic compound at the bottom of the solder ball to corrode. The upward bending of the bottom of the solder ball also facilitates the extension of corrosion downward. When the corrosion reaches a certain extent, the solder ball is disconnected from the aluminum pad, and the product will fail as an open circuit. Utility Model Content

[0006] The utility model improves the reliability of the product by changing the shape of the solder ball. By increasing the depth of the solder ball embedded in the aluminum pad and reducing the gap between the aluminum extrusion and the solder ball, the wrapping of the aluminum extrusion on the solder ball is improved, so that the bottom of the solder ball is bent downward, which can prevent impurities such as water vapor from entering the bottom of the solder ball. Thus, the reliability of the product is improved.

[0007] One aspect of the present disclosure provides a bonding structure for chip packaging bonding, comprising a solder pad, a solder ball and a solder wire, wherein the solder pad is connected to the solder wire via the solder ball, the solder ball is configured to be formed by applying an instantaneous high voltage to the end of the metal solder wire, and the bottom of the solder ball welded to the solder pad is configured to be bent downward, wherein an aluminum extrusion is formed around the solder ball on the solder pad, and a gap between the solder ball and the aluminum extrusion is less than 1um.

[0008] One aspect of the present disclosure provides a bonding structure for chip package bonding, wherein the depth of the aluminum extrusion is 3.6-6.2 um.

[0009] An aspect of the present disclosure provides a bonding structure for chip package bonding, wherein the pad comprises an aluminum pad, and the bonding wire comprises a copper bonding wire.

[0010] One aspect of the present disclosure provides a bonding structure for chip package bonding, wherein the bonding wire comprises a metal wire with a copper outer layer plated with other metals.

[0011] An aspect of the present disclosure provides a bonding structure for chip package bonding, wherein the type of the chip package is configured to include a plastic package.

[0012] An aspect of the present disclosure provides a bonding structure for chip package bonding, wherein the type of the chip package is configured to include a plastic package.

[0013] One aspect of the present disclosure provides a bonding structure for chip package bonding, wherein the chip package is configured to correspond to a copper process with a process of 40 nm.

[0014] One aspect of the present disclosure provides a bonding structure for chip package bonding, wherein the pad comprises an aluminum pad having a thickness of 2.8 um, and an opening of the pad is 55×55 um.

[0015] One aspect of the present disclosure provides a bonding structure for chip package bonding, wherein the copper bonding wire comprises a palladium-plated copper wire with a diameter of 20 um.

[0016] One aspect of the present disclosure provides a bonding structure for chip package bonding, wherein the downwardly curved shape is configured such that an edge of the bottom of the solder ball is lower than a center of the bottom of the solder ball. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other aspects, features and advantages of certain embodiments of the present disclosure will become more apparent from the following description taken in conjunction with the accompanying drawings, in which:

[0018] Figure 1A schematic diagram showing a plastic packaged chip formed by a bonding process;

[0019] Figure 2 shows the front view of the copper ball and the aluminum pad after bonding in the conventional bonding process;

[0020] Figure 3 shows a top view of a copper ball bonded to an aluminum pad in a conventional bonding process;

[0021] Figure 4 A cross-sectional view of a solder ball along a diameter in a conventional bonding process is shown;

[0022] Figure 5 A flow chart showing a bonding method for bonding a solder ball to a solder pad according to an embodiment of the present utility model; and

[0023] Figure 6 A cross-sectional view along the diameter of a solder ball in a bonding process according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0024] Before proceeding to the following detailed description, it may be advantageous to set forth the definitions of certain words and phrases used throughout this patent document. The terms "coupling", "connection" and their derivatives refer to any direct or indirect communication or connection between two or more elements, regardless of whether those elements are in physical contact with each other. The terms "transmission", "reception" and "communication" and their derivatives cover direct and indirect communication. The terms "include" and "comprise" and their derivatives refer to including but not limited to. The term "or" is inclusive, meaning and / or. The phrases "associated with...", "corresponding to..." and their derivatives refer to including, including within, interconnecting, including, including within, connecting or connecting with, coupling or coupling with, communicating with, cooperating, interweaving, parallel, close to, binding or binding with, having, having attributes, having a relationship or having a relationship with, etc. The term "controller" refers to any device, system or part thereof that controls at least one operation. Such a controller can be implemented with hardware, or a combination of hardware and software and / or firmware. The functions associated with any particular controller can be centralized or distributed, whether local or remote. The phrase "at least one of", when used with a list of items, means that different combinations of one or more of the listed items may be used, and only one of the items in the list may be required. For example, "at least one of A, B, C" includes any of the following combinations: A, B, C, A and B, A and C, B and C, A and B and C.

[0025] Definitions for other specific words and phrases are provided throughout this patent document. Those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior and future uses of such defined words and phrases.

[0026] In this patent document, the application combination of modules and the division level of submodules are only used for illustration. Without departing from the scope of the present disclosure, the application combination of modules and the division level of submodules can have different modes. The embodiments of the present disclosure can be implemented in different forms and should not be interpreted as being limited to the embodiments set forth herein. On the contrary, these embodiments are provided to make the present disclosure thorough and complete, and to fully convey exemplary implementation methods to those skilled in the art. The embodiments of the present disclosure can be combined to form additional embodiments.

[0027] The present disclosure will be described in detail below with reference to exemplary embodiments of the present disclosure. However, the present disclosure is not limited to the embodiments described herein, and it can be implemented in many different forms. The described embodiments are only used to make the present disclosure thorough and complete, and to fully convey the concept of the present disclosure to those skilled in the art. The features of the various embodiments described can be combined or replaced with each other, unless explicitly excluded or should be excluded according to the context.

[0028] In the present disclosure, the singular form of an element may refer to its plural form, and the plural form of an element may also refer to its singular form. For example, "element" or "an element" may refer to each other with "at least one element", "one or more elements" or "a plurality of elements" etc.

[0029] Figure 1 A schematic diagram showing a plastic packaged chip formed by a bonding process.

[0030] refer to Figure 1 The pad 2 on the chip 1 and the chip carrier 4 are connected by a wire bonding machine using a metal wire 3. The metal wire includes a copper wire, and the pad includes an aluminum pad. The aluminum pad is exposed by opening a window, and the size of the window is determined according to different processes.

[0031] Figure 2 shows a front view of a copper ball bonded to an aluminum pad in a conventional bonding process; and Figure 3 A top view of a copper ball bonded to an aluminum pad in a conventional bonding process is shown.

[0032] refer to Figure 2 Due to the welding process of the bonding process, the instantaneous high voltage generated by the wire bonding machine burns the tail of the welding wire 3 into a ball shape, and then the splitter drives the copper ball to move and quickly press the copper ball onto the aluminum pad to achieve welding.

[0033] Therefore, the solder ball 9 at the tail of the metal solder wire 3 becomes flattened due to the compression with the solder pad 2, and the solder ball 9 at the tail of the metal solder wire 3 becomes flattened due to the compression with the solder pad 2. Figure 3 It can be seen that the area of ​​the pad 9 is larger than that of the metal bonding wire 3 so as to form a strong bond with the pad 2 .

[0034] Figure 4 The cross-sectional view along the diameter of the solder ball in the conventional bonding process is shown.

[0035] refer to Figure 4 , the gap between the solder ball 9 of the metal solder wire 3 formed by the extrusion of the splitter 13 and the aluminum extrusion 10 on the pad 2 is large, the bottom of the solder ball 9 is in an upwardly curved shape 11, and the depth of the solder ball 9 embedded in the aluminum pad is shallow. Generally, according to the traditional bonding process, the depth of the solder ball embedded in the aluminum extrusion is 1.2 to 1.6 um, the distance between the side wall of the solder ball and the angle of the aluminum extrusion is 3.5 to 4.5 um, and the bottom of the solder ball 9 is in an upwardly curved or nearly horizontal shape.

[0036] In order to solve the above problems, a chip packaging bonding method for improving chip packaging reliability is provided. In this method, by increasing the depth of the solder ball embedded in the aluminum pad and reducing the gap between the aluminum extrusion and the solder ball, the wrapping of the solder ball by the aluminum extrusion is improved, so that the bottom of the solder ball is bent downward, which can prevent impurities such as water vapor from entering the bottom of the solder ball. Thus, the reliability of the product is improved.

[0037] Figure 5 A flow chart of a bonding method for bonding a solder ball to a solder pad according to an embodiment of the present utility model is shown.

[0038] In the bonding process between the pad and the solder ball, the welding forming steps can be mainly divided into three stages: forming, friction and bonding.

[0039] First, in step S501, an initial bonding ball is formed by applying instantaneous high voltage to the end of a metal bonding wire using a wire bonding machine, and the bonding wire is moved toward a pad to prepare for bonding, wherein the metal bonding wire comprises a copper wire, and the pad comprises an aluminum pad.

[0040] At step S502, a forming phase operation is performed, in which the initial bonding solder ball (e.g., copper ball) formed by the bonding wire is brought into contact with the pad and a downward forming pressure is applied thereto to achieve the initial bonding solder ball forming. In addition, an ultrasonic wave is output to the copper ball through the bonding head of the wire bonding machine, and the output direction of the ultrasonic wave is the longitudinal direction of the two-dimensional horizontal plane, so that the copper ball formed at the end of the bonding wire begins to gradually deform under pressure, and its bottom is uniformly expanded along the direction of the ultrasonic wave output. According to an embodiment of the utility model, the welding condition of the solder ball and the pad is adjusted by adjusting parameters such as the applied ultrasonic energy, the applied pressure, and the operation time.

[0041] According to an embodiment of the present invention, for example, a downward pressure is applied to the copper ball by a riving knife with a first forming pressure.

[0042] According to an embodiment of the present invention, downward pressure is applied to the copper ball by a cleaver, and the cleaver is configured as a first type of cleaver. Preferably, the first type of cleaver includes a relatively small type of cleaver.

[0043] Although the forming stage can be set to a segmented pressure mode including staged pressure application to improve the welding of the solder ball and the solder pad, the number of added pressure mode segments will have an adverse effect on production efficiency. Therefore, according to an embodiment of the utility model, a segmented pressure mode is included in the forming stage.

[0044] At step S503, a friction phase operation is performed. The friction phase operation is used to further improve the solder ball morphology and form a large amount of intermetallic compounds between the solder ball and the aluminum pad. In the friction mode, while applying pressure in the longitudinal direction and outputting ultrasonic waves, the workbench carrying the chip moves in the transverse direction, that is, perpendicular to the direction of ultrasonic wave output, so that the chip reciprocates in the transverse direction. Through the interaction in the transverse direction and the longitudinal direction, the welding of the solder ball and the pad is improved, and intermetallic compounds are formed therebetween.

[0045] According to the embodiment of the utility model, the solder ball moves in the longitudinal direction during the forming stage and moves in the transverse direction during the friction stage, so that the solder ball will be evenly spread in both the transverse and longitudinal directions to avoid forming an ellipsoid in a certain direction.

[0046] According to the embodiment of the utility model, the welding condition is adjusted by adjusting the pressure applied in the longitudinal direction, the energy of the ultrasonic wave, the friction cycle, the friction amplitude and the operation time.

[0047] Although the friction stage can be set to include a segmented friction mode to improve the welding of the solder ball and the pad, the added number of friction mode segments will have an adverse effect on production efficiency. Therefore, according to an embodiment of the utility model, the friction stage includes a segmented friction mode.

[0048] At step S504, a bonding phase operation is performed to form a final solder ball shape and further increase the intermetallic compound between the solder ball and the aluminum pad, so that the solder ball and the aluminum pad are truly bonded.

[0049] During the bonding stage operation, a downward bonding pressure is applied to the solder ball by a wedge. In addition, ultrasonic waves are output to the copper ball by a bonding head of a wire bonding machine, and the output direction of the ultrasonic waves is the longitudinal direction of a two-dimensional horizontal plane.

[0050] According to an embodiment of the present invention, in order to increase the depth of the solder ball embedded in the aluminum pad, reduce the gap between the aluminum extrusion and the solder ball, and make the bottom of the solder ball bend downward, the bonding stage is configured to include two pressure modes.

[0051] According to an embodiment of the utility model, the welding condition between the solder ball and the solder pad in the two-stage pressure mode is adjusted by adjusting the parameters such as the applied bonding ultrasonic energy, the applied bonding pressure and the bonding time. In the first stage of the two-stage pressure mode, the welding condition between the solder ball and the solder pad is adjusted by the first bonding pressure, the first bonding ultrasonic energy and the first bonding time; and in the second stage of the two-stage pressure mode, the welding condition between the solder ball and the solder pad is adjusted by the second bonding pressure, the second bonding ultrasonic energy and the second bonding time.

[0052] Preferably, since the operation in the bonding stage is used to form the final solder ball morphology and further increase the intermetallic compounds between the solder ball and the aluminum pad to achieve true bonding between the solder ball and the aluminum pad, the first bonding pressure and the second bonding pressure are preferably configured to be greater than the first forming pressure applied in the forming stage.

[0053] According to an embodiment of the utility model, a two-stage pressure mode is used in the bonding stage, the diameter of the solder ball will increase, and the risk of aluminum extrusion and aluminum pad window opening will also increase. In order to reduce the above risk, a second type of splitting knife is used in the two-stage pressure mode, wherein the hole diameter (H) and the inner chamfer diameter (Chamfer Diameter, CD) of the second type of splitting knife are set to be larger than those of the first type of splitting knife.

[0054] According to an embodiment of the utility model, by configuring the bonding stage to include two pressure modes, in the second pressure mode of the two pressure modes, a second bonding pressure is used to perform a downward pressing operation through a splitting knife, so that the bottom of the solder ball presents a downward bending shape, and at the same time, by configuring the splitting knife as a second type of splitting knife with a larger CD value, the gap between the aluminum extrusion and the solder ball is reduced. In addition, by setting the H value of the second type of splitting knife to a larger value, the ball diameter of the solder ball is controlled not to be too large, thereby reducing the risk of the aluminum extrusion exceeding the pad retaining wall.

[0055] Figure 6 1 is a cross-sectional view of a solder ball along a diameter showing a bonding process according to an embodiment of the present invention.

[0056] refer to Figure 6In the bonding stage including the two-stage pressure mode, the gap between the solder ball 9 of the metal solder wire 3 formed by the extrusion of the splitter 13 and the aluminum extrusion 10 on the pad 2 is small, and the bottom of the solder ball 9 is bent downward 12, that is, the edge of the bottom of the solder ball is lower than the center of the bottom of the solder ball. The depth of the solder ball 9 embedded in the aluminum pad is deep, 3.6 to 6.2um, which is much higher than the 1.2 to 1.6um under the traditional process; at the same time, the gap between the solder ball and the aluminum extrusion is less than 1um, which is also much lower than the 3.5 to 4.5um under the traditional process.

[0057] According to an embodiment of the utility model, since in the bonding stage including two-stage pressure modes, the second bonding ultrasonic energy and the second bonding pressure in the second stage pressure mode and the first bonding ultrasonic energy in the first stage pressure mode have a more significant effect on the height of the aluminum extrusion, it is preferred to set the second bonding ultrasonic energy and the second bonding pressure in the second stage pressure mode and the first bonding ultrasonic energy in the first stage pressure mode to adjust the height of the aluminum extrusion.

[0058] The chip packaging bonding method according to the embodiment of the utility model can be applied to the application scenario where the chip packaging type is plastic packaging. In the plastic packaging scenario according to the utility model, the chip pad is configured as an aluminum pad and has a thickness of 2.8um, and wherein the pad window is 55×55um. In the above scenario, the chip corresponding process is a 40nm copper process, wherein the welding wire includes a copper wire, and is preferably configured as a palladium-plated copper wire with a diameter of 20um, wherein the outer layer of the palladium-plated copper wire is plated with a very thin layer of palladium to reduce the oxidation of the copper ball during the bonding process, however, the copper material is still the main participant in the bonding process.

[0059] Since the thickness of the 2.8um aluminum pad is a thick aluminum pad, a large aluminum extrusion is likely to occur during the packaging process, and the window size is close to the packaging process limit, making it easy for the aluminum extrusion to hit the window retaining wall; in addition, the 40nm copper process is a process that is sensitive to craters, in which the metal under the aluminum pad is likely to be cracked, so for this type of plastic packaging, the wire bonding process requirements are relatively high. The chip packaging bonding method according to the embodiment of the utility model can be applied to the plastic packaging scenario configured as above by increasing the depth of the solder ball embedded in the aluminum pad, reducing the gap between the aluminum extrusion and the solder ball, and making the bottom of the solder ball present a downward curved shape.

[0060] In addition, according to the chip packaging bonding method of the embodiment of the utility model, the reliability of the product is improved by changing the shape of the solder ball. By increasing the depth of the solder ball embedded in the aluminum pad, reducing the gap between the aluminum extrusion and the solder ball, and improving the wrapping of the aluminum extrusion on the solder ball, the bottom of the solder ball is made to bend downward, which can prevent halogen and water vapor from entering the bottom of the solder ball, so that the product produced by the above method can pass the reliability project test with harsh conditions, such as HAST, THB and other reliability tests while meeting the conventional reliability requirements.

[0061] According to an embodiment of the present invention, the connection process between the chip and the welding wire is an ultrasonic hot pressing process.

[0062] According to an embodiment of the utility model, the chip pad is made of aluminum, and also includes a pad in which a small amount of copper is added to the main material aluminum in order to improve conductivity.

[0063] According to an embodiment of the present invention, the welding wire is made of copper, and also includes a metal wire whose main material is copper and whose outer layer is plated with other metals to improve oxidation resistance.

[0064] The block diagrams of circuits, devices, apparatuses, equipment, and systems involved in the present disclosure are only illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As will be appreciated by those skilled in the art, these circuits, devices, apparatuses, equipment, and systems may be connected, arranged, or configured in any manner as long as the desired purpose can be achieved.

[0065] Although the present disclosure has been described with exemplary embodiments, various changes and modifications may be suggested to one skilled in the art. The present disclosure is intended to encompass such changes and modifications as fall within the scope of the appended claims.

[0066] Any description in this disclosure should not be construed as implying that any particular element, step, or function is an essential element that must be included in the claims scope. The scope of the patented subject matter is limited solely by the claims.

[0067] Exemplary embodiments according to the present disclosure have been disclosed herein, and although specific terms are employed, they are used and interpreted only in a general and descriptive sense and not for limiting purposes. In some cases, features, characteristics, and / or elements described in conjunction with a particular embodiment may be used alone or in combination with features, characteristics, and / or elements described in conjunction with other embodiments, unless otherwise stated. Therefore, it will be understood by those skilled in the art that various changes in form and detail may be made to the present disclosure without departing from the spirit and scope of the claims.

Claims

1. A bonding structure for chip packaging bonding, comprising a pad, a solder ball and a solder wire, characterized in that: The pad is connected to the welding wire through the welding ball. The solder ball is configured to be formed by applying instantaneous high voltage to the end of the metal wire, and the bottom of the solder ball soldered to the pad is configured to be bent downward. An aluminum extrusion is formed on the pad around the solder ball, and a gap between the solder ball and the aluminum extrusion is less than 1 um.

2. The bonding structure according to claim 1, characterized in that: The depth of the aluminum extrusion is 3.6-6.2 um.

3. The bonding structure according to claim 1, characterized in that: The pad includes an aluminum pad, and the solder wire includes a copper solder wire.

4. The bonding structure according to claim 1, characterized in that: The welding wire comprises a metal wire with an outer layer of copper plated with other metals.

5. The bonding structure according to claim 1, characterized in that: The type of chip package is configured to include plastic packaging.

6. The bonding structure according to claim 1, characterized in that: The type of chip package is configured to include plastic packaging.

7. The bonding structure according to claim 1, characterized in that: The chip package is configured to correspond to a copper process with a process of 40 nm.

8. The bonding structure according to claim 3, characterized in that: The pad includes an aluminum pad having a thickness of 2.8 um, and an opening of the pad is 55×55 um.

9. The bonding structure according to claim 3, characterized in that: The copper welding wire comprises a palladium-plated copper wire with a diameter of 20 um.

10. The bonding structure according to claim 1, characterized in that: The downwardly curved shape is configured such that an edge of the bottom of the solder ball is lower than a center of the bottom of the solder ball.

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