A wire bonding device and method based on ultrafast laser ablation

Abstract

The present invention discloses a wire bonding device and method based on ultrafast laser ablation, which relates to the field of ultrafast laser welding application technology. The device includes an ultrafast laser processing system, a fixture and a positioning system. An ultrafast laser is used to generate an ultrafast pulse beam of femtosecond magnitude, and the laser path is adjusted by a reflector. Then, the incident laser beam is focused on the sample surface by a galvanometer and focusing mirror system. Then, the gold wire is positioned by microscopic imaging of a camera so that it is close to the sample surface. Then, the laser is turned on to achieve ablation and sputtering on the sample surface according to a specified path. The sputtering generated by the metal material under femtosecond laser ablation will partially adhere to the edge of the contact between the gold wire and the metal surface and gradually deposit. Then, the high-temperature melt heats the gold wire and the metal surface through heat conduction to form a bond, thereby forming a stable weld. The present invention improves the strength and efficiency of wire bonding.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultrafast laser welding applications, and in particular relates to a wire bonding device and method based on ultrafast laser ablation. Background Art

[0002] Wire bonding is one of the important process technologies in semiconductor packaging. Its purpose is to weld the two ends of the metal lead to the chip and the pin respectively to form an electrical connection. During the bonding process, the lead contacts the pad metal under the combined action of ultrasonic energy, pressure or heat, and interatomic diffusion occurs to achieve the purpose of bonding. Wire bonding occupies a mainstream position in electronic packaging because of its simple process, mature technology, low cost, and suitability for a variety of packaging forms. Wire bonding is a type of wire bonding process. It is a method of bonding the wires to the chip pads and substrate pins respectively through the combined action of ultrasonic vibration and bonding force, while the substrate is heated or the gold wire is heated, so as to achieve physical interconnection between the chip and the substrate circuit. However, due to the high cost of gold wire, in order to reduce the packaging cost, various gold wire substitutes have been launched on the market: copper wire or silver wire and other materials. Among them, bonding copper wire materials have begun to be used because of their better thermal and electrical properties, but due to their high hardness, they are easy to cause chip damage during bonding, and are prone to corrosion in non-airtight packaging, which directly affects the reliability of the device after bonding. Therefore, they can only be used in some mid- and low-end products; bonding silver wire has gradually begun to be used in microelectronic packaging due to its excellent electrothermal properties, good stability and appropriate cost factors, but pure silver wire has low strength, easy electron migration, and difficult to control the growth of intermetallic compounds. The application in the packaging field is also subject to certain restrictions.

[0003] Wire bonding is the most commonly used bonding technology in electronic packaging, mainly including gold wire ball bonding and gold wire wedge bonding. The basic process steps of these two technologies are similar, including welding the first solder joint on the chip surface, forming a connecting wire arc, and forming a second solder joint on the lead frame or substrate. However, wire bonding failures often occur in these processes, and the main reasons include cratering, cracking and warping of bonding points, inconsistent bonding tail wires, cracks or deformation at the root of the lead, and debonding of bonding points. According to statistics, in semiconductor microelectronic packaging, about 1 / 4 to 1 / 3 of semiconductor device failures are caused by chip interconnection. The losses caused by failure and reduced reliability caused by wire bonding are far greater than the losses of the process itself.

[0004] Traditional methods improve processing results by adjusting parameters, but it is difficult to meet the requirements of high reliability and high efficiency wire bonding. Therefore, further research and development of new methods are needed to solve this problem. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a wire bonding device and method based on ultrafast laser ablation, so as to provide means and tools for the research in the field of ultrafast laser welding to meet the actual needs of scientific research and industrial production.

[0006] The object of the present invention is achieved through the following technical solutions:

[0007] A wire bonding device based on ultrafast laser ablation, the device comprising:

[0008] An ultrafast laser processing system, the ultrafast laser processing system comprising a laser processing optical path and a motion platform, the laser processing optical path is used to generate an ultrashort pulse beam and focus the ultrashort pulse beam on the surface of a metal material, the motion platform comprises a designated laser path, the motion platform is used to place the metal material and process the metal material with the ultrashort pulse beam according to the designated laser path;

[0009] A clamp, wherein the clamp is used to fix the lead wire on the surface of the metal material;

[0010] A positioning system includes an illumination optical path and a microscopic imaging optical path, and is used for real-time detection of positioning leads.

[0011] Furthermore, the ultrafast laser processing system includes an ultrafast laser emitter, a beam expander, a first reflector, a main control host, and a galvanometer and focusing mirror system. The main control host controls the ultrafast laser to generate an ultrashort pulse beam. The ultrashort pulse beam is expanded by the beam expander and then the optical path is adjusted by the first reflector. Finally, the beam is focused on the surface of the metal material by the galvanometer and focusing mirror system. The first reflector is a dichroic mirror that reflects near-infrared wavelengths, specific ultraviolet wavelengths or green light, and transmits white light. The specific wavelength is 200 to 380 nm.

[0012] Furthermore, the fixture includes a mechanical clamping fixture or a glass ribbon fixture. When the fixture is a mechanical clamping fixture, the ultrafast laser energy density generated by the ultrafast laser processing system is not less than 0.08 J / cm 2 When the fixture is a glass ribbon fixture, the ultrafast laser energy density generated by the ultrafast laser processing system is not less than 7.3×10 12 J / cm 2 .

[0013] Furthermore, the illumination light path includes an illumination laser emitter, which is located directly above where the metal material is placed and emits an illumination light beam downward.

[0014] Furthermore, the microscopic imaging optical path includes a CCD camera, an objective lens, an eyepiece, a filter set and a second reflector, wherein the second reflector is located above the first reflector, and the second reflector is a half-reflective mirror, which reflects 50% of white light and transmits 50% of white light. The centers of the CCD camera, the eyepiece and the second reflector are on the same horizontal line, and the center of the second reflector is on the same vertical line as the center of the first reflector and the objective lens.

[0015] Furthermore, the lead wire has a diameter of 5-30 μm.

[0016] Furthermore, the wavelength of the ultrafast laser is in the range of 266-2000 nm.

[0017] Furthermore, the designated laser path is an arcuate processing path and is parallel to the lead.

[0018] Furthermore, when the fixture is a mechanical clamping fixture, the ultrafast laser energy density generated by the ultrafast laser processing system is not less than 0.08 J / cm 2 When the fixture is a glass ribbon fixture, the ultrafast laser energy density generated by the ultrafast laser processing system is not less than 7.3×10 12 J / cm 2 .

[0019] On the other hand, the present invention further provides a wire bonding method based on ultrafast laser ablation, the method is implemented based on any of the aforementioned wire bonding devices based on ultrafast laser ablation, and the method comprises:

[0020] Place the metal material on the moving platform, and clamp the wire to be bonded to the surface of the metal material;

[0021] The positioning system detects and locates the lead in real time to ensure that the lead is bonded at the specified position. The ultrafast laser processing system performs laser processing according to the specified laser path. The metal material melts, abslates and sputters under laser ablation to produce molten metal. The molten metal adheres and gradually deposits on the edge of the contact between the gold wire and the metal material and spreads out. Then the molten metal heats the gold wire and the metal surface through heat conduction to form a weld or bond.

[0022] The beneficial effects of the present invention are:

[0023] (1) Ultrafast laser welding of gold wire to the surface of metal material changes the traditional wire bonding method. Through the melting reaction of the metal material surface to the laser processing, the metal material is melted and sputtered to the wire bonding point, and then the metal melt is deposited and cooled to form a high-efficiency and high-strength bonding wire. The present invention avoids the failure of traditional wire bonding by ultrafast laser processing of the metal material surface to cause melting and sputtering, and effectively improves the reliability of gold wire bonding.

[0024] (2) Ultrafast laser welding gold wire bonding reduces the number of gold wire bonding steps. Through the close contact between the gold wire and the surface of the metal material, and then through the ultrafast laser processing of the metal material surface, an efficient and high-strength welding effect can be obtained, making the wire bonding process simpler and more effectively integrated into normal production and processing. On the other hand, ultrafast laser welding gold wire bonding has a unique welding principle, which produces high-strength welding through the sputtering, deposition and cooling of the molten metal material itself, which makes other lead materials (such as copper wire, silver wire, etc.) can be used in this welding method.

[0025] (3) Ultrafast laser ablates the surface of the metal material, causing the generated metal particles to sputter and then deposit, and most of the welding between the gold wire lead and the metal material occurs at the edge of the lead, thereby ensuring the inherent characteristics of the gold wire lead. Different from the solder joints of the traditional bonding method, the present invention does not directly process the gold wire lead, thereby retaining the various characteristics of the gold wire lead to ensure the reliability of bonding and the stability of processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic structural diagram of a wire bonding device based on ultrafast laser ablation according to an embodiment of the present invention;

[0027] Figure 2 is a schematic diagram of the scanning path of the gold wire and the ultrafast laser according to an embodiment of the present invention;

[0028] Figure 3 It is a schematic diagram of the ablated sputtered molten material being deposited, cooled and welded at the edge of the contact point between the gold wire and the surface of the metal material according to an embodiment of the present invention.

[0029] Reference numerals:

[0030] 1-illumination laser emitter; 2-microscope imaging optical path; 3-eyepiece; 4-CCD camera; 5-ultrafast laser emitter; 6-main control computer; 7-laser beam; 8-beam expander; 9-ultrafast laser processing path; 10-metal material; 11-lead material; 12-objective lens; 13-galvanometer and focusing lens system; 14-reflector; 15-illumination optical path; 16-metal melt. DETAILED DESCRIPTION

[0031] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0032] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making any creative work shall fall within the scope of protection of the present invention.

[0033] Traditional methods improve processing results by adjusting parameters, but it is difficult to meet the requirements of high reliability and high efficiency wire bonding. Therefore, further research and development of new methods are needed to solve this problem.

[0034] In order to solve the above technical problems, the following embodiments of a wire bonding device and method based on ultrafast laser ablation are proposed in the present invention.

[0035] Example 1

[0036] This embodiment provides a wire bonding device based on ultrafast laser ablation, referring to Figure 1 ,like Figure 1 The figure shows a schematic diagram of the structure of the wire bonding device based on ultrafast laser ablation of this embodiment, which includes an ultrafast laser processing system, a microscopic imaging optical path 2, an illumination optical path and a fixture.

[0037] Ultrafast laser processing path 9: It is composed of ultrafast laser emitter 5, beam expander 8, reflector 14, main control computer 6 and galvanometer and focusing mirror system 13. Its direction is that the ultrafast laser emitter 5 generates an ultrashort laser beam 7, which is expanded by the beam expander 8 and then adjusted by the reflector 14, and then passes through the galvanometer and focusing mirror system 13 to focus the beam on the surface of the metal material 10.

[0038] Microscopic imaging optical path 2 and illumination optical path 15: composed of CCD camera 4, illumination laser emitter 1, objective lens 12, eyepiece 3, filter set and reflector 14. Since the diameter of lead material 11 is very small, there is a large error in positioning and clamping lead material 11 by human eyes, so the microscopic imaging optical path is set to detect and position lead material 11 in real time through CCD camera 4. The lower reflector is a dichroic mirror, which reflects near-infrared wavelength or green light, and specific wavelength of ultraviolet light, and transmits white light; the upper reflector is a semi-reflective mirror, which reflects 50% of white light and transmits 50% of white light, wherein the specific wavelength of ultraviolet light is in the wavelength range of 200-380nm.

[0039] The metal material 10 is placed on a moving platform, the lead material 11 is in tight contact with the surface of the metal material 10 by means of a mechanical clamping fixture or a glass tape clamp and is monitored in real time by a CCD camera 4, the laser beam 7 performs laser processing according to a specified ultrafast laser processing path 9, the metal material 10 undergoes melting, ablation and sputtering under femtosecond laser ablation and produces a metal melt 16, the metal melt 16 adheres to and gradually deposits on the edge of the contact between the lead material 11 and the metal material 10 and spreads out, and then the metal melt 16 heats the lead material 11 and the metal surface through heat conduction to form a high-strength weld or bond.

[0040] In this embodiment, the lead material 11 has a diameter of 5-30 μm.

[0041] In this embodiment, the wavelength of the ultrafast laser is in the range of 266-2000 nm.

[0042] In this embodiment, the lead material 11 may be gold wire, silver wire, copper wire or other conductive materials.

[0043] In this embodiment, the metal material is copper, invar, titanium alloy, aluminum alloy, steel or the like.

[0044] In this embodiment, the ultrafast laser processing path 9 is an arcuate processing path and is parallel to the gold wire. Figure 2 ,like Figure 2 Shown is a schematic diagram of the gold wire and ultrafast laser scanning path of this embodiment.

[0045] In this embodiment, the ultrafast laser energy density required for clamping by the mechanical clamping fixture is relatively low, about 0.08 J / cm 2 The ultrafast laser energy density required when the glass ribbon clamp is clamped is much higher, greater than 7.3×10 12 J / cm 2 .

[0046] Reference Figure 3 ,like Figure 3 The schematic diagram of the embodiment of the present invention is that the ablated sputtered melt is deposited and cooled at the edge of the contact between the gold wire and the metal material surface and then welded. The metal material 10 is melted, ablated and sputtered to produce a metal melt 16, which is gradually deposited on both sides of the lead material 11. After the fusion and cooling of the metal melt 16, the lead material 11 and the surface of the metal material 10 are efficiently welded or bonded.

[0047] Example 2

[0048] In this embodiment, the metal material 10 is aluminum alloy and the lead material 11 is gold wire. The size of the aluminum alloy is about 10mm×7mm×3mm, the diameter of the gold wire is about 25μm, and the crystal surface used needs to be polished to ensure high-quality contact. It is clamped using a glass tape clamp and detected in real time by a CCD camera 4 to ensure that the lead material 11 is in tight contact with the surface of the metal material 10 as required by the experiment. Subsequently, laser processing is performed according to the steps in the method for ultrafast laser high-strength welding of gold wire and metal material surface provided in the above embodiment.

[0049] Among them, the laser beam 7 emitted by the ultrafast laser is reflected by the reflector 14 through the main control computer 6 and then injected into the galvanometer and focusing mirror system 13, so that the ultrafast laser is focused on the upper surface of the metal material 10. The pulse width of the ultrafast laser is set to 35fs, the maximum pulse energy is 3.5mJ, the repetition frequency is 1KHz, and the output wavelength is 800nm. The ultrafast laser emitter 5 and the three-dimensional motion platform of the main control computer 6 are processed according to the set ultrafast laser processing path 9, and the heated molten metal 16 is sputtered to the edge of the contact between the lead material 11 and the surface of the metal material 10 and deposited, and then spread out and cooled at the contact point, so as to achieve efficient and high-quality welding and bonding of the lead material 11 and the metal material 10 at the edge of the contact between the lead material 11 and the surface of the metal material 10.

[0050] Example 3

[0051] In this example, the metal material 10 is a pure copper sheet and the lead material 11 is a silver microwire. The thickness of the pure copper sheet is selected to be 125μm, the diameter of the silver microwire is about 25μm, and the crystal surface used needs to be polished to ensure high-quality contact. The lead material 11 is clamped separately using a glass tape clamp and a mechanical clamp and is detected in real time by a CCD camera 4 to ensure that the lead material 11 is in tight contact with the surface of the metal material 10 as required by the experiment. Subsequently, laser processing is performed according to the steps in the method for ultrafast laser high-strength welding of gold wire to the surface of a metal material provided in the above embodiment.

[0052] Among them, the laser beam 7 emitted by the ultrafast laser is reflected by the reflector 14 through the main control computer 6 and then injected into the galvanometer and focusing mirror system 13, so that the ultrafast laser is focused on the upper surface of the metal material 10. The pulse width of the ultrafast laser is set to 35fs, the maximum pulse energy is 3.5mJ, the repetition frequency is 1KHz, and the output wavelength is 800nm. The ultrafast laser emitter 5 and the three-dimensional motion platform of the main control computer 6 are processed according to the set ultrafast laser processing path 9, and the heated molten metal 16 is sputtered to the edge of the contact between the lead material 11 and the surface of the metal material 10 and deposited, and then spread out and cooled at the contact point, so as to achieve efficient and high-quality welding and bonding of the lead material 11 and the metal material 10 at the edge of the contact between the lead material 11 and the surface of the metal material 10.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A wire bonding method based on ultrafast laser ablation, characterized in that: The method is implemented based on an ultrafast laser ablation wire bonding device, the device comprising: An ultrafast laser processing system, the ultrafast laser processing system comprising a laser processing optical path and a motion platform, the laser processing optical path is used to generate an ultrashort pulse beam and focus the ultrashort pulse beam on the surface of a metal material, the motion platform comprises a designated laser path, the motion platform is used to place the metal material and process the metal material with the ultrashort pulse beam according to the designated laser path; A clamp, wherein the clamp is used to fix the lead wire on the surface of the metal material; A positioning system, the positioning system comprising an illumination optical path and a microscopic imaging optical path, for real-time detection of positioning leads; The method comprises: Place the metal material on the moving platform, and clamp the wire to be bonded to the surface of the metal material; The positioning system detects and locates the lead in real time to ensure that the lead is bonded at the specified position. The ultrafast laser processing system performs laser processing according to the specified laser path. The metal material melts, abslates and sputters under laser ablation to produce molten metal. The molten metal adheres and gradually deposits on the edge of the contact between the gold wire and the metal material and spreads out. Then the molten metal heats the gold wire and the metal surface through heat conduction to form a weld or bond.

2. The wire bonding method based on ultrafast laser ablation according to claim 1, characterized in that: The ultrafast laser processing system includes an ultrafast laser emitter, a beam expander, a first reflector, a main control host, and a galvanometer and focusing mirror system. The main control host controls the ultrafast laser to generate an ultrashort pulse light beam. The ultrashort pulse light beam is expanded by the beam expander and then the optical path is adjusted by the first reflector. Finally, the light beam is focused on the surface of the metal material by the galvanometer and focusing mirror system. The first reflector is a dichroic mirror that reflects near-infrared wavelengths, specific ultraviolet wavelengths or green light and transmits white light. The specific wavelength is 200 to 380 nm.

3. The wire bonding method based on ultrafast laser ablation according to claim 1, characterized in that: The fixture includes a mechanical clamping fixture or a glass ribbon fixture. When the fixture is a mechanical clamping fixture, the ultrafast laser energy density generated by the ultrafast laser processing system is not less than 0.08 J / cm 2 When the fixture is a glass ribbon fixture, the ultrafast laser energy density generated by the ultrafast laser processing system is not less than 7.3×10 12 J / cm 2 .

4. The wire bonding method based on ultrafast laser ablation according to claim 1, characterized in that: The illumination light path includes an illumination laser emitter, which is located directly above where the metal material is placed and emits an illumination light beam downward.

5. The wire bonding method based on ultrafast laser ablation according to claim 2, characterized in that: The microscopic imaging optical path includes a CCD camera, an objective lens, an eyepiece, a filter group and a second reflector, wherein the second reflector is located above the first reflector, and the second reflector is a half-reflective mirror, which reflects 50% of white light and transmits 50% of white light. The centers of the CCD camera, the eyepiece and the second reflector are on the same horizontal line, and the center of the second reflector is on the same vertical line as the center of the first reflector and the objective lens.

6. The wire bonding method based on ultrafast laser ablation according to claim 1, characterized in that: The lead wire has a diameter of 5-30 μm.

7. The wire bonding method based on ultrafast laser ablation according to claim 1, characterized in that: The wavelength of the ultrafast laser is in the range of 266-2000 nm.

8. The wire bonding method based on ultrafast laser ablation according to claim 1, characterized in that: The designated laser path is an arcuate processing path and is parallel to the lead.

9. The wire bonding method based on ultrafast laser ablation according to claim 1, characterized in that: The lead wires include gold wire leads, copper wire leads or silver wire leads.

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