Laser welding system and method

Abstract

The invention relates to a laser welding system and method. The laser welding system is used for welding a chip on a wafer to a back plate and comprises a carrying table, a laser welding assembly and a control system. The laser welding assembly is located above the carrying table, and the laser welding assembly is electrically connected with the control system; the carrying table comprises a carrying surface for carrying the back plate and the wafer, and an electromagnetic adsorption device is arranged below the carrying surface; a magnetic layer is arranged on the substrate of the wafer; and the control system is configured to enable the laser welding assembly and the electromagnetic adsorption device to weld the chip to the back plate. By applying the scheme of the invention, adverse effects caused by non-uniform bonding and wafer warping can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of laser welding, and particularly to a laser welding system and method. Background Art

[0002] As a new generation of display technology, compared with LCD and OLED technologies, Micro-LED has higher brightness, better luminous efficiency, and at the same time has the performance of low power consumption and long life. In the process of Micro-led manufacturing process flow, massive welding is an important link for efficient improvement of massive transfer. During the massive welding process, the chips are fixedly grown on the wafer. The wafer and the backplane are positioned on the download table of the laser welding machine. The laser welding machine presses and fixes the wafer and the backplane on the download table through a snap ring. Since there is a layer of light-emitting chips between the wafer and the backplane, when the snap ring presses the wafer and the backplane, if there is no support of the light-emitting chips below the pressed part of the snap ring or only presses on the corner position of the light-emitting chips, it will cause the wafer to bend, resulting in gaps between some chips on the wafer and the backplane (mainly between the chip electrodes and the backplane pads). And this gap will cause poor welding during the subsequent laser welding process, thus seriously affecting the welding yield.

[0003] Therefore, how to solve the problem of poor welding caused by warping between the wafer and the backplane during the laser welding process is an urgent problem to be solved at present. Summary of the Invention

[0004] In view of the above deficiencies of the prior art, the purpose of the present application is to provide a laser welding system and method, aiming to solve the problem of poor welding caused by warping between the wafer and the backplane during the existing laser welding process.

[0005] A laser welding system for welding chips on a wafer to a backplane, comprising a stage, a laser welding component and a control system; the laser welding component is located above the stage, and the laser welding component is electrically connected to the control system;

[0006] The stage includes a bearing surface for bearing the backplane and the wafer, and an electromagnetic adsorption device is arranged below the bearing surface; a magnetic layer is arranged on the substrate of the wafer; and

[0007] The control system is configured to enable the laser welding component and the electromagnetic adsorption device to weld the chips to the backplane.

[0008] The above laser welding system is provided with an electromagnetic adsorption device on the carrier stage and a magnetic layer on the substrate of the wafer. When the wafer is placed on the backplane, the electromagnetic adsorption device is controlled by the control system to generate a magnetic force. In addition to adsorbing the wafer, this magnetic force can effectively offset the extrusion deformation generated by the buckle on the wafer, reduce the warpage amount of the wafer, so that the chip of the wafer contacts the backplane, improve the bonding yield, and reduce the occurrence of virtual soldering.

[0009] In one embodiment, the bearing surface is divided into a plurality of electromagnetic adsorption zones by the electromagnetic adsorption device. At least one electromagnetic adsorption part is provided in an electromagnetic adsorption zone, and the electromagnetic adsorption part is electrically connected to the control system.

[0010] In one embodiment, the electromagnetic adsorption part includes a power supply, an induction coil and a variable resistor; the variable resistor is connected between the power supply and the induction coil.

[0011] In one embodiment, the magnetic layer includes a plurality of magnetic parts, and each of the magnetic parts is at least partially embedded in the substrate.

[0012] In one embodiment, along the extension direction perpendicular to the substrate, the height of the magnetic part embedded in the substrate is not greater than one-third of the height of the substrate.

[0013] In one embodiment, each of the magnetic parts is located on the side of the substrate facing away from the chip, and each of the magnetic parts is regularly distributed on the substrate.

[0014] In one embodiment, the cross-sectional area of at least some of the magnetic parts is different from the cross-sectional area of the remaining magnetic parts.

[0015] In one embodiment, the magnetic part is located at the channel between adjacent chips, and at least one magnetic part exists at the channel between adjacent chips.

[0016] In one embodiment, the chip includes a Mini led chip or a Micro led chip.

[0017] Based on the same inventive concept, the present application also provides a laser welding method, which is applied to the laser welding system as described in any one of the foregoing, and includes:

[0018] Stacking and placing the backplane and the wafer on the bearing surface in sequence; wherein, a magnetic layer is provided on the substrate of the wafer;

[0019] Controlling the electromagnetic adsorption device to generate a magnetic force to adsorb the whole or part of the wafer; and

[0020] Controlling the laser welding assembly to weld the contact part between the chip and the backplane.

[0021] In the above laser welding method, by controlling the operation of the electromagnetic adsorption device, a magnetic force is generated to adsorb the whole or part of the wafer. In addition to adsorbing the wafer, this magnetic force can also effectively counteract the squeezing deformation of the wafer caused by the retaining ring, reduce the warpage amount of the wafer, so that the chip of the wafer contacts the backplane, improve the bonding yield, and reduce the occurrence of virtual soldering. Description of the Drawings

[0022] Figure 1 It is a schematic diagram of placing a wafer and a backplane on a retaining ring before laser welding in the prior art;

[0023] Figure 2 It is a schematic structural diagram of a laser welding system in an embodiment of the present application;

[0024] Figure 3 It is a schematic diagram of the arrangement of the electromagnetic adsorption part in an embodiment of the present application;

[0025] Figure 4 It is a schematic circuit diagram of the electromagnetic adsorption part in an embodiment of the present application;

[0026] Figure 5 It is a schematic diagram of the arrangement of the electromagnetic adsorption part in another embodiment of the present application;

[0027] Figures 6 - 12 It is a schematic diagram of different structures of the same wafer provided by the present application;

[0028] Figure 13 It is a schematic flowchart of a laser welding method in an embodiment of the present application.

[0029] Description of the Reference Numerals:

[0030] 10 - Carrier stage; 20a - Laser welding assembly; L1 - Induction coil; R1 - Adjustable resistor; B1 - Power supply; MD - Chip; ST - Substrate; CS1 - First magnetic part; CS2 - Second magnetic part; CB1 - Third magnetic part; CB2 - Fourth magnetic part; CB3 - Fifth magnetic part; CB4 - Sixth magnetic part; CB5 - Seventh magnetic part; Wf - Wafer; Bp - Backplane. Detailed Embodiments

[0031] To facilitate the understanding of the present application, the present application will be described more comprehensively below with reference to the relevant drawings. Preferred embodiments of the present application are shown in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of the present application more thorough and comprehensive.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terms used in the specification of this application are for the purpose of describing particular embodiments only and are not intended to limit this application.

[0033] It should be understood that spatial relationship terms such as "under", "beneath", "below", "underneath", "above", "over" and the like are used herein to describe the relationship of one element or feature shown in the figures to other elements or features. It should be understood that, in addition to the orientation shown in the figures, spatial relationship terms also include different orientations of the device during use and operation. For example, if the device in the figures is flipped, an element or feature described as "under" or "beneath" or "underneath" another element or feature will be oriented "over" the other element or feature. Thus, the exemplary terms "under" and "beneath" can include both an upper and a lower orientation. In addition, the device may also include additional orientations (such as, rotated 90 degrees or other orientations), and the spatial descriptors used herein are to be interpreted accordingly.

[0034] As used herein, the singular forms "a", "an" and "the" may also include the plural forms unless the context clearly dictates otherwise. It should also be understood that when the terms "comprise" and / or "include" are used in this specification, the presence of the stated features, integers, steps, operations, elements and / or components can be determined, but one or more other features, integers, steps, operations, elements, components and / or groups thereof are not precluded from being present or added. Also, as used herein, the term "and / or" includes any and all combinations of the associated listed items.

[0035] Embodiments of the invention are described herein with reference to cross-sectional views that are schematic illustrations of ideal embodiments (and intermediate structures) of the invention, and it is to be expected that variations in the shapes as a result of, for example, manufacturing techniques and / or tolerances. Accordingly, embodiments of the invention should not be limited to the particular shapes of regions shown herein, but include shape deviations resulting from, for example, manufacturing techniques. For example, an implanted region shown as rectangular will typically have rounded or curved features at its edges and / or an implanted concentration gradient, rather than a binary change from the implanted region to the non-implanted region. Similarly, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions shown in the figures are substantially schematic, and their shapes do not represent the actual shapes of regions of the device and do not limit the scope of the invention.

[0036] may be referred to Figure 1, as described in the background art of the present application, in the process of Micro-led manufacturing process, mass soldering is an important link for the efficient improvement of mass transfer. During the mass soldering process, the chips are fixedly grown on the wafer. The wafer and the backplane are positioned on the download table of the laser welding machine. The laser welding machine presses and fixes the wafer and the backplane on the download table through a snap ring. Since there is a layer of light-emitting chips between the wafer and the backplane, when the snap ring presses the wafer and the backplane, if there is no support of the light-emitting chips under the pressed part of the snap ring or only presses on the corner position of the light-emitting chips, it will cause the wafer to bend, resulting in a gap between some chips on the wafer and the backplane (mainly between the chip electrodes and the backplane pads). And this gap will cause poor soldering during the subsequent laser soldering process, thus seriously affecting the soldering yield.

[0037] Based on this, the present application hopes to provide a solution that can solve the above technical problems, and its detailed content will be described in the subsequent embodiments.

[0038] As Figure 2 shown, and can be referred to Figures 6 - 12 simultaneously. A laser welding system of the present application, which is mainly used to weld the chips MD on the wafer Wf to the backplane Bp. The laser welding system may include a stage 10, a laser welding component 20a, and a control system (not shown in the figure); the laser welding component 20a is located above the stage 10, and the laser welding component 20a is electrically connected to the control system; the stage 10 includes a bearing surface (not shown in the figure) for bearing the backplane Bp and the wafer Wf, and an electromagnetic adsorption device (not shown in the figure) is provided below the bearing surface; a magnetic layer (not shown in the figure) is provided on the substrate ST of the wafer Wf; the control system is configured to enable the laser welding component 20a and the electromagnetic adsorption device to weld the chip MD to the backplane Bp.

[0039] For the above laser welding system, by providing an electromagnetic adsorption device on the stage and a magnetic layer on the substrate of the wafer, when the wafer is placed on the backplane, the control system is used to control the electromagnetic adsorption device to work, so that it generates a magnetic force. In addition to adsorbing the wafer, this magnetic force can also effectively offset the extrusion deformation generated by the snap ring on the wafer, reduce the warping amount of the wafer, so that the chips of the wafer are in contact with the backplane, improve the bonding yield, and reduce the occurrence of poor soldering.

[0040] The wafer Wf of the present application mainly includes a substrate ST and several chips MD grown on the substrate ST. Among them, the substrate ST can be a transparent substrate, and the material of the transparent substrate includes inorganic materials or group III-V semiconductor materials. The inorganic materials include silicon carbide (SiC), germanium (Ge), sapphire, lithium aluminate (LiAlO2), zinc oxide (ZnO), glass or quartz. The group III-V semiconductor materials include indium phosphide (InP), gallium phosphide (GaP), gallium nitride (GaN), aluminum nitride (AlN) materials. The substrate ST should have sufficient strength to mechanically support the epitaxial layer and be able to transmit the light emitted from the epitaxial layer. The thickness of the substrate ST can be selected to be 50 μm or more. In addition, in order to facilitate the subsequent possible bonding process, mechanical processing (thinning) needs to be performed on the substrate ST, and the selected thickness of the substrate ST generally does not exceed 300 μm. The chip MD can include Mini led chips or Micro led chips.

[0041] Reference can be made to Figure 3 , the bearing surface of the present application is divided into a plurality of electromagnetic adsorption zones (not shown in the figure) by the electromagnetic adsorption device. At least one electromagnetic adsorption part (not shown in the figure) is provided in an electromagnetic adsorption zone, and the electromagnetic adsorption part is electrically connected to the control system. In this specific embodiment, the bearing surface is divided into 3 electromagnetic adsorption zones by the electromagnetic adsorption device. The 3 electromagnetic adsorption zones are arranged in concentric circles. It can be understood that in other embodiments, the plurality of electromagnetic adsorption zones can also be equally divided (such as Figure 5 shown), or other ways of dividing a circle into different regions should also be considered. Figure 3 In, the regions with different line widths represent different electromagnetic adsorption zones, and each electromagnetic adsorption zone is provided with an electromagnetic adsorption part. Further reference can be made to Figure 4 , the electromagnetic adsorption part mainly includes a power supply B1, an induction coil L1 and a variable resistor R1; the variable resistor R1 is connected between the power supply B1 and the induction coil L1. By adjusting the resistance value of the variable resistor R1, the magnitude of the current flowing through the induction coil L1 is adjusted, so as to generate different magnitudes of magnetic suction force. Please refer back to Figure 3 , which is the case where the induction coil L1, the variable resistor R1 and the power supply B1 are in different planes, Figure 3 In, the positive connection terminals 1+, 2+ and 3+ and the negative connection terminals 1-, 2- and 3- of the induction coil L1 are respectively connected to the variable resistor R1 and the power supply B1 on their respective circuits through vias.

[0042] Further, the number of turns and wire pitch of the induction coil L1 in different regions can be the same or different. It should be understood that the factors affecting the number of turns of the induction coil L1 can be the specific position of the electromagnetic adsorption area, the warping position of the wafer Wf, etc., and the factors affecting the wire pitch of the induction coil L1 can be the spacing between the chips MD and the warping position of the wafer Wf, etc.

[0043] Similarly, taking Figure 3 as an example, considering that the warping position of the wafer Wf is usually in the central region, therefore, when arranging the induction coils, the number of turns of the induction coil L1 located in the outer circle can be set to 4 turns (for example only), the number of turns of the induction coil L1 located in the middle circle is also set to 4 turns, and the number of turns of the induction coil L1 located at the center of the circle is set to 5 turns or more. Correspondingly, the wire pitch S1 of the induction coil L1 located in the outer circle is greater than the wire pitch S2 of the induction coil L1 located in the middle circle, and at the same time, S2 is greater than the wire pitch S3 of the induction coil L1 located at the center of the circle. Therefore, it can be ensured that a strong magnetic attraction force is generated in the area corresponding to the center of the wafer Wf to offset or weaken the compressive deformation generated by the snap ring. It can be understood that based on the concept of the present application, the number of turns and wire pitch of the induction coil L1 in different regions can be selected and adjusted according to the actual needs of those skilled in the art, and the present application will not be further elaborated herein.

[0044] In this specific embodiment, the magnetic layer can be a single layer or composed of multiple discrete components. Specifically, the magnetic layer of the present application can include several magnetic parts, and the magnetism of these magnetic parts is opposite to the electromagnetism generated after the aforementioned induction coil L1 is energized to achieve mutual attraction.

[0045] Further, in order to ensure that during the operation of the electromagnetic adsorption device, the magnetic parts are not attracted away from the wafer surface by the magnetic force generated by the induction coil L1, each of the magnetic parts of the present application is arranged to be at least partially embedded in the substrate ST, that is to say, each magnetic part can be partially embedded in the substrate ST, or can be entirely embedded in the substrate ST, or some magnetic parts can be partially embedded in the substrate ST and the remaining magnetic parts can be entirely embedded in the substrate ST, which usually also depends on the warping degree, position of the wafer Wf and the magnitude of the magnetic force generated by the induction coil L1.

[0046] Since the thickness of the substrate ST is usually between dozens and hundreds of nanometers, therefore, in order to ensure that after the magnetic part is embedded in the substrate ST, the substrate ST will not be damaged during the bonding process, therefore, in this specific embodiment, the height of the magnetic part embedded in the substrate in the direction perpendicular to the extension of the substrate is not greater than one-third of the height of the substrate.

[0047] Reference can be made to Figures 6 - 12 . It is a schematic diagram of the setting method of the magnetic layer of the present application. Among them, Figures 6 to 7This is the case where the magnetic layer and the chip MD are located on the same side, and the magnetic layer is mainly disposed at the channel between adjacent chips MD. Figures 8 - 12 This is the case where the magnetic layer and the chip MD are on different sides of the substrate. At the same time, the magnetic parts are regularly distributed on the substrate ST. Now, the structures of the magnetic layers in the two cases will be described in detail. It can be understood that Figures 6 - 12 In the corresponding embodiments, the main difference lies in the setting of the magnetic layer. For the convenience of description, the magnetic parts in different drawings are marked and distinguished subsequently. However, it should be clear that this marking and distinction does not mean that there are essential differences in the materials, manufacturing methods, etc. of the magnetic parts in different drawings.

[0048] As Figure 6 and Figure 7 shown, the magnetic layers disposed at the channels between adjacent chips MD are respectively shown. Figure 6 The first magnetic part CS1 shown in Figure 7 is mainly disposed and filled in the channel between adjacent chips MD, and the width of the first magnetic part CS1 is the same as the width of the channel. And

[0049] Figure 8 The several third magnetic parts CB1 shown in

[0050] Figure 9 are also located at the channels between adjacent chips MD. By using the channels between adjacent chips MD, the interference of the chip MD itself on the magnetic force can be reduced. In this specific embodiment, the width of the third magnetic part CB1 is the same as the width of the channel, and the height of its embedding in the substrate ST is not greater than one-third of the height of the substrate ST.

[0051] Figures 10 - 12 shows the situation where the cross-sectional area of some magnetic parts is different from that of the rest of the magnetic parts. Among them, Figure 10 the fifth magnetic part CB3 in Figure 11 is mainly located directly below the chip MD. Since the cross-sectional area of the magnetic part increases, in order to avoid damage to the substrate ST due to excessive magnetic force, in this specific embodiment, the fifth magnetic part CB3 is disposed directly below the chip MD. shows the case of a magnetic part with a larger area. The sixth magnetic part CB4 in this embodiment straddles two chips MD and covers the channel.Figure 12 The situation where the fourth magnetic part CB2 is located at the channel is shown. At the same time, there is a situation where some of the fourth magnetic parts CB2 cover the channel. It should be understood that based on the concept of this application, those skilled in the art can have more deformations on the basis of this application, and this application will not elaborate further here.

[0052] Referring to Figure 13 , this application also provides a laser welding method, which is applied to the laser welding system as described in any one of the foregoing. This method includes steps S100 - step S300:

[0053] Step S100, stacking the backplane and the wafer on the bearing surface in sequence; wherein, a magnetic layer is provided on the substrate of the wafer.

[0054] Step S200, controlling the electromagnetic adsorption device to generate a magnetic force to adsorb the whole or part of the wafer; and

[0055] Step S300, controlling the laser welding component to weld the contact part between the chip and the backplane.

[0056] In the above laser welding method, by controlling the electromagnetic adsorption device to work, a magnetic force is generated to adsorb the whole or part of the wafer. In addition to adsorbing the wafer, this magnetic force can also effectively offset the extrusion deformation generated by the snap ring on the wafer, reduce the warpage amount of the wafer, so that the chip of the wafer contacts the backplane, improve the bonding yield, and reduce the occurrence of virtual soldering.

[0057] It can be understood that for the similarities between this laser welding method and the foregoing laser welding system, reference can be made to the foregoing embodiments for understanding, and this application will not elaborate further here.

[0058] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above description, and all such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A laser welding system for welding chips on a wafer to a backplane, characterized in that, it includes a stage, a laser welding component and a control system; the laser welding component is located above the stage, and the laser welding component is electrically connected to the control system; the stage includes a bearing surface for bearing the backplane and the wafer, and an electromagnetic adsorption device is provided below the bearing surface; a magnetic layer is provided on the substrate of the wafer; and the control system is configured to enable the laser welding component and the electromagnetic adsorption device to weld the chip to the backplane.

2. The laser welding system according to claim 1, characterized in that, the bearing surface is divided into a plurality of electromagnetic adsorption areas by the electromagnetic adsorption device, at least one electromagnetic adsorption part is provided in an electromagnetic adsorption area, and the electromagnetic adsorption part is electrically connected to the control system.

3. The laser welding system according to claim 2, characterized in that, the electromagnetic adsorption part includes a power supply, an induction coil and an adjustable resistor; the adjustable resistor is connected between the power supply and the induction coil.

4. The laser welding system according to claim 2, characterized in that, the magnetic layer includes a plurality of magnetic parts, and each of the magnetic parts is at least partially embedded in the substrate.

5. The laser welding system according to claim 4, characterized in that, along the extension direction perpendicular to the substrate, the height of the magnetic part embedded in the substrate is not greater than one-third of the height of the substrate.

6. The laser welding system according to claim 5, characterized in that, each of the magnetic parts is located on the side of the substrate facing away from the chip, and each of the magnetic parts is regularly distributed on the substrate.

7. The laser welding system according to claim 6, characterized in that, the cross-sectional areas of at least some of the magnetic parts are different from those of the rest of the magnetic parts.

8. The laser welding system according to claim 5, characterized in that, the magnetic part is located at the channel between adjacent chips, and there is at least one such magnetic part at the channel between adjacent chips.

9. The laser welding system according to any one of claims 1-8, characterized in that, the chip includes a Mini led chip or a Micro led chip.

10. A laser welding method, characterized in that, applied to the laser welding system according to any one of claims 1-9, the laser welding method includes: stacking the backplane and the wafer on the bearing surface in sequence; wherein, a magnetic layer is provided on the substrate of the wafer; controlling the electromagnetic adsorption device to generate a magnetic force to adsorb the whole or part of the wafer; and controlling the laser welding component to weld the contact part between the chip and the backplane.

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