Patent Publication Number: US-2022238471-A1

Title: Metal bump structure and manufacturing method thereof and driving substrate

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 110103177, filed on Jan. 28, 2021. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND 
     Technical Field 
     The disclosure relates to a bump structure and the manufacturing method thereof and a substrate, and in particular relates to a metal bump structure and the manufacturing method thereof and a driving substrate having the metal bump structure. 
     Description of Related Art 
     At present, active-matrix driving (AM Driving) micro light emitting diode displays (micro LED display) mostly use thin film transistor (TFT) glass substrates to drive the light emitting diodes (LEDs). However, because of thin firm process, the metal conductors on the thin film transistors and the Indium Tin Oxide (ITO) in the pixel area are only nanoscale. When the LEDs or surface mount devices (SMDs) are to be solder-bonded on the ITO conductive layer, they cannot form a reliable intermetallic compound (IMC) so as to be bonded together. In order to solve the above-mentioned problems, electroplating is currently implemented to form a thick copper layer on the ITO conductive layer. However, the process of electroplating thick copper is lengthy and complicated, which not only increases manufacturings cost but also causes environmental pollution because it is a wet process. 
     SUMMARY OF THE INVENTION 
     The disclosure provides a metal bump structure and the manufacturing method thereof, which has simple manufacturing process, low cost, and does not cause environmental pollution. 
     The disclosure further provides a driving substrate, including the metal bump structure, which has better structural reliability. 
     A manufacturing method of a metal bump structure is provided includes the following steps. A driving base is provided. At least one pad and an insulating layer are already formed on the driving base. The at least one pad is formed on an arrangement surface of the driving base and has an upper surface. The insulating layer covers the arrangement surface of the driving base and covers the at least one pad, and exposes a part of the upper surface of the at least one pad. A patterned metal layer is formed on the upper surface of the at least one pad exposed by the insulating layer, and extends to cover a part of the insulating layer. An electro-less plating process is performed so as to form at least one metal bump on the patterned metal layer. A first extension direction of the at least one metal bump is perpendicular to a second extension direction of the driving base. 
     In an embodiment of the disclosure, the steps of forming the patterned metal layer include forming a catalyst layer on the insulating layer and on the upper surface of the at least one pad exposed by the insulating layer, and performing an activation process and a patterning process on the catalyst layer so as to form the patterned metal layer. 
     In an embodiment of the disclosure, a method of forming the catalyst layer includes an inkjet printing method. 
     In an embodiment of the disclosure, a material of the catalyst layer includes nano-palladium (Nano-Pd), or any nano metal that can reduce chemical copper, such as nano-gold or nano-silver. 
     In an embodiment of the disclosure, the activation process includes a laser activation process or a heating process. 
     In an embodiment of the disclosure, a material of the patterned metal layer includes palladium, gold, or silver. 
     In an embodiment of the disclosure, a material of the metal bump includes copper, gold, tin or nickel. 
     In an embodiment of the disclosure, a cross-sectional shape of the metal bump includes a circle-like shape or a rectangular shape. 
     In an embodiment of the disclosure, a material of the at least one pad includes Indium Tin Oxide (ITO), or any sputtered metal layer such as titanium, copper, molybdenum, aluminum or chromium. 
     In an embodiment of the disclosure, a thickness of the metal bump is between 1 micrometer and 10 micrometers. 
     A metal bump structure of the disclosure is disposed on a driving base. A pad and an insulating layer are disposed on the driving base. The pad is disposed on an arrangement surface of the driving base and has an upper surface. The insulating layer covers the arrangement surface of the driving base and covers the pad, and exposes a part of the upper surface of the pad. The metal bump structure includes a patterned metal layer and a metal bump. The patterned metal layer is formed on the upper surface of the pad exposed by the insulating layer, and extends to cover a part of the insulating layer. The metal bump is disposed on the patterned metal layer, where a first extension direction of the metal bump is perpendicular to a second extension direction of the driving base. 
     In an embodiment of the disclosure, a material of the patterned metal layer includes palladium, or any nano metal that can reduce chemical copper, such as gold or silver. 
     In an embodiment of the disclosure, a material of the metal bump includes copper, gold, tin or nickel. 
     In an embodiment of the disclosure, a cross-sectional shape of the metal bump includes a circle-like shape or a rectangular shape. 
     In an embodiment of the disclosure, a thickness of the metal bump is between 1 micrometer and 10 micrometers. 
     A driving substrate of the disclosure includes a driving base, at least one active element, at least one pad, an insulating layer, and at least one metal bump structure. The driving base includes an arrangement surface. The at least one active element is disposed on the arrangement surface of the driving base. The at least one pad is disposed on the arrangement surface of driving base and has an upper surface. The insulating layer covers the arrangement surface of the driving base, covers the at least one active element, and covers the at least one pad, and the insulating layer exposes a part of the upper surface of the at least one pad. The metal bump structure includes a patterned metal layer and a metal bump. The patterned metal layer is disposed on the upper surface of the at least one pad exposed by the insulating layer, and extends to cover a part of the insulating layer. The metal bump is disposed on the patterned metal layer. A first extension direction of the metal bump is perpendicular to a second extension direction of the driving base. 
     In an embodiment of the disclosure, a material of the patterned metal layer includes palladium, and a material of the metal bump includes copper, gold, tin or nickel. 
     In an embodiment of the disclosure, a cross-sectional shape of the metal bump includes a circle-like shape or a rectangular shape. 
     In an embodiment of the disclosure, a thickness of the metal bump is between 1 micrometer and 10 micrometers. 
     In an embodiment of the disclosure, a material of the at least one pad includes ITO, or any sputtered metal layer such as titanium, copper, molybdenum, aluminum or chromium. 
     Based on the above, according to the manufacturing method of the metal bump structure of the disclosure, the metal bump is formed through an electro-less plating process. Compared with the existing wet electroplating process to form metal bumps, dry process is adopted in the disclosure so as to form metal bumps, which has simple manufacturing process, low cost, and does not cause environmental pollution. In addition, with the driving substrate of the metal bump structure of the disclosure, when the light-emitting element is subsequently bonded, good intermetallic compound can be formed between the light-emitting element and the metal bump structure, which has better structural reliability. 
     In order to make the above-mentioned features of the disclosure more obvious and understandable, the embodiments are specifically described below in conjunction with the accompanying drawings for detailed description as follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure. 
         FIG. 1A  to  FIG. 1D  are schematic cross-sectional views of a manufacturing method of a metal bump structure according to an embodiment of the disclosure. 
         FIG. 2  is a schematic cross-sectional view of a metal bump structure according to another embodiment of the disclosure. 
         FIG. 3A  is a schematic cross-sectional view of a driving substrate according to an embodiment of the disclosure. 
         FIG. 3B  is a schematic cross-sectional view of a light-emitting element on a driving substrate of  FIG. 3A . 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the exemplary embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
       FIG. 1A  to  FIG. 1D  are schematic cross-sectional views of a manufacturing method of a metal bump structure according to an embodiment of the disclosure. Please refer to  FIG. 1A  for the manufacturing method of the metal bump structure of the present embodiment. First, a driving base  110  is provided. At least one pad (two pads  120  are shown schematically) and an insulating layer  130  have been formed on the driving base  110 . The pad  120  is formed on an arrangement surface  112  of the driving base  110  and has an upper surface  122 . The insulating layer  130  covers the arrangement surface  112  of the driving base  110  and covers the pad  120 , and exposes a part of the upper surface  122  of the pad  120 . Here, the driving base  110  is, for example, a thin film transistor (TFT) glass substrate, and the material of the pad  120  is, for example, ITO, or any sputtered metal layer such as titanium, copper, molybdenum, aluminum, or chromium. That is, the pad  120  and a pixel electrode on the driving base  110  are on the same layer, and both are made of ITO. 
     Next, referring to  FIG. 1C , a patterned metal layer  210  is formed on the upper surface  122  of the pad  120  exposed by the insulating layer  130 , and extends to cover a part of the insulating layer  130 . In detail, please refer to  FIG. 1B  for the steps of forming the patterned metal layer  210 . A catalyst layer  210   a  is formed on the insulating layer  130  and on the upper surface  122  of the pad  120  exposed by the insulating layer  130 . A positive projection of the catalyst layer  210   a  on the driving base  110  is larger than a positive projection of the corresponding pad  120  on the driving base  110 . Here, the method for forming the catalyst layer  210   a  is, for example, an inkjet printing method, and a material of the catalyst layer  210   a  is, for example, nano-palladium, or any nano metal that may reduce chemical copper, such as nano-gold or nano-silver. 
     Next, please refer to both  FIG. 1B  and  FIG. 1C . An activation process and a patterning process are performed on the catalyst layer  210   a  so as to form the patterned metal layer  210 . A positive projection of patterned metal layer  210  on the driving base  110  is smaller than a positive projection of the corresponding pad  120  on the driving base  110 . Here, the activation process is, for example, a laser activation process or a heating process. If nano-palladium (in an ion state) is used as the catalyst layer  210   a , metal palladium can be formed through the activated catalyst layer  210   a , and then the patterned metal layer  210  can be formed by patterning the metal palladium. As a result, the material of the patterned metal layer of the present embodiment is embodied as palladium, or any nano metal that may reduce chemical copper, such as gold or silver. 
     Finally, referring to  FIG. 1D , an electro-less process is performed so as to form at least one metal bump (two metal bumps  220   a  are schematically shown) on the patterned metal layer  210 . The electro-less plating process is based on oxidation-reduction reaction, which has a low cost and short production time, in which desired shape is selectively formed according to requirements. A first extension direction D 1  of the metal bump  220   a  is perpendicular to a second extension direction D 2  of the driving base  110 . Here, a material of the metal bump  220   a  is, for example, copper, gold, or nickel. A cross-sectional shape of the metal bump  220   a  is, for example, a rectangular shape, and a thickness T of the metal bump  220   a  is, for example, between 1 micrometer and 10 micrometers. At this point, the manufacturing of the metal bump structure  200   a  is completed. 
     In terms of structure, referring again to  FIG. 1D , the metal bump structure  200   a  is disposed on the driving base  110 . A pad  120  and an insulating layer  130  are disposed on the driving base  110 . The pad  120  is disposed on the arrangement surface  112  of driving base  110  and has the upper surface  122 . The insulating layer  130  covers the arrangement surface  112  of the driving base  110  and covers the pad  120 , and exposes a part of the upper surface  122  of the pad  120 . The metal bump structure  200   a  includes the patterned metal layer  210  and metal bump  220   a . The patterned metal layer  210  is disposed on the upper surface  122  of the pad  120  exposed by the insulating layer  130 , and extends to cover a part of the insulating layer  130 , where the material of the patterned metal layer  210  is palladium, for example, or any nano metal that may reduce chemical copper, such as gold or silver. The metal bump  220   a  is disposed on the patterned metal layer  210 , where a first extension direction D 1  of the metal bump  220   a  is perpendicular of second extension direction D 2  of the driving base  110 . Here, a material of the metal bump  220   a  is, for example, copper, gold, or nickel, and a cross-sectional shape of the metal bump  220   a  is, for example, a rectangular shape, and a thickness T of the metal bump  220   a  is, for example, between 1 micrometer and 10 micrometers. 
     Since in the present embodiment, the metal bump  220   a  is formed through the electro-less plating process, compared with the existing wet electroplating process to form metal bumps, the metal bump structure  200   a  of the present embodiment adopts dry process to form the metal bump  220   a , which has simple manufacturing process, low cost, and does not cause environmental pollution. 
     Note that the reference numerals and some contents of the aforementioned embodiment are used in the following embodiments, where the same numeral is used to represent the same or similar components, and the description of the same technical content is omitted. For the description of omitted contents, please refer to the aforementioned embodiment, which will not be repeated in the following embodiments. 
       FIG. 2  is a schematic cross-sectional view of a metal bump structure according to another embodiment of the disclosure. Please refer to both  FIG. 1D  and  FIG. 2 . The metal bump structure  200   b  of the present embodiment is similar to the metal bump structure  200   a . The difference between the two is: in the present embodiment, a cross-sectional shape of the metal bump  220   b  of the metal bump structure  200   b  is embodied as a circle-like shape. In other words, the metal bump structure  200   a  may be further subjected to a high-temperature reflow process to form a desired shape of the metal bump  220   b.    
       FIG. 3A  is a schematic cross-sectional view of a driving substrate according to an embodiment of the disclosure.  FIG. 3B  is a schematic cross-sectional view of disposing a light-emitting element on a driving substrate of  FIG. 3A . First please refer to  FIG. 3A . In the present embodiment, a driving substrate  100  includes the driving base  110 , the at least one pad (two pads  120  are shown schematically), the insulating layer  130 , at least one active element (one active element  140  is schematically shown), and the at least one metal bump structure (two metal bump structures  200   a  are shown schematically). The driving base  110  has the arrangement surface  112 , where the driving base  110  is, for example, a thin film transistor (TFF) glass substrate. The active element  140  is disposed on the arrangement surface  112  of the driving base  110 . The active element  140  is, for example, a thin film transistor, but the disclosure is not limited thereto. The pad  120  is disposed on the arrangement surface  112  of the driving base  110  and has the upper surface  122 . A material of the pad  120  is, for example, ITO, or any sputtered metal layer such as titanium, copper, molybdenum, aluminum, or chromium. That is, the pad  120  and a pixel electrode on the driving base  110  are on the same layer, and both are made of ITO. The insulating layer  130  covers the arrangement surface  112  of the driving base  110 , covers the active element  140 , and covers the pad  120 , and the insulating layer  130  exposes a part of the upper surface  122  of the pad  120 . The metal bump structure  200   a  includes the patterned metal layer  210  and metal bump  220   a . The patterned metal layer  210  is disposed on the upper surface  122  of the pad  120  exposed by the insulating layer  130 , and extends to cover a part of the insulating layer  130 . The metal bump  220   a  is disposed on the patterned metal layer  210 . A first extension direction D 1  of the metal bump  220   a  is perpendicular to second extension direction D 2  of the driving base  110 . 
     With reference to  FIG. 3B , a light-emitting element  300  is disposed on the driving substrate  100  to so as form a display with the driving substrate  100 , where the light-emitting element  300  is disposed on the metal bump  220   a  of the metal bump structure  200   a . Furthermore, the light-emitting element  300  is, for example, a micro LED, where each light-emitting element  300  is bonded to two metal bump structures  200   a  of the driving substrate  100  by flip-chip bonding. The light-emitting element  300  is structurally and electrically connected to an upper surface  222  of the metal bump  220   a , and is electrically connected to the pad  120  through the metal bump  220   a  and the patterned metal layer  210 . Since the metal bump  220   a  with a certain thickness is formed by electro-less plating process in the present embodiment, when the light-emitting element  300  and the metal bump structure  200   a  are solder-bonded, a good intermetallic compound may be formed between the light-emitting element  300  and the metal bump structure  200   a , such that better structure reliability can be achieved. 
     Based on the above, according to the manufacturing method of the metal bump structure of the disclosure, the metal bump is formed through an electro-less plating process. Compared with the existing wet electroplating process to form metal bumps, dry process is adopted in the disclosure to form metal bumps, which has the simple manufacturing process, low cost, and does not cause environmental pollution. In addition, with the driving substrate of the metal bump structure of the disclosure, when the light-emitting element is subsequently bonded, good intermetallic compound interface can be formed between the light-emitting element and the metal bump structure, which has better structural reliability. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents.