Patent Application
20220209084
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2020-216923, filed on Dec. 25, 2020, the entire contents of which are incorporated herein by reference.
An embodiment of the present invention relates to an LED module in which a light emitting diode (LED) is mounted in a bare chip state. An embodiment of the present invention relates to a pixel structure of a display device in which pixels are formed by light emitting diodes.
A micro LED display is known in which a microscopic light emitting diode called a micro LED is mounted on pixels arranged in a matrix. The micro LED displays are common to organic EL displays using organic electroluminescent devices in that pixels are self-light emitting. While the organic EL displays directly form organic electroluminescent elements on substrates called backplanes on which thin film transistors (TFTs) are fabricated, the micro LED displays differ in that LED chips fabricated on sapphire substrates and the like are mounted on backplanes.
The micro LED display is mounted on a backplane with micro LEDs face down. A flowable conductive paste or solder is used to mount the micro LEDs. In this case, it is necessary to precisely control the application position and the application amount of the conductive paste or solder. However, it is necessary to take care of short-circuits between electrodes due to the small chip size of micro LEDs.
An LED module in an embodiment according to the present invention includes a first electrode, a second electrode arranged isolated from the first electrode, a first bump on the first electrode, a second bump on the second electrode, a protrusion between the first electrode and the second electrode, and an LED chip having a first pad electrode and a second pad electrode. The protrusion has insulating properties, the first pad electrode of the LED chip is disposed opposite the first electrode, the second pad electrode is disposed opposite the second electrode, the first pad electrode is connected to the first electrode through the first bump, and the second pad electrode is connected to the second electrode through the second bump.
A display device in an embodiment according to the present invention includes a first electrode arranged in a region where pixels are formed, a second electrode arranged isolated from the first electrode, a first bump on the first electrode, a second bump on the second electrode, a protrusion arranged between the first electrode and the second electrode, and an LED chip having a first pad electrode and a second pad electrode. The protrusion has insulating properties, the first pad electrode of the LED chip is disposed opposite the first electrode, the second pad electrode is disposed opposite the second electrode, the first pad electrode is connected to the first electrode through the first bump, and the second pad electrode is connected to the second electrode through the second bump.
Hereinafter, embodiments of the present invention will be described with reference to the drawings and the like. The present invention may be carried out in various forms without departing from the gist of the invention thereof, and is not to be construed as being limited to any of the following embodiments. Although the drawings may schematically represent the width, thickness, shape, and the like of each part in comparison with the actual embodiment in order to clarify the description, they are merely examples and do not limit the interpretation of the present invention. In the present specification and each of the figures, elements similar to those described previously with respect to the figures already mentioned are designated by the same reference numerals (or numbers followed by a, b, etc.), and a detailed description thereof may be omitted as appropriate. Furthermore, the characters “first” and “second” appended to each element are convenient signs used to distinguish each element, and have no further meaning unless specifically described.
As used herein, where a member or region is “on” (or “below”) another member or region, this includes cases where it is not only directly on (or just under) the other member or region but also above (or below) the other member or region, unless otherwise specified. That is, it includes the case where another component is included in between above (or below) other members or regions. In the following description, unless otherwise specified, it is assumed that the LED chips are “on” or “above the substrate when the substrate is used as a reference and that the substrate is “under” or “below” the LED chips when the LED chips are used as a reference.
The micro LED in the present invention refers to an LED having a chip size of several micrometers or more and 100 micrometers or less, and the mini LED refers to an LED having a chip size of 100 micrometers or more. An embodiment of the present invention can use LEDs of any size and can be used depending on the pixel size of the LED module and the display device.
The LED module 100 has a structure in which an LED chip 104 is mounted on a first electrode 108 and a second electrode 110 which are arranged on an insulating surface 105. The insulating surface 105 is formed of an insulating substrate. The insulating surface 105 may also be formed by a first insulating layer 106 disposed on a substrate 102. Although not shown in
The first electrode 108 and the second electrode 110 are spaced apart on the insulating surface 105. In other words, the first electrode 108 and the second electrode 110 are electrically isolated from each other. The first electrode 108 and the second electrode 110 are arranged to match the spacing of a pair of electrodes (first pad electrode 116, second pad electrode 118) arranged with the LED chip 104, as will be described below.
Although not limited to the material forming the first electrode 108 and the second electrode 110, a conductive material having fluidity during coating or dropping and a material having good wettability are selected. The first electrode 108 and the second electrode 110 are formed of a conductive material such as, for example, gold (Au), copper (Cu), silver (Ag), tin (Sn), and aluminum (Al). The first electrode 108 and the second electrode 110 are formed of a thickness of 0.5 μm to 2 μm, 0.8 μm to 1.5 μm. Although the distance between the first electrode 108 and the second electrode 110 is arbitrary, when the LED chip 104 is a micro LED, the distance is 10 μm or less.
The LED chip 104 is a two-terminal device having a first pad electrode 116 and a second pad electrode 118 for so-called flip-chip mounting. For example, the LED chip 104 is mounted on the substrate 102, and the first pad electrode 116 and the second pad electrode 118 are arranged on the surface facing the first electrode 108 and the second electrode 110. One of the first pad electrode 116 and the second pad electrode 118 is connected to a p-type semiconductor layer while the other is connected to an n-type semiconductor layer. From such a connection structure, one of the first pad electrode 116 and the second pad electrode 118 is referred to as the p electrode and the other as the n electrode. Preferably, the first pad electrode 116 and the second pad electrode 118 are formed of a metal material to improve wettability with a flowable conductive material and have a metal surface such as gold (Au) or silver (Ag) to improve wettability with the flowable conductive material. This type of first pad electrode 116 and second pad electrode 118 are formed of a thickness of about 1 μm to 5 μm.
The LED chip 104 is mounted on the substrate 102 using a first bump 112 and a second bump 114. The first pad electrode 116 and the first electrode 108 are electrically connected by the first bump 112 and the second pad electrode 118 and the second electrode 110 are electrically connected by the second bump 114.
The first bump 112 and the second bump 114 are formed of a conductive material having fluidity in their initial state (prior to curing). For example, a conductive paste is used as the first bump 112 and the second bump 114. A silver paste, a carbon paste, or a paste having silver and carbon mixed therewith is used as the conductive paste. Tin may also be used as the solder paste for the first bump 112 and the second bump 114. For example, tin bumps may be used as the first bump 112 and the second bump 114. The first bump 112 and the second bump 114 have a height of about 1 μm to 10 μm in a state where they are dropped onto the first electrode 108 and the second electrode 110.
The conductive paste has fluidity, and is hardened by baking or simply drying after dropping onto an object. To form the first bump 112 and the second bump 114 by using a conductive paste, it is necessary to precisely control the position and the dropping amount to each of the first electrode 108 and the second electrode 110. When too much conductive paste is dropped, widening and shorting between the electrodes occurs. On the other hand, if the amount of conductive paste which is dropped is too small, the electrical continuity will be defective, and the force (adhesive force) that fixes the LED chip 104 will decrease, resulting in a problem of peeling.
In addition, after the conductive paste or solder paste is dropped onto the first electrode 108 and the second electrode 110, when the LED chip 104 is placed on the first electrode 108 and the second electrode 110 and pressed, there is a phenomenon in which the conductive paste spreads laterally. Excessive pressing force on the LED chip 104 increases the spread of the conductive paste and causes adjacent conductive paste to come into contact with each other. Further, when the amount conductive paste or the solder paste which is dropped is too large, the spread of the conductive paste or the solder paste becomes large, and the first electrode 108 and the second electrode 110 are short-circuited. When conductive paste or solder paste is used to form the first bump 112 and the second bump 114, precise control of the dropping amount is required. However, since the LED chip 104 has a small size, it is difficult to precisely control the dropping amount of the conductive paste and the solder paste.
For such microstructures, the LED module 100 according to the present embodiment has a structure in which a protrusion 120 is arranged between the first electrode 108 and the second electrode 110 that forms a contact with the LED chip 104. The protrusion 120 is disposed on the insulating surface 105 so as to cross areas where the first electrode 108 and the second electrode 110 are isolated. The protrusion 120 has insulating properties has a height (thickness) at which an upper end is arranged higher than an upper surface of the first electrode 108 and the second electrode 110. This type of protrusion 120 is formed of an insulating material. The protrusion 120 also may have a configuration in which the surface of the conductive material is covered with an insulating film.
The protrusion 120 is formed using, for example, an insulating film such as silicon oxide (SiO2) or aluminum oxide (Al2O3). The protrusion 120 may also be formed of organic insulating materials such as acrylics or epoxies, and the like.
The presence of the protrusion 120 prevents one or both of the first bump 112 and the second bump 114 from flowing and short-circuiting the first electrode 108 and the second electrode 110 when the first bump 112 and the second bump 114 are provided on the first electrode 108 and the second electrode 110 and the LED chip 104 is mounted. In other words, when the LED chip 104 is mounted on the substrate 102, even if the first bump 112 and the second bump flow laterally due to pressing, it is possible to prevent the bumps from coming into contact with each other by inhibiting the flow of the first bump 112 and the second bump 114 by the protrusion 120.
As shown in
Preferably, the height L1 of the protrusion 120 is greater than the sum of the thickness T1 of the first electrode 108 and the thickness T2 of the first pad electrode 116 and is not in contact with the LED chip 104. Also, the height L1 of the protrusion 120 is preferably higher than the height corresponding to the thickness T1 of the first electrode 108, and lower than the height corresponding to the sum of the thickness T1 of the first electrode 108, the thickness T2 of the first pad electrode 116, and the thickness T3 of the first bump 112. The height L1 of the protrusion 120 prevents interference with the LED chip 104 and allows the LED chip 104 to be electrically connected to the first electrode 108 and the second electrode 110 securely by the first bump 112 and the second bump 114, by satisfying such relationships. Further, since the protrusion 120 has the height L1, it is possible to suppress misalignment when the LED chip 104 is mounted. Even if some positional misalignment occurs when mounting the first bump 112 and the first electrode 108, and the second bump 114 and the second electrode 110, the protrusion 120 serves as a stopper for the first bump 108 and the second bump 114, and excessive positional misalignment can be suppressed, thereby preventing a defect when mounting the LED chip 104.
Alternatively, as shown in
As shown in
Similar to the configuration shown in
This embodiment illustrates a display device having an LED module configuration as shown in the first embodiment.
The first electrode 108 is arranged to overlap with a contact hole which passes through the third insulating layer 128 and the second insulating layer 126 and is connected to the scanning signal line 306. The second electrode 110 is arranged to overlap a contact hole which passes through the third insulating layer 128 and is connected to the data signal line 308. A passivation layer 130 may be further arranged on the top layer of the first electrode 108 and the second electrode 110.
The LED chip 104 is connected by the first pad electrode 116 to the first electrode 108 via the first bump 112 and the second pad electrode 118 to the second electrode 110 via the second bump 114. The provision of the protrusion 120 between the first electrode 108 and the second electrode 110 prevents short circuits between the electrodes of the LED chip 104 even when the first bump 112 and the second bump 114 are flowing. In other words, the protrusion 120 in the pixel 302 can provide a margin in the process of forming the first bump 112 and the second bump 114, thereby improving the productivity and the yield of the display device 300.
While the present embodiment illustrates an example in which a passive matrix type pixel is configured by an LED module, the present embodiment is not limited thereto, and may also be applied to an active matrix type pixel in which the light emission of the individual pixels is controlled by pixel circuit by a transistor.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-216923 | Dec 2020 | JP | national |
