Flip LED chip and light-emitting device

Abstract

According to the flip LED chip and the light-emitting device provided by the utility model, the n-pole area is in a regular pattern, is located at the central position of the chip, and is used for forming an n-type electrode; the p-pole regions are at least located at two vertex angles at diagonal positions in the chip and are used for forming p-type electrodes; the n-type electrode is arranged in the central area of the chip and connected with the n-type semiconductor layer through the through hole, heat dissipation through the n-pole electrode is facilitated when the chip works, and the p-type electrode is at least arranged at the two vertex angles, located at the diagonal positions, of the chip, so that when reflow soldering is conducted, even if one side is suspended, the p-type electrode on the other side can make good contact with a packaging substrate, and the reliability of the chip is improved. The condition of pseudo soldering of the p-type electrode is avoided, and the reliability of the product is greatly improved.

Description

Technical Field

[0001] The utility model relates to the technical field of semiconductors, in particular to a flip-chip LED chip and a light-emitting device. Background Art

[0002] High-power flip-chip LED chips are widely used in lighting applications such as automotive headlights, flashlights, searchlights, stage lights, and projectors. These technologies typically require high current densities, placing higher demands on the chip's heat dissipation performance. Conventional methods for flip-chip LED chips typically create two chip electrode pads of equal area. In this configuration, the gap (gap) formed by the two chip electrode pads is typically located in the middle of one electrode surface. However, high-power flip-chip LED chips generate high temperatures in this middle area during operation. The lack of a pad structure in this area compromises heat dissipation in this region, resulting in flip-chip LED chips having inferior heat dissipation performance to vertical LED chips of the same power.

[0003] To address these technical issues, some researchers have proposed increasing the area of ​​the n-pole pad, creating two pads, one large and one small. This approach allows the gap formed by the two chip electrode pads to be closer to the side of the chip. While this structure improves the heat dissipation performance of the flip-chip LED chip, it has been found in practice that when the chip is soldered to the surface of the package substrate, the p-pole pad will float and warp, causing a cold solder joint, resulting in poor electrical contact and malfunction of the chip. Utility Model Content

[0004] In order to overcome the above shortcomings, the utility model provides a flip-chip LED chip and a light-emitting device, which improve the heat dissipation performance of the flip-chip and effectively avoid the technical problem of cold solder joints during reflow soldering.

[0005] The technical solution provided by this utility model is:

[0006] In one aspect, the present invention provides a flip-chip LED chip, which is square in shape and includes:

[0007] growth substrate;

[0008] A semiconductor multilayer structure formed on the surface of the growth substrate includes an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer stacked in sequence, and the surface is divided into an n-pole region and a p-pole region, wherein the p-pole region is disposed at least at two diagonal corners of the LED chip;

[0009] a reflective metal structure formed on a surface of one side of the p-type semiconductor layer in the semiconductor multilayer structure;

[0010] An n-type electrode through hole formed in the n-pole region and penetrating to the n-type semiconductor layer;

[0011] An insulating layer extending to the sidewall of the n-type electrode through-hole is formed on the surface of the reflective metal structure, and a p-type electrode through-hole connected to the reflective metal structure is configured in a portion of the insulating layer located in the p-pole region;

[0012] an n-type electrode formed by connecting all n-type electrode through-holes in the n-pole region to the surface of the insulating layer;

[0013] The p-type electrode is formed on the surface of the reflective metal structure and connects the p-type electrode through holes located in the p-pole region at the same vertex angle.

[0014] In another aspect, the present invention provides a light emitting device, comprising:

[0015] A packaging substrate, with an n-pole solder joint and a p-pole solder joint provided on the surface;

[0016] The flip-chip LED chip is soldered to the surface of the package substrate, wherein the n-type electrode is connected to the n-pole solder joint on the surface of the package substrate, and the p-type electrode is connected to the p-pole solder joint on the surface of the package substrate;

[0017] A fluorescent adhesive layer formed at least on the light-emitting surface of the LED chip;

[0018] A transparent light-emitting structure formed on the surface of the fluorescent adhesive layer;

[0019] A reflective adhesive layer is provided at least around the LED chip.

[0020] The flip-chip LED chip and light-emitting device provided by the present invention arrange the n-type electrode in the central area of ​​the chip and connect it to the n-type semiconductor layer through the n-type electrode through-hole, which is conducive to heat dissipation through the n-type electrode when the chip is working. The p-type electrode is arranged at least at two diagonal corners of the chip. In this way, during reflow soldering, even if one side is suspended in the air, the p-type electrode on the other side can still make good contact with the packaging substrate, avoiding the problem of p-pole cold soldering, thereby greatly improving the reliability of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a structural diagram of the first embodiment of the flip-chip LED chip in the present invention;

[0022] Figure 2 for Figure 1 A cross-sectional view of a flip-chip LED chip along line AA;

[0023] Figure 3 This is a comparison chart of the test results of chip A and chip B in this utility model;

[0024] Figure 4This is a structural diagram of a second embodiment of a flip-chip LED chip in the present invention;

[0025] Figure 5 This is a structural diagram of a third embodiment of a flip-chip LED chip in the present invention;

[0026] Figure 6 This is a schematic structural diagram of a fourth embodiment of a flip-chip LED chip in the present invention;

[0027] Figure 7 This is a structural diagram of an embodiment of the light-emitting device of the present invention;

[0028] Figure 8 for Figure 7 A schematic top view of the light-emitting device shown.

[0029] Reference numerals:

[0030] 10-growth substrate, 20-semiconductor multilayer structure, 21-n-type semiconductor layer, 22-light-emitting layer, 23-p-type semiconductor layer, 30-reflective metal structure, 40-insulating layer, 41-n-type electrode through-hole, 42-p-type electrode through-hole, 51-n-type electrode, 52-p-type electrode, 100-packaging substrate, 200-flip-chip LED chip, 300-fluorescent adhesive layer, 400-light-emitting structure, 500-reflective adhesive layer. DETAILED DESCRIPTION

[0031] In order to more clearly illustrate the implementation cases of the present invention or the technical solutions in the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without inventive work.

[0032] One embodiment of the present utility model provides a flip-chip LED chip, which is square in shape as a whole. The chip comprises: a growth substrate; a semiconductor multilayer structure formed on the surface of the growth substrate, comprising an n-type semiconductor layer, a light-emitting layer and a p-type semiconductor layer stacked in sequence, and the surface is divided into an n-pole region and a p-pole region, the p-pole region being arranged at least at two opposite corners of the LED chip; a reflective metal structure formed on the surface of one side of the p-type semiconductor layer in the semiconductor multilayer structure; an n-type electrode through-hole formed in the n-pole region and penetrating to the n-type semiconductor layer; an insulating layer formed on the surface of the reflective metal structure and extending to the sidewall of the n-type electrode through-hole, wherein a portion of the insulating layer located in the p-pole region is provided with a p-type electrode through-hole connected to the reflective metal structure; an n-type electrode formed on the surface of the insulating layer connecting all the n-type electrode through-holes in the n-pole region; and a p-type electrode formed on the surface of the reflective metal structure and connecting the p-type electrode through-holes in the p-pole region located at the same vertex angle.

[0033] The flip-chip LED chip is square in shape as a whole, with dimensions ranging from 30mil to 160mil. The specific size can be determined according to actual application needs. For example, it can be designed as a square with consistent length and width, or as a rectangle with one adjacent side longer than the other. The semiconductor multilayer structure includes an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer, which are sequentially grown on the surface of a transparent growth substrate such as sapphire or silicon carbide. When an appropriate voltage is applied to them, electrons in the n-type semiconductor layer recombine with holes in the p-type semiconductor layer in the light-emitting layer to emit light of a specific wavelength. Since the flip-chip emits light from the other side where the electrode is located, a reflective metal structure is further provided on the surface of the p-type semiconductor layer to reflect the light emitted toward the side where the electrode is located. The reflective metal structure contains conductive metals with high reflectivity, such as Ag and Al. The p-type and n-type electrodes can be made of any conventional material, such as Sn (tin), Cu (copper), Ni (nickel), and their alloys (such as AuSn alloy). For high-power flip-chips, electrodes made of AuSn alloy are often used. When using easily oxidized materials such as Cu, an anti-oxidation protective layer such as Ni or Au should also be formed on its surface. To prevent short circuits between the p-type and n-type electrodes, an insulating layer is provided on the surface of the reflective metal structure to isolate the conductive structures of different electrical properties. With the exception of the n-type and p-type electrode through-holes that subsequently conduct electricity to the semiconductor multilayer structure, the insulating layer essentially covers the entire chip surface.

[0034] The n-pole region is used to form an n-type electrode to conduct electricity to the n-type semiconductor layer in the chip, and utilizes the excellent thermal conductivity of the electrode metal to dissipate the heat generated during the operation of the chip. In order to ensure that the electrode has good conductivity and heat dissipation effects on the chip, the position of the n-pole region is in the center of the chip, that is, it can at least cover the center point where the chip diagonals intersect, and the area occupied is at least half of the entire chip area. In order to evenly expand the current, the shape of the n-pole region can also be set to a symmetrical regular figure, which can generally be a regular polygon, circle, rhombus, triangle, etc. The use of such a symmetrical shape design can maximize the balance of the current diffusion speed and distribution in multiple directions, so that the current expands evenly in all directions; in other embodiments, it can also be set to an irregular shape, which can be determined according to the actual application requirements of the chip.

[0035] By setting an n-type electrode through-hole in the n-pole region, which passes through the reflective metal structure, the p-type semiconductor layer and the n-type semiconductor layer, it is convenient to conduct electricity to the n-type semiconductor layer. The n-type electrode through-hole passes through the reflective metal structure, the light-emitting layer and the p-type semiconductor layer to the n-type semiconductor layer, and is obtained by etching the semiconductor multilayer structure in the n-pole region using etching technologies such as ICP (inductively coupled plasma) dry etching; in order to prevent the conductive material in the n-type electrode through-hole from conducting electricity to the reflective metal structure, the light-emitting layer and the p-type semiconductor layer on the side wall of the through-hole, an insulating material (such as SiO2, SiN, etc.) is also formed on the side wall of the through-hole, that is, the insulating layer is set after the through-hole is etched. In this way, the insulating layer can be conveniently formed on the side wall of the through-hole to prevent the conductive material in the subsequent n-type electrode through-hole from conducting electricity to the side wall. It should be understood that the insulating layer is not formed at the bottom of the n-type electrode through-hole. Subsequently, all n-type electrode through-holes in the n-pole region are further connected to the surface of the insulating layer in the n-pole region to form an n-type electrode. The n-type electrode is formed in the n-pole region. That is to say, the area of ​​the n-pole region referred to above is the area of ​​the n-type electrode, that is, the n-type electrode is in the center of the chip and can at least cover the center point where the diagonals of the chip intersect, and the area occupied is at least half of the area of ​​the entire chip. The specific content will not be repeated here.

[0036] At the same time, since the installation of n-type electrode through-holes requires sacrificing the light-emitting layer and p-type semiconductor layer, if too many n-type electrode through-holes are provided, more of the light-emitting layer and p-type semiconductor layer must be removed, which has a negative impact on the chip's luminescence performance; if too few n-type electrode through-holes are provided, it is not conducive to forming a good conductive effect on the n-type semiconductor layer. Therefore, in practical applications, the design of n-type electrode through-holes must comprehensively consider factors such as the chip's luminescence performance and current expansion. Before industrial application, simulation methods can be used to simulate the performance of LED chips (electrical test yield, failure under high current aging, light decay, etc.) with different n-type electrode through-hole sizes and numbers. After selecting a certain number of design schemes, further verification through different DOE (Design of Experiments) experiments can be carried out to select a reasonable design scheme.

[0037] By forming a p-type electrode through-hole in the p-pole region that penetrates to the surface of the reflective metal structure, it is convenient to conduct electricity to the p-type semiconductor layer. Since the entire surface of the p-type semiconductor layer is provided with a reflective metal structure, the reflective metal structure can be directly used to uniformly conduct electricity to the p-type semiconductor layer. The p-type electrode through-hole only needs to penetrate the insulating layer. Subsequently, a p-type electrode is formed in the p-type electrode through-hole and on the surface of the reflective metal structure. Then, the current flows through the p-type electrode and the reflective metal structure to the p-type semiconductor layer. The p-pole region is used to open a p-type electrode through-hole to conduct electricity to the p-type semiconductor layer. To ensure the reflow soldering effect and avoid problems such as cold soldering, the p-pole region is located at at least two diagonal positions of the chip, that is, p-type electrodes are formed at least at the two top corners of the diagonal position of the square chip, and the connection line between the two p-type electrodes crosses the n-type electrode. This design allows the n-type electrode in the center of the chip to be in good contact with the packaging substrate when the chip is placed on the surface of the packaging substrate, and the p-type electrodes at the two diagonals are at the farthest distance from each other in the chip. Even if the center of gravity of the chip is not in the center area and one side of the chip is tilted, the other side can still be in good contact with the packaging substrate. No matter how the chip is placed, there is always one p-type electrode at different positions that can fully contact the solder joint on the packaging substrate, thereby avoiding poor conductivity of the chip caused by cold soldering. The specific number of p-type electrodes can be designed based on application requirements. If the chip itself is small (e.g., 30-45 mil), to maximize the n-type electrode area and facilitate heat dissipation, p-type electrodes can be placed only at the two diagonal corners. If the chip itself is large, three, four, or even more p-type electrodes can be provided. With this design, the center of gravity of the LED chip is located at the center of the overall LED chip pattern, or offset toward one of the p-pole regions, ensuring that at least one of the p-type electrodes at the corners forms a good bond with the package substrate. Furthermore, high temperatures degrade the luminous performance of LED chips; therefore, chip heat dissipation plays a crucial role in ensuring the LED chip's luminous intensity. Compared to traditional flip-chip LED chips, where the n-type and p-type electrodes have equal areas and are located on both sides of the same chip surface, this configuration with the n-type electrode located at the center of the chip facilitates heat dissipation. This enhanced heat dissipation reduces the chip's temperature, thereby increasing luminous intensity. This phenomenon is more pronounced at higher current densities.

[0038] In addition, the present embodiment is an improvement to the above-described embodiment. The reflective metal structure formed on the surface of the p-type semiconductor layer includes: a p-type ohmic contact layer formed on the surface of the p-type semiconductor layer; a dielectric reflective layer formed on the surface of the p-type ohmic contact layer, with conductive vias formed therein; and a metal reflective layer formed on the surface of the dielectric reflective layer and within the conductive vias. The reflective metal structure in the LED chip provides ohmic contact, conductivity, and reflection for the p-type semiconductor layer. The fabrication process includes vapor deposition, photolithography, and a lift-off process. During the fabrication process, the p-type ohmic contact layer is deposited on the surface of the p-type semiconductor layer. The p-type ohmic contact layer can be made of a material such as ITO (a transparent conductive layer) to form an ohmic contact with the p-type semiconductor layer. The dielectric reflective layer can be made of a dielectric material such as SiO2, SiN, or Al2O3. The dielectric reflective layer is deposited using plasma-enhanced chemical vapor deposition to enhance reflective performance. Since the dielectric reflective layer material has poor electrical conductivity, it is necessary to prepare conductive vias in the dielectric reflective layer through photolithography and a wet etching process using an oxide etchant (BOE). Then, metal materials are filled on the surface of the dielectric reflective layer and in the conductive vias to form a metal reflective layer. The metal material can be selected from one or more of Al, Cr, Ti, Ni, and Ag. Usually, the metal material inside the conductive via and the metal reflective layer on the surface of the dielectric reflective layer are formed as one piece and have the same material. The metal reflective layer is connected to ITO through the conductive vias. Generally speaking, a plurality of evenly distributed conductive vias are formed in the dielectric reflective layer, which can evenly extend the current to the p-type semiconductor layer. For example Figure 1 As shown, the conductive through-holes in the dielectric reflective layer are uniformly distributed throughout the LED chip (including the n-pole region, the p-pole region, and the gap between the n-pole region and the p-pole region), and are generally smaller than the n-type electrode through-holes 41 that penetrate the n-type semiconductor layer. Moreover, for chips with higher current intensity, the distribution density of the conductive through-holes is greater than that of ordinary chips. While ensuring the reflection performance, as many conductive through-holes as possible are provided. After the LED chip is energized, the current flows through the p-type electrode to the metal reflective layer, and then passes through these uniformly distributed conductive through-holes, uniformly expanding to the entire p-type semiconductor layer in the LED chip.

[0039] The following describes the structure of a flip-chip LED chip through an example. Figure 1 and Figure 2 ( Figure 2 for Figure 1As shown in the cross-sectional schematic diagram along the middle line AA, the LED chip is square in shape as a whole and includes: a growth substrate 10; a semiconductor multilayer structure 20 formed on the surface of the growth substrate 10, including an n-type semiconductor layer 21, a light-emitting layer 22 and a p-type semiconductor layer 23 stacked in sequence, and the surface is divided into an n-pole region and a p-pole region; the n-pole region is arranged in a regular symmetrical pattern at the center of the LED chip to form an n-type electrode; the p-pole region is located at two diagonal positions of the chip to form a p-type electrode. As can be seen from the figure, the n-pole region and the p-pole region are symmetrically arranged along the two diagonals of the LED chip; a reflective metal structure 30 ( Figure 2 The reflective metal structure is simplified, where the conductive vias are Figure 2); n-type electrode through-holes 41 formed in the n-pole region and extending through the n-type semiconductor layer; an insulating layer 40 formed on the surface of the reflective metal structure 30 and extending to the sidewalls of the n-type electrode through-holes, and a p-type electrode through-hole 42 connected to the reflective metal structure is provided in a portion of the insulating layer located in the p-pole region; an n-type electrode 51 formed on the surface of the insulating layer connecting all n-type electrode through-holes in the n-pole region; a p-type electrode 52 formed in the p-type electrode through-hole and on the surface of the reflective metal structure; the n-type electrode 51 and the p-type electrode 52 are of the same height, so that when they are inverted and reflowed on the surface of the packaging substrate, they can simultaneously contact the surface of the packaging substrate. In this example, three electrodes are formed on the same side of the chip, including an n-type electrode 51 located at the center of the chip and two p-type electrodes 52 located at diagonal positions. The two p-type electrodes are arranged at the top corners of the chip in an equilateral right triangle with the help of the top corners of the chip, and the n-type electrode is located on the surface of the chip except for the p-type electrode, and a gap is formed between the n-type electrode and the two p-type electrodes; and the n-type electrode is symmetrically arranged on the surface of the n-pole region along the two symmetry axes of the overall chip, and the p-type electrode is symmetrically arranged on the surface of each p-pole region along the two symmetry axes of the overall chip; that is, the entire chip presents a symmetrical pattern along the two diagonals of the rectangle, and the center of gravity of the chip is located at the center of the overall pattern of the LED chip: due to the two The connection line between the p-type electrodes crosses the n-type electrodes, rather than being on one side of the n-type electrodes. Therefore, during reflow soldering, when the chip electrodes are placed upside down on the surface of the package substrate with the chip electrodes facing downward, the chip as a whole will not be biased to one side. Even if the center of gravity of the chip is accidentally biased to one side, the p-pole regions are located at the vertices of the two diagonal positions. No matter which side the chip is offset to, at least one p-pole region on the side where the center of gravity is located can fully contact the package substrate. In other words, the center of gravity can be biased to at least one of the p-pole regions. Since the two p-type electrodes are not located on the same side, but are located at a diagonal position, it can also be ensured that at least one of the two p-type electrodes can fully contact the solder joint on the package substrate. In other embodiments, in addition to an equilateral right triangle, the p-type electrode can also form other shapes, such as a fan, a circle, or even an irregular shape. This embodiment does not limit the shape of the p-type electrode. Generally, the lines at the angle between the n-type electrode 51 and the p-type electrode 52 are designed to be arc-shaped to prevent current from gathering at the tip of the n-type electrode or the p-type electrode. The arc shape can be formed using drawing software, such as the automatic fillet function in CAD, or by other methods, as long as the two adjacent edges transition naturally through the arc.

[0040] The following comparative experiment illustrates the heat dissipation effect of the flip-chip LED chip in this example. Chip A is the example in which the n-type electrode is located in the middle of the chip and the p-type electrode is located at the two diagonal corners of the chip. Chip B is a traditional inverted structure LED chip in which the n-type electrode and p-type electrode are equal in area and are distributed on the left and right sides of the same surface of the chip: except for the different positions of the n-type electrode and the p-type electrode, the other structures of chip A and chip B, such as the shape and size of the chip and the internal structure of the chip, are the same, and the sum of the areas of the n-type electrode and the p-type electrode of chip A is equal to that of chip B. The luminous flux (in lm) of chip A and chip B is measured under a driving current that increases regularly from 200mA to 2400mA (increases by 200mA each time) to compare the luminous intensity of the two. 12 sets of data are obtained for each chip, and the test results are plotted as shown below. Figure 3 As shown, Figure 3 In the graph, the horizontal axis represents the drive current (in mA), and the vertical axis represents the luminous flux of the LED chip (in lm) measured at the corresponding drive current. The test data for chip A are shown as solid dots, which are connected sequentially to form the solid line in the graph. The test data for chip B are shown as hollow dots, which are connected sequentially to form the dashed line in the graph. As can be seen from the graph, regardless of the drive current, the luminous flux of chip A is always greater than that of chip B. Furthermore, the luminous flux difference between chips A and B increases as the drive current increases. This experimental data demonstrates that compared to conventional flip-chip LED chips with equal n-type and p-type electrodes located on the left and right sides of the same chip surface, the flip-chip LED chip structure in this example, with the n-type electrode located at the center and the p-type electrode at the top corner, achieves better heat dissipation, thereby increasing the luminous intensity of the flip-chip LED chip. This enhanced luminous intensity is particularly significant at higher current densities.

[0041] To avoid chip unreliability caused by poor soldering due to the chip's center of gravity being biased to one side, the position of the p-type electrode also includes:

[0042] In one embodiment, the p-pole regions are located at three corners of the LED chip, and the p-pole regions at the three corners are symmetrical to each other, and the n-pole regions are symmetrical along at least one diagonal line of another corner except the p-pole regions. Figure 4As shown, in this example, four electrodes are formed on the same side of the chip, including an n-type electrode 51 located in the center of the chip and two p-type electrodes 52 located at opposite corners. The three p-type electrodes are arranged at the corners of the chip in an equilateral right triangle, using the chip's vertex angles as a guide. The n-type electrodes are located on the chip surface, excluding the p-type electrodes, with a gap between them. The n-type electrodes are symmetrically arranged along the diagonal line of the other vertex angle, excluding the p-type electrodes, on the surface of the n-pole region. The p-type electrodes are symmetrically arranged on the surface of the p-pole region. Compared with the previous example, this example adds a p-type electrode. Although the center of gravity of the chip may not be in the center area, the three p-type electrodes are located in different directions and are symmetrical with each other (including symmetry along the chip's midline or along the chip's diagonals). Regardless of which side the chip is tilted to, one or two p-type electrodes on the side with the center of gravity can fully contact the solder joints on the package substrate. This helps prevent the phenomenon of p-type electrode cold solder joints when the chip's center of gravity is tilted to one side.

[0043] In one embodiment, the p-pole regions are located at the four corners of the chip except the n-pole region, and the p-pole regions at the four corners are symmetrical to each other, and the n-pole region and the p-pole region are symmetrically arranged along the symmetry axis of the LED chip. Figure 5 As shown, in this example, a total of five electrodes are formed on the same side of the chip, including an n-type electrode 51 located at the center of the chip and p-type electrodes 52 located at the four corners of the chip. The four p-type electrodes are arranged at the corners of the chip in the form of equilateral right triangles using the corners of the chip. The n-type electrodes are located on the surface of the chip in the form of regular octagons except for the p-type electrodes. There is a gap between the n-type electrodes and the p-type electrodes. The n-type electrodes are symmetrically arranged on the surface of the n-pole region along the symmetry axis of the LED chip, and the p-type electrodes are symmetrically arranged on the surface of each p-pole region along the symmetry axis of the LED chip. Compared with the previous example, this example further adds a p-type electrode. The center of gravity of the chip is located in the central region, and the four p-type electrodes are located in different directions. Each pair forms a symmetrical relationship (including symmetry along the midline of the chip or symmetry along the diagonal lines of the chip). This makes the chip less likely to float or warp. Even if floating or warping occurs, no matter which side the chip is tilted to, it can be ensured that the two p-type electrodes on the side where the center of gravity is located can fully contact the solder joints on the package substrate.

[0044] Generally speaking, the LED chip structures in the above three examples have problems such as current concentration at the location of the p-type electrode, which leads to slightly lower luminous efficiency at the top corner; therefore, a circular light-emitting structure with an area smaller than the light-emitting surface is usually used for covering during packaging, and a reflective adhesive layer is provided in the area outside the light-emitting structure so that light is emitted only from the light-emitting structure. In this way, the four corners of the chip with lower luminous efficiency are not in the actual light-emitting range, that is, the light-emitting area of ​​the square chip is actually a circle within the light-emitting surface; in addition, the light-emitting structure can also be designed in other shapes besides the circle, such as polygons, ellipses, etc., as long as the area is smaller than the light-emitting surface of the chip, it is sufficient not to cover the location of the p-type electrode of the LED chip during packaging. To improve the above example, strip-shaped n-type electrode through holes can be further provided on the outside of the two right-angled sides of the p-type electrode, such as Figure 6 As shown, in addition to the n-type electrode through-hole 41 formed in the n-pole region and penetrating to the n-type semiconductor layer, the four p-type electrodes 52 located at the top corners of the chip also have strip-shaped n-type electrode through-holes 41 formed on the outside of each right-angled side close to the edge of the chip. This allows the current at the top corners to be better expanded, which is beneficial to the current diffusion at the four corners and increases the luminous efficiency of the four corners of the chip. Since the top corners where the P-type electrodes are located in this example also have good luminous efficiency, the light at the top corners can be directly emitted during packaging, that is, the area where the light is emitted can be the same as the actual area of ​​the light-emitting surface, that is, the actual light-emitting area of ​​the square chip is also a square consistent with the light-emitting surface of the chip.

[0045] Another embodiment of the present invention is a light emitting device, such as Figure 7 and Figure 8 ( Figure 8 for Figure 7 ), comprising: a packaging substrate 100, having an n-pole solder joint and a p-pole solder joint provided on its surface; the flip-chip LED chip 200, connected to the n-pole solder joint on the surface of the packaging substrate via an n-type electrode, and connected to the p-pole solder joint on the surface of the packaging substrate via a p-type electrode; a fluorescent adhesive layer 300 formed at least on the light-emitting surface of the LED chip; a light-emitting structure 400 formed on the surface of the fluorescent adhesive layer; and a reflective adhesive layer 500 provided at least around the LED chip.

[0046] The packaging substrate can be a ceramic packaging substrate, which is used to package flip-chips. The surface is formed with solder joints and there are electrical connection structures such as through holes inside. The setting of the surface solder joints matches the position of the chip electrodes to be packaged, including n-pole solder joints and p-pole solder joints. The flip-chip LED chip 200 is square, and the n-type electrode is connected to the n-pole solder joint on the surface of the packaging substrate by reflow soldering, while the p-type electrode is connected to the p-pole solder joint on the surface of the packaging substrate. A fluorescent glue layer is also provided on the surface of the chip. The fluorescent glue layer prepared before packaging is pasted on the light-emitting surface of the flip-chip. In order to ensure light emission, the area of ​​the fluorescent glue layer pasted on the surface of the LED chip after cutting is larger than the area of ​​the light-emitting side of the LED chip. However, in other embodiments, there is also a fluorescent glue layer with an area less than or equal to the area of ​​the light-emitting surface of the LED chip. The specific design can be based on actual application requirements. When the prepared fluorescent adhesive layer is pasted on the surface of the LED chip, there is still a layer of adhesive with good adhesion between the fluorescent adhesive layer and the surface of the LED chip. However, the adhesive layer is not conducive to the heat dissipation of the chip. Therefore, in actual applications, for chips with high current density, a steel mesh spraying method is usually used to directly spray phosphor on the surface of the LED chip and then solidify to form a fluorescent adhesive layer. Figure 7 As shown, the fluorescent adhesive layer 300 is formed not only on the light-emitting surface of the LED chip, but also on the light-emitting side of the LED chip. The adhesive layer is reduced by spraying and then curing, which is conducive to better heat dissipation of the LED chip. The transparent light-emitting structure is the light-emitting window of the chip. It should generally be smaller than the size of the chip and can be made of transparent materials such as glass. Its shape can be designed according to the light-emitting requirements of the product and can be designed to be circular, polygonal, etc. In this embodiment, the transparent light-emitting structure is a circular glass piece, which is arranged on the surface of the fluorescent adhesive layer and is smaller than the area of ​​the chip. In this way, since the four corners of the chip are not within the range covered by the light-emitting structure, even if the luminous efficiency at the four corners of the chip is low, the light output intensity of the entire chip can be guaranteed. A reflective adhesive layer (silicone uniformly doped with reflective particles such as TiO2) is filled around the LED chip to form a white wall structure to reflect the light emitted from the four sides of the LED chip. In order to reduce the light-emitting angle of the LED device and reduce light leakage around it, the upper surface of the surrounding reflective adhesive layer should be as flush as possible with the upper surface of the light-emitting structure.

[0047] Another embodiment of the present invention provides a method for packaging a light emitting device, comprising the following steps:

[0048] S10. Provide a packaging substrate, with an n-pole solder joint and a p-pole solder joint provided on the surface.

[0049] The packaging substrate can be a ceramic packaging substrate, which is used to package flip chips. It has solder joints on the surface and electrical connection structures such as through holes inside. The setting of the surface solder joints matches the electrode positions of the chip to be packaged, including n-pole solder joints and p-pole solder joints: If the LED chip to be packaged is Figure 1As shown, the n-type electrode is arranged in the center area of ​​the chip, and the p-type electrode is arranged at the two diagonal corners of the chip. Then the n-pole solder joints and the p-pole solder joints in the package substrate to be provided are also arranged in a manner corresponding to the chip electrodes. In a certain area of ​​the substrate, the n-pole solder joints are arranged in the center according to the size and shape of the n-type electrode on the chip, and the p-pole solder joints are arranged at the two diagonal corners according to the size and shape of the p-type electrode on the chip. If the LED chip to be packaged is Figure 4 As shown, the n-type electrode is set in the center area of ​​the chip, and the p-type electrode is set at the three symmetrical corners of the chip. Then, in a certain area of ​​the package substrate to be provided, the n-pole solder joint is set at the center position according to the size and shape of the n-type electrode on the chip, and the p-pole solder joint is set at the three symmetrical corners according to the size and shape of the p-type electrode on the chip; if the LED chip to be packaged is Figure 5 As shown, the n-type electrode is arranged in a regular octagon in the center area of ​​the chip, and the p-type electrode is arranged at the four corners of the chip. Then, in a certain area of ​​the packaging substrate to be provided, the n-pole solder joint is arranged at the center position according to the size and shape of the n-type electrode on the chip, and the p-pole solder joint is arranged at the four corners according to the size and shape of the p-type electrode on the chip; and so on. Since the solder joint is generally made of metal material and is easily oxidized, a protective layer and other structures are also included on its surface to provide a solderable surface that is not easily oxidized during subsequent welding. For the sake of detailed description, the following is an introduction to the packaging process using a flip-chip LED chip with the n-type electrode arranged in the center area of ​​the chip and the p-type electrodes arranged at the two diagonal corners of the chip as an example.

[0050] S20, forming flux on the surfaces of the n-pole solder joint and the p-pole solder joint respectively.

[0051] Flux aids and promotes soldering, and also contains chemical additives that protect and prevent oxidation. The flux used here is typically viscous, which helps the LED chip adhere. At room temperature, it is a paste. At high temperatures, the flux (including its various solvents and additives) evaporates into the air, melting the gold-tin alloy electrodes in the LED chip and forming a secure connection with the corresponding solder joints. The method of forming the flux on the surface of the substrate can specifically be a steel screen printing method, in which openings are formed on the steel plate according to the positions of the n-pole solder joints and the p-pole solder joints, the openings on the steel screen are aligned with the positions of the solder joints on the substrate and flux is coated on the steel screen, so that the flux is formed on the surface of the solder joints on the substrate through the openings; or the flux can also be applied by spot coating, in which the flux is accurately dipped onto the surface of the n-pole solder joints and the p-pole solder joints on the substrate by a mechanical operating arm on the equipment; no matter which method is used, the flux formed on the surfaces of the n-pole solder joints and the p-pole solder joints are finally separated from each other and cannot touch each other, but in order to form a good connection with the chip electrodes later, the amount of flux on the solder joint surface should not be too little, and the amount of flux should not be too much to avoid flooding the sides of the LED chip or even the light-emitting surface, thereby affecting the light emission; therefore, a suitable amount of flux of appropriate size and thickness should be formed on the surface of the packaging substrate according to the specific size, shape and structure of the LED chip to be packaged and its electrodes. This embodiment does not impose any restriction on the specific method to be selected. In the actual packaging process, it is sufficient as long as an appropriate amount of flux can be formed at the n-pole soldering point and the p-pole soldering point on the packaging substrate.

[0052] S30, placing the flip-chip LED chip on the surface of the package substrate, with the side of the chip with the electrode facing the package substrate, the n-type electrode corresponding to the n-pole solder joint, and the p-type electrode corresponding to the p-pole solder joint.

[0053] The flip-chip LED chips used here have an n-type electrode located in the center of the chip, and p-type electrodes located at at least two diagonally opposite corners of the chip. When the chips are transferred to the package substrate, the n-type electrode in the center of each flip-chip LED chip corresponds to the n-pole solder joint on the package substrate, and the p-type electrodes located at the two diagonally opposite corners of the chip correspond to the p-pole solder joints on the package substrate. The chips are then placed on a flux surface for mounting. For flip-chip LED chips, especially high-power ones, the electrodes are typically made of a gold-tin alloy with excellent oxidation resistance and high strength. However, due to the large amount of expensive gold contained, the electrode thickness is generally small (between 3μm and 4μm). During soldering, once the temperature reaches the eutectic temperature of the gold-tin alloy, the flux evaporates, the gold-tin alloy melts, and connects to the solder joints. At this point, whether the melted LED chip electrodes can fully contact the solder joints on the package substrate becomes a key factor in determining soldering quality. Since the flux is in a paste form at room temperature and cannot provide stable support, when the electrode of the LED chip is placed in it, it is very likely that one side of the LED chip will be lifted up due to the unstable center of gravity of the chip itself, external vibration, etc.; in this case, it is easy for two traditional chip electrode pads of the same area or two pads of one large and one small to have only one electrode in close contact with the solder joint, while the other electrode is lifted up and cannot contact the solder joint. Since the chip electrode is a gold-tin alloy and has a small thickness, the lifted electrode may contact the flux but not the solder joint, appearing to be suspended from the solder joint, but it cannot be detected from the appearance alone, resulting in the flux volatilizing after the temperature rises during the subsequent reflow soldering, but the electrode is not connected to the solder joint, resulting in a cold solder joint. In the LED chip of this embodiment, since the n-type electrode is located in the central area, no matter which side of the chip is tilted, the n-type electrode can fully contact the n-pole solder joint on the substrate. At the same time, the p-type electrode is arranged at least at two diagonal corners of the chip, and the p-type electrodes at the two diagonal corners are at the farthest distance from each other in the chip. Even if the center of gravity of the chip is not in the central area and one side of the chip is tilted, the other side can still make good contact with the packaging substrate. No matter which side of the chip is tilted, the p-type electrodes at different positions can always fully contact the solder joint on the packaging substrate. That is to say, when the flip-chip LED chip is placed stably on the surface of the packaging substrate, the n-type electrode fully contacts the flux on the surface of the n-pole solder joint, and each p-type electrode in the chip fully contacts the flux on the surface of the corresponding p-pole solder joint. When the flip-chip LED chip is tilted toward at least one side of the p-type electrode and placed on the surface of the packaging substrate, the n-type electrode fully contacts the flux on the surface of the n-pole solder joint, and at least the p-type electrode on the tilted side of the flip-chip LED chip can fully contact the flux on the surface of the corresponding p-pole solder joint.

[0054] S40, subjecting the package substrate with the flip-chip LED chip to a reflow soldering operation to fix and solder the LED chip.

[0055] After the above steps, the flip-chip LED chip is attached to the surface of the package substrate's solder joints via flux, ensuring full contact with the solder joints. The package substrate with the flip-chip LED chip is then placed in a reflow oven set to a pre-set temperature and time for reflow soldering. During the reflow process, the temperature rises to the eutectic temperature of the gold-tin alloy, and the flux evaporates as the temperature rises. The LED chip's electrodes (including the n-type and p-type electrodes) melt and connect to the solder joints. The flip-chip LED chip is then soldered to the substrate surface, with the chip's n-type electrode firmly soldered to the n-pole solder joint on the package substrate, and the chip's p-type electrode firmly soldered to the p-pole solder joint on the package substrate. After reflow soldering, the process also includes cleaning to remove any residual flux residue and other substances that may be present on the substrate surface, and inspecting the soldering quality.

[0056] S50, forming a fluorescent adhesive layer on the light-emitting surface of the LED chip, and forming a transparent light-emitting structure on the surface of the fluorescent adhesive layer.

[0057] The fluorescent adhesive layer can be formed by pasting a prepared fluorescent adhesive layer, or by steel mesh spraying. If the prepared fluorescent adhesive layer is pasted, it specifically includes: pasting the pre-prepared fluorescent adhesive layer on the light-emitting surface of the flip chip. In order to ensure light emission, the area of ​​the fluorescent adhesive layer pasted on the surface of the LED chip after cutting is larger than the area of ​​the light-emitting side of the LED chip. However, in other embodiments, there is also a fluorescent adhesive layer with an area less than or equal to the area of ​​the light-emitting surface of the LED chip. The specific design can be based on the actual application requirements. When the prepared fluorescent adhesive layer is pasted on the surface of the LED chip, there is also a layer of adhesive layer with good adhesion between the fluorescent adhesive layer and the surface of the LED chip. However, the adhesive layer is not conducive to the heat dissipation of the chip. Therefore, in actual applications, for chips with a higher current density, steel mesh spraying is usually used to directly spray phosphor on the surface of the LED chip and then solidify to form a fluorescent adhesive layer. The curing after spraying reduces the adhesive layer, which is conducive to better heat dissipation of the LED chip.

[0058] The transparent light-emitting structure serves as the chip's light-emitting window. It should generally be smaller than the chip itself and made of transparent materials such as glass. Its shape can be designed based on the product's light-emitting requirements, and can be circular, polygonal, or otherwise. In this embodiment, the transparent light-emitting structure is a circular glass sheet, positioned on the surface of the fluorescent adhesive layer and smaller than the chip itself. This ensures that the chip's corners are not within the structure's coverage area, ensuring consistent light output from the entire chip, even if the chip's luminous efficiency is low at the corners.

[0059] S60, providing a reflective adhesive layer at least around the flip-chip LED chip.

[0060] A reflective adhesive layer (silica gel uniformly doped with reflective particles such as TiO2) is placed around the surface of the package substrate and around the LED chip to form a white wall structure to reflect light emitted from all sides of the LED chip. In this embodiment, to reduce the light emission angle of the LED device and minimize light leakage from all sides, the upper surface of the surrounding reflective adhesive layer should be as flush as possible with the upper surface of the light-emitting structure. Therefore, the side surfaces of the reflective adhesive layer not only cover the side surfaces of the LED chip, but also cover the side surfaces of the fluorescent adhesive layer and the side surfaces of the transparent light-emitting structure. In other embodiments, such as LED chips that do not require a transparent light-emitting structure and emit light directly from the surface of the fluorescent adhesive layer, the reflective adhesive layer can also cover only the side surfaces of the LED chip, so that light emitted from the LED chip toward the side surfaces is reflected to the light-emitting surface, enters the fluorescent adhesive layer from the light-emitting surface, and is directly emitted after being excited. In this case, the step of surrounding the reflective adhesive layer can be performed before forming the fluorescent adhesive layer, that is, after reflow soldering is completed. The reflective adhesive layer is first placed around the flip-chip LED chip, with the surface of the reflective adhesive layer flush with the light-emitting surface of the LED chip, and then the fluorescent adhesive layer is formed on the light-emitting surface of the LED chip. Therefore, this embodiment does not limit the order of the steps of forming the fluorescent adhesive layer and surrounding the reflective adhesive layer, and those skilled in the art can determine it according to the actual structure of the product.

[0061] It should be noted that the above embodiments can be freely combined as needed. The above description is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention, and such improvements and modifications should also be considered as the scope of protection of the present invention.

Claims

1. A flip-chip LED chip, characterized in that: The flip-chip LED chip is square in shape and includes: growth substrate; A semiconductor multilayer structure formed on the surface of the growth substrate includes an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer stacked in sequence, and the surface is divided into an n-pole region and a p-pole region, wherein the p-pole region is disposed at least at two diagonal corners of the LED chip; a reflective metal structure formed on a surface of one side of the p-type semiconductor layer in the semiconductor multilayer structure; An n-type electrode through hole formed in the n-pole region and penetrating to the n-type semiconductor layer; An insulating layer extending to the sidewall of the n-type electrode through-hole is formed on the surface of the reflective metal structure, and a p-type electrode through-hole connected to the reflective metal structure is configured in a portion of the insulating layer located in the p-pole region; an n-type electrode formed by connecting all n-type electrode through-holes in the n-pole region to the surface of the insulating layer; The p-type electrode is formed on the surface of the reflective metal structure and connects the p-type electrode through holes located in the p-pole region at the same vertex angle.

2. The flip-chip LED chip according to claim 1, wherein: The center of gravity of the LED chip is located at the center point of the LED chip, or at least biased towards one of the p-pole regions.

3. The flip-chip LED chip according to claim 2, wherein: The p-pole region is arranged at two diagonal corners of the LED chip, and the n-pole region and the p-pole region are symmetrically arranged along the two diagonal lines of the LED chip; The n-type electrode is symmetrically arranged on the surface of the n-pole region along the two diagonal lines, and the p-type electrode is symmetrically arranged on the surface of each p-pole region along the two diagonal lines.

4. The flip-chip LED chip according to claim 2, wherein: The p-pole regions are arranged at the four corners of the LED chip, the p-pole regions at the four corners are symmetrical to each other, and the n-pole regions and the p-pole regions are symmetrically arranged along the symmetry axis of the LED chip; The n-type electrode is symmetrically arranged on the surface of the n-pole region along the symmetry axis of the LED chip, and the p-type electrode is symmetrically arranged on the surface of each p-pole region along the symmetry axis of the LED chip.

5. The flip-chip LED chip according to claim 4, wherein: The n-type region is positive. The n-type electrode is arranged in a regular octagon on the surface of the n-type region.

6. The flip-chip LED chip according to claim 2, wherein: The p-pole regions are arranged at three corners of the LED chip, and the p-pole regions at the three corners are arranged symmetrically in pairs, and the n-pole regions are arranged symmetrically along at least a diagonal line of another corner except the p-pole regions. The n-type electrodes are symmetrically arranged on the surface of the n-pole region at least along a diagonal line where another vertex except the p-pole region is located; and the p-type electrodes are symmetrically arranged in pairs on the surface of the p-pole region.

7. The flip-chip LED chip according to any one of claims 1 to 6, wherein: The reflective metal structure comprises: A p-type ohmic contact layer formed on the surface of the p-type semiconductor layer; a dielectric reflective layer formed on a surface of the p-type ohmic contact layer, wherein the dielectric reflective layer has a conductive through hole; A metal reflective layer is formed on the surface of the dielectric reflective layer and inside the conductive through hole.

8. A light emitting device, characterized in that: include: A packaging substrate, with an n-pole solder joint and a p-pole solder joint provided on the surface; The flip-chip LED chip according to any one of claims 1 to 7 is soldered to the surface of the package substrate, wherein: The n-type electrode is connected to the n-pole solder joint on the surface of the package substrate, and the p-type electrode is connected to the p-pole solder joint on the surface of the package substrate; A fluorescent adhesive layer formed at least on the light-emitting surface of the LED chip; A transparent light-emitting structure formed on the surface of the fluorescent adhesive layer; A reflective adhesive layer is provided at least around the LED chip.

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