Inverted COB (Chip On Board) packaging circuit board and electronic equipment

Abstract

The invention relates to a flip COB packaging circuit board and electronic equipment, in the circuit board, an insulating layer is arranged on a first surface of a first ceramic layer, a conductive layer is arranged on the insulating layer, a second ceramic layer is connected to a second surface of the first ceramic layer, and one surface, opposite to the first ceramic layer, of the second ceramic layer is connected with a third ceramic layer; welding spot layers are arranged on the conductive layer, and electrodes of the LED chips are connected with the welding spot layers; the temperature sensing unit is arranged in the mounting hole of the second ceramic layer, the temperature sensing area of the first ceramic layer is provided with a temperature sensing metal conducting strip, the first ceramic layer is provided with a first via hole, the temperature sensing metal conducting strip is electrically connected with the conducting layer through the first via hole, and the electric energy input end of the temperature sensing unit is electrically connected with the temperature sensing metal conducting strip. And the temperature sensing unit is attached to the temperature sensing metal conducting strip. Therefore, the temperature sensing unit can be close to the LED chip, and the temperature sensing metal conductive sheet is used for temperature conduction, so that the temperature sensing unit can accurately and sensitively detect the temperature of the LED chip.

Description

Technical Field

[0001] The present invention relates to the technical field of manufacturing flip-chip COB packaged circuit boards, and particularly to flip-chip COB packaged circuit boards and electronic devices. Background Art

[0002] LED (Light Emitting Diode), a light-emitting diode, is a solid-state semiconductor device that can convert electrical energy into visible light. It has the advantages of low energy consumption, fast response, high brightness, and long service life.

[0003] With the continuous development of LED technology, COB (Chip On Board) packaging has been widely used. Compared with traditional SMD (Surface Mount Device) packaging, the density of LED chips in COB packaging is higher, and therefore, the heat accumulation degree is higher.

[0004] Flip-chip COB packaging is a packaging process in which LED chips are directly connected to a circuit board through processes such as microbumps, eliminating the structure of welding gold wires in front-mounted COB. For flip-chip COB packaged circuit boards, they are more sensitive to temperature. As the temperature of the circuit board increases, it is easy to cause CTE (Coefficient of Thermal Expansion Mismatch) mismatch in flip-chip solder joints, resulting in solder joint failure of LED chips.

[0005] In this regard, it is necessary to detect the temperature of the COB packaged circuit board in real time to avoid circuit board failures. A common temperature detection method is to install a surface-mounted temperature sensor on the surface or the back of the substrate and use the surface-mounted temperature sensor to detect the temperature of the COB packaged circuit board. The current surface-mounted temperature sensors are far from the LED chips, resulting in the inability to accurately detect the temperature changes of the LED chips. Summary of the Invention

[0006] Based on this, it is necessary to provide a flip-chip COB packaged circuit board and an electronic device.

[0007] A flip-chip COB packaged circuit board includes: a multi-layer ceramic substrate, a plurality of LED chips, and a temperature sensing unit;

[0008] The multi-layer ceramic substrate includes a conductive layer, an insulating layer, a first ceramic layer, a second ceramic layer, and a third ceramic layer. The insulating layer is disposed on a first surface of the first ceramic layer, the conductive layer is disposed on the insulating layer, the second ceramic layer is connected to a second surface of the first ceramic layer, and a surface of the second ceramic layer facing away from the first ceramic layer is connected to the third ceramic layer;

[0009] A plurality of solder joint layers are provided on the conductive layer, and the electrodes of each LED chip are correspondingly connected to each solder joint layer;

[0010] The second ceramic layer is provided with mounting holes, the temperature sensing unit is disposed in the mounting holes, a temperature sensing area aligned with the mounting holes is provided on the second surface of the first ceramic layer, a temperature sensing metal conductive sheet is provided in the temperature sensing area, the first ceramic layer is provided with a first via hole, the temperature sensing metal conductive sheet is electrically connected to the conductive layer through the first via hole, the power input end of the temperature sensing unit is electrically connected to the temperature sensing metal conductive sheet, and the temperature sensing unit is attached to the temperature sensing metal conductive sheet.

[0011] In one embodiment, the insulating layer is coated on the outside of each solder joint layer.

[0012] In one embodiment, the width of each solder joint layer gradually decreases from the end close to the LED chip to the end far from the LED chip.

[0013] In one embodiment, the end face of each solder joint layer close to the LED chip is set as an arc surface.

[0014] In one embodiment, the thermal expansion coefficients of the first ceramic layer, the second ceramic layer, and the third ceramic layer increase in sequence.

[0015] In one embodiment, a temperature control unit is further included. The temperature control unit is disposed on the surface of the multi-layer ceramic substrate. The third ceramic layer is provided with a third via hole. The temperature sensing unit is electrically connected to the temperature control unit through the third via hole, and the temperature control unit is electrically connected to the conductive layer.

[0016] In one embodiment, the temperature control unit is disposed on the side of the third ceramic layer facing away from the second ceramic layer, and the position of the temperature control unit on the third ceramic layer is offset from the position of the mounting hole on the second ceramic layer. A first circuit layer and a second circuit layer are provided on the side of the third ceramic layer facing away from the second ceramic layer. The temperature control unit is connected to the third via hole through the first circuit layer. The first ceramic layer, the second ceramic layer, and the third ceramic layer are provided with fourth via holes at positions close to the outer edge of the conductive layer. The temperature control unit is connected to the fourth via hole through the second circuit layer, and the fourth via hole is connected to the conductive layer.

[0017] In one embodiment, the temperature sensing unit is connected to the third via hole through a wire.

[0018] In one embodiment, a light-transmitting adhesive layer is further included. The light-transmitting adhesive layer is connected to the first ceramic layer and covers the outside of each LED chip.

[0019] An electronic device includes the flip-chip COB packaging circuit board described in any of the above embodiments.

[0020] For the above flip-chip COB packaging circuit board and electronic device, through the above structure, the temperature sensing unit can be close to the LED chip, and the temperature-sensitive metal conductive sheet is used for efficient temperature conduction, so that the temperature sensing unit can accurately and sensitively detect the temperature of the LED chip. In addition, an insulating layer is provided on the surface of the first ceramic layer, and the flexible insulating layer is used to support the conductive layer. The insulating layer can adapt to the expansion or contraction of the LED chip by elastic deformation, thereby absorbing stress and effectively avoiding CTE mismatch. Description of the Drawings

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0022] Figure 1 It is a schematic partial cross-sectional structure diagram of a flip-chip COB packaging circuit board according to an embodiment;

[0023] Figure 2 It is a schematic partial cross-sectional structure diagram of a flip-chip COB packaging circuit board according to an embodiment;

[0024] Figure 3 It is a schematic partial cross-sectional structure diagram of a flip-chip COB packaging circuit board according to another embodiment;

[0025] Figure 4 It is a schematic enlarged partial structure diagram of a flip-chip COB packaging circuit board according to still another embodiment.

[0026] Description of the Reference Numerals:

[0027] 10. Flip-chip COB package circuit board; 100. Multilayer ceramic substrate; 200. LED chip; 300. Temperature sensing unit; 310. Temperature-sensitive metal conductive sheet; 400. Temperature control unit; 110. First ceramic layer; 120. Second ceramic layer; 130. Third ceramic layer; 140. Conductive layer; 150. Insulating layer; 151. First insulating layer; 152. Second insulating layer; 160. Solder joint layer; 121. Mounting hole; 101. First via hole; 102. Second via hole; 103. Third via hole; 104. Fourth via hole; 105. Fifth via hole; 106. Sixth via hole; 131. First circuit layer; 132. Second circuit layer; 133. Third circuit layer; 122. Accommodating hole; DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] like Figure 1 and Figure 2 As shown, it is a flip-chip COB package circuit board 10 according to an embodiment of the present invention, comprising: a multi-layer ceramic substrate 100, a plurality of LED chips 200 and a temperature sensing unit 300;

[0030] The multilayer ceramic substrate 100 includes a conductive layer 140, an insulating layer 150, a first ceramic layer 110, a second ceramic layer 120 and a third ceramic layer 130, wherein the insulating layer 150 is disposed on a first surface of the first ceramic layer 110, the conductive layer 140 is disposed on the insulating layer 150, the second ceramic layer 120 is connected to a second surface of the first ceramic layer 110, and a surface of the second ceramic layer 120 facing away from the first ceramic layer 110 is connected to the third ceramic layer 130;

[0031] A plurality of solder joint layers 160 are disposed on the conductive layer 140 , and electrodes of each LED chip 200 are connected to each solder joint layer 160 correspondingly;

[0032] The second ceramic layer 120 is provided with a mounting hole 121, the temperature sensing unit 300 is disposed in the mounting hole 121, a temperature sensing area aligned with the mounting hole 121 is formed on the second surface of the first ceramic layer 110, a temperature sensing metal conductive sheet 310 is disposed in the temperature sensing area, the first ceramic layer 110 is provided with a first via hole 101, the temperature sensing metal conductive sheet 310 is electrically connected to the conductive layer 140 through the first via hole 101, the power input end of the temperature sensing unit 300 is electrically connected to the temperature sensing metal conductive sheet 310, and the temperature sensing unit 300 is attached to the temperature sensing metal conductive sheet 310.

[0033] In this embodiment, the multi-layer ceramic substrate 100 is also referred to as an LTCC (Low Temperature Co-fired Ceramic) substrate. The multi-layer ceramic substrate 100 includes a plurality of ceramic layers, and each ceramic layer can also be referred to as a green ceramic sheet. The ceramic layers are press-fitted together by a mechanical axial pressing method. Among them, the ceramic hole formed on the second ceramic layer 120 is used to accommodate the temperature sensing unit 300, and the first ceramic layer 110 is connected to the second ceramic layer 120 to close the mounting hole 121. The specific installation process is as follows: First, a mounting hole 121 is drilled on the second ceramic layer 120. For example, a mounting hole 121 is drilled on the second ceramic layer 120 by using a laser drill. A temperature sensing metal conductive sheet 310 is fabricated in the temperature sensing area corresponding to the mounting hole 121 of the second ceramic layer 120 on the second surface of the first ceramic layer 110, and a first via hole 101 connected to the temperature sensing metal conductive sheet 310 is fabricated on the first ceramic layer 110. The temperature sensing unit 300 is installed on the temperature sensing metal conductive sheet 310, and the second surface of the first ceramic layer 110 and the first surface of the second ceramic layer 120 are bonded together to close the mounting hole 121. The second surface of the second ceramic layer 120 is bonded to the third ceramic layer 130, and the first ceramic layer 110, the second ceramic layer 120, and the third ceramic layer 130 are press-fitted together to obtain the substrate layer of the multi-layer ceramic substrate 100. It is worth mentioning that the mounting hole 121 can be a blind hole or a through hole. For example, the mounting hole 121 is a blind hole with an opening facing the first ceramic layer 110 and a closed bottom. For example, the mounting hole 121 is a through hole, and the first ceramic layer 110 and the third ceramic layer 130 respectively close both ends of the mounting hole 121.

[0034] In this embodiment, the LED chip 200 is fabricated by a flip-chip COB packaging method. The conductive layer 140 is electrically connected to each LED chip 200 through a solder joint layer 160. The conductive layer 140 is also connected to a power source for supplying power to each LED chip 200. In this embodiment, the first ceramic layer 110 supports the insulating layer 150, the insulating layer 150 supports the conductive layer 140, and provides isolation between different circuits in the conductive layer 140, so that different circuits in the conductive layer 140 are insulated from each other.

[0035] In this embodiment, the conductive layer 140 can also supply power to the temperature sensing unit 300. Specifically, the conductive layer 140 is electrically connected to the temperature-sensitive metal conductive sheet 310 through the first via 101 of the first ceramic layer 110. In this way, the temperature-sensitive metal conductive sheet 310 is provided with corresponding welding positions to be connected to the pins of the temperature sensing unit 300. The pins of the temperature sensing unit 300 are arranged at both ends of the temperature sensing unit 300, and an induction area is arranged in the middle of the temperature sensing unit 300. The induction area is attached to the temperature-sensitive metal conductive sheet 310. In this way, the temperature-sensitive metal conductive sheet 310 can not only conduct electricity to the temperature sensing unit 300 to supply power to it, but also conduct heat. For example, the temperature-sensitive metal conductive sheet 310 includes a plurality of conductive sub-sheets that are isolated from each other. The first via 101 is provided with two or more. Each first via is connected to a conductive sub-sheet. Each conductive sub-sheet is provided with a welding position, and the welding position of each conductive sub-sheet is connected to a pin of the temperature sensing unit 300. In this way, a short circuit in the power supply to the temperature sensing unit 300 can be avoided.

[0036] Specifically, the temperature-sensitive metal conductive sheet 310 is made of aluminum foil or copper foil and has good thermal conductivity. The conductive layer 140 is connected to the LED chip 200 and can absorb the heat generated by the light emission of the LED chip 200. Moreover, the resistance of the conductive layer 140 itself will also cause it to generate heat. A conductive and heat-conductive material is injected into the first via 101. For example, copper is plated on the side wall of the first via 101. In this way, the heat of the conductive layer 140 can more accurately reflect the heat of the LED chip 200. The conductive layer 140 is connected to the temperature-sensitive metal conductive sheet 310 through the first via 101 and can conduct the heat to the temperature-sensitive metal conductive sheet 310.

[0037] It should be understood that in a traditional COB packaged circuit board, the temperature sensor is installed at the periphery of the circuit layer on the surface of the substrate, while the LED chip 200 is located within the circuit layer range and connected to the circuit layer. In this way, the distance between the temperature sensor and the LED chip 200 is relatively large, and the temperature change of the LED chip 200 cannot be accurately detected. In the prior art CN107768366A, the temperature sensor is arranged in the component placement through hole of the first functional green ceramic sheet, so that there is only one layer of top green ceramic sheet between the temperature sensor and the LED chip 200. In this way, although the distance between the temperature sensor and the LED chip 200 can be effectively reduced and the sensitivity of temperature detection can be improved. However, on the one hand, this structure is applicable to the face-up COB package and not applicable to the flip-chip COB package. The reason is that an insulating layer 150 is arranged on the surface of the substrate of the flip-chip COB package, and the insulating layer 150 is not conducive to heat conduction. If the prior art is directly applied to the flip-chip COB scheme, the temperature sensor will be insensitive due to the influence of the insulating layer 150. On the other hand, in this prior art, the electrical interconnection wires are arranged on the top green ceramic sheet. If the electrodes of the LED chip 200 are directly connected to the electrical interconnection wires, when the temperature rises, it is easy to cause CTE mismatch. The LED chip 200 and the green ceramic sheet have different degrees of expansion due to temperature change, resulting in internal stress, causing the solder joint layer 160 to be subjected to opposite acting forces at both ends in the displacement direction, bearing shear stress, and causing the solder joints to deform or break. To avoid the above situation, in this embodiment, an insulating layer 150 is arranged on the first surface of the first ceramic layer 110, and the elastic deformation of the insulating layer 150 is used to absorb stress, thereby avoiding CTE mismatch. And a thermally conductive temperature-sensitive metal conductive sheet 310 is arranged on the second surface of the first ceramic layer 110. Through the heat conduction of the first via 101 and the temperature-sensitive metal conductive sheet 310, the defect of the decrease in thermal conductivity caused by the arrangement of the insulating layer 150 can be made up for.

[0038] Through the above structure in this embodiment, the temperature sensing unit 300 can be close to the LED chip 200, and the thermally conductive temperature-sensitive metal conductive sheet 310 is used for efficient heat conduction, so that the temperature sensing unit 300 can accurately and sensitively detect the temperature of the LED chip 200. In addition, an insulating layer 150 is arranged on the surface of the first ceramic layer 110, and the flexible insulating layer 150 is used to support the conductive layer 140. The insulating layer 150 can adapt to the expansion or contraction of the LED chip 200 by elastic deformation, thereby absorbing stress and effectively avoiding CTE mismatch.

[0039] In order to further avoid CTE mismatch, in one embodiment, as Figure 2As shown, the insulating layer 150 covers the outside of each solder joint layer 160. In this embodiment, the insulating layer 150 includes a first insulating layer 151 and a second insulating layer 152. The first insulating layer 151 is disposed on the first surface of the first ceramic layer 110, and the first insulating layer 151 is provided with a second via 102 connected to the first via 101. The conductive layer 140 is disposed on the first insulating layer 151. The second insulating layer 152 is disposed on the first insulating layer 151 and between each circuit of the conductive layer 140 to isolate each circuit of the conductive layer 140. Moreover, the height of the second insulating layer 152 on the first insulating layer 151 is greater than the height of the conductive layer 140 and less than or equal to the sum of the heights of the conductive layer 140 and the solder joint layer 160. The second insulating layer 152 covers and is disposed on the outside of the solder joint layer 160 and is connected to the solder joint layer 160. In this embodiment, by covering the outside of the solder joint layer 160 with the insulating layer 150, the insulating layer 150 can absorb the deformation energy of the conductive layer 140 and the solder joint layer 160, provide buffering for the conductive layer 140 and the solder joint layer 160, and play a supporting role for the solder joint layer 160, avoiding the fracture or deformation of the solder joint layer 160 caused by CTE mismatch.

[0040] In order to enable the insulating layer 150 to have better flexibility and elasticity and better thermal conductivity so that heat can be conducted to the temperature sensing unit 300, in one embodiment, the material of the insulating layer 150 includes epoxy resin, wherein the epoxy resin is mixed with a thermal conductive filler, and the thermal conductive filler includes alumina. In this embodiment, by using epoxy resin and mixing alumina in the epoxy resin, the thermal conductivity of the insulating layer 150 can be effectively improved, thereby efficiently conducting the heat of the LED chip 200 to the first ceramic layer 110 and then to the temperature sensing unit 300. In one embodiment, the epoxy resin is a glass fiber reinforced epoxy resin, which has excellent mechanical properties, good thermal stability and thermal conductivity, and can well support the conductive layer 140 and the LED chip 200.

[0041] In one embodiment, the installation hole 121 is filled with thermal conductive silica gel. In this embodiment, the thermal conductive silica gel fills the gap between the temperature sensing unit 300 and the temperature sensing metal conductive sheet 310. In this embodiment, by filling the installation hole 121 with the thermal conductive silica gel, the temperature sensing unit 300 is made more secure in the installation hole 121. In addition, the thermal conductive silica gel has insulating properties. By filling the gap between the temperature sensing unit 300 and the temperature sensing metal conductive sheet 310 with the thermal conductive silica gel, insulation can be achieved between the parts of the temperature sensing unit 300 and the temperature sensing metal conductive sheet 310 other than the welding positions and the pins, avoiding short circuits. In addition, the thermal conductive silica gel can also efficiently conduct the heat of the temperature sensing metal conductive sheet 310 to the temperature sensing unit 300, improving the temperature detection accuracy and sensitivity.

[0042] In one embodiment, the minimum distance between adjacent electron - conducting sheets is greater than twice the aperture diameter of the first via 101 and less than three times the aperture diameter of the first via 101. In this embodiment, the thermal conductive silicone is filled between adjacent electron - conducting sheets. In this way, a structure similar to a capacitor is formed between the electron - conducting sheets, which is likely to generate parasitic capacitance. And since the electron - conducting sheets are also connected to the first via 101, two - direction parasitic capacitances will be generated. One is the capacitance formed between the edge electric fields of adjacent electron - conducting sheets, which is the lateral edge capacitance. The other is the longitudinal via - electron - conducting sheet capacitance formed by the vertical electric - field coupling between the first via and adjacent electron - conducting sheets. The magnitude of the lateral edge capacitance C edge is inversely proportional to the distance s between adjacent electron - conducting sheets, C edge ∝1 / s, while the magnitude of the longitudinal via - electron - conducting sheet capacitance C via is related to the aperture diameter d of the first via and the distance s between adjacent electron - conducting sheets. Among them, the longitudinal via - electron - conducting sheet capacitance is proportional to the coupling area A and inversely proportional to the sum of the aperture diameter d of the first via and the distance s between adjacent electron - conducting sheets, that is, C via ∝A / (s + d), and the coupling area A is inversely proportional to the distance s between the electron - conducting sheets. The smaller the distance s, the larger the electric - field overlap region between adjacent electron - conducting sheets and the larger the coupling area. It can be seen that when the aperture diameter d of the first via is greater than the distance s between adjacent electron - conducting sheets, the edge electric field decays greatly with the increase of the distance, and the lateral edge capacitance is significantly reduced, while the longitudinal via - electron - conducting sheet capacitance is reduced due to the decrease of the coupling area; when the aperture diameter d of the first via is less than the distance s between adjacent electron - conducting sheets, the lateral edge capacitance rises sharply, and the longitudinal via - electron - conducting sheet capacitance increases due to the increase of the coupling area. Therefore, in order to reduce the parasitic capacitance, in this embodiment, the minimum distance between adjacent electron - conducting sheets is greater than twice the aperture diameter of the first via 101, that is, s≥2d, which can effectively suppress the parasitic capacitance and at the same time meet the LTCC process constraints and reliability requirements. In addition, it should be understood that the distance s between adjacent electron - conducting sheets cannot be too large. If the distance s is set to be large, it is easy to cause the overall area of the temperature - sensitive metal conductive sheet 310 to be small, which is not conducive to heat conduction. Therefore, the minimum distance between adjacent electron - conducting sheets is less than three times the aperture diameter of the first via 101, which can effectively maintain the overall area of the temperature - sensitive metal conductive sheet 310, ensure the heat - conduction efficiency, and improve the detection accuracy of the temperature - sensing unit 300.

[0043] In order to improve the strength of the solder joint layer 160 and avoid the fracture or deformation of the solder joint layer 160, in one embodiment, as Figure 2As shown, the width of each solder joint layer 160 gradually decreases from the end close to the LED chip 200 to the end far from the LED chip 200. In this embodiment, the width of the top of each solder joint layer 160 is greater than the width of the bottom, so that the connection area between the top of the solder joint layer 160 and the electrode of the LED chip 200 is increased, realizing sufficient connection with the LED chip 200, increasing the anti-shear area, effectively avoiding breakage, and the bottom of the solder joint layer 160 can effectively utilize the buffer of the insulating layer 150 to avoid breakage due to being close to the insulating layer 150. Thus, the connection strength of the solder joint layer 160 is improved as a whole, and breakage or deformation of the solder joint layer 160 is avoided.

[0044] In one embodiment, as Figure 2 shown, the end face of each solder joint layer 160 close to the LED chip 200 is set as an arc surface. In this embodiment, the end face of the solder joint layer 160 is set as an arc surface, and the solder pad corresponding to the electrode of the LED chip 200 is set as an arc bump. In this way, the two can be matched, so as to realize reducing local stress concentration by geometric self-alignment, and the shear stress in the direction parallel to the ceramic substrate can be dispersed to the direction perpendicular to the ceramic substrate, thereby reducing the transverse shear stress of the solder joint layer 160 and effectively avoiding breakage or deformation of the solder joint layer 160.

[0045] In one embodiment, the width of each solder joint layer 160 gradually decreases from the end close to the LED chip 200 to the end far from the LED chip 200, and the end face of each solder joint layer 160 close to the LED chip 200 is set as an arc surface. In this embodiment, the solder joint layer 160 is arranged in an inverted trapezoid. Since the connection area between the top and the electrode of the LED chip 200 is large, the anti-shear area is effectively increased, and breakage is effectively avoided. Moreover, the top end face is arc-shaped, which can effectively disperse the shear stress in the direction parallel to the ceramic substrate to the direction perpendicular to the ceramic substrate, reducing the transverse shear stress of the solder joint layer 160. In addition, the larger arc-shaped end face can better reduce local stress concentration and effectively avoid breakage or deformation of the solder joint layer 160.

[0046] In one embodiment, the thermal expansion coefficients of the first ceramic layer 110, the second ceramic layer 120, and the third ceramic layer 130 increase in sequence.

[0047] In this embodiment, the ceramic content in the first ceramic layer 110, the second ceramic layer 120, and the third ceramic layer 130 decreases in sequence. For example, the first ceramic layer 110 is formed by sintering ceramics, the second ceramic layer 120 is formed by sintering ceramics with copper powder and glass powder added, and the third ceramic layer 130 is formed by sintering ceramics with aluminum powder added. In this way, the metal powder content in the first ceramic layer 110, the second ceramic layer 120, and the third ceramic layer 130 increases in sequence. The coefficient of thermal expansion (CTE) of the first ceramic layer 110 is 5 to 6.5 ppm / °C, the coefficient of thermal expansion of the second ceramic layer 120 is 8 to 8.5 ppm / °C, and the coefficient of thermal expansion of the third ceramic layer 130 is 10 to 12 ppm / °C. It should be understood that the coefficient of thermal expansion of the LED chip 200 is 2.6 ppm / °C. Compared with the second ceramic layer 120 and the third ceramic layer 130, the first ceramic layer 110 has the characteristic of a low coefficient of thermal expansion and a closer coefficient of thermal expansion to the LED chip 200, which can reduce the internal stress caused by the difference in the degree of thermal expansion between the first ceramic layer 110 and the LED chip 200 and avoid CTE mismatch. Moreover, the metal powder content in the second ceramic layer 120 and the third ceramic layer 130 located at the bottom layer gradually increases, which can form a thermal expansion gradient between the three ceramic layers, gradually absorb the stress caused by the expansion difference, and disperse the stress. In addition, the second ceramic layer 120 and the third ceramic layer 130 with a higher metal powder content have higher hardness and strength, can effectively support the first ceramic layer 110, and have a higher thermal conductivity, can effectively absorb the heat from the upper layer and diffuse it to the outside, making the heat dissipation effect of the multi-layer ceramic substrate 100 better.

[0048] In one embodiment, as Figure 3 shown, the flip-chip COB package circuit board 10 further includes a temperature control unit 400. The temperature control unit 400 is disposed on the surface of the multi-layer ceramic substrate 100. The third ceramic layer 130 is provided with a third via 103. The temperature sensing unit 300 is electrically connected to the temperature control unit 400 through the third via 103, and the temperature control unit 400 is electrically connected to the conductive layer 140.

[0049] In this embodiment, the temperature sensing unit 300 can be a patch-type temperature sensor, and the temperature control unit 400 is a temperature control chip. The temperature control unit 400 can also be referred to as an overheat protection control unit. The temperature control unit 400 realizes signal transmission with the temperature sensing unit 300 through the third via 103. The temperature sensing unit 300 sends the detected temperature signal to the temperature control unit 400. The temperature control unit 400 is used to detect the temperatures of the LED chip 200 and the multi-layer ceramic substrate 100 through the temperature sensing unit 300. The temperature control unit 400 realizes the control of the current of the LED chip 200 through the electrical connection with the circuit on the conductive layer 140. When the temperatures of the LED chip 200 and the multi-layer ceramic substrate 100 are greater than the preset temperature, the current of the LED chip 200 is controlled to decrease, thereby reducing the luminous brightness of the LED chip 200, so as to realize the dynamic adjustment of the temperature of the LED chip 200 and avoid overheating. It is worth mentioning that in the prior art, it is considered to set the thermal protection IC and the temperature sensor in the component placement through-hole at the same time. On the one hand, a placement hole with a larger area is required, and a hole with a larger area needs to be opened in the second ceramic layer 120, which affects the rigidity of the second ceramic layer 120. On the other hand, when the temperature control unit 400 is set in the placement hole, vias need to be set on the first ceramic layer 110. In this way, there will be more vias in the temperature sensing area, increasing the parasitic capacitance generated by the vias and affecting the signal transmission of the circuit board. Therefore, in this embodiment, the temperature control unit 400 is set outside the mounting hole 121, and the third via 103 connecting the temperature control unit 400 and the temperature sensing unit 300 is set in the third ceramic layer 130, avoiding the third via 103 and the first via 101 being concentrated in the temperature sensing area at the same time and reducing the parasitic capacitance.

[0050] In one embodiment, as Figure 3 shown, the temperature control unit 400 is set on the side of the third ceramic layer 130 facing away from the second ceramic layer 120, and the position of the temperature control unit 400 on the third ceramic layer 130 is staggered from the position of the mounting hole 121 on the second ceramic layer 120. A first circuit layer 131 and a second circuit layer 132 are provided on the side of the third ceramic layer 130 facing away from the second ceramic layer 120. The temperature control unit 400 is connected to the third via 103 through the first circuit layer 131. Fourth vias 104 are provided at the positions of the first ceramic layer 110, the second ceramic layer 120, and the third ceramic layer 130 near the outer edge of the conductive layer 140. The temperature control unit 400 is connected to the fourth via 104 through the second circuit layer 132. The fourth via 104 is connected to the conductive layer 140.

[0051] In this embodiment, the first circuit layer 131 and the second circuit layer 132 are formed on the back surface of the third ceramic layer 130 by means of screen printing or mask printing, for realizing the electrical connection between the temperature control unit 400, the temperature sensing unit 300 and the conductive layer 140. Among them, the fourth via 104 is located at a position close to the outer edge of the conductive layer 140 and has a relatively large distance from the third via 103, which can effectively avoid the problem of large parasitic capacitance caused by concentrated vias. Moreover, the temperature control unit 400 is staggered from the mounting hole 121, so that the temperature control unit 400 is located outside the mounting hole 121, making the temperature control unit 400 far away from the via, avoiding being affected by the parasitic capacitance of the via, and thus improving the signal integrity.

[0052] In one embodiment, the temperature sensing unit 300 is connected to the third via 103 through a wire (not shown in the figure). In this embodiment, one end of the wire is electrically connected to the signal pin of the temperature sensing unit 300, and the other end of the wire is connected to the third via 103, so as to realize the electrical connection between the temperature sensing unit 300 and the third via 103. The manufacturing and connection process is as follows: first, one end of the wire is soldered to the signal pin of the temperature sensing unit 300, then the second ceramic layer 120 and the third ceramic layer 130 are pressed together, and the other end of the wire is passed through the third via 103 of the third ceramic layer 130. Subsequently, copper plating connected to the other end of the wire is formed in the third via 103.

[0053] In one embodiment, as Figure 4 shown, a receiving hole 122 is provided on the second ceramic layer 120 at a position close to the outer edge of the conductive layer 140. The temperature control unit 400 is disposed in the receiving hole 122. The third ceramic layer 130 is provided with a fifth via 105 in the area aligned with the receiving hole 122, and the first ceramic layer 110 is provided with a sixth via 106 in the area aligned with the receiving hole 122. A third circuit layer 133 is provided on the surface of the third ceramic layer 130 facing away from the second ceramic layer 120. The position of the third via 103 on the third ceramic layer 130 is aligned with the temperature sensing area of the first ceramic layer 110. The third via 103 is connected to the third circuit layer 133. The third circuit layer 133 is connected to the temperature control unit 400 through the fifth via 105, and the temperature control unit 400 is connected to the conductive layer 140 through the sixth via 106.

[0054] In this embodiment, the temperature control unit 400 is disposed in the accommodation hole 122, separately placed in different holes from the temperature sensing unit 300, reducing the area of a single hole and avoiding excessive impact on the overall rigidity of the second ceramic layer 120. The temperature control unit 400 is connected to the temperature sensing unit 300 through the fifth via 105, the third circuit layer 133, and the third via 103, and is connected to the conductive layer 140 through the sixth via 106 to achieve the connection of the circuit with the conductive layer 140. This embodiment is different from the above embodiment in that the temperature control unit 400 is not disposed on the back surface of the third ceramic layer 130, but in the accommodation hole 122 of the second ceramic layer 120. On the one hand, it avoids the reduction of the rigidity of the second ceramic layer 120 caused by the excessive area of a single hole. On the other hand, it avoids the problem of increased parasitic inductance caused by the excessive length of the via (the fourth via 104) connecting to the conductive layer 140, thereby effectively ensuring the integrity of the signal transmission of the flip-chip COB package circuit board 10.

[0055] In this embodiment, the connection structure of the temperature control unit 400 with the fifth via 105 and the sixth via 106 in the accommodation hole 122 can adopt the connection structure of the temperature sensing unit 300 with the first via 101 and the third via 103 in the mounting hole 121. In this embodiment, no redundant description is given here.

[0056] In one embodiment, the flip-chip COB package circuit board 10 further includes a light-transmitting adhesive layer, which is connected to the first ceramic layer 110 and covers the outside of each LED chip 200.

[0057] In this embodiment, the light-transmitting adhesive layer is used to encapsulate and protect each LED chip 200, and guide and diffuse the light emitted by the LED chip 200 to the outside. In this embodiment, the material of the light-transmitting adhesive layer is transparent epoxy resin, and fluorescent powder particles are mixed in the transparent epoxy resin. In this way, each LED chip 200 can be encapsulated by the light-transmitting adhesive layer to avoid the entry of dust and moisture. In addition, the light-transmitting adhesive layer has good light transmittance and better light scattering characteristics, making the overall light output of the flip-chip COB package circuit board 10 more uniform and the brightness higher.

[0058] In one embodiment, an electronic device is provided, including the flip-chip COB package circuit board 10 described in any of the above embodiments.

[0059] In this embodiment, through the above structure of the flip-chip COB packaged circuit board 10, the temperature sensing unit 300 can be close to the LED chip 200, and the temperature-sensitive metal conductive sheet 310 is used for efficient temperature conduction, so that the temperature sensing unit 300 can accurately and sensitively detect the temperature of the LED chip 200. In addition, an insulating layer 150 is provided on the surface of the first ceramic layer 110, and the flexible insulating layer 150 is used to support the conductive layer 140. The insulating layer 150 can adapt to the expansion or contraction of the LED chip 200 by elastic deformation, thereby absorbing stress, and further effectively avoiding CTE mismatch. Furthermore, the service life of the flip-chip COB packaged circuit board 10 is effectively improved, thereby improving the service life of the electronic device.

[0060] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered that the scope described in this specification.

[0061] The above-described embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A flip-chip COB packaging circuit board, characterized in that: include: Multilayer ceramic substrate, multiple LED chips and temperature sensing unit; The multilayer ceramic substrate comprises a conductive layer, an insulating layer, a first ceramic layer, a second ceramic layer and a third ceramic layer, wherein the insulating layer is arranged on a first surface of the first ceramic layer, the conductive layer is arranged on the insulating layer, the second ceramic layer is connected to a second surface of the first ceramic layer, and a surface of the second ceramic layer facing away from the first ceramic layer is connected to the third ceramic layer; A plurality of solder point layers are arranged on the conductive layer, and electrodes of each LED chip are connected to each solder point layer correspondingly; The second ceramic layer is provided with a mounting hole, the temperature sensing unit is arranged in the mounting hole, the second surface of the first ceramic layer has a temperature sensing area aligned with the mounting hole, the temperature sensing area is provided with a temperature-sensitive metal conductive sheet, the first ceramic layer is provided with a first via hole, the temperature-sensitive metal conductive sheet is electrically connected to the conductive layer through the first via hole, the power input end of the temperature sensing unit is electrically connected to the temperature-sensitive metal conductive sheet, and the temperature sensing unit is attached to the temperature-sensitive metal conductive sheet.

2. The flip-chip COB packaging circuit board according to claim 1, characterized in that: The insulating layer is coated on the outer side of each solder joint layer.

3. The flip-chip COB packaging circuit board according to claim 1, characterized in that: The width of each solder joint layer gradually decreases from an end close to the LED chip to an end far away from the LED chip.

4. The flip-chip COB packaging circuit board according to claim 1, characterized in that: The end surface of each soldering point layer close to one end of the LED chip is configured as an arc surface.

5. The flip-chip COB packaging circuit board according to claim 1, characterized in that: The thermal expansion coefficients of the first ceramic layer, the second ceramic layer and the third ceramic layer increase in sequence.

6. The flip-chip COB packaging circuit board according to claim 5, characterized in that: It also includes a temperature control unit, which is arranged on the surface of the multilayer ceramic substrate. The third ceramic layer has a third via hole. The temperature sensing unit is electrically connected to the temperature control unit through the third via hole. The temperature control unit is electrically connected to the conductive layer.

7. The flip-chip COB packaging circuit board according to claim 6, characterized in that: The temperature control unit is arranged on the side of the third ceramic layer facing away from the second ceramic layer, and the position of the temperature control unit on the third ceramic layer is staggered from the position of the mounting hole on the second ceramic layer. The first circuit layer and the second circuit layer are arranged on the side of the third ceramic layer facing away from the second ceramic layer. The temperature control unit is connected to the third via hole through the first circuit layer. The first ceramic layer, the second ceramic layer and the third ceramic layer are provided with a fourth via hole at a position close to the outer edge of the conductive layer. The temperature control unit is connected to the fourth via hole through the second circuit layer, and the fourth via hole is connected to the conductive layer.

8. The flip-chip COB packaging circuit board according to claim 6, characterized in that: The temperature sensing unit is connected to the third via hole through a wire.

9. The flip-chip COB packaging circuit board according to any one of claims 1 to 8, characterized in that: It also includes a light-transmitting adhesive layer, which is connected to the first ceramic layer and covers the outer side of each of the LED chips.

10. An electronic device, characterized in that: The invention comprises the flip-chip COB package circuit board as described in any one of claims 1 to 9.

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