Flip-chip LED light source

Abstract

The present invention discloses a flip-chip LED light source comprising a substrate and at least one LED chip. The LED chip is bonded to the front surface of the substrate via a first surface having electrodes, and the second surface of the LED chip serves as a light-emitting surface and faces away from the first surface. At least one pair of P and N electrodes of the at least one LED chip is thermally connected to the front surface of the substrate via a plurality of spaced-apart thermal conductors, wherein the maximum dimension a of any of the thermal conductors in a direction parallel to the first surface is less than the minimum spacing d between the P and N electrodes. The flip-chip LED light source provided by the present invention combines flip-chip soldering technology with self-aligned isolation technology, improving chip yield and reducing thermal expansion stress at the soldering interface. It also reduces the requirement for greater than equipment alignment accuracy, thereby reducing production costs and increasing productivity.

Description

Technical Field

[0001] The present invention relates to an LED light source, in particular to an inverted LED light source, and belongs to the technical field of semiconductors. Background Art

[0002] In flip-chip LEDs, to ensure chip yield and prevent short circuits between the chip PN electrodes during bonding, a certain distance between the PN electrodes is required. On the other hand, to reduce junction temperature, the contact area between the chip and the substrate needs to be as large as possible, and the distance between the PN electrodes as small as possible. Traditional flip-chip technology usually requires equipment with very high alignment accuracy, which increases production costs.

[0003] For example, the existing flip-chip LED light source structure is as follows Figure 1 As shown in the figure, however, due to the limitation of production technology, the processing accuracy of the metal layer spacing on the substrate is currently at the sub-micron level, and the spacing d1 of the PN electrodes on the existing chip is ≥150μm; the heat transfer diagram is shown in the figure. Figure 2 As shown, heat needs to be transported horizontally to the electrode area within the chip first, and then vertically to the substrate. This will increase the heat transport distance and thus increase the thermal resistance. In order to improve the chip's heat dissipation capacity and electrical conductivity, the substrate's metal layer needs to have a size that matches the chip's electrodes. Therefore, the equipment needs to have high alignment accuracy during packaging. The structural alignment error is the spacing between the PN electrodes, otherwise it is easy to cause a short circuit. The chip generates a lot of heat when it emits light. The chip and the metal layer material have a large contact area and different thermal expansion coefficients, which easily generate thermal expansion stress on their contact surfaces, resulting in reduced device reliability. Summary of the Invention

[0004] The present invention mainly adopts a method combining traditional flip-chip technology with isolation self-alignment technology to provide a flip-chip LED light source, which improves chip yield, reduces junction temperature, and reduces production costs, thereby overcoming the shortcomings of the existing technology.

[0005] To achieve the aforementioned object of the invention, the technical solutions adopted by the present invention include:

[0006] An embodiment of the present invention provides a flip-chip LED light source, comprising a substrate and at least one LED chip, wherein the LED chip is bonded to the front surface of the substrate via a first surface having an electrode, and the second surface of the LED chip is a light-emitting surface and is opposite to the first surface; at least one pair of P electrodes and N electrodes of the at least one LED chip are thermally connected to the front surface of the substrate via a plurality of spaced-apart thermal conductors, and the maximum dimension a of any thermal conductor in a direction parallel to the first surface is smaller than the minimum spacing d between the P electrode and the N electrode.

[0007] In some more specific embodiments, the epitaxial layer of the LED chip includes a plurality of unit cells that can emit light independently. The plurality of unit cells are arranged in series and / or in parallel with each other, each unit cell is matched with a P electrode and an N electrode, and each pair of P electrodes and N electrodes is thermally connected to the substrate through multiple heat conductors.

[0008] The aforementioned unit cells are device units with independent and complete functions. The conductive semiconductor layers of any two unit cells are isolated, making each unit cell electrically independent. Metal interconnects allow multiple unit cells to be electrically connected, forming a larger device and achieving higher device performance, such as increased power. The aforementioned unit cells can be light-emitting elements such as semiconductor lasers, LEDs, or electronic components such as diodes.

[0009] In other more specific embodiments, the flip-chip LED light source includes multiple LED chips, each LED chip is matched with a P electrode and an N electrode, and each pair of P electrodes and N electrodes is thermally connected to the substrate through multiple heat conductors.

[0010] Furthermore, d>a≥2μm.

[0011] Furthermore, the distance c between two adjacent heat conductors is ≥1 μm.

[0012] In some more specific implementation schemes, at least one pair of pads is distributed on the front surface of the substrate, and the P electrode and the N electrode are electrically connected to a pad respectively.

[0013] In some more specific embodiments, the pad is further electrically connected to a conductive layer disposed on the back side of the substrate via a conductive channel penetrating the substrate.

[0014] In some more specific embodiments, the back side of the substrate is further covered with a heat dissipation metal layer.

[0015] In some more specific embodiments, the heat conductor is an island structure formed on the front surface of the substrate, and two adjacent island structures are electrically isolated from each other.

[0016] In some more specific implementations, the island structure is fixed to the P electrode or N electrode by welding.

[0017] In some more specific embodiments, the material of the heat conductor includes metal or ceramic, but is not limited thereto.

[0018] In some more specific embodiments, the shape of the heat conductor includes a cuboid, a cube, a cylinder, a truncated cone or a prism, but is not limited thereto.

[0019] Compared with the prior art, the present invention has at least the following advantages:

[0020] 1) The flip-chip LED light source provided by the present invention combines flip-chip soldering technology with self-aligned isolation technology. The size of the thermal conductor is no longer limited by existing substrate processing technology, and the size of the thermal conductor can be reduced to the micron level.

[0021] 2) The heat generated by the light-emitting area of ​​the flip-chip LED light source provided by the embodiment of the present invention can be directly transferred downward through the heat conductor to the substrate, reducing the heat transmission distance, thereby reducing thermal resistance, improving chip yield, and reducing junction temperature issues;

[0022] 3) Since the thermal conductors are electrically isolated and their width is smaller than the spacing between the P and N electrodes, short circuits do not occur, which reduces the requirements for equipment alignment accuracy. The alignment error is half the size of the P and N electrode areas, reducing costs.

[0023] 4) The contact area between a single heat conductor and the P electrode or N electrode is small, and the thermal stress on the contact surface is greatly reduced, thereby increasing the reliability of the device;

[0024] 5) The flip-chip LED light source provided by the embodiment of the present invention reduces the thermal expansion stress of the welding interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0026] Figure 1 This is a structural diagram of a flip-chip LED light source in the prior art;

[0027] Figure 2 This is a schematic diagram of heat transfer of a flip-chip LED light source in the prior art;

[0028] Figure 3 This is a schematic structural diagram of a flip-chip LED light source in Example 1 of the present invention;

[0029] Figure 4 This is a schematic structural diagram of a flip-chip LED light source in Example 1 of the present invention;

[0030] Figure 5 This is a schematic structural diagram of a flip-chip LED light source in Example 2 of the present invention;

[0031] Figure 6 This is a schematic diagram of heat transfer of a flip-chip LED light source in a typical embodiment of the present invention. DETAILED DESCRIPTION

[0032] In view of the shortcomings of the prior art, the inventors of this case, after long-term research and extensive practice, have proposed the technical solution of the present invention. The following will further explain this technical solution, its implementation process and principles.

[0033] Example 1

[0034] See also Figure 3 and Figure 4 A flip-chip LED light source includes a substrate 30 and at least one LED chip 10. The LED chip 10 is combined with the front surface of the substrate 30 via a first surface having an electrode, and the second surface of the LED chip 10 is a light-emitting surface and is opposite to the first surface.

[0035] Among them, the LED chip is a high-voltage, high-power integrated flip chip with good flatness. The epitaxial layer of the LED chip 10 may include an N-type GaN layer 11, an active layer 12, and a P-type GaN layer 13 formed in sequence on the substrate 20; further, an insulating layer 14 may be provided on the epitaxial layer; the epitaxial layer is processed to form a plurality of unit cells arranged in an array form, and the plurality of unit cells are connected in series and / or in parallel, and each unit cell is matched with a P electrode 15 and an N electrode 16, and the P electrode 15 and the N electrode 16 are spaced apart from each other, and the minimum distance between the two can be defined as d.

[0036] Alternatively, the flip-chip LED light source includes a substrate 30 and multiple LED chips (the LED chips are ordinary flip-chips with good flatness) 10, and the multiple LED chips are connected in series and / or in parallel. Each LED chip 10 is matched with a P electrode 15 and an N electrode 16. Each pair of P electrodes 15 and N electrodes 16 are spaced apart from each other, and the minimum distance between the two can be defined as d.

[0037] A plurality of spaced-apart heat conductors 40 are provided on the front surface of the insulating substrate 30. The heat conductors 40 are island structures formed on the front surface of the substrate 40, and two adjacent island structures are electrically isolated from each other. The LED chip 10 is combined with the front surface of the substrate 30 via a first surface having a P electrode 15 and an N electrode 16. The P electrode 15 and the N electrode 16 are welded to the heat conductor 40. The P electrode 15 and the N electrode 16 of the LED chip are thermally connected to the front surface of the substrate 30 via the plurality of spaced-apart heat conductors 40. In a direction parallel to the first surface of the LED chip 10, the maximum size of the heat conductor can be defined as a, and the distance between two adjacent heat conductors can be defined as c, where d>a≥2μm, and c≥1μm.

[0038] Depend on Figure 4As can be seen in FIG, the relative positional relationship between the P electrode 15, the N electrode 16 and the heat conductor 40 can be seen in regions A and B. Since the heat conductors are electrically isolated from each other and the maximum size of the heat conductor is smaller than the distance between the P electrode and the N electrode, there will be no short circuit problem. Therefore, the alignment accuracy requirement of the equipment is low, and the alignment error is half the area size of the P electrode or N electrode. Figure 3 or Figure 4 As shown, during flip-chip packaging, different positional relationships between the thermal conductor and the P electrode and N electrode will not cause a short circuit between the P electrode and the N electrode; and the contact area between a single thermal conductor and the P electrode or N electrode is small, and the thermal stress of the contact surface is greatly reduced, thereby increasing the reliability of the device.

[0039] In addition, solder pads 51 and solder pads 52 are also provided on the front surface of the insulating substrate 30. The solder pads 51 and solder pads 52 are respectively provided on both sides of the multiple heat conductors 40. The P electrode 15 and the N electrode 16 are electrically connected to the solder pads 51 and solder pads 52 respectively. The solder pads 51 and solder pads 52 are also electrically connected to external leads 60.

[0040] The heat conductor 40 may be made of metal or ceramic, and may be shaped like a cuboid, a cube, a cylinder, a truncated cone, or a prism.

[0041] It should be noted that the minimum distance d between the P electrode 15 and the N electrode 16 is greater than the maximum size a of the heat conductor. Figure 3 or Figure 4 It can be understood that the minimum spacing between the P electrode 15 and the N electrode 16 and the maximum size of the heat conductor are spacings in the same reference direction. For example, the direction parallel to the first surface of the LED chip 10 can be used as the reference direction, or the width direction of the heat conductor can be used as the reference direction.

[0042] See also Figure 6 As shown, the embodiment of the present invention provides that the heat generated by the light-emitting area of ​​the flip-chip LED light source can be directly transferred downward to the insulating substrate through the heat conductor, thereby reducing the heat transmission distance and lowering the thermal resistance.

[0043] Example 2

[0044] See also Figure 5The structure of a flip-chip LED light source in this embodiment is substantially identical to that of the flip-chip LED light source in Example 1. The difference is that, in this embodiment, external leads 60 are not provided on the front surface of the insulating substrate 30. Instead, conductive layers 53 and 54 are provided on the back surface of the insulating substrate 30. The solder pads 51 and 52 are electrically connected to the conductive layers 53 and 54 on the back surface of the substrate, respectively, via conductive channels 31 and 32 that penetrate the substrate 30. This allows electrical leads to be drawn from the back surface of the insulating substrate. The conductive channels and conductive layers can both be made of metal, which facilitates the timely transfer of heat generated by the LED chip.

[0045] In some more specific embodiments, a heat dissipation metal layer 70 is further provided on the back side of the substrate 30 . The heat dissipation metal layer 70 is electrically isolated from the conductive layers 53 and 54 , and the heat dissipation metal layer 70 can be connected to a heat sink.

[0046] It should be noted that when the material of the heat conductor in the embodiment of the present invention is metal, a metal material with good thermal conductivity can be selected, and the material of the conductive metal layer can be a metal material with good electrical conductivity, which will not be listed here one by one.

[0047] Self-aligned isolation technology: Since the substrate is provided with a metal island (i.e., an island-shaped thermal conductor) that is electrically isolated and smaller than the chip electrode spacing, when the flip chip is soldered to the substrate, the chip electrodes and the metal island do not need to be precisely aligned to achieve chip self-alignment welding and there is no short circuit between the electrodes.

[0048] The flip-chip LED light source provided by the present invention combines flip-chip soldering technology with self-aligned isolation technology. The size of the heat conductor is no longer limited by existing substrate processing technology, and the size of the heat conductor can be reduced to the micron level. In addition, the heat generated by the light-emitting area of ​​the flip-chip LED light source provided by the embodiment of the present invention can be directly transmitted downward to the substrate through the heat conductor, reducing the heat transmission distance, thereby reducing thermal resistance, improving chip yield, and lowering junction temperature. In addition, since the heat conductors are electrically isolated from each other and the width of the heat conductor is less than the spacing between the P and N electrodes, short circuit problems will not occur, thereby reducing the requirements for equipment alignment accuracy. The alignment error is half the area size of the P and N electrodes, reducing costs. In particular, the contact area between a single heat conductor and the P electrode or N electrode is small, and the thermal stress on the contact surface is greatly reduced, thereby increasing the reliability of the device.

Claims

1. A flip-chip LED light source, characterized in that The invention comprises a substrate and at least one LED chip, wherein the LED chip is bonded to the front surface of the substrate with a first surface having electrodes, and the second surface of the LED chip is a light-emitting surface and faces away from the first surface; at least one pair of P electrodes and N electrodes of the at least one LED chip is thermally connected to the front surface of the substrate via a plurality of spaced-apart thermal conductors, wherein the maximum dimension a of any thermal conductor in a direction parallel to the first surface is less than the minimum spacing d between the P electrodes and the N electrodes; d>a≥2μm; and the distance c between two adjacent thermal conductors is ≥1μm; The heat conductor is an island structure formed on the front surface of the substrate, and two adjacent island structures are electrically isolated from each other.

2. The flip-chip LED light source according to claim 1, characterized in that: The epitaxial layer of the LED chip includes a plurality of unit cells that can emit light independently. The plurality of unit cells are arranged in series and / or in parallel. Each unit cell is matched with a P electrode and an N electrode, and each pair of P electrodes and N electrodes is thermally connected to the substrate through multiple heat conductors.

3. The flip-chip LED light source according to claim 1 or 2, characterized in that: The flip-chip LED light source includes a plurality of LED chips, each LED chip is matched with a P electrode and an N electrode, and each pair of P electrodes and N electrodes is thermally connected to the substrate through a plurality of heat conductors.

4. The flip-chip LED light source according to claim 1, wherein: At least one pair of pads is distributed on the front surface of the substrate, and the P electrode and the N electrode are electrically connected to a pad respectively.

5. The flip-chip LED light source according to claim 4, characterized in that: The pad is also electrically connected to a conductive layer disposed on the back side of the substrate via a conductive channel penetrating the substrate.

6. The flip-chip LED light source according to claim 1, characterized in that: The back side of the substrate is also covered with a heat dissipation metal layer.

7. The flip-chip LED light source according to claim 1, characterized in that: The island structure is fixed to the P electrode or the N electrode by welding.

8. The flip-chip LED light source according to claim 1, characterized in that: The material of the heat conductor includes metal or ceramic.

9. The flip-chip LED light source according to claim 1, characterized in that: The shape of the heat conductor includes a cuboid, a cube, a cylinder, a truncated cone or a prism.

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