A flip-chip COB packaging structure

Abstract

The present application relates to the field of packaging, and in particular to a flip-chip COB packaging structure, comprising a substrate, a chip, a packaging layer, a backplane, and an umbrella portion; the chip array is distributed on one side surface of the substrate, and each chip has at least two electrodes electrically connected to the substrate; a plurality of through holes are provided on the substrate, the through holes corresponding to the chips one-to-one, and each through hole is arranged between the electrodes of its corresponding chip; the backplane is arranged on the side of the substrate away from the chip, and the umbrella portion is fixedly connected to the side of the backplane close to the substrate and corresponds one-to-one with the through holes; the umbrella portion includes an umbrella column and an umbrella cap, one end of the umbrella column is fixed to the backplane, and the other end is connected to the umbrella cap, the umbrella column is configured to pass through the through hole, the umbrella cap is located between the chip and the substrate and abuts against the substrate, the size of the umbrella cap close to the backplane is larger than the through hole and smaller than the spacing between the corresponding electrodes, and the umbrella cap surface is insulated; the packaging layer covers all chips. The present application can effectively reduce the possibility of short circuits during the reflow soldering process of the flip-chip COB packaging structure.

Description

Technical Field

[0001] The present application relates to the field of packaging, and in particular to a flip-chip COB packaging structure. Background Art

[0002] Chip-on-board (COB) packaging technology involves attaching a bare chip to the surface of a substrate and then making electrical connections. COB packaging primarily includes two methods: face-up and flip-up. Flip-up involves placing electrodes on the side of the chip closest to the substrate and then attaching them to the substrate circuitry.

[0003] The common fixing method for flip-chip COB technology is reflow soldering, which is to pre-set a certain amount of solid flux on the surface of each electrode of the electronic component. After the chip is placed in the predetermined position, the entire board is heated to melt the flux and infiltrate the electrodes on the substrate. After cooling and solidification, a stable connected circuit board is formed.

[0004] The aforementioned technology has the following problem: when the entire board is heated, the liquid flux soaks into the substrate electrodes and may also come into contact with nearby flux. If this occurs, it can cause a short circuit and burn the board. Therefore, a flip-chip COB package structure that can prevent short circuits is needed. Summary of the Invention

[0005] In order to solve the problem that flip-chip COB is prone to short circuit during the reflow soldering process and ensure the qualified rate of the flip-chip COB packaging structure, the present application provides a flip-chip COB packaging structure.

[0006] This application provides a flip-chip COB packaging structure, which adopts the following technical solutions:

[0007] A flip-chip COB packaging structure includes a substrate, a chip, a packaging layer, a backplane, and an umbrella portion. The chip array is distributed on one side of the substrate, and each chip has at least two electrodes electrically connected to the substrate via solder. The substrate is provided with a plurality of through-holes, each corresponding one-to-one to the chips, and each through-hole is arranged between the electrodes of its corresponding chip. The backplane is provided on a side of the substrate facing away from the chips. The umbrella portion is fixedly connected to a side of the backplane near the substrate and corresponds one-to-one to the through-holes. The umbrella portion includes an umbrella post and an umbrella cap. One end of the umbrella post is fixed to the backplane and the other end is connected to the umbrella cap. The umbrella post is configured to pass through the through-hole. The umbrella cap is located between the chip and the substrate and abuts the substrate. The size of the umbrella cap near the backplane is larger than the through-hole and smaller than the spacing between the corresponding electrodes. The umbrella cap surface is insulated. The packaging layer covers the entire side of the substrate near the chip and encapsulates all the chips.

[0008] By adopting the above technical solution, multiple electrodes of the same chip are separated by the umbrella cover. During the reflow soldering process, the melted flux is blocked by the umbrella cover, thereby preventing conduction between different electrodes and thus preventing the entire package structure from burning.

[0009] Preferably, the umbrella column and the umbrella cover are designed as an integral whole, and the umbrella cover is made of elastic insulating material.

[0010] By adopting the above technical solution, the entire umbrella part is designed as an integrated unit. During the bonding process between the substrate and the back panel, the umbrella part passes through the through hole of the substrate, the umbrella column passes through both ends of the through hole, and the umbrella cover is unfolded on the side of the substrate away from the back panel. On the one hand, this increases the barrier area and optimizes the anti-short circuit effect. On the other hand, the edge of the umbrella cover abuts against the substrate, which also has a clamping effect on the bonding between the substrate and the back panel.

[0011] Preferably, the umbrella cover is provided with a through-column hole along its axis, the through-column hole passes through the umbrella cover, and the umbrella column passes through the through-column hole and abuts against the chip.

[0012] By adopting the above technical solution, one end of the umbrella column is fixed to the backplane, and the other end is in contact with the chip. Under normal working scenarios, when the chip generates heat, the heat can be efficiently discharged by the umbrella column, maintaining a lower operating temperature of the entire packaging structure.

[0013] Preferably, the umbrella cover and the umbrella column are designed to be split, and a column-through hole is opened on the side of the umbrella cover close to the umbrella column, and the umbrella column passes through the through hole and then enters the column-through hole.

[0014] By adopting the above technical solution, the umbrella cover and umbrella column are designed to be separated. During the actual installation process, they can be assembled from both sides of the base plate. After the umbrella cover and umbrella column are connected, the base plate and the back plate can also be fixed together. In addition, because it is no longer emphasized that the umbrella cover needs to pass through the through hole of the base plate, the choice of umbrella cover can be more flexible. When the umbrella cover is based on a metal with good thermal conductivity, the thermal conductive structure of the base plate has a larger thermal conductive contact surface with the chip, and the thermal conductive effect is better.

[0015] Preferably, a flange is provided on the umbrella column, and correspondingly, a groove matching with the flange is provided in the through-column hole, and the flange and the hole opening of the through-column hole are interference fit.

[0016] By adopting the above technical solution, the umbrella cover is mounted on the umbrella column. After reaching the predetermined position, it is difficult to fall out due to environmental disturbances, and has high stability during work and production.

[0017] Preferably, a boss is provided on one side of the umbrella cover close to the back plate, the outer diameter of the boss is smaller than the diameter of the through hole, the through-column hole passes through the boss, and the boss is configured to be inserted between the through hole and the umbrella column.

[0018] By adopting the above technical solution, the positioning between the umbrella cover and the substrate is no longer completely dependent on the umbrella column. The umbrella cover and the substrate can be positioned even if they are separated from the umbrella column. In the actual production process, the assembly of the substrate, umbrella cover and chip can be completed first, and then the backplane and umbrella column can be assembled.

[0019] Preferably, the umbrella cover is made of red copper, its surface is coated with insulating paint, and the column holes are coated with thermal paste.

[0020] By adopting the above technical solution, under the premise of ensuring the technical effect of "separating multiple electrodes of the same chip from each other" of this application, the umbrella part has a larger heat conduction area and better heat conduction performance. In actual use, the heat dissipation performance of the packaging structure is better; secondly, during the packaging process, the backplane is heated, and the heat can also be transferred to the packaging glue between the chip and the substrate through the umbrella column and the umbrella cover. The temperature of the packaging glue rises, the viscosity decreases, the fluidity increases, its filling ability is enhanced, and bubbles can be discharged faster.

[0021] Preferably, the thermal conductivity of the material selected for the back plate and the umbrella column is greater than or equal to 400 W / (m·K).

[0022] By adopting the above technical solution, the heat generated by the chip during operation can be quickly transferred to the backplane, which then shares the heat and exchanges heat with the air or other radiators to achieve efficient heat dissipation.

[0023] Preferably, a surface of the umbrella cover close to the chip is provided with densely distributed needle punctures, and the spacing between adjacent needle punctures is less than 10 μm.

[0024] By adopting the above technical solution, during the encapsulation process, when bubbles in the encapsulation glue come into contact with the needle, the needle will destroy the surface tension of the bubbles and break them. When the size of the bubbles is smaller than the critical precipitation radius, the bubbles will spontaneously annihilate, achieving the defoaming effect.

[0025] Preferably, the wetting angle between the punctured surface and the flux is greater than 90°, and the wetting angle between the punctured surface and the material of the packaging layer is less than 60°.

[0026] By adopting the above technical solution, on the one hand, the flux has a tendency to shrink into a ball on the surface of the needle puncture and the umbrella cover, and tends to be attached to the flux ball on the electrode, thereby preventing the conduction of each electrode; on the other hand, the encapsulation glue has a tendency to spontaneously squeeze into the needle puncture gap and squeeze out the air. The molecular force on the surface of the encapsulation glue provides the driving force for its filling.

[0027] In summary, this application includes at least one of the following beneficial technical effects:

[0028] 1. The umbrella cover in the flip-chip COB packaging structure is set between the substrate and the chip, separating the multiple electrodes of the same chip and avoiding short circuits caused by contact between melted flux during the reflow process.

[0029] 2. The surface of the umbrella cover of the flip-chip COB packaging structure is provided with spikes. The distance between adjacent spikes is smaller than the bubbles that may be generated by the packaging glue, so as to destroy the surface tension of the bubbles and avoid the formation of pores in the packaging structure.

[0030] 3. The umbrella part of the flip-chip COB packaging structure passes through the substrate. On the one hand, during the manufacturing process, the backplane is heated, which can transfer heat to the umbrella cover, heating the packaging glue to increase the fluidity of the packaging glue and assist in defoaming; on the other hand, during use, the umbrella part can more efficiently conduct heat away from the chip, achieving better heat dissipation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a cross-sectional schematic diagram of the flip-chip COB packaging structure of Example 1 of the present application.

[0032] Figure 2 yes Figure 1 A partial enlarged view of area A in the middle.

[0033] Figure 3 It is a cross-sectional schematic diagram of the flip-chip COB packaging structure of Example 2 of the present application.

[0034] Figure 4 yes Figure 3The first partial magnification of area B in the middle.

[0035] Figure 5 yes Figure 3 The second partial magnification of area B in the middle.

[0036] Description of reference numerals:

[0037] 1. Substrate; 11. Through hole; 2. Chip; 21. Electrode; 22. Solder; 3. Backplane; 4. Umbrella; 41. Umbrella column; 42. Umbrella cover; 5. Packaging layer. DETAILED DESCRIPTION

[0038] The following is combined with Figure 1-5 This application is described in further detail.

[0039] The present application discloses a flip-chip COB packaging structure.

[0040] Example 1

[0041] refer to Figure 1 , a flip-chip COB packaging structure, including a substrate 1, a chip 2, a backplane 3, an umbrella part 4 and a packaging layer 5.

[0042] The substrate 1 is a PFC board or an FPC board. A circuit is printed or etched on one surface of the substrate 1. A plurality of cylindrical through holes 11 are provided in the non-circuit area of ​​the substrate 1. The through holes 11 pass through both sides of the substrate 1. The through holes 11 are chamfered at the end facing away from the circuit to facilitate insertion of the umbrella portion 4.

[0043] Preferably, the substrate 1 is formed by combining copper foil and a ceramic base, and the circuit is etched on the copper foil surface of the substrate 1 .

[0044] The chips 2 are arrayed on the side of the substrate 1 with the circuit, corresponding one-to-one to the through-holes 11, and the orthographic projection of the through-holes 11 falls on the center of the chip 2. Each chip 2 has at least two electrodes 21 electrically connected to the substrate 1. Specifically, the electrodes 21 of the chip 2 are connected to the circuit of the substrate 1 through a flux 22, and can also be welded to the preset electrodes 21 on the substrate 1; the orthographic projection of the through-holes 11 separates multiple electrodes 21 on the same chip 2.

[0045] The back plate 3 is arranged on the side of the substrate 1 away from the circuit. Its size matches that of the substrate 1 and the material is preferably copper. In one embodiment of the present embodiment, the substrate 1 and the back plate 3 are bonded to each other, and thermal paste is evenly coated on the contact surface of the two. The thermal paste can be silver paste, silicone grease, etc.; in another embodiment of the present embodiment, there is an array of thermal pads distributed between the substrate 1 and the back plate 3 to avoid direct bonding between the substrate 1 and the back plate 3.

[0046] refer to Figure 2On the side of the backplane 3 closest to the substrate 1, an umbrella portion 4 is provided, corresponding one-to-one with each through-hole 11. The umbrella portion 4 includes an umbrella post 41 and an umbrella cap 42. The umbrella cap 42 is a hemispherical shell made of elastic insulating material. Its outer surface faces the chip 2, its inner surface is connected to the umbrella post 41, and its edge abuts the substrate 1. When the umbrella cap 42 is in the retracted state, the entire umbrella portion 4 can pass through the through-hole 11. When the umbrella cap 42 is in the extended state, it separates the electrodes 21 of the corresponding chip 2.

[0047] The umbrella cap 42 has a through-hole formed along its axial direction. The through-hole can be any of a countersunk hole, cylindrical hole, countersunk hole, or truncated cone hole. The umbrella post 41 is a copper rod with one end fixed to the backplate 3 and the other end passing through the through-hole 11 and the through-hole to abut against the chip 2. Preferably, the shape of the end of the umbrella post 41 away from the backplate 3 matches the through-hole.

[0048] The umbrella portion 4 also includes a plurality of punctures evenly arranged on the side of the umbrella cover 42 close to the chip 2. The punctures are evenly distributed on the surface of the umbrella cover 42. The distance between adjacent punctures is less than or equal to 10 microns, and the puncture material does not wet the molten flux 22.

[0049] In another implementation of this embodiment, the through holes 11, the chip 2 and the umbrella portion 4 are not distributed in an array, and the same technical effect can still be achieved while maintaining a one-to-one correspondence.

[0050] The packaging layer 5 covers the entire substrate 1 on the side close to the chip 2 and encapsulates all the chips 2 and electrodes 21 . The packaging material and the needle-piercing material are mutually infiltrated before curing.

[0051] In another embodiment of the present application, the chip 2 is an LED, mini LED or other light source chip 2, the umbrella column 41 is made of optical fiber, the back panel 3 is a light-distributing plate, or a plurality of light-guiding holes are opened on the back panel 3, through which the optical fibers pass to recycle the light from the back of the light source chip 2, thereby increasing the light utilization rate.

[0052] The implementation principle of Example 1 is:

[0053] The umbrella portion 4, through-hole 11, and chip 2 are arranged in a one-to-one correspondence. When the backplate 3 and substrate 1 are brought close together, the umbrella portion 4 passes through the through-hole 11, and the umbrella cap 42 is first compressed and then expanded on the other side of the substrate 1, separating the electrodes 21 of the corresponding chip 2. One end of the umbrella column 41 is fixed to the backplate 3, and the other end abuts the chip 2. At the same time, the thermal paste is squeezed by the substrate 1 and backplate 3, sliding around to fill the gap between the backplate 3 and substrate 1.

[0054] During the reflow process, the melted flux 22 is blocked by the insulating umbrella cover 42, preventing the flux 22 from flowing in a melted state and contacting each other, causing conduction between the electrodes 21 and inducing a short circuit. Moreover, the puncture structure on its surface and the choice of material for the umbrella cover 42 effectively prevent the melted flux 22 from infiltrating and diffusing along the surface of the umbrella cover 42, further enhancing the barrier effect. Specifically, the puncture structure and the material of the umbrella cover 42 can increase the surface tension of the molten flux 22 after contacting the umbrella part 4, causing the flux 22 to tend to aggregate into a spherical shape on the surface of the umbrella part 4. The flux 22 itself also has aggregation tension, so the flux 22 tends to adhere to the flux 22 mass at the electrode 21, rather than diffusing to the surroundings, causing conduction between different electrodes 21.

[0055] During the packaging process, bubbles formed by entrained air exist inside the packaging glue due to turbulence, stirring, and other reasons. On the one hand, bubbles tend to adhere to the solid surface. When the bubbles adhere to the surface of the umbrella part 4, the puncture structure can destroy the surface tension of the bubbles, causing the bubbles to become unstable and shatter. The packaging glue that is mutually infiltrated with the punctures quickly fills the position where the bubbles were originally attached and in contact, and the bubbles are discharged. The impact of bubbles that are smaller than the distance between adjacent punctures on the packaging structure can be ignored. Moreover, according to the Gibbs-Thomson formula, bubbles of this size tend to have a smaller radius and will self-annihilate during standing. On the other hand, the backplane 3 can be heated, and the heat is reversely conducted to the side of the substrate 1 close to the chip 2 through the umbrella part 4, so that the temperature of the packaging glue between the substrate 1 and the chip 2 rises. Correspondingly, the viscosity decreases, the fluidity increases, and the discharge of bubbles is further accelerated.

[0056] During use, because the umbrella portion 4 passes through the substrate 1 and the umbrella column 41 connects the chip 2 and the back plate 3, the heat generated by the chip 2 can be more efficiently conducted to the back plate 3. Compared with the common flat-plate heat dissipation structure, the heat dissipation effect of this embodiment is better.

[0057] Example 2

[0058] refer to Figure 3 、 Figure 4 The difference between this embodiment and embodiment 1 is that:

[0059] The umbrella cover 42 and the umbrella column 41 are of split design, and the umbrella cover 42 is made of metal with good thermal conductivity, with an insulating layer plated on its outer surface and thermal paste coated in the column hole.

[0060] The shape of the umbrella cap 42 is no longer limited to a hemispherical shell, and can be a circular cake, a truncated cone, a hemisphere, etc. However, the contact surface between the umbrella cap 42 and the substrate 1 is still a closed figure, and the contact surface is between the electrodes 21 of the corresponding chip 2 to limit the contact between the molten solder 22.

[0061] A flange is provided on the umbrella column 41, and correspondingly, a groove matching the flange is provided in the through-column hole of the umbrella cover 42. The flange has an interference fit with the hole opening of the through-column hole and a transition fit with the groove.

[0062] A boss pierced by a through-hole is provided on one side of the umbrella cover 42 close to the back plate 3, and the outer diameter of the boss is smaller than the through hole 11 of the base plate 1. Preferably, the outer diameter of the boss gradually increases in a direction away from the back plate 3 to guide assembly.

[0063] The implementation principle of Example 2 is:

[0064] In Example 1, the configuration of the umbrella portion 4 is as follows: "When the back plate 3 and the substrate 1 are brought into close proximity, the umbrella portion 4 passes through the through hole 11, the umbrella cap 42 is first compressed, and then expanded on the other side of the substrate 1, separating the electrodes 21 of the corresponding chip 2. One end of the umbrella column 41 is fixed to the back plate 3, and the other end abuts the chip 2."

[0065] In this embodiment, the umbrella portion 4 is a split design, with the umbrella column 41 fixedly connected to the back panel 3. When the back panel 3 is in contact with the substrate 1, the umbrella column 41 passes through the through hole 11 of the substrate 1; the umbrella cover 42 is assembled from the side of the substrate 1 away from the back panel 3, and is sleeved on the umbrella column 41 through the through-column hole and abuts against the substrate 1.

[0066] Because the umbrella column 41 is provided with a flange that is interference-fitted with the opening of the through-column hole, when the umbrella column 41 is inserted into the through-column hole and assembled in place, the flange is clamped in the groove to form a stable connection.

[0067] For easy assembly, the umbrella cover 42 can also be preheated, and the expanded through-holes will be loosely matched with the umbrella posts 41 . After being assembled and cooled, the through-holes will shrink to prevent the umbrella posts 41 from falling out.

[0068] In another embodiment of the present application, the flange of the umbrella column 41 and the groove of the umbrella cover 42 are also interference fit, but the diameter of the groove is slightly larger than the diameter of other parts of the through-column hole. Similarly, after preheating and cooling after assembly, the groove covers the flange, and the umbrella cover 42 and the umbrella column 41 are locked with each other.

[0069] The design of the boss facilitates the positioning of the umbrella cap 42 and the base plate 1. Depending on the specific assembly conditions, the base plate 1 and the back plate 3 can be first attached, the umbrella posts 41 can be passed through the through holes 11, and then the umbrella cap 42 can be fixed. Alternatively, all the umbrella caps 42 can be placed on the surface of the base plate 1 before the back plate 3 is assembled. In the latter case, the chip 2 can also be fixed to the base plate 1 before the back plate 3 and the umbrella posts 41 are assembled.

[0070] refer to Figure 5Since there is no need to consider the deformation of the umbrella cover 42 during the process of passing through the through hole 11, the range of choices for the material and structure of the umbrella cover 42 is wider. Optionally, the umbrella cover 42 can be designed as a flat cylinder with two bottom surfaces respectively contacting the chip 2 and the substrate 1, and made of a metal material with good thermal conductivity, which can provide a larger heat conduction area and better heat conduction effect.

[0071] The above are all preferred embodiments of the present application, and are not intended to limit the scope of protection of the present application. Therefore, any equivalent changes made based on the structure, shape, and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A flip-chip COB packaging structure, comprising a substrate (1), a chip (2), and a packaging layer (5), characterized in that: It also includes a back plate (3) and an umbrella portion (4); The chips (2) are arrayed on one side surface of the substrate (1), and each chip (2) has at least two electrodes (21) electrically connected to the substrate (1) via solder (22); The substrate (1) is provided with a plurality of through holes (11), the through holes (11) corresponding to the chips (2) one by one, and each through hole (11) is arranged between the electrodes (21) of the corresponding chip (2); The back plate (3) is arranged on a side of the substrate (1) facing away from the chip (2), and the umbrella portion (4) is fixedly connected to a side of the back plate (3) close to the substrate (1) and corresponds one-to-one with the through hole (11); The umbrella portion (4) includes an umbrella column (41) and an umbrella cover (42), one end of the umbrella column (41) is fixed to the back plate (3), and the other end is connected to the umbrella cover (42), the umbrella column (41) is configured to pass through the through hole (11), the umbrella cover (42) is located between the chip (2) and the substrate (1) and abuts against the substrate (1), the size of the umbrella cover (42) on the side close to the back plate (3) is larger than the through hole (11) and smaller than the spacing between the corresponding electrodes (21), and the surface of the umbrella cover (42) is insulated; the thermal conductivity of the material selected for the back plate (3) and the umbrella column (41) is greater than or equal to 400 W / (m·K), the umbrella cover (42) is provided with dense needle punctures on the side close to the chip (2), and the spacing between adjacent needle punctures is less than 10 μm; The packaging layer (5) covers the entire side of the substrate (1) close to the chip (2) and encapsulates all the chips (2).

2. The flip-chip COB packaging structure according to claim 1, wherein: The umbrella column (41) and the umbrella cover (42) are designed as an integral unit, and the umbrella cover (42) is made of elastic insulating material.

3. The flip-chip COB packaging structure according to claim 2, wherein: The umbrella cover (42) is provided with a through-column hole along its axis, the through-column hole passes through the umbrella cover (42), and the umbrella column (41) passes through the through-column hole and abuts against the chip (2).

4. The flip-chip COB packaging structure according to claim 1, wherein: The umbrella cover (42) and the umbrella column (41) are of split design. A column through hole is provided on one side of the umbrella cover (42) close to the umbrella column (41). The umbrella column (41) passes through the through hole (11) and then enters the column through hole.

5. The flip-chip COB packaging structure according to claim 4, wherein: The umbrella column (41) is provided with a flange, and correspondingly, the through-column hole is provided with a groove that matches the flange, and the flange and the hole of the through-column hole are interference fit.

6. The flip-chip COB packaging structure according to claim 4, wherein: The umbrella cover (42) is provided with a boss on one side close to the back plate (3), the outer diameter of the boss is smaller than the diameter of the through hole (11), the through-column hole passes through the boss, and the boss is configured to be inserted between the through hole (11) and the umbrella column (41).

7. The flip-chip COB packaging structure according to claim 4, wherein: The umbrella cover (42) is made of red copper, its surface is coated with insulating paint, and the column holes are coated with thermal conductive paste.

8. The flip-chip COB packaging structure according to claim 1, wherein: The wetting angle between the needle-punched surface and the flux (22) is greater than 90°, and the wetting angle between the needle-punched surface and the material of the packaging layer (5) is less than 60°.

Images