Device and method for directly printing high coplanarity tin alloy bump array for electronic packaging

Abstract

The invention discloses a device and method for directly printing a high coplanarity tin alloy convex dot array for electronic packaging, belonging to the field of preparing tin alloy convex dot array for electronic packaging; the device comprises a uniform tin alloy micro-droplet injection device, a micro-domain heating component, a height detection device and a convex dot array forming platform; the uniform tin alloy micro-droplet injection device injects tin alloy micro-droplets onto a substrate through a nozzle to form convex dots; the height detection device is arranged on the outer side of the substrate, and is used to detect the height of the convex dots and send a control signal to the micro-domain heating component; the micro-domain heating component is installed on the nozzle of the uniform tin alloy micro-droplet injection device, and comprises a height fine-tuning device and a micro-domain heating device, and the distance between the micro-domain heating device and the substrate is adjusted by the height fine-tuning device; the top of the convex dots is locally heated and melted by the micro-domain heating device, and its initial oscillation height is adjusted to effectively reduce the convex dot height error, thereby achieving the purpose of printing and forming a high coplanarity tin alloy convex dot array on a normal temperature substrate in one step.

Description

Technical Field

[0001] The invention belongs to the field of preparation of tin alloy convex dot arrays for electronic packaging, and in particular relates to a device and method for directly printing a tin alloy convex dot array with high coplanarity for electronic packaging. Background Art

[0002] As electronic products develop towards miniaturization, multi-function, high density and large scale, more and more components are beginning to adopt ball grid array (BGA) packaging, that is, by setting tiny and uniform solder balls on the surface of the chip as the I / O end of the circuit to interconnect with the printed circuit board (PCB). Compared with traditional pin type packaging, BGA packaging has higher pin density, shorter pin length, smaller signal transmission delay and higher reliability, and has gradually become a widely used packaging method.

[0003] Directly printing a high coplanarity tin alloy bump array on a room temperature substrate is a challenge currently faced by BGA packaging technology. The coplanarity of the bump array in the BGA package determines the packaging quality. If the bump height error in the bump array is too large, defects such as solder joint leakage and cold solder joints are prone to occur during chip mounting. And as chip packaging density continues to increase and packaging size continues to decrease, BGA packaging has higher and higher requirements for the high consistency of the bump array.

[0004] There are two main processes for large-scale preparation of bump arrays. One is the mask-based screen printing process, which relies on a mask to scrape a certain amount of solder paste into the pad, and then forms a bump array through reflow heating. Since the amount of solder paste on a single pad is difficult to accurately control, the mask-based screen printing process is difficult to prepare a tin alloy bump array with high coplanarity.

[0005] The other is to use uniform metal droplet jetting technology to directly print the bump array. This technology forms uniform tin alloy droplets with a certain speed by applying external force to the molten tin alloy. The tin alloy droplets collide with the deposition substrate at a certain speed and then solidify layer by layer during the oscillation process. Due to differences in the surface roughness and material properties of the substrate, the solidification time of tin droplets at different positions is different, so it is impossible to ensure that the bumps solidify at the same oscillation height. Therefore, the bump array directly printed using uniform metal droplet jetting technology has a large height difference.

[0006] After the bump array is prepared, the uniform metal droplet injection technology usually restores the bumps to a spherical shape through reflow or laser heating to improve coplanarity. Reflow requires heating the entire chip or the entire deposition area, which will cause thermal damage to the chip. Laser heating, a micro-domain heating method, can reduce thermal damage to the substrate, but laser heating has the disadvantage of defocusing and burning the substrate (chip or circuit board).

[0007] At present, the existing technology is to print bumps on a heated substrate (above about 100°C), prolong the solidification time of the bumps, and solidify them after the bump oscillation stops. This method can effectively reduce the height difference of the bumps. This method can print a tin alloy bump array with a high coplanarity in one step, but it requires the substrate to be kept above 100°C for a long time, which will cause thermal damage to the chip. Therefore, most BGA package bump arrays are difficult to be directly prepared using uniform metal droplet injection technology.

[0008] In summary, the current devices used for preparing tin alloy bump arrays are difficult to achieve direct printing of high coplanarity tin alloy bump arrays on room temperature substrates. Therefore, it is urgent to develop a high coplanarity tin alloy bump array direct printing device for electronic packaging. Summary of the invention

[0009] Technical issues to be solved:

[0010] In order to avoid the shortcomings of the prior art, the present invention provides a device and method for directly printing a high coplanarity tin alloy bump array for electronic packaging, the device comprising a uniform tin alloy droplet ejection device, a micro-domain heating device, a height detection device and a bump array forming platform. The micro-domain heating device is connected to the uniform tin alloy droplet ejection device through a fixed sleeve. After the uniform tin alloy droplet ejection device ejects tin alloy droplets onto the substrate, the droplets begin to oscillate, and when the droplet oscillation height enters the detection range of the height detection device, the micro-domain heating device starts to work. The working height of the micro-domain heating device is adjusted by the increment generated in the vertical direction by the thermal expansion of the fixed sleeve. By slightly adjusting the working height of the micro-domain heating device, the micro-domain at the top of the oscillating droplet is subjected to radiation and convection heating, the top solidification time is extended, and the top is ensured to solidify after stopping oscillation, so as to effectively reduce the bump height error, thereby achieving the purpose of printing and forming a high coplanarity tin alloy bump array on a room temperature substrate in one step.

[0011] The technical scheme of the present invention is: a high coplanarity tin alloy bump array direct printing device for electronic packaging, comprising a uniform tin alloy droplet ejection device, a micro-domain heating component, a height detection device and a bump array forming platform; the uniform tin alloy droplet ejection device ejects tin alloy droplets onto a substrate of the bump array forming platform through a nozzle to form bumps; the height detection device is arranged on the outside of the substrate, and is used to detect the height of the bumps and send a start / stop signal to the micro-domain heating component;

[0012] The micro-domain heating component is installed on the nozzle of the uniform tin alloy droplet injection device, and includes a height fine-tuning device and a micro-domain heating device. The height fine-tuning device is used to adjust the distance between the micro-domain heating device and the substrate; the micro-domain heating device is used to locally heat and melt the top of the bump, adjust its initial oscillation height, and realize the height control of the bump solidified after oscillation.

[0013] A further technical solution of the present invention is: the height fine-tuning device includes a heat-resistant layer, a fixed sleeve, and a heating sleeve, and the fixed sleeve is coaxially sleeved on the outer periphery of the nozzle; the heat-resistant layer is arranged between the inner circumference of the fixed sleeve and the outer circumference of the nozzle, and is used to block the temperature influence of the nozzle on the fixed sleeve; the heating sleeve is sleeved on the periphery of the fixed sleeve, so that the fixed sleeve produces a controllable micron-level increment in the vertical direction after heat expansion, thereby adjusting the distance between the micro-domain heating device and the substrate.

[0014] A further technical solution of the present invention is: it also includes a heat insulation layer, which is sleeved on the periphery of the heating sleeve to block the influence of its heat on the substrate.

[0015] A further technical solution of the present invention is: it also includes a temperature controller, the heating sleeve is connected to an external temperature controller, and the temperature of the heating sleeve is controlled by the temperature controller.

[0016] A further technical solution of the present invention is: the micro-domain heating device is a sleeve structure, which is installed on the lower end of the fixed shaft sleeve through the internal thread of the upper end, and its lower end is opposite to the top of the bump, and the top of the bump is evenly heated to ensure the uniformity of the structure of the tin alloy bump.

[0017] A further technical solution of the present invention is: the height detection device comprises a laser, a right angle bracket, a lifting platform, and a photoelectric sensor; the laser and the photoelectric sensor are located on both sides of the substrate and are respectively installed on the lifting platform through the right angle bracket, and the center of the laser and the center of the photoelectric sensor are ensured to be at the same horizontal height;

[0018] By adjusting the lifting platform, the distance between the laser beam emitted by the laser and the substrate is controlled.

[0019] A further technical solution of the present invention is: the convex dot array forming platform includes a moving platform and a substrate, the substrate is installed on the moving platform through the substrate, and serves as a printing substrate for tin alloy droplets. The moving platform can move along the XYZ axis.

[0020] A further technical solution of the present invention is: the uniform tin alloy droplet injection device includes a cooling circulating water device, a piezoelectric ceramic, a crucible, an exciting rod, a heating furnace, a nozzle, a heat insulation plate, and a piezoelectric ceramic driver. The piezoelectric ceramic is arranged above the crucible and controlled by the piezoelectric ceramic driver; the top of the exciting rod is connected to the piezoelectric ceramic, and the bottom extends into the crucible; the heating furnace is arranged at the periphery of the crucible for controlling the temperature of the crucible; the nozzle is installed at the outlet of the bottom of the crucible for injecting tin alloy droplets; the heat insulation plate is arranged at the bottom of the crucible for blocking the influence of the heat in the crucible on the temperature of the substrate; the cooling circulating water device is connected to the piezoelectric ceramic for cooling the piezoelectric ceramic.

[0021] A method for directly printing a high coplanarity tin alloy bump array for electronic packaging, the specific steps are as follows:

[0022] Step 1: Adjust the lifting platform so that the distance H1 between the laser beam emitted by the laser and the substrate meets the condition: h

[0023] Step 2: In an environment where the oxygen content is less than 100 ppm, a uniform tin alloy droplet ejection device is started to eject tin alloy droplets from the nozzle onto the substrate;

[0024] Step 3: The droplet oscillates. When the droplet oscillation height is greater than H1, the height fine-tuning device and the micro-domain heating device receive the signal from the photoelectric sensor and start working: first, the temperature controller controls the heating sleeve to heat the fixed sleeve, and the increment generated by the fixed sleeve being heated in the vertical direction is used to adjust the distance between the micro-domain heating device and the substrate to H; then, the top of the bump is heated and melted by the micro-domain heating device; when the bump oscillation height is less than H1 within the set time, the micro-domain heating device stops working after receiving the signal from the photoelectric sensor, and the bump printing is completed.

[0025] A further technical solution of the present invention is: in step 3, after the fixed sleeve is heated, a thermal expansion increment ΔL=L·α·(t2-t1) is generated in the vertical direction, where L is the axial length of the fixed sleeve, α is the thermal expansion coefficient of the fixed sleeve, t2 is the heating temperature of the fixed sleeve, and t1 is the ambient temperature.

[0026] Beneficial Effects

[0027] The beneficial effect of the present invention is that the present invention provides a coaxial micro-domain heating device with precisely adjustable working height. The micro-domain heating device is coaxially connected to the nozzle through a fixed sleeve, and the fixed sleeve is a material with controllable thermal expansion. When heated by the heating sleeve, it can produce a micron-level controllable increment in the vertical direction, thereby achieving the effect that the working height of the micro-domain heating device can be precisely adjusted.

[0028] Since the thermal gradient of the micro-domain heating device is large when it is working, a narrow temperature zone (25℃-183℃) can be formed at the bottom of the micro-domain heating device. The working height of the micro-domain heating device is finely adjusted so that the bumps are within the temperature zone after deposition, and finally the top of the bumps are locally melted while the substrate is kept at room temperature. This method can effectively solve the problem of thermal damage to the substrate during the preparation of high coplanarity tin alloy bump arrays. Using this coaxial micro-domain heating device with precisely adjustable height, it is possible to directly prepare high coplanarity tin alloy bump arrays (within a standard deviation of 5μm) at room temperature on the substrate. BRIEF DESCRIPTION OF THE DRAWINGS ​

[0029] Figure 1 It is a schematic diagram of the overall device of the present invention;

[0030] Figure 2 It is a schematic diagram of the working principle of the height detection device;

[0031] Explanation of the accompanying drawings: 1-cooling circulating water device, 2-piezoelectric ceramics, 3-crucible, 4-excitation rod, 5-heating furnace, 6-nozzle, 7-heat-resistant layer, 8-heat insulation board, 9-fixed sleeve, 10-heating sleeve, 11-heat insulation layer, 12-micro-domain heating device, 13-laser, 14-right angle frame, 15-lifting platform, 16-photoelectric sensor, 17-piezoelectric ceramic driver, 18-motion platform, 19-substrate, 20-substrate, 21-temperature controller, 22-laser beam, 23-photoelectric sensor output signal, 24-bump. DETAILED DESCRIPTION

[0032] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0033] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0034] Reference Figure 1 As shown, the present embodiment is a high coplanarity tin alloy bump array direct printing device for electronic packaging, which is composed of a uniform tin alloy droplet ejection device, a micro-domain heating component, a height detection device and a bump array forming platform:

[0035] The uniform tin alloy droplet ejection device comprises a cooling circulating water device 1, a piezoelectric ceramic 2, a crucible 3, an excitation rod 4, a heating furnace 5, a nozzle 6, a heat insulation board 8, and a piezoelectric ceramic driver 17. The piezoelectric ceramic 2 is arranged above the crucible 3 and is controlled by the piezoelectric ceramic driver 17; the top of the excitation rod 4 is connected to the piezoelectric ceramic 2, and the bottom extends into the crucible 3; the heating furnace 5 is arranged at the periphery of the crucible 3 to control the temperature of the crucible 3; the nozzle 6 is installed at the outlet of the bottom of the crucible 3 to eject tin alloy droplets; the heat insulation board 8 is arranged at the bottom of the crucible 3 to block the influence of the heat in the crucible on the temperature of the substrate 20; the cooling circulating water device 1 is connected to the piezoelectric ceramic 2 to cool the piezoelectric ceramic 2. The piezoelectric ceramic 2 and the excitation rod 4 are connected by threads, and the piezoelectric ceramic 2 generates vibration to drive the excitation rod 4. The micro-vibration of the excitation rod 4 is transmitted to the nozzle 6, and the molten tin alloy liquid is forced to deform to generate tin alloy droplets.

[0036] The micro-domain heating part includes a micro-domain heating device 12 and a height fine-tuning device. The height fine-tuning device is composed of a heat-resistant layer 7, a fixed sleeve 9, a heating sleeve 10, a heat-insulating layer 11, and a temperature controller 21. The heat-resistant layer 7 is attached to the inner wall of the fixed sleeve 9 to prevent the heat from the nozzle 6 from being transferred to the fixed sleeve 9, so that the temperature of the fixed sleeve 9 is completely controlled by the heating sleeve 10, thereby realizing the controllable thermal expansion of the fixed sleeve 9. The fixed sleeve 9 is sleeved on the outside of the nozzle 6, and the micro-domain heating device 12 is connected to the lower end of the fixed sleeve 9 through a threaded connection. The micro-domain heating device 12 is coaxial with the nozzle 6 through the fixed sleeve 9, and then the micro-domain heating device 12 is coaxial with the tin alloy bump, and finally the uniform heating of the top of the tin alloy bump is achieved to ensure the uniformity of the structure of the tin alloy bump. The heating sleeve 10 is sleeved onto the outer surface of the upper end of the fixed sleeve 9. The temperature of the heating sleeve 10 is controlled by the temperature controller 21, so that the fixed sleeve 9 expands due to heat and produces a controllable micron-level increment in the vertical direction, thereby adjusting the distance between the micro-domain heating device 12 and the substrate 20. By utilizing the temperature difference generated by the micro-domain heating device in a narrow space band, high-temperature heating of the top of the bump is achieved, while the chip substrate remains at room temperature.

[0037] The fixed sleeve 9 is characterized in that after being heated, a thermal expansion increment ΔL=L·α·(t2-t1) is generated in the vertical direction, where L is the length of the fixed sleeve 9, α is the thermal expansion coefficient of the fixed sleeve 9, t2 is the heating temperature of the fixed sleeve, and t1 is the ambient temperature.

[0038] The height detection part includes a laser 13, a right angle bracket 14, a lifting platform 15, and a photoelectric sensor 16. The laser 13 and the photoelectric sensor 16 are respectively located on both sides of the substrate 20, and the two end surfaces are parallel to the two side surfaces of the substrate 20. The center of the laser 13 and the center of the photoelectric sensor 16 are at the same horizontal height. The laser 13 and the photoelectric sensor 16 are fixed to the lifting platform 15 by using the right angle bracket 14, and the distance H1 between the laser beam 22 and the substrate 20 is controlled by adjusting the lifting platform 15.

[0039] The laser 13 is characterized in that the height H1 between the laser beam 17 emitted by the laser 13 and the substrate 20 should satisfy the following relationship:

[0040] The bump array forming part includes a moving platform 18 and a substrate 19; the substrate 19 is made of a heat-insulating material.

[0041] The high coplanarity tin alloy bump array direct printing device for electronic packaging is placed in a low oxygen environment (oxygen content is below 100 ppm).

[0042] Embodiment: High coplanarity bump array device for K4T1G164QG-BCF7 flash memory chip packaging;

[0043] First, according to the K4T1G164QG-BCF7 packaging requirements, the lifting platform 15 is adjusted so that the distance H1 between the laser beam 22 and the substrate 20 is 0.4 mm.

[0044] Then, the required nozzle 6 is selected according to the size of the bump, cleaned and installed on the crucible 3; the tin alloy is filled into the crucible 3, and the heating furnace 5 is mounted on the crucible 3; the cooling circulating water 1 is started, and the crucible 3 is heated to 280°C through the heating furnace 5 to melt the solid tin alloy inside into liquid, and keep warm for 15 minutes; the piezoelectric ceramic drive pulse parameters are adjusted, and the piezoelectric ceramic driver 17 is started, so that the piezoelectric ceramic 2 drives the excitation rod 4 to vibrate to generate stress waves, and tin alloy droplets with a size of 350μm are ejected.

[0045] Finally, after the tin alloy droplets are sprayed onto the substrate 20, the droplets will oscillate. When the droplet oscillation height is greater than H1, the micro-domain heating device 12 starts to work after receiving the signal from the photoelectric sensor 16; the heating sleeve 10 is controlled by the temperature controller 21 to heat the fixed sleeve 9, and the distance between the micro-domain heating device 12 and the substrate 20 is adjusted to H = 1.321mm by utilizing the increment generated by the heating of the fixed sleeve 9 in the vertical direction. At this time, the temperature of the top of the bump is 224.1°C, the top of the tin alloy bump is fully heated, and the temperature of the bottom substrate is only 26.7°C, and no thermal damage will occur.

[0046] ​When the oscillation height is less than H1 within the set time, the micro-domain heating device 12 stops working after receiving the signal sent by the photoelectric sensor 16, and the convex point printing is completed.

[0047] The motion trajectory of the motion platform 18 is planned according to the bump array morphology of the K4T1G164QG-BCF7 flash memory chip, and finally the printing of the entire bump array is completed.

[0048] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A device for directly printing a high coplanarity tin alloy bump array for electronic packaging, characterized in that: The invention comprises a uniform tin alloy droplet ejection device, a micro-domain heating component, a height detection device and a bump array forming platform; the uniform tin alloy droplet ejection device ejects tin alloy droplets onto a substrate of the bump array forming platform through a nozzle to form bumps; the height detection device is arranged on the outer side of the substrate, and is used to detect the height of the bumps and send a start / stop signal to the micro-domain heating component; The micro-domain heating assembly is installed on the nozzle of the uniform tin alloy micro-droplet injection device, and includes a height fine-tuning device and a micro-domain heating device. The distance between the micro-domain heating device and the substrate is adjusted by the height fine-tuning device; the top of the convex point is locally heated and melted by the micro-domain heating device, and its initial oscillation height is adjusted to achieve the height control of the convex point solidified after oscillation; the micro-domain heating device is a sleeve structure, which is installed on the lower end of the fixed shaft sleeve through the internal thread at the upper end, and its lower end is opposite to the top of the convex point, and the top of the convex point is uniformly heated to ensure the uniformity of the structure of the tin alloy convex point; The height fine-tuning device includes a heat-resistant layer, a fixed sleeve, and a heating sleeve. The fixed sleeve is coaxially sleeved on the outer periphery of the nozzle; the heat-resistant layer is arranged between the inner peripheral surface of the fixed sleeve and the outer peripheral surface of the nozzle to block the temperature influence of the nozzle on the fixed sleeve; the heating sleeve is sleeved on the periphery of the fixed sleeve so that the fixed sleeve will produce a controllable micron-level increment in the vertical direction after thermal expansion, thereby adjusting the distance between the micro-domain heating device and the substrate.

2. According to claim 1, a high coplanarity tin alloy bump array direct printing device for electronic packaging, characterized in that: It also includes a heat insulation layer, which is sleeved on the periphery of the heating sleeve to block the influence of its heat on the substrate.

3. The device for directly printing a high coplanarity tin alloy bump array for electronic packaging according to claim 1, characterized in that: It also includes a temperature controller, and the heating sleeve is connected to an external temperature controller, and the temperature of the heating sleeve is controlled by the temperature controller.

4. The device for directly printing a high coplanarity tin alloy bump array for electronic packaging according to claim 1, characterized in that: The height detection device includes a laser, a right-angle bracket, a lifting platform, and a photoelectric sensor; the laser and the photoelectric sensor are located on both sides of the substrate and are respectively installed on the lifting platform through the right-angle bracket, and the center of the laser and the center of the photoelectric sensor are ensured to be at the same horizontal height; By adjusting the lifting platform, the distance between the laser beam emitted by the laser and the substrate is controlled.

5. The device for directly printing a high coplanarity tin alloy bump array for electronic packaging according to claim 1, characterized in that: The convex dot array forming platform comprises a moving platform and a base body, a substrate is mounted on the moving platform through the base body, and serves as a printing substrate for tin alloy droplets. The moving platform can move along the XYZ axis.

6. A high coplanarity tin alloy bump array direct printing device for electronic packaging according to any one of claims 1 to 5, characterized in that: The uniform tin alloy droplet injection device includes a cooling circulating water device, piezoelectric ceramics, a crucible, an exciting rod, a heating furnace, a nozzle, a heat insulation plate, and a piezoelectric ceramic driver. The piezoelectric ceramics are arranged above the crucible and controlled by the piezoelectric ceramic driver; the top of the exciting rod is connected to the piezoelectric ceramics, and the bottom extends into the crucible; the heating furnace is arranged at the periphery of the crucible for controlling the temperature of the crucible; the nozzle is installed at the outlet of the bottom of the crucible for injecting tin alloy droplets; the heat insulation plate is arranged at the bottom of the crucible for blocking the influence of the heat in the crucible on the temperature of the substrate; the cooling circulating water device is connected to the piezoelectric ceramics and is used for cooling the piezoelectric ceramics.

7. A method for directly printing a high coplanarity tin alloy bump array for electronic packaging, which is implemented based on the device for directly printing a high coplanarity tin alloy bump array for electronic packaging as claimed in claim 1; characterized in that The specific steps are as follows: Step 1: Adjust the lifting platform so that the distance between the laser beam emitted by the laser and the substrate H 1. Satisfy the conditions: h < H 1 < h + h / 2, where h is the bump height, h is the height error allowed by the bump array; Step 2: In an environment where the oxygen content is less than 100 ppm, a uniform tin alloy droplet ejection device is started to eject tin alloy droplets from the nozzle onto the substrate; Step 3: The droplet oscillates. When the droplet oscillation height is greater than H 1, the height fine-tuning device and the micro-domain heating device receive the signal from the photoelectric sensor and start working: first, the temperature controller controls the heating sleeve to heat the fixed sleeve, and the increment generated by the fixed sleeve in the vertical direction is used to adjust the distance between the micro-domain heating device and the substrate to H; then, the micro-domain heating device heats and melts the top of the bump; when the bump oscillation height is less than 1 within the set time, the micro-domain heating device is used to heat the top of the bump; H At 1, the micro-domain heating device stops working after receiving the signal sent by the photoelectric sensor, and the convex point printing is completed.

8. A method for directly printing a high coplanarity tin alloy bump array for electronic packaging according to claim 7, characterized in that: In step 3, the fixed sleeve generates a thermal expansion increment in the vertical direction after being heated. ,in is the axial length of the fixed sleeve, is the thermal expansion coefficient of the fixed sleeve, To fix the sleeve heating temperature, is the ambient temperature.

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