A local vacuum hot press mechanism for non-flow underfill

Abstract

This invention relates to a processing technology for the underfilling process of flip chips, and more specifically, to a localized vacuum thermopressing mechanism for non-flowing underfilling. The mechanism includes a thermopressing assembly and a vacuum sealing assembly. The vacuum sealing assembly is vertically and flexibly positioned above the thermopressing assembly. The vacuum sealing assembly includes a vacuum sealing cover and a sealing rubber ring, which is positioned between the vacuum sealing cover and the thermopressing assembly. The thermopressing assembly includes a thermopressing base plate, on which a heat insulation plate, a ceramic heating element, a heat spreader plate, and a heating panel are stacked sequentially. The upper surface of the ceramic heating element is flush with the upper surface of the heat insulation plate. The heat spreader plate maintains its positional stability through gravity and the pressure of the upper heating panel. The ceramic heating element heats according to a preset temperature curve. This invention solves the problem of filling voids or chip damage caused by uneven temperature and pressure distribution, and also addresses the system dynamic stability issues caused by material flow and bump deformation during bonding.

Description

Technical Field

[0001] This invention relates to the processing technology of flip chip underfill process, and more specifically to a local vacuum thermo-pressing mechanism for non-flowing underfill. Background Technology

[0002] In semiconductor chip packaging processes, non-flow underfill (NCF) technology has been widely used in flip-chip interconnect packaging due to its excellent packaging reliability. This technology fills and protects the bump gaps by pre-attaching a non-conductive NCF film between the chip and the substrate, followed by thermosetting and curing. This effectively improves the chip's impact resistance and resistance to damp heat, and is one of the core technologies in the current high-end chip packaging field.

[0003] Existing vacuum hot pressing equipment still has many shortcomings in practical applications: Traditional hot pressing mechanisms mostly adopt an overall vacuum chamber design, which takes a long time to establish a vacuum environment, and the temperature and pressure distribution inside the chamber is easily affected by airflow, resulting in poor uniformity of NCF film bonding and difficulty in ensuring complete filling of the bump gaps; NCF film feeding mostly relies on manual assistance or simple conveying devices, and NCF blocks of specific specifications are prone to positional shifts and warping during the conveying process, and the carrier film peeling operation and the feeding process are not well connected, affecting production efficiency; the alignment of the chip and NCF film relies on a single vision system, which has insufficient alignment accuracy, and combined with the movement error of the motion table, it is easy to cause deviations in edge alignment after bonding; the coordinated control accuracy of temperature and pressure during hot pressing is insufficient, the sealing performance of sealing components is unstable, and the local vacuum degree cannot meet the process requirements, which in turn leads to problems such as incomplete curing of NCF resin and insufficient filling of bump gaps.

[0004] These defects severely impact the reliability and yield of chip packaging. Furthermore, existing mechanisms lack optimized design for the linkage between NCF film base film connection, carrier film peeling, and thermopressing processes, resulting in cumbersome process connections and an inability to adaptively adjust thermopressing parameters based on chip bump distribution characteristics, making it difficult to adapt to the packaging requirements of different chip sizes. Therefore, there is an urgent need to design a local vacuum thermopressing mechanism that integrates high-precision feeding, accurate alignment, stable sealing, and coordinated temperature and pressure control to address the aforementioned technical challenges. Summary of the Invention

[0005] The purpose of this invention is to provide a local vacuum hot pressing mechanism for non-flowing bottom filling, which solves the problem of filling voids or chip damage caused by uneven temperature and pressure distribution, and can also solve the problem of system dynamic stability caused by material flow and bump deformation during bonding.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A local vacuum hot pressing mechanism for non-flowing bottom filling includes a hot pressing assembly and a vacuum sealing assembly. The vacuum sealing assembly is vertically and flexibly disposed above the hot pressing assembly. The vacuum sealing assembly includes a vacuum sealing cover and a sealing rubber ring, which is disposed between the vacuum sealing cover and the hot pressing assembly.

[0008] The hot pressing assembly includes a hot pressing base plate, on which an insulation plate, a ceramic heating element, a heat spreader plate, and a heating panel are stacked in sequence. The upper surface of the ceramic heating element is flush with the upper surface of the insulation plate.

[0009] A K-type thermocouple is installed at the center of the side of the heat spreader. The heat spreader maintains a stable position by gravity and the pressure of the heating panel above. The ceramic heating element heats the material according to a preset temperature curve. The upper surface of the heating panel is used to place the chip to be bonded and the NCF film.

[0010] When the vacuum sealing cover descends, the sealing rubber ring snaps onto the hot-pressed base plate to form a sealed cavity.

[0011] The vacuum sealing cover is raised and lowered by a Z-axis lifting platform. A pressure sensor is installed between the Z-axis lifting platform and the vacuum sealing cover. The pressure sensor is fixedly connected to the Z-axis lifting platform, and the lower end of the pressure sensor is fixedly connected to the vacuum sealing cover through a flat pressure head. The Z-axis lifting platform, the pressure sensor and the vacuum sealing cover form a rigid series structure. The pressure sensor is used to measure the actual downward pressure on the chip during the hot pressing process in real time.

[0012] The vacuum sealing cover is connected to a vacuum generating unit, which includes a vacuum pump, a vacuum pipeline and a vacuum solenoid valve. One end of the vacuum pipeline is connected to the vacuum pump and the other end is connected to the air extraction port of the vacuum sealing cover.

[0013] It also includes a fixed base plate, a Z-axis lifting platform mounted on the fixed base plate, an X-axis linear displacement slide mounted on the fixed base plate, and a hot-pressed base plate mounted on the X-axis moving end of the X-axis linear displacement slide.

[0014] An NCF film feeding module is installed on the fixed base plate. The NCF film feeding module is equipped with NCF film rolls. The NCF film feeding module conveys the pre-cut NCF film and places it flat on the upper surface of the heating panel.

[0015] It also includes a control system, which consists of a PID temperature controller, a solid-state relay, and a data acquisition module.

[0016] The PID temperature controller receives the temperature signal from the K-type thermocouple and controls the on / off state of the ceramic heating element through a solid-state relay to achieve closed-loop temperature control with a temperature control accuracy of ±0.1℃. The data acquisition module receives the signal from the pressure sensor and records the pressure changes during the hot pressing process in real time with a pressure control accuracy of ±0.1N.

[0017] The beneficial effects of this invention are as follows:

[0018] By employing an integrated hot-press bonding process, only one heating treatment is required during the encapsulation of the single-layer chip and NCF film, reducing the performance degradation of NCF materials and chip bump damage caused by repeated high temperatures. By directly connecting a pressure sensor in series between the lifting platform and the vacuum sealing cover, direct and accurate measurement of the downward pressure exerted on the chip during hot pressing is achieved, providing an accurate data foundation for pressure closed-loop control. Compared to traditional hot-press devices, this invention features a simpler structure, a shorter pressure measurement path, and smaller errors, effectively improving the accuracy and response speed of pressure control. This suppresses filling voids caused by uneven temperature and pressure distribution, significantly improving product yield and packaging reliability. Attached Figure Description

[0019] The present invention will now be described in further detail with reference to the accompanying drawings and specific implementation methods.

[0020] Figure 1 This is a schematic diagram of the hot-pressed base plate structure of the present invention;

[0021] Figure 2 This is a schematic diagram of the local vacuum hot pressing mechanism for non-flowing bottom filling according to the present invention;

[0022] Figure 3 This is a side view of the local vacuum hot pressing mechanism for non-flowing bottom filling according to the present invention;

[0023] Figure 4 This is a schematic diagram of the working process of the local vacuum hot pressing mechanism for non-flowing bottom filling according to the present invention.

[0024] In the figure: 1. Hot pressing base plate; 2. Insulation plate; 3. Ceramic heating element; 4. Heat spreader plate; 5. Heating panel; 6. Vacuum sealing cover; 7. Sealing rubber ring; 8. Pressure sensor; 9. Z-axis lifting platform; 10. Fixed base plate; 11. NCF film feeding module; 12. NCF film roll; 13. X-axis linear displacement slide. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings.

[0026] like Figures 1 to 4 As shown below, the structure and function of a local vacuum hot pressing mechanism for non-flowing bottom filling will be described in detail.

[0027] A local vacuum hot pressing mechanism for non-flowing bottom filling includes: a hot pressing assembly, a vacuum sealing assembly, a vacuum generating unit, a Z-axis lifting platform 9, a fixed base plate 10, an NCF film feeding module 11, an X-axis linear displacement slide 13, and a control system.

[0028] The hot pressing assembly includes a hot pressing base plate 1, an insulation plate 2, a ceramic heating element 3, a heat spreader plate 4, and a heating panel 5;

[0029] The hot-press base plate 1 is a rectangular plate structure made of 304 stainless steel, with dimensions of 80mm×80mm×10mm. M4 countersunk holes are provided at the four corners of the hot-press base plate 1 for fixing the base plate to the displacement stage of the X-axis linear displacement slide 13 with M4 screws. A 50mm×50mm×14mm rectangular positioning groove is provided at the center of the upper surface of the hot-press base plate 1 for placing the insulation plate 2, ceramic heating element 3, heat spreader plate 4 and heating panel 5.

[0030] The insulation board 2 is a rectangular plate structure made of FR4 water-green epoxy resin fiberglass board, with dimensions of 50mm×50mm×5mm. The insulation board 2 is placed in the positioning groove in the center of the hot-pressing base plate 1. A rectangular mounting groove of 40mm×40mm×2mm is opened in the center of the upper surface of the insulation board 2 for placing the ceramic heating element 3. The insulation board 2 and the hot-pressing base plate 1 are limited by the positioning groove and do not require additional fixing.

[0031] The ceramic heating element 3 is a rectangular plate structure made of alumina ceramic material, with dimensions of 40mm×40mm×2mm, an operating voltage of 220V, and a heating power of 200W. The ceramic heating element 3 is placed in the rectangular mounting groove of the insulation plate 2, and the upper surface of the ceramic heating element 3 is flush with the upper surface of the insulation plate 2. Two nickel leads of the ceramic heating element 3 are led out from the lead groove opened on the side of the insulation plate 2 and connected to the power control system outside the vacuum sealing cover 6.

[0032] The heat spreader 4 is a rectangular plate structure made of T2 copper material, with dimensions of 50mm×50mm×4mm. The heat spreader 4 is directly stacked on top of the ceramic heating plate 3. A blind hole with a diameter of 2.2mm and a depth of 25mm is opened in the center of the side of the heat spreader 4 for installing a K-type thermocouple. The heat spreader 4 maintains a stable position by gravity and the pressure of the heating panel 5 above it.

[0033] The heating panel 5 is a rectangular plate structure made of 304 stainless steel, with dimensions of 50mm×50mm×3mm. The heating panel 5 is directly stacked on top of the heat spreader 4. The upper surface of the heating panel 5 is used to place the chip to be bonded and the NCF film. The heating panel 5 is held in place by the downward pressure applied by the hot press head above.

[0034] The vacuum sealing assembly includes a vacuum sealing cover 6 and a sealing rubber ring 7. The vacuum sealing cover 6 is an inverted bell-shaped cover structure made of 304 stainless steel. The upper end of the vacuum sealing cover 6 is fixedly connected to the lower end of the pressure sensor 8. A square sealing groove is provided at the lower opening of the vacuum sealing cover 6, and the sealing rubber ring 7 is installed in the sealing groove. The vacuum sealing cover 6 is lowered under the drive of the Z-axis lifting platform 9, and the sealing rubber ring 7 is pressed against the shallow groove on the surface of the hot-pressing base plate 1 to form a sealed vacuum cavity.

[0035] The sealing rubber ring 7 is a square ring made of fluororubber material, with an inner diameter of 59mm, an outer diameter of 61mm, and a thickness of 3.6mm. The sealing rubber ring 7 is installed in the sealing groove at the opening of the vacuum sealing cover 6. When the vacuum sealing cover 6 is pressed down, the sealing rubber ring 7 undergoes a 20% compression deformation to achieve vacuum sealing.

[0036] The vacuum generating unit includes a vacuum pump, a vacuum pipeline, and a vacuum solenoid valve. The vacuum pump is powered by 24V DC, has a power of 10W, and a maximum flow rate of 15L / min. One end of the vacuum pipeline is connected to the vacuum pump, and the other end is connected to the air extraction port of the vacuum sealing cover 6. The vacuum generating unit can raise the vacuum level of the sealed cavity to -80kPa.

[0037] The Z-axis lifting platform 9 has a stroke of 10mm, a repeatability of ±1μm, and a maximum load capacity of 20kg, or approximately 196N. A pressure sensor 8 with a range of 0-500N and an accuracy of 0.1%FS is installed between the pressure head and the hot press table to monitor the pressing force in real time.

[0038] The pressure sensor 8 is a spoke-type pressure sensor. The upper end of the pressure sensor 8 is connected to the middle fixing plate by an M8 screw. The fixing plate is installed below the Z-axis lifting platform 9 by an M6 screw. The lower end of the pressure sensor 8 is fixedly connected to the vacuum sealing cover 6 through a flat pressure head. The three form a rigid series structure. The pressure sensor 8 is used to measure the actual downward pressure on the chip during the hot pressing process in real time. The range is 0-500N, the accuracy is 0.1N, the accuracy class is 0.05%, the sampling frequency is greater than 100Hz, and the pressure signal is fed back to the control system.

[0039] Z-axis lifting platform 9 is mounted on fixed base plate 10. X-axis linear displacement slide 13 is mounted on fixed base plate 10. Hot pressing base plate 1 is mounted on the X-axis moving end of X-axis linear displacement slide 13. NCF film feeding module 11 is mounted on fixed base plate 10. NCF film roll 12 is provided on NCF film feeding module 11.

[0040] The NCF film feeding module 11 consists of a conveyor belt mechanism, which is responsible for both supplying and winding the NCF film roll 12, leaving a lamination station in the middle. The conveyor belt drive wheel is designed with a diameter of 10mm, and the required driving torque T=F×r=1.196×0.005=0.00598N·m≈0.006N·m. It is driven by a 42 series stepper motor, which has a holding torque of about 0.3-0.5N·m, to achieve precise stepping of the NCF film and ensure that the NCF film can enter the lamination area in a stable posture and be in an ideal state before entering the subsequent processes.

[0041] The control system includes a PID temperature controller, a solid-state relay, and a data acquisition module. The PID temperature controller receives the temperature signal from the K-type thermocouple and controls the on / off state of the ceramic heating element through the solid-state relay to achieve closed-loop temperature control with a temperature control accuracy of ±0.1℃. The data acquisition module receives the signal from the pressure sensor and records the pressure changes during the hot pressing process in real time with a pressure control accuracy of ±0.1N.

[0042] The NCF membrane feeding module 11 and the X-axis linear displacement slide 13 are fixed to the fixed base plate 10 of the test bench by M3 and M5 screws, respectively. The hot pressing base plate 1 is fixed to the X-axis moving end of the X-axis linear displacement slide 13 by M4 screws.

[0043] The following is a detailed description of the usage process of a local vacuum hot pressing mechanism for non-flowing bottom filling.

[0044] The NCF film feeding module 11 transports and flattens the pre-cut NCF film onto the upper surface of the heating panel 5, completing the initial positioning of the NCF film through the positioning marks on the edge of the heating panel 5; the vacuum nozzle of the hot press head picks up the single-layer chip, and the vision alignment system completes the precise alignment of the chip and the NCF film; the X-axis linear displacement slide 13 and stepper motor are controlled to move the chip and film quickly to directly below the Z-axis lifting stage 9; the Z-axis lifting stage 9 is controlled to move downward, so that the vacuum sealing cover 6 quickly approaches the NCF film to a distance of 1mm and then stops. The upper surface of the heating panel 5 needs to be precision ground, with a thickness of no more than 0.02mm and a surface roughness Ra of no more than 0.8μm to ensure that the NCF film is placed flat.

[0045] The vacuum sealing cover 6 is activated, and the Z-axis lifting platform 9 continues to move downwards. The vacuum sealing cover 6 contacts the hot-pressing base plate 1 and presses the sealing rubber ring 7 to form a sealed cavity. The vacuum generating unit is activated to raise the vacuum level of the cavity to -80 kPa. The Z-axis lifting platform 9 continues to press down, and the pressure sensor 8 monitors the downward pressure on the chip in real time. The downward movement stops when the downward pressure reaches 2 N. The compression of the sealing rubber ring is controlled within the range of 15%-25%. The sealing ring is made of fluororubber material, which can withstand temperatures up to 200℃, ensuring stable sealing performance during the 130℃ hot pressing process.

[0046] The ceramic heating element 3 is activated, and heating is performed according to the preset temperature curve: the temperature is increased to 80°C at a rate of 20°C / min, and held for 3 minutes to initially soften the NCF film; then the temperature is increased to 120°C at a rate of 15°C / s, and constant pressure is maintained during this stage by the Z-axis lifting stage 9; when the temperature reaches 130°C, the hot pressing pressure is increased to 150N and held for 10 minutes to complete the full filling and pre-curing of the NCF material between the chip bumps; during the hot pressing process, the pressure sensor continuously monitors the pressure, and the control system maintains constant pressure according to the pressure feedback signal; after the hot pressing is completed, the temperature is reduced to 60°C at a rate of 20°C / min, and the Z-axis lifting stage 9 simultaneously reduces the pressure to 1N; when the temperature drops to 50°C, the vacuum pump delivers gas to the cavity, the vacuum sealing cover 6 is lifted to break the vacuum, the X-axis linear displacement slide 13 and the Z-axis lifting stage 9 return to the initial position, and the chip with the NCF film pre-bonded is transferred to the next process. The heating temperature is controlled by PID closed-loop control with a temperature control accuracy of ±1℃; pressure sensor 8 collects pressure data in real time with a sampling frequency greater than 100Hz, and the control system maintains constant pressure by adjusting the driving force of the lifting platform with a pressure control accuracy of ±0.1N.

[0047] It should be noted that while preferred embodiments of this application are provided in the specification and accompanying drawings, this application can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are not intended to impose additional limitations on the content of this application; their purpose is to provide a more thorough and comprehensive understanding of the disclosure of this application. Furthermore, the above-described technical features can be combined with each other to form various embodiments not listed above, all of which are considered to be within the scope of this utility model specification. Moreover, those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A local vacuum hot-pressing mechanism for non-flowing bottom filling, comprising a hot-pressing assembly and a vacuum sealing assembly, characterized in that: The vacuum sealing assembly is vertically and vertically positioned above the hot pressing assembly. The vacuum sealing assembly includes a vacuum sealing cover (6) and a sealing rubber ring (7), with the sealing rubber ring (7) positioned between the vacuum sealing cover (6) and the hot pressing assembly.

2. The local vacuum hot pressing mechanism for non-flowing bottom filling according to claim 1, characterized in that: The hot pressing assembly includes a hot pressing base plate (1), on which a heat insulation plate (2), a ceramic heating element (3), a heat spreader plate (4) and a heating panel (5) are stacked in sequence. The upper surface of the ceramic heating element (3) is flush with the upper surface of the heat insulation plate (2).

3. A local vacuum hot pressing mechanism for non-flowing bottom filling according to claim 2, characterized in that: A K-type thermocouple is installed at the center of the side of the heat spreader (4). The heat spreader (4) maintains a stable position by relying on gravity and the pressure of the upper heating panel (5). The ceramic heating element (3) heats according to the preset temperature curve. The upper surface of the heating panel (5) is used to place the chip to be bonded and the NCF film.

4. A local vacuum hot pressing mechanism for non-flowing bottom filling according to claim 3, characterized in that: When the vacuum sealing cover (6) descends, the sealing rubber ring (7) snaps onto the hot-pressed base plate (1) to form a sealed cavity.

5. A local vacuum hot pressing mechanism for non-flowing bottom filling according to claim 4, characterized in that: The vacuum sealing cover (6) is raised and lowered by the Z-axis lifting platform (9). A pressure sensor (8) is provided between the Z-axis lifting platform (9) and the vacuum sealing cover (6). The pressure sensor (8) is fixedly connected to the Z-axis lifting platform (9). The lower end of the pressure sensor (8) is fixedly connected to the vacuum sealing cover (6) through a flat pressure head. The Z-axis lifting platform (9), the pressure sensor (8) and the vacuum sealing cover (6) form a rigid series structure. The pressure sensor (8) is used to measure the actual downward pressure on the chip during the hot pressing process in real time.

6. A local vacuum hot pressing mechanism for non-flowing bottom filling according to claim 5, characterized in that: The vacuum sealing cover (6) is connected to a vacuum generating unit, which includes a vacuum pump, a vacuum pipeline and a vacuum solenoid valve. One end of the vacuum pipeline is connected to the vacuum pump and the other end is connected to the air extraction port of the vacuum sealing cover.

7. A local vacuum hot pressing mechanism for non-flowing bottom filling according to claim 6, characterized in that: It also includes a fixed base plate (10), a Z-axis lifting platform (9) installed on the fixed base plate (10), an X-axis linear displacement slide (13) installed on the fixed base plate (10), and a hot-pressed base plate (1) installed on the X-axis moving end of the X-axis linear displacement slide (13).

8. A local vacuum hot pressing mechanism for non-flowing bottom filling according to claim 7, characterized in that: The fixed base plate (10) is equipped with an NCF film feeding module (11), and an NCF film roll (12) is provided on the NCF film feeding module (11). The NCF film feeding module (11) transports the pre-cut NCF film and places it flat on the upper surface of the heating panel (5).

9. A local vacuum hot pressing mechanism for non-flowing bottom filling according to claim 8, characterized in that: It also includes a control system, which consists of a PID temperature controller, a solid-state relay, and a data acquisition module.

10. A local vacuum hot pressing mechanism for non-flowing bottom filling according to claim 9, characterized in that: The PID temperature controller receives the temperature signal from the K-type thermocouple and controls the on / off state of the ceramic heating element (3) through a solid-state relay to achieve closed-loop temperature control with a temperature control accuracy of ±0.1℃. The data acquisition module receives the signal from the pressure sensor (8) and records the pressure change during the hot pressing process in real time with a pressure control accuracy of ±0.1N.

Images