A temperature-pressure multi-stage cooperative control bottom glue filling method

Abstract

The application provides a temperature-pressure multi-stage cooperative control bottom glue filling method, and belongs to the field of infrared detector preparation; problems of failure caused by air inclusion, low filling rate and internal stress generated by solidification during bottom glue filling of large array focal plane infrared detection chips are solved; the method comprises the following steps: preheating and viscosity reduction; normal pressure capillary initial filling; medium pressure high temperature rapid filling; pressure relief and glue bubble removal; when the glue filling area meets the requirements, the pressure in the vacuum oven is rapidly released to normal pressure, the temperature is always kept unchanged at the optimal glue flow temperature point, and the glue bubbles are removed by pressure release; glue low pressure internal stress release and stepwise temperature increase solidification: after filling, low pressure is applied to the vacuum oven for pressure keeping, and then the glue is solidified by using a segmented temperature increase mode; the application is applied to bottom glue filling.

Description

Technical Field

[0001] This application relates to the field of infrared detector fabrication technology, and in particular to a bottom adhesive filling method with multi-stage temperature-pressure coordinated control. Background Technology

[0002] Flip-chip bonding is a crucial method for interconnecting chips and readout circuits. However, a gap exists between the chip and the readout circuit in this technology. Due to the difference in their coefficients of thermal expansion, stress may occur, leading to fatigue fracture at the solder joint and affecting the device's lifespan. The emergence of filler adhesive technology effectively solves this problem. In addition, filler adhesive can effectively prevent moisture and other problems from affecting reliability and can also effectively improve the overall interconnect quality.

[0003] However, current bottom filler adhesive technology still has some significant problems: 1. As chip size increases, gaps decrease, and solder ball array structures become more complex, adhesive tends to trap air during flow, creating air pockets that cause stress concentration at the point of contact, thus increasing the risk of failure. 2. The filling of adhesive relies more on capillary force, and the filling speed is limited by the viscosity of the adhesive, surface tension, and the size of the gap. For large-area, narrow-gap devices, the filling time is long, which seriously affects the production speed. 3. During the curing process, the adhesive shrinks in volume, generating internal stress, which may damage the chip or dielectric layer. Summary of the Invention

[0004] To address the issues of air inclusions leading to failure, low filling rate, and internal stress during curing of large-area focal plane array (e.g., 1280*1024, 640*512) infrared detection chips during bottom adhesive filling, this application proposes a bottom adhesive filling method with multi-stage temperature-pressure coordinated control. This method effectively reduces air inclusions, significantly improves the filling rate, and alleviates internal stress during curing, particularly for large-area focal plane arrays (e.g., 1280*1024, 640*512).

[0005] The technical solution adopted in this application is: a bottom adhesive filling method with multi-stage coordinated control of temperature and pressure, comprising the following steps: Step 1: Preheating and viscosity reduction: After removing moisture from the infrared detector device that has completed the flip-chip welding process, place it in a vacuum oven for preheating and heat preservation. Step 2: Atmospheric pressure capillary initial filling: Place the preheated device on the fixture, and allow the liquid adhesive to initially fill the device by relying on capillary force without external pressure; Step 3: Medium-pressure high-temperature rapid filling: Place the initially filled device into a vacuum oven and raise the temperature of the vacuum oven to the optimal temperature point for adhesive flow under medium pressure, so that the adhesive can fill rapidly. Step 4: Depressurize to remove air bubbles in the glue: When the glue filling area meets the requirements, quickly release the pressure in the vacuum oven to normal pressure, and keep the temperature at the optimal temperature point for glue flow. Use the pressure release to remove air bubbles from the glue. Step 5: Releasing internal stress of the adhesive under low pressure and curing by step heating: After filling, apply low pressure to the vacuum oven and maintain the pressure, and then use a step heating method to cure the adhesive.

[0006] Furthermore, the preheating temperature in step 1 is set to the temperature at which the target adhesive viscosity drops to the process reference viscosity range, where the reference viscosity is the viscosity at which the dynamic viscosity of the adhesive drops to 40%~60% of the initial room temperature viscosity.

[0007] Furthermore, the optimal temperature for glue flow in step 3 is the temperature corresponding to the lowest melt viscosity of the glue; the range of medium pressure is the effective driving pressure under the premise that the glue does not overflow.

[0008] Furthermore, the medium pressure is 0.2~0.5MPa.

[0009] Furthermore, in step 4, when the glue-filled area reaches more than 90% of the device area, a pressure relief operation is performed.

[0010] Furthermore, the segmented heating method in step 5 is designed based on the curing kinetics curve of the adhesive. First, the temperature is raised to the gelation initiation temperature of the adhesive to complete the initial cross-linking and shaping, and then the temperature is gradually increased to the complete curing temperature of the adhesive.

[0011] Furthermore, the low pressure in step 5 is 0.05~0.1 MPa.

[0012] The advantages of this application over the prior art are as follows: Significantly reduces void ratio: Through an active pressure relief and bubble removal mechanism, micro-bubbles inside the filling area are effectively removed, making it especially suitable for large-area arrays and high-density flip-chip bonding devices; Significantly improves filling efficiency: The medium-pressure, high-speed filling stage makes the glue flow rate far exceed that of simple capillary force drive, shortening the production cycle; Effectively relieves curing internal stress: By step-by-step heating and low-pressure holding, the colloidal shrinkage stress is released, improving the low-temperature reliability of the device. Attached Figure Description

[0013] The following description, in conjunction with the accompanying drawings, further illustrates this application: Figure 1This is a schematic diagram of the method flow provided in the embodiments of this application. Detailed Implementation

[0014] like Figure 1 As shown, this application provides a bottom adhesive filling method with multi-stage temperature-pressure synergistic control, which abandons the single capillary force and introduces multi-stage temperature-pressure synergistic effect. By actively applying controllable external pressure and precisely controlling temperature changes, the flow of adhesive is guided and controlled in stages.

[0015] This application upgrades the bottom filling adhesive process from the traditional "single capillary force driven" to a four-stage physical field process with multi-parameter coordinated control of "temperature-pressure-time": Phase 1: Preheating and viscosity reduction – Preheating the device before filling reduces the viscosity of the adhesive, creating conditions for rapid flow in the subsequent process.

[0016] Phase 2: Atmospheric pressure capillary initial filling - using capillary force to allow the glue to naturally wet and fill part of the channel, avoiding external pressure causing circuit breakage or excessive air encapsulation.

[0017] Phase 3: Medium-pressure, high-temperature, rapid filling – Apply 0.2~0.5MPa pressure and heat to the optimal temperature point for adhesive flow, so that the adhesive can rapidly fill the central area and main flow channels of the chip at a speed far exceeding capillary force.

[0018] Phase 4: Depressurization and bubble removal – When filling is nearing completion, the pressure is rapidly released to atmospheric pressure. By utilizing the pressure dependence of gas solubility, microbubbles are nucleated, aggregated, and expelled.

[0019] Stage 5: Low-pressure step curing – Apply low pressure of 0.05~0.1MPa and use step heating (first to partial cross-linking, then to the final curing temperature) to release the internal stress caused by volume shrinkage and thermal expansion mismatch.

[0020] The specific implementation steps of the method in this application include: Step 1: Preheating to Reduce Viscosity, Insulating the Flip-Chip Components After Dehumidification: After dehumidification, place the components that have completed the flip-chip bonding process into an oven for the first stage of preheating (temperature T1℃). This allows the components to heat up uniformly and is maintained at this temperature for a period of time. This temperature is set below the initial curing temperature of the adhesive, ensuring that the viscosity of the adhesive is effectively reduced at this temperature. This stage is used to reduce the viscosity of the adhesive during filling, preparing it for subsequent flow.

[0021] The preheating temperature T1 is set to the temperature at which the target adhesive viscosity drops to the process reference viscosity range. The reference viscosity is defined as the dynamic viscosity of the adhesive dropping to 40%~60% of the initial room temperature viscosity. This step can reduce the flow resistance of the adhesive and create flow conditions for subsequent spreading. The preheating time is set according to the adhesive rheological curve to ensure that the adhesive viscosity is uniform throughout the board.

[0022] Step 2: Initial dispensing of adhesive under normal pressure via capillary filling: Place the preheated component on the fixture and dispense adhesive using a single-point or line-drilling method. Allow the liquid adhesive to initially fill the channel using capillary force without external pressure (filling time is t1, approximately 10 minutes). This stage allows the adhesive to naturally wet and fill some channels, preventing adhesive breaks or excessive air trapping caused by initial external pressure.

[0023] Step 3: High-Pressure, High-Temperature Rapid Filling of Adhesive. Under medium pressure and temperature T2, allow the adhesive to fill for a certain period of time: Place the initially filled device in a vacuum oven and start the medium pressure (P1), which is a moderate pressure (e.g., 0.2~0.5MPa); simultaneously, raise the oven temperature to the second stage temperature (T2), which is higher than T1 but still lower than the adhesive's curing temperature; maintain this condition for a certain time t2 (the time varies depending on the array size, approximately 10 minutes); under the synergistic effect of medium pressure P1 and temperature T2, the adhesive propagates forward at a relatively fast speed, quickly filling the central area and main channels of the device. This stage is the main stage of efficient filling.

[0024] T2 temperature is the optimal temperature for adhesive flow (i.e., the temperature corresponding to the lowest melt viscosity of the adhesive); the range of pressure P1 is the effective driving pressure under the premise that the adhesive does not overflow, so that the adhesive flow rate exceeds the pure capillary flow rate and quickly completes the filling of the chip center area and the main channel; the pressure at this stage causes the free microbubbles in the gap to be compressed and dissolved in the adhesive matrix.

[0025] Step 4: Depressurize to remove adhesive air bubbles: When the adhesive filling front is nearly complete (e.g., reaching 90% of the device area, observe the adhesive wall positions on both sides), quickly release the external pressure to atmospheric pressure; keep the temperature constant at T2; depressurization is crucial during this process. Tiny air bubbles compressed or dissolved in the adhesive under pressure P1 will precipitate due to decreased solubility when the pressure is suddenly released. They will then be propelled towards the front or flow out along the opposite side of the device (non-filling port) by the final capillary force of the adhesive, effectively eliminating microscopic voids.

[0026] The "pressure relief and bubble removal" stage involves rapidly releasing the cavity pressure to atmospheric pressure after medium-pressure, high-speed filling. This operation utilizes the physical principle that the solubility of gas in a liquid decreases as pressure decreases. This causes tiny bubbles that were previously dissolved or compressed in the adhesive under pressure to nucleate and grow. These bubbles are then pushed towards the filling front or expelled from the venting side as the adhesive continues to flow, significantly reducing the void ratio.

[0027] Step 5: Low-pressure stress release and stepped temperature curing of the adhesive: After filling, apply low-pressure constraints (pressure P2, such as 0.05~0.1MPa). The temperature rise curve is designed according to the adhesive curing kinetics curve, using a stepped temperature rise program: first, heat to the adhesive gelation initiation temperature to complete preliminary cross-linking and shaping, then gradually increase to the adhesive's complete curing temperature; the low-pressure constraint combined with segmented temperature rise gradually releases the interfacial stress caused by the volume shrinkage and thermal expansion mismatch of the cured adhesive. This stage can effectively alleviate the generation of internal stress.

[0028] This application can achieve the following technical effects: Multi-stage temperature and pressure synergy: The filling process is divided into four stages: "capillary filling - medium-pressure high-speed filling - pressure relief and de-bubbling - low-pressure internal stress release", which realizes precise control of glue flow. Active depressurization and degassing: By actively depressurizing, the pressure dependence of gas solubility in liquid is utilized to force out microscopic, difficult-to-remove bubbles, which is impossible with capillary forces. Stepped internal stress release: By controlling the curing reaction process, a stress relaxation stage is provided before the adhesive cures, significantly reducing the internal stress of the device.

[0029] The bottom-filling adhesive process proposed in this application, based on a multi-stage temperature-pressure synergy, is conceived by actively applying different pressure and temperature physical fields in stages to guide the adhesive to achieve rapid, bubble-free, and low-stress filling in the narrow gap between the chip and the readout circuit. This effectively solves the inherent physical process challenges in large-area, narrow-gap flip-chip devices, such as "bubble encapsulation," "low filling efficiency," and "excessive curing internal stress."

[0030] The method of this application involves several steps: preheating to reduce viscosity → initial capillary filling at normal pressure → rapid filling at medium pressure and high temperature → depressurization and defoaming → low-pressure stepwise temperature rise and curing. Based on pre-set multi-stage pressure-temperature-time process parameters, the adhesive can be rapidly filled without real-time feedback. Instead, the flow behavior and curing process of the adhesive are optimized by actively changing the cavity pressure and temperature. The process is simple and effective.

[0031] This application is the first to apply the physical principle of "pressure mutation-induced bubble precipitation" to the underfill process of flip-chip bonding. Specifically: During the medium-pressure, high-temperature filling stage, the solubility of gas in the adhesive increases due to the increase in pressure, and microbubbles are compressed or dissolved. When the pressure is rapidly released to normal pressure, the solubility of gas decreases sharply, and supersaturated gas will nucleate at micro-defects or particles to form microbubbles. These microbubbles are pushed to the filling front by the adhesive in the subsequent normal pressure capillary flow and are discharged from the venting side.

[0032] After filling, this application incorporates a curing stress release stage combining "low-pressure holding" and "stepped heating." Specifically, before the adhesive is fully cured, it undergoes segmented heating and low pressure (0.05~0.1 MPa) to induce partial cross-linking while maintaining a certain level of fluidity. In this state: The stress generated by the volume shrinkage of the colloidal substance can be released through viscous flow; The thermal stress caused by the difference in thermal expansion coefficients between the chip and the substrate was also relaxed. Then, the temperature is raised to the final curing temperature to complete the curing process, thereby significantly reducing the risk of stress failure of the device in low-temperature operating environments (such as 77K).

[0033] The process parameters (temperature, pressure, time) of this application can be flexibly adjusted according to the device array size (e.g., 640×512, 1280×1024) and gap size, and are particularly suitable for: Large-area array devices: The medium-pressure high-speed filling stage solves the problem of excessively long traditional capillary filling time; Narrow gap devices: The active pressure relief and bubble removal mechanism solves the problem of bubbles being difficult to remove from small channels; Heat-sensitive devices: Stepped curing effectively reduces the damage to the chip and dielectric layer caused by thermal and shrinkage stresses.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A bottom adhesive filling method with multi-stage coordinated temperature-pressure control, characterized in that: Includes the following steps: Step 1: Preheating and viscosity reduction: After removing moisture from the infrared detector device that has completed the flip-chip welding process, place it in a vacuum oven for preheating and heat preservation. Step 2: Atmospheric pressure capillary initial filling: Place the preheated device on the fixture, and allow the liquid adhesive to initially fill the device by relying on capillary force without external pressure; Step 3: Medium-pressure high-temperature rapid filling: Place the initially filled device into a vacuum oven and raise the temperature of the vacuum oven to the optimal temperature point for adhesive flow under medium pressure, so that the adhesive can fill rapidly. Step 4: Depressurize to remove air bubbles in the glue: When the glue filling area meets the requirements, quickly release the pressure in the vacuum oven to normal pressure, and keep the temperature at the optimal temperature point for glue flow. Use the pressure release to remove air bubbles from the glue. Step 5: Releasing internal stress of the adhesive under low pressure and curing by step heating: After filling, apply low pressure to the vacuum oven and maintain the pressure, and then use a step heating method to cure the adhesive.

2. The bottom adhesive filling method with multi-stage temperature-pressure coordinated control according to claim 1, characterized in that: The preheating temperature in step 1 is set to the temperature at which the target adhesive viscosity drops to the process reference viscosity range, where the reference viscosity is the viscosity at which the dynamic viscosity of the adhesive drops to 40%~60% of the initial room temperature viscosity.

3. The bottom adhesive filling method with multi-stage temperature-pressure coordinated control according to claim 1, characterized in that: The optimal temperature for glue flow in step 3 is the temperature corresponding to the lowest melt viscosity of the glue; the range of medium pressure is the effective driving pressure under the premise that the glue does not overflow.

4. The bottom adhesive filling method with multi-stage coordinated temperature-pressure control according to claim 3, characterized in that: The medium pressure is 0.2~0.5MPa.

5. The bottom adhesive filling method with multi-stage temperature-pressure coordinated control according to claim 1, characterized in that: In step 4, when the glue fills more than 90% of the device area, a pressure relief operation is performed.

6. The bottom adhesive filling method with multi-stage temperature-pressure coordinated control according to claim 1, characterized in that: The segmented heating method in step 5 is designed based on the curing kinetics curve of the adhesive. First, the temperature is raised to the gelation initiation temperature of the adhesive to complete the initial cross-linking and shaping, and then the temperature is gradually increased to the complete curing temperature of the adhesive.

7. The bottom adhesive filling method with multi-stage temperature-pressure coordinated control according to claim 6, characterized in that: The low pressure in step 5 is 0.05~0.1 MPa.

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