With the advancements in heterogeneous packaging and artificial intelligence, 2.5D and 3D packaging have emerged as the core of future technological growth. Chips are becoming increasingly complex, and integration density is also rising. Consequently, precise alignment of molds in FOWLP (Fan-Out Wafer-Level Packaging) or FOPLP (Fan-Out Package-Level Packaging) processes on large-sized substrates over a large area becomes crucial. Misalignment can lead to poor electrical contact or mechanical instability, directly affecting performance. The challenge lies in maintaining consistency across the entire bonding area while accurately aligning multiple chips!
     1. Key considerations for temperature control:
     · Uniform heating: Large chips or wafers require uniform heating to avoid localized overheating or insufficient heating.
     · Material properties: Different materials expand at different rates with temperature, so managing temperature gradients is crucial.
     · Bonding materials: The bonding temperature needs to be within a specific range for the materials used, typically between 200°C and 400°C, depending on the bonding material (such as solder or flux).
     · Local heating: Using heating technology (such as laser heating) to target heat to specific areas is highly effective. This minimizes thermal gradients, especially in large-area bonding. It can be precisely controlled through a feedback system.

     · Controlled chamber environment: For uniform heating, a heating plate or thermal chuck provides a controlled temperature zone. Ideally, the entire system should be insulated to reduce heat loss and ensure consistency.
     · Advanced sensors: Infrared thermal imaging devices or thermocouples are deployed around the bonding area to monitor temperature. These sensors should be integrated with PID (Proportional-Integral-Derivative) controllers to enable real-time adjustments
     2. Temperature distribution calculation:
     To achieve uniform temperature distribution, the heat conduction equation and Fourier's law of heat conduction can be utilized. To ensure uniform heating, it is necessary to minimize the temperature gradient ΔT, and the system must dissipate heat uniformly. The heat input q must be adjusted based on the properties of the material (thermal conductivity and specific heat) to ensure uniform heating.

     q = heat flux (W), k = thermal conductivity of the material (W/m·K), A = cross-sectional area (square meters), ΔT = temperature difference (K), L = temperature gradient distance (m)
     3. Pressure control and pressure calculation in high-precision TCB
     · Uniform pressure distribution: The pressure must be evenly distributed across the substrate, especially for large chips. If the pressure is uneven, it may lead to uneven bonding, resulting in areas with poor electrical or mechanical performance.
     · Local pressure variation: Pressure may vary due to material properties or the size of the bonded mold/substrate. It is crucial to adjust the pressure during different stages of bonding, especially during the transition phase between the heating and bonding stages.
     Closed-loop pressure control: Apply pressure uniformly along the Z-axis. The actual pressure exerted on the bonding area can be monitored in real-time using a pressure sensor feedback system
     · Uniform pressure distribution: Flexible structural design can be adopted to uniformly distribute pressure across the surface.
     · Dynamic pressure adjustment: The pressure can be adjusted dynamically to ensure uniform bonding throughout the entire process. For instance, the initial pressure can be reduced to avoid chip deformation, while the pressure can gradually increase as the temperature rises.
     Pressure calculation formula: P=F/A, where P represents pressure, F represents applied force (in Newtons), and A represents area (in square meters). For example, if the bonding area is A=0.02m², and the bonding force is F=1000N, and the required bonding pressure is uniform across the entire area, then the pressure=F/A=1000/0.02=50000Pa. This indicates that the pressure applied to the bonding area needs to reach 50000Pa to achieve uniform bonding.

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