Board-level packaging process for suppressing warping

Abstract

The invention relates to the technical field of semiconductor packaging, and discloses a board-level packaging process capable of inhibiting warping, which comprises the following steps: coating a packaging substrate with a liquid plastic package material, heating and curing the plastic package material to obtain a packaging substrate with a plastic package layer, carrying out non-uniform heating according to a set temperature field function in the heating and curing process, and carrying out heat treatment on the plastic package material to obtain the packaging substrate with the plastic package layer; and / or applying a pressure to a local portion of the package substrate. Non-uniform heating is adopted in the liquid molding compound curing process, and particularly gradient heating is performed on the packaging substrate, so that the thermocuring processes of different areas are performed according to a specific sequence, stress accumulation in the curing process is effectively reduced, the warping phenomenon of the packaging substrate is remarkably reduced and effectively inhibited, and the packaging quality of the packaging substrate is improved. The yield and the reliability of a packaged product are improved, and the problem of overlarge warping of the packaging substrate caused by heating and curing is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor packaging, and in particular to a board-level packaging process for suppressing warping. Background Art

[0002] Among advanced semiconductor packaging technologies, fan-out panel level packaging (FOPLP) has become one of the important directions of next-generation packaging processes due to its high integration, high density, excellent electrical performance and low thickness. FOPLP technology embeds the chip into the panel-level packaging structure and adds an external fan-out layer to achieve electrical interconnection, thereby reducing package size and cost and improving signal transmission efficiency. However, due to the complexity of the FOPLP packaging structure and the diversity of materials used, warpage problems will occur during the actual manufacturing process, seriously affecting the quality and reliability of the package. Therefore, how to reduce and control warpage in FOPLP has become a research focus in the current technology field. Summary of the Invention

[0003] In view of the above-mentioned defects, the purpose of the present invention is to propose a board-level packaging process that suppresses warping, so as to solve the problem of warping caused by heating and curing during the manufacturing process of fan-out board-level packaging substrates.

[0004] To achieve this object, the present invention adopts the following technical solutions:

[0005] A board-level packaging process for suppressing warping includes first coating a liquid molding compound on a packaging substrate, and then heating and curing the molding compound to obtain a packaging substrate having a molding layer. During the heating and curing process, uneven heating is performed according to a set temperature field function, and / or pressure is applied to a part of the packaging substrate.

[0006] Preferably, the heating temperature field distribution function of the non-uniform heating is:

[0007] T(x,y)=k1(x 2 +y 2 ) n +T0;

[0008] Wherein, the center of the substrate is the coordinate origin, k1=±300~1000℃ / m 2n , n = 0.7 ~ 1.5, T0 is the curing temperature of the plastic compound.

[0009] Preferably, the warpage function w(x, y) of each point on the packaging substrate is obtained by pre-uniformly heating the packaging substrate coated with liquid molding compound, or by real-time monitoring the packaging substrate during the heating and curing process. The second-order partial derivatives of the warpage function w(x, y) of different regions of the packaging substrate are:

[0010]

[0011] The heating temperature field distribution function of the non-uniform heating is:

[0012] T(x,y)=T0+k2A1(x,y);

[0013] Wherein, k2 = ±100~1000℃·m, T0 is the curing temperature of the plastic compound.

[0014] Preferably, the warpage function w(x, y) of each point on the packaging substrate is obtained by pre-uniformly heating the packaging substrate coated with liquid molding compound, or by real-time monitoring the packaging substrate during the heating and curing process. The first-order partial derivative of the warpage w(x, y) of the packaging substrate in different regions is:

[0015]

[0016] The heating temperature field distribution function of the non-uniform heating is:

[0017] T(x,y)=T0+k3A2(x,y);

[0018] Where: k3 = ±1000~5000℃, T0 is the curing temperature of the plastic compound.

[0019] Preferably, the non-uniform heating is achieved by using a non-uniform heat source.

[0020] Preferably, the non-uniform heat source includes at least one of laser zone heating, non-uniform airflow heating, microwave heating or programmable resistance heating.

[0021] Preferably, the uneven heating is achieved by arranging one or more heat insulation plates between the heat source and the packaging substrate.

[0022] Preferably, a hollow hole is provided in the middle of the heat insulation board, and the hollow hole is square, diamond, X-shaped or circular, and the heat insulation board is used in one or more combinations.

[0023] Preferably, the packaging substrate is uniformly heated to obtain a warpage function w(x, y) at each point on the packaging substrate, and a region with a larger warpage is selected to apply pressure in the opposite direction of the actual warpage:

[0024] F = -kw0;

[0025] Wherein, w0 is the average value of w(x, y) in the selected area, and k = 0.05 to 0.3 kPa / mm.

[0026] A packaging substrate is prepared using the above-mentioned fan-out panel-level packaging process, and has a warpage of less than 1 mm.

[0027] The technical solution provided by the present invention can have the following beneficial effects:

[0028] 1. By using uneven heating during the curing process of the liquid plastic compound, especially implementing a gradient temperature increase on the package substrate, the thermal curing process of different areas is carried out in a specific order, effectively reducing the stress accumulation during the curing process, thereby significantly reducing and effectively suppressing the warping of the package substrate, and improving the yield and reliability of the packaged product.

[0029] 2. Non-uniform heating allows targeted heating adjustments to key areas based on the specific shape, material distribution, and stress concentration areas of the package structure. During the packaging process, parameters such as temperature distribution, heating time, and heating rate can be flexibly adjusted based on actual warpage conditions, achieving a highly controllable and adaptable process, thereby addressing the warpage challenges posed by different package designs and material combinations.

[0030] 3. By setting the temperature field function and combining it with the partial derivative of the package substrate warpage to set the heating temperature, and utilizing high-precision heating equipment (such as laser local heating and programmable resistors), the temperature of each region can be precisely adjusted to ensure that the temperature control accuracy meets the requirements. This effectively solves the problem of poor warpage control caused by temperature errors in traditional methods, ensuring the stability and reliability of the warpage suppression effect.

[0031] 4. Compared with the traditional method that requires additional auxiliary components (such as pressure plates, frames, etc.) or complex thermal management solutions to suppress warping, the warping problem is solved by optimizing the heating method itself, without the need to add additional heat dissipation components such as heat sinks or special mechanical stress application devices, thereby simplifying the process flow to a certain extent, saving material costs and layout space on the packaging substrate, and reducing production costs.

[0032] 5. By controlling the heating source, a heating temperature field distribution is formed at the center and around the substrate, which is different, so that the center and around the plastic encapsulation material on the substrate have a sequential curing completion order.

[0033] 6. According to the value of the second-order partial derivative of w(x, y) of the warpage degree of the package substrate in different areas, set the corresponding heating temperature to balance the thermal expansion of different areas, so that the high stress area is cured first or last to balance the internal stress and reduce warpage.

[0034] 7. Warping is reduced by compensating for the thermal stress caused by warping through the thermal stress generated by the temperature field gradient. The corresponding heating temperature is set according to the value of the first-order partial derivative of the warping degree w(x,y) in different areas of the package substrate to balance the thermal expansion of different areas and reduce warping.

[0035] 8. It is difficult to use multiple non-uniform heating methods (such as laser, hot air flow, and microwaves) simultaneously and make them work synergistically. Designs are made based on the characteristics of different heating methods. Laser local heating can accurately act on a specific small area; hot air flow heating can provide relatively uniform low-temperature heating over a large area; and microwave heating can achieve rapid internal heating. In specific implementation, a reasonable combination is made based on the package structure and warping conditions. Laser is used in local stress concentration areas, and hot air flow is used in overall slow heating areas to ensure that the advantages of each heating method complement each other and form an effective non-uniform heating temperature field.

[0036] 9. By using a thermal insulation board, local heat conduction is limited, thereby forming a local temperature difference, thereby reducing the thermal expansion of the area, preventing local excessive warping, and improving packaging quality and reliability.

[0037] 10. Reduce warpage by continuously applying pressure F during the curing process. In a specific embodiment, pressure in the desired direction is applied to the package substrate using methods such as gravity pressing of a pressure block, external force-supported pressure of a pressure block, or vacuum traction of a suction cup.

[0038] 11. Through uneven heating and the use of thermal insulation boards, heat conduction is limited to form local temperature differences, further reducing local thermal expansion, controlling the distribution of stress within the package substrate, rebalancing the internal stress in each area of ​​the package substrate, reducing the overall warping amplitude, and preventing local excessive warping. During the entire curing process, a pressure F opposite to the actual warping direction is applied to the package substrate to further reduce the warping of the package substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A flowchart of an embodiment of the present invention.

[0040] Figure 2 It is a structural diagram of an embodiment of the present invention.

[0041] Figure 3 It is a structural diagram of another embodiment of the present invention.

[0042] Figure 4 It is a structural diagram of another embodiment of the present invention.

[0043] Figure 5 It is a structural diagram of another embodiment of the present invention.

[0044] Figure 6 It is a structural diagram of another embodiment of the present invention.

[0045] Figure 7 It is a structural diagram of another embodiment of the present invention.

[0046] Figure 8This is a warpage cloud diagram of the package substrate after uniform heating and curing in the comparative example.

[0047] Figure 9 This is a warpage cloud diagram of the package substrate after uneven heating and curing using a heat insulation board according to the present invention.

[0048] Figure 10 This is a warpage cloud diagram of the packaging substrate after uneven heating and curing using a heat insulation board with hollow holes according to the present invention, where a is a square hollow hole size of 30x30mm, b is a square hollow hole size of 50x50mm, and c is a square hollow hole size of 100x100mm.

[0049] Among them: packaging substrate 1, heat insulation board 2, ceramic rod 3, quartz plate with holes 4, heat source 5, pressure block 6. DETAILED DESCRIPTION

[0050] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0051] In the description of the present invention, it should be understood that the terms "longitudinal", "transverse", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction, and therefore should not be understood as limiting the present invention. In addition, features defined as "first" or "second" may explicitly or implicitly include one or more such features, and are used to distinguish between the described features, without distinction of order or importance.

[0052] In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0053] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0054] The following describes embodiments of the present invention in conjunction with the accompanying drawings.

[0055] A board-level packaging process for suppressing warping includes first coating a liquid molding compound on a packaging substrate, and then heating and curing the molding compound to obtain a packaging substrate having a molding layer. During the heating and curing process, uneven heating is performed according to a set temperature field function, and / or pressure is applied to a part of the packaging substrate.

[0056] like Figure 2 As shown, by adopting non-uniform heating during the curing process of the liquid plastic compound, especially implementing gradient heating of the package substrate, the thermal curing process of different areas is carried out in a specific order, effectively reducing the stress accumulation during the curing process, thereby significantly reducing and effectively suppressing the warping of the package substrate, and improving the yield and reliability of the packaged product.

[0057] Non-uniform heating allows targeted heating adjustments to critical areas based on the specific shape, material distribution, and stress concentration areas of the package structure. During the packaging process, parameters such as temperature distribution, heating time, and heating rate can be flexibly adjusted based on actual warpage conditions, achieving a highly controllable and adaptable process, thus addressing the warpage challenges posed by varying package designs and material combinations.

[0058] By setting the temperature field function and combining it with the partial derivative of the package substrate warpage to set the heating temperature, and utilizing high-precision heating equipment (such as laser local heating and programmable resistors), the temperature of each region can be precisely adjusted to ensure that the temperature control accuracy meets the requirements. This effectively solves the problem of poor warpage control caused by temperature errors in traditional methods, ensuring the stability and reliability of the warpage suppression effect.

[0059] Compared with traditional methods that require additional auxiliary components (such as pressure plates, frames, etc.) or complex thermal management solutions to suppress warping, the warping problem is solved by optimizing the heating method itself, without the need to add additional heat dissipation components such as heat sinks or special mechanical stress application devices, thereby simplifying the process flow to a certain extent, saving material costs and layout space on the packaging substrate, and reducing production costs.

[0060] Preferably, the heating temperature field distribution function of the non-uniform heating is:

[0061] T(x,y)=k1(x 2 +y 2 ) n +T0;

[0062] Wherein, the center of the substrate is the coordinate origin, k1=±300~1000℃ / m 2n , n = 0.7 ~ 1.5, T0 is the curing temperature of the plastic compound.

[0063] By controlling the heating source, a heating temperature field distribution different from that at the center of the substrate and at its periphery is formed, so that the center and the periphery of the plastic encapsulation material on the substrate are cured in a sequential order.

[0064] This temperature field distribution function, using the two-dimensional spatial variables x and y and the parameters n and k1, accurately describes the temperature variations at different locations on the package substrate. The range and step size of x and y can be adjusted appropriately based on factors such as the specific shape and size of the package substrate and the chip layout. Combined with the optimization of n and k1, highly customized control of the temperature field across the entire package substrate can be achieved. For example, in the area near the chip, the temperature can be adjusted according to a specific curve by setting appropriate parameters. This ensures that the thermal expansion of the chip matches that of the surrounding material, reducing warping caused by temperature unevenness.

[0065] Complex structures like fan-out panel-level packages often have significantly different material properties and heat conduction paths across different regions. The flexibility of this temperature field function allows it to adapt well to this complexity. By adjusting the value of n, the temperature gradient can be altered. Setting a smaller n in areas with faster heat conduction allows for a smoother temperature transition, while increasing n in areas where heat conduction is hindered or temperature-sensitive enhances temperature control. This ensures temperature uniformity and a reasonable curing sequence across the entire package substrate during the curing process, effectively reducing the risk of warping.

[0066] k1 determines the magnitude of the temperature field variation with position and is used to control the temperature gradient distribution in different areas of the package substrate. By adjusting k1, the order and speed of heating and curing can be optimized, balancing the stress accumulation caused by differences in the coefficient of thermal expansion (CTE) of the material, thereby suppressing overall warping.

[0067] When k1 approaches 0, the temperature gradient almost disappears (T(x,y) ≈ T0), making effective temperature differential control impossible. This causes the curing process in different areas of the package substrate to proceed synchronously. Stress cannot be released through gradient temperature increase, but instead accumulates and intensifies, ultimately increasing warpage and potentially even becoming uncontrollable.

[0068] If k1 is within ±300 but non-zero (such as ±100), the temperature gradient is insufficient, which may lead to an unclear curing sequence between the center and the edge, insufficient offset of local thermal expansion differences, and limited warpage improvement effect.

[0069] If k1 exceeds the range of ±1000: Too high k1 will cause the temperature gradient to be too severe. For example, when k1=+1000℃ / m 2n When K1=-1000℃ / m 2n, a sudden drop in edge temperature may lead to incomplete curing and a decrease in the mechanical properties of the material. Both situations will aggravate stress concentration and even cause cracking or functional failure of the package substrate.

[0070] n represents the nonlinear adjustment parameter of the temperature gradient, which is used to adjust the nonlinear degree of the gradient of temperature as it changes with the x and y coordinates.

[0071] When n = 1, the temperature field may exhibit a relatively linear trend. When n > 1, as |x+y| increases, the rate of temperature rise or fall accelerates, resulting in a nonlinear temperature gradient. This more accurately adapts to the varying sensitivity of different regions of the package substrate to temperature changes, enabling complex temperature field distributions, effectively controlling the thermal curing sequence and stress distribution, and reducing warpage. For example, in critical areas such as the edge of the package substrate or around the chip, a larger value may be required to create a steeper temperature gradient, ensuring that these areas cure in a specific order.

[0072] When n < 0.7, the power exponent n in the temperature distribution function is too small (e.g., n = 0.5), the temperature variation with distance tends to be flat, the temperature difference between the center and the edge is insufficient, and the gradient effect of the curing sequence is weakened. This may lead to insufficient stress release, inability to effectively offset thermal expansion differences, and poor overall warpage control.

[0073] When n>1.5, an excessively large n (e.g., n=2.0) will cause the temperature to rise sharply with the square of the distance, resulting in extremely high temperatures in the center and a sharp drop in temperature at the edges. This extreme gradient can lead to overheating in the center, material decomposition, or delayed curing at the edges, resulting in poor bonding. Furthermore, due to the large differences in local curing speeds, new stress sources are generated, exacerbating warpage.

[0074] Preferably, the warpage function w(x, y) of each point on the packaging substrate is obtained by pre-uniformly heating the packaging substrate coated with liquid molding compound, or by real-time monitoring the packaging substrate during the heating and curing process. The second-order partial derivatives of the warpage function w(x, y) of different regions of the packaging substrate are:

[0075]

[0076] The heating temperature field distribution function of the non-uniform heating is:

[0077] T(x,y)=T0+k2A1(x,y);

[0078] Wherein, k2 = ±100~1000℃·m, T0 is the curing temperature of the plastic compound.

[0079] According to the value of the second-order partial derivative of w(x, y) of the warpage degree in different areas of the package substrate, the corresponding heating temperature is set to balance the thermal expansion of different areas, so that the high-stress area is cured first or last to balance the internal stress and reduce warpage.

[0080] k2 represents the temperature compensation per unit warpage curvature, which is used to convert the local curvature of the warpage into a temperature adjustment value. The warpage curvature A1(x,y) reflects the degree of curvature of the local area (such as convexity or concavity).

[0081] Setting the heating temperature based on the second-order partial derivative F1(x,y) of the warpage w(x,y) in different regions of the package substrate accurately reflects the substrate's deformation. Because the second-order partial derivative of warpage accurately reveals stress concentration and gradient changes in deformation, adjusting the temperature based on this information allows for direct temperature compensation in high-stress and warpage-prone areas. For example, in areas where the absolute value of the second-order partial derivative is large, indicating drastic stress changes, the function calculates an appropriate higher or lower temperature (depending on the sign of k2 and the value of F1(x,y)) to balance the stresses by causing the material to expand or contract thermally, effectively suppressing the occurrence and development of warpage. Compared to heating methods that do not consider the degree of warpage, this method allows for more precise control of the package substrate's flatness.

[0082] During the packaging process, the substrate's warpage and stress distribution change dynamically as the material's thermal curing reaction progresses. This temperature field distribution function adapts to these changes in real time by adjusting the temperature based on the real-time second-order partial derivative of the warpage. In the early stages of curing, some areas may have low stress, resulting in low F1(x,y) values ​​and small heating temperature increments calculated by the function. As curing progresses, if stress concentration in certain areas causes an increase in F1(x,y), the function increases the heating temperature accordingly, maintaining effective warpage control and ensuring substrate stability throughout the entire packaging process. This improves product quality consistency and reliability, and reduces the rate of defective products caused by warpage.

[0083] When k2 ranges from 0 to ±100, if the absolute value of k2 is too small (e.g., k2 = ±50), the temperature compensation is insufficient to balance the high-stress areas indicated by the second derivative of warpage. For example, if a region requires +80°C compensation to offset stress, but the actual compensation is only +50°C, the region will still experience residual warpage due to uneven thermal expansion, and the overall flatness improvement will be limited.

[0084] When k2 exceeds ±1000, excessive k2 (e.g., k2 = ±1500) can lead to over-compensation. For example, if a region requires +200°C compensation but is actually subjected to +300°C, this can cause local overheating and material deformation, or local overcooling and solidification stagnation. This, in turn, can generate reverse stress in the compensation region, complicating the warpage, such as wavy deformation, and even damaging the package structure.

[0085] Preferably, the warpage function w(x, y) of each point on the packaging substrate is obtained by pre-uniformly heating the packaging substrate coated with liquid molding compound, or by real-time monitoring the packaging substrate during the heating and curing process. The first-order partial derivative of the warpage w(x, y) of the packaging substrate in different regions is:

[0086]

[0087] The heating temperature field distribution function of the non-uniform heating is:

[0088] T(x,y)=T0+k3A2(x,y);

[0089] Where: k3 = ±1000~5000℃, T0 is the curing temperature of the plastic compound.

[0090] Warpage is reduced by compensating for the thermal stress caused by warping through the thermal stress generated by the temperature field gradient. The corresponding heating temperature is set according to the value of the first-order partial derivative of the warpage degree w(x,y) in different areas of the package substrate to balance the thermal expansion of different areas and reduce warping.

[0091] Setting the heating temperature based on the first-order partial derivative F2(x,y) of the warpage w(x,y) in different regions of the package substrate can reflect the warpage trend. Unlike the second-order partial derivative function, the first-order partial derivative focuses on the rate of change of warpage in each direction. This function allows precise adjustment of the heating temperature based on the value of F2(x,y) and k3 in areas with a high warpage rate, modifying the material's thermal properties to accommodate or offset this trend. This effectively prevents rapid local warpage from causing increased deformation of the entire package substrate, ensuring stable package substrate flatness.

[0092] In actual packaging, warpage can exhibit complex distribution patterns, rather than simple symmetry or regular shapes. This function, based on first-order partial derivatives, better captures this complexity. For irregular warpage patterns, differentiated temperature control can be implemented based on the warpage rate of change in different directions and locations. Larger temperature adjustments are applied to localized areas with high warpage rates, while maintaining moderate temperatures in relatively stable areas. Compared to heating methods based solely on fixed rules or simple parameters, this provides more flexibility in addressing complex and diverse warpage situations, improving the ability to resolve warpage issues across different packaging processes and material combinations, and ultimately enhancing the reliability and consistency of product packaging quality.

[0093] k3 is the warpage compensation coefficient, representing the temperature compensation per unit warpage gradient. It is used to convert the warpage slope (warpage gradient) into a temperature adjustment value. The warpage gradient A2(x,y) reflects the slope variation of a local area, such as a concave edge or wrinkles in the flexible substrate.

[0094] When k3 approaches 0, the temperature compensation T(x,y) = T0 + k3A2(x,y) becomes nearly ineffective, making it impossible to compensate for warpage via first-order derivative-guided thermal expansion differences. For example, if a region requires ±800°C compensation to offset linear warpage, but the actual compensation is only ±500°C, residual stress will still prevent adequate warpage correction.

[0095] When k3 is between 0 and ±1000, the compensation capability is limited, which may result in residual linear warping on the long side or in a local area (for example, in Example 7, it is only reduced to 0.6 mm instead of lower).

[0096] When k3 exceeds ±5000, excessively high k3 can lead to drastic fluctuations in temperature compensation. For example, if k3 = ±6000, the compensation temperature may exceed the material's temperature limit, resulting in a localized temperature spike of 500°C, inducing carbonization, delamination, or glass transition of the molding compound. Negative values ​​can cause a sudden drop in regional temperature, leading to incomplete curing or bond failure. Extreme temperature differences can also create reverse stress gradients within the package substrate, causing wavy deformation or microcracks.

[0097] Preferably, the non-uniform heating is achieved by using a non-uniform heat source.

[0098] Preferably, the non-uniform heat source includes at least one of laser zone heating, non-uniform airflow heating, microwave heating or programmable resistance heating.

[0099] It is difficult to use multiple non-uniform heating methods (such as laser, hot air flow, and microwaves) at the same time and make them work synergistically. Designs are made based on the characteristics of different heating methods. Laser local heating can accurately act on a specific small area; hot air flow heating can provide relatively uniform low-temperature heating over a large area; and microwave heating can achieve rapid internal heating. In specific implementation, a reasonable combination is made based on the package structure and warping conditions. Laser is used in local stress concentration areas, and hot air flow is used in the overall slow heating area to ensure that the advantages of each heating method complement each other and form an effective non-uniform heating temperature field.

[0100] Preferably, the uneven heating is achieved by arranging one or more heat insulation plates between the heat source and the packaging substrate.

[0101] During heating, the heat generated by the bottom heating source heats the package substrate and the thermal insulation board via thermal radiation. Areas of the package substrate not blocked by the thermal insulation board reach the curing temperature first. As heating time increases, the package substrate itself conducts heat, and the temperature of other areas blocked by the thermal insulation board slowly rises to the curing temperature. The entire package substrate gradually cures from the areas not blocked by the thermal insulation board to the areas blocked by the thermal insulation board. By using the thermal insulation board, local heat conduction is limited, creating a local temperature difference, which in turn reduces thermal expansion in that area, prevents local excessive warping, and improves package quality and reliability.

[0102] Comprehensively consider the structural and stress distribution characteristics of the package substrate. The chip mounting area, a heat-concentrated and temperature-sensitive area prone to warping due to differential thermal expansion, is typically a key location for thermal insulation board placement. At the junctions of different materials, sudden changes in thermal conductivity can easily lead to stress concentration, making this a key location for thermal insulation board placement. For example, at the edges where the chip connects to the substrate, or at the junctions between circuit boards with different layers, thermal simulation data and stress-strain models of the package substrate are analyzed to precisely locate these warping-prone areas, thereby determining the placement of the thermal insulation board. This effectively reduces local thermal expansion and stress accumulation, thereby minimizing the risk of warping.

[0103] Determining the placement of thermal shields requires comprehensive consideration of multiple factors. First, a thermal analysis of the package substrate is required to understand the temperature distribution and thermal stress in different areas during heating. For areas where temperatures rise rapidly and where significant thermal stress can easily lead to warping, such as around the chip or at the junction of different materials, thermal shields should be prioritized. Depending on the structural characteristics of the package substrate, if heat-sensitive components or functional areas are present, placing thermal shields near them can prevent overheating from affecting performance. For example, placing a thermal shield above a high-precision circuit area can prevent temperature fluctuations from interfering with signal transmission.

[0104] From the perspective of temperature field function, the temperature field described by the above-mentioned temperature field distribution function is used to analyze the temperature change trend at different positions in the function. Insulation boards are set in areas where the temperature gradient suddenly changes or high temperature is concentrated to adjust heat transfer, make the temperature distribution more uniform, and reduce warping problems caused by local overheating. In this way, the insulation boards can be reasonably arranged through the uneven heating scheme, effectively reducing the risk of warping of the package substrate and improving the package quality.

[0105] The setting method of the heat insulation board can achieve a stable spacing through a bracket or a fixing device. The height of the bracket can be adjusted according to the power of the heat source, the material of the heat insulation board and the desired temperature difference. If the power of the heat source is large, it may be necessary to appropriately increase the spacing between the heat source and the heat insulation board to prevent the heat insulation board from being damaged by overheating or excessively affecting heat transfer. The thermal conductivity of the heat insulation board material also affects the spacing setting. Materials with low thermal conductivity can allow a smaller spacing from the heat source, while materials with low thermal conductivity need to increase the spacing from the heat source. In production, multiple experimental tests are usually carried out to monitor temperature changes at different positions and the warping of the packaging substrate, and optimize and determine the appropriate spacing distance and fixing method to ensure that the heat insulation board can effectively form a local temperature difference and achieve control of warping.

[0106] The number of thermal shields is determined primarily based on the size of the package substrate, its structural complexity, and the distribution of warpage-sensitive areas. For large or complex package substrates with multiple warpage-prone areas (such as multiple chip mounting areas or areas where different materials meet), multiple thermal shields may be required. Thermal stress simulation analysis of the package substrate can be performed to identify critical areas with concentrated stress and drastic temperature changes. This can be used as a reference to determine the number of thermal shields needed to ensure that each warpage-prone area is effectively controlled, reducing the overall risk of warpage.

[0107] The size of the thermal insulation board is closely related to the scope of the critical area it covers. If the heat-affected zone around a chip is large and the temperature gradient varies significantly, the corresponding thermal insulation board should be large enough to cover this area to effectively regulate temperature and stress. At the same time, the layout of other components or circuits on the package substrate must be considered to prevent the installation of the thermal insulation board from affecting other functional structures. Generally, the boundaries of the critical area are determined based on thermal analysis. Then, based on the actual installation space and process requirements, the size of the thermal insulation board is appropriately adjusted to ensure that it can meet the temperature control requirements without interfering with the normal function of the package substrate.

[0108] The type of thermal insulation board is determined by the required thermal insulation performance and temperature control effect. If a large temperature difference is to be formed locally, a material with good thermal insulation and low thermal conductivity should be selected to make the thermal insulation board; if a specific temperature gradient distribution is to be achieved, a thermal insulation material with a certain thermal conductivity direction or a special structure may be required. For example, near temperature-sensitive chips, a high-performance ceramic thermal insulation board may be selected; in some areas with precise temperature gradient requirements, a multi-layer composite thermal insulation material or a thermal insulation board with a microstructure can be used. Through experiments and simulations, the effects of different types of thermal insulation boards in actual packaging environments are compared to select the most suitable type.

[0109] Insulation panels can be made from materials such as mica, ceramic fiber, and aerogel. Mica offers excellent thermal insulation and a certain degree of high-temperature resistance; ceramic fiber is lightweight, provides excellent thermal insulation, and exhibits strong chemical stability; and aerogel is a new, highly efficient thermal insulation material with exceptionally high thermal insulation efficiency.

[0110] The thickness of the insulation board is selected according to the actual situation and material. The thickness of the mica insulation board is between 0.1 and 2 mm. The thinner mica sheet can meet the basic insulation requirements while minimizing the packaging space occupied, which is suitable for packaging scenarios with high space requirements. The thickness of the ceramic fiber insulation board is about 2 to 5 mm, and its thickness can be adjusted according to the specific insulation requirements and packaging process. The thickness of the aerogel insulation board is in the range of 0.5 to 3 mm. Due to its excellent thermal insulation performance, even a thin thickness can have a significant insulation effect, which helps to effectively control the temperature without increasing the packaging thickness. In actual applications, it is necessary to comprehensively consider factors such as packaging process, cost, and thermal insulation effect to determine the specific material and thickness of the insulation board.

[0111] Preferably, a hollow hole is provided in the middle of the heat insulation board, and the hollow hole is square, diamond, X-shaped or circular, and the heat insulation board is used in one or more combinations.

[0112] A variety of thermal insulation boards can be used in various combinations, such as being set in different areas or overlapping in different shapes. Different shapes will form different temperature fields and can be set as needed based on the warping of the package substrate after uniform heating.

[0113] The shape and size of the thermal insulation board's perforations are crucial for precisely controlling heat conduction and creating the desired temperature differential. Extensive experiments have determined how the size and shape of the perforations (square, diamond, etc.) affect the temperature field and warpage in various packaging scenarios. For example, experiments have shown that the smaller the central square perforation, the lower the warpage of the finished product. This allows for optimized thermal insulation board design, effectively limiting heat conduction during heating, creating an ideal local temperature differential, and reducing thermal expansion and warpage in specific areas.

[0114] The specific shape of the hollow hole depends on the required temperature field distribution and packaging structure. The square shape is suitable for regular areas, such as directly above the chip or a large area of ​​uniform heating. It can provide a stable and uniform thermal insulation effect, making the temperature change in the lower area relatively gentle. Diamond and X shapes are often used in areas with specific temperature gradient requirements. For example, in multi-layer circuit boards, their unique shapes can be used to guide heat transfer along the designed path and coordinate the thermal expansion of different layers. The circle has advantages in areas where a gentle temperature transition is required, such as the edges of high-precision, thin circuit boards, to avoid warping caused by sudden temperature changes. In practical applications, different shapes of thermal insulation boards are often selected or combined according to the functional zoning, material distribution and heat flow simulation results of the packaging substrate to achieve the best thermal management and warping control effects.

[0115] The characteristics of hollow holes of different shapes are as follows:

[0116] Square Holes: Create relatively regular and stable temperature zones on the package substrate. During heating, heat is radiated to the package substrate through the square holes, ensuring uniform heating of the corresponding area. This promotes a stable thermal curing process within the area and reduces localized thermal stress concentration. For example, installing a heat shield with square holes above the chip area or functional areas requiring high temperature uniformity can ensure the packaging quality of key areas and reduce the risk of warping caused by localized uneven heating. The square areas are also easy to process and position, making them easier to operate and control dimensional accuracy in actual production.

[0117] Diamond-shaped hollow holes: These holes can create a unique temperature gradient distribution across the package substrate. Compared to a square, the corners and sides of a diamond have greater differences in distance from the heat source. During heating, this creates a temperature field that gradually shifts from the center of the diamond toward the corners. This temperature field is suitable for packaging structures with specific temperature gradient requirements. For example, in circuit boards with multiple layers and varying thermal expansion coefficients, a heat shield with diamond-shaped hollow holes can guide heat transfer along a specific path, allowing different layers of material to solidify under a suitable temperature gradient. This effectively coordinates the thermal expansion differences between layers, reduces overall warping, and improves package reliability.

[0118] X-shaped hollow holes: can create multiple intersecting temperature zones on the package substrate. The X-shaped structure causes heat to form a complex heat flow distribution when passing through the hollow holes, resulting in different temperature changes at the intersections and branch areas. For package substrates with multiple chips or complex circuit layouts, X-shaped hollow holes can provide differentiated heating based on the thermal requirements of different chips or circuit modules. In areas where the chip power is different or the temperature sensitivity is different, the X-shaped thermal insulation board can achieve fine local temperature control, balance the thermal expansion of each area, reduce warping caused by local overheating or overcooling, and improve the flatness and electrical performance stability of the package substrate.

[0119] Circular perforations provide a gentler transition in thermal radiation. The circular perimeter lacks sharp corners, allowing for a relatively gradual temperature gradient as heat is transferred from the perforation to the package substrate, creating a more continuous temperature gradient around the perimeter. Using thermal insulation panels with circular perforations near materials or structures that are sensitive to temperature fluctuations and prone to warping due to thermal shock can reduce stress concentration caused by sudden temperature changes. For example, at the edges of high-precision, thin circuit boards, circular thermal insulation panels can effectively prevent warping caused by overheating, protecting the integrity and performance of the board.

[0120] Preferably, the packaging substrate is uniformly heated to obtain a warpage function w(x, y) at each point on the packaging substrate, and a region with a larger warpage is selected to apply pressure in the opposite direction of the actual warpage:

[0121] F = -kw0;

[0122] Wherein, w0 is the average value of w(x, y) in the selected area, and k = 0.05 to 0.3 kPa / mm.

[0123] Warping is reduced by continuously applying pressure F during the curing process. In a specific embodiment, pressure in a desired direction is applied to the package substrate by means of gravity pressing of a pressing block, pressing of a pressing block supported by an external force, or vacuum pulling of a suction cup.

[0124] When k < 0.05 kPa / mm, the applied pressure is too low (e.g., k = 0.02 kPa / mm) to effectively offset the warpage caused by curing shrinkage. For example, if w0 = 2 mm, then F = -0.02 × 2 = -0.04 kPa. This pressure is insufficient to correct the deformation, and the final warpage value may only be reduced from 2.2 mm to 2.0 mm, failing to meet high flatness requirements.

[0125] When k > 0.3 kPa / mm, an excessively large k (e.g., k = 0.4 kPa / mm) can result in excessive pressure (F = -0.4 × 2 = -0.8 kPa), potentially crushing internal package substrate structures, such as microbumps or circuits, or causing substrate delamination. Especially in thin packages (e.g., the 0.3 mm substrate in Example 6), excessive pressure can directly lead to mechanical damage.

[0126] A packaging substrate is prepared using the above-mentioned fan-out panel-level packaging process, and has a warpage of less than 1 mm.

[0127] Through uneven heating and the use of thermal insulation boards, heat conduction is limited to form local temperature differences, further reducing local thermal expansion, controlling the distribution of stress within the package substrate, rebalancing the internal stress in each area of ​​the package substrate, reducing the overall warping amplitude, and preventing local excessive warping. During the entire curing process, a pressure F opposite to the actual warping direction is applied to the package substrate to further reduce the warping of the package substrate.

[0128] Comparative Example

[0129] The size of the package substrate 1 is 150×150 mm 2 First, evenly apply 3mm thick plastic compound on the surface of the package substrate 1, and evenly heat it to obtain the finished product. The warpage value is as follows Figure 8 shown.

[0130] Example 1

[0131] The size of the package substrate 1 is 150×150 mm 2 ,like Figure 1 、 Figure 3 and Figure 4 As shown, first evenly apply 3mm thick plastic compound on the surface of the package substrate 1, and then 2The heat insulation board 2 is placed on the perforated quartz board 4 supported by the ceramic rod 3 and arranged between the heat source 5 and the package substrate 1. Then the package substrate 1 is heated and solidified to obtain the finished product. The warpage value is as follows: Figure 9 shown.

[0132] By adding the thermal insulation board, the warpage value of the finished product is greatly reduced.

[0133] Example 2

[0134] The size of the package substrate 1 is 150×150 mm 2 First, evenly apply 3mm thick plastic compound on the surface of the package substrate 1, using a size of 150×150mm 2 The heat insulation board is cut into square hollow holes of different sizes, and the heat insulation board 2 with directional hollow holes is placed on the perforated quartz plate 4 supported by the ceramic rod 3, and is set between the heat source 5 and the packaging substrate 1. The packaging substrate 1 is then heated and cured to obtain a finished product.

[0135] The warpage value of the final product varies with the size of the hollow hole. The smaller the hollow hole area, the lower the warpage value of the finished product. This is because the stress concentration on multiple interfaces is released during the step-by-step curing process, which reduces the final warpage value. For comparison, a single controlled temperature increase without using a heat shield is performed, and the warpage value of the finished product is as follows: Figure 10 As shown in the figure, package warpage increases with increasing heating rate. This is because increasing heating rate accelerates the crosslinking and curing process of the EMC molecular chains, causing more stress accumulation and thus increasing warpage. This comparison shows that by using thermal insulation panels in specific areas to reduce heat conduction, thereby achieving localized temperature reduction and controlling warpage, warpage can be reduced.

[0136] Example 3

[0137] The package substrate size is 400×400mm, for example Figure 2 As shown in the figure, the temperature field function is used to solve the problem of severe center warping (2.0mm) caused by uniform heating of a 400×400mm large-size package substrate:

[0138] T(x,y)=k1(x 2 +y 2 ) n +T0;

[0139] The curing temperature of the plastic compound is T0, which is 200℃ and k1=800℃ / m 2.4 , n = 1.2, causing the center area to be heated first to 260°C and then slowly to 200°C at the edges, forming a curing sequence from the inside out. This method reduces center warpage to 0.5mm and edge warpage to 0.4mm by slowing stress accumulation at the edges, significantly improving the flatness of large-scale package substrates.

[0140] Example 4

[0141] The package substrate size is 500×500mm. When uniformly heated, the edge of the package substrate will be warped (1.8mm) due to uneven thermal expansion. Figure 5 As shown, a heat shield with diamond-shaped perforations is used. The shield measures 500 x 500 mm, with a 50 mm side. The shield covers the edges, limiting heat transfer and allowing the center to quickly heat up to 240°C while the edges reach only 180°C. By suppressing edge thermal expansion, the overall warpage is reduced to 0.6 mm, making it suitable for controlling edge stress in large packages.

[0142] Example 5

[0143] The package substrate size is 300×300mm. When uniformly heated, the stress of the package substrate is concentrated. The chip solder joint area of ​​the package substrate is a high stress area with a warpage of 1.5mm. The warpage distribution w(x,y) is measured and its second-order partial derivative A1(x,y) is calculated using the temperature field function:

[0144] T(x,y)=T0+k2A1(x,y);

[0145] Among them, the curing temperature T0 of the plastic encapsulation material is 200℃, k2=500℃·m, and the heating temperature field is adjusted according to the function T(x,y)=200+500A1(x,y). The warpage value is reduced to 0.7mm, achieving precise stress balance.

[0146] Example 6

[0147] The size of the package substrate is 600×600mm. When uniformly heated, the package substrate is deformed as a whole. Figure 7 As shown in the figure, for the overall warpage (2.2mm) of a 600×600mm large-size package substrate caused by material shrinkage, reverse pressure compensation is used, according to the formula:

[0148] F = -kw0;

[0149] Where k = 0.25 kPa / mm, according to the formula F = -0.25w0, by placing four pressure blocks 6 at the four corners of the package substrate 1, the pressure block 6 is a square iron block with a bottom side length of 50 mm, and the weight of a single pressure block 6 is 34.375 N. A pressure F / 4 = 55 / 4 = 13.75 kPa opposite to the warping direction is applied until the curing is completed. The final warping value is reduced to 0.8 mm, meeting the high flatness requirement of large-size package warping value ≤ 1 mm and complying with the package substrate flatness grade Class 3 (IPC-6012 standard).

[0150] Example 7

[0151] Laser and microwave combined heating is adopted. The size of the package substrate is 350×350mm and the thickness is 0.3mm. In order to solve the problem of local overheating of the 0.3mm thin package substrate, laser and microwave combined heating is adopted. The laser (power 800W / cm 2 ) Scan the four corners and the center to 210 ° C, and microwave-assisted heating of the remaining areas to 180 ° C to form an uneven heating temperature field, resulting in a finished product warpage of 0.3 mm, which is suitable for high-precision thin packaging.

[0152] Example 8

[0153] The package substrate size is 550×550mm. It warps 1.6mm when uniformly heated. The warpage distribution w(x,y) is measured and its first-order partial derivative A2(x,y) is calculated using the temperature field function:

[0154] T(x,y)=T0+k3A2(x,y);

[0155] Among them, the curing temperature T0 of the plastic encapsulation material is 200℃, k3=3000℃, and the heating temperature field is adjusted according to the function T(x,y)=200+3000A2(x,y). The warpage is reduced to 0.6mm and the flatness is increased by 62%, effectively solving the problem of large-size deformation.

[0156] Example 9

[0157] The size of the package substrate is 600×600mm. When uniformly heated, the stress in the center of the package substrate is concentrated, and the warpage of the center area due to concentrated thermal expansion is 1.5mm. Figure 6 As shown, a thermal insulation board with X-shaped perforations (100mm long, 10mm wide, and a 90° angle between adjacent sides) is used. The X-shaped perforations guide heat along a radial path, preferentially transferring it to the center. The edges, constrained by the insulation, form a decreasing temperature gradient from the center (240°C) to the edges (180°C). This achieves precise temperature control, prompting the center to solidify first and release stress, avoiding stress concentration caused by heat accumulation in the center. Compared to square or diamond-shaped perforations, X-shaped perforations can evenly disperse the heat flow path, adapting to the multi-directional stress balance requirements of large-scale package substrates, ultimately reducing the center warpage value to 0.4mm while improving the overall structural stability.

[0158] Other structures and operations according to the embodiments of the present invention are well known to those skilled in the art and will not be described in detail here.

[0159] Throughout this specification, reference to terms such as "embodiment" or "example" indicates that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0160] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the claims and their equivalents.

Claims

1. A board-level packaging process for suppressing warpage, characterized by: First, a liquid molding compound is coated on the packaging substrate, and the molding compound is heated and cured to obtain a packaging substrate with a molding layer. During the heating and curing process, uneven heating is performed according to a set temperature field function, and / or pressure is applied to a part of the packaging substrate.

2. The board-level packaging process for suppressing warpage according to claim 1, characterized in that: The heating temperature field distribution function of the non-uniform heating is: T(x,y)=k1(x 2 +y 2 ) n +T0; Among them, the center of the substrate is the coordinate origin, k1=±300~1000℃ / m2 n , n = 0.7 ~ 1.5, T0 is the curing temperature of the plastic compound.

3. The board-level packaging process for suppressing warpage according to claim 1, wherein: By pre-uniformly heating the package substrate coated with liquid molding compound, or by real-time monitoring the package substrate during the heating and curing process, the warpage function w(x, y) at each point on the package substrate is obtained. The second-order partial derivative of the warpage function w(x, y) in different regions of the package substrate is: The heating temperature field distribution function of the non-uniform heating is: T(x,y)=T0+k2A1(x,y); Wherein, k2 = ±100~1000℃·m, T0 is the curing temperature of the plastic compound.

4. The board-level packaging process for suppressing warpage according to claim 1, wherein: By pre-uniformly heating the package substrate coated with liquid molding compound, or by real-time monitoring the package substrate during the heating and curing process, the warpage function w(x, y) of each point on the package substrate is obtained. The first-order partial derivative of the warpage w(x, y) of the package substrate in different regions is: The heating temperature field distribution function of the non-uniform heating is: T(x,y)=T0+k3A2(x,y); Where: k3 = ±1000~5000℃, T0 is the curing temperature of the plastic compound.

5. The board-level packaging process for suppressing warpage according to claim 1, wherein: The non-uniform heating is achieved by using a non-uniform heat source.

6. The board-level packaging process for suppressing warpage according to claim 5, characterized in that: The non-uniform heat source includes at least one of laser zone heating, non-uniform airflow heating, microwave heating or programmable resistance heating.

7. The board-level packaging process for suppressing warpage according to claim 1, wherein: The non-uniform heating is achieved by arranging one or more heat insulation plates between the heat source and the packaging substrate.

8. The board-level packaging process for suppressing warpage according to claim 7, characterized in that: A hollow hole is provided in the middle of the heat insulation board. The hollow hole is square, diamond, X-shaped or circular. The heat insulation board is used in one or more combinations.

9. The board-level packaging process for suppressing warpage according to claim 1, wherein: By uniformly heating the package substrate, the warpage function w(x,y) of each point on the package substrate is obtained. The area with the largest warpage is selected and a pressure opposite to the actual warpage direction is applied: F = -kw0; Wherein, w0 is the average value of w(x, y) in the selected area, and k = 0.05 to 0.3 kPa / mm.

10. A packaging substrate, characterized in that: The fan-out panel-level packaging process according to any one of claims 1 to 9 is used for preparation, and the warpage is less than 1 mm.

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