SOP solder ball leveling method based on cutting process

Abstract

The invention discloses an SOP (Small Outline Package) solder ball leveling method based on a cutting process, which relates to the technical field of semiconductor processing, and comprises the following steps: acquiring a substrate on which solder balls are mounted, and fixing the substrate on a processing platform of cutting equipment; measuring the initial height of the solder ball, and setting the downward probing depth of a blade of cutting equipment based on the initial height and a preset target height; and starting the cutting equipment, and mechanically cutting the top of the solder ball by using a blade of the cutting equipment. The redundant part at the top of the solder ball can be cut off through the cutting equipment, leveling of the solder ball is achieved, and special hot pressing equipment depended on by a traditional technology does not need to be adopted. According to the technical scheme, a packaging enterprise can directly use existing cutting equipment to implement transformation without depending on a special hot-pressing production line of a substrate manufacturer, especially in the small-batch trial production stage, the enterprise can autonomously control the production rhythm, and the problem of research and development stagnation caused by dependence of an external supply chain is effectively relieved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor processing technology, and in particular to a method for leveling SOP solder balls based on a cutting process. Background Technology

[0002] As semiconductor packaging technology advances towards high-density integration, the chip size of flip-chip products continues to increase, placing higher demands on substrate soldering processes. Against this backdrop, the SOP (Solder On Pad) process has been widely adopted due to its advantage in improving solder joint reliability. The core of this process is the precise flattening of the micro-solder balls on the substrate pads. Traditional methods rely on specialized thermoforming equipment—heating and softening the solder balls and applying vertical mechanical pressure to induce plastic deformation, ultimately forming a flat solder joint surface that meets the requirements.

[0003] The industry currently faces a triple dilemma: First, the equipment required for this hot-pressing process is complex and expensive, integrating a precision temperature control system, a hydraulic pressurization module, and a high-precision positioning mechanism, resulting in high equipment procurement and maintenance costs. Second, there is a significant technological gap in the domestic substrate manufacturing industry chain in this field; most manufacturers lack the relevant equipment and technological accumulation to provide qualified SOP substrate processing services. More importantly, a few leading international substrate suppliers who possess this technology typically set minimum order quantities, explicitly refusing small-batch trial production orders due to capacity allocation and economic considerations. This supply chain structure severely restricts packaging companies in the early stages of product development: when new products are in the verification phase, companies cannot obtain the necessary substrates through the domestic supply chain, nor can they meet the order volume requirements of foreign manufacturers, forcing the R&D process to be interrupted. Even in rare cases where contract manufacturing services can be obtained at extremely high premiums, problems such as uncontrollable delivery cycles and poor technical communication severely hinder R&D efficiency. Summary of the Invention

[0004] The technical problem to be solved by the embodiments of the present invention is: how to flatten the micro solder balls on the substrate pads.

[0005] To address the aforementioned problems, this invention proposes a method for leveling SOP solder balls based on a cutting process, comprising: S1, Obtain the substrate with solder ball mounting completed, and fix the substrate on the processing platform of the cutting equipment; S2, Measure the initial height of the solder ball, and set the blade depth of the cutting device based on the initial height and the preset target height; S3, start the cutting equipment and use the blade of the cutting equipment to mechanically cut the top of the solder ball.

[0006] A further technical solution is that, after step S3, the method further includes: S4, Measure the height of the cut solder ball and determine whether the height of the cut solder ball reaches the target height; S5. If the height of the cut solder ball does not reach the target height, the blade depth of the cutting device is reset based on the height of the cut solder ball and the target height, and the process proceeds to step S3.

[0007] A further technical solution is that determining whether the height of the cut solder ball reaches the target height includes: Determine whether the difference between the height of the cut solder ball and the target height is less than a preset difference threshold; If the difference between the height of the cut solder ball and the target height is less than a preset difference threshold, it is determined that the height of the cut solder ball has reached the target height. If the difference between the height of the cut solder ball and the target height is not less than a preset difference threshold, it is determined that the height of the cut solder ball has not reached the target height.

[0008] A further technical solution is that measuring the initial height of the solder ball includes: The initial height of the solder ball is measured using a preset height measuring unit; The measurement of the height of the cut solder ball includes: The height of the cut solder ball is measured using a preset height measurement unit.

[0009] A further technical solution is that, in step S3, the cutting process is carried out at room temperature without applying an external heat source.

[0010] A further technical solution is that the initial height of the solder ball is 25±5um.

[0011] A further technical solution is that the target height is 10±5um.

[0012] A further technical solution is that the cutting equipment is a Tape Saw cutter.

[0013] A further technical solution is that the blade rotation speed of the Tape Saw cutting machine is set to 1000-5000 rpm.

[0014] A further technical solution is that, before step S1, the method further includes: cleaning the substrate to remove flux from the substrate.

[0015] Compared with the prior art, the technical effects achieved by the embodiments of the present invention include: This invention provides a method for SOP solder ball leveling based on a cutting process, comprising: acquiring a substrate with solder balls already mounted; fixing the substrate on the processing platform of a cutting device; measuring the initial height of the solder balls; setting the blade depth of the cutting device based on the initial height and a preset target height; starting the cutting device; and mechanically cutting the top of the solder balls using the blade of the cutting device. This invention can remove excess material from the top of the solder balls using a cutting device, achieving leveling of the solder balls without the need for dedicated thermoforming equipment required by traditional processes. By applying the technical solution of this invention, packaging companies can directly modify existing cutting equipment without relying on the substrate manufacturer's dedicated thermoforming production line. Especially in the small-batch trial production stage, companies can independently control the production pace, effectively alleviating the R&D stagnation problem caused by dependence on external supply chains. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] One or more embodiments are illustrated by way of example with reference numerals in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0019] Figure 1 A schematic flowchart of a SOP solder ball leveling method based on a cutting process is provided for an embodiment of the present invention; Figure 2 A schematic diagram illustrating the principle of a SOP solder ball leveling method based on a cutting process, provided in an embodiment of the present invention; Figure 3 The SOP process flow diagram provided for embodiments of the present invention. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Similar component reference numerals in the drawings represent similar components. Obviously, the embodiments described below are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0022] It should also be understood that the terminology used in this specification of embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of the invention. As used in this specification of embodiments of the invention and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0023] See Figures 1-2 This invention proposes a method for leveling SOP solder balls based on a cutting process, the method comprising the following steps: S1, Obtain the substrate with solder ball mounting completed, and fix the substrate on the processing platform of the cutting equipment.

[0024] In practice, a substrate with solder ball mounting completed is obtained and fixed on the processing platform of a cutting device. For example, the substrate can be fixed using a pre-set fixture on the processing platform.

[0025] See Figure 3 In some preferred embodiments, prior to step S1, the method further includes cleaning the substrate to remove flux from the substrate.

[0026] In this invention, a flux cleaning step is added before cutting to address the inherent contamination risk of mechanical cutting: residual flux softens and adheres to the cutting teeth in the high-temperature cutting zone (local temperature >80°C during blade friction), causing fluctuations in cutting force. This invention removes surface organic matter through plasma cleaning or solvent spraying, exposing the solder ball's bare metal body and ensuring uniform force distribution during the cutting process.

[0027] S2, Measure the initial height of the solder ball, and set the cutting depth of the blade based on the initial height and the preset target height.

[0028] In practice, the initial height of the solder ball is measured, and the cutting depth of the blade is set based on the initial height and a preset target height. Specifically, the cutting depth is equal to the difference between the initial height and the target height.

[0029] In some preferred embodiments, the initial height of the solder ball is measured by a preset height measuring unit.

[0030] In this invention, the height of the solder balls is measured by a height measuring unit (such as a laser displacement sensor), replacing manual micrometer measurement. This height measuring unit is integrated with the cutting equipment to form an online inspection system. Its technical advantages are: first, non-contact measurement avoids mechanical probes scratching the surface of the solder balls, which is especially important for protecting small-diameter micro-solder joints; second, the laser scanning rate can reach thousands of points per second, achieving 100% inspection of all solder balls on the board.

[0031] In some preferred embodiments, the initial height of the solder ball is 25±5 μm. For example, the initial height of the solder ball can be 20 μm, and the present invention does not specifically limit this.

[0032] Furthermore, the target height is 10±5µm. For example, a target height of 10µm ensures that the cut solder balls can achieve reliable electrical connections.

[0033] S3, start the cutting equipment and use the blade of the cutting equipment to mechanically cut the top of the solder ball.

[0034] In practice, the cutting equipment is started, and the blade of the cutting equipment is used to mechanically cut the top of the solder ball. The depth to which the blade penetrates is based on the setting in step S2. The blade penetration depth refers to the depth to which the blade penetrates from the highest point of the solder ball.

[0035] In some preferred embodiments, in step S3, the cutting process is carried out at room temperature without the application of an external heat source.

[0036] In this invention, "room temperature" refers to a temperature environment of 20-25°C, or room temperature. Using room temperature cutting completely avoids the inherent defects of hot pressing: firstly, eliminating the heating step greatly saves energy; secondly, it eliminates stress deformation caused by differences in the coefficients of thermal expansion (CTE) of the materials. For example, in hot pressing, the solder balls and the substrate experience thermal displacement differences at high temperatures, leading to uneven local bonding. Mechanical cutting, performed in thermodynamic equilibrium, effectively avoids these thermal displacement differences.

[0037] In some preferred embodiments, after step S3, the method further includes: S4. Measure the height of the cut solder ball and determine whether the height of the cut solder ball reaches the target height.

[0038] S5. If the height of the cut solder ball does not reach the target height, reset the depth of the blade of the cutting device based on the height of the cut solder ball and the target height, and go to step S3.

[0039] In specific implementation, height detection and feedback adjustment are added after the cutting action to form a closed-loop control system. Specifically, the real-time measurement of the height of the solder ball after cutting in step S4 can identify the processing errors caused by tool wear or substrate deformation; when the detected value does not meet the standard, in S5, the depth of the blade is recalculated based on the dynamic difference between the measured height and the target height (instead of a fixed compensation value). For example, when the residual height after the first cutting exceeds the standard, the system automatically increases the depth of the second cutting according to the difference ratio. This adaptive adjustment mechanism improves the process stability in three aspects: First, it compensates for the attenuation of the cutting force caused by tool wear and avoids batch height non-compliance (the yield rate drops sharply at the end of the tool life in traditional open-loop processing); Second, it eliminates the local height fluctuations caused by substrate warping and ensures the flatness of the whole board through point-by-point calibration; Third, it reduces the dependence on the operator's experience, and the system autonomously completes the accuracy iteration.

[0040] In some preferred embodiments, the height of the cut solder ball is measured by a preset height measurement unit.

[0041] In the present invention, the height measurement of the solder ball after cutting is performed by a height measurement unit (such as a laser displacement sensor), ensuring the accuracy of the measurement.

[0042] In some preferred embodiments, the above step "judging whether the height of the cut solder ball reaches the target height" specifically includes the following steps: judging whether the difference between the height of the cut solder ball and the target height is less than a preset difference threshold; if the difference between the height of the cut solder ball and the target height is less than the preset difference threshold, it is determined that the height of the cut solder ball reaches the target height; if the difference between the height of the cut solder ball and the target height is not less than the preset difference threshold, it is determined that the height of the cut solder ball does not reach the target height.

[0043] In specific implementation, a quantitative criterion for reaching the height standard is constructed through a preset difference threshold, converting the subjective "meeting the standard" judgment into an objective mathematical comparison. When the absolute difference between the measured height and the target height is less than the threshold, it is determined to be qualified, avoiding over-processing (such as the qualified product being cut twice, resulting in insufficient height); when the difference exceeds the threshold, the re-cutting process is triggered to ensure that the unqualified product must be repaired. The essence of this threshold design is to seek an optimal solution between processing efficiency and accuracy: if the threshold is too wide, the critical defective products will be let go, resulting in local virtual soldering during welding; if the threshold is too strict, the detection frequency will be greatly increased, reducing the equipment utilization rate.

[0044] In some preferred embodiments, the cutting device is a Tape Saw cutter. The blade rotation speed of the Tape Saw cutter is set to 1000-5000 rpm.

[0045] In this invention, a tape saw cutter is used with a limited rotation speed of 1000-5000 rpm to maximize the utilization of equipment resources. If the rotation speed is too low (e.g., below 1000 rpm), the solder balls are prone to ductile tearing, resulting in burrs on the cut surface; if the rotation speed is too high (e.g., above 5000 rpm), solder shavings are likely to splash and contaminate the substrate. Within the preferred rotation speed range of 1000-5000 rpm, the blade linear velocity is matched with the solder ball strain rate, achieving a brittle fracture mode. The solder balls undergo adiabatic shearing at the critical shear strain rate, forming a smooth and flat cut surface, thereby ensuring the quality of the cut.

[0046] This invention provides a method for SOP solder ball leveling based on a cutting process, comprising: acquiring a substrate with solder balls already mounted; fixing the substrate on the processing platform of a cutting device; measuring the initial height of the solder balls; setting the blade depth of the cutting device based on the initial height and a preset target height; starting the cutting device; and mechanically cutting the top of the solder balls using the blade of the cutting device. This invention can remove excess material from the top of the solder balls using a cutting device, achieving leveling of the solder balls without the need for dedicated thermoforming equipment required by traditional processes. By applying the technical solution of this invention, packaging companies can directly modify existing cutting equipment without relying on the substrate manufacturer's dedicated thermoforming production line. Especially in the small-batch trial production stage, companies can independently control the production pace, effectively alleviating the R&D stagnation problem caused by dependence on external supply chains.

[0047] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0048] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0049] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0050] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0051] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0052] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. The illustrative expressions of the above terms in this specification should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0053] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Since these modifications and variations fall within the scope of the claims and their equivalents, this invention also intends to include these modifications and variations.

[0054] The above description describes specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for flattening SOP solder balls based on a cutting process, characterized by, The method comprises the following steps: S1, obtaining a substrate on which solder balls have been mounted, and fixing the substrate on a machining platform of a cutting device; S2, measuring an initial height of the solder balls, and setting a depth of a blade of the cutting device based on the initial height and a preset target height; S3, starting the cutting device, and mechanically cutting the top of the solder balls by using the blade of the cutting device.

2. The SOP solder ball flattening method based on a cutting process according to claim 1, wherein, After step S3, the method further comprises: S4, measuring a height of the solder balls after cutting, and determining whether the height of the solder balls after cutting reaches the target height; S5, if the height of the solder balls after cutting does not reach the target height, resetting the depth of the blade of the cutting device based on the height of the solder balls after cutting and the target height, and returning to step S3.

3. The SOP solder ball flattening method based on a cutting process according to claim 2, wherein, The determination of whether the height of the solder balls after cutting reaches the target height comprises: determining whether a difference between the height of the solder balls after cutting and the target height is less than a preset difference threshold value; if the difference between the height of the solder balls after cutting and the target height is less than the preset difference threshold value, determining that the height of the solder balls after cutting reaches the target height; if the difference between the height of the solder balls after cutting and the target height is not less than the preset difference threshold value, determining that the height of the solder balls after cutting does not reach the target height.

4. The SOP solder ball flattening method based on a cutting process according to claim 2, wherein, The measurement of the initial height of the solder balls comprises: measuring the initial height of the solder balls by using a preset height measuring unit. The measurement of the height of the solder balls after cutting comprises: measuring the height of the solder balls after cutting by using a preset height measuring unit.

5. The cut-process based SOP tin ball flattening method of claim 1, wherein, In step S3, the cutting process is performed at room temperature without applying an external heat source.

6. The cut-process based SOP tin ball flattening method of claim 1, wherein, The initial height of the solder balls is 25±5 um.

7. The SOP solder ball flattening method based on a cutting process according to claim 6, wherein, The target height is 10±5 um.

8. The SOP solder ball flattening method based on a cutting process according to claim 1, wherein, The cutting device is a Tape Saw cutting machine.

9. The SOP solder ball flattening method based on a cutting process according to claim 8, wherein, The rotating speed of the blade of the Tape Saw cutting machine is set to 1000-5000 rpm.

10. The SOP solder ball flattening method based on a cutting process according to claim 1, wherein, Before step S1, the method further comprises cleaning the substrate to remove flux on the substrate.

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