A WF process and its application in DFN packaging

Abstract

The present invention belongs to the field of DFN packaging technology and provides a WF process and its application in DFN packaging. The WF process includes: forming grooves in the side of the DFN package so that the solder pads extend from the bottom to the side; forming a nickel coating on the side solder pads of the DFN package using a chemical electroplating method; and performing quality inspection on the formed nickel coating. Through the WF process, the present invention can significantly enhance the soldering strength and reliability of the side solder pads of the DFN package, improving the overall performance and stability of the package. The formation of the nickel coating not only enhances the corrosion resistance and wear resistance of the solder pads, but also improves the electrical conductivity of the solder pads, resulting in superior performance of the DFN package in applications.

Description

Technical Field

[0001] The present invention relates to the technical field of DFN packaging, and in particular to a WF process and its application in DFN packaging. Background Art

[0002] The DFN (Dual-Flat-no-lead) package is a common electronic packaging format. Due to its small size, light weight, and excellent electrical performance, it is widely used in the packaging of power devices (such as MOSFETs and IGBTs), LEDs, laser diodes, and other electronic components. With the trend toward higher performance and smaller size in electronic products, the demand for DFN packages continues to increase, especially in scenarios requiring high power density and high reliability.

[0003] Traditional DFN packaging processes typically utilize reflow soldering technology. The basic process is as follows: 1. The package (including the chip) is fixed to the substrate through a molding process. 2. Multiple solder pads (typically made of metal materials such as copper or tin) are placed on the bottom of the package. 3. Flux is applied to the pads, and the package is then aligned with the corresponding pads on the PCB (printed circuit board). 4. Reflow soldering equipment (typically using infrared heating or hot air circulation) heats the package and PCB, melting the flux and forming solder, ultimately establishing an electrical connection between the package and the PCB.

[0004] The traditional DFN packaging process has the following major issues in practical applications: First, AOI inspection is inconvenient. Traditional AOI inspection equipment usually performs optical inspection from the top of the package, while the pads are located at the bottom of the package. This makes it impossible to directly observe the soldering quality of the bottom pads, which can easily lead to missed inspections or false inspections. Second, the solder climbing performance and pad wettability are insufficient. In the traditional DFN packaging process, the solder climbing height on the pad is insufficient, resulting in the solder not being able to evenly cover the entire pad, which easily forms air holes or gaps, further increasing the risk of solder defects.

[0005] In summary, the traditional DFN packaging process has significant shortcomings in terms of soldering quality and inspection efficiency. These issues not only affect the reliability of the packaged product but also increase production costs and time. Therefore, an improved packaging process is urgently needed to address these issues by optimizing pad design, flux selection, and soldering process parameters, thereby improving soldering reliability and production efficiency.

[0006] The WF process refers to the Wettable-Flanks process. The WF process mainly optimizes the side structure design of the DFN package to improve the wettability of the pad and the welding quality, while facilitating AOI inspection.

[0007] Therefore, it is necessary to provide a WF process and its application in DFN packaging. Summary of the Invention

[0008] The present invention provides a WF process and its application in DFN packaging. Through the WF process, the welding strength and reliability of the side pads of the DFN package can be significantly enhanced, thereby improving the overall performance and stability of the package. The formation of the nickel plating layer not only enhances the corrosion resistance and wear resistance of the pads, but also improves the electrical conductivity of the pads, so that the DFN package exhibits more superior performance in application.

[0009] The present invention provides a WF process, comprising:

[0010] Step 1: Create a groove on the side of the DFN package so that the pad extends from the bottom to the side.

[0011] Step 2: Using a chemical electroplating method, a nickel plating layer is formed on the pads on the side of the DFN package;

[0012] Step 3: Perform quality inspection on the formed nickel plating layer.

[0013] Furthermore, the groove has an inclination angle of 30°-60° and a depth of 0.1-0.3 mm.

[0014] Furthermore, the cross section of the groove is trapezoidal or semicircular.

[0015] Furthermore, the thickness of the nickel plating layer is 6-10 μm.

[0016] Furthermore, the thickness change rate of the nickel plating layer after 108 hours of high-temperature cooking is ≤2%; the high-temperature temperature range is 120°C to 122°C.

[0017] Furthermore, the solder coverage area of the nickel plating layer is ≥95%, and the porosity is ≤0.5%.

[0018] An application of a WF process in DFN packaging includes:

[0019] Use WF process for DFN package packaging;

[0020] The encapsulated DFN package is electrically connected to the external circuit by welding using the pads on the side.

[0021] The performance of the packaged DFN package and external circuit is tested.

[0022] Furthermore, the thrust value of the device in the packaged DFN package is obtained based on a thrust test.

[0023] Furthermore, the pads on the side of the DFN package are optically inspected by AOI inspection equipment.

[0024] Furthermore, optical inspection of the pads on the side of the DFN package is performed using AOI inspection equipment, which also includes obtaining a welding quality score of the pads on the side of the DFN package, specifically:

[0025] The multi-angle annular light source array is used to illuminate the pads on the side of the DFN package in a time-sharing manner to obtain multi-angle images;

[0026] Perform wavelet transform fusion on multi-angle images to generate high-contrast fused images;

[0027] Use the improved U-Net++ network to segment the pad area in the high-contrast fusion image. The improved U-Net++ network integrates the CBAM attention module and the morphological constraint loss function;

[0028] Based on the 3D topography reconstruction results of the pad area in the segmented high-contrast fused image, the pad wetting angle and coverage are calculated, and the welding quality score is obtained. Based on the comparison result between the welding quality score and the set welding quality score threshold, automatic rework or production process optimization suggestions are triggered.

[0029] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0030] 1. The present invention effectively increases the area of the pad by opening a groove on the side of the DFN package and forming a nickel plating layer in the groove, thereby improving the welding reliability and stability between the DFN package and the external circuit.

[0031] 2. Nickel plating has good corrosion resistance and high temperature resistance. After high-temperature cooking, the thickness change rate is small, ensuring the reliability of the DFN package in long-term working environments.

[0032] 3. Optical inspection of the side pads of the DFN package using AOI equipment can quickly and accurately evaluate the welding quality, improving production efficiency and product quality.

[0033] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description and the accompanying drawings.

[0034] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0036] Figure 1 Schematic diagram of a WF process step;

[0037] Figure 2 A schematic diagram of the steps of applying a WF process to DFN packaging;

[0038] Figure 3 Schematic diagram of the steps in the method for obtaining a weld quality score. DETAILED DESCRIPTION

[0039] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0040] The present invention provides a WF process, such as Figure 1 Shown, including:

[0041] Step 1: Create a groove on the side of the DFN package so that the pad extends from the bottom to the side.

[0042] Step 2: Using a chemical electroplating method, a nickel plating layer is formed on the pads on the side of the DFN package;

[0043] Step 3: Perform quality inspection on the formed nickel plating layer.

[0044] The working principle of the above technical solution is as follows: in order to implement a WF process, the present invention first extends the pad from the bottom to the side of the DFN package by opening a groove. This can increase the contact area between the pad and the external environment, providing a better adhesion foundation for the subsequent electroplating process; then, a nickel plating layer is formed on the pad using a chemical electroplating method. The nickel plating layer not only has good conductivity and corrosion resistance, but also can effectively protect the pad from the influence of the external environment; finally, the formed nickel plating layer is quality tested to ensure the uniformity and integrity of the plating layer to meet the requirements of the subsequent packaging process.

[0045] The beneficial effects of the above technical solution are as follows: the solution provided in this embodiment can effectively increase the contact area of the side pads of the DFN package, thereby improving the reliability and stability of the connection between the pads and the outside; at the same time, the formation of the nickel plating layer not only enhances the conductivity and corrosion resistance of the pads, but also provides an additional protective layer for the package, further extending the service life of the product; in addition, through the quality inspection step, the uniformity and integrity of the plating are ensured, effectively avoiding package failures caused by plating quality problems, and improving production efficiency and product quality.

[0046] In one embodiment, the groove has an inclination angle of 30°-60° and a depth of 0.1-0.3 mm.

[0047] The working principle of the above technical solution is: the inclination angle of the groove design is controlled between 30°-60°, which can ensure that the pad can maximize the contact area while extending to the side, while maintaining the stability and reliability of the structure, and avoid uneven plating or falling off due to excessive angles during the electroplating process; and the depth is set to 0.1-0.3mm, which is designed based on electroplating efficiency and plating quality. Too shallow may lead to insufficient plating adhesion, and too deep may increase the difficulty and cost of electroplating, and even affect the overall strength of the package.

[0048] The beneficial effects of the above technical solution are as follows: by adopting the solution provided in this embodiment, the groove design further strengthens the connection between the pad and the external environment, laying a solid foundation for the subsequent electroplating process; by precisely controlling the inclination angle and depth of the groove, not only the electroplating effect is optimized, but also the performance and reliability of the entire DFN package are improved.

[0049] In one embodiment, the cross section of the groove is trapezoidal or semicircular.

[0050] The working principle of the above technical solution is: the trapezoidal or semicircular cross-section design can further optimize the flow and distribution of the electroplating solution in the groove; the trapezoidal cross-section can guide the electroplating solution to cover the pad surface more evenly through its gradually changing width, reducing dead corners and unevenness during the electroplating process; and the semicircular cross-section, with its smooth curve, helps the electroplating solution form a more stable liquid film in the groove, further improving the uniformity and density of the coating.

[0051] The beneficial effect of the above technical solution is that the solution provided by this embodiment helps to improve the electroplating efficiency and the quality of the plating layer, thereby enhancing the overall performance and reliability of the DFN package.

[0052] In one embodiment, the thickness of the nickel plating layer is 6-10 μm.

[0053] The working principle of the above technical solution is as follows: As a key component of the DFN package, the thickness control of the nickel plating layer is crucial to the overall performance. When the thickness of the nickel plating layer is maintained in the range of 6-10μm, it can effectively enhance the bonding strength between the pad and the package while providing sufficient conductivity and corrosion resistance. The selection of this thickness is based on a comprehensive consideration of the nickel ion deposition rate, plating stress, and package reliability during the electroplating process. The nickel plating layer is formed by the nickel ions in the electroplating solution undergoing a reduction reaction on the pad surface under the action of an electric field. During the electroplating process, by precisely controlling the composition, temperature, current density and other parameters of the electroplating solution, it is possible to ensure that the nickel ions are uniformly and quickly deposited on the pad surface, forming a nickel plating layer of the desired thickness. At the same time, the thickness uniformity of the nickel plating layer is also achieved by precisely controlling the electroplating time and the flow state of the electroplating solution.

[0054] The beneficial effect of the above technical solution is that the overall performance and reliability of the DFN package can be further improved by adopting the solution provided by this embodiment.

[0055] In one embodiment, the thickness change rate of the nickel plating layer after 108 hours of high-temperature cooking is ≤2%; the high-temperature temperature range is 120° C. to 122° C.

[0056] The working principle of the above technical solution is as follows: This data indicator reflects the stability of the nickel plating in high temperature and high humidity environments; DFN packages may encounter various harsh environmental conditions in actual use, especially in high temperature and high humidity environments, where the stability and durability of the plating are crucial; a 108-hour high-temperature cooking test in the temperature range of 120°C to 122°C can simulate the impact of extreme environments on the nickel plating, thereby evaluating its performance in actual applications; a nickel plating thickness change rate of ≤2% means that the thickness of the plating remains almost unchanged during the high-temperature cooking process, which proves that the plating has good heat and moisture resistance and can maintain stable performance and structure in harsh environments.

[0057] The beneficial effect of the above technical solution is that the solution provided by this embodiment not only helps to improve the overall reliability of the DFN package, but also extends its service life and meets the needs of various high-demand application scenarios.

[0058] In one embodiment, the solder coverage area of the nickel plating layer is ≥95%, and the porosity is ≤0.5%.

[0059] The working principle of the above technical solution is: this data indicator reflects the good bonding ability between the nickel plating and the solder and the density of the internal plating; during the soldering process of the DFN package, the solder needs to fully cover the plating surface to ensure good electrical connection and heat conduction. The nickel plating solder coverage area ≥95% means that most of the plating surface can be effectively covered by the solder, reducing connection problems caused by poor welding; at the same time, porosity is an important indicator for measuring internal defects in the plating. A porosity of ≤0.5% indicates that the internal structure of the plating is dense, reducing the risk of corrosion and performance degradation caused by pores.

[0060] The beneficial effect of the above technical solution is: by adopting the solution provided by this embodiment, a high solder coverage area and low porosity are achieved, thereby improving the soldering reliability and long-term stability of the DFN package.

[0061] An application of WF process in DFN packaging, such as Figure 2 Shown, including:

[0062] Use WF process for DFN package packaging;

[0063] The encapsulated DFN package is electrically connected to the external circuit by welding using the pads on the side.

[0064] The performance of the packaged DFN package and external circuit is tested.

[0065] The working principle of the above technical solution is as follows: To realize the application of the WF process in DFN packaging, the present invention applies the WF process to the DFN package body, which ensures the quality and reliability of the package body. Then, the DFN package body treated by the WF process is connected to the external circuit through its side pads. This connection method not only improves the stability of the connection, but also effectively reduces signal loss during the connection process. Finally, the packaged DFN package body and the external circuit are comprehensively performance tested. This step ensures the accuracy and reliability of the entire packaging and connection process, thereby meeting the needs of demanding application scenarios.

[0066] The beneficial effect of the above technical solution is that: by adopting the solution provided by this embodiment, the application of the WF process in DFN packaging can be realized, and excellent performance and reliability are provided for the package.

[0067] In one embodiment, the thrust value of the device in the packaged DFN package is obtained based on a thrust test.

[0068] The working principle of the above technical solution is as follows: During the thrust test, professional testing equipment is used to apply a certain thrust to the packaged DFN device to evaluate its connection strength. This test ensures that when the device is subjected to external pressure or mechanical stress, the connection between its package and the external circuit remains stable and reliable. The acquisition of thrust value not only provides important data support for device quality assessment, but also provides a reliable reference basis for subsequent application scenario selection.

[0069] The beneficial effect of the above technical solution is: by adopting the solution provided in this embodiment, the actual effect of the WF process in DFN packaging can be further verified, ensuring that the packaged device can meet the application requirements of high reliability and stability.

[0070] In one embodiment, the pads on the side of the DFN package are optically inspected by AOI inspection equipment.

[0071] The working principle of the above technical solution is: during the AOI equipment inspection process, a high-resolution camera is used to capture the image of the side of the package, and the image is analyzed through advanced image processing algorithms. This inspection can accurately identify whether there are defects in the pads, such as poor welding, missing or contaminated problems.

[0072] The beneficial effects of the above technical solution are as follows: adopting the solution provided by this embodiment not only improves the detection efficiency, but also ensures the quality consistency of the DFN package, providing a high-quality foundation for the subsequent electronic assembly process.

[0073] In one embodiment, optical inspection of the pads on the side of the DFN package is performed using AOI inspection equipment, and further includes obtaining a soldering quality score of the pads on the side of the DFN package, such as Figure 3 As shown, specifically:

[0074] A multi-angle annular light source array is used to illuminate the pads on the side of the DFN package in a time-sharing manner to obtain multi-angle images. A ring-shaped LED array is used to time-sharingly trigger the light sources at three different angles: 0°, 30°, and 60°. Polarizers are used to suppress specular reflections.

[0075] Perform wavelet transform fusion on multi-angle images to retain high-frequency edge information and generate high-contrast fused images;

[0076] The improved U-Net++ network is used to segment the pad area in the high-contrast fusion image. The improved U-Net++ network integrates the CBAM attention module and the morphological constraint loss function. The CBAM attention module is embedded in the U-Net++ to enhance the extraction of pad area features. The morphological constraint loss function specifically adds pad geometry constraints to the cross entropy loss.

[0077] Based on the 3D topography reconstruction results of the pad area in the segmented high-contrast fused image, the pad wetting angle and coverage are calculated, and the welding quality score is calculated. Based on the comparison result of the welding quality score with the set welding quality score threshold, automatic rework or production process optimization suggestions are triggered. Specifically, Gray code stripes are projected onto the side of the pad, height information is obtained through phase solution, and a 3D point cloud is generated in combination with the AOI equipment image. The indicators for the welding quality score are defined. The indicators include pad wetting angle, coverage, roughness and offset distance. Among them, the pad wetting angle reflects the fluidity of the solder, the coverage reflects the pad contact area ratio, and the roughness reflects the standard deviation of the 3D topography. The offset distance reflects the deviation of the pad center. The calculation formula for the welding quality score is:

[0078]

[0079] Represents the welding quality score, 、 Both represent global balance factors; represents the weight of wettability, represents the weight of coverage, represents the weight of wettability, The weight representing the coverage; represents the pad wetting angle; represents coverage; represents roughness; Represents the offset distance; Express Sigmoid normalization is performed to evaluate the wettability of the pad; Express Sigmoid normalization is performed to evaluate welding integrity; Express Sigmoid normalization is performed to evaluate the uniformity of the pad surface; Express Sigmoid normalization is performed to evaluate alignment accuracy.

[0080] The working principle of the above technical solution is as follows: in order to accurately evaluate the welding quality of DFN package, the present invention adopts a multi-angle annular light source array to time-share the illumination of the side of the pad, and comprehensively captures the detailed information of the pad by acquiring multi-angle images; the time-shared triggering mechanism of the annular LED array ensures the precise control of light sources at different angles, effectively suppresses mirror reflection, and improves image quality; then the wavelet transform fusion technology is used to fuse the multi-angle images, which not only retains the high-frequency edge information but also generates a high-contrast fused image, providing strong support for subsequent pad area segmentation; the improved U-Net++ network plays a key role in pad area segmentation. By embedding the CBAM attention module, it can more accurately extract pad area features and enhance the recognition ability of the model; at the same time, the introduction of the morphological constraint loss function further constrains the pad geometry and improves the segmentation accuracy; this series of optimization measures makes the segmentation of the pad area more accurate and efficient. In terms of 3D topography reconstruction, the pad topography is accurately reconstructed by projecting Gray code stripes onto the side of the pad, using phase resolution technology to obtain height information, and combining it with AOI equipment images to generate a 3D point cloud. On this basis, welding quality scoring indicators including pad wetting angle, coverage, roughness, and offset distance are defined to comprehensively evaluate welding quality. These indicators not only reflect key information such as solder fluidity, pad contact area ratio, 3D topography standard deviation, and alignment accuracy, but also provide a strong basis for subsequent welding quality control. Finally, by comprehensively considering the weights and normalization results of various indicators, the welding quality score is calculated. Based on the comparison of the welding quality score with the set welding quality score threshold, automatic rework or production process optimization suggestions are triggered. This scoring system is not only highly accurate and reliable, but also can provide effective guidance and support for the welding quality control of DFN packages.

[0081] The beneficial effects of the above technical solution are as follows: the solution provided in this embodiment can significantly improve the assessment accuracy and efficiency of the welding quality of DFN packages; the multi-angle annular light source array time-sharing illumination technology effectively solves the mirror reflection problem, improves image quality, and lays a solid foundation for subsequent processing; the application of wavelet transform fusion technology not only retains the key details of the image, but also enhances the image contrast, making the pad area segmentation more accurate; the improved U-Net++ network combined with the CBAM attention module further improves the accuracy and efficiency of pad feature extraction, and the introduction of the morphological constraint loss function further constrains the pad geometry, ensuring high segmentation accuracy; in addition, through three-dimensional morphology reconstruction technology and the definition of welding quality scoring indicators, a comprehensive and accurate assessment of welding quality is achieved.

[0082] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A WF process, characterized in that: include: Step 1: Create a groove on the side of the DFN package so that the solder pad extends from the bottom to the side. The groove has an inclination angle of 30°-60° and a depth of 0.1-0.3mm; the cross section of the groove is trapezoidal or semicircular; Step 2: Use chemical electroplating to form a nickel coating on the pads on the side of the DFN package. The thickness of the nickel coating is 6-10 μm. The thickness change rate of the nickel coating after 108 hours of high-temperature cooking is ≤2%. The high-temperature temperature range is 120°C to 122°C. The solder coverage area of the nickel coating is ≥95%, and the porosity is ≤0.5%. Step 3: Perform quality inspection on the formed nickel plating layer; including: Perform optical inspection on the pads on the side of the DFN package using AOI inspection equipment; Obtain the soldering quality score of the pads on the side of the DFN package, specifically: A multi-angle annular light source array is used to illuminate the pads on the side of the DFN package in a time-sharing manner to obtain multi-angle images. A ring-shaped LED array is used to time-sharingly trigger the light sources at three different angles: 0°, 30°, and 60°. Polarizers are used to suppress specular reflections. Perform wavelet transform fusion on multi-angle images to retain high-frequency edge information and generate high-contrast fused images; The pad region in the high-contrast fused image is segmented using an improved U-Net++ network that integrates the CBAM attention module and the morphological constraint loss function. The CBAM attention module is embedded in the U-Net++. The morphological constraint loss function specifically adds pad geometry constraints to the cross entropy loss. Based on the 3D topography reconstruction results of the pad area in the segmented high-contrast fused image, the pad wetting angle and coverage are calculated, and the welding quality score is obtained. Based on the comparison result of the welding quality score with the welding quality score threshold, automatic rework or production process optimization suggestions are triggered. Specifically, Gray code stripes are projected onto the side of the pad, height information is obtained through phase solution, and a 3D point cloud is generated in combination with the AOI equipment image. The indicators for the welding quality score are defined. The indicators include pad wetting angle, coverage, roughness and offset distance. Among them, the pad wetting angle reflects the fluidity of the solder, the coverage reflects the pad contact area ratio, and the roughness reflects the standard deviation of the 3D topography. The offset distance reflects the deviation of the pad center. The calculation formula for the welding quality score is: Represents the welding quality score, 、 Both represent global balance factors; represents the weight of wettability, represents the weight of coverage, represents the weight of wettability, The weight representing the coverage; represents the pad wetting angle; represents coverage; represents roughness; Represents the offset distance; Express Sigmoid normalization is performed to evaluate the wettability of the pad; Express Sigmoid normalization is performed to evaluate welding integrity; Express Sigmoid normalization is performed to evaluate the uniformity of the pad surface; Express Sigmoid normalization is performed to evaluate alignment accuracy.

2. An application of a WF process according to claim 1 in DFN packaging, characterized in that: include: Use WF process for DFN package packaging; The encapsulated DFN package is electrically connected to the external circuit by welding using the pads on the side. The performance of the packaged DFN package and external circuit is tested.

3. The application of the WF process in DFN packaging according to claim 2, characterized in that: The thrust value of the device in the packaged DFN package is obtained based on the thrust test.

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