Method for improving warping and vacuum adsorption adaptability of AMB substrate

Abstract

The invention discloses a method for improving warping and vacuum adsorption suitability of an AMB substrate, which comprises the following steps: step S1, setting the thickness of a base layer of the AMB substrate and performing a copper reduction process, in which the AMB substrate comprises a front copper foil layer, a ceramic substrate and a back copper foil layer from top to bottom; s2, dividing the front surface into a high-density area and a low-density area according to the density difference of the circuit conducting bar grooves of the copper foil layer on the front surface; and S3, the local copper reduction amount of the back copper foil layer is correspondingly adjusted for the high-density area and the low-density area, and dynamic matching of the front and back copper proportions is achieved. The back copper foil layer is precisely thinned, and the front and back copper proportions are dynamically adjusted by combining the density difference of the front circuit conducting bar grooves, so that the stress of the substrate is balanced fundamentally, the local structure of the back is optimized, local warping is further eliminated, the overall warping amount of the substrate is controlled to be 0.03-0.08 mm, the vacuum adsorption requirement is met, and the automatic production efficiency is improved.

Description

Technical Field

[0001] This invention relates to a method for improving the warpage and vacuum adsorption compatibility of AMB substrates. Background Technology

[0002] As the core packaging component of high-power IGBT modules, the AMB substrate generally adopts a three-layer structure of "thick copper and thin ceramic" to meet the requirements of high current carrying capacity: a front copper foil layer (0.45-1.05mm), a ceramic substrate (0.25-0.50mm), and a back copper foil layer (0.45-1.05mm). During the substrate manufacturing process, the front copper foil layer needs to be etched with circuit strips to form conductive paths. However, the difference in the coefficients of thermal expansion between copper foil and ceramic (copper approximately 17ppm / ℃, ceramic approximately 4ppm / ℃) will generate residual thermal stress after the soldering and etching processes, causing the substrate to warp towards the front copper foil layer.

[0003] With the automation upgrade of packaging production lines, the transfer of AMB substrates is generally achieved using vacuum nozzles. These nozzles create negative pressure by tightly adhering to the front copper foil layer. If the substrate warpage exceeds 0.1mm, a gap will form between the nozzle and the front side, causing negative pressure leakage and adhesion failure. According to industry production data, the vacuum adhesion failure rate of existing AMB substrates due to warpage reaches 25%-30%. This not only causes frequent production line downtime for adjustments but also damages the substrate edges due to forced adhesion, increasing production costs.

[0004] Existing technologies only focus on the impact of room temperature warpage on subsequent chip soldering, without considering the high requirements for substrate flatness (≤0.08mm) for automated adsorption, and cannot solve the problem of thermal bonding adsorption failure. Existing solutions only release stress by etching grooves in the copper foil layer on the back side, without optimizing the stress distribution from the root cause of "matching the amount of copper on the front and back sides", resulting in limited improvement in warpage (reduction of about 30%), which still cannot meet the adsorption requirements. The stress optimization strategy is not adjusted in combination with the distribution differences of the circuit strip grooves on the front side, resulting in obvious warpage in local areas of the substrate (such as areas with dense grooves), forming adsorption dead zones.

[0005] Therefore, in response to the problem that existing AMB substrates warp due to thermal stress, leading to vacuum adsorption failure in automated production lines, and the shortcomings of existing stress balancing solutions that are limited and cannot adapt to adsorption requirements, a method is provided to improve the warping and vacuum adsorption adaptability of AMB substrates. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, this invention provides a method for improving the warpage and vacuum adsorption adaptability of AMB substrates. By precisely thinning the copper foil layer on the back side and dynamically adjusting the copper ratio between the front and back sides in conjunction with the density difference of the circuit strip trenches on the front side, the substrate stress is balanced from the root. At the same time, the local structure on the back side is optimized to further eliminate local warpage, so that the overall warpage of the substrate is controlled within 0.03-0.08mm, meeting the requirements of vacuum adsorption and improving the efficiency of automated production.

[0007] The technical solution to achieve the above objectives is: A method for improving the warpage and vacuum adsorption compatibility of AMB substrates includes: Step S1, AMB substrate base layer thickness setting and copper reduction process, wherein the AMB substrate consists of a front copper foil layer, a ceramic substrate, and a back copper foil layer from top to bottom; Step S2: Based on the density difference of the copper foil layer circuit strip trenches on the front side, the front side is divided into a high-density area and a low-density area. Step S3: Adjust the local copper reduction amount of the back copper foil layer for the corresponding high-density and low-density areas to achieve dynamic matching of the copper ratio on the front and back sides.

[0008] Preferably, in step S1, setting the thickness of the AMB substrate base layer includes: The thickness of the copper foil layer on the front side is 0.45-1.05mm; The thickness of the ceramic substrate is 0.25-0.50 mm; The original thickness of the copper foil layer on the back is 0.45-1.05mm.

[0009] Preferably, in step S1, the copper reduction process includes precise copper reduction on the back side and dynamic calibration of the copper reduction amount; in, The precise copper reduction on the back side employs a chemical wet thinning process to thin the copper foil layer on the back side as a whole, ultimately retaining 95% ± 3% of the original thickness; The dynamic calibration of copper reduction is achieved by monitoring the copper foil thinning process on the back side in real time using a laser thickness gauge. Thickness data is collected every 10 seconds, and thinning is stopped immediately when the thickness reaches the target value, which is 95% ± 3% of the original thickness.

[0010] Preferably, in step S1, the thinning solution used in the chemical wet thinning process is a sulfuric acid-hydrogen peroxide system with a concentration of 15%-20% and a temperature of 40-45℃.

[0011] Preferably, in step S2, the front side is divided into a high-density area and a low-density area based on the density difference of the copper foil layer circuit strip trenches. High-density area: The spacing between circuit strips is ≤0.8mm. The copper foil on the front side of this area has a large amount of etching and residual stress is concentrated, so it is necessary to enhance the stress release on the back side. Low-density area: The spacing between circuit strips is >0.8mm. In this area, there is a large amount of copper foil retained on the front side, and the stress is more dispersed. It is necessary to retain an appropriate amount of copper on the back side to ensure the strength of the substrate.

[0012] Preferably, in step S3, adjusting the local copper reduction amount of the back copper foil layer includes: The high-density area corresponds to the back side: the copper content is reduced by 1%-2% on the basis of retaining 95%, and finally the original thickness is retained to 93%-94%. Stress balance is strengthened by increasing the copper content difference. Low-density areas correspond to the back side: maintain the overall copper reduction, i.e., retain 95%±3%.

[0013] Preferably, in step S3, the copper ratio matching verification is performed by calculating the stress distribution in different regions using finite element simulation software, so that the stress difference between the front and back sides after adjustment is ≤50MPa and the local warping is ≤0.05mm.

[0014] Preferably, in step S3, for different AMB substrate shapes, i.e., the shape difference between rectangular and square AMB substrates, an auxiliary stress-relieving structure is designed in a local area of ​​the back copper layer to further eliminate edge warping: Rectangular substrate: At both ends of the copper foil layer on the back side along the length direction, corresponding to the high-density area on the front side, shallow grooves with a width of 0.3-0.5mm and a depth of 0.05-0.08mm are processed. The shallow grooves are arranged along the width direction with a spacing of 5-8mm and a quantity of 4-6 grooves, which are used to release edge stress in the length direction. Square substrate: Shallow grooves of the same specifications are processed on the four edge areas of the copper layer on the back side, corresponding to the high-density area on the front side. 3-5 grooves are arranged on each edge to eliminate local warping at the four edges.

[0015] Preferably, in step S3, the shallow trench processing technology adopts a chemical wet micro-engraving process, with an SG value of 1.15-1.25, a sulfuric acid concentration of 8%-12%, and a sodium chloride concentration of 15-50 ml / L.

[0016] Compared with the prior art, the beneficial effects of the present invention are: This invention precisely thins the copper foil layer on the back side and dynamically adjusts the copper ratio on the front and back sides by combining the density difference of the circuit strip grooves on the front side. This balances the substrate stress from the root and optimizes the local structure on the back side to further eliminate local warping. The overall warping of the substrate is controlled within 0.03-0.08mm, which meets the requirements of vacuum adsorption and improves the efficiency of automated production. This invention achieves a 60% increase in stress release efficiency and a 50% increase in substrate flatness uniformity through a three-level stress optimization approach of "overall copper reduction + local adjustment + auxiliary shallow trench". This invention combines chemical thinning with laser thickness measurement to control copper reduction accuracy within ±0.005mm. During mass production, the substrate thickness consistency deviation is ≤2%, meeting the requirements of large-scale automated production. This invention dynamically adjusts the amount of copper reduction (retaining 93%-94% in high-density areas and 95%±3% in low-density areas) to avoid excessive copper reduction, while maintaining the substrate bending strength at ≥220MPa, which is superior to industry standards. The present invention can flexibly adjust the amount of copper reduction and shallow trench parameters according to the substrate shape (rectangular / square) and the front circuit strip design (different trench densities) to adapt to the packaging requirements of IGBT modules with different power levels. Attached Figure Description

[0017] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a flowchart of a method for improving the warpage and vacuum adsorption compatibility of AMB substrates according to the present invention; Figure 2 This is a schematic diagram of copper reduction on the back side of the AMB substrate in this invention; Figure 3 This is a schematic diagram of the AMB substrate before copper reduction in this invention; Figure 4 This is a schematic diagram of the copper ratio on the front and back sides of the AMB substrate calculated and then subtracted from the copper content in this invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] like Figure 1-4 As shown, a method for improving the warpage and vacuum adsorption compatibility of an AMB substrate includes: Step S1, AMB substrate base layer thickness setting and copper reduction process, wherein the AMB substrate consists of a front copper foil layer, a ceramic substrate, and a back copper foil layer from top to bottom.

[0020] In this embodiment, the AMB substrate base layer thickness setting includes: The thickness of the copper foil layer on the front side is 0.45-1.05mm, which meets the circuit's conductivity and current carrying requirements; The ceramic substrate thickness is 0.25-0.50mm to ensure insulation performance and thermal conductivity efficiency; The original thickness of the copper foil layer on the back is 0.45-1.05mm.

[0021] In this embodiment, the copper reduction process includes precise copper reduction on the back side and dynamic calibration of the copper reduction amount; in, The precise copper reduction on the back side employs a chemical wet thinning process to thin the copper foil layer on the back side as a whole, ultimately retaining 95% ± 3% of the original thickness; for example, the original thickness of the copper foil on the back side is 0.6 mm, and the thickness is controlled to be 0.57-0.585 mm after thinning. The dynamic calibration of copper reduction is achieved by using a laser thickness gauge to monitor the copper foil thinning process on the back side in real time. Thickness data is collected every 10 seconds. When the thickness reaches the target value, i.e., 95% ± 3% of the original thickness, the thinning is stopped immediately to ensure that the copper reduction accuracy is controlled within ± 0.005 mm.

[0022] In the embodiments, the thinning solution used in the chemical wet thinning process is a sulfuric acid-hydrogen peroxide system with a concentration of 15%-20% and a temperature of 40-45℃.

[0023] Step S2: Based on the density difference of the copper foil layer circuit strip trenches on the front side, the front side is divided into a high-density area and a low-density area.

[0024] In this embodiment, based on the density difference of the copper foil layer circuit strip trenches on the front side, the front side is divided into a high-density area and a low-density area, wherein, High-density area: The spacing between circuit strips is ≤0.8mm. The copper foil etching on the front side of this area is extensive, and residual stress is concentrated. It is necessary to enhance the stress release on the back side. Low-density area: The spacing between circuit strips is >0.8mm. In this area, there is a large amount of copper foil retained on the front side, and the stress is more dispersed. It is necessary to retain an appropriate amount of copper on the back side to ensure the strength of the substrate.

[0025] In another embodiment, the amount of copper reduction on the back side can be adjusted according to the "percentage of residual copper foil area on the front side" (rather than the trench density) - when the percentage of residual area on the front side is <60%, the copper on the back side is reduced to 93%-94% of the original thickness; when the percentage is ≥60%, the copper is reduced to 95%±3%, which can also achieve stress balance and adapt to substrates with different circuit designs.

[0026] Step S3: Adjust the local copper reduction amount of the back copper foil layer for the corresponding high-density and low-density areas to achieve dynamic matching of the copper ratio on the front and back sides.

[0027] In this embodiment, adjusting the local copper reduction amount of the back copper foil layer includes: The high-density area corresponds to the back side: the copper content is reduced by 1%-2% on the basis of retaining 95%, and finally the original thickness is retained to 93%-94%. Stress balance is strengthened by increasing the copper content difference. Low-density areas correspond to the back side: maintain the overall copper reduction, i.e., retain 95%±3%.

[0028] In the embodiment, the copper ratio matching verification was performed by calculating the stress distribution in different regions using finite element simulation software, so that the stress difference between the front and back sides after adjustment was ≤50MPa and the local warping was ≤0.05mm.

[0029] In this embodiment, to address the differences in AMB substrate shapes, specifically the shape differences between rectangular and square AMB substrates, an auxiliary stress-relieving structure is designed in a localized area of ​​the back copper layer to further eliminate edge warping. Rectangular substrate (length > width 1.5 times): At both ends of the copper foil layer on the back side along the length direction, corresponding to the high-density area on the front side, shallow grooves with a width of 0.3-0.5mm and a depth of 0.05-0.08mm are processed. The shallow grooves are arranged along the width direction with a spacing of 5-8mm and a quantity of 4-6 grooves, which are used to release edge stress in the length direction. Square substrate (length / width ≈ 1): Shallow grooves of the same specifications are processed on the four edge areas of the copper layer on the back side, corresponding to the high-density area on the front side. 3-5 grooves are arranged on each edge to eliminate local warping at the four edges.

[0030] In this embodiment, the shallow trench processing technology adopts a chemical wet micro-etching process with an SG value of 1.15-1.25, a sulfuric acid concentration of 8%-12%, and a sodium chloride concentration of 15-50 ml / L, in order to precisely control the damage of chemical etching to the copper surface and ensure the flatness of the copper foil layer on the back side.

[0031] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving the warpage and vacuum adsorption compatibility of AMB substrates, characterized in that, include: Step S1, AMB substrate base layer thickness setting and copper reduction process, wherein the AMB substrate consists of a front copper foil layer, a ceramic substrate, and a back copper foil layer from top to bottom; Step S2: Based on the density difference of the copper foil layer circuit strip trenches on the front side, the front side is divided into a high-density area and a low-density area. Step S3: Adjust the local copper reduction amount of the back copper foil layer for the corresponding high-density and low-density areas to achieve dynamic matching of the copper ratio on the front and back sides.

2. The method for improving the warpage and vacuum adsorption adaptability of an AMB substrate according to claim 1, characterized in that, In step S1, the setting of the base layer thickness of the AMB substrate includes: The thickness of the copper foil layer on the front side is 0.45-1.05mm; The thickness of the ceramic substrate is 0.25-0.50 mm; The original thickness of the copper foil layer on the back is 0.45-1.05mm.

3. The method for improving the warpage and vacuum adsorption adaptability of an AMB substrate according to claim 2, characterized in that, In step S1, the copper reduction process includes precise copper reduction on the back side and dynamic calibration of the copper reduction amount. in, The precise copper reduction on the back side employs a chemical wet thinning process to thin the copper foil layer on the back side as a whole, ultimately retaining 95% ± 3% of the original thickness; The dynamic calibration of copper reduction is achieved by monitoring the copper foil thinning process on the back side in real time using a laser thickness gauge. Thickness data is collected every 10 seconds, and thinning is stopped immediately when the thickness reaches the target value, which is 95% ± 3% of the original thickness.

4. The method for improving the warpage and vacuum adsorption adaptability of an AMB substrate according to claim 3, characterized in that, In step S1, the thinning solution used in the chemical wet thinning process is a sulfuric acid-hydrogen peroxide system with a concentration of 15%-20% and a temperature of 40-45℃.

5. The method for improving the warpage and vacuum adsorption adaptability of an AMB substrate according to claim 1, characterized in that, In step S2, based on the density difference of the copper foil layer circuit strip trenches on the front side, the front side is divided into a high-density area and a low-density area, wherein... High-density area: The spacing between circuit strips is ≤0.8mm. The copper foil on the front side of this area has a large amount of etching and residual stress is concentrated, so it is necessary to enhance the stress release on the back side. Low-density area: The spacing between circuit strips is >0.8mm. In this area, there is a large amount of copper foil retained on the front side, and the stress is more dispersed. It is necessary to retain an appropriate amount of copper on the back side to ensure the strength of the substrate.

6. The method for improving the warpage and vacuum adsorption adaptability of an AMB substrate according to claim 5, characterized in that, In step S3, the local copper reduction amount of the back copper foil layer is adjusted accordingly, including: The high-density area corresponds to the back side: the copper content is reduced by 1%-2% on the basis of retaining 95%, and finally the original thickness is retained to 93%-94%. Stress balance is strengthened by increasing the copper content difference. Low-density areas correspond to the back side: maintain the overall copper reduction, i.e., retain 95%±3%.

7. The method for improving the warpage and vacuum adsorption adaptability of an AMB substrate according to claim 6, characterized in that, In step S3, the copper ratio matching verification is performed by calculating the stress distribution in different regions using finite element simulation software, so that the stress difference between the front and back sides after adjustment is ≤50MPa and the local warping is ≤0.05mm.

8. The method for improving the warpage and vacuum adsorption adaptability of an AMB substrate according to claim 7, characterized in that, In step S3, for different AMB substrate shapes, namely the shape differences between rectangular and square AMB substrates, an auxiliary stress-relieving structure is designed in a local area of ​​the back copper layer to further eliminate edge warping. Rectangular substrate: At both ends of the copper foil layer on the back side along the length direction, corresponding to the high-density area on the front side, shallow grooves with a width of 0.3-0.5mm and a depth of 0.05-0.08mm are processed. The shallow grooves are arranged along the width direction with a spacing of 5-8mm and a quantity of 4-6 grooves, which are used to release edge stress in the length direction. Square substrate: Shallow grooves of the same specifications are processed on the four edge areas of the copper layer on the back side, corresponding to the high-density area on the front side. 3-5 grooves are arranged on each edge to eliminate local warping at the four edges.

9. The method for improving the warpage and vacuum adsorption adaptability of an AMB substrate according to claim 8, characterized in that, In step S3, the shallow trench processing adopts a chemical wet micro-engraving process with an SG value of 1.15-1.25, a sulfuric acid concentration of 8%-12%, and a sodium chloride concentration of 15-50 ml / L.

Images