Method for improving warping degree of copper-based LTCC (Low Temperature Co-Fired Ceramic) substrate by adding balance blocks

Abstract

The invention provides a method for improving the warping degree of a copper-based LTCC (Low Temperature Co-Fired Ceramic) substrate by adding balance blocks, which is characterized in that the balance blocks made of copper slurry are respectively added in the peripheral areas of the front surface and the back surface of the LTCC substrate. The peripheral area is the peripheral area outside the functional area of the LTCC substrate; the balance blocks are arranged on the outer side of the functional area of the LTCC substrate in a surrounding mode. The balance blocks are symmetrically arranged on the front face and the back face of the LTCC substrate, and the sizes of the balance blocks on the front face and the back face are completely the same. The warping control is obvious; the method is high in process compatibility; the size precision is high; the economic benefit is obvious; the device is symmetrical in structure and good in stability.

Description

Technical Field

[0001] This invention belongs to the field of electronic packaging technology, and relates to copper-based LTCC substrates, specifically to a method for improving the warpage of copper-based LTCC substrates by adding a balance block. Background Technology

[0002] Low-temperature co-fired ceramic (LTCC) technology is one of the core packaging technologies widely used in modern microwave communications, RF modules, and power devices. Copper-based LTCCs are favored due to their excellent conductivity and low cost; however, the oxidation tendency of copper and the mismatch in the coefficient of thermal expansion (CTE) between copper and the ceramic layer lead to significant internal stress during high-temperature sintering, resulting in severe substrate warping. This warping problem is particularly pronounced in products with large areas, asymmetric wiring, or significant edge effects.

[0003] Warpage not only affects the precision of subsequent processes such as surface mount technology (SMT) and soldering, but can also lead to device cracking and connection failure, severely reducing product yield. Traditional solutions include optimizing lamination pressure, adjusting temperature rise profiles, and using support fixtures, but these methods often have limited effectiveness or increase process complexity.

[0004] While there have been attempts to compensate for stress by adding dummy patterns in existing technologies, these are mostly focused on tungsten and molybdenum material systems. There is still no systematic solution for copper-based LTCC, especially for high-adhesion copper pastes. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for improving the warpage of copper-based LTCC substrates by adding balance blocks, thereby solving the technical problem that the deformation control capability of copper-based LTCC substrates during sintering needs to be further improved in the prior art.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0007] A method for improving the warpage of copper-based LTCC substrates by adding balance blocks, wherein balance blocks composed of copper paste are added to the peripheral areas of the front and back sides of the LTCC substrate.

[0008] The present invention also has the following technical features.

[0009] The copper paste used is of grade Cu-L201-YK33.

[0010] The peripheral area is the peripheral area outside the functional area of ​​the LTCC substrate; the balance block is arranged in a ring around the functional area of ​​the LTCC substrate.

[0011] The balance block maintains a distance of 0.5 to 1.2 mm from the edge of the functional area of ​​the LTCC substrate.

[0012] The length of the balance block is 1.3 to 2 times the length of the functional area of ​​the LTCC substrate; the width of the balance block is 1.3 to 2 times the width of the functional area of ​​the LTCC substrate.

[0013] The balance blocks are symmetrically arranged on both the front and back sides of the LTCC substrate, and the balance blocks on the front and back sides are exactly the same size.

[0014] The aspect ratio of the balancing block is ≤2:1.

[0015] The copper-based LTCC substrate is printed and laminated in multiple layers using copper-based LTCC green ceramic tape and copper paste.

[0016] The copper-based LTCC substrate was co-fired at 950°C in a wet nitrogen protective atmosphere to achieve densification and conductor forming.

[0017] Compared with the prior art, the present invention has the following technical effects.

[0018] (I) The warpage control of the present invention is significant: by adjusting the stress of the balance block, the warpage of the actual product (such as a 21mm x 16mm substrate) is reduced from 300μm to less than 100μm, with outstanding improvement effect.

[0019] (II) The present invention has strong process compatibility: it is applicable to existing LTCC production lines. Only the balance block graphic needs to be added to the layout. There is no need to adjust the sintering equipment or process, and it is easy to promote.

[0020] (III) The present invention has high dimensional accuracy: the size of the balance block surrounds the front and back of the product, and the overall length-to-width ratio of the substrate is ≤2:1, which effectively ensures the consistency of shrinkage rate.

[0021] (IV) The economic benefits of this invention are significant: it significantly reduces waste caused by warping and improves performance and product reliability.

[0022] (V) The structure of the present invention is symmetrical and has good stability: the symmetrical arrangement of the front and back avoids the introduction of new asymmetrical stress and prevents twisting or corner warping. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the front-side balance block layout.

[0024] Figure 2 This is a schematic diagram of the back balance block layout.

[0025] Figure 3 This is a schematic diagram showing the dimensional relationship between the balance block and the functional area of ​​the LTCC substrate.

[0026] The specific content of the present invention will be further explained in detail below with reference to the embodiments. Detailed Implementation

[0027] It should be noted that, unless otherwise specified, all components and methods in this invention are based on components and methods known in the prior art.

[0028] The key to this invention lies in utilizing the material properties of Cu-L201-YK33 paste as an "active stress source" rather than a passive filler, and achieving regulation of the substrate stress field through reasonable layout. The balancing blocks do not participate in electrical connections, but exist only as a mechanical compensation structure.

[0029] The method of the present invention uses Cu-L201-YK33 slurry balance blocks of a specific size symmetrically arranged around the periphery of the front and back sides of the substrate to achieve stress reversal compensation by utilizing the compressive stress brought about by their high adhesion, effectively suppressing substrate warping during sintering and significantly improving product flatness and reliability.

[0030] The balance block of the present invention is directly defined through photoplotting files during the layout design stage, without changing the original process flow and without requiring additional equipment or procedures.

[0031] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0032] Example: This embodiment presents a method for improving the warpage of copper-based LTCC substrates by adding balance blocks. This method is implemented after the functional pattern design of the LTCC substrate is completed, such as... Figure 1 and Figure 2 As shown, balance blocks (also known as balance block patterns) made of copper paste are added to the periphery of the front and back sides of the LTCC substrate.

[0033] As a preferred embodiment, the copper paste used is Cu-L201-YK33 grade copper paste. Cu-L201-YK33 grade copper paste has excellent adhesion and is tightly bonded to the ceramic substrate during sintering, generating inward compressive stress. This stress acts on the edge of the substrate, forming a reverse torque that resists the tensile stress in the central region, thereby effectively suppressing overall warping.

[0034] As a preferred embodiment of this invention, such as Figure 1 and Figure 2As shown, the peripheral area is the area outside the functional area of ​​the LTCC substrate; the balance block is arranged in a ring around the functional area of ​​the LTCC substrate, and the balance block and the edge of the functional area of ​​the LTCC substrate are kept at a distance of 0.5-1.2mm.

[0035] In a preferred embodiment, the length of the balancing block is 1.3 to 2 times the length of the functional area of ​​the LTCC substrate; the width of the balancing block is 1.3 to 2 times the width of the functional area of ​​the LTCC substrate. Specifically, in this embodiment... Figure 3 As shown, a frame-shaped balancing block made of Cu-L201-YK33 paste is added around the front and back sides of the substrate, 0.5mm from the edge. The outer edge of the frame is parallel to the edge of the substrate, and the total size is 28mm×27mm, forming a closed ring shape.

[0036] As a preferred embodiment of this invention, such as Figure 1 and Figure 2 As shown, the balance blocks are symmetrically arranged on both the front and back sides of the LTCC substrate, and the balance blocks on both sides are exactly the same size. This forms a symmetrical edge stress field, ensuring stress symmetry and preventing distortion.

[0037] As a preferred embodiment of this invention, such as Figure 3 As shown, the aspect ratio of the balance block is ≤2:1. This is to control the uniformity of the shrinkage rate of the substrate in the X and Y directions and avoid new deformation caused by anisotropic shrinkage.

[0038] As a preferred embodiment, the copper-based LTCC substrate uses Zhenhua Yunke YK33 copper-based LTCC green ceramic tape and Cu-L201-YK33 grade copper paste to complete pattern printing and multilayer lamination. Specifically, in this embodiment, as shown... Figure 3 As shown, a 21mm × 16mm copper-based LTCC substrate was selected, using Zhenhua Yunke YK33 green ceramic tape in a 10-layer laminated structure. The conductor used was Cu-L201-YK33 copper paste. The original design lacked edge balance blocks, and the average warpage measured after sintering reached 300μm. This invention, by adding balance blocks, reduces the overall warpage of the substrate from over 200μm to less than 100μm. In the preferred embodiment, the warpage of the 21mm × 16mm substrate is reduced from 300μm to less than 100μm.

[0039] In a preferred embodiment, the copper-based LTCC substrate is co-fired at 950°C in a wet nitrogen protective atmosphere to achieve densification and conductor formation. Specifically, after patterning is completed, screen printing, lamination, cutting, and sintering are performed according to conventional procedures. The sintering conditions are: heating rate 3°C / min, peak temperature 950°C, holding time 15 minutes, and wet nitrogen atmosphere.

[0040] In this specific embodiment, after sintering, a non-contact profilometer was used to measure the substrate deformation. The results showed that the maximum warpage was only about 60μm, which met the requirements for subsequent packaging.

[0041] Specifically in this embodiment, when the size of the balance block is too small (<20% of the substrate size), stress compensation is insufficient; if it is too large, excessive stress compensation will cause reverse warping. The optimal range is 30% to 100% of the substrate size.

[0042] Furthermore, if the balancing block is set on only one side, a significant distortion occurs, verifying the importance of symmetrical arrangement.

[0043] Comparative example: Compared with the embodiments, this comparative example uses the same structure but without the balancing block, or uses a low-adhesion slurry as the balancing block material, neither of which can effectively suppress warping. This indicates that the high adhesion of Cu-L201-YK33 slurry is one of the key factors for the effectiveness of this invention.

Claims

1. A method for improving the warpage of copper-based LTCC substrates by adding balance blocks, characterized in that, This method involves adding balance blocks made of copper paste to the peripheral areas of the front and back sides of an LTCC substrate.

2. The method for improving the warpage of copper-based LTCC substrates by adding balance blocks as described in claim 1, characterized in that, The copper paste used is of grade Cu-L201-YK33.

3. The method for improving the warpage of copper-based LTCC substrates by adding balance blocks as described in claim 1, characterized in that, The peripheral area is the peripheral area outside the functional area of ​​the LTCC substrate; the balance block is arranged in a ring around the functional area of ​​the LTCC substrate.

4. The method for improving the warpage of copper-based LTCC substrates by adding balance blocks as described in claim 3, characterized in that, The balance block maintains a distance of 0.5 to 1.2 mm from the edge of the functional area of ​​the LTCC substrate.

5. The method for improving the warpage of copper-based LTCC substrates by adding balance blocks as described in claim 3, characterized in that, The length of the balance block is 1.3 to 2 times the length of the functional area of ​​the LTCC substrate; the width of the balance block is 1.3 to 2 times the width of the functional area of ​​the LTCC substrate.

6. The method for improving the warpage of copper-based LTCC substrates by adding balance blocks as described in claim 1, characterized in that, The balance blocks are symmetrically arranged on both the front and back sides of the LTCC substrate, and the balance blocks on the front and back sides are exactly the same size.

7. The method for improving the warpage of copper-based LTCC substrates by adding balance blocks as described in claim 1, characterized in that, The aspect ratio of the balancing block is ≤2:

1.

8. The method for improving the warpage of copper-based LTCC substrates by adding balance blocks as described in claim 1, characterized in that, The copper-based LTCC substrate is printed and laminated in multiple layers using copper-based LTCC green ceramic tape and copper paste.

9. The method for improving the warpage of copper-based LTCC substrates by adding balance blocks as described in claim 1, characterized in that, The copper-based LTCC substrate was co-fired at 950°C in a wet nitrogen protective atmosphere to achieve densification and conductor forming.

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