Method for improving warping change of copper-clad ceramic carrier plate before and after packaging

Abstract

The invention relates to the technical field of electronic packaging, in particular to a method for improving warping change of a copper-clad ceramic carrier plate before and after packaging. Comprising the following steps that 1, S1, a convex face clamp and a concave face clamp are spliced to form a jig; s2, placing the warped copper-clad ceramic carrier plate in the middle of the jig; annealing correction and cooling; obtaining an initial product; 2, the initial product is put into the nitrogen heating furnace again to be heated, the temperature is recovered to the room temperature, and packaging is conducted; and the copper-clad ceramic carrier plate with the warping change improved after packaging is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of electronic packaging, in particular to a method for improving the warpage change before and after packaging of a copper-clad ceramic carrier. Background Art

[0002] With the growth of the automotive power module field, the application of copper-clad ceramic substrates in power components is becoming increasingly common. At present, customers have increasingly stringent requirements for product quality, which is not limited to the control of substrate warpage before packaging, but also extends to the warpage standard after packaging is completed. In the prior art, due to the difference in thermal expansion coefficients between the materials used in the substrate, the substrate itself is prone to a certain warpage shape; under the continuous action of high temperature during welding, the stress distribution inside the substrate is dynamically adjusted, thereby causing changes in the warpage state. These warping phenomena and their changes will cause compatibility issues between the substrate surface and electronic components, and may eventually cause welding defects such as voids and other quality problems.

[0003] In summary, it is of great significance to reduce the customer's soldering void rate and avoid thermal stress in the later use process to the greatest extent, and to obtain a method to improve the warpage change before and after the copper-clad ceramic substrate package. Summary of the invention

[0004] The object of the present invention is to provide a method for improving the front and rear warpage variation of a copper-clad ceramic substrate package, so as to solve the problems raised in the prior art.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for improving the front and rear warpage variation of a copper-clad ceramic substrate package, comprising the following steps:

[0007] Step 1: S1: splice the convex fixture and the concave fixture to form a jig; S2: place the warped copper-clad ceramic carrier in the middle of the jig; anneal and correct, cool; obtain the initial product;

[0008] Step 2: Place the initial product in a nitrogen heating furnace for heating treatment again, restore it to room temperature, and package it to obtain the finished product.

[0009] More optimally, the sintering process of the warped copper-clad ceramic substrate is as follows: stack the ceramic and copper sheets, place a convex fixture on the top, and sinter at 900°C for 20 minutes; during the sintering process, due to the different thermal expansion coefficients of ceramic and copper, there is a certain tensile stress. When the two are stacked together, the initial bonding position and bonding development direction of the sintering are uncontrollable, resulting in uncontrollable distortion of the substrate after sintering due to the influence of stress distribution. After the ceramic and copper sheets are stacked together, a convex fixture is placed on the top to fix the initial bonding position of the ceramic and copper on the central axis and develop to both sides along the central axis, so that the stress distribution is uniform and the warping shape of the substrate after sintering is consistent. At this time, the warping direction of the copper-clad ceramic substrate is defined as concave (-).

[0010] Furthermore, due to the warping problem of the copper-clad ceramic substrate, a fixture with a specific curvature is further used for annealing correction. The fixture with the corresponding curvature is selected according to the target warping value, and the substrate is placed within the limit range of the fixture; the prepared product and the fixture are placed in a nitrogen heating furnace and heated to 330°C and kept warm for 2 hours; during the annealing process, the substrate will soften to a certain extent, so that the shape of the substrate succumbs to the shape of the fixture; after correction, the warping direction of the substrate changes from concave (-) to convex (+), and the warping value is reduced to a level close to the curvature of the fixture. After cooling to room temperature with the furnace, the substrate is removed from the fixture.

[0011] Therefore, the warped copper-clad ceramic substrate after sintering has a warping problem, which needs to be solved before packaging; in the solution, the copper-clad ceramic substrate with the warping problem is placed in a jig with a specific structure for further annealing and correction, and then subjected to heat treatment for thermal release.

[0012] During the annealing correction process, a fixture with a corresponding curvature is selected according to the target warping value, and the copper-clad ceramic substrate is placed within the limit range of the fixture; during the annealing process, the copper in the warped copper-clad ceramic substrate will soften to a certain extent. At this time, the ceramic substrate is pressed down so that the shape of the warped copper-clad ceramic substrate succumbs to the shape of the fixture; after correction, the warping direction of the copper-clad ceramic substrate changes from concave (-) to convex (+), and the warping value is reduced to a level close to the curvature of the fixture.

[0013] During the heating process, the initial product is placed in a heating furnace with a protective atmosphere (nitrogen or reducing atmosphere), and the temperature curve refers to the reflow curve (i.e., heating treatment parameters) when the substrate is packaged. After the stress of the substrate is released, the warpage is maintained within a small range and will not change significantly when it is packaged and used by the client.

[0014] Preferably, the warped copper-clad ceramic carrier is aligned with the central axis of the jig.

[0015] More optimally, the convex surface of the convex fixture and the concave surface of the concave fixture are both arc surfaces, which are an outer arc and an inner arc respectively, and the two correspond to each other; the curvature of the arc surface is ≤1.4mm.

[0016] Among them, the customized curvature of the fixture makes the correction process more efficient and targeted, reducing unnecessary material waste and energy consumption. At the same time, because the correction force is moderate and uniform, it avoids the problem of over-correction or under-correction, thereby improving the product yield and quality stability.

[0017] More optimally, the convex surface of the convex clamp and the concave surface of the concave clamp are both provided with limiters, which are convex limiters and concave limiters respectively, and the two correspond to each other; the height of the limiters is 4 to 6 mm.

[0018] Among them, the internal limit of the fixture ensures that the warped copper-clad ceramic carrier is precisely aligned with the center axis of the fixture during the heating correction process, effectively preventing the left and right deviation of the carrier due to uneven heating or mechanical stress during the heating process. This precise positioning helps to achieve a more uniform stress distribution, thereby improving the correction effect; the limit structure not only limits the lateral movement of the carrier, but also provides stable support for the carrier through its L-shaped design and appropriate width (3mm) and length (10mm), avoiding further deformation or warping caused by lack of constraints during the heating process; in addition, the limit size of the fixture (138mm wide × 190mm long) matches the size of the carrier, ensuring the wide applicability of the solution to carriers of different specifications. At the same time, this design also facilitates the rapid replacement of fixtures to meet the needs of products of different sizes or shapes.

[0019] More optimally, the limiters are all L-shaped and distributed at the four corners of the fixture; the left and right inner spacing of the limiters is 135-140 mm, and the upper and lower spacing is 180-200 mm; the limiter width is 2-4 mm and the length is 8-12 mm.

[0020] In a further embodiment, the carrier plate comprises a rectangle of 135-140 mm x 180-200 mm.

[0021] In a further solution, the product warpage is usually within 0.6 thousandths of the diagonal length before the curvature of the fixture is improved.

[0022] More optimally, when the warping of the copper-clad ceramic carrier is concave, the convex fixture is placed below it and the concave fixture is placed above it; when the warping of the copper-clad ceramic carrier is convex, the convex fixture and the concave fixture are both rotated 180°.

[0023] More optimally, the process parameters of the annealing correction are: nitrogen atmosphere, heating to 320-340° C. and keeping warm for 2-3 hours.

[0024] Preferably, the fixture material includes silicon carbide.

[0025] Among them, the material of the fixture is silicon carbide, which does not react with the raw materials of the carrier, has high thermal conductivity and low thermal expansion coefficient, and the fixture does not deform or change during the softening of the carrier. In addition, heavy-pressure sintered silicon carbide also has high hardness, high melting point, high wear resistance and corrosion resistance, as well as excellent oxidation resistance, high temperature strength, chemical stability and thermal shock resistance, and has better durability.

[0026] More optimally, the process parameters of the heating treatment are: the gas introduced is nitrogen or a mixture of nitrogen and reducing gas, the heating treatment temperature is 250-350° C., and the heating treatment time is 5-20 min.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. By setting the combination position of the fixed warped copper-clad ceramic carrier and the jig on the central axis, this method makes the stress distribution more uniform, thereby reducing the distortion of the carrier.

[0029] 2. Through the design of the fixture, there are limiters inside the fixture to ensure that the carrier plate is aligned with the center axis of the fixture to prevent deviation and ensure the feasibility of the annealing correction process.

[0030] 3. Through annealing correction, the warping direction is effectively controlled and the warping value is reduced. It helps to improve the flatness and bonding quality of the substrate surface, which may indirectly reduce the soldering void rate.

[0031] 4. Through heating treatment (stress release), the stability of the product during subsequent use is ensured and the generation of thermal stress is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] 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:

[0033] Figure 1 It is the outer arc and inner arc diagram of convex and concave fixtures;

[0034] Figure 2 The height, length and width diagram of the internal limit of the fixture;

[0035] Figure 3 The warped copper-clad ceramic substrate is placed in the middle of the fixture;

[0036] Figure 4 Prepare overall flow chart for finished product;

[0037] Figure 5 3D image of the warpage morphology of the copper-clad ceramic substrate after packaging - before optimization;

[0038] Figure 6 The warpage of the copper-clad ceramic substrate after packaging - before optimization;

[0039] Figure 7 3D image of the warpage morphology before and after stress release;

[0040] Figure 8 This is a graph showing the change in warpage value before and after stress release. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] Pre-preparation: The ceramic and copper sheets are stacked, a convex fixture is placed on the top, and sintered at 900°C for 20 minutes to obtain a warped copper-clad ceramic board.

[0043] Embodiment 1: A method for improving the front and rear warpage variation of a copper-clad ceramic substrate package, comprising the following steps:

[0044] Step 1: S1: Prepare convex fixtures and concave fixtures, and splice them to form a fixture. There are limits inside the convex fixtures and concave fixtures: the convex surface of the convex fixture and the concave surface of the concave fixture are both arc surfaces, which are outer arc and inner arc respectively. The two correspond to each other, and the arc curvature of the fixture is controlled to be 1mm, the limit height is 5mm, and the limits are all L-shaped, distributed at the four corners of the fixture; the inner left and right spacing of the limit is 138mm, and the upper and lower spacing is 190mm; the limit width is 3mm and the length is 10mm; the carrier is 138×190mm 2 Rectangle;

[0045] S2: placing the warped copper-clad ceramic substrate in the middle of the jig; when the copper-clad ceramic substrate is warped to be concave, the convex fixture is placed below it, and the concave fixture is placed above it; when the copper-clad ceramic substrate is warped to be convex, the fixture is rotated 180°; in a nitrogen atmosphere, heating to 330°C, keeping the temperature for 2 hours, cooling, taking out, and obtaining a primary product;

[0046] Step 2: Place the primary product in a nitrogen heating furnace again and heat it at 300°C for 12 minutes under a nitrogen atmosphere, return it to room temperature, and package it to obtain a finished product.

[0047] Comparative Example 1: Based on Example 1, the radian of the camber of the jig is controlled to be 0.5 mm, and the other specific steps are the same as those of Example 1.

[0048] Comparative Example 2: Based on Example 1, the radian of the jig is controlled to be 0.75 mm, and the remaining specific steps are the same as those in Example 1.

[0049] Comparative Example 3: Based on Example 1, the radian of the camber of the jig is controlled to be 1.25 mm, and the remaining specific steps are the same as those of Example 1.

[0050] Performance test: The test standard for the warpage test is "GB / T 25257-2010 Method for Determining Warpage of Optical Functional Films". The test results are shown in Table 1:

[0051]

[0052] Table 1

[0053] Conclusion: It can be seen from the data in the above table that for the copper-clad ceramic substrate obtained by the preparation method of the present invention after packaging, when the curvature value decreases, the warping phenomenon at room temperature will be weakened accordingly, and the warping amount is almost consistent with the curvature of the fixture. After simulating the client packaging conditions, the internal stress is released, resulting in a smaller curvature of the fixture and a lower degree of warping. However, as the curvature of the fixture continues to decrease, the effect of warpage optimization gradually tends to be flat. From a practical operation point of view, the reduction of the curvature of the fixture will increase the complexity and difficulty of its manufacturing. Therefore, after weighing the warpage control and manufacturing feasibility, it was decided to select 1.0mm as the optimal value of the curvature of the fixture.

[0054] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A method for improving the front and rear warpage change of copper-clad ceramic substrate packaging, characterized in that: The following steps are involved: Step 1: S1: splice the convex fixture and the concave fixture to form a jig; S2: place the warped copper-clad ceramic carrier in the middle of the jig; anneal and correct, cool; obtain the initial product; Step 2: Place the initial product in a nitrogen heating furnace for heating treatment again, restore it to room temperature, and package it to obtain the finished product.

2. The method for improving the front and rear warpage variation of copper-clad ceramic substrate packaging according to claim 1, characterized in that: The warped copper-clad ceramic carrier is aligned with the central axis of the jig.

3. The method for improving the front and rear warpage variation of copper-clad ceramic substrate packaging according to claim 1, characterized in that: The convex surface of the convex fixture and the concave surface of the concave fixture are both arc surfaces, which are respectively an outer arc and an inner arc, and the two correspond to each other; the curvature of the arc surface is ≤1.4mm.

4. The method for improving the front and rear warpage variation of copper-clad ceramic substrate packaging according to claim 1, characterized in that: The convex surface of the convex clamp and the concave surface of the concave clamp are both provided with limiters, which are convex limiters and concave limiters respectively, and the two correspond to each other; the height of the limiters is 4 to 6 mm.

5. The method for improving the front and rear warpage variation of copper-clad ceramic substrate packaging according to claim 4, characterized in that: The limiters are all L-shaped and distributed at the four corners of the fixture; the inner left and right spacing of the limiters is 135-140 mm, and the upper and lower spacing is 180-200 mm; the limiter width is 2-4 mm and the length is 8-12 mm.

6. The method for improving the front and rear warpage variation of copper-clad ceramic substrate packaging according to claim 1, characterized in that: When the copper-clad ceramic carrier board has a concave warp, the convex fixture is placed below it and the concave fixture is placed above it; when the copper-clad ceramic carrier board has a convex warp, the convex fixture and the concave fixture are both rotated 180 degrees.

7. The method for improving the front and rear warpage variation of copper-clad ceramic substrate packaging according to claim 1, characterized in that: The process parameters of the annealing correction are: nitrogen atmosphere, heating to 320-340° C. and keeping warm for 2-3 hours.

8. The method for improving the front and rear warpage variation of copper-clad ceramic substrate packaging according to claim 1, characterized in that: The material of the fixture includes silicon carbide.

9. The method for improving the front and rear warpage variation of copper-clad ceramic substrate packaging according to claim 1, characterized in that: The process parameters of the heating treatment are: the gas introduced is nitrogen or a mixture of nitrogen and reducing gas, the heating treatment temperature is 250-350° C., and the heating treatment time is 5-20 minutes.

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