Aluminum oxide ceramic substrate high-precision through hole machining method based on pre-sintering process

Abstract

The high-precision laser drilling method for the aluminum oxide ceramic substrate is efficient, low in cost and high in quality, and through the steps of high-temperature presintering, secondary high-temperature sintering, double-face grinding and polishing, high-temperature degradation and the like, the defect that after existing aluminum oxide ceramic is sintered into mature ceramic, the laser drilling efficiency is greatly improved is effectively overcome. The problems of edge breakage, slag, cracks and the like are easily caused by high-power laser drilling, and the method can be applied to processing and manufacturing of thin film ceramic circuit substrates and DPC substrates for various microwave components and packaging modules.

Description

Technical Field

[0001] The present invention belongs to the field of microelectronics, and particularly relates to a high-precision through-hole processing method for alumina ceramic substrates based on a pre-sintering process. Background Art

[0002] As a thin-film circuit substrate, the alumina ceramic substrate has excellent thermal conductivity, electrical insulation, and mechanical strength, and is widely used in the fields of microelectronics, optoelectronics, power semiconductors, etc., especially as a key core component in high-power and high-frequency electronic packaging. Substrates are generally divided into ordinary substrates and via metallization substrates according to their structures. For via substrates, it is necessary to process via structures inside the substrate by mechanical or laser means, and then perform surface and in-hole metallization processes.

[0003] The alumina ceramic substrate belongs to high-hard and brittle materials. Using traditional mechanical processing methods is extremely likely to cause cracks in it, resulting in a low yield rate, and it is suitable for scenarios with a small number of holes and low requirements for drilling quality. High-density drilling substrates generally use high-power laser drilling, which has the advantages of high efficiency and low cost. The traditional laser drilling targets are sintered mature ceramic substrates. Due to the high-hard and brittle characteristics of ceramics, even for non-contact laser processing technology, large thermal stresses generated locally in the material during irradiation will cause chipping, slagging, and cracking around and inside the holes, resulting in the risk of metal film peeling during the subsequent hole metallization process. Especially for high-frequency circuit substrates, it even affects the product quality and performance. Although picosecond, femtosecond lasers, etc. can solve the above problems caused by thermal stress, their costs are high and the efficiency is low, and they cannot meet the engineering production requirements for substrate products with high drilling quality requirements and high hole density.

[0004] Therefore, how to effectively solve the problems of chipping, slagging, and cracking generated by laser drilling of ceramic substrates under the premise of high efficiency and low cost, and achieve high-precision via substrate processing, has become a difficult problem that urgently needs to be solved in the manufacture of high-reliability and high-performance ceramic circuit substrates at present. Summary of the Invention

[0005] To this end, the present invention overcomes the problems of chipping, slagging, and cracking that are likely to occur during high-power laser drilling after sintering alumina ceramics into mature ceramics, and proposes a high-precision laser drilling method for alumina ceramic substrates with high efficiency, low cost, and high quality. This method can be applied to the processing and manufacturing of various microwave components, thin-film ceramic circuit substrates for packaging modules, and DPC substrates. This method specifically includes the following steps:

[0006] 10) Laminating alumina green ceramic sheets: After cutting the alumina green ceramic sheets formed by tape casting, they are laminated, and the number of laminated layers is determined according to the thickness requirements of the product. The appearance of the laminated part is complete without defects and the surface is pollution-free.

[0007] 20) High-temperature pre-sintering: The stacked green alumina ceramic blocks are subjected to pre-sintering treatment. The pre-sintering temperature is controlled to be lower than the normal sintering temperature. Taking alumina as an example, the pre-sintering temperature is 1540°C to 1560°C, the heating rate is 10 to 15°C / min, the holding time is 1 to 1.5 h, and the cooling rate is 15 to 20°C / min. On the one hand, pre-sintering endows it with certain mechanical strength while the material is not completely densified and embrittled, which is convenient for laser drilling; on the other hand, it enables the substrate shape and thickness dimensions to complete full shrinkage and shaping, thus avoiding the problem of dimensional shrinkage deviation caused by re-sintering after green ceramic drilling. After pre-sintering, the substrate is required to have a complete appearance without defects and no contamination on the surface.

[0008] 30) Laser drilling: A high-power infrared laser is used to perform high-precision drilling on the substrate after pre-sintering is completed. The hole diameter is determined according to product requirements, generally 0.1 mm to 0.5 mm; since the substrate is in an incompletely sintered state at this time and the ceramic material is not completely embrittled, laser drilling can avoid phenomena such as chipping, slag, and cracks at the hole mouth and inside the hole.

[0009] 40) Secondary high-temperature sintering: After the substrate is laser-drilled, the normal alumina sintering temperature is adopted, generally 50 to 100°C higher than the pre-sintering temperature, the heating rate is 5 to 10°C / min, the holding time is slightly higher than the pre-sintering temperature by 0.5 to 1.5 h, and the heating rate and cooling rate are the same as the pre-sintering parameters. The substrate is subjected to secondary high-temperature sintering. On the one hand, it makes the ceramic substrate completely densified and the mechanical strength reaches the normal ceramic state; on the other hand, it can repair the micro-defects or hidden cracks generated during the laser drilling process. After secondary high-temperature sintering, the appearance of the substrate is inspected, and it is required that the surface is clean and there are no redundant substances; and the bending strength of the substrate is tested, and it is required to be greater than 350 MPa.

[0010] 50) Double-sided grinding and polishing: After the substrate is subjected to secondary high-temperature sintering, the warpage and surface roughness of the substrate cannot meet the requirements of thin-film wiring. Through the grinding and polishing process, on the one hand, the substrate thickness meets the product requirements and the warpage of the substrate is ensured not to exceed 1 μm / mm; on the other hand, the surface roughness of both sides of the substrate is less than 80 nm.

[0011] 60) High-temperature annealing: The polished substrate is subjected to annealing treatment. The highest annealing temperature is 1580°C to 1640°C, the heating rate is 10 to 15°C / min, the holding time is 2 to 3 h, and the cooling rate is 15 to 20°C / min, so that the ceramic substrate is further densified. This process can further repair the micro-defects or hidden cracks generated during the laser drilling process. After high-temperature annealing, the appearance of the substrate is inspected, and it is required that the surface is clean and there are no redundant substances; observing the through-hole edge with a 20-fold microscope shows no cracks; and the bending strength of the substrate is tested, and it is required to be greater than 350 Mpa, finally realizing the processing of high-precision through-hole substrates.

[0012] Finally, through typical thin-film process flows such as sputtering, photolithography, and electroplating, after the manufacture of the substrate thin-film metallization is completed, the integrity and adhesion of the metallization inside the substrate holes are tested.

[0013] The beneficial effects of the present invention are as follows

[0014] 1. Low cost: The method steps for punching holes in the substrate in the present invention are simple. Compared with the traditional punching process for mature ceramics, the punching rate is faster, about 20% higher, and there is no need to introduce new materials, so the cost is low and the product consistency is high.

[0015] 2. High punching quality: The punching process for the substrate in the present invention effectively solves problems such as chipping, slagging, and cracking. After a strength comparison test with a substrate punched by ordinary laser, there is no obvious difference between the two.

[0016] 3. High popularization: The present invention can be applied to other ceramic substrates, including materials such as aluminum nitride substrates and beryllium oxide.

[0017] 4. It has high application value and economic benefits. Description of the Drawings

[0018] Figure 1 It is a process flow chart for the high-precision through-hole processing of an alumina ceramic substrate.

[0019] Figure 2 It is a schematic structural diagram of a green alumina ceramic sheet after tape casting and lamination, before sintering.

[0020] Figure 3 It is a schematic structural diagram of the laminated alumina substrate after high-temperature pre-sintering.

[0021] Figure 4 It is a schematic structural diagram of the alumina substrate after laser punching after high-temperature pre-sintering.

[0022] Figure 5 It is a schematic structural diagram of the alumina substrate after laser punching after secondary high-temperature sintering.

[0023] Figure 6 It is a schematic structural diagram of the substrate after double-sided grinding and polishing after secondary sintering.

[0024] Figure 7 It is a schematic structural diagram of high-temperature annealing after double-sided grinding and polishing.

[0025] The meanings of the reference numerals are: 1 - laminated green ceramic sheet; 2 - high-temperature pre-sintered alumina substrate; 3 - alumina substrate after secondary high-temperature sintering; 4 - surface of the substrate after grinding and polishing; 5 - alumina substrate after high-temperature annealing. Detailed Embodiments

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0027] As Figure 1 shown, the high-precision via-hole processing method for alumina ceramic substrates based on the pre-sintering process of the present invention includes the following steps:

[0028] 10) Laminating alumina green ceramic sheets: Taking the requirements of an alumina ceramic product with a thickness of 0.635 mm and a pore diameter of 0.3 mm as an example, prepare alumina green ceramic sheets formed by tape casting. The outer dimensions are cut to 200 mm * 200 mm, the single-layer thickness is 0.1 mm, a total of 10 layers are laminated, the lamination temperature is 75 °C, the pressure is 2000 PSI, and the time is 20 min. After lamination, check under a 20-fold microscope to be complete, confirm no defects, and the substrate surface is free of contamination;

[0029] 20) High-temperature pre-sintering: After degumming the laminated alumina green ceramic blocks, perform pre-sintering treatment. The pre-sintering temperature is set at 1560 °C, the heating rate is 10 °C / min, the holding time is 1 h, and the cooling rate is 20 °C / min. After the substrate is cooled to room temperature, take it out and measure the thickness of the sintered substrate to be 0.8 mm and the outer dimensions to be 180 mm * 180 mm, meeting the product application requirements; after pre-sintering, it is required that the substrate appearance is complete without defects and the surface is free of contamination;

[0030] 30) Laser drilling: Use a high-power laser to perform high-precision drilling on the substrate after pre-sintering is completed. The front hole diameter is 0.32 mm, the back hole diameter is 0.3 mm, the hole pitch is 0.5 mm, and the number of holes is 1000. The laser wavelength of 1064 nm, the laser power of 50 W, and the pulse width of 200 ns are adopted. Observe the front and back sides of the substrate under a 20-fold microscope, and there are no phenomena such as burrs, slag, cracks, etc. at the hole openings, as Figure 4 shown.

[0031] 40) Secondary high-temperature sintering: After the laser drilling of the substrate is completed, perform secondary sintering. The sintering temperature is set at 1600 °C, the heating rate is 8 °C / min, the holding time is 2 h, and the cooling rate is 15 °C / min. After the substrate is cooled to room temperature, take it out and measure the thickness of the sintered substrate to be 0.8 mm and the outer dimensions to be 180 mm * 180 mm, and measure the flexural strength of 3 sampled ceramic substrates by the three-point method. The average value is 562 Mpa, and the minimum value is 501 Mpa, meeting the index requirements of GB / T 14620-2013 standard ≥ 300 Mpa;

[0032] 50) Double-sided grinding and polishing: After the secondary high-temperature sintering of the substrate, both the front and back sides are ground and polished simultaneously to make the thickness, warpage, and roughness meet the product requirements. The measurement results of the substrate after cleaning are as follows: the average substrate thickness is 0.638 mm, the warpage is 0.8 μm / mm, and the average roughness of both the front and back sides is 35 nm, as Figure 6 shown;

[0033] 60) High-temperature annealing: The punched substrate is subjected to high-temperature annealing treatment. The highest annealing temperature is set at 1600 °C, the heating rate is 15 °C / min, the holding time is 2 h, the cooling rate is 15 °C / min, and it is taken out after cooling to room temperature. The appearance of the substrate is inspected, and it is required that the surface is clean and there are no extra substances; a 20-fold microscope is used to observe that there are no cracks at the edge of the through hole; and the flexural strength of the substrate is tested, and it is required to be greater than 350 MPa. Finally, the manufacturing of the high-precision through-hole substrate is completed, as Figure 7 shown.

[0034] Finally, through typical thin-film process flows such as sputtering, photolithography, and electroplating, after the thin-film metallization of the substrate is completed, the integrity and adhesion of the metallization inside the substrate holes are tested to meet the product use and reliability requirements.

[0035] The present invention is not limited to the above specific embodiments, and the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made based on the technical essence of the present invention to the above embodiments shall be included in the protection scope of the present invention.

Claims

1. A high-precision via hole processing method for alumina ceramic substrates based on a pre-sintering process, characterized in that: Specifically, it includes the following steps: 10) Laminating alumina green ceramic sheets: The alumina green ceramic sheets formed by tape casting are cut and then laminated to ensure that the appearance of the laminated parts is complete without defects and the surface is free of contamination. 20) High-temperature pre-sintering: The laminated alumina green ceramic blocks are subjected to pre-sintering treatment. The pre-sintering temperature is controlled to be lower than the normal sintering temperature. After pre-sintering, the appearance of the substrate should be complete without defects and the surface is free of contamination. 30) Laser drilling: A high-power infrared laser is used to drill high-precision holes in the substrate after pre-sintering is completed. 40) Secondary high-temperature sintering: After the laser drilling of the substrate is completed, the substrate is subjected to secondary high-temperature sintering at the normal sintering temperature. On the one hand, it makes the ceramic substrate completely densified and the mechanical strength reaches the normal ceramic state. On the other hand, it can repair the micro-defects or hidden cracks generated during the laser drilling process. After secondary high-temperature sintering, the appearance of the substrate is inspected, and it is required that the surface is clean, without any extra substances, and the bending strength of the substrate is tested. 50) Double-sided grinding and polishing: The substrate after secondary high-temperature sintering is subjected to double-sided grinding and polishing. 60) High-temperature annealing: The ground and polished substrate is annealed. After high-temperature annealing, the appearance of the substrate is inspected, and it is required that the surface is clean, without any extra substances, and finally the processing of the high-precision through-hole substrate is achieved. Finally, through sputtering, photolithography, and electroplating thin film processes, the thin film metallization of the substrate is completed, and the integrity and adhesion of the metallization inside the holes of the substrate are tested.

2. The high-precision through-hole processing method for an alumina ceramic substrate based on a pre-sintering process according to claim 1, characterized in that: In the step 20) of high-temperature pre-sintering, the pre-sintering temperature is 1540°C to 1560°C, the heating rate is 10 to 15°C / min, the holding time is 1 to 1.5 h, and the cooling rate is 15 to 20°C / min.

3. A high-precision through-hole processing method for an alumina ceramic substrate based on a pre-sintering process according to claim 1, characterized in that: In the step 30) of laser drilling, the aperture size is 0.1 mm to 0.5 mm.

4. A high-precision through-hole processing method for an alumina ceramic substrate based on a pre-sintering process according to claim 1, characterized in that: In the step 40) of secondary high-temperature sintering, the sintering temperature is 50 to 100°C higher than the pre-sintering temperature, the heating rate is 5 to 10°C / min, and the holding time is 0.5 to 1.5 h higher than the pre-sintering temperature.

5. A high-precision via-hole processing method for an alumina ceramic substrate based on a pre-sintering process according to claim 1, characterized in that: In the step 50) of double-sided grinding and polishing, the warpage of the substrate after grinding and polishing does not exceed 1 μm / mm, and the surface roughness of both sides of the substrate is less than 80 nm.

6. A high-precision through-hole processing method for an alumina ceramic substrate based on a pre-sintering process according to claim 1, characterized in that: In the step 60) of high-temperature annealing, the annealing temperature is 1580°C to 1640°C, the heating rate is 10 to 15°C / min, the holding time is 2 to 3 h, and the cooling rate is 15 to 20°C / min.

7. A high-precision through-hole processing method for an alumina ceramic substrate based on a pre-sintering process according to claim 1, characterized in that: After high-temperature annealing, the appearance of the substrate is inspected, and it is required that the surface is clean, without any extra substances, there are no cracks at the edges of the through-holes, and the bending strength test requires a value greater than 350 Mpa.

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