CN111593349A

CN111593349A - Chemical milling liquid for preparing ultrathin titanium foil and milling method

Info

Publication number: CN111593349A
Application number: CN202010494890.1A
Authority: CN
Inventors: 葛荘; 贺贤汉; 欧阳鹏; 王斌; 马敬伟; 张恩荣
Original assignee: Jiangsu Fulede Semiconductor Technology Co ltd
Current assignee: Jiangsu Fulede Semiconductor Technology Co ltd
Priority date: 2020-06-03
Filing date: 2020-06-03
Publication date: 2020-08-28
Anticipated expiration: 2040-06-03
Also published as: CN111593349B

Abstract

The invention relates to a chemical milling liquid for preparing an ultrathin titanium foil and a milling method, wherein the milling liquid comprises the following components: 15-25% of hydrofluoric acid solution, 1-3% of nitric acid solution, 5-8% of glacial acetic acid solution, 0.1-0.5 g/100mL of corrosion inhibition stabilizer of milling liquid and the balance of pure water. The milling method comprises the following steps: 1) degreasing and cleaning the surface of the titanium foil: ultrasonically dipping and washing the titanium foil to be treated in acetone, absolute ethyl alcohol and pure water for 5-10 min in sequence, and drying and taking out; 2) chemical milling: immersing the titanium foil treated in the step 1) in the chemical milling liquid for 1-4 min for milling; 3) surface cleaning: and sequentially soaking and washing the milled titanium foil in acetone and pure water for 6-10 min. Because the corrosion inhibition stabilizer is added in the milling liquid, the chemical milling liquid added with the stabilizer is uniform in milling, can obviously relieve the wrinkling phenomenon of the surface of the titanium foil, is high in stability, and is more suitable for processing ultrathin titanium foil soldering lugs.

Description

Chemical milling liquid for preparing ultrathin titanium foil and milling method

Technical Field

The invention belongs to the technical field of semiconductor substrate preparation, relates to a copper-clad ceramic substrate titanium foil soldering lug preparation technology, and particularly relates to chemical milling liquid and a milling method for preparing an ultrathin titanium foil.

Background

The copper-clad ceramic substrate is the most excellent packaging material for a high-voltage high-power module in the field of semiconductors, and has the characteristics of high heat conduction, excellent insulating property, excellent solderability, large current carrying capacity and the like. High temperature direct bonding (DBC, also known as DCB) technology, high temperature active brazing (AMB) technology, electroplating (DPC) technology, and laser activation technology (LAM) are the main technologies for manufacturing copper-clad ceramic substrates at present. The copper-clad ceramic substrate prepared by the AMB technology has the advantages of excellent cold and hot impact resistance, high copper ceramic peeling strength, high cold and hot circulation reliability and the like, and has wide market and application prospects.

Sintering is the most critical part of the AMB technology, and the reduction of the production cost has important significance for industrial mass production on the premise of ensuring the quality. The soldering lug/solder is one of the cores of the AMB sintering technology, meanwhile, due to the AMB process requirement and quality control, an ultrathin titanium foil is required to be used as the soldering lug, the ultrathin titanium foil is mostly applied to the fields of aerospace, loudspeaker sound films and the like, the titanium foil with relatively thick titanium foil (more than or equal to 10 mu m) needs to be rolled for many times, the requirements on equipment and processing technology are strict, the production cost is high, and the problem therewith is the increase of the production cost of the AMB copper-clad plate. Therefore, how to reduce the thickness of the thicker titanium foil by a simple process to be applied to sintering of the AMB copper-clad plate has important significance for reducing cost of the AMB product.

In the field of metal substrate ultra-thinning, chemical milling is an optional mode, and for titanium foil, HF-HNO is mostly adopted₃Chemical milling liquid of the system. HF-HNO₃The milling liquid of the system has the advantage of high speed when the titanium foil is thinned, but has the problems of uneven milling, erosion, excessive wrinkling on the surface of the titanium foil, easy failure of the milling liquid and the like. Thus, conventional HF-HNO is used₃Systematic millingThe cutting liquid is difficult to prepare the ultra-thin titanium foil with excellent quality.

Disclosure of Invention

In order to solve the defects of the prior art, the invention uses a novel corrosion inhibition stabilizer, the chemical milling liquid added with the stabilizer is milled uniformly, can obviously relieve the wrinkling phenomenon of the surface of the titanium foil, has high stability, and is more suitable for processing the ultrathin titanium foil soldering lug.

The key point of the invention for solving the technical problem is to add a novel corrosion inhibition stabilizer, and the principle is that the diffusion rate of ions is reduced by increasing the viscosity of the solution so as to reduce the milling rate, thereby avoiding the over-corrosion of the surface of the titanium foil caused by exponential increase of the later milling rate. Furthermore, by optimizing HF-HNO₃The proportion of the system milling liquid ensures that the novel ultra-thin titanium foil chemical milling liquid has more stable performance.

The invention provides a chemical milling liquid for preparing an ultrathin titanium foil, which consists of the following components in part by weight: 15-25% of hydrofluoric acid solution, 1-3% of nitric acid solution, 5-8% of glacial acetic acid solution, 0.1-0.5 g/100mL of corrosion inhibition stabilizer of milling liquid and the balance of pure water.

Preferably, the chemical mass fraction of the hydrofluoric acid solution is 3%; the chemical mass fraction of the nitric acid solution is 63 percent; the chemical mass fraction of the glacial acetic acid solution is 99.5%. The corrosion inhibition stabilizer is one or more of polyacrylamide, polyvinyl alcohol and sodium silicate.

Among the three stabilizers, polyacrylamide is preferred, the effect is optimal, and a small amount of the stabilizer is effective; polyvinyl alcohol and sodium silicate are slightly less effective than polyacrylamide, and the three can also be mixed for use.

The second aspect of the invention provides a milling method for preparing an ultrathin titanium foil, which comprises the following steps:

1) degreasing and cleaning the surface of the titanium foil: ultrasonically dipping and washing the titanium foil to be treated in acetone, absolute ethyl alcohol and pure water for 5-10 min in sequence, and drying and taking out;

2) chemical milling: immersing the titanium foil treated in the step 1) in the chemical milling liquid for 1-4 min for milling;

3) surface cleaning: and sequentially soaking and washing the milled titanium foil in acetone and pure water for 6-10 min.

Preferably, in the step 1), the titanium foil to be treated is ultrasonically soaked and washed in an acetone solution for 3min to 5 min; ultrasonically soaking and washing in absolute ethyl alcohol for 1-3 min; ultrasonically soaking and washing in pure water for 1-3 min. The drying condition is that the mixture is placed in a drying oven with the temperature of 80-100 ℃ for 10-15 min.

Preferably, in step 2), slight ultrasonic vibration is performed while the chemical milling is performed.

Preferably, in the step 3), the titanium foil is soaked and washed in an acetone solution for 3min to 5min and in pure water for 3min to 5 min.

The invention has the following beneficial effects:

firstly, the addition of the corrosion inhibition stabilizer improves the viscosity of the chemical milling liquid, reduces the diffusion rate of ions, further reduces the milling rate during milling, avoids the occurrence of the condition of titanium foil surface over-corrosion caused by exponential increase of the later milling rate, contributes to improving the stability of the milling liquid, and ensures efficient and stable milling. Experiments prove that the chemical milling liquid added with the stabilizing agent has uniform milling, can obviously relieve the wrinkling phenomenon of the surface of the titanium foil, has high stability, and is more suitable for processing ultrathin titanium foil soldering lugs.

Secondly, the chemical milling liquid has low price, high efficiency, stability and uniform milling, and can obviously relieve the wrinkling phenomenon of the surface of the titanium foil. Compared with rolled ultrathin titanium foils, the ultrathin titanium foil prepared by the method disclosed by the invention is low in cost, can meet the quality requirement of a copper-clad ceramic substrate on a titanium foil soldering lug, is beneficial to reducing the preparation cost of the titanium foil, and further reduces the preparation cost of the AMB copper-clad plate.

Drawings

FIG. 1 is a flow chart of the present invention for preparing an ultra-thin titanium foil;

FIG. 2 is a comparison of the surface state of a titanium foil milled according to the present invention with that of a titanium foil milled by a conventional method, wherein (a) is an ultra-thin titanium foil prepared in example 1 and (b) is an ultra-thin titanium foil prepared in comparative example 1;

fig. 3 is a schematic diagram of the selected position of the copper-ceramic peel strength test strip.

Detailed Description

The following embodiments are implemented on the premise of the technical scheme of the present invention, and give detailed implementation modes and specific operation procedures, but the protection scope of the present invention is not limited to the following embodiments.

The reagents and starting materials used in the present invention are commercially available or can be prepared according to literature procedures. The experimental procedures, in which specific conditions are not noted in the following examples, are generally carried out according to conventional conditions or according to conditions recommended by the manufacturers.

Example 1 ultra-thin titanium foil milling and AMB copper-clad ceramic substrate preparation

First, chemical milling liquid preparation

The preparation method of the chemical milling liquid in a laboratory comprises the following steps: slowly adding 10-15 mL of glacial acetic acid, 30-40 mL of nitric acid and 100-150 mL of hydrofluoric acid into 200mL of pure water in sequence, and adding the pure water to prepare 600mL of solution; and then slowly adding 0.6-0.8 g of corrosion inhibition stabilizer powder into the solution while stirring by using a glass rod, wherein the solution is prepared and used as soon as possible, and the solution is not recommended to be stored for more than 24 hours.

Wherein, the chemical mass fraction of the hydrofluoric acid solution is 3 percent; the chemical mass fraction of the nitric acid solution is 63 percent; the chemical mass fraction of the glacial acetic acid solution is 99.5%.

The corrosion inhibition stabilizer is one or a mixture of more of polyacrylamide, polyvinyl alcohol and sodium silicate.

Secondly, milling and cutting ultra-thin titanium foil

1) Degreasing and cleaning the surface of the titanium foil: ultrasonically dipping and washing the titanium foil to be treated in an acetone solution for 3-5 min, ultrasonically dipping and washing in absolute ethyl alcohol for 1-3 min, ultrasonically dipping and washing in pure water for 1-3 min, drying and taking out. The drying condition is that the mixture is placed in a drying oven with the temperature of 80-100 ℃ for 10-15 min.

2) Chemical milling: immersing the titanium foil processed in the step 1) in chemical milling liquid for 150s for milling, and carrying out slight ultrasonic vibration in the milling process to improve the milling efficiency.

3) Surface cleaning: and sequentially soaking and washing the milled titanium foil in acetone and pure water for 3-5 min to finish milling the titanium foil, wherein the thickness of the milled titanium foil is milled to 5 mu m of ultrathin titanium foil from 10 mu m.

Preparation of three, AMB copper-clad ceramic substrate

The 5-micron ultrathin titanium foil is used as a soldering terminal, and procedures such as vacuum sintering, film pasting, exposure, development, etching and the like are carried out according to the sequence of an AMB (advanced manufacturing Board) process, so that a copper-clad ceramic substrate experimental sample (copper ceramic thickness 0.3/0.325/0.3mm, silicon nitride ceramic) with a specified pattern is prepared.

Comparative example 1

The comparative example used a conventional chemical milling solution without added corrosion inhibiting stabilizer to treat the titanium foil, the remainder being identical to example 1.

Comparative example 2

In this comparative example, a copper-clad ceramic substrate (0.3/0.325/0.3 mm in thickness of copper porcelain, silicon nitride ceramic) was manufactured using an ultrathin rolled titanium foil as a solder piece, and after cleaning and degreasing the surface of the rolled titanium foil having a thickness of 5 μm, a copper-clad ceramic substrate test sample (0.3/0.325/0.3 mm in thickness of copper porcelain, silicon nitride ceramic) having a predetermined pattern was prepared in accordance with the AMB process sequence in example 1.

Example 2 milling fluid stability determination

This example is a method for visually determining the stability of a chemical milling solution, which is used to test the stability of the chemical milling solutions used in example 1 and comparative example 1. the specific method is to take titanium foil pieces with a thickness of 10 μm and a side length of 20mm × 20mm, place the titanium foil pieces into two solutions, and record the time required for complete dissolution (HF-HNO according to the present invention)₃The time required for the complete dissolution of the system solution is 4min-5min), the used milling solution (2 titanium foils are processed each time, the specification of the titanium foils is 198mm × 98mm × 10 μm, and 0, 1, 2 and 3 times of

processing

0, 2, 4 and 6 titanium foils respectively) is tested according to the method, when the time required for dissolution is not obviously prolonged (0s-10s) compared with the time required for dissolution before use (0 th time), the solution is stable when 10s-60s, and the solution fails when the time is more than 60 s.

The results of the tests of the chemical milling liquids used in example 1 and comparative example 1 are shown in table 1:

table 1 summary of milling fluid usage times for example 1 and comparative example 1

Example 3 surface State observation of titanium foil

This example is an observation of the surface state of the titanium foil after chemical milling, and is used to examine the milling uniformity of the chemical milling solution used in example 1 and comparative example 1. As shown in FIG. 2, compared with the conventional chemical milling liquid, the novel chemical liquid of the present invention can alleviate the wrinkling phenomenon on the surface of the titanium foil, has fewer over-etched portions, and has high milling uniformity.

Example 4 evaluation of basic Properties of copper-clad ceramic substrate

The embodiment is an evaluation method of the basic performance of a copper-clad ceramic substrate, which is used for judging whether a titanium foil after chemical milling can meet the requirement of an AMB process on the quality of a welding sheet. The specific test method comprises a copper ceramic peel strength test and a water cooling impact test.

The test strips for the copper-ceramic peel strength test are 5mm in width, and the selected positions are shown in FIG. 3. And (2) performing water-cooling impact test, wherein the impact temperature is set to be 20-355 ℃, heating the heating plate at 355 ℃ for 2min, then quickly placing the heating plate in cold water for 1min to form a cycle, performing ultrasonic scanning flaw detection (SAM) test before the cold-hot cycle, performing SAM test every 10 cycles for 90 times, and performing SAM test every 5 cycles after 90 times until obvious warping and cracking phenomena are found in an SAM image of the copper-clad plate.

For example 1, comparative example 2, the test results are shown in table 2, and the test results show that: under the same thickness, the copper clad laminate prepared by adopting the ultrathin titanium foil subjected to chemical milling and liquification milling of the invention and the copper clad laminate prepared by directly rolling the ultrathin titanium foil (comparative example 2) have smaller basic performance difference. The peel strength of the copper-clad plate made of the ultrathin titanium foil after chemical milling can meet the quality requirement (>10N/mm) of the AMB copper-clad plate, and the copper-clad plate has excellent cold and thermal shock resistance, while the product quality requirement cannot be met by adopting the conventional chemical milling liquid (comparative example 1).

Therefore, the chemical milling liquid and the milling method for preparing the ultrathin titanium foil are reasonable and feasible, and the prepared product has excellent performance and practical value.

TABLE 2 comparison of the results of peel strength test and water-cooling impact test of copper porcelain

Numbering	Peel strength/N.mm^-1	Number of cold and hot impacts/times when warping and cracking fail
			Example 3	14.34	>120
Comparative example 1	5.26	30
			Comparative example 2	15.28	>120

While the preferred embodiments of the present invention have been described in detail, it will be understood by those skilled in the art that the invention is not limited thereto, and that various changes and modifications may be made without departing from the spirit of the invention, and the scope of the appended claims is to be accorded the full scope of the invention.

Claims

1. The chemical milling liquid for preparing the ultrathin titanium foil is characterized by comprising the following components:

15-25% of hydrofluoric acid solution, 1-3% of nitric acid solution, 5-8% of glacial acetic acid solution, 0.1-0.5 g/100mL of corrosion inhibition stabilizer of milling liquid and the balance of pure water.

2. The chemical milling solution for preparing ultra-thin titanium foil as claimed in claim 1, wherein:

wherein the chemical mass fraction of the hydrofluoric acid solution is 3%; the chemical mass fraction of the nitric acid solution is 63%; the chemical mass fraction of the glacial acetic acid solution is 99.5%.

3. The chemical milling solution for preparing ultra-thin titanium foil as claimed in claim 2, wherein:

wherein, the corrosion inhibition stabilizer is one or more of polyacrylamide, polyvinyl alcohol and sodium silicate.

4. The milling method for preparing the ultrathin titanium foil by adopting the chemical milling liquid in the claim 1 is characterized by comprising the following steps:

5. The milling method for preparing the ultrathin titanium foil as recited in claim 1, wherein:

in the step 1), ultrasonically dipping and washing the titanium foil to be treated in an acetone solution for 3-5 min; ultrasonically soaking and washing in absolute ethyl alcohol for 1-3 min; ultrasonically soaking and washing in pure water for 1-3 min,

the drying condition is that the mixture is placed in a drying oven with the temperature of 80-100 ℃ for 10-15 min.

6. The milling method for preparing the ultrathin titanium foil as recited in claim 1, wherein:

wherein, in the step 2), slight ultrasonic vibration is carried out during chemical milling.

7. The chemical milling solution for preparing ultra-thin titanium foil as claimed in claim 1, wherein:

wherein, in the step 3), the titanium foil is soaked and washed in acetone solution for 3min to 5min and in pure water for 3min to 5 min.