CN113319387B

CN113319387B - Large-scale preparation method of heat exchange enhancement microstructure

Info

Publication number: CN113319387B
Application number: CN202110677082.3A
Authority: CN
Inventors: 房晓龙; 韩鸿恩; 杨晓龙
Original assignee: Nanjing University of Aeronautics and Astronautics
Current assignee: Nanjing University of Aeronautics and Astronautics
Priority date: 2021-06-18
Filing date: 2021-06-18
Publication date: 2022-04-12
Anticipated expiration: 2041-06-18
Also published as: CN113319387A

Abstract

The invention discloses a large-scale preparation method of a heat exchange enhancement microstructure, and belongs to the technical field of electromachining. The method specifically comprises the following steps: step 1: electroforming a layer of metal A on the upper surface of the substrate, and then polishing and grinding the metal A; step 2: coating a layer of template on the surface of the polished metal A, and forming through holes on the surface of the template to obtain a workpiece; and step 3: performing electrolytic machining on the workpiece; and 4, step 4: dripping copper etching solution at the electrolytic machining position of the workpiece for etching; and 5: and cleaning the workpiece to obtain the enhanced heat exchange microstructure. The method has the characteristics of safety, high efficiency and suitability for large-area large-scale production, and the material of the substrate can be changed according to actual requirements so as to adapt to production with various requirements.

Description

Large-scale preparation method of heat exchange enhancement microstructure

Technical Field

The invention belongs to the technical field of electromachining, and particularly relates to a large-scale preparation method of a heat exchange enhancement microstructure.

Background

The Omniphobic microstructure (all-hydrophobic microstructure) is a blind hole-shaped structure with a small opening and a large interior, and researches show that a super-hydrophobic surface based on the microstructure has a series of excellent performances such as enhanced heat exchange, self-cleaning and pollution prevention, and belongs to one of surface textures. The surface texture technology refers to a technology that the surface of a workpiece has array patterns of pits, bulges, grooves, scales and the like with certain shapes, sizes and distribution. The surface texture with micro/nano scale plays a vital role in the aspects of energy exchange, signal transmission, bionics, friction and abrasion and the like, and shows a wide development prospect in many fields. At present, the preparation method of the surface texture structure comprises an imprinting technology, a mechanical vibration processing technology, an abrasive particle jet processing technology, a laser processing technology, an electric spark processing technology and electrolytic processing, but the imprinting technology is generally limited by characteristics such as hardness of workpiece materials, and is difficult to realize on a metal workpiece; the mechanical vibration processing technology is a method that a cutter has reciprocating vibration with a certain rule under the action of servo drive, a workpiece is processed, and simultaneously the surface texture is processed on the surface of the workpiece by matching the motion of the cutter, mechanical residual stress is always existed in the cutting process of the method, the processing quality of the surface texture is influenced, and the method needs one processing and is not suitable for large-scale preparation; the abrasive particle jet machining technology, the laser machining technology and the electric spark machining technology can be used for preparing the micro-pit structure on the metal surface, but only one micro-pit structure can be prepared, the micro-pit structure can be prepared in a laboratory, and large-area preparation is time-consuming and labor-consuming and low in efficiency. In conclusion, the methods all have the defects of long preparation time, complicated steps, low efficiency and incapability of large-scale production, and the prepared structure is also a simple micro-groove and micro-pit structure, so that the development of the preparation method of the heat exchange microstructure which is safe and efficient and is suitable for large-scale large-area production is of great significance.

Disclosure of Invention

In view of the above, the invention provides a large-scale preparation method of a heat exchange enhancing microstructure, and aims to rapidly process a large-area evaporation cooling super-hydrophobic microstructure and realize industrial production.

In order to achieve the technical purpose, the invention provides the following technical scheme:

a large-scale preparation method of a heat exchange enhancement microstructure comprises the following steps:

step 1: electroforming a layer of metal A on the upper surface of the substrate, and then polishing and grinding the metal A;

step 2: coating a layer of template on the surface of the polished metal A, and forming through holes on the surface of the template to obtain a workpiece;

and step 3: performing electrolytic machining on the workpiece to remove the uncovered metal A layer;

and 4, step 4: dripping copper etching solution on the electrolytic machining position of the workpiece for etching, wherein the addition amount is based on the condition that the etching solution does not exceed the metal A layer;

and 5: and (3) pouring out the redundant copper etching liquid after the copper is dissolved for a specified time (3-5min), and cleaning the workpiece to obtain the enhanced heat exchange microstructure.

The substrate comprises copper, nickel, iron, etc. The metal A comprises nickel, iron or an alloy.

Further, the metal A is a metal capable of electroforming or electroplating and capable of being selectively and chemically dissolved with copper (selective chemical dissolving solution refers to a chemical solution which can obviously dissolve the metal A and simultaneously has a trace amount of metal or is not dissolved in the substrate), and the thickness of the metal A is between 20 and 50 micrometers.

Further, the polishing standard of the step 1 is that the surface roughness Ra of the metal A is less than 0.2.

Further, the template in step 2 is a photoresist template or a PDMS template. The diameter of the through hole is 100 mu m.

The photoresist mold is preferably SU-8 dry film photoresist, and is pre-baked during film covering to soften the photoresist and improve the bonding force with the substrate, and is post-baked after exposure to cause crosslinking reaction inside the photoresist mold.

Further, the thickness of the photoresist mold is 20-50 μm; the thickness of the PDMS template is 150-250 μm.

Further, when the template in the step 2 is a photoresist template, the template is removed after the workpiece is cleaned in the step 5; and (3) when the template is the PDMS template, removing the template after the step (3) and reusing the template.

Further, the electrolytic processing time in the step 3 is 2-3 min. The electrolyte used in electrolytic machining is sodium nitrate solution, the voltage is 12V, the duty ratio is 20%, and the pressure is 0.1 MPa.

Further, the copper etching solution in the step 4 is an acidic copper chloride etching solution or an alkaline copper chloride etching solution (the acidic copper chloride etching solution comprises, by mass, 5% of copper chloride, 10% of concentrated hydrochloric acid, 25% of hydrogen peroxide and 60% of water), and the alkaline copper chloride etching solution comprises 100g/L of copper chloride, 100g/L of ammonium chloride and 700mg/L of ammonium monohydrate). It is desirable to be able to corrode copper without causing significant corrosion to the surrounding metal a.

Further, the etching temperature in step 4 is 20-40 ℃. The etching time is 3-5 min.

The dissolving in the step 5 is performed for a specified time to prevent the etching solution from dissolving too much copper, so that the size of the cavity is too large. And in the etching process, mechanical stirring is carried out simultaneously in a soaking mode, and the operation is carried out at a ventilation and exhaust position.

A plurality of microstructures can be processed on the same substrate at the same time, and the method can also process on a curved surface.

The invention adopts different types of substrates and metals A and uses different types of etching solutions. For example, copper for the substrate and nickel for the metal A, and an acidic copper etching solution can be used.

The invention also provides a heat exchange enhancement microstructure.

The micro electrochemical machining is a machining method for obtaining a high-precision and micro-size part in a micro-scale range (1 mu m-1 mm) by applying an electrochemical machining principle. In many occasions, the micro electrochemical machining has unique advantages, such as high machining efficiency, good forming precision, easy control of material removal, wide range of materials suitable for machining, no consideration of mechanical characteristics such as strength, hardness and the like of workpiece materials, no abrasion of tools in the machining process, no stress generated on workpieces and the like.

Mask microfabrication is an electrochemical machining method combined with a mask lithography technique. The method comprises coating a layer of photoresist on the surface (single side or double sides) of a workpiece, forming an exposed surface with a certain pattern on the workpiece after photoetching development, selectively dissolving the exposed part which is not protected by the photoresist by electrolytic processing, and finally processing the workpiece with the required shape. Because the metal dissolution is isotropic, the metal is dissolved in the radial direction and the transverse direction at the same time, so the invention strictly controls the dissolution shape, reduces the transverse dissolution as much as possible and the like to ensure the processing precision of the mask micro-electrolysis.

Electroforming is a precise additive manufacturing technology in electrochemical machining, and its electrochemical principle is a process of utilizing metal ion cathode electrodeposition principle to deposit metal, alloy or composite material on conductive master mould (core mould), and separating it from master mould to obtain product. The shape and surface roughness values of such electroformed parts are similar to those of the master mould.

Compared with the prior art, the invention has the beneficial effects that:

the electrochemical machining is a non-contact machining, has no cutting force and cutting heat in the machining, does not generate deformation, residual stress, work hardening, burrs, flashes and the like, has good machining surface quality and wide machining range, is not limited by the strength, the hardness and the toughness of the material, and can machine metal materials which are difficult to cut and have high strength, high hardness, high toughness and the like. According to the invention, the metal layer is cast on the substrate by adopting an electroforming processing mode, then the SU-8 dry film photoresist is used, and the photoresist is coated by adopting a film coating mode, so that the pattern on the mask plate can be copied onto the photoresist with high precision, the defects of uneven thickness, bubbles and the like caused by a spin coating process are avoided, the steps of spin coating, prebaking and the like are saved, and the processing time is saved. Compared with liquid photoresist, the SU-8 dry film photoresist is more convenient to use, the thickness is more accurately controlled, the super-thick photoresist can be prepared in a multi-layer dry film stacking mode, and the application scene is wider. In addition, as the photoresist is a non-metal material, the photoresist can be dissolved by an organic solvent and cannot influence other metal materials. In the method, the SU-8 dry film photoresist can be subjected to pre-baking treatment to soften the photoresist for application to curved surfaces and complex molded surfaces, so that the heat exchange microstructure can be processed on the complex molded surfaces. And then adding etching solution, and utilizing mask micro electrolytic machining to simultaneously etch all the micro pits to rapidly prepare the large-area reinforced heat exchange microstructure.

Although the PDMS template is troublesome to manufacture, the SU-8 dry film photoresist can be replaced by the PDMS template for recycling, and the PDMS template can be applied to a curved substrate, so that the application range is wider.

The traditional methods for preparing the heat exchange enhancement microstructure, such as a chemical corrosion method, a solution soaking method, a sol-gel method, femtosecond laser processing, chemical vapor deposition, electrostatic spinning and related composite processing technologies, have the defects of chemical pollution, ultra-clean and high-vacuum operation conditions, long preparation time, complex processing steps and the like, so that the heat exchange enhancement microstructure is restricted from entering wider industrial application. The processing method using the electrochemical principle in the method has the advantages of relatively simple equipment, simple and convenient operation, low cost and high efficiency, and provides possibility for industrialized production of the evaporation cooling microstructure.

In production, the size of the heat exchange enhancing microstructure may vary with the demand. At the moment, the chemical etching time is changed, so that the method is simple and rapid, and the process adaptability is strong. Meanwhile, the material of the substrate can be changed according to the actual requirement, so that the method is suitable for production with various requirements.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.

FIG. 1 is a cross-sectional view of a metal A electroformed on a substrate according to example 1;

FIG. 2 is a cross-sectional view of example 1 coating a PDMS template with a through-hole template;

FIG. 3 is a sectional view of an electrolytic metal A in example 1;

FIG. 4 is a cross-sectional view of example 1 after removing the PDMS template;

FIG. 5 is a sectional view of example 1 with copper etching solution added;

FIG. 6 is a cross-sectional view of a microstructure for enhancing heat exchange of example 1;

number designation in the figures: 1-substrate, 2-metal A layer, 3-template, 4-copper etching liquid and 5-reinforced heat exchange microstructure.

Detailed Description

Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but as a more detailed description of certain aspects, features and embodiments of the invention.

It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Further, for numerical ranges in this disclosure, it is understood that each intervening value, between the upper and lower limit of that range, is also specifically disclosed. Every smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in a stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference herein for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.

It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present disclosure without departing from the scope or spirit of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification. The specification and examples are exemplary only.

As used herein, the terms "comprising," "including," "having," "containing," and the like are open-ended terms that mean including, but not limited to.

The acid copper chloride etching solution or the alkaline copper chloride etching solution used in the invention is a finished product purchased in the market.

Example 1

Step 1): electroforming a nickel metal layer A2 with the thickness of 25 mu m on the upper surface of the copper substrate 1, and then polishing the nickel metal layer A2 until the surface roughness Ra of the nickel metal layer A is less than 0.2;

step 2): coating a PDMS template 3 on the surface of the polished nickel metal layer A, and forming through holes on the surface of the template to obtain a workpiece, wherein the thickness of the PDMS template 3 is 250 micrometers, the diameter of each micro through hole is 100 micrometers, and the number of the micro through holes is 30X 30;

step 3): carrying out electrolytic machining on the workpiece, wherein the voltage is 12V, the duty ratio is 20%, the electrolyte is 100g/L of sodium nitrate solution, the pressure is 0.1MPa, and the electrolysis time is 2 min;

step 4): removing the PDMS template 3, then dropwise adding an acidic copper etching solution 4 at the electrolytic machining position of the workpiece, and etching for 4min at the temperature of 30 ℃; in the etching process, mechanical stirring is carried out simultaneously in a soaking mode, and the operation is carried out at a ventilation exhaust position;

step 5): and (4) pouring out the redundant acid copper etching solution, and cleaning the workpiece to obtain the enhanced heat exchange microstructure 5.

Fig. 1 to fig. 6 are flow charts of the preparation of the microstructure for enhancing heat exchange according to the present embodiment.

The embodiment can simultaneously process 900 microgrooves of 30 × 30, and the microgrooves have complete structures, no defects such as flash, burr and bubbles, and uniform sizes.

Example 2

Step 1): electroforming a nickel layer A2 with the thickness of 25 mu m on the upper surface of the iron-based sheet 1, and then polishing the nickel layer A2 until the surface roughness Ra of the nickel layer A2 is less than 0.2;

step 2): coating a layer of SU-8 dry film photoresist die 3 with through holes on the surface of the polished nickel metal layer A2 to obtain a workpiece, wherein the thickness of the SU-8 dry film photoresist die 3 is 25 micrometers, the diameter of each micro through hole is 100 micrometers, and the number of the micro through holes is 30 x 30;

step 4): then dropwise adding an acidic copper chloride etching solution 4 to the electrolytic machining position of the workpiece, and etching for 4min at the temperature of 30 ℃; in the etching process, mechanical stirring is carried out simultaneously in a soaking mode, and the operation is carried out at a ventilation exhaust position;

step 5): and pouring out the redundant copper etching solution 4, cleaning the workpiece, and removing the SU-8 dry film photoresist mold 3 to obtain the enhanced heat exchange microstructure 5.

Example 3

The difference from example 1 is that the substrate is copper and the metal a is gold.

Example 4

The difference from example 1 is that the substrate is nickel and metal a is copper.

Comparative example 1

The same abrasive jet machining method as in example 1 was used to machine 900 microgrooves 30 × 30 in a time period 20 times longer than that of example 1.

Comparative example 2

The same laser machining method as in example 1 was used to machine 900 microgrooves 30 × 30, which took 22 times longer than example 1, and the resulting microstructures were of poor quality.

Comparative example 3

The difference from example 2 is that step 2 is not carried out.

The obtained microstructure has the defects of cracks, non-uniform microgroove structures and the like.

Comparative example 4

The difference from example 2 is that step 3 was not carried out.

The whole preparation process takes long time, and the shape difference between the grooves is large.

Comparative example 5

The difference from example 2 is that step 4 is not carried out.

The grooves need to be processed one by one, and batch production cannot be realized, so that the time is consumed.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included therein.

Claims

1. A large-scale preparation method of a heat exchange enhancement microstructure is characterized by comprising the following steps:

and step 3: performing electrolytic machining on the workpiece;

and 4, step 4: dropwise adding etching liquid to the electrolytic machining position of the workpiece for etching;

and 5: and cleaning the workpiece to obtain the enhanced heat exchange microstructure.

2. The method according to claim 1, wherein the metal a is a metal capable of electroforming or electroplating, and the thickness of the metal a is between 20 and 50 μm.

3. The method according to claim 1, wherein the polishing in step 1 is performed to a surface roughness Ra < 0.2 of the metal a.

4. The method according to claim 1, wherein the template in step 2 is a photoresist template or a PDMS template.

5. The production method according to claim 4, wherein the photoresist film has a thickness of 20 to 50 μm; the thickness of the PDMS template is 150-250 μm.

6. The method according to claim 4, wherein when the template in step 2 is a photoresist template, the template is removed after the workpiece is cleaned in step 5; and when the template is a PDMS template, removing the template after the step 3.

7. The method of claim 1, wherein the electrolytic processing time of step 3 is 2-3 min.

8. The method according to claim 1, wherein the etching solution of step 4 is a copper etching solution.

9. The method according to claim 1, wherein the etching temperature in step 4 is 20 to 40 ℃.