WO2023170323A1

WO2023170323A1 - Method for manufacturing channels, wells and/or complex structures in glass

Info

Publication number: WO2023170323A1
Application number: PCT/ES2023/070124
Authority: WO
Inventors: Maria del Carmen BAO VARELA; Ana Isabel Gomez Varela; Raul SANCHEZ CRUZ; Maria Teresa Flores Arias; Bastian CARNERO GROBA
Original assignee: Universidade De Santiago De Compostela
Priority date: 2022-03-11
Filing date: 2023-03-07
Publication date: 2023-09-14
Also published as: ES2912039A1; ES2912039B2

Abstract

The present invention relates to a process for processing glass using a laser source. More particularly, this process comprises making structures with different geometries and depths in glass substrates, using a subaquatic indirect laser ablation method.

Description

DESCRIPTION

Procedure to manufacture channels, wells and/or complex structures in glass

Invention sector

The present invention relates to a process for processing glass using a laser source. More particularly, this process comprises the realization of structures with different geometries and depths on glass substrates, using an underwater indirect laser ablation method.

Background

Microfluidics is a field of great interest due to its multiple applications in chemistry, engineering and medicine. Microfluidic devices can have very complex structures, in which the channel can be considered the most basic unit. Through laser ablation it is possible to create structures with varied dimensions and geometries on glass substrates. Glass is one of the most interesting substrates in the field of microfluidics because it offers better conditions for experiments in terms of chemical stability and optical quality for inspection. Furthermore, a master of a microfluidics device made of glass can be reused numerous times.

Taking advantage of the impurities in the glass, it is possible to manufacture structures by laser ablation, even for substrates that are transparent at the laser wavelength. However, the dimensions of these structures are on the order of tens of micrometers (Daniel Nieto, Justo Arines, and María Teresa Flores-Arias, "Fluence ablation threshold dependence on tin impurities in commercial soda-lime glass," Appl. Opt. 53 , 5416-5420 (2014)). To fabricate larger structures (in the millimeter range), the most appropriate technique is indirect laser ablation or laser-induced plasma-assisted ablation (LIPAA). This technique consists of focusing a laser on a metallic target located under glass or a transparent material at the wavelength of the laser used (Zhang J, Sugioka K, Midorikawa K. Laser-induced plasma-assisted ablation of fused quartz using the fourth harmonic of a Nd +:YAG laser. Appl Phys A Mater Sci Process 1998;67:545-9). The plasma generated by the interaction of the laser with the metallic target allows the ablation of the rear face of the glass to begin (Zhang, J., Sugioka, K. & Midorikawa, K. High-quality and high- efficiency machining of glass materials by laser-induced plasma-assisted ablation using conventional nanosecond UV, visible, and infrared lasers. Appl Phys A 69, S879-S882 (1999), Koji Sugioka, Katsumi Midorikawa, Hiroshi Yamaoka, Yutaka Gomi, Masayoshi Otsuki, Ming Hui Hong, Dong Jiang Wu, Lai Lee Wong, and Tow Chong Chong "Glass microprocessing by laser-induced plasma-assisted ablation: fundamental to industrial applications", Proc. SPIE 5506, Nonresonant Laser-Matter Interaction (NLMI-11), (15 July 2004)). As an example, with this technique, structures of millimeter dimensions have been manufactured that simulate large blood vessels, in particular, bifurcations of coronary arteries (Aymerich M, Alvarez E, Bao-Varela C, Moscoso I, González-Juanatey JR, Flores- Arias MT. Laser technique for the fabrication of blood vessels-like models for preclinical studies of pathologies under flow conditions. Biofabrication 2017;9:025033). In this case, it was necessary to refocus the laser to obtain channels with a maximum depth of 1.2 mm with the limitation that the method only allows obtaining inclined walls.

The manufacture of different glass elements with depths of the order of several millimeters continues to be a challenge today. The depth of the channels obtained by LIPAA is limited, mainly due to the accumulation of the ablated material between the glass and the target. An et al. (An R, Li Y, Dou Y, Yang H, Gong Q. Simultaneous multimicrohole drilling of soda-lime glass by water-assisted ablation with femtosecond laser pulses. Opt Express 2005; 13 : 1855) proposed the use of water to reduce the Material redeposition and the laser beam blocking effect when drilling micrometer holes in soda-lime glass using femtosecond laser pulses. In this case, the laser is focused on the back of the glass substrate that is drilled directly with the laser and as the channel is manufactured it is filled with water. Internal channels are obtained with maximum diameters of between 3 and 20 micrometers and lengths of up to approximately 90 micrometers.

Brief description of the invention

The authors of the present invention have developed a procedure that allows manufacturing channels, wells and/or complex structures in a glass with straight walls, that is, perpendicular to the faces of the glass. The procedure allows manufacturing these channels, wells and/or complex structures with a minimum depth of 500 pm ensuring that the walls are straight. But in addition, the procedure also allows achieving greater depths, up to 5 mm, keeping the walls straight. Thus, the invention is directed to glasses with these channels, wells and/or complex structures and to the manufacturing process.

The present invention refers to a glass characterized by having channels, wells and/or complex structures with vertical walls and the depth of the channels, wells and/or complex structures being greater than 500 pm.

The invention is also directed to a procedure for manufacturing channels, wells and/or complex structures in glass, which comprises: focusing a laser beam on a metal sheet through the glass, where the glass is placed parallel to the metal sheet, and between the glass and the metal sheet there is a transparent liquid selected from the group consisting of deionized water, distilled water, ethanol, methanol and acetone.

The invention is also directed to a glass characterized by having channels, wells and/or complex structures with vertical walls and the depth being greater than 500 pm, obtainable by the process of the invention.

Description of the figures

To complement the description of the present invention and in order to help a greater understanding of its characteristics, certain figures are attached that are exclusively illustrative and are not limiting.

Figure 1 shows a diagram with the experimental setup in the ablation zone. Fasteners (2) are placed on the glass substrate (1) to prevent the glass from moving due to the pressure exerted during the manufacturing process. The figure also represents the laser beam (3), the metallic target (4), separators (5) and deionized water (6).

Figure 2a shows a reconstructed 3D confocal image of a representative rectangular channel, and in Figure 2b its corresponding profile.

Figure 3a shows a top view of an array of 3 mm diameter wells made of soda-lime glass. In Figure 3b you can see the depth of the wells manufactured. Detailed description of the invention

Definitions

In the present invention, the term "wells" refers to holes with walls perpendicular to the faces of the glass whose base can have different shapes, among others circular, oval, rectangular or square.

In the present invention, the expression "complex structures" refers to structures composed of the combination of straight channels and channels that draw curves, or combinations of channels with different geometries and combinations of wells and/or wells and channels.

In the present invention, the expression “straight wall” refers to the fact that the lateral faces of the channels and/or wells and/or complex structures are perpendicular to the faces of the glass.

In the present invention, the term "passes" refers to the number of times the laser is struck on the metal following the pattern of the previously designed shape.

In the present invention, the term "refocus" refers to refocusing the laser beam onto the metallic target.

The present invention refers to a glass characterized by having channels, wells and/or complex structures with vertical walls and the depth of the channels, wells and/or complex structures being greater than 500 pm. In a particular embodiment the depth of the channels, wells and/or complex structures is preferably between 500 mm and 2 mm, more preferably between 2 mm and 5 mm, more preferably between 3 mm and 5 mm, even more preferably between 4 mm and 5 mm. mm.

The manufacture of channels, wells and/or complex structures in glass with vertical walls and the depth of the channels, wells and/or complex structures being greater than 500 pm, preferably between 500 pm and 2mm, more preferably between 2 mm and 5 mm , more preferably between 3 mm and 5 mm, even more preferably between 4 mm and 5 mm, is possible thanks to the method of the invention. In the method of the invention, the laser beam is focused on the metal sheet through the glass. The metal sheet absorbs the wavelength of the laser, as a target to induce the plasma. In this way an indirect ablation is achieved. In this indirect ablation, the glass is ablated by the action of the plasma generated in the process of interaction of the laser beam with the metal, unlike direct ablation in which the laser action takes place on the glass directly. In the procedure of the invention, the effects of mechanical shock waves, the induced ablation plume and the generation of cavitation bubbles are combined to give rise to the ablation of the rear face of the glass, the face facing the metal sheet. .

Lfri, an expert in the field, knows and is capable of selecting the necessary parameters in the experiment for indirect ablation to occur. The values of these parameters and their combinations are known in the art or may arise from testing them, such as power, pulse duration, frequency, and speed at which the laser moves. The expert will be able to reach the optimal combinations for each case.

In the process of the invention, a transparent liquid selected from the group consisting of deionized water, distilled water, ethanol, methanol and acetone is used. This liquid facilitates the expulsion of the material during glass ablation. Due to the effect of the liquid, the thermal load and the redeposition of material remains in the work area of interest are reduced because the specific heat capacity of the liquid used and the thermal conductivity are greater than that of air. Thanks to this, excess heat is transported by the liquid away from the work area faster than through air. The liquid may have a cooling effect. Likewise, the extracted material is prevented from solidifying again on the substrate. On the other hand, the plasma generated in the ablation process absorbs part of the incident laser energy and reduces the coupling of the laser energy with the surface of the material. The incorporation of the liquid causes both the size and duration of the plasma to be reduced. The delay in the start of plasma formation causes the overlap with the laser pulse to decrease, reducing the shielding effect and improving the efficiency of the process. The liquid incorporated in the process can be sealed or introduced as a flow. In the latter case, the flow further favors the dragging of excess material extracted from the substrate. The process described in the present invention has the advantage of allowing shapes to be obtained in the glass that can be simple such as channels or wells, and also complex structures.

Furthermore, this process has the advantage that the walls obtained in these shapes are straight, straighter than those obtained with other techniques. It is even possible to achieve structures with walls perpendicular to the faces of the substrate with a minimum depth of 500 pm.

One of the main advantages of the method of the invention is that it allows the manufacture of channels, wells and/or complex structures with depths ranging from 500 μm to 1.4 mm, with vertical walls and without the need to refocus the laser, with surfaces interiors with roughness between 10 and 20 pm (as demonstrated in example 1). It also allows greater depths to be reached, even up to 5 mm, after successive refocusing of the laser beam and the introduction of a liquid flow, which favors the removal of excess material (as demonstrated in example 2). A possible experimental scheme to carry out the process of the invention is illustrated in Figure 1.

Thus, the procedure includes an additional stage in which the laser is refocused. And the method may also comprise another additional step in which the flow of the liquid is introduced.

In a particular embodiment, the process comprises an additional heat treatment step. This thermal treatment allows the roughness of the structures to be modified, which will depend on the heating ramps and the time and temperature maintained during the treatment. In a particular embodiment, the thermal heating is maintained between 1.5 hours and 3 hours at a temperature between 500°C and 650°C.

Possible materials used

For the invention, a nanosecond pulsed laser is preferably used. Thus, among the nanosecond pulsed lasers, the Nd:YVO4 laser emitting at the fundamental wavelength of 1064 nm, and the Nd:YAG laser emitting at the fundamental wavelength or at 532 nm, at 355 nm and at 266 nm, are preferred. nm. In general, the metal sheet could be made of any metal since all of them can be treated with a laser by selecting the appropriate laser parameters. In a particular embodiment, the metal sheet is selected from a sheet of steel, brass, chrome and silver. The steel can be carbon steel or stainless steel.

In the process of the invention, the best results are obtained when the glass is soda-lime, borosilicate glass, pyrex® or quartz.

One way of carrying out the invention is to place the glass at a distance from the metal sheet of between 0.07 mm and 0.58 mm. This ensures that the effect of material ablation on the glass is more efficient.

In a particular embodiment, the liquid covers a portion of the glass less than 80% of the thickness of the glass, preferably less than 70%, more preferably less than 50%.

In another preferred embodiment, the glass-metal sheet assembly is arranged so that displacement is avoided and is flat.

It is also possible to move the entire metal sheet, the glass, and optionally the liquid between them, keeping the direction of incidence of the laser beam fixed.

Optimized parameters

In a particular embodiment, the laser beam moves along the metal sheet. In a more particular embodiment, this displacement is carried out by means of a system of galvanometric mirrors. In a preferred embodiment, the laser light has a beam travel speed of between 200 mm/s and 600 mm/s. At speeds different from this range there may be damage to the edges of the structure. In a preferred embodiment, the laser has a repetition rate of between 8 and 12 kHz. At repetition rates different from this range there may be an increase in damage to the edges of the structure.

To optimize the results of the procedure, the laser light is applied in a number of passes equal to or greater than 10 passes. In this way it is possible to obtain straight walls in channels, wells and/or complex structures of only 500 pm. To obtain greater depths it is possible to increase the number of passes, for example between 10 and 75 passes, and preferably between 20 and 50 passes. In the present invention, the best results when manufacturing rectangular wall channels, wells and/or other complex structures are obtained when the following work parameters are used: 30 passes, average power of 4.92 W, repetition rate of 10 kHz and beam travel speed of 200 mm/s.

Compared to other glass machining processes, the procedure of the present invention, in addition to allowing structures of very varied sizes to be manufactured, presents other advantages such as simplicity and flexibility of design, making it possible to manufacture complex elements with great depth compared to other glass structuring procedures, such as direct writing by laser ablation, selecting the appropriate machining parameters for each structure.

Methods and experimental design

The following examples serve to illustrate the present invention and do not constitute a limitation thereof.

Example 1.

The starting point is an experimental setup as shown in Figure 1. This setup includes the generation of plasma through the ablation of a 150 m thick steel target (H+S PRÁZISIONSFOLIEN GmbH, VohenstrauB, Germany) using a Q laser. -Nd:YVO4 switch (Rofin; Plymouth, MI, USA), emitting at a wavelength of 1064 nm, and with a pulse duration of 20 ns. The glass to be structured is a soda-lime glass transparent at the wavelength of the laser source and which is kept separated from the metal sheet by a distance equal to 145 ± 15 pm. The glass-metal sheet assembly is immersed in deionized water and a set of weights is placed on it to prevent displacement during the structuring of the glass and guarantee the flatness of the system. During the generation of plasma induced by the interaction of the laser with the metal sheet, cavitation bubbles and shock waves are produced that propagate from the metal to the glass, favoring the ablation process. To obtain rectangular profile channels and different depths, the following working parameters are used: average power of 4.92 W, repetition rate of 10 kHz and movement speed of the 200mm/s beam. The results obtained by confocal microscopy are shown in Table 1.

Table 1. Relationship between the depth obtained for the channels depending on the number of laser passes performed.

A reconstructed 3D confocal image of a representative rectangular channel is shown in Figure 2a) and the corresponding profile in Figure 2b). The working laser parameters used in this case are an operating wavelength of 1064 nm, beam travel speed of 200 mm/s and 30 laser passes. Another parameter that can be modified during manufacturing is the roughness of the bottom of the channels. Table 2 shows the evolution of the roughness evaluated based on the arithmetic mean of the surface S(a) over an area of 250x250 pm ² with the laser repetition rate, using an average power of 4.92 W. and beam travel speed of 200 mm/s.

Table 2. Values obtained for the bottom roughness based on the arithmetic mean of the surface (Sa) of the channels as a function of the laser repetition rate. The measurements have been carried out in accordance with the ISO 25178 standard. Example 2.

Using a variant of the previous example, channels, or other types of structures, with greater depths can be achieved. In this case, instead of a container with sealed water, a flow of water is introduced that allows the waste material generated during the ablation to be carried away, avoiding the redeposition of said waste on the bottom and on the edges of the channels. Furthermore, in this example the laser beam is refocused on the steel metal sheet to guarantee the continuity of the ablation process. In particular, maintaining the laser working parameters of example 1, rectangular channels and wells have been manufactured, such as those shown in Figure 3, with a depth of 4.22 mm.

As can be seen from the results of examples 1 and 2, the procedure of the invention allows controlling the depth of the manufactured rectangular channels and their roughness by varying the working laser parameters and the number of laser passes used.

Claims

1. Procedure for manufacturing channels, wells and/or complex structures in a glass substrate of the type that has vertical walls and the depth of the channels, wells and/or complex structures being greater than 500 pm, characterized in that it comprises: place the glass substrate parallel to a metal sheet and place between the glass and the metal sheet a transparent liquid selected from the group consisting of deionized water, distilled water, ethanol, methanol and acetone, said liquid facilitates the expulsion of the material during glass ablation, focusing a laser beam on a metal sheet through the glass, so that the metal sheet absorbs the wavelength of the laser and induces plasma to produce an indirect ablation of the face of the glass that faces it. the metal sheet, and where the laser light comes from a nanosecond pulsed laser.

2. Method according to claim 1, comprising an additional laser refocusing step.

3. Method according to any of the preceding claims, which comprises introducing a flow of liquid.

4. Method according to any of the preceding claims, which comprises an additional heat treatment step to modify the roughness of the structures.

5. Procedure according to any of the previous claims, where the glass is placed at a distance from the metal sheet of between 0.07 mm and 0.58 mm.

6. Method according to any of the preceding claims, wherein the laser light moves along the metal sheet at a beam travel speed of between 200 mm/s and 600 mm/s.

7. Method according to any of the preceding claims, wherein the laser light has a beam repetition rate of between 8 and 12 kHz.

8. Method according to any of the preceding claims, wherein the laser light is applied in a number of passes equal to or greater than 10 passes. Method according to any of the previous claims, wherein the laser light is applied with an average power of 4.92 W, and moves along the metal sheet at a beam displacement speed of between 200 mm/s and 600 mm/s. , with a repetition rate of 10kHz and is applied in 30 passes.