Substrate bonding method, substrate bonding system, and microfluidic device

Abstract

The present invention bonds two substrates firmly at low cost, without modifying surfaces.　A substrate bonding system (10) includes a temporary bonding unit (11) that superimposes, on a first substrate (21) made of a first resin with a first glass transition temperature, a second substrate (22) made of a second resin with a second glass transition temperature lower than the first glass transition temperature, and pressure-bonds the substrates together at a predetermined temperature and a predetermined pressure. The predetermined temperature is a temperature between the first glass transition temperature and the second glass-transition temperature. The substrate bonding system (10) further includes a final bonding unit that heats the mutually pressure-bonded first substrate and second substrate, at a temperature substantially equal to the second glass transition temperature, for a predetermined time.

Description

Technical Field

[0001] The present invention relates to a method for bonding two substrates to each other, a substrate bonding system, and a microfluidic device.

Background Art

[0002] In recent years, in the fields of biology, medicine, and analysis, microfluidic devices such as cartridges and lab-on-chips have been widely used. Such microfluidic devices are created by bonding another resin substrate to a resin substrate in which channels composed of grooves and recesses are formed.

[0003] In order to bond two substrates, an adhesive or a substrate with an adhesive is used, or the surface of the substrate is exposed to a solvent to dissolve the surface for bonding. However, adhesives or solvents may remain on the channel surface of the microfluidic device, and the adhesives or solvents may affect the test results and measurement results.

[0004] Citation Document 1 discloses bonding two plastic resin substrates by thermocompression bonding without using adhesives or solvents. However, in Citation Document 1, it is necessary to perform pressure bonding at a temperature exceeding the glass transition temperature of the substrate, and there is a possibility that the fine channels of the microfluidic device may be blocked or deformed, or the substrate itself including the microfluidic device may be warped.

[0005] Therefore, Citation Document 2 and Citation Document 3 disclose a method of performing surface modification on the substrates to be bonded in advance by plasma treatment, corona discharge treatment, etc. and then performing pressure bonding at a low temperature.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Non-Patent Document 1

[0007] However, since the hydrogen bonds created by surface modification are broken when exposed to moisture, the adhesion of the substrate cannot be maintained for a long period of time. In particular, if microfluidic devices are used for liquid delivery or placed at high temperatures in a reagent-sealed state, the microfluidic devices may be damaged due to their low water resistance.

[0008] Furthermore, when surface modification is performed using vacuum ultraviolet treatment, autofluorescence remains on the substrate, making it unsuitable for applications requiring fluorescence observation. While surface modification with less autofluorescence is possible, the equipment required is extremely expensive and involves vacuum processes, making mass production inefficient.

[0009] Furthermore, surface modification of the entire substrate alters its wettability, which in turn alters the liquid flow within the channel. Additionally, surface wettability changes over time, which presents another challenge.

[0010] Furthermore, surface modification can affect the surface of the substrate opposite to the side to which it is to be bonded. In such cases, the substrate may end up bonding to the mold during press bonding. Additionally, if surface modification is performed before bonding the substrate, the resulting product will be more expensive.

[0011] Furthermore, similar problems can arise in applications such as simply bonding two substrates together or encapsulating other components between two substrates.

[0012] Therefore, there is a need for a substrate bonding method, substrate bonding system, and microfluidic device that can bond two substrates inexpensively and firmly without using adhesives or solvents, without causing the substrates to warp or deform, and without surface modification. [Means for solving the problem]

[0013] According to one aspect of the present disclosure, a substrate bonding method is provided, comprising: a preparation step of preparing a first substrate made of a first resin having a first glass transition temperature and a second substrate made of a second resin having a second glass transition temperature lower than the first glass transition temperature; and a temporary bonding step of superimposing the second substrate on the first substrate and pressing them together at a predetermined temperature and pressure, wherein the predetermined temperature is a temperature between the first glass transition temperature and the second glass transition temperature; and further comprising a final bonding step of heating the first substrate and the second substrate, which are pressed together, at a temperature approximately equal to the second glass transition temperature for a predetermined time.

[0014] In another embodiment, a substrate bonding system is provided, comprising: a temporary bonding unit that superimposes a second substrate made of a second resin having a second glass transition temperature lower than the first glass transition temperature onto a first substrate made of a first resin having a first glass transition temperature, and presses them together at a predetermined temperature and pressure, wherein the predetermined temperature is a temperature between the first glass transition temperature and the second glass transition temperature; and a final bonding unit that heats the first substrate and the second substrate, which are pressed together, at a temperature approximately equal to the second glass transition temperature for a predetermined time. [Effects of the Invention]

[0015] In these embodiments, after the two base materials are pressure-bonded (temporary bonding step) at a temperature between the first glass transition temperature and a second glass transition temperature lower than it, the base materials are heated (main bonding step) at a temperature approximately equal to the second glass transition temperature. The temperature applied to the two base materials only needs to be always lower than the first glass transition temperature. Therefore, without using an adhesive or a solvent, without the base materials warping or undergoing shape deformation, and without performing surface modification, the two base materials can be bonded cheaply and firmly. Furthermore, the reliability of the microfluidic device created by such an adhesive method can be enhanced.

[0016] The objects, features, and advantages of the present invention will become even clearer from the following description of the embodiments related to the accompanying drawings.

Brief Description of the Drawings

[0017] [Figure 1] It is a schematic diagram showing a base material bonding system based on the present disclosure. [Figure 2A] It is a top view of the first base material. [Figure 2B] It is a top view of another first base material. [Figure 3A] It is a side view of the first base material in another embodiment. [Figure 3B] It is a side view of the first base material and the second base material in another embodiment. [Figure 4A] It is a partial side view of the first base material and the second base material in an example. [Figure 4B] It is a diagram showing the relationship between the time of the main bonding step and the amount of drop of the second base material.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Throughout the drawings, common reference numerals are assigned to corresponding components. FIG. 1 is a schematic view showing a substrate adhesion system based on the present disclosure. The substrate adhesion system 10 shown in FIG. 1 is used to adhere a first substrate 21 and a second substrate 22 in at least partial surface contact with each other. Note that the "substrate" in the present specification is a concept including both plates and films.

[0019] The first substrate 21 is formed from a first resin having a first glass transition temperature Tg1. The second substrate 22 is formed from a second resin having a second glass transition temperature Tg2 lower than the first glass transition temperature Tg1. In one example, the first resin is a cycloolefin polymer and the second resin is a cycloolefin copolymer.

[0020] FIG. 2A is a top view of the first substrate. As shown in FIG. 2A, it is preferable that at least one of a groove A and a recess B is formed on the surface of the first substrate 21. The groove A and the recess B form channels of a microfluidic device. In an embodiment not shown, instead of the recess B or in addition to the recess B, through holes may be formed. Also, the second substrate 22 is preferably flat.

[0021] Alternatively, as shown in FIG. 2B, the surface of the first substrate 21 may be flat, and the flat first substrate 21 and the second substrate 22 may simply be adhered. Alternatively, another member may be encapsulated between the first substrate 21 and the second substrate 22.

[0022] Referring to FIG. 1 again, the substrate adhesion system 10 includes a temporary adhesion unit 11 that superimposes the second substrate 22 on the first substrate 21 and presses them against each other at a predetermined temperature and a predetermined pressure, and a main adhesion unit 12 that heats the mutually pressed first substrate 21 and second substrate 22 over a predetermined time. The temporary adhesion unit 11 is preferably, for example, a press machine, and the main adhesion unit 12 is preferably, for example, a thermostatic bath. However, other devices having functions equivalent to those described later may be used as the temporary adhesion unit 11 and the main adhesion unit 12.

[0023] The operation of the substrate bonding system 10 of the present invention will be described below. First, a first substrate 21 and a second substrate 22 are prepared. The thickness of the first substrate 21 is preferably 5 mm or less, more preferably 2 mm or less, and the thickness of the second substrate 22 is preferably 10 μm to 1 mm, and even more preferably 30 μm to 200 μm. When the first substrate 21 is thicker than the second substrate 22 in this way, the first substrate 21 functions as a base, and the second substrate 22 functions as a cover that covers the surface of the first substrate 21. Therefore, it is advantageous when a channel structure consisting of grooves A and recesses B is formed on the surface of the first substrate 21. Note that the thicknesses of the first substrate 21 and the second substrate 22 are not limited to the above and may be the same thickness. Furthermore, it is preferable that the first substrate 21 is formed by injection molding and the second substrate 22 is formed by extrusion molding.

[0024] Preferably, the areas of the first substrate 21 and the second substrate 22 are approximately equal. Alternatively, the area of ​​the second substrate 22 may be smaller than the area of ​​the first substrate 21, as long as the second substrate 22 has a sufficient area to cover the channel structure or specific parts of the first substrate 21.

[0025] Next, the first base material 21 and the second base material 22 are supplied to the temporary bonding unit 11. In the temporary bonding unit 11, for example in a press machine, the second base material 22 is superimposed on the first base material 21. The superimposed first base material 21 and second base material 22 are then placed between the upper die 15 and the lower die 16. In embodiments not shown, the first base material 21 may be superimposed on the second base material 22. Alternatively, in other embodiments not shown, the first base material 21 may be placed between the upper die 15 and the lower die 16 so as to be sandwiched between the two second base materials 22.

[0026] The temperature T1 of the upper mold 15 and lower mold 16 of the temporary bonding unit 11 is set to a value between the first glass transition temperature Tg1 of the first substrate 21 and the second glass transition temperature Tg2 of the second substrate 22, or the temperature T1 may be approximately equal to the lower glass transition temperature Tg2. Alternatively, if the bonding interface between the first substrate 21 and the second substrate 22 is at temperature T1, the upper mold 15 and lower mold 16 may be set to temperatures other than T1, for example, the lower mold 16 may be at a temperature lower than T1.

[0027] When the temperature T1 is set in this way, the first substrate 21 will not deform or warp due to the heat of the temporary bonding unit 11. Therefore, this is particularly advantageous when a channel structure is formed in the first substrate 21. In contrast, since the temperature T1 is higher than the second glass transition temperature Tg2, the second substrate 22 softens at temperature T1, and as a result becomes tacky and adheres to the first substrate 21.

[0028] Furthermore, the pressure applied to press the first substrate 21 and the second substrate 22 is a value sufficient to obtain adhesive strength, for example, 1 MPa or more, more preferably 3 MPa or more. Similarly, the pressing time applied to press the first substrate 21 and the second substrate 22 is also a value sufficient to obtain adhesive strength, for example, 30 seconds or more, preferably 60 seconds or more, more preferably 120 seconds or more. Note that the pressure and pressing time of the temporary bonding unit 11 also vary depending on the material and shape of the first substrate 21 and the second substrate 22.

[0029] As mentioned above, the second glass transition temperature Tg2 of the second substrate 22 is lower than the first glass transition temperature Tg1 of the first substrate 21. The difference between temperature T1 and the first glass transition temperature Tg1 is preferably 5 to 40°C, more preferably 5 to 20°C, and the difference between temperature T1 and the second glass transition temperature Tg2 is preferably 0 to 40°C, more preferably 0 to 20°C. Alternatively, the difference between the first glass transition temperature Tg1 and the second glass transition temperature Tg2 is preferably 5 to 40°C, more preferably 10 to 30°C. In other words, it is required to prepare a first substrate 21 and a second substrate 22 having such glass transition temperatures Tg1 and Tg2.

[0030] In this way, the first substrate 21 and the second substrate 22 are temporarily bonded together in the temporary bonding unit 11. Then, the temporarily bonded first substrate 21 and the second substrate 22 are supplied to the main bonding unit 12.

[0031] In this bonding unit 12, the first substrate 21 and the second substrate 22, which have been temporarily bonded, are placed in an environment with a temperature T2 for a predetermined time. In order to completely bond the first substrate 21 and the second substrate 22, it is preferable that the predetermined time in this bonding unit 12 be relatively long. For example, the predetermined time is 30 minutes or more, preferably 60 minutes or more, and more preferably 120 minutes or more.

[0032] The temperature T2 is approximately equal to the second glass transition temperature Tg2 of the second substrate 22. The temperature T2 may be slightly lower or slightly higher than the second glass transition temperature Tg2. In one embodiment, the temperature T2 is the second glass transition temperature Tg2 ± 20°C. More preferably, the temperature T2 is the second glass transition temperature Tg2 ± 10°C. The temperature T2 is related to the required arrangement time, which is set appropriately depending on the required specifications, product shape, product cycle time, etc.

[0033] When a large constant-temperature bath is used as the bonding unit 12, multiple temporarily bonded substrates can be processed at once. Alternatively, when a reflow oven is used as the bonding unit 12, multiple temporarily bonded substrates can be processed sequentially on the line.

[0034] Here, Figure 4A, described later, is a partial side view of the first substrate 21 and the second substrate 22 after the temporary bonding process and before the main bonding process in one embodiment. In Figure 4A, the second substrate 22, which is thinner than the first substrate 21, is used. As mentioned above, the temperature T1 in the temporary bonding process is higher than the second glass transition temperature Tg2, so when the temporary bonding process is completed, the loosened second substrate 22 may fall into the recess B of the first substrate 21. The amount the second substrate 22 falls into the recess B is greater the larger the dimensions of the recess B.

[0035] Since the temperature T2 of the main bonding unit 12 is approximately equal to the second glass transition temperature Tg2, the second base material 22 shrinks, and as a result, the fall of the second base material 22 into the concave portion B is eliminated. Therefore, when the first base material 21 has the groove A and the concave portion B, it is possible to avoid changes in the dimensions of their internal spaces, and a microfluidic device having channels with required dimensions can be formed.

[0036] Thus, in the present disclosure, after temporarily bonding at the temperature T1 (Tg2 < T1 < Tg1) in the temporary bonding unit 11, main bonding is performed at the temperature T2 (T2 ≒ Tg2) in the main bonding unit 12. Since the temperature T1 is higher than the second glass transition temperature Tg2, the second base material 22 relaxes in the temporary bonding unit 11, but since the temperature T2 is approximately equal to the second glass transition temperature Tg2, the second base material 22 shrinks, and as a result, the relaxation of the second base material 22 is eliminated in the main bonding unit 12.

[0037] In the present disclosure, since temperatures lower than the first glass transition temperature Tg1 are used in both the temporary bonding process and the main bonding process, the entire first base material 21 does not warp or deform, and the shape of the channel structure such as the groove A and / or the concave portion B does not change. Therefore, the two base materials 21 and 22 can be bonded cheaply and firmly without warping of the base material. Furthermore, a highly reliable bonded product composed of the first base material 21 and the second base material 22 can be provided. Further, as described above, when the first base material 21 having the groove A and / or the concave portion B formed on both the front and back surfaces is sandwiched between two second base materials 22, the grooves A and / or the concave portions B formed on the front and back surfaces of the first base material 21 can be simultaneously blocked by the two second base materials 22, which is advantageous.

[0038] Furthermore, in this disclosure, there is no need to use adhesives, adhesive-backed cover materials, etc., and no residues of these remain. In addition, in this disclosure, there is no need to pre-modify the surfaces of the first substrate 21 and the second substrate 22 by vacuum ultraviolet treatment, plasma treatment, or corona discharge treatment. Also, autofluorescence that may occur during vacuum ultraviolet treatment does not remain on the first substrate 21 and the second substrate 22. Furthermore, unlike plasma treatment and corona discharge treatment, the wettability of the surfaces of the first substrate 21 and the second substrate 22 does not change, so it does not affect the liquid flowability. Furthermore, since no surface modification is performed, the substrates 21 and 22 do not adhere to the mold of the press machine. For these reasons, in this disclosure, the two substrates 21 and 22 can be bonded inexpensively. Furthermore, if it is desired to hydrophilize the flow channels such as groove A and / or recess B by surface modification, the two substrates 21 and 22 may be bonded as described above after surface modification. This enables a strong seal with high water resistance.

[0039] As mentioned above, in one example, the first resin of the first substrate 21 is a cycloolefin polymer, and the second resin of the second substrate 22 is a cycloolefin copolymer. Generally, such olefin resins are preferred for microfluidic devices because they have low water absorption and low adsorption of proteins, etc., but they are considered difficult to bond to substrates. However, in this disclosure, substrates made of such olefin resins can be bonded without surface modification. Therefore, it is also possible to provide an olefin-based adhesive consisting of the first substrate 21 and the second substrate 22.

[0040] Furthermore, if required, a press machine may be used as the bonding unit 12, and a predetermined pressure, for example, lower than that used in the temporary bonding process, may be applied to the first substrate 21 and the second substrate 22 in this bonding process as well.

[0041] Figure 3A is a side view of the first substrate in another embodiment. The first substrate 21 shown in Figure 3A has a plurality of fine irregularities 21a formed on its surface. These irregularities 21a are assumed to be considerably smaller than the grooves A and recesses B described above.

[0042] Since the temperature T1 of the temporary bonding unit 11 is higher than the second glass transition temperature Tg2 of the second substrate 22, the second substrate 22 softens during temporary bonding, allowing it to penetrate into the uneven portion 21a of the first substrate 21. This demonstrates that a strong adhesive effect can be achieved even with a shorter temporary bonding process time. The uneven portion 21a may be formed simultaneously with the creation of the first substrate 21, for example, during injection molding, or it may be formed after the creation of the first substrate 21. Example 1

[0043] The first substrate 21 and the second substrate 22 shown in Table 1 were prepared. The first substrate 21 is made of cycloolefin polymer (COP), with a first glass transition temperature Tg1 of 100°C and a thickness of 1.2 mm. The second substrate 22 is made of cycloolefin copolymer (COC), with a second glass transition temperature Tg2 of 78°C and a thickness of 0.1 mm. The reagent was pre-filled into the recess B of the first substrate 21. The same procedure was followed for Comparative Examples 1 and 2. [Table 1]

[0044] As shown in Table 2, in the preliminary bonding step of Example 1, the temperature T1 was set to 90°C, the pressure to 4.4 MPa, and the time to 120 seconds, while in the main bonding step, the temperature T2 was set to 80°C and the time to 2 hours. Furthermore, in the preliminary bonding steps of Comparative Examples 1 and 2, the temperature T1 was set to 90°C, the pressure to 8 MPa, and the time to 120 seconds, and the main bonding step was not performed. In Comparative Example 2, surface modification treatment was performed using vacuum ultraviolet light before the preliminary bonding step. A press machine was used as the preliminary bonding unit 11, and a constant temperature bath was used as the main bonding unit 12. [Table 2]

[0045] The adhesives prepared in this manner for Example 1 and Comparative Examples 1 and 2 were separately heated at 42°C for accelerated testing. In Example 1, the reagent filled in recess B did not leak even after more than 48 hours. In Comparative Example 1, the reagent filled in recess B leaked after 1 to 10 hours (due to variations among multiple samples and variations in the position of recesses within the same sample). In Comparative Example 2, the reagent filled in recess B leaked after 1 to 6 hours. Therefore, this disclosure provides an olefin-based adhesive with high water resistance. Example 2

[0046] Figure 4A is a partial side view of the first and second substrates in Example 2. The first substrate 21 and the second substrate 22 are the same as those in Example 1 in Table 1. The depth of the recess B formed in the first substrate 21 is 0.7 mm.

[0047] When the temporary bonding process is performed under the conditions of Example 1 shown in Table 1, the second substrate 22 partially sinks into the recess B of the first substrate 21, as shown in Figure 4A. Let Z be the amount of sinking of the upper surface of the second substrate 22 at the position corresponding to recess B. The ease of sinking varies depending on the bonding conditions and material properties.

[0048] Figure 4B shows the relationship between the time of the main bonding process and the amount of sinking of the second substrate. As shown in Figure 4B, immediately after the preliminary bonding process (time zero for the main bonding process), the amount of sinking Z is approximately 0.11 mm. Then, the main bonding process is performed under the conditions of Example 1 shown in Table 1. After performing the main bonding process for at least 2 hours, the amount of sinking Z becomes 0.02 mm, indicating that the sinking has been largely eliminated.

[0049] In Example 2, the duration of this bonding process should ideally be such that the amount of depression Z is largely eliminated and the water resistance (see Table 2) is satisfied.

[0050] Furthermore, in Examples 1 and 2, the first resin of the first substrate 21 and the second resin of the second substrate 22 are olefin polymers. Specifically, the first resin is a cycloolefin polymer (COP), and the second resin is a cycloolefin copolymer (COC). In this case, olefin polymers can be applied to the bonding of devices such as optical components and medical packaging, where they are particularly useful.

[0051] Naturally, two other types of resins that satisfy the relationship between the first glass transition temperature Tg1 and the second glass transition temperature Tg2 (Tg1 > Tg2) can also be used as the first and second resins. Alternatively, if the glass transition temperatures are different, the same type of resin with different specifications, such as different molecular weights, such as cycloolefin polymers, may be used as the first and second resins. Furthermore, if the relationship between the first glass transition temperature Tg1 and the second glass transition temperature Tg2 (Tg1 > Tg2) is satisfied, a cycloolefin copolymer (COC) may be selected as the first resin and a cycloolefin polymer (COP) may be selected as the second resin. Microfluidic devices including a first substrate and a second substrate bonded by the substrate bonding method and / or substrate bonding system of this disclosure are also included in the scope of this disclosure.

[0052] While embodiments of the present invention have been described above, it will be understood by those skilled in the art that various modifications and changes can be made without departing from the scope of disclosure of the claims described later. [Explanation of Symbols]

[0053] 10 Substrate Adhesion Systems 11 Temporary bonding unit 12 adhesive units 21 First base material 21a Uneven part 22 Second base material

Claims

1. A preparation step of preparing a first substrate made of a first resin having a first glass transition temperature and a second substrate made of a second resin having a second glass transition temperature lower than the first glass transition temperature, The process includes a temporary bonding step of superimposing the second substrate onto the first substrate and pressing them together at a predetermined temperature and pressure without surface modification, wherein the predetermined temperature is between the first glass transition temperature and the second glass transition temperature. moreover, This bonding step includes heating the first and second substrates, which are pressed together, at a temperature approximately equal to the second glass transition temperature for a predetermined time without applying pressure. At least one of grooves and recesses is formed on the surface of the first substrate that contacts the second substrate. A substrate bonding method comprising: if the second substrate falls into at least one of the grooves and recesses after the temporary bonding step, the main bonding step shrinks the second substrate to prevent it from falling into at least one of the grooves and recesses.

2. The substrate bonding method according to claim 1, wherein the first substrate and the second substrate are not pressed together in the bonding step described above.

3. The difference between the predetermined temperature and the first glass transition temperature is 5°C or more, preferably 10°C or more, and The substrate bonding method according to claim 1 or 2, wherein the difference between the predetermined temperature and the second glass transition temperature is 5°C or more, preferably 10°C or more.

4. The substrate bonding method according to any one of claims 1 to 3, wherein the difference between the first glass transition temperature and the second glass transition temperature is 10°C to 40°C, preferably 20°C to 30°C.

5. The substrate bonding method according to any one of claims 1 to 4, wherein the first resin is one of a cycloolefin polymer and a cycloolefin copolymer, and the second resin is the other of a cycloolefin polymer and a cycloolefin copolymer.

6. The substrate bonding method according to Claim 1, wherein the thickness of the first substrate is 5 mm or less, the thickness of the second substrate is 10 μm to 1 mm, and the first substrate is thicker than the second substrate.

7. A temporary bonding unit comprising a first substrate made of a first resin having a first glass transition temperature, on which a second substrate made of a second resin having a second glass transition temperature lower than the first glass transition temperature is superimposed and pressed together at a predetermined temperature and a predetermined pressure, wherein the predetermined temperature is a temperature between the first glass transition temperature and the second glass transition temperature. moreover, The bonding unit comprises heating the first and second substrates, which are pressed together, at a temperature approximately equal to the second glass transition temperature for a predetermined time without applying pressure. At least one of grooves and recesses is formed on the surface of the first substrate that contacts the second substrate. A substrate bonding system in which, after the first substrate and the second substrate are pressed together in the temporary bonding unit, the second substrate falls into at least one of the grooves and recesses, the second substrate is shrunk during heating in the main bonding unit to prevent the second substrate from falling into at least one of the grooves and recesses.

8. The substrate bonding system according to claim 7, wherein the thickness of the first substrate is 5 mm or less, the thickness of the second substrate is 10 μm to 1 mm, and the first substrate is thicker than the second substrate.

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