JP7312946B2 - Bonding structure and bonding method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an adhesive structure and an adhesive method for adhering different or similar substrates without using an adhesive.

When two substrates are bonded together with an adhesive, the bonded structure consisting of these substrates cannot be used for products that require heat resistance because the adhesive is weak against heat, and the adhesive changes the dielectric constant of the bonding interface, making it unsuitable for printed circuit boards and the like.

Therefore, as a method for bonding two substrates without using an adhesive, as shown in Patent Document 1, there is a method in which —OH groups are generated on the surface of a fluororesin sheet by plasma treatment, and the surface of this fluororesin sheet is bonded to a metal member.

However, it cannot be said that the actual adhesive strength obtained by reactions of functional groups such as dehydration condensation with —OH groups is strong, and for example, sufficient adhesive strength has not been obtained so far for difficult-to-adhere substrates such as Teflon.

Patent No. 5152784

Therefore, the present invention has been made to solve the above-mentioned problems, and the main object thereof is to enable strong adhesion without using an adhesive even to a difficult-to-adhere substrate.

That is, the adhesive structure according to the present invention is an adhesive structure comprising a surface of a first base material and a surface of a second base material bonded to the surface of the first base material, wherein functional groups are present on the surfaces of the first base material and the second base material, and at least some of these functional groups are bonded without reacting with each other.

According to such an adhesive structure, at least some of the functional groups present on the surfaces of the first and second substrates are bonded without reacting with each other, for example, by molecular bonding. Therefore, even if the first and second substrates are difficult-to-adhere materials such as Teflon, these substrates can be firmly adhered.

As an embodiment for obtaining sufficient adhesion to a difficult-to-adhere substrate, the functional group present on one surface of the first substrate or the second substrate is preferably —NHx. Note that x is a natural number of 1 or more.

As the functional group that bonds to -NHx without reacting, the functional group present on the other surface of the first substrate or the second substrate is preferably at least one of -H, -NHx, -COH, -COOH, -OH, -F, and -CFx. Note that x is a natural number of 1 or more.

One embodiment in which the effects of the present invention are exhibited more remarkably includes the case where the first base material or the second base material is a difficult-to-adhere material such as fluororesin, liquid crystal polymer, COP resin, or engineering plastic.

For example, as a specific configuration of the functional group formed on the surface of the resin base material, the functional group is bound to the dangling bond formed on the surface of the first base material or the second base material.

For example, as a specific configuration of the functional group formed on the surface of the metal base material, the functional group is bound to the microcracks formed on the surface of the first base material or the second base material. The term "microcracks" as used herein includes micro-anchors to atomic lattice defects.

Further, the bonding method according to the present invention is a method characterized in that functional groups are generated on the surface of a first substrate by plasma treatment, functional groups are generated on the surface of a second substrate different from the first substrate by plasma treatment, and at least part of the functional groups generated on the surfaces of the first substrate and the second substrate are bonded without reacting with each other.
Even with such an adhesion method, even if the first base material and the second base material are difficult to adhere to such as Teflon, these base materials can be strongly adhered, similar to the effects of the above-described adhesion structure.

According to the present invention configured as described above, it is possible to firmly bond even a difficult-to-bond substrate without using an adhesive.

1 is a diagram schematically showing the configuration of a plasma processing apparatus according to this embodiment; FIG. The flowchart figure which shows the procedure of the adhesion|attachment method in the same embodiment. The conceptual diagram which shows the structure of the adhesion|attachment structure in the same embodiment. The conceptual diagram which shows the bonding aspect of the functional group in the same embodiment. Analysis results of X-ray analysis of the adhesion structure in the same embodiment. Analysis results of X-ray analysis of the adhesion structure in the same embodiment. The flowchart figure which shows the procedure of the adhesion|attachment method in other embodiment.

A bonding structure and bonding method according to an embodiment of the present invention will be described with reference to the drawings.

<Device configuration>
First, an apparatus for manufacturing a bonded structure will be described.

This apparatus is a plasma processing apparatus 100 for plasma-processing the surface of a base material. As shown in FIG. 1, it comprises a vacuum chamber 1, a lower electrode 2 provided in the vacuum chamber 1 to support the base material W, an upper electrode 3 arranged opposite to the base material W in the vacuum chamber 1, and a high frequency power supply 4. The high frequency power supply 4 supplies high frequency power of, for example, 13.50 MHz to the lower electrode 2, and the upper electrode 3 is grounded to generate plasma P in the vacuum chamber 1. are Further, the plasma processing apparatus 100 is configured to be switchable between grounding the lower electrode 2 and supplying high-frequency power to the upper electrode 3 depending on the material of the base material, the type of reaction gas, and the like.

Thus, the plasma processing apparatus 100 of this embodiment is used to generate functional groups on the surface of the base material W, and is configured to supply the process gas G corresponding to the functional groups to be generated into the vacuum chamber 1.

<Adhesion method>
Next, the procedure for bonding the first base material and the second base material of different types or the same type using the plasma processing apparatus described above without using an adhesive will be described with reference to the flowchart of FIG. 2 and the conceptual diagram of FIG.

The first base material and the second base material are, for example, plate-shaped ones, and specifically, those made of metals such as copper, aluminum, and iron, PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxyalkane), FEP (perfluoroethylene propene copolymer), LCP (liquid crystal polymer), COP (cycloolefin polymer), PI (polyimide), engineering plastics and other difficult-to-adhesive resins, and amorphous materials such as glass.

In the following, a method for bonding different types of first base material and second base material, which are used, for example, as printed circuit boards, will be described. The first base material is made of fluororesin, and the second base material is made of a metal such as copper.

First, a first base material (hereinafter also referred to as a resin base material) is plasma-treated by the plasma treatment apparatus described above to form dangling bonds on the surface of the resin base material as shown in FIG. 3 (S1). Depending on the type and structure of the base material, a plasma treatment for forming dangling bonds may be separately performed prior to functional group impartation.

Specifically, by plasma etching the resin base material, F atoms are separated from C—F bonds on the surface to form dangling bonds (dangling bonds) of C atoms, and the reactivity of the surface of the resin base material is activated.

Next, as shown in FIG. 3, a desired functional group (hereinafter also referred to as a first functional group) is bonded to the dangling bond (S2).

Specifically, by selecting a gas species corresponding to the first functional group as the process gas described above and supplying it into the vacuum chamber, the first functional group becomes plasma and bonds with the dangling bond.

In this embodiment, an amino group, which is a hydrophilic functional group, is formed on the surface of the resin substrate as the first functional group, and the process gas is an amino group-containing gas such as ammonium gas.

More specifically, ammonium gas is supplied to the vacuum chamber at a flow rate of 1 sccm or more, and under an atmosphere in which the process pressure is maintained at 1 to 1,000 Pa, a high frequency of 1 to 100 MHz is applied at a power density of 0.01 to 3 W/cm ² to perform high frequency low pressure plasma treatment.
The process gas may be a mixed gas of an amino group-containing gas and a rare gas or inert gas (He, Ne, Ar, Kr, Xe, N ₂ ).

As a result, the amino groups —NH (secondary amino group) and —NH ₂ (primary amino group) are plasmatized and bonded to dangling bonds formed on the surface of the resin substrate.

Here, the formation of the first functional groups in S2 may be performed together with the formation of the dangling bonds in S1, or may be performed as a separate step from S1 after the formation of the dangling bonds in S1, in consideration of, for example, the material of the base material and the type of the first functional groups.

That is, if the resin substrate is plasma-etched while supplying the amino group-containing gas into the vacuum chamber, the formation of amino groups proceeds along with the formation of dangling bonds, so the steps S1 and S2 proceed simultaneously as one step.

On the other hand, if the resin substrate is plasma-etched while supplying a process gas other than the amino group-containing gas, such as a halogen gas, into the vacuum chamber, the process gas is switched from the halogen gas to the amino group-containing gas after the formation of the dangling bond to form the first functional groups, and the steps S1 and S2 proceed as separate steps.

Next, as shown in FIG. 3, the second base material (hereinafter also referred to as the copper base material) is plasma-treated by the above-described plasma processing apparatus to form so-called microcracks on the surface of the copper base material (S3). The term "microcracks" as used herein includes micro-anchors to atomic lattice defects.

Specifically, by plasma etching a copper base material, defects (microcracks including minute anchors to atomic lattice defects) on the surface of several nm to several hundred nm or smaller are formed as structures for binding functional groups.

Next, as shown in FIG. 3, desired functional groups (hereinafter also referred to as second functional groups) are bonded to the microcracks, which are microstructures (S4).
Specifically, by selecting a gas species corresponding to the second functional group as the process gas described above and supplying it into the vacuum chamber, the second functional group is plasmatized and bonded to the microcracks.

In this embodiment, —H or —OH (hydroxy group) is formed as a second functional group on the surface of the copper base material, and the process gas used includes hydrogen gas. For example, hydrogen gas itself may be used, or hydrogen gas may be mixed and diluted with a rare gas or an inert gas.

More specifically, hydrogen gas is supplied to the vacuum chamber at a flow rate of 1 sccm or more, and under an atmosphere in which the process pressure is maintained at 1 to 1,000 Pa, a high frequency of 1 to 100 MHz is applied at a power density of 0.01 to 3 W/cm ² to perform high frequency low pressure plasma treatment.
The process gas may be a mixed gas of hydrogen gas and rare gas or inert gas (He, Ne, Ar, Kr, Xe, N ₂ ).

As a result, -H and -OH are plasmatized and bonded to microcracks formed on the surface of the copper substrate.

As with the formation of the first functional group in S2, the formation of the second functional group in S4 may be performed together with the formation of the microcracks in S3, or may be performed as a separate step from S3 after the formation of the microcracks in S3, in consideration of, for example, the material of the substrate and the type of the second functional group.

That is, if the copper substrate is plasma-etched while supplying a mixed gas of, for example, hydrogen gas and argon gas into the vacuum chamber, the formation of functional groups such as —H and —OH proceeds along with the formation of microcracks, so the steps S3 and S4 proceed simultaneously as one step.

On the other hand, if the copper substrate is plasma-treated while supplying a process gas other than hydrogen gas, such as argon gas, into the vacuum chamber, microcracks can be formed in the copper substrate, and then the process gas can be switched from argon gas to hydrogen gas or a mixed gas of hydrogen gas and a rare gas or an inert gas to form a second functional group, and the steps S3 and S4 proceed as separate steps.

Through the steps S1 to S4 described above, the first functional group and the second functional group are formed from the surfaces of the first and second substrates, respectively, with a thickness ranging from the atomic level to several tens of nanometers.

In this embodiment, the first functional group is formed on the resin base material, which is the first base material, and then the second functional group is formed on the copper base material, which is the second base material.

Then, as shown in FIG. 3, the surface of the resin base, which is the first base, on which the first functional group is formed faces the surface of the copper base, which is the second base, on which the second functional group is formed, and the first base and the second base are brought into close contact (S5).

This close contact step is a step of applying a load to the first substrate and the second substrate in order to make the surface of the first substrate and the surface of the second substrate as flat as possible and bring them close together.
The method for bringing the surface of the first base material and the surface of the second base material into close contact is not limited to pressurization, and may be appropriately changed to a method using vacuum drawing or the like.

In the present embodiment, the resin base material and the copper base material are heated in the intimate contact step. Specifically, the load applied to the first base material and the second base material is 0.5 kg/cm ² and the heating temperature is 100°C.

In this way, when the surface of the first base material and the surface of the second base material are flattened as much as possible, for example, when they are close to several nanometers, an attractive force is generated between the first functional group and the second functional group.

<Adhesion structure>
No adhesive is interposed between the surface of the first base material and the surface of the second base material that are bonded in this way, in other words, no organic material different from the first base material and the second base material is interposed between these surfaces.

Then, as shown in FIG. 4, the adhesive structure formed by bonding the surface of the first base material and the surface of the second base material is characterized in that at least part of the functional groups present on the surface of the first base material and at least part of the functional groups present on the surface of the second base material are bonded without reacting with each other.

Specifically, in the example shown in FIG. 4(a), between the terminal functional group present on one surface of the first substrate and the second substrate and —H present on one surface of the first substrate and the second substrate, an attractive force is generated due to the different polarities of these, and by this force, at least part of the functional groups present on the surfaces of the first substrate and the second substrate are bonded by hydrogen bonding.

In the example shown in FIG. 4(b), an attractive force is generated by the polarity generated by the bias of electrons in the molecule, and this force causes the functional groups present on the surfaces of the first and second substrates to be bonded by intermolecular force (van der Waals force).

The spectra shown in FIGS. 5 and 6 are the results of X-ray analysis of the adhesive structure of the present embodiment. Specifically, in order to confirm intermolecular bonding, the adhered resin base material (first base material) and copper base material (second base material) are peeled off, and the surface of the copper base material is analyzed by XPS or the like.
More specifically, in order to confirm the presence of organic matter by confirming the C1s peak, the measurement was performed while etching the surface (measurement surface) of the copper substrate by 2 nm at a time.
The reason for analyzing the surface of the copper base material is that the fracture strength of the resin base material is weaker than that of the copper base material, and even if the resin base material is analyzed, only the elements and bonds derived from the resin base material are analyzed.

First, as shown in FIG. 6A, at an etching depth of 0 nm (before etching), the composition ratio of C—F2 bonds was 100%, and a resin peak was confirmed.
Moreover, as shown in FIG. 6(d), at an etching depth of 6 nm, there is no C1s peak, indicating that the organic substance (resin) reaches the inside of the copper substrate without being confirmed.

On the other hand, as shown in FIGS. 6(b) and 6(c), at etching depths of 2 nm and 4 nm, peaks derived from C—N bonds indicating the presence of amino groups (—NHx), which are the first functional groups, were confirmed.
This proves that the amino group (--NHx), which is the first functional group, and the hydroxy group (--OH), which is the second functional group, are included in the adhesive structure without reacting with each other.

And according to the adhesion structure of this embodiment, as shown in the following Table 1, it turns out that adhesiveness can be improved significantly compared with the conventional adhesion structure.

As described above, according to the bonding structure and the bonding method according to the present embodiment, it is possible to obtain stronger bonding strength than in the past, and it is possible to strongly bond even a difficult-to-bond substrate made of resin such as PTFE, PFA, FEP, or PI to another substrate without using an adhesive.

It should be noted that the present invention is not limited to the above embodiments.

For example, in the above embodiment, —H was formed on the surface of the copper substrate, but one or more functional groups selected from the group consisting of —NHx (amino group), —COH (aldehyde group), —COOH (carboxy group), —OH (hydroxy group), —F, and —CFx may be formed on the surface of the copper substrate. Note that x is a natural number of 1 or more (same below).

Further, in the above embodiment, the case of bonding the resin base material and the copper base material is described, but the same kind of base material, for example, two copper base materials or two resin base materials may be bonded together.
For example, when bonding two resin base materials together, as shown in FIG. 7, amino groups are formed on the surface of one base material, and one or more functional groups selected from the group consisting of -H, -NHx (amino group), -COH (aldehyde group), -COOH (carboxy group), -OH (hydroxy group), -F, and -CFx are formed on the surface of the other base material.

In addition, although the copper base material was described as the second base material in the above embodiment, an aluminum base material, a steel base material, or the like may be used.
In this case, one or more functional groups selected from the group consisting of —H, —NHx (amino group), —COH (aldehyde group), —COOH (carboxy group), —OH (hydroxy group), —F (fluoro group), and —CFx may be formed on the surface of the aluminum or steel substrate.

In addition, the combination of the first base material and the second base material may be the same or different base material selected from the group consisting of fluororesin, COP, LCP, PI, PET, engineering plastics, iron, copper, and aluminum.

Moreover, in the above embodiment, the case of bonding two substrates was described, but the bonding structure and bonding method according to the present invention may be applied when bonding three or more substrates of the same type or different types.

In addition, various modifications and combinations of the embodiments may be made as long as they do not contradict the gist of the present invention.

X...Plasma processing apparatus P...Plasma 1...Vacuum chamber 2...Lower electrode 3...Upper electrode 4...High frequency power supply

Claims (3)

An adhesive structure comprising a surface of a first substrate and a surface of a second substrate bonded to the surface of the first substrate,
The first base material is made of at least one of PTFE, PFA, FEP, or LCP difficult-to-adhere resins ,
There is a functional group bonded to the dangling bond formed on the surface of the first base material,
There are functional groups bonded to dangling bonds or microcracks formed on the surface of the second substrate,
the functional group present on the surface of the first substrate includes —NHx,
the functional group present on the surface of the second substrate is at least one of —H, —NHx, —COH, —COOH, —OH, —F, and —CFx;
At least part of the functional groups present on the surface of the first substrate and the functional groups present on the surface of the second substrate are bonded without reacting with each other, and the adhesive structure is characterized in that the first substrate and the second substrate do not contain a modifier for improving adhesion. 2. The adhesive structure according to claim 1, wherein the second base material is fluororesin, liquid crystal polymer, COP resin, or engineering plastic. Forming dangling bonds on the surface of a first substrate made of at least one of PTFE, PFA, FEP, or LCP difficult-to-adhesive resins by plasma treatment, binding functional groups to the dangling bonds,
Forming dangling bonds or microcracks by plasma treatment on the surface of a second substrate different from the first substrate, bonding a functional group to the dangling bonds or the microcracks,
the functional group present on the surface of the first substrate includes —NHx,
the functional group present on the surface of the second substrate is at least one of —H, —NHx, —COH, —COOH, —OH, —F, and —CFx;
At least part of the functional groups present on the surface of the first substrate and the functional groups present on the surface of the second substrate are bonded without using a modifier for improving adhesiveness and without reacting with each other.