JP7449647B2 - Manufacturing method of particle-filled sheet - Google Patents

Description

The present invention relates to a method of manufacturing a particle-filled sheet .

For example, as a particle-filled sheet filled with particles, a particle-filled sheet having a base sheet, a plurality of through holes penetrating the base sheet in the thickness direction, and a particle filling portion formed in each through hole is used. Are known.

When the particles constituting the particle-filled portion have conductivity, the particle-filled sheet has conductivity. In this case, the particle-filled sheet is capable of absorbing mechanical shocks and distortions (irregularities), making it possible to achieve compact electrical connections without using means such as soldering or mechanical fitting. It has features such as being able to make soft connections. Furthermore, particle-filled sheets also allow fine-pitch connections. For this reason, particle-filled sheets are used to achieve electrical connections between electronic components (e.g. between printed circuit boards and leadless chip carriers or liquid crystal panels, etc.), e.g. in the field of computers, digital cameras, displays, etc. It is widely used as a connector for connection purposes (hereinafter also referred to as a "connection connector"). Furthermore, the particle-filled sheet is also used as a connector (hereinafter also referred to as "inspection connector") in a product inspection device for electronic components. For example, particle-filled sheets may be used as connectors for testing various printed circuit boards.

Japanese Patent Application Publication No. 2009-245745 Japanese Patent Application Publication No. 2009-140866 Japanese Patent Application Publication No. 10-247536

Incidentally, particle-filled sheets are required to have particle-filled portions with even higher aspect ratios. Here, the aspect ratio of the particle-filled portion is a value obtained by dividing the thickness of the particle-filled sheet by the pitch of the particle-filled portion, and increases as the particle-filled sheet becomes thicker or as the pitch of the particle-filled portion becomes narrower.

For example, when a particle-filled sheet (a conductive particle-filled sheet) is used as an inspection connector for a ball grid array board (a type of printed circuit board mentioned above), the particle-filled sheet is required to have a high aspect ratio of the particle-filled part. There are many things. In recent ball grid array substrates, balls, which are electrodes, are often arranged at a very fine pitch. Therefore, in order to ensure that the particle-filled portion comes into contact with each ball, it is necessary to form the particle-filled portion at a fine pitch. Furthermore, there is a relatively large variation in the height of the ball (for example, a variation of about 10 to 100 μm). Therefore, in order for the particle-filled sheet to deform to accommodate such variations and to ensure that the particle-filled portion contacts each ball, the particle-filled sheet must have sufficient thickness. For this reason, the particle-filled sheet is required to have a high aspect ratio of the particle-filled portion.

Patent Documents 1 to 3 disclose methods for producing a particle-filled sheet having conductivity. In the technique disclosed in Patent Document 1, by partially applying a parallel magnetic field to the particle paste film, conductive particles are concentrated in a part of the particle paste film (the part to which the parallel magnetic field is applied). In this state, the particle paste film is cured. In the technique disclosed in Patent Document 2, through holes are formed in a base sheet. Then, the through hole is filled with a conductive material. Here, in Patent Document 2, in addition to ion milling and lithography, methods for forming through holes include arranging hydrophilic polymer chains in a lattice shape in a base sheet, and then selecting the hydrophilic polymer chains. Also disclosed is a method for removing it. In Patent Document 2, through holes are filled with a conductive substance by electrolytic plating or electroless plating.

In the technique disclosed in Patent Document 3, after a through hole is formed in a base sheet using a laser or the like, the through hole is filled with particle paste. Here, the particle paste is a mixture of conductive particles and uncured resin. Next, by applying a parallel magnetic field to the particle paste in the through holes, the conductive particles in the particle paste are arranged in the thickness direction of the base sheet. The particle paste is then allowed to harden.

However, neither method could make the particle-filled sheet sufficiently high in aspect. For example, in the technique disclosed in Patent Document 1, when attempting to form particle-filled portions at a fine pitch in a thick base sheet, adjacent parallel magnetic fields will interfere with each other. For this reason, when the base sheet is thick, the particle-filled portions cannot be formed at a fine pitch. With the techniques disclosed in Patent Documents 2 and 3, it was not possible to form through holes at a fine pitch when the base sheet was thick.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a new and improved method for manufacturing a particle-filled sheet in which the particle-filled portion has a high aspect ratio. There is a particular thing.

According to another aspect of the invention:
A method for manufacturing a particle-filled sheet , the method comprising:
The particle-filled sheet is
A base sheet having transparency in at least one wavelength band from 200 to 1600 nm;
a plurality of through holes that penetrate the base sheet from the front surface to the back surface of the base sheet;
a particle filling portion formed in each of the plurality of through holes;
has
The particle-filled portion does not protrude from both the front surface and the back surface of the base sheet,
The base sheet has elasticity,
Any region of the base sheet is a high aspect region where the aspect ratio of the particle filling portion is 0.5 or more,
The method for manufacturing the particle-filled sheet includes:
forming a plurality of the through holes in the base sheet by irradiating the base sheet with a short pulse laser in a wavelength band in which the base sheet has transparency;
forming the particle filling portion in each of the plurality of through holes;
including;
There is provided a method for manufacturing a particle-filled sheet, characterized in that the pulse interval of the short pulse laser is in nanoseconds or less.

Here, the unit of the pulse interval of the short pulse laser may be femtoseconds or less.
The particle-filled sheet may be a particle-filled sheet used as a connection connector or an inspection connector electrically connected to an electronic component.
The arrangement of the plurality of through holes is set to correspond to the plurality of electrodes of the electronic component to be connected or inspected,
The pitch of the plurality of through holes may be equal to or less than the pitch of the plurality of electrodes of the electronic component.
The terminals of the electronic component are arranged at a fine pitch of 200 μm or less,
In the high aspect region, the pitch of the through holes may be 200 μm or less.
The particle-filled sheet is used as a connector for testing a ball grid array substrate,
The thickness of the base sheet may be 100 μm or more.
An inorganic substance may be attached to the wall surface of the through hole.
The base sheet may be made of a rubber material.
The elasticity of the base sheet may be 70 or less in hardness type A (JIS K 7215-1986).
The particles included in the particle filling part may be elastic conductive particles.

As explained above, according to the present invention, a particle-filled sheet in which the particle-filled portion has a high aspect ratio is provided.

FIG. 1 is a perspective view showing the appearance of a particle-filled sheet according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of a particle-filled sheet according to the same embodiment. FIG. 3 is a plan view showing an example of the arrangement of particle filling parts. 1 is a flowchart showing an overview of a method for manufacturing a particle-filled sheet. It is a perspective view showing an outline of a method of forming a through hole in a base material sheet. FIG. 3 is a cross-sectional view showing an outline of a method for forming through holes in a base sheet. It is a perspective view showing an outline of a method of filling a through hole with particles for filling. FIG. 2 is a cross-sectional view showing an outline of a method for filling a through hole with filler particles. It is a perspective view showing an outline of another method of filling a through-hole with particles for filling. FIG. 7 is a cross-sectional view showing an outline of another method for filling a through hole with filler particles. FIG. 2 is a cross-sectional view showing how a base sheet is irradiated with a short pulse laser in a condensed manner. FIG. 2 is an explanatory diagram for explaining the depth of focus of a short pulse laser. FIG. 2 is a cross-sectional view showing how a continuous wave laser (CW laser) is focused and irradiated onto a base sheet. FIG. 2 is a cross-sectional view showing how a continuous wave laser (CW laser) is condensed and irradiated onto a base sheet that absorbs continuous wave laser. It is a cross-sectional photograph of a particle-filled sheet. FIG. 2 is a side view showing an example of a conductivity evaluation device. FIG. 3 is a plan view showing how the pressing surface of the probe contacts the particle-filled sheet.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that, in this specification and the drawings, components having substantially the same functional configurations are designated by the same reference numerals and redundant explanation will be omitted. Note that the drawing is only schematic and may differ from the actual dimensions.

<1. Structure of particle-filled sheet>
First, the structure of the particle-filled sheet 1 according to this embodiment will be explained based on FIGS. 1 to 3. As shown in FIGS. 1 to 3, the particle-filled sheet 1 includes a base sheet 10, a plurality of through-holes 20 formed in the base sheet 10, and particle-filled portions 30 formed in the through-holes 20. have

The base sheet 10 is a sheet-like member. The base sheet 10 has transparency in at least one wavelength band from 200 to 1600 nm. Although details will be described later, in this embodiment, by condensing and irradiating the base sheet 10 with a short pulse laser in a wavelength band in which the base sheet 10 has transparency, a through hole with a high aspect ratio is formed in the base sheet 10. Form 20. "Transparency" in this embodiment means exhibiting a total light transmittance of 80% or more. The total light transmittance is preferably 90% or more. The reason why the wavelength band in which the base sheet 10 has transparency is 200 to 1600 nm is because the wavelength of the laser used for various processing is generally within this range (YAG laser: about 266 to 1030 nm, Erbium-doped fiber laser: approximately 1550 nm). In other words, as long as it has transparency within this wavelength band, processing according to this embodiment is possible. The lower limit of the wavelength band in which the base sheet 10 has transparency may be 300 nm or more.

The base sheet 10 may have characteristics other than those described above. The characteristics that the base sheet 10 has may be determined depending on the use of the particle-filled sheet 1, for example. For example, when the particle-filled sheet 1 is used for a connection connector, an inspection connector, or the like, the base sheet 10 preferably has elasticity and insulation properties. Of course, the use of the particle-filled sheet 1 is not limited to these, and it can also be used as a film for MEMS (Micro Electro Mechanical Systems), for example. When the base sheet 10 has elasticity (more specifically, indentation elasticity), it is possible to softly connect the particle-filled sheet 1 to the electronic component to be connected or inspected (hereinafter also simply referred to as "electronic component"). can. For example, when the electronic component is a ball grid array substrate, elastic deformation of the base sheet 10 absorbs variations in the height of each ball, making it possible to more reliably bring each ball into contact with the particle filling section 30. . If the base sheet 10 does not have elasticity, there is a possibility that the ball with a large height will be damaged by the base sheet 10 when the particle filling section 30 is brought into contact with a ball with a small height.

Here, the degree of elasticity of the base sheet 10 may be adjusted as appropriate depending on the use of the particle-filled sheet 1 or desired characteristics. For example, when the particle-filled sheet 1 is used for a connection connector, an inspection connector, etc., the base sheet 10 is designed so that the particle-filled sheet 1 is soft against electronic components (in other words, so as not to damage the electronic components). ) It suffices if it has enough elasticity to be connected. For example, the elasticity of the base sheet 10 is preferably 70 or less in hardness type A (JIS K 7215-1986), more preferably 30 or less. In this case, the particle-filled sheet 1 can be softly connected by electronic components.

The degree of insulation of the base sheet 10 may be adjusted as appropriate depending on the use of the particle-filled sheet 1 or desired characteristics, but it is preferable that the electrical resistivity is 1×10 ³ Ω·cm or more, for example. It is more preferably 1×10 ⁵ Ω·cm or more, and more preferably 1×10 ⁷ Ω·cm or more. Thereby, unintended conduction of the particle-filled sheet 1 can be suppressed.

The material constituting the base sheet 10 is selected from materials that satisfy the above characteristics. Examples of materials constituting the base sheet 10 include conjugated diene rubbers such as polybutadiene rubber, natural rubber, polyisoprene rubber, styrene-butadiene copolymer rubber (styrene-butadiene rubber), acrylonitrile-butadiene copolymer rubber, and These hydrogenated products, block copolymer rubbers such as styrene-butadiene-diene block copolymer rubber, styrene-isoprene block copolymer, and hydrogenated products thereof, chloroprene rubber, urethane rubber, polyester rubber, epichlorohydrin rubber , silicone rubber, ethylene-propylene copolymer rubber (ethylene propylene rubber), ethylene-propylene-diene copolymer rubber, nitrile rubber, fluororubber, acrylic rubber, and butyl rubber. When weather resistance is required for the particle-filled sheet 1, it is preferable to use a material other than conjugated diene rubber. Here, Table 1 shows the characteristics of some materials (appearance color, absorption band) and examples of compatible laser wavelengths (wavelengths at which the material exhibits transparency). G indicates conformity and NG indicates nonconformity. Each material exhibits transparency to lasers in wavelength bands other than the absorption band.

The thickness T (see FIG. 2) of the base sheet 10 may be adjusted as appropriate depending on the intended use of the particle-filled sheet 1 or desired characteristics. For example, when the particle-filled sheet 1 is used for a connection connector, an inspection connector, or the like, the thickness T of the base sheet 10 is preferably 100 μm or more. When the base sheet 10 has such a thickness T, the indentation deformability is sufficiently large (that is, the particle-filled sheet 1 is sufficiently deformed when pushed), and the unevenness of electronic components (for example, the electrodes) is height variations) can be absorbed more reliably. For example, when the particle-filled sheet 1 is used as an inspection connector for a ball grid array substrate, the height of the balls on the ball grid array substrate may vary within a range of about 10 to 100 μm. Therefore, when the amount of elastic deformation of the base sheet 10 is estimated to be about 10 to 30%, if the thickness T of the base sheet 10 is 100 μm or more, the variation in the height of the balls of the ball grid array substrate can be sufficiently suppressed. Can be absorbed. The thickness of the base sheet 10 is more preferably 300 μm or more. The upper limit of the thickness may be set depending on the use of the particle-filled sheet 1 or desired characteristics, and may be, for example, 500 μm or less.

As shown in FIGS. 1 and 2, the through holes 20 are holes that penetrate the base sheet 10 from the front surface to the back surface thereof, and a plurality of through holes 20 are formed in the base sheet 10. The shape of the opening surface of the through hole 20 is not particularly limited, and may be, for example, circular, oval, or rectangular. However, in consideration of workability when forming the through holes 20 at a fine pitch, the shape of the opening surface of the through holes 20 is preferably circular or elliptical.

The arrangement of the through holes 20 may be, for example, a staggered arrangement, a rectangular arrangement, a random arrangement, or an arrangement other than these. . The arrangement of the through holes 20 may be set depending on the use of the particle-filled sheet 1 and the like. For example, when the particle-filled sheet 1 is used as a connector for connection or a connector for inspection, the arrangement of the through holes 20 may be set to correspond to electronic components to be connected or inspected. That is, the arrangement of the through-holes 20 may be set so that the particle-filled portion 30 contacts desired electrodes (basically all electrodes) in the electronic component.

The pitch P of the through-holes 20 (in other words, the pitch of the particle-filled portions 30) may also be set depending on the use of the particle-filled sheet 1. For example, when the particle-filled sheet 1 is used as a connection connector or an inspection connector, the pitch P of the through holes 20 is preferably less than or equal to the pitch of the electrodes of an electronic component, and more preferably narrower than the pitch of the electrodes. preferable. Here, as shown in FIG. 3, the pitch P of the through holes 20 is the distance between the center point P0 of the through hole 20 and the center point P0 of the through hole 20 closest to the through hole 20. The center point P0 means the center point of the aperture surface. In other words, the pitch P is a so-called minimum pitch.

In this embodiment, any region of the base sheet 10 is a high aspect region. Here, the high aspect region is a region where the aspect ratio of the through hole 20 is 0.5 or more. The aspect ratio of the through holes 20 is a value obtained by dividing the thickness T of the base sheet 10 by the pitch of the through holes 20, and is synonymous with the aspect ratio of the particle filling portion 30. In this way, in this embodiment, a high aspect ratio of 0.5 or more is achieved. The aspect ratio is more preferably 1.0 or more, and more preferably 2.0 or more.

In the high aspect region, the through holes 20 are arranged at a fine pitch. For example, when the thickness of the base sheet 10 is 100 μm, the pitch P of the through holes 20 is 200 μm or less. In other words, even if the base sheet 10 is thick, the through holes 20 are formed at a fine pitch.

In recent years, terminals of electronic components are often arranged at a fine pitch of 200 μm or less, and the particle-filled sheet 1 is also required to be connected to such fine-pitch terminals. As described above, since the high aspect area is formed in the particle-filled sheet 1, the particle-filled sheet 1 can also be connected to electronic components in which terminals are arranged at a fine pitch. That is, it is possible to sufficiently absorb the unevenness of the electronic component (for example, variations in the height of the electrodes), and it is also possible to bring the particle filling portion 30 into contact with each electrode.

For example, the particle-filled sheet 1 in which the thickness of the base sheet 10 is 100 μm and the pitch P of the through holes 20 is 200 μm or less can be used as a connector for inspection of a ball grid array board in which balls are arranged at a fine pitch of 200 μm. It can be suitably used. In other words, since the particle-filled sheet 1 has a sufficient thickness, it can sufficiently absorb variations in the height of the balls. Furthermore, since the through holes 20 (that is, the particle filling portions 30) are arranged at a fine pitch, the particle filling portions 30 can be brought into contact with each ball. When the pitch of the balls is 200 μm or less, the pitch P of the through holes 20 may be set to be equal to or less than the pitch of the balls.

The pitch P of the through holes 20 in the high aspect region is preferably 200 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. Thereby, the particle-filled sheet 1 can be reliably connected to the electronic component in which the electrodes are arranged at a fine pitch. The lower limit of the pitch P is not particularly limited, but may be 3 μm or more, or 10 μm or more.

The diameter of the through-holes 20 may be adjusted depending on the use of the particle-filled sheet 1 or the required characteristics, but for example, the lower limit may be 1 μm or more, 3 μm or more, or 5 μm or more. It may be. The upper limit may be 30 μm or less, 25 μm or less, or 20 μm or less.

In addition, although it is preferable that the entire area of the particle-filled sheet 1 is a high aspect area, only a part of the area may be a high aspect area. For example, only some of the electrodes arranged on an electronic component may be arranged at a fine pitch. In this case, only the region connected to the electrodes arranged at a fine pitch needs to be a high aspect region.

Preferably, an inorganic substance is attached to the wall surface of the through hole 20. This improves the slipperiness of the wall surface of the through hole 20. As will be described later, in the manufacturing process of the particle-filled sheet 1, a particle paste containing particles for filling is poured into the through-holes 20. Therefore, if the wall surface of the through hole 20 has good slipperiness, the particle paste can be smoothly poured into the through hole 20. Although details will be described later, the through holes 20 are formed by irradiating the base sheet 10 with focused short pulse laser light. At this time, debris is formed on the wall surface of the through hole 20. This debris can be the above-mentioned inorganic substance. The type of inorganic substance varies depending on the material of the base sheet 10, but for example, when the base sheet 10 is made of silicone resin, the inorganic substance is SiO _x or Si.

Particle filling portion 30 is formed within through hole 20 . The particle filling section 30 has a large number of filling particles filled in the through hole 20 . The type, characteristics, etc. of the filling particles are not particularly limited, and may be appropriately determined depending on the use of the particle-filled sheet 1, etc. For example, the filling particles may be conductive particles or insulating particles (eg, resin particles). For example, when the particle-filled sheet 1 is used for a connection connector, an inspection connector, or the like, the filling particles include conductive particles. The filling particles are required to have fluidity so that they can be poured into the through holes 20 during the manufacturing process. When the filling particles are conductive particles, the conductive particles are required to have not only fluidity but also elasticity to maintain electrical contact with the electrodes of the electronic component even when the particle-filled sheet 1 is indented and deformed. It will be done. From this point of view, the conductive particles are preferably conductive particles made of a conductive metal such as Ni, Cu, Ag, or Fe, or coated particles in which core particles made of resin are coated with the above-mentioned conductive metal. . On the other hand, examples of the resin constituting the insulating particles include thermoplastic resins such as polyester and acrylic polymer, as well as silicone rubber particles. The particle filling section 30 may contain a binder in order to prevent the filling particles from falling off from the through holes 20. Examples of the material constituting the binder include materials similar to those of the base sheet 10, as well as acrylic polymers, epoxy polymers, and the like. When weather resistance is required for the particle-filled sheet 1, it is preferable to use something other than conjugated diene rubber, and in particular, from the viewpoint of moldability and electrical properties, it is preferable to use acrylic polymer or silicone rubber. . The mixing ratio of the filler particles and the binder may be adjusted depending on the use of the particle-filled sheet 1 or desired characteristics.

In this way, since the high aspect area is formed in the particle-filled sheet 1, the particle-filled sheet 1 can be more reliably connected to an electronic component in which electrodes are arranged at a fine pitch.

<2. Overview of the manufacturing method for particle-filled sheets>
Next, the outline of the method for manufacturing the particle-filled sheet 1 will be explained along the flowchart shown in FIG. In step S10, as shown in FIGS. 5 and 6, a plurality of through holes 20 are formed in the base sheet 10 by condensing and irradiating the base sheet 10 with a short pulse laser L. In this embodiment, by using a short pulse laser, the through hole 20 with a high aspect ratio can be formed. Details of step S10 will be described later.

In step S20, a particle filling portion 30 is formed in the through hole 20. Here, the method of forming the particle-filled portions 30 in the through-holes 20 is not particularly limited, and any filling method that is common in each field to which the particle-filled sheet 1 is applied (for example, the field of electronic materials) can be used. For example, the particle-filled portion 30 may be formed in the through-hole 20 by imprinting, press-fitting, dipping, or the like using a particle paste. An example of a specific method will be explained based on FIGS. 7 and 8.

7 and 8 show an example of a so-called imprinting method. As shown in these figures, a base sheet 10 is placed on a substrate 105, and a particle paste 110 is spread on the base sheet 10. Here, the particle paste 110 includes filler particles and an uncured binder. The uncured binder is, for example, a resin monomer, oligomer, or prepolymer constituting the binder. A catalyst (for example, an organic peroxide, a fatty acid azo compound, a hydrosilylation catalyst, etc.) for curing the uncured binder may be further added to the particle paste.

Next, by moving the particle paste 110 on the base sheet 10 using the squeegee 100, the particle paste 110 is imprinted (ie, filled) into the through holes 20. Then, the uncured binder in the particle paste 110 is cured. The curing method varies depending on the type of binder, but for example, heat treatment may be used. Thereby, the particle-filled sheet 1 is produced.

The method of forming the particle filling portion 30 using the particle paste 110 is not limited to the above, and may be the method shown in FIGS. 9 and 10, for example. 9 and 10 show an example of a so-called dipping method. As shown in these figures, by storing the particle paste 110 in the water tank 120, a particle paste bath is formed in the water tank 120. Next, the base sheet 10 is immersed in the particle paste bath while the inside of the water tank 120 is suctioned by the vacuum pump 130. As a result, the through holes 20 are filled with the particle paste 110. Next, the base sheet 10 is pulled out of the particle paste bath, and the particle paste 110 in the through holes 20 is cured. Thereby, the particle-filled sheet 1 is produced.

In step S30, the particle-filled sheet 1 is inspected. The inspection is to determine whether the particle-filled sheet 1 has desired characteristics. For example, when the particle-filled sheet 1 is used as a connection connector, an inspection connector, or the like, the particle-filled sheet 1 is required to have electrical conductivity. In this case, in this step, the conductivity of the particle-filled sheet 1 is tested. The conductivity test is performed using, for example, an evaluation device 500 shown in FIG. 16. The specific testing method will be explained in Examples. Of course, the inspection method is not limited to the method shown in the example, and any inspection that is performed to evaluate the quality of the particle-filled sheet 1 may be performed. The particle-filled sheet 1 that passed the inspection is made into a product.

FIG. 15 shows a cross-sectional photograph of the particle-filled sheet 1 actually produced by the above manufacturing method. This cross-sectional photograph was obtained by observing the cross section of the particle-filled sheet 1 with an optical microscope. In this example, the thickness of the base sheet 10 is 250 μm, and the pitch P of the through holes 20 is 100 μm. Therefore, the aspect ratio is 2.5. Note that the filling particles are conductive particles. The diameter of one through hole 20 is 21.5 μm in region A on the upper end side (laser incidence surface side) and 9.1 μm in region B on the lower end side, and although a slight taper is formed, There is no practical problem.

<3. Details of the process in step S10>
Next, details of the process in step S10 will be explained based on FIGS. 11 to 14. In step S10, as described above, a plurality of through holes 20 are formed in the base sheet 10 by condensing the short pulse laser L onto the base sheet 10. The focused irradiation is performed using, for example, an objective lens.

Here, the base sheet 10 has transparency in at least one wavelength band from 200 to 1600 nm. Therefore, in step S10, the base sheet 10 is irradiated with a short pulse laser L having a wavelength band in which the base sheet 10 has transparency. For example, according to Table 1, when the base sheet 10 is made of silicone rubber, the wavelength of the short pulse laser L may be appropriately selected from within the range of 343 to 1550 nm. Furthermore, the pulse interval of the short pulse laser L needs to be in units of nanoseconds or less. That is, the unit of the pulse interval in this embodiment is, for example, nanosecond, picosecond, femtosecond, or attosecond. The unit of the pulse interval is preferably femtoseconds or less.

The base sheet 10 has transparency in the wavelength band of the short pulse laser L. Therefore, at first glance, it seems that the short pulse laser L passes through the base sheet 10. However, when the inventor irradiated the base sheet 10 with the short pulse laser L, it was found that through holes 20 were formed. As shown in FIG. 11, it is considered that ablation occurred at the focal point L1 of the short pulse laser L, and the base sheet 10 absorbed the energy of the short pulse laser L. In other words, by condensing and irradiating the short pulse laser L onto the base sheet 10, the short pulse laser L is transmitted at areas other than the focal point L1, while at the focal point L1, a temporally and spatially strong light amount ( energy) is applied to the base sheet 10 to generate ablation (multiphoton absorption). That is, by causing the base sheet 10 to absorb energy at the light focusing point L1 at an absorption rate of two-photon absorption or three-photon absorption, the light focusing point L1 and the base material around it are decomposed, melted, or evaporated. Through this, the through hole 20 is formed. Note that such a phenomenon occurs only when the pulse interval is in units of nanoseconds or less.

Note that if the depth of focus is 1/2 or more of the thickness T of the base sheet 10, ablation occurs throughout the thickness direction of the base sheet 10, and the through holes 20 can be formed. The depth of focus is schematically shown in FIG. FIG. 12 shows how the short pulse laser L is focused by the objective lens 50. Depth of focus (DOF) means the distance in the optical axis direction until the laser diameter expands to 2×√2×ω with respect to the spot diameter 2ω (ω: radius of the spot diameter). The depth of focus is expressed by the following equations (1) and (2). Equations (1) and (2) are also shown in FIG.

DOF=2πω ² /λ (1)
2ω=2λ/πNA (2)

In formulas (1) and (2), λ is the wavelength (μm) of the short pulse laser L, and NA is the numerical aperture of the objective lens 50. Therefore, by adjusting the wavelength of the short pulse laser L and the numerical aperture of the objective lens 50, the depth of focus can be adjusted.

Note that when the depth of focus is smaller than 1/2 of the thickness T of the base sheet 10, the focal point L1 is set in the thickness direction of the base sheet 10 while the base sheet 10 is irradiated with the short pulse laser L. Just sweep it. An example of a method for performing such sweeping is a method in which the base sheet 10 is placed on a linear stage or the like and the stage is moved. Thereby, a through hole 20 with a high aspect ratio can be formed. Note that the diameter of the through hole 20 is approximately the same as the spot diameter 2ω, and the taper is hardly formed in many cases.

Note that the high aspect ratio through holes 20 are formed only by irradiating the transparent base sheet 10 with the short pulse laser L, as described above. For example, as shown in FIG. 13, when the continuous wave laser L10 is focused and irradiated onto the base sheet 10, the continuous wave laser L10 simply passes through the base sheet 10, and no ablation occurs.

Further, as shown in FIG. 14, when the continuous wave laser L10 is condensed and irradiated onto the base sheet 10A that absorbs the continuous wave laser L10, the portion irradiated with the continuous wave laser L10 is removed, so that the through hole is It is temporarily formed. However, in order to form the through holes, it is necessary to arrange the light condensing point on the back side of the base sheet 10A. Furthermore, the through hole has a tapered shape, and the opening surface on the laser incidence side becomes larger. Therefore, as the base sheet 10A becomes thicker, the opening surface of the through-holes on the laser incident side becomes larger, so that the through-holes cannot be formed at a fine pitch. In other words, through holes cannot be formed with a high aspect ratio. For example, it is very difficult to form through holes with a pitch of 200 μm in the base sheet 10A with a thickness of 200 μm. In order to make the through holes fine pitch, it is necessary to reduce the area of the opening surface. However, in this case, as shown in FIG. 14, the continuous wave laser L10 may not reach the back side of the base sheet 10A. In this case, the hole 20A that is formed does not become a through hole. A similar phenomenon can be seen even if the continuous wave laser L10 is replaced with a short pulse laser L.

<1. Example 1>
(1-1. Preparation of particle-filled sheet)
Next, an example of this embodiment will be described. In Example 1, a particle-filled sheet was produced by the following steps.

First, a highly transparent silicone sheet (thickness: 200 um) manufactured by Hagitech was prepared as a base sheet. The total light transmittance of the base sheet at a wavelength of 800 nm was measured using a spectrophotometer and was found to be 90% or more. Further, the durometer hardness (Type A; JIS K7215-1986) of the base sheet was measured using a durometer and was found to be 30.

Then, the base sheet was placed on the glass substrate. Next, a short pulse laser having a wavelength of 800 nm and a pulse width of 220 femtoseconds was focused by an objective lens MPlanApox2 manufactured by Mitutoyo, and then irradiated onto the base sheet to form a plurality of through holes. Here, since the numerical aperture of the objective lens was 0.055, the depth of focus was 168 μm. Therefore, the through holes could be formed without moving the base sheet. The through holes were arranged in a rectangular array, and the pitch was 100 μm. Therefore, the aspect ratio was 2.0.

Next, core particles made of acrylic resin were plated with Au to prepare conductive particles having a particle size of 3 μm. A particle paste was prepared by mixing the conductive particles and a binder. The particle paste was then spread on the base sheet. Next, the through holes were filled with the particle paste by moving the particle paste on the base sheet using a urethane squeegee. The particle paste within the through holes was then hardened. A particle-filled sheet was produced through the above steps. The properties of the particle-filled sheet are summarized in Table 1.

<2. Evaluation＞
(2-1. Completion of particle filling section)
The cross section of the particle-filled sheet 1 in the thickness direction was observed to confirm whether the intended particle-filled portion was formed within the base sheet. Even if there is only one place in the cross section where a particle-filled part is not formed (for example, the particle-filled part does not penetrate the base sheet, or the particle-filled part is connected to another adjacent particle-filled part, etc.) If so, the evaluation was set as fail (NG), and in other cases, the evaluation was set as pass (G). In addition, any of the particle-filled parts present in the cross section was picked up and its diameter was measured. Specifically, the diameter of the opening surface on the upper end side (laser incident surface side) and the diameter of the opening surface on the lower end side of the through hole constituting the particle filling part were measured. The results are summarized in Table 2. In Table 2, if the diameter on the upper end side and the diameter on the lower end side are almost the same, either value is shown, and if there is variation, both values are shown.

(2-2. Conductivity evaluation)
Next, the conductivity of the particle-filled sheet was evaluated using an evaluation apparatus 500 shown in FIG. This evaluation device 500 is a device used in the inspection in step S30 described above. The evaluation device 500 includes a stage 510, a substrate 520 provided on the stage 510, a conductive layer 530 covering the substrate, a conductive probe 540, and a tester 550. A tester measures resistance values. The diameter of the pressing surface of the probe (the surface that contacts the particle-filled sheet) is 200 μm. The diameter of the pressing surface is set to be larger than at least the pitch (minimum pitch) of the particle filling portions.

A particle-filled sheet was placed on the conductive layer 530, and the particle-filled sheet was pushed into the top surface with a pressure of 400 mN using a probe 540. As shown in FIG. 17, the pressing surface of the probe 540 contacts a plurality of particle-filled parts. In this state, the electrical resistance value Ω was measured using a tester 550. Resistance values were measured at ten arbitrary locations on the upper surface of the particle-filled sheet, and the largest value was taken as the resistance value of the particle-filled sheet. Table 2 describes relative values and evaluations when the resistance value of Example 1 is set to 100. When the resistance value was 1000 or more, the conductivity was evaluated as failing (NG), and in other cases, it was evaluated as passing (G). The results are summarized in Table 2.

(2-3. Indentation deformability evaluation)
Indentation deformability was evaluated using evaluation device 500. Specifically, a particle-filled sheet was placed on the conductive layer 530, and the particle-filled sheet was pushed into the top surface of the sheet using a probe 540 with a pressing force of 400 mN. The amount of pushing in μm at this time was measured. If the amount of indentation is 3 μm or less, the indentation deformability is evaluated as failure (NG), if the amount of indentation is more than 3 μm and less than 5 μm, it is evaluated as N (level with no practical problem), and otherwise, it is evaluated as pass (G). It was evaluated as follows. The results are summarized in Table 2.

(2-4. Overall judgment)
A test item that passed all evaluation items or was at a level that poses no problem in practical use was judged to be a pass in the overall judgment, and a case in which even one of the evaluation items failed was judged to be a fail in the overall judgment. The results are summarized in Table 2.

<2. Example 2>
The same treatment as in Example 1 was performed except that the conductive particles were Au nanoparticles with a diameter of 30 nm. The results are summarized in Table 2.

<3. Example 3>
The same treatment as in Example 1 was performed except that a fluororubber sheet (Daiel T-530) manufactured by Daikin Industries, Ltd. was used as the base sheet. The results are summarized in Table 2.

<4. Example 4>
The same treatment as in Example 1 was carried out, except that the base sheet was a highly transparent silicone sheet (thickness: 100 um) manufactured by Hagitech, and the pitch of the through holes was 10 μm. The results are summarized in Table 2.

<5. Example 5>
The same process as in Example 1 was performed except that the wavelength of the short pulse laser was 355 nm and the objective lens was MPlanApox1 manufactured by Mitutoyo. Here, since the numerical aperture of the objective lens was 0.02, the depth of focus was 565 μm. The results are summarized in Table 2.

<6. Example 6>
The same process as in Example 1 was performed except that the wavelength of the short pulse laser was 1550 nm. The depth of focus was 326 μm. The results are summarized in Table 2.

<7. Example 7>
The same treatment as in Example 1 was performed except that the base sheet was a highly transparent silicone sheet (thickness: 50 um) manufactured by Hagitech. The results are summarized in Table 2.

<8. Example 8>
The same treatment as in Example 1 was carried out, except that the base sheet was a highly transparent silicone sheet (thickness: 100 um) manufactured by Hagitech, and the pitch of the through holes was 200 um. The results are summarized in Table 2.

<8. Comparative example 1>
Particles with iron as the core particle and gold plating on the surface were dispersed in silicone rubber (product name: SIM-240, manufactured by Shin-Etsu Chemical Co., Ltd.), and the particles were heated to 150°C with a magnetic field applied from above and below to orient the particles. A curing treatment was performed by heating for 30 minutes. This produced a particle-filled sheet. This particle-filled sheet was evaluated in the same process as in Example 1. The results are summarized in Table 2.

<9. Comparative example 2>
The same treatment as in Example 1 was performed except that the base sheet was changed to a black silicone sheet (E12S10) manufactured by Hagitech. This base sheet absorbs short pulse laser with a wavelength of 800 nm. The results are summarized in Table 2.

As is clear from Table 2, good results were obtained in Examples 1 to 8 that met the requirements of this embodiment. In particular, in Examples 1 to 6 and 8 where the thickness was 100 μm or more, good results were obtained including indentation deformability. On the other hand, in Comparative Example 1, since the particle-filled portion was formed by magnetic field orientation, it was not possible to form a particle-filled portion with a high aspect ratio. In Comparative Example 2, since the base sheet absorbed the short pulse laser, it was not possible to form a particle-filled portion with a high aspect ratio.

Although preferred embodiments of the present invention have been described above in detail with reference to the accompanying drawings, the present invention is not limited to such examples. It is clear that a person with ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea stated in the claims. It is understood that these also naturally fall within the technical scope of the present invention.

1 Particle-filled sheet 10 Base sheet 20 Through-hole 30 Particle-filled part

Claims (10)

A method for manufacturing a particle-filled sheet , the method comprising:
The particle-filled sheet is
A base sheet having transparency in at least one wavelength band from 200 to 1600 nm;
a plurality of through holes that penetrate the base sheet from the front surface to the back surface of the base sheet;
a particle filling portion formed in each of the plurality of through holes;
has
The particle-filled portion does not protrude from both the front surface and the back surface of the base sheet,
The base sheet has elasticity,
Any region of the base sheet is a high aspect region where the aspect ratio of the particle filling portion is 0.5 or more,
The method for manufacturing the particle-filled sheet includes:
forming a plurality of the through holes in the base sheet by irradiating the base sheet with a short pulse laser in a wavelength band in which the base sheet has transparency;
forming the particle filling portion in each of the plurality of through holes;
including;
A method for producing a particle-filled sheet, characterized in that the unit of the pulse interval of the short pulse laser is nanoseconds or less. 2. The method for producing a particle-filled sheet according to claim 1 , wherein a pulse interval unit of the short pulse laser is femtoseconds or less. The production of a particle-filled sheet according to claim 1 or 2 , wherein the particle-filled sheet is a particle-filled sheet used as a connection connector or an inspection connector electrically connected to an electronic component. Method . The arrangement of the plurality of through holes is set to correspond to the plurality of electrodes of the electronic component to be connected or inspected,
4. The method for manufacturing a particle-filled sheet according to claim 3 , wherein the pitch of the plurality of through holes is equal to or less than the pitch of the plurality of electrodes of the electronic component. The terminals of the electronic component are arranged at a fine pitch of 200 μm or less,
5. The method for manufacturing a particle-filled sheet according to claim 3 , wherein the pitch of the through holes is 200 μm or less in the high aspect region. The particle-filled sheet is used as a connector for testing a ball grid array substrate,
The method for producing a particle-filled sheet according to any one of claims 1 to 5 , wherein the base sheet has a thickness of 100 μm or more. The method for producing a particle-filled sheet according to any one of claims 1 to 5, characterized in that an inorganic substance is attached to the wall surface of the through hole. The method for producing a particle-filled sheet according to any one of claims 1 to 7, wherein the base sheet is made of a rubber material. The particle-filled sheet according to any one of claims 1 to 8 , wherein the elasticity of the base sheet is 70 or less in hardness type A (JIS K 7215-1986). Production method . The method for producing a particle-filled sheet according to any one of claims 1 to 9 , wherein the particles contained in the particle-filled part are elastic, conductive particles.

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