JPH08222818A - Flexible circuit board with adhering function - Google Patents

Abstract

PURPOSE: To obtain a flexible circuit board with an adhering function which hardly brings about such problems as a fault in the external appearance of a release liner covering an adhesive surface and peeling of the liner in a process of solder reflow or in a washing process and, moreover, of which the release liner makes paper particle little at the time of machining such as cutting. CONSTITUTION: An adherent layer 2 is provided in a part or the whole of one surface 1b or both surfaces of a flexible circuit board 1 and a release liner 3 is provided further on this adherent layer. The release liner is constructed of a vinylidene chloride copolymer film formed on one or both surfaces of a paper base and of a release property giving layer provided on the vinylidene chloride copolymer film. For the purpose of forming the adherent layer, it is preferable that a pressure sensitive adhesive double coated sheet is stuck on a prescribed part of the circuit board.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible circuit board having an adhesive function on one side or both sides. More specifically, a release liner for protecting the surface having the adhesive function has heat resistance and water resistance. The present invention relates to a flexible circuit board which is excellent and has little paper dust generated during processing such as cutting.

[0002]

2. Description of the Related Art Conventionally, a flexible circuit board (hereinafter referred to as "FPC") in which the entire circuit board has flexibility has one surface or a surface for fixing to a device or mounting a bracket. In many cases, double-sided adhesive sheets are attached to both sides to give them an adhesive function. Also,
The surface (adhesive surface) showing this adhesive function to the outside is protected by a release liner. The FPC in this state
C, connectors, brackets, etc. are mounted at predetermined positions by solder reflow, and then washed. And
After the cleaning process, the release liner is removed, the adhesive surface is opened and the remaining brackets are fixed there.

For this reason, the double-sided pressure-sensitive adhesive sheet and release liner used for FPC are required to withstand the heat during the solder reflow process and the cleaning liquid during the cleaning process. This is a requirement specific to FPC. Further, in recent years, the cleaning solution for removing flux and impurity ions after solder reflow has been changed from the conventional CFC system to an aqueous system from the viewpoint of global environment protection, and the release liner that comes into direct contact with the cleaning solution has a particularly high water resistance. Needed. Conventionally, as a base material for a release liner of a double-sided pressure-sensitive adhesive sheet, a paper base material such as high-quality paper, glassine paper, or kraft paper, or a base material obtained by laminating polyethylene or the like on these paper base materials has been used.

[0004]

However, when these release liners are used for protection of the adhesive surface of the double-sided PSA sheet attached to the FPC, the release liner is impregnated with an aqueous cleaning solution at the time of the washing process and peeled off. There was a problem such as the liner peeling off (water absorption peeling). On the other hand, even when polyethylene laminated paper is used as a release liner for the purpose of preventing water from coming off in the washing process, the air trapped in the paper expands due to the heat of the solder reflow process, and the laminated film is removed. There were cosmetic problems such as breakthroughs and foaming. A release sheet using a plastic film such as polyethylene terephthalate (PET) or polyethylene (PE) as a base material may be used as the release liner. However, even in this case, the release sheet shrinks due to heat during the solder reflow process,
The FPC is curled, the IC and chip parts are lifted up, and there is a drawback that soldering cannot be performed. Further, when a release liner of a paper base is used, when the FPC is punched into a predetermined shape together with the release liner attached to the release liner, paper dust is generated from the release liner and adheres to the end surface of the adhesive layer. It was a problem.

An object of the present invention is to perform a solder reflow process,
Alternatively, during the cleaning step, problems such as poor appearance and peeling of the release liner that covers the adhesive surface are less likely to occur, and further,
It is an object of the present invention to provide an FPC with an adhesive function, which has less paper dust generated from a release liner during processing such as cutting.

[0006]

Means for Solving the Problems F with an adhesive function of the present invention
The PC has the following features. (1) An adhesive layer is provided on one or both sides of the FPC in a part or all of the area, and a release liner is provided on the adhesive layer. The release liner is provided on one or both sides of a paper substrate. A vinylidene chloride-based copolymer film is formed, and a peelability-imparting layer is provided on the vinylidene chloride-based copolymer film.
C. (2) The vinylidene chloride copolymer film contains a vinylidene chloride unit in an amount of 80 to 92% by weight and has a weight average molecular weight of 100,000 to
400,000 copolymers with a thickness of 1 to 20 μm and an elongation of 1
The FPC with an adhesive function according to (1) above, which comprises a latex coating film of 0 to 100%, and the release property-imparting layer comprises a radiation-curable silicone-based release agent. (3) The FPC with an adhesive function according to the above (1), wherein the adhesive layer is formed by attaching a double-sided adhesive sheet to the FPC.

[0007]

By applying a vinylidene chloride copolymer film to one or both surfaces of the paper base material of the release liner used for the FPC having an adhesive function, the release liner can be
It becomes possible to withstand the heat during the solder reflow process for the PC and also withstand the aqueous cleaning solution during the cleaning process. Further, when the vinylidene chloride-based copolymer film is formed on the surface of the paper substrate, by impregnating the paper substrate with a part of the vinylidene chloride-based copolymer,
Even if cutting processing such as punching processing is applied to FPC,
Generation of paper dust from the release liner is suppressed.

[0008]

EXAMPLES The present invention will be described in more detail with reference to examples. FIG. 1 is a diagram schematically showing the structure of an FPC with an adhesive function according to an embodiment of the present invention.
FIG. 3 is a cross-sectional view of the case where the is cut perpendicularly to the front and back surfaces. In the figure, reference numeral 1 is an FPC, and an adhesive layer 2 is provided on one side 1a or 1b or a desired area on both sides thereof, and an adhesive function capable of adhering or adhering to an external object is given to the area. This adhesive layer 2
1 has a structure in which the adhesive surface of is further covered with the release liner 3. The present embodiment is an example in which the adhesive layer 2 is provided on the surface 1b on the back side of the substrate surface 1a on which the circuit pattern is formed. FIG. 2 is a diagram schematically showing an example of the structure of the release liner 3 and, like FIG. 1, shows a cross-sectional view when the release liner is cut perpendicularly to the front and back surfaces. Is. In the example shown in the figure, a vinylidene chloride-based copolymer film 32 is formed on one surface of a paper base material 31, and a release property imparting layer 33 made of a release agent is formed thereon.

The FPC used in the present invention may be any flexible circuit board. The example of FPC shown in FIG. 1 is an example of a general structure.
The circuit pattern 12 is formed on the base substrate 11.

The adhesive layer may be provided on any surface such as one surface or both surfaces of the FPC.
The area where the adhesive layer is provided may be the entire area or a part of one surface or both surfaces of the FPC. The adhesive layer may have any structure as long as it can impart an adhesive function to the surface of the FPC, but the adhesive is directly applied to the surface of the FPC by applying, spraying or depositing. Examples thereof include those formed by forming a double-sided pressure-sensitive adhesive sheet in advance using a similar pressure-sensitive adhesive and attaching the double-sided pressure-sensitive adhesive sheet. Of these, sticking of the double-sided pressure-sensitive adhesive sheet is preferable because the pressure-sensitive adhesive layer can be easily formed. Next, the double-sided PSA sheet that can be used in the present invention will be described.

The double-sided pressure-sensitive adhesive sheet that can be used in the present invention is not particularly limited as long as it satisfies heat resistance and component fixing characteristics, and is a mode in which only the pressure-sensitive adhesive is formed into a sheet shape (sheet shape). Representative examples thereof include a pressure-sensitive adhesive), a mode in which a sheet-shaped pressure-sensitive adhesive is provided on both sides of a substrate, and a mode in which a pressure-sensitive adhesive is impregnated into a porous substrate. The adhesive is
It is not particularly limited as long as it is commonly used, and examples thereof include natural rubber-based, synthetic rubber-based, acrylic pressure-sensitive adhesives, silicone-based pressure-sensitive adhesives, among others, heat resistance,
An acrylic pressure-sensitive adhesive is preferable from the viewpoint of weather resistance. As the component fixing property of the pressure-sensitive adhesive, the adhesive strength is preferably 5 N / 20 mm or more, more preferably 8 N / 20 mm or more. The thickness of the pressure-sensitive adhesive is preferably 5 to 300 μm, more preferably 20 to 180 μm from the viewpoint of adhesiveness and workability.
m is good. The adhesive may contain known additives such as a cross-linking agent, a plasticizer, a tackifier, an antiaging agent, a stabilizer, a filler, and a pigment, if necessary.

When the double-sided pressure-sensitive adhesive sheet has a base material, examples of the base material include non-woven fabric, paper, Japanese paper, and plastic films such as PP, PET, PE and PVC. Among them, thin paper is preferable from the viewpoint of heat resistance. The thickness of the base material of the double-sided pressure-sensitive adhesive sheet is preferably 80 μm or less, more preferably 50 μm or less from the viewpoint of heat resistance and processability. The base material of the double-sided pressure-sensitive adhesive sheet may be blended with known additives such as a crosslinking agent, a plasticizer, an antioxidant, a stabilizer, a filler, and a pigment, if necessary.

The method for producing the double-sided pressure-sensitive adhesive sheet may be any known method and is not particularly limited. For example, a method for producing a solvent-based pressure-sensitive adhesive by casting on a substrate, or a pressure-sensitive adhesive for a release liner described below. Examples thereof include a method of applying and drying.

The release liner used in the present invention has a structure that protects the surface of the adhesive layer and is peelable when the adhesive surface is exposed.
It is characterized in that it has a peelability-imparting layer on a paper substrate whose one or both surfaces are surface-treated with a vinylidene chloride-based copolymer film. As the base material used for the release liner,
A paper base material is preferable from the viewpoint of good heat resistance, and any material can be used as long as it can withstand the temperature (usually 230 ° C.) in the solder reflow step and the strength of the paper itself does not significantly decrease. As such a material, for example, a paper base material that has been conventionally used for a release liner, such as high-quality paper, glassine paper, and kraft paper, can be mentioned as a preferable material. The thickness of the paper substrate is not particularly limited as long as the workability when peeling the release liner is difficult, but is generally 1 mm or less, preferably 5 μm to 500 μm.

The vinylidene chloride copolymer film provided on the surface of the paper substrate can be formed by using various copolymers containing vinylidene chloride as a main component. The vinylidene chloride-based copolymer film may be formed on one side or both sides of the paper substrate, and may be selected according to the application. The copolymerization component other than vinylidene chloride may be various ones such as vinyl chloride and acrylonitrile. The vinylidene chloride-based copolymer has a vinylidene chloride unit content of 80 to 92% by weight and a weight average molecular weight of 10%.
Those of 10,000 to 400,000 are preferable. The content of vinylidene chloride unit is less than 80% by weight, or the weight average molecular weight is 10
If it is less than 10,000, pinholes are likely to occur in the formed vinylidene chloride-based copolymer film, the moisture-proof effect is insufficient, and the release liner may have poor dimensional stability. On the other hand, when the content of the vinylidene chloride unit exceeds 92% by weight, a film which is brittle and easily causes pinholes may be formed, and when the weight average molecular weight exceeds 400,000, when the coating solution is used, especially latex In that case, the film-forming property of the particles may be deteriorated and a film having a poor moisture-proof effect may be formed.

As the vinylidene chloride copolymer, any of those generally commercially available can be used, and examples thereof include "Saran latex L-502 and L-409" manufactured by Asahi Kasei Corporation. Saran latex L-5
02 is the content of vinylidene chloride units; about 83% by weight,
Weight average molecular weight: about 120,000. Saran latex L-409 has a vinylidene chloride unit content of about 91% by weight and a weight average molecular weight of about 180,000.

As a method for forming a vinylidene chloride copolymer film on the surface of a paper substrate, the vinylidene chloride copolymer is formed into an appropriate coating liquid such as a latex or a solution with a solvent, which is used as a surface of the paper substrate. Alternatively, it can be applied by coating on a rubber-like polymer film described below to form a coating film. As the above-mentioned form of the coating liquid, latex or emulsion is generally preferable in view of workability and quality of the release liner.

The thickness of the vinylidene chloride copolymer film is not particularly limited as long as it satisfies the heat resistance in the solder reflow step and the water resistance in the washing step, but is generally 1 to 20 μm. The growth rate is 1
It is preferably 0 to 100%. Its thickness is 1 μm
If the elongation is less than 10% or the elongation is less than 10%, pinholes are likely to occur in the copolymer film, the moisture-proof effect becomes insufficient, and the release liner may have poor dimensional stability. On the other hand, when the thickness exceeds 20 μm, the rigidity of the release liner becomes too large and may be unnecessarily peeled off from the adhesive surface due to curling or the like, and when the elongation exceeds 100%, it is applied to paper to form a roll. Blocking may occur in the wound state. After forming a vinylidene chloride-based copolymer film on a paper substrate, corona treatment may be carried out, if necessary, in order to improve the adhesion to the release agent to be treated on the film.

In the release liner used in the present invention, a rubber-like polymer film may be formed as a sealing material on the surface of the paper base material, if necessary, for the purpose of suppressing pinholes. When the surface of the paper base material has large irregularities, the attachment is particularly effective. Therefore, the rubber-like polymer film is provided between the paper base material and the vinylidene chloride-based copolymer film.

The thickness of the rubber-like polymer film is preferably 1 to 20 μm. If the thickness is less than 1 μm, the release liner may be poor in dimensional stability because pinholes or defective portions are likely to occur, and if it exceeds 20 μm, the release liner becomes too rigid and curls or the like may cause the release liner to be less than the adhesive surface. It may come off if necessary.

The rubber-like polymer film is formed by forming the rubber-like polymer into an appropriate coating liquid such as a latex or a solution with a solvent and applying it to the surface of the paper base material to form a coating film. You can As the form of the coating liquid, latex or emulsion is generally preferable in view of workability and quality of the release liner.

As the material of the rubber-like polymer film, for example, chloroprene rubber, urethane type polymer, acrylic polymer, SB type rubber or the like can be used. In addition, it is synthesized by using one or more kinds of monomers including unsaturated carboxylic acid ester, aromatic vinyl compound, unsaturated carboxylic acid, vinyl cyanide compound, aliphatic diene, halogen-substituted vinyl compound, carboxylic acid vinyl ester and the like. Polymers etc. may also be used.

Specific examples of the above-mentioned unsaturated carboxylic acid ester include methyl methacrylate, butyl acrylate,
2-ethylhexyl acrylate, glycidyl methacrylate, 2-hydroxyethyl acrylate, methacrylic acid 2
-Hydroxyethyl, diethylene glycol diacrylate, trimethylolpropane triacrylate and the like.

Specific examples of the aromatic vinyl compound include styrene, vinyltoluene and divinylbenzene, and specific examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, itaconic acid, maleic acid and fumaric acid. Specific examples of the vinyl cyan compound include acrylonitrile and methacrylonitrile.

Specific examples of the aliphatic diene include butadiene and isoprene, specific examples of the halogen-substituted vinyl compound include vinyl chloride, and specific examples of the carboxylic acid vinyl ester include vinyl acetate and the like, a vinylamide compound. Specific examples of include acrylamide and N-methylol acrylamide.

The latex of a polymer composed of the above-mentioned monomers is obtained by a suitable method such as a method of emulsion-polymerizing one or more kinds of monomers by a known method using a polymerization initiator or an emulsifier. be able to. A rubber-like polymer that can be preferably used in terms of adhesion to a vinylidene chloride-based copolymer film is a butadiene-based polymer such as SBR, (meth)
For example, an acrylic polymer whose main component is an acrylic ester.

In the release liner used in the present invention, a coating film in which two or more rubber-like polymers are mixed can be prepared by mixing two or more latexes.
Preferred rubbery polymer membranes are soft and, above all,
The elongation is 10% or more, and particularly 100% or more.
If the rubber-like polymer film is too hard, pinholes are likely to occur due to cracking, the release liner may have poor dimensional stability, and the rigidity may increase, resulting in unnecessary peeling from the adhesive surface.

The release liner used in the present invention is a vinylidene chloride copolymer film from the viewpoint of imparting good disintegration property by a simple operation of high-speed stirring in water and thus providing smooth papermaking without trouble. Thickness of 1 to 7
It is preferable that the thickness is μm, especially 2 to 5 μm. Further, the thickness of the rubber-like polymer film provided as necessary is 1 to 10
μm, especially 1 to 7 μm, and particularly preferably 2 to 5 μm.

The vinylidene chloride copolymer film and the rubber-like polymer film in the release liner used in the present invention may contain, if necessary, a filler such as calcium carbonate, clay, talc, silica, a dispersant thereof, or a filler. Appropriate additives such as a tackifier, a tackifier and a plasticizer can be mixed.

In order to give the release liner releasability to the adhesive layer, a releasability-providing layer made of a release agent is formed on the vinylidene chloride copolymer film. The release agent may have high adhesiveness to the vinylidene chloride-based copolymer film and low adhesiveness to the adhesive layer,
A treatment for imparting releasability may be performed using a generally known release agent. For example, a silicone treatment for stripping with a curable silicone polymer containing dimethylpolysiloxane as a main component, a long-chain alkyl treatment for stripping with a long-chain alkyl acrylate copolymer, application of a fluorine-based stripping agent, and the like. Silicone treatment containing dimethylpolysiloxane as a main component is preferable from the viewpoint of peeling force. As the silicone treatment for peeling, a thermosetting silicone such as an addition reaction type or a condensation reaction type, or a radiation curing type silicone such as an electron beam curing type or an ultraviolet curing type can be used.

The thickness of the peelability-imparting layer can be in conformity with the conventional one and is generally 10 μm or less, but from the viewpoint of peelability, it is preferably 0.01 to 5.0 μm, more preferably 0.03. ˜3.0 μm is preferable.

As the silicone-based release agent, a suitable one such as a thermosetting type such as a solution type, an emulsion type or a solventless type, or a radiation curing type such as an ultraviolet ray or an electron beam may be used. Among them, the radiation-curable silicone-based release agent is preferable from the viewpoints of adhesion with the vinylidene chloride-based copolymer film and prevention of pinholes. RC-72 for radiation curable silicone release agents
6, RC-705, RC-711, RC-704, UV
There are commercially available products such as -9300 and UV-2775 (both are trade names, manufactured by Cold Schmidt or manufactured by Toray Silicone).

Below, the FPC with an adhesive function of the present invention,
An FPC with an adhesive function having a conventional release liner was specifically manufactured, and the results of comparing the effects of the release liner are shown. The adhesive layer was formed by attaching a double-sided adhesive sheet to an FPC. [Production Experimental Example 1] A vinylidene chloride-based copolymer having a weight average molecular weight of 120,000 and containing vinylidene chloride units in an amount of 83% by weight with a bar coater on both sides of a high-quality paper having a basis weight of 100 g / m ² as a paper substrate. Latex (“Saran Latex L-502”) is applied to give a thickness of 3 μm and an elongation of 29%.
To form a vinylidene chloride-based copolymer film, and apply a radiation-curable silicone-based release agent onto the vinylidene chloride-based copolymer film, and cure with an electron beam of 3 Mrad to obtain a thickness of 1
A release liner having a thickness of μm was formed to produce a release liner.
An acrylic adhesive solution was applied to the release agent-treated surface of the release liner so that the thickness after drying was 40 μm and dried to obtain a laminate of the release liner and the double-sided adhesive sheet. .. The laminate of the release liner and the double-sided pressure-sensitive adhesive sheet was attached to one surface of the target FPC to obtain an FPC with a pressure-sensitive adhesive function. Here, the acrylic adhesive solution is 100 parts of 2-ethylhexyl acrylate and 5 parts of acrylic acid.
Parts, benzoyl peroxide 0.2 parts and ethyl acetate 165
It was adjusted by adding 4 parts of an isocyanate-based cross-linking agent to a polymer polymerized by a conventional method in a formulation of 1 part.

[Manufacturing Experimental Example 2] An FPC with an adhesive function was obtained in the same manner as in Manufacturing Experimental Example 1 except that the release liner was replaced with a glassine paper having a basis weight of 70 g / m ² .

[Manufacturing Experimental Example 3] An FPC with an adhesive function was obtained in the same manner as in Manufacturing Experimental Example 1 except that the paper base material of the release liner was changed to kraft paper having a basis weight of 73 g / m ² .

[Production Experimental Example 4] Using the same vinylidene chloride copolymer latex as in Production Experimental Example 1, a basis weight of 70 g
After a vinylidene chloride-based copolymer film having a thickness of 3 μm was formed on one side of a glassine paper of 1 m / m ² , a release liner having a thickness of 1 μm was formed on the opposite side of the paper to prepare a release liner. An FPC with an adhesive function was obtained in the same manner as in Production Experimental Example 1.

[Comparative Experimental Example 1] Instead of a vinylidene chloride-based copolymer film, low-density polyethylene was laminated to a thickness of 20 μm on both sides of a high-quality paper having a basis weight of 100 g / m ² .
Addition reaction type thermosetting silicone release agent is applied on it and heated at 110 ° C for 1 minute to cure to a thickness of 1μ.
An FPC with an adhesive function was obtained in the same manner as in Production Experimental Example 1 except that the m peelability-imparting layer was formed.

[Comparative Experimental Example 2] An FPC with an adhesive function was obtained in the same manner as in Production Experimental Example 1 except that the peelability imparting layer was formed directly on the glassine paper having a basis weight of 70 g / m ² .

Comparative Experiment Example 3 Production Experiment Example 1 except that a peelability-imparting layer was formed on the polyethylene side of a single-sided polyethylene laminated kraft paper having a basis weight of 73 g / m ^2.
An FPC with an adhesive function was obtained in the same manner as in.

[Comparative Experimental Example 4] Instead of the vinylidene chloride-based copolymer film, glassine paper having a basis weight of 70 g / m ² was laminated with low-density polyethylene at a thickness of 20 μm on one side, except that it was used. An FPC with an adhesive function was obtained in the same manner as in Production Experimental Example 4.

Production Experiments 1 to 4 and Comparative Experiment 1
The FPC with adhesive function obtained in ~ 4 was used as a sample and evaluated by the following tests. (1) The sample was heated using an infrared heating device so that the maximum temperature of the sample was maintained at 230 ° C. for 5 seconds, and then the state of the double-sided pressure-sensitive adhesive sheet of the sample was visually observed. . (2) The sample was immersed in warm water at 55 ° C., subjected to ultrasonic waves for 2 minutes, and then pulled up. After repeating this four times, the state of the double-sided pressure-sensitive adhesive sheet of the sample was visually observed. (3) The amount of paper dust adhered to the cut surface after the sample was punched was visually observed. Table 1 shows the results.

[0042]

[Table 1]

From the results shown in Table 1, all of the manufacturing experimental examples are superior in heat resistance and cleaning resistance to those of the comparative experimental examples, and paper dusts adhering to the end face during punching are generated. I was able to confirm that it was suppressed.

[0044]

EFFECT OF THE INVENTION The FPC with an adhesive function of the present invention withstands heat during the solder reflow process and the cleaning liquid during the cleaning process, and is less likely to cause problems such as poor appearance and peeling of the release liner that covers the adhesive surface. Further, the vinylidene chloride-based copolymer impregnated in the paper was able to suppress paper dust residue generated from the release liner during processing such as punching and cutting.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing an example of the structure of an FPC with an adhesive function of the present invention.

FIG. 2 is a diagram schematically showing an example of the structure of a release liner used in the present invention.

[Explanation of symbols]

 1 FPC (Flexible Circuit Board) 2 Adhesive Layer 3 Release Liner

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Koji Kuno 1-2-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto Denko Co., Ltd. (72) Shinji Iguchi 1-2-1 Shimohozumi, Ibaraki City, Osaka Prefecture No. Nitto Denko Corporation

Claims (3)

[Claims] 1. A flexible circuit board is provided with an adhesive layer on one or both sides of a part or all of the area, and a release liner is provided on the adhesive layer. A flexible circuit board with an adhesive function, characterized in that a vinylidene chloride copolymer film is formed on one side or both sides, and a peelability imparting layer is provided on this vinylidene chloride copolymer film. 2. A vinylidene chloride-based copolymer film having a thickness of 1 to 2 made of a copolymer containing 80 to 92% by weight of vinylidene chloride units and having a weight average molecular weight of 100,000 to 400,000.
The flexible circuit board with an adhesive function according to claim 1, which is composed of a latex coating film having a thickness of 0 μm and an elongation of 10 to 100%, and the release property-imparting layer is composed of a radiation-curable silicone-based release agent. 3. The flexible circuit board with an adhesive function according to claim 1, wherein the adhesive layer is formed by attaching a double-sided adhesive sheet to the flexible circuit board.