JPH02187478A - Releasable tacky adhesive - Google Patents

Abstract

PURPOSE:To provide the subject tacky adhesive containing a specific polymerizable polymer and a polyfunctional oligomer at specific ratios, having high cohesivity and adhesivity before irradiation with radiation, giving low adhesivity after hardening and effective in facilitating the cutting and pick-up work of a semiconductor wafer. CONSTITUTION:The objective tacky adhesive is composed mainly of (A) 100 pts.wt. of a polymerizable polymer of alkyl acrylate and/or alkyl methacrylate having an iodine value of 0.5-20 and containing radiation-polymerizable unsaturated bond in the molecule (e.g. a reaction product of a carboxyl group containing monomer with an epoxy group-containing monomer or an isocyanate group- containing monomer) and (B) 1-50 pts.wt. of a radiation-polymerizable polyfunctional oligomer (e.g. trimethylolpropane triacrylate).

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a removable adhesive, particularly the above-mentioned adhesive for an adhesive sheet used when cutting (dicing) a semiconductor wafer into small element pieces and picking up the pieces. Regarding drugs.

[Conventional technology]

Conventionally, after a semiconductor wafer is pasted and fixed on an adhesive sheet, the wafer is cut along the element shape with a rotating round blade, and the formed element pieces are then picked up from the adhesive sheet and transferred to the mounting process at the same time. The direct pickup method has been adopted as it is desirable in terms of workability and productivity.

As this type of adhesive sheet, for example,
As disclosed in Japanese Patent No. 8572, there is known a pressure-sensitive adhesive prepared by adding a radiation-polymerizable polyfunctional oligomer to an acrylic acid alkyl ester-based and/or methacrylic acid alkyl ester-based polymer on a transparent substrate. ing.

The method for using this radiation-polymerizable adhesive sheet is to paste a semiconductor wafer onto it, cut it into small element pieces, and then irradiate the portion of the sheet corresponding to the element pieces to be picked up with radiation to reduce the adhesive strength. Then, the element pieces in this area are picked up by pushing them up from the adhesive sheet side with a needle and adsorbing them with air tweezers. In other words, the reason why a radiation-polymerizable adhesive is used is to reduce its adhesive strength through polymerization and curing during pickup, thereby making the pickup operation easier.

[Problem to be solved by the invention]

However, in the above-mentioned known pressure-sensitive adhesive sheets, when the amount of polyfunctional oligomer in the pressure-sensitive adhesive is small, the polymerization curing speed due to radiation irradiation is slowed down, and the decrease in adhesive strength is also small; on the other hand, when the amount is increased, , the cohesive force before irradiation with radiation decreases, which tends to cause misalignment when cutting into small element pieces, and the elongation of the adhesive decreases after curing, so when the adhesive sheet is stretched when separating and picking up small element pieces. However, there were problems such as cracks occurring in the adhesive layer and small pieces of the element scattering.

Therefore, the present invention provides a removable adhesive that avoids the above-mentioned problems caused by the amount of polyfunctional oligomers and allows better performance in cutting and picking up semiconductor wafers into small element pieces. The purpose is to

[Means to solve the problem]

As a result of intensive studies to achieve the above object, the inventors discovered that a specific acrylic acid alkyl ester and/or methacrylic acid having a radiation-polymerizable unsaturated bond introduced into the molecule as a base polymer for the adhesive. When an alkyl ester polymer is used and a polyfunctional oligomer is blended into this polymer, the cohesive force and adhesive force before radiation irradiation are large, and the polymerization and curing speed due to radiation irradiation is fast, and the adhesive strength after curing is low. This invention was completed based on the knowledge that a removable adhesive with a large reduction in deterioration could be obtained, and that it would be possible to significantly improve the work of cutting semiconductor wafers into small pieces of elements and the work of picking them up.

That is, the present invention provides an acrylic acid alkyl ester-based and/or methacrylic acid alkyl ester-based polymerizable polymer having a radiation-polymerizable unsaturated bond in the molecule and having an iodine value of 0.5 to 20; This polymer 1
The present invention relates to a removable pressure-sensitive adhesive containing as a main component a radiation-polymerizable polyfunctional oligomer in a ratio of 1 to 50 parts by weight to 00 parts by weight.

[Structure and operation of the invention]

The polymerizable polymer used in this invention is an acrylic acid alkyl ester-based and/or methacrylic acid alkyl ester-based polymer [hereinafter simply referred to as (meth)acrylic polymer] with radiation-polymerizable unsaturated bonds introduced into the molecule. This is because the conduction of this unsaturated bond is
1 is expressed as an iodine value of 0.5 to 20, preferably 1 to 10
This is the range of Here, if the iodine value is less than 0.5, the decrease in adhesive strength after polymerization and curing will be small, and if it exceeds 20, the elongation of the adhesive after polymerization and curing will be small. Not suitable for

When such a polymerizable polymer is blended with a radiation-polymerizable polyfunctional oligomer, the entire adhesive layer is uniformly and quickly polymerized and crosslinked to become integrated by radiation irradiation.
The increase in elastic modulus due to polymerization and curing becomes significant, resulting in a significant decrease in adhesive strength.

Therefore, since there is no need to increase the amount of polyfunctional oligomer blended more than necessary, there is no risk of problems such as a decrease in cohesive force before radiation irradiation or a decrease in elongation after polymerization and curing.

On the other hand, with conventional adhesives made by blending polyfunctional oligomers with non-polymerizable (meth)acrylic polymers, only the polyfunctional oligomers are polymerized and cured by radiation irradiation, and the polymer and the above polymers are bonded to each other in a microscopic manner. As a result of phase separation, the physical properties of the polymer remain as they are, so that the decrease in adhesive strength is small. In order to compensate for this, increasing the amount of polyfunctional oligomer causes problems such as a decrease in cohesive force before radiation irradiation and a decrease in elongation after polymerization and curing, as described above.

The above-mentioned polymerizable polymer used in this invention can be obtained by synthesizing in advance a (meth)acrylic polymer having a functional group in its molecule (hereinafter referred to as a (meth)acrylic polymer having a functional group), It can be obtained by reacting a compound having a functional group that reacts with the above functional group and a radiation-polymerizable unsaturated bond (hereinafter referred to as a functional group-containing unsaturated compound).

The functional group-containing (meth)acrylic polymer is an acrylic acid alkyl ester and/or a methacrylic acid alkyl ester in which the number of carbon atoms in the alkyl group is usually in the range of 2 to 18, as in the case of general (meth)acrylic polymers. It is obtained by copolymerizing an ester as the main monomer with a functional group-containing monomer and, if necessary, other modifying monomers that can be copolymerized with these monomers, and its molecular weight usually has a weight average molecular weight of 20~
It is about 2 million.

The above functional group-containing monomers include carboxyl group-containing monomers such as acrylic acid and methacrylic acid, hydroxyl group-containing monomers such as hydroxyethyl acrylate and hydroxyethyl methacrylate, and epoxy group-containing monomers such as glycidyl acrylate and glycidyl methacrylate. , isocyanate group-containing monomers such as isocyanate ethyl acrylate and isocyanate ethyl methacrylate, and amino group-containing monomers such as aminoethyl acrylate and aminoethyl methacrylate. The amount of these functional group-containing monomers used is usually 1 to 20% by weight, preferably 2 to 10% by weight, based on the total weight of the monomer.

Further, as other copolymerizable modifying monomers, any of various monomers used in general (meth)acrylic polymers such as vinyl acetate, acrylonitrile, and styrene can be used.

The amount used is preferably 30% by weight or less based on the total monomer.

As the functional group-containing unsaturated compound to be reacted with such a functional group-containing (meth)acrylic polymer, the same functional group-containing monomers as described above can be used depending on the functional group of the polymer. For example, if the functional group of the above polymer is a carboxyl group, an epoxy group-containing monomer or an isocyanate group-containing monocer is used, if the same functional group is a hydroxyl group, an isocyanate group-containing monomer is used, and if the same functional group is an epoxy group, a carboxyl group is used. When the containing monomer or the amide group-containing monomer such as acrylamide has the same functional group as an amino group, an epoxy group-containing monomer is used.

In the reaction between the functional group-containing (meth)acrylic polymer and the functional group-containing unsaturated compound, the amount used is selected such that the iodine value of the polymerizable polymer obtained by this reaction falls within the above range, and the reaction raw materials are When it contains isocyanate groups, etc., it is sufficient to use non-reactive ethyl acetate, toluene, etc. as a solvent, and carry out the reaction usually at 20 to 50°C for 1 to 10 hours, using an appropriate catalyst if necessary. It's okay to do that.

The polyfunctional oligomer used in this invention usually has a molecular weight of 10,000 or less, and more preferably has a molecular weight of s so that the adhesive layer can be efficiently formed into a three-dimensional network by radiation irradiation. , ooo or less and the number of radiation-polymerizable unsaturated bonds in the molecule is preferably 2 to 6. Such particularly suitable multifunctional oligomers include, for example, trimethylolpropane triacrylate, tetramethylolmethanetetraacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol monohydroxypentaacrylate, dipentaerythritol hexaacrylate or Examples include methacrylate a similar to the above. In addition, 1.4-butylene glycol diacrylate, 1.6-hexanediol diacrylate, polyethylene glycol diacrylate, commercially available oligoester acrylates, or methacrylates similar to those mentioned above can also be used.

As the polyfunctional oligomer, one type of the above-mentioned compounds may be used alone, or two or more types may be used in combination. The amount used is 1 to 50 parts by weight, preferably 5 to 20 parts by weight, based on 100 parts by weight of the above polymerizable polymer.

When the amount is less than 1 part by weight, the increase in the glass transition point after polymerization and curing due to radiation irradiation is small, and the crosslinking rate is also small, so that the decrease in adhesive strength is small. If the amount exceeds 50 parts by weight, plasticization of the adhesive before irradiation becomes significant, causing misalignment and poor adhesion when cutting semiconductor wafers, and problems such as insufficient elongation of the adhesive after irradiation. It's coming.

The removable pressure-sensitive adhesive of the present invention contains the above-mentioned polymerizable polymer and polyfunctional oligomer as essential components. In addition, when active light such as ultraviolet rays is used as radiation for polymerization and curing, a photopolymerization initiator is usually added. It is preferable to mix them.

Examples of the photopolymerization initiator include isopropyl benzoin ether, isobutyl benzoin ether, benzophenone, Michler's ketone, chlorothioxanthone,
Examples include dodecylthioxanthone, dimethylthioxanthone, diethylthioxanthone, acetophenone diethyl ketal, benzyl dimethyl ketal, α-hydroxycyclohexylphenyl ketone, 2-hydroxymethylphenylpropane, and one or more of these may be used alone or in combination. can be used in combination.

The amount of the photopolymerization initiator to be used is preferably in the range of 0.1 to 5 parts by weight based on 100 parts by weight of the above polymerizable polymer. If the amount used is too small, the three-dimensional reticulation of the adhesive by radiation irradiation will be insufficient and the degree of decrease in adhesive strength will be too small, which is not preferable. On the other hand, if the amount used is too large, not only the corresponding effect will not be obtained, but also the photopolymerization initiator will remain on the surface of the adherend, which is not preferable. In addition, if necessary, an amine compound such as triethylamine, tetraethylpentamine, dimethylaminoethanol, etc. may be used together with this photopolymerization initiator as a photopolymerization accelerator.

In addition to the above-mentioned components, the removable adhesive of the present invention may optionally contain general adhesives such as isocyanate compounds, melamine compounds, and epoxy compounds in order to adjust the cohesive force of the adhesive. Various polyfunctional compounds may be appropriately blended.

Further, known additives such as plasticizers, resins, surfactants, waxes, and particulate fillers can also be added.

In order to produce a pressure-sensitive adhesive sheet using a removable pressure-sensitive adhesive constructed in this way, this pressure-sensitive adhesive is applied onto a base material by a known method, and then dried if necessary to give a thickness of usually 5 to 40 μm.
What is necessary is to form an adhesive layer having a thickness of about m. As the base material, a plastic film is preferable, and when using actinic rays such as ultraviolet rays as the radiation, usually 1
Transparent substrates that can transmit light of 80 to 460 nm are usually made of polyethylene, polypropylene, polyethylene terephthalate, polyvinyl chloride, etc., with a thickness of 10 to 100 μm.
A plastic film of about 100 ml is suitable.

In order to cut, separate, and pick up a semiconductor wafer into small element pieces using this adhesive sheet, the adhesive sheet is first applied to the semiconductor wafer and then cut into small element pieces using a conventional method. At this time, the 180 degree peel adhesive force (peel speed 300/min) to the semiconductor wafer is usually 200 to 1
,000 g/25 cranes, and the small element pieces do not peel off from this adhesive sheet even under the water pressure of about 2 kg/ca1 normally applied during the above-mentioned cutting, and are well held on the sheet.

Next, before picking up this element piece, it is irradiated with active light such as ultraviolet rays, ionizing radiation such as Ryuko rays, and gamma rays to polymerize and harden it. As a result, the tackiness of the adhesive sheet is almost completely lost, and the adhesive force to the element pieces is significantly reduced to usually 150 g/25a+ or less at 180 degree peel adhesive force (peel speed 300 mm/min). For this reason,
The subsequent pick-up process has been greatly improved, and the transition to the mounting process is also smooth. Further, even if the adhesive sheet is stretched during the above-mentioned pickup to make the pickup operation easier, there is no problem such as cracks in the adhesive layer.

〔Effect of the invention〕

As described above, in this invention, by blending a specific amount of a polyfunctional oligomer into a specific polymerizable polymer, the cohesive force and adhesive force before radiation irradiation are large, and the polymerization and curing speed due to radiation irradiation is increased. It is possible to obtain a removable adhesive that is fast and exhibits a large drop in adhesive strength after curing, and this adhesive can greatly improve the work of cutting semiconductor wafers into small pieces of elements and the work of picking them up. can.

〔Example〕

Next, examples of the present invention will be described in more detail. In addition, hereinafter, parts are parts by weight. Moreover, the iodine value was measured and calculated based on the Das method under reaction conditions of 40° C. for 24 hours.

Example 1 79 parts of n-butyl acrylate, 15 parts of ethyl acrylate, 1 part of acrylic acid and 5 parts of 2-hydroxyethyl acrylate were copolymerized in toluene by a conventional method to obtain a polymer having a weight average molecular weight of 650,000. A polymer solution containing a functional group-containing polymer and having a solid content concentration of 35% by weight was obtained.

Next, a functional group-containing polymer 10
0 parts of 2-isocyanate ethyl methacrylate (
Add 3.5 parts of MDI (manufactured by Showa Rodeo Co., Ltd.) and heat at 40°C.
By reacting for 6 hours, the iodine value reached 5.
A polymer solution containing the polymerizable polymer No. 2 was prepared.

To this polymerizable polymer solution, 20 parts of pentaerythritol triacrylate per 100 parts of the polymerizable polymer,
A removable adhesive solution was prepared by blending 0.5 part of benzophenone and 0.3 part of a polyisocyanate compound (Coronate, manufactured by Nippon Polyurethane Co., Ltd.).

This solution was applied to a polypropylene film with a thickness of 38 μm and dried by heating to form an adhesive layer with a thickness of 10 IJm, and a release paper was bonded to the upper surface of the adhesive layer to form an adhesive sheet. After removing the release paper and bonding a silicon wafer with a diameter of 101 to the adhesive layer surface, the initial adhesive strength was measured based on JIS-Z-0237, and it was found to be 550 g/25 fl.
However, the effective absorbed dose of electron beam to the adhesive layer was 2 Mra.
d (voltage 150 KeV, current 5 mA)@, and then the adhesive strength was examined and found to have significantly decreased to Log/25n+.

Next, a semiconductor wafer with a diameter of 5 inches was attached to this adhesive sheet, and the wafer was cut into element pieces of 50 mm in size using a rotating round blade. Although this cutting was performed while washing with water at a pressure of 2 kg/cJ, no small pieces of the element were peeled off at that time. After this cutting, light generated by a high-pressure mercury lamp (40 W/cm) is focused from the base material side of the adhesive sheet and irradiated for 5 seconds only on the part corresponding to the element piece to be picked up. The small element piece was picked up by pushing it up with a needle and adsorbing it with air tweezers. This pick-up operation was very easy, and no transfer of the adhesive layer to the element pieces was observed, nor was there any scattering of adjacent element pieces.

Example 2 80 parts of n-butyl acrylate, 15 parts of ethyl acrylate, and 5 parts of acrylic acid were copolymerized by emulsion polymerization to obtain a solid functional group-containing polymer having a weight average molecular weight of 980,000.

Next, by adding 5 parts of glycidyl methacrylate to 100 parts of this functional group-containing polymer and reacting it in toluene at 40°C for 24 hours, the solid content concentration containing the polymerizable polymer with an iodine value of 6.0 was determined. was used as a polymer solution containing 20% by weight.

Example 1 is as follows except that this polymerizable polymer solution was used.
A removable adhesive and a pressure-sensitive adhesive sheet were prepared in the same manner as above, and the initial adhesive strength of this sheet and the adhesive strength after electron beam irradiation were examined, and the initial adhesive strength was 520 g.
/ 25 mm, adhesive strength after electron beam irradiation is 20 g
/ 251m. In addition, when cutting and picking up a semiconductor wafer were performed using this adhesive sheet in the same manner as in Example 1, both operations were performed as in Example 1.
I was able to do it just as well.

Example 3 88 parts of n-butyl acrylate, 5 parts of acrylonitrile, and 7 parts of glycidyl methacrylate were copolymerized in ethyl acetate by a conventional method to obtain a solid content containing a functional group-containing polymer having a weight average molecular weight of 580,000. A polymer solution containing 30% by weight was obtained.

Next, a functional group-containing polymer 10
By adding 3 parts of acrylic acid to 0 parts and reacting at 40° C. for 24 hours, a polymer solution containing a polymerizable polymer having an iodine value of 6.5 was obtained.

Example 1 is as follows except that this polymerizable polymer solution was used.
A removable adhesive and a pressure-sensitive adhesive sheet were prepared in the same manner as above, and the initial adhesive strength of this sheet and the adhesive strength after electron beam irradiation were examined, and the initial adhesive strength was 280 g.
/ 25 ms, adhesive strength after electron beam irradiation is 10 g
/25 mm. Further, when cutting and picking up a semiconductor wafer were performed using this adhesive sheet in the same manner as in Example 1, both operations were successfully performed as in Example 1.

Comparative Example 1 A removable adhesive and a pressure-sensitive adhesive sheet were prepared in the same manner as in Example 1, except that 20 parts of pentaerythritol triacrylate was not used. When the initial adhesive strength and adhesive strength after electron beam irradiation of this pressure-sensitive adhesive sheet were examined, the initial adhesive strength was 450 g/25 mm, and the adhesive strength after electron beam irradiation was 180 g/25 mm. Further, when cutting and picking up a semiconductor wafer were performed using this adhesive sheet in the same manner as in Example 1, the cutting work was performed well, but the picking up work was not performed well.

Comparative Example 2 Pentaerythritol triacrylate and a polyisocyanate compound were blended directly into the functional group-containing polymer without reacting the functional group-containing polymer with 2-isocyanate ethyl methacrylate, that is, without creating a polymerizable polymer. Except for this, a removable adhesive and a pressure-sensitive adhesive sheet were prepared in the same manner as in Example 1.

When the initial adhesive strength and the adhesive strength after electron beam irradiation of this pressure-sensitive adhesive sheet were examined, the initial adhesive strength was 520 g/25 Tsuru, and the adhesive strength after electron beam irradiation was 350 g/25 fl. In addition, when this adhesive sheet was used to cut and pick up a semiconductor wafer in the same manner as in Example 1, both operations could not be performed satisfactorily.

Claims (1)

[Claims] (1) An acrylic acid alkyl ester-based and/or methacrylic acid alkyl ester-based polymer having a radiation-polymerizable unsaturated bond in the molecule and having an iodine value of 0.5 to 20, and this polymer 100 A removable adhesive comprising as a main component a radiation-polymerizable polyfunctional oligomer in a proportion of 1 to 50 parts by weight.