Adhesive bonding and miscellaneous chemical manufacture – Surface bonding means and/or assembly means therefor – With means applying wave energy or electrical energy...
Reexamination Certificate
2002-01-25
2004-12-21
Copenheaver, Blaine (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Surface bonding means and/or assembly means therefor
With means applying wave energy or electrical energy...
C156S285000, C156S286000, C156S295000, C156S556000, C156S273700, C156S275500, C156S275700
Reexamination Certificate
active
06833053
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thin film bonding method, and more particularly, to a thin film bonding method and a bonding method and apparatus of an optical disk using the same.
2. Description of the Background Art
Recently, following the compact disk (CD) generalized as an optical recording medium, a digital versatile disk (DVD) has been proposed with its standardized size, and various products such as a DVD-ROM, a DVD-RAM, a DVD-R, a DVD-RW and a DVD+RW are becoming common.
Such DVD has a remarkably improved recording density compared to the existing CD and is expected to be widely spread.
For example, the capacity of the DVD is about 4.7 Giga bytes (GB) on the basis of a single-sided single layer, storing a movie of about 2 hours in a VHS class.
Among the optical recording mediums, as shown in
FIG. 1
, a reproduction-exclusive optical recording medium includes a first substrate
2
having an information record layer with a pit pattern and a reflection film, and a second substrate
6
attached to the first substrate
2
through an adhesive agent
4
applied at an upper portion of the first substrate
2
.
The first substrate
2
is a light transmission layer, typically made of a co-polymer substance such as a polycarbonate, and has a thickness of 0.6 mm.
One side of the first substrate
2
is used as an information record layer for recording information by forming the pit pattern, a guide groove, or the like, and the reflection film is formed on the information record layer to reflect a laser beam (LB) made incident through the first substrate
2
.
As a dummy substrate, the second substrate
6
is made of the same material as that of the first substrate
2
, serving as a protection layer for preventing deformation of the first substrate
2
and a degradation of the reflection film.
The second substrate
6
also has the thickness of about 0.6 mm the same as the first substrate
2
and bonded onto the reflection film of the first substrate
2
by an adhesive agent
4
.
Accordingly, the optical recording medium, having the structure that the second substrate
6
serving as a protection layer and the first substrate
2
having information are bonded, have the thickness of 1.2 mm, and formed as a disk type having the diameter of 12 cm.
In the optical recording medium, in order to record information or read information from the medium, a laser beam (LB) generated from an optical pick-up (not shown) is transmitted through the first substrate
2
and irradiated on the information record layer.
In such a case, a size of a beam spot formed on the information record layer determining a record density of the optical recording medium is in proportion to a wavelength of a corresponding light source contained in the optical pick-up and in inverse proportion to a numerical aperture (NA) of the objective lens.
Accordingly, in order to improve a record density of the optical recording medium, it is essential to use a light source having a short wavelength with respect to the thickness of the first substrate
2
and an objective lens having a large numerical aperture.
However, in case of increasing the numerical aperture of the objective lens, since a coma aberration of the optical disk to a tilt is drastically increased in proportion to the third power (NA
3
) of the numerical aperture, a reliability of the recorded optical information is degraded.
In addition, as shown in
FIGS. 2A and 2B
, the coma aberration is increased in proportion to the fourth power (t
4
) of the thickness of transparent substrates
10
and
12
transmitting the light.
The coma aberration will now be described in detail with reference to
FIGS. 2A and 2B
.
As shown in
FIGS. 2A and 2B
, when the laser beam (LB) focussed by the objective lens (OL) passes through a first substrate
10
(having a first thickness) of
FIG. 2A and a
first substrate
12
(having a second thickness) of
FIG. 2B
, respectively, a tilt angle (&thgr;
1
) and an angle (&thgr;
2
) due to the laser beam (LB) refracted inside the substrates are formed. If the substrates
10
and
12
are made of the same material, have the same tilt angle (&thgr;
1
), and have the same thickness (i.e., the first thickness=the second thickness), the angles (&thgr;
2
) refracted inside the substrates
10
and
12
will also be formed to be the same, so that a focus for each substrate
10
and
12
is formed at the same position. However, if the substrates
10
and
12
have different thickness (i.e., the first and the second thickness are different), the position (f) of the focus forming an image varies depending on the thickness of the substrates
10
and
12
.
Accordingly, as for the laser beam (LB) sensitive to the thickness of its transmitting substrate has a greater position deflection (&dgr;
1
) when it transmits the first substrate
10
than a position deflection (&dgr;
2
) when it transmits the tilted thin first substrate
12
.
In this manner, if the irradiation position of the laser beam (LB) is deviated from a normal position after passing the first substrate
12
, a bad effect is made on a focusing control or a tracking control, resulting in that a critical error is generated in recording or reproducing information.
In order to prevent the problems, for an optical recording medium having a recording capacity of higher than about 20 GB, an objective lens having a high numerical aperture and an optical recording medium having a thin light transmission layer substrate has been proposed.
In the proposal, as shown in
FIG. 3
, the optical disk includes a first substrate
14
forming a protection layer and a thin second substrate
18
bonded on the first substrate
14
by means of an adhesive agent
16
and having an information record layer formed with a pit pattern and a reflection film.
In the construction, the second substrate
18
transmitting the laser beam (LB) has the thickness of 0.1 mm in order to minimize dependence on the substrate thickness of the coma aberration.
The first substrate
14
bonded onto the second substrate
18
through the adhesive agent
16
is a protection layer and has a thickness of 1.1 mm for a compatibility with the existing optical disks having the thickness of 1.2 mm.
However, even though the optical disk having the thin second substrate
18
as a light transmission layer can minimize generation of the coma aberration, since the second substrate
18
is too thin to be put to a practical use with its poor productivity. The reason is because it is not easy to bond the extremely thin second substrate
18
onto the first substrate
14
.
The bonding method of the optical disk as shown in
FIG. 3
will now be described with reference to
FIGS. 4 and 5
.
First, in a first step (S
20
), the first substrate
14
is mounted on a disk type optical disk support member
15
combined at an upper portion of a rotational shaft
17
included in an optical disk bonding apparatus
19
.
In a second step (S
22
), the first substrate
14
mounted on the optical disk support member
15
is rotated, on which a liquid adhesive agent hardened by ultraviolet rays is applied to form a layer of adhesive agent
16
.
In a third step (S
24
), the thin second substrate
18
having a reflection film is mounted on the adhesive agent layer
16
.
In a fourth step (S
26
), pressure is applied at one time onto the entire surface of the second substrate
18
, and due to the weight of the second substrate
18
, the ultraviolet hardening resin
16
spreads relatively uniformly at the interface of the first substrate
14
and the second substrate
18
.
In a fifth step (S
28
), ultraviolet rays are irradiated to harden the adhesive agent layer
16
.
However, in the conventional optical disk bonding method as described above, since the entire surface of the second substrate
18
is pressurized at one time, air is trapped between the first substrate
14
and the second substrate
18
or the thickness of the adhesive agent layer
16
is uneven.
Large air bubbles due to the air trapped between the fi
Jeong Tae Hee
Kim Myong Ryong
Copenheaver Blaine
Lee Hong Degerman Kang & Schmadeka
LG Electronics Inc.
Rossi Jessica
LandOfFree
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