U.S. patent application number 10/761835 was filed with the patent office on 2004-08-05 for method for manufacturing digital micro-mirror device (dmd).
This patent application is currently assigned to Samsung Electronic Co., Ltd.. Invention is credited to Choi, Jong-Kon.
Application Number | 20040150083 10/761835 |
Document ID | / |
Family ID | 19668340 |
Filed Date | 2004-08-05 |
United States Patent
Application |
20040150083 |
Kind Code |
A1 |
Choi, Jong-Kon |
August 5, 2004 |
Method for manufacturing digital micro-mirror device (DMD)
Abstract
A method for manufacturing a semiconductor package is disclosed.
A wafer including a plurality of semiconductor chips is provided.
Each chip has one or more mirrors mounted thereon. Further, a
plurality of bond pads formed on a periphery of the chip. Next, a
photoresist is formed over the one or more mirrors. Then, the
semiconductor chips are singulated from the wafer. One ore more
semiconductor chips are mounted on a base substrate. The bond pads
of the semiconductor chip are electrically connected with the base
substrate. The photoresist is then removed from the semiconductor
chips.
Inventors: |
Choi, Jong-Kon;
(Chungcheongnam-do, KR) |
Correspondence
Address: |
MARGER JOHNSON & MCCOLLOM PC
1030 SW MORRISON STREET
PORTLAND
OR
97205
US
|
Assignee: |
Samsung Electronic Co.,
Ltd.
Suwon-city
KR
|
Family ID: |
19668340 |
Appl. No.: |
10/761835 |
Filed: |
January 20, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10761835 |
Jan 20, 2004 |
|
|
|
09847620 |
May 2, 2001 |
|
|
|
6720206 |
|
|
|
|
Current U.S.
Class: |
257/678 ;
257/E21.499 |
Current CPC
Class: |
H01L 2224/45124
20130101; H01L 2924/14 20130101; G02B 26/0841 20130101; H01L
2924/01079 20130101; H01L 2224/73265 20130101; H01L 2924/10253
20130101; H01L 2924/01046 20130101; H01L 2224/48472 20130101; H01L
2924/3025 20130101; H01L 2224/45144 20130101; H01L 24/45 20130101;
H01L 2224/48091 20130101; H01L 21/50 20130101; H01L 2924/16235
20130101; H01L 2224/48091 20130101; H01L 2924/00014 20130101; H01L
2224/48472 20130101; H01L 2224/48091 20130101; H01L 2924/00
20130101; H01L 2924/10253 20130101; H01L 2924/00 20130101; H01L
2224/45144 20130101; H01L 2924/00014 20130101; H01L 2224/45124
20130101; H01L 2924/00014 20130101 |
Class at
Publication: |
257/678 |
International
Class: |
H01L 023/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 10, 2000 |
KR |
2000-24951 |
Claims
What is claimed is:
1. A digital micro-mirror device (DMD) packages, comprising: a base
substrate having a top surface and a bottom surface; a metallic
layer formed on the top surface of the base substrate; a metallic
adhesive formed on the metallic layer; a semiconductor chip mounted
on the metallic adhesive, the base substrate electrically connected
with the semiconductor chip; one or more mirrors mounted on the
semiconductor chip; a hermetic sealing means covering the
semiconductor chip including the one more mirrors.
2. The DMD package of claim 1, which further comprises a heat sink
attached on the bottom surface of the base substrate.
Description
[0001] This application is a divisional of U.S. patent application
Ser. No. 09/847,620 filed on May 2, 2001, now pending, which is
herein incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method for manufacturing
semiconductor device packages, and more particularly to a method
for manufacturing digital micro-mirror device (DMD) packages.
[0004] 2. Description of the Related Arts
[0005] In order to keep pace with the development of personal
computers, a display has been developed from a cathode-ray tube
type display into a liquid crystal display or a mirror type
display. Especially, with the increasing demand for digital
broadcasting appliances, a digital light processing (DLP)
technology for high resolution becomes more and more important. A
DMD, which is an essential component for the DLP technology,
requires significant expertise in the manufacturing process for
mirrors so that high reliability and low cost in the manufacturing
process can be obtained.
[0006] The DMD process involves driving the mirrors, and thus the
proper driving of mirrors is very important. Further, moisture and
dust within the packages affect the picture quality or resolution
of the DMD as well as its reliability or durability. Therefore,
during the fabrication of the DMD packages, the DMD packages
themselves need to be protected from moisture and dust.
[0007] FIG. 1 is a plan view showing a conventional semiconductor
chip 12 for the DMD, and FIG. 2 is a cross-sectional view showing a
DMD package 100 containing the semiconductor chip 12 of FIG. 1.
With reference to FIG. 1 and FIG. 2, the semiconductor chip 12 is
attached to an upper surface 21 of a base substrate 20 by
interposing an Ag-epoxy adhesive 30 therebetween. The semiconductor
chip 12 and the base substrate 20 are electrically interconnected
to each other with one or more bonding wires 40. In order to
protect the semiconductor chip 12 from external environmental
stresses, a metal sealing ring 24 with a predetermined height is
provided at the periphery of the upper surface 21 of the base
substrate 20.
[0008] The components, including the semiconductor chip 12, are
hermetically sealed up with a window lid 50. A heat sink stud 60 is
attached to the lower surface 23 of the base substrate 20. The
window lid 50 comprises a metal lid frame 52 contacting the metal
sealing ring 24, and a window 54. A reflectance coating film 56 is
applied to the lower surface of the window 54 along the periphery
thereof. The metal sealing ring 24 and the base substrate 20 form a
cavity 29, and a moisture getter (absorbent) 58 is attached to the
lower surface of the metal lid frame 52 of the window lid 50 within
the cavity 29. External terminals (not shown) are formed on the
lower surface 23 of the base substrate 20.
[0009] A plurality of mirrors 16 (only a typical one of which is
depicted in FIG. 2) are formed on the active surface of the
semiconductor chip 12 at the center thereof, and one or more
electrode pads 14 are formed on the active surface at the periphery
thereof for interconnection via the one or more bonding wires
40.
[0010] FIG. 3 is a flow chart 90 describing a manufacturing process
of the conventional DMD package 100. Each step of the manufacturing
process is described briefly below.
[0011] A wafer comprising a plurality of the semiconductor chips 12
is prepared (step 71). Herein, a photoresist film is formed on the
upper surface of the wafer in the predetermined portion. The
photoresist film prevents damage to the mirrors 16 from the
external environment by covering the mirrors 16. The photoresist
film is not formed on the electrode pads 14.
[0012] Prior to wafer-breaking, the wafer is half-cut (step 72).
The photoresist film on the upper surface of the wafer is removed
(step 73), and to shield the mirrors 16 from dust or moisture, a
first anti-sticking film is formed thereon (step 74). The wafer is
broken and separated into individual semiconductor chips 12 (step
75). A breaking means in a dome shape is brought into contact with
to the back surface of the wafer and urged upwardly. As a result,
the half-cut wafer is broken into a plurality of individual
semiconductor chips 12.
[0013] In the wafer-breaking step, silicon particle scraps are
generated. Therefore, the silicon particles are removed (step
76).
[0014] The semiconductor chip 12 is attached to the upper surface
21 of the base substrate 20 by the Ag-epoxy adhesive 30 (step 77),
and the Ag-epoxy adhesive 30 is cured (step 78). The semiconductor
chip 12 is electrically interconnected to the base substrate 20
with the bonding wires 40 (step 79).
[0015] The organic compounds remaining on the upper surface 21 of
the base substrate 20, the semiconductor chip 12 on the surface 21,
and the bonding wires 40 are removed (step 80). A second
anti-sticking film is formed thereon (step 81).
[0016] The metal sealing ring 24 is mounted on the upper surface 21
of the base substrate 20, and the components are hermetically
sealed by the window lid 50 having the moisture getter 58 attached
thereon (step 82).
[0017] The heat sink stud 60 is attached to the lower surface 23 of
the base substrate 20 (step 83). The DMD package 100 is thus
complete.
[0018] The above-described method for manufacturing the
conventional DMD packages has several problems as follows;
[0019] The manufacturing process is very complicated. The major
reason is that the manufacturing process for the conventional DMD
package employs the wafer-breaking method for separating the wafer
into individual semiconductor chips 12. Since the wafer-breaking
method comprises a first step of half-cutting the wafer and a
second step of breaking the wafer, compared to the full-cutting
method, which completely cuts the wafer at once, this method
further involves an additional step, i.e. the wafer-breaking
step.
[0020] Even if the full-cutting method is employed to prevent this
drawback, another problem occurs in the step of removing the
photoresist after separating the wafer into the semiconductor chips
by the full-cutting method. Conventionally, the wafer comprising
separated semiconductor chips has the adhesive tape on its back
surface. In the photoresist-removing step after the wafer-cutting
step, the adhesive from the adhesive tape and the photoresist are
unnecessarily removed together. Thus, the individual semiconductor
chips can be undesirably detached from the adhesive tape.
Therefore, the conventional manufacturing process normally cannot
employ the full-cutting method.
[0021] The mirrors within the semiconductor chip 12 can be easily
damaged by the silicon particles generated in the wafer-breaking
step. The silicon particles positioned between the mirrors 16
cannot be properly removed by the washing step. Since the
wafer-breaking step is carried out after the step of removing the
photoresist, damage to the mirrors 16 by the silicon particles
commonly occurs.
[0022] Since the Ag-epoxy adhesive is used to attach the
semiconductor chip 12 to the base substrate 20, moisture enters the
package due to the hygroscopicity of the Ag-epoxy. Further, an
exhaust gas generated during the curing of the Ag-epoxy adhesive
contaminates the mirrors 16 on the active surface of the
semiconductor chip 12. Therefore, it is preferable to use solder as
the adhesive means. However, with the use of the solder, damage
such as the burning of the first anti-sticking film or the
deformation of the mirrors can occur. In other words, to attach the
semiconductor chip to the base substrate, the solder must be melted
at a temperature of 150.degree. C. or more. Such a high temperature
causes the burning of the first anti-sticking film or the
deformation of the mirrors 16 in the semiconductor chip 12.
SUMMARY OF THE INVENTION
[0023] Accordingly, an object of the present invention is to
simplify the manufacturing process of the DMD packages.
[0024] Another object of the present invention is to prevent
failures generated in the sequence of steps including first
half-cutting and second full-cutting the wafer. Still another
object of the present invention is to prevent failures due to the
use of the Ag-epoxy adhesive.
[0025] In order to achieve the foregoing and other objects, a
method for manufacturing digital micro-mirror device (DMD) packages
comprises preparing a wafer including a plurality of DMD
semiconductor chips, each chip having a plurality of mirrors formed
on the center of an active surface, a plurality of electrode pads
formed on the edges of the active surface, and a photoresist for
protecting the mirrors. The method further comprises forming a
metallic layer on a back surface of the wafer, said metallic layer
being made of a metal having a low melting point. It further
comprises separating the wafer into the individual semiconductor
chips. It also comprises attaching each semiconductor chip to an
upper surface of a base substrate with an adhesive made of a metal
having a low melting point. The method then comprises the steps of
interconnecting the electrode pads of the semiconductor chip to the
base substrate with a bonding wire, removing the photoresist from
the semiconductor chips, and forming an anti-sticking film on the
active surface of the semiconductor chip for protecting the
semiconductor chips from dust and moisture. Finally, the method
comprises hermetically sealing the semiconductor chip and the
bonding wires on the upper surface of the base substrate by using a
window lid.
[0026] It is preferable that the metallic layer is made of a metal
having a low melting point selected from the group consisting of
Va, Au, Ni, Ag, Cu, Al, Pb, Sn, Sb, Pd and metallic compounds
thereof.
[0027] The step of forming a metallic layer comprises lapping the
back surface of the wafer and forming on the back surface a
metallic layer made of a metal having a low melting point.
[0028] Solder is preferably used as the metal adhesive having a low
melting point.
[0029] After the step of hermetically sealing the semiconductor
chip and the bonding wires, the manufacturing method of the DMD
packages further comprises attaching a heat sink stud to the lower
surface of the base substrate. Further, it is preferable that the
step of hermetically sealing the semiconductor chip and the bonding
wires is carried out at a temperature which is no higher than the
temperature of the step of attaching the semiconductor chip to the
base substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The various features and advantages of the present invention
will be readily understood with reference to the following detailed
description taken in conjunction with the accompanying drawings,
wherein like reference numerals designate like structural elements,
and, in which:
[0031] FIG. 1 is a schematic plan view showing a conventional
semiconductor chip for digital micro-mirror device (DMD);
[0032] FIG. 2 is a cross-sectional view showing a conventional DMD
package containing the semiconductor chip of FIG. 1;
[0033] FIG. 3 is a flowchart describing a conventional
manufacturing process of the DMD package in FIG. 2;
[0034] FIG. 4 is a cross-sectional view showing a DMD package in
accordance with an embodiment of the present invention;
[0035] FIG. 5 is a flow chart describing a manufacturing process of
the DMD package in FIG. 4;
[0036] FIGS. 6 through FIG. 16 illustrate schematically each step
of the manufacturing process in FIG. 5; wherein FIG. 6 is a
schematic plan view that illustrates a wafer used in the DMD
packages; FIG. 7 is a plan view that illustrates the manufactured
wafer;
[0037] FIG. 8 is a cross-sectional view taken along the line 8-8 in
FIG. 7;
[0038] FIG. 9 is a partial cross-sectional view showing
back-lapping the wafer;
[0039] FIG. 10 is a cross-sectional view that illustrates forming a
metal layer on the back surface of the wafer;
[0040] FIG. 11 is a cross-sectional view that illustrates cutting
the wafer into individual semiconductor chip;
[0041] FIG. 12 is a cross-sectional view that illustrates attaching
a semiconductor chip to a base substrate;
[0042] FIG. 13 is a cross-sectional view that illustrates
wire-bonding;
[0043] FIG. 14 is a cross-sectional view that illustrates removing
the photoresist;
[0044] FIG. 15 is a cross-sectional view that illustrates
hermetically sealing the package with a window lid; and
[0045] FIG. 16 is a cross-sectional view that illustrates attaching
a heat sink stud on the lower surface of the base substrate.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] Preferred embodiments of the present invention will be
described below with reference to the accompanying drawings.
[0047] FIG. 4 is a cross-sectional view showing a DMD package 200
in accordance with an embodiment of the present invention. With
reference to FIG. 4, a semiconductor chip 112 is attached to an
upper surface 121 of a base substrate 120 with a metallic adhesive
130 having a low melting point, and a metallic layer 115 made of a
metal having a low melting point is formed on the back surface of
the semiconductor chip 112. The base substrate is preferably a
ceramic board, a plastic board, or a printed circuit board. Herein,
the metallic layer 115 enables the metallic adhesive 130 to be
firmly attached to the semiconductor chip 112. Other components are
the same as those of the conventional DMD package 100 of FIG. 1.
Referring to FIGS. 5 through 16, a manufacturing process of the DMD
packages in accordance with an embodiment of the present invention
is described below.
[0048] FIG. 5 is a flow chart 190 illustrating a manufacturing
process of the DMD package 200 in FIG. 4. FIGS. 6 through 16 show
each step of the manufacturing process of FIG. 5.
[0049] As shown in FIGS. 6 through 8, the manufacturing process
starts with preparing the wafer 110 (step 191). The silicon wafer
110 comprises a plurality of mirror-driving integrated circuits
(not shown) formed by conventional techniques. A plurality of
semiconductor chips 112 is formed on the wafer 110. Scribe lines
118 are also formed between the neighboring semiconductor chips
112, where the circuits are not formed.
[0050] The photoresist 113 is formed on a predetermined portion of
the upper surface 10a of the wafer 110. The photoresist 113
prevents damage to the mirrors 116 from the external environment.
The photoresist 113 is not formed on the electrode pads 114.
[0051] A metallic layer 115 is formed on the back surface 110b of
the wafer (step 192). The metallic layer 115 enables the metallic
adhesive to be firmly attached to the back surface 110b of the
wafer 110. As shown in FIG. 9, the back surface 110b is lapped with
a lapping device 180. Because the silicon oxide layer is naturally
formed on the back surface of the wafer 110, if the metallic layer
is formed on the back surface of the wafer 110 without any
treatment, adhesion between the back surface of the wafer 110 and
the metallic layer 115 can be undesirably weak.
[0052] For this reason, in this embodiment, the back surface 110b
is lapped with the lapping device 180. However, the back surface
may be lapped by any suitable conventional etching techniques. As
shown in FIG. 10, the metallic layer 115 is formed on the lapped
back surface 110b of the wafer 110. With respect to the adhesive
means and the temperature in the chip attachment process, it is
preferable to use a metal having a low melting point as the
metallic layer 115. For example, the metal can be Va (Vanadium), Au
(Gold), Ni (Nickel), Ag (Silver), Cu (Copper), Al (Aluminum), Pb
(Lead), Sn (Tin), Sb (Stibium), Pd (Palladium) and metal-containing
compounds thereof. Of course, the present invention is not limited
to such metals and compounds. Those of ordinary skill in the art
should also be aware the other suitable metals or metallic
compounds are well within the broad scope of the present
invention.
[0053] As shown in FIG. 11, the wafer 110 is separated into
individual semiconductor chips 112 by the full-cutting method (step
193). A scribe blade 170 saws the wafer 110 along the scribe lines
118 and thereby separates the wafer 110 into individual
semiconductor chips 112. This wafer-sawing step is carried out with
the wafer 110 having the adhesive tape (not shown) attached to the
back surface 10b of the wafer 110. Then, the wafer-washing step is
performed.
[0054] Since the mirrors 116 of the semiconductor chips 112 are
coated with the photoresist 113, damage to the mirrors 116 by
contaminants such as silicon particles during the wafer sawing
process can be prevented.
[0055] Conventionally, a step of removing the photoresist normally
follows the washing step. However, with the conventional method, a
delamination problem of the semiconductor chip from the adhesive
tape occurs. In order to prevent this problem, in accordance with
the embodiment of the present invention, as shown in FIG. 12, a
chip attachment step (step 194) is followed. Each of the
semiconductor chips 112 is separated from the wafer (110 in FIG.
11), and attached to the upper surface 121 of the base substrate
120 by interposing an adhesive 130 having a low melting point such
as solder therebetween. Herein, the adhesive 130 is solidified at
room temperature, and therefore the curing step for the Ag-epoxy
adhesive is omitted. Since a metallic layer 115 is formed on the
back surface of the semiconductor chip 112, the adhesive 130 is
more firmly attached to the semiconductor chip 112. The adhesive
130 can be provided in various forms such as a ribbon, paste, wire
or any other suitable patterns.
[0056] If the adhesive 130 is used, the die-attaching step is
carried out at higher temperature than if the Ag-epoxy adhesive is
used. For example, with the solder, the die attaching step is
processed at a temperature of approximately 150.degree. C. or more.
However, since the mirrors 116 of the semiconductor chip are coated
with the photoresist 113, although the die-attaching step is
carried out at a high temperature, the mirrors 116 of the
semiconductor chips are not damaged.
[0057] Although this embodiment uses the base substrate 120 having
a flat upper surface, other base substrates having a dented upper
surface may be used. For the base substrate, however, a ceramic
substrate having low hygroscopicity and high thermal conductivity
preferably is used, although other plastic substrates or a printed
circuit board may be used.
[0058] As shown in FIG. 13, the wire-bonding step is carried out
(step 195). Herein, the ball-bonding method using an Au bonding
wire or the wedge-bonding method using an Al bonding wire may be
alternatively employed. FIG. 13 shows the wedge-bonding method
between the electrode pads 114 of the semiconductor chip 112 and
the base substrate 120.
[0059] As shown in FIG. 14, the photoresist (113 in FIG. 13) is
removed (step 196), and an anti-sticking film is formed (step 197).
The photoresist 113 is not removed until after the wire-bonding
step. This prevents the contamination of the mirrors 116 due to
dust or moisture. However, after the wire-bonding step, the
photoresist 113 on the mirrors 116 is removed, because the mirrors
116 in the semiconductor chip 112 are protected from the outside
when sealing the components including the semiconductor chip with
the window lid. Then, the anti-sticking film for preventing the
sticking of dust or moisture is formed.
[0060] The photoresist 113 is removed from the semiconductor chip
112 attached to the base substrate 120. The embodiment of the
present invention discloses the manufacturing process of the DMD
packages, on which a single semiconductor chip 112 is mounted on
the base substrate 120. However, it still falls within the spirit
and scope of the present invention that a plurality of the
semiconductor chips 112 are mounted on the base substrate 120 in
rows, and multiple packages are simultaneously manufactured. In
such case, the photoresist 113 formed on a plurality of the
semiconductor chips 112 are collectively removed.
[0061] As shown in FIG. 15, the components including the
semiconductor chip 112 are hermetically sealed (step 198). In order
to protect the semiconductor chip 112 on the base substrate 120 and
the bonding wire 140 from the external environment, the
semiconductor chip 112 and the bonding wire 140 are hermetically
sealed. A window lid 150 is attached to a metal sealing ring 124 on
the periphery of the base substrate 120 by thermo-compression, and
thereby the cavity (129 in FIG. 4) containing the semiconductor
chip 112 is hermetically sealed.
[0062] The window lid 150 comprises a metal lid frame 152 in
contact with the metal sealing ring 124, and a window 154
perforating the metal lid frame 152 on the center. A reflectance
coating film 156 is formed on the lower surface of the window 154
on its periphery, and a moisture getter 158 is attached to a lower
surface of the metal lid frame 152.
[0063] In order to prevent the bonding wires 140 from contacting
the lower surface of the window lid 150 attached to the metal
sealing ring 124, it is preferable that a distance between the
upper surface of the base substrate 120 and the lower surface of
the window lid 150 is greater than the height of the bonding
wire.
[0064] When the metal lid frame 152 is attached to the metal
sealing ring 124 by thermo-compression, a portion of the metal lid
frame 152 attached to the metal sealing ring 124 has a thickness
less than the thickness of the other portion of the metal lid frame
152. This allows the effective heat transfer from a
thermo-compression means through the upper surface of the metal lid
frame 152. An adhesive means having a lower melting point than that
of the above-described metal adhesive 130 is used between the metal
sealing ring 124 and the metal lid frame 152. This prevents the
conventional deformation problem that results from re-melting the
metal adhesive 130.
[0065] As shown in FIG. 16, the heat sink stud 160 is attached
(step 199). In order to effectively draw heat away from
heat-generating semiconductor chip 112, the heat sink stud 160 is
attached to the lower surface 123 of the base substrate below the
semiconductor chip 112. The manufacture of the improved DMD package
200 is complete.
[0066] Accordingly, in the manufacturing process of the present
invention, since the photoresist is not removed immediately after
the separation of the wafer into individual semiconductor chips,
but is removed after the wire-bonding step, the present invention
simplifies the manufacturing process of the DMD packages as
follows:
[0067] First, since the wafer is sawed by the full-cutting method,
the present invention thus reduces the number of steps required for
individual semiconductor chip 112 singulation. Second, because the
mirrors 116 of the semiconductor chip 112 are protected with the
photoresist 113, the present invention can omit the conventional
step of forming the first anti-sticking film. The present invention
also omits the conventional step of removing undesirable organic
particulate or compounds after the wire-bonding step. During the
step for removing the photoresist, the present invention also
removes any the organic compounds remaining on the upper surface of
the base substrate, the semiconductor chip and the bonding
wire.
[0068] In the present invention, the mirrors 116 of the
semiconductor chip 112 are protected by the photoresist 113.
Therefore, instead of the Ag-epoxy adhesive, a metal having a low
melting point such as a solder can be used in the chip-attaching
step. Although the chip attaching step is carried out at high
temperatures, the mirrors 116 formed with the photoresist thereon
thus are prevented from high temperature damage (e.g. deformation)
that may otherwise occur. Accordingly, the present invention solves
the affixation and out-gassing problems described above involving a
metal adhesive with a low melting point and an Ag-epoxy adhesive
(relating to the hygroscopicity of the Ag-epoxy adhesive and the
exhaust gas generated during curing of the Ag-epoxy).
[0069] Further, because the photoresist-removing step is performed
with the semiconductor chip being mounted on the base substrate
120, it is very easy to handle the inverted DMD semiconductor chip
112.
[0070] Although preferred embodiments of the present invention have
been described in detail hereinabove, it should be understood that
many variations and/or modifications of the basic inventive
concepts herein taught which may appear to those skilled in the art
will still fall within the spirit and scope of the present
invention as defined in the appended claims.
* * * * *