U.S. patent application number 09/782180 was filed with the patent office on 2001-10-25 for semiconductor device and method of manufacturing the same.
Invention is credited to Sumikawa, Masato, Tanaka, Kazumi.
Application Number | 20010033016 09/782180 |
Document ID | / |
Family ID | 18559126 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010033016 |
Kind Code |
A1 |
Sumikawa, Masato ; et
al. |
October 25, 2001 |
Semiconductor device and method of manufacturing the same
Abstract
A semiconductor device is manufactured in a method including the
steps of: abrasing a surface of a wafer opposite that thereof
having a solder ball serving as an external connection electrode;
and reinforcing the abrased surface with resin serving as a
back-surface reinforcement member. More specifically, the resin is
resin of rubber type, silicone type, epoxy type, polyimide type or
urethane type. Preferably, previously grinding the surface to be
abrased is previously ground to produce the device in a reduced
process time. The structure can advantageously prevent a solder
connection from breaking as an LSI chip fails to bend in response
when the entire package receives force and thus bends.
Inventors: |
Sumikawa, Masato;
(Kashihara-shi, JP) ; Tanaka, Kazumi; (Osaka,
JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
18559126 |
Appl. No.: |
09/782180 |
Filed: |
February 14, 2001 |
Current U.S.
Class: |
257/697 ;
257/E23.119; 257/E23.12; 257/E23.132 |
Current CPC
Class: |
H01L 2924/01078
20130101; H01L 2924/01012 20130101; H01L 2924/01004 20130101; H01L
2224/16 20130101; H01L 2924/3511 20130101; H01L 23/293 20130101;
H01L 2924/01322 20130101; H01L 23/296 20130101; H01L 2224/274
20130101; H01L 23/3171 20130101 |
Class at
Publication: |
257/697 |
International
Class: |
H01L 023/48 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 14, 2000 |
JP |
2000-034855 (P) |
Claims
What is claimed is:
1. A semiconductor device including a semiconductor substrate
having a surface provided with an external connection electrode and
a surface opposite that with said external connection electrode,
abrased and reinforced with a back-surface reinforcement
member.
2. The semiconductor device of claim 1, wherein said back-surface
reinforcement member is formed of resin.
3. The semiconductor device of claim 2, wherein said resin is
formed of a material having an elastic modulus of
1.5.times.10.sup.6 N/m.sup.2 to 5.0.times.10.sup.6 N/m.sup.2.
4. The semiconductor device of claim 2, wherein said resin is
selected from the group consisting of resin of rubber type, resin
of silicone type, resin of epoxy type, resin of polyimide type and
resin of urethane type.
5. A method of manufacturing a semiconductor device comprising the
steps of: abrasing a surface of a semiconductor substrate opposite
to a surface thereof having an external connection electrode; and
applying resin on said surface abrased.
6. The method of claim 5, further comprising the step of cutting
said semiconductor substrate after the step of applying.
7. The method of claim 5, further comprising the step of previously
grinding said surface to be abrased.
8. The method of claim 6, further comprising the step of previously
grinding said surface to be abrased.
9. The method of claim 5, wherein in the step of applying, said
resin is printed.
10. The method of claim 6, wherein in the step of applying, said
resin is printed.
11. The method of claim 7, wherein in the step of applying, said
resin is printed.
12. The method of claim 8, wherein in the step of applying, said
resin is printed.
13. The method of claim 5, wherein in the step of applying, said
resin is applied by spin-coating.
14. The method of claim 6, wherein in the step of applying, said
resin is applied by spin-coating.
15. The method of claim 7, wherein in the step of applying, said
resin is applied by spin-coating.
16. The method of claim 8, wherein in the step of applying, said
resin is applied by spin-coating.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to semiconductor
devices and particularly to semiconductor devices that can be
packaged with enhanced anti-bendability.
[0003] 2. Description of the Background Art
[0004] In recent years, semiconductor devices have been further
reduced in size and further increased in density to meet a demand
for smaller and lighter mobile phones, mobile information equipment
and other similar electronics and electronic equipment. To meet
this demand there has been proposed bare-chip packaging, a
technique applied in mounting an LSI chip directly on a printed
circuit board.
[0005] Reference will now be made to FIGS. 5A and 5B to describe
bare-chip packaging. As a bare chip, an LSI chip 7 has thereon an
electrode on which ball-bonding is for example employed to provide
a metal bump 14 thereon to serve as an external connection
electrode. With reference to FIG. 5A, with metal bump 14 aligned
with an electrode 10 provided on a printed circuit board 9 to be
packaged, LSI chip 7 is packaged on printed circuit board 9
facedown. FIG. 5B shows a complete packaging.
[0006] The market for mobile equipment such as mobile phones and
PHSs has significantly expanded. As such, technological innovation
has been promoted therefor and bare-chip packaging has thus been
increasingly adopted. Conventionally, a package is impaired in
reliability generally when temperature cycle causes thermal stress
and thermal distortion resulting in defects. In addition, mobile
equipment carried by a user can disadvantageously bend when it
receives external force. Furthermore, disadvantageous bending
stress can instantly occurs when mobile equipment is dropped.
Furthermore, in a process for manufacturing such mobile equipment,
bending stress can occur in a printed circuit board while
components are packaged. As such, it is also an important condition
that mobile equipment have a mechanically reliable structure
impervious to bending stress and the like.
[0007] Herein, the semiconductor device shown in FIGS. 5A and 5B
has main components with their respective Young's moduli, as
follows:
[0008] LSI chip (Si): approximately 12 to 14.times.10.sup.10
N/m.sup.2
[0009] Printed circuit board: approximately 0.5 to
2.5.times.10.sup.10 N/m.sup.2 and it can be understood that LSI
chip 7 is formed of a material hard to bend as compared with the
printed circuit board. As such, when force is exerted on printed
circuit board 9 to bend it, LSI chip 7 does not accordingly bends.
Thus, stress concentrates at a solder connection connecting printed
circuit board 9 and LSI chip 7 together and when the limit of the
stress has been reached the solder connection disadvantageously
breaks and thus disconnects.
[0010] The present invention therefore contemplates a semiconductor
device capable of alleviating such a disadvantage as described
above when the entirety of a printed circuit board receives force
exerted to bend it, and a method of manufacturing the same.
SUMMARY OF THE INVENTION
[0011] To achieve the above object the present invention can
provide a semiconductor device including a semiconductor substrate
having a surface provided with an external connection electrode and
a surface opposite that with the external connection electrode,
abrased and reinforced with a back-surface reinforcement member. As
such, the semiconductor substrate can be abrased and thus reduced
in thickness to bend in response while a level of rigidity can be
ensured as the semiconductor substrate is reinforced with the
back-surface reinforcement member.
[0012] In the present invention preferably the back-surface
reinforcement member is formed of resin. Since resin has a low
elastic modulus it can reinforce the semiconductor substrate
without affecting the bendability of the semiconductor device.
[0013] In the present invention still preferably the resin is
formed of a material having an elastic modulus of
1.5.times.10.sup.6 N/m.sup.2 to 5.0.times.10.sup.6 N/m.sup.2. More
specifically, the resin is selected from the group consisting of
resin of rubber type, resin of silicone type, resin of epoxy type,
resin of polyimide type and resin of urethane type. Thus, the resin
can reinforce the semiconductor substrate without impairing the
bendability of the substrate. Applying such resins can also prevent
the substrate from chipping or being scratched.
[0014] The present invention provides a method of manufacturing a
semiconductor device including the steps of: abrasing a surface of
a semiconductor substrate opposite to that of the semiconductor
substrate provided with an external connection electrode, and
applying resin on the abrased surface of the semiconductor
substrate. As such, the semiconductor device can be reduced in
thickness to bend in response. As the semiconductor substrate is
reinforced with resin, the semiconductor device can be produced
with a level of rigidity ensured.
[0015] In the present invention preferably the method further
includes the step of cutting the semiconductor substrate after the
step of applying. As such, the present method can be readily
applied in mass-production.
[0016] In the present invention still preferably the method further
includes the step of grinding the surface of the semiconductor
substrate to be abrased. As such, the semiconductor substrate can
be processed in a reduced time.
[0017] In the present invention, preferably, in the step of
applying, the resin is printed. As such, highly viscous resin can
also be distributed and thus applied.
[0018] Furthermore, in the present invention, preferably, in the
step of applying, the resin is applied by spin-coating. Thus the
resin can be applied rapidly, reduced in thickness, uniformly.
[0019] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] In the drawings:
[0021] FIGS. 1A-1E are cross sections each showing a step of a
process for manufacturing a semiconductor device in a first
embodiment of the present invention;
[0022] FIG. 2 is a cross section of a semiconductor device in a
second embodiment of the present invention;
[0023] FIG. 3A is a view for illustrating a model in the form of a
rectangular parallelepiped employed for considering stress
occurring when an LSI chip is bent and
[0024] FIG. 3B illustrates the model that is bent;
[0025] FIG. 4 is a view of the FIG. 3A model provided for
considering an amount by which the center of the model descends
when the model is bent;
[0026] FIG. 5A illustrates a procedure of bare-chip mounting in
prior art and
[0027] FIG. 5B is a cross section of a completed bare-chip
package.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] First Embodiment
[0029] FIG. 3A shows a model in the form of a rectangular
parallelepiped having a thickness a and a width b, as seen in cross
section, applied to consider how LSI chip 7 bends. When this model
is bent as shown in FIG. 3B, its upper side as seen in the figure
expands due to tensility, its lower side as seen in the figure
contracts due to pressure, and intermediate therebetween exists a
neutral layer which neither expands nor contracts. Assuming that on
average the model's expansion and contraction are balanced, the
neutral layer includes the barycenter of the cross section. If the
neutral layer has a small portion dx forming an angle dO with
respect to a center of curvature C and having a radius of curvature
p then a thin layer dz spaced from the neutral layer by a distance
zand having an area dS, which is equal to bdz, in cross section has
an expansion rate of:
[(.rho.+z)d.theta.-.rho.d.theta.]/.rho.d.theta.=z/.rho. (1).
[0030] As such, this layer experiences a tensility dT of
E(z/.rho.)dS. If a stick neither expands nor contracts on average,
its upper half as seen in cross section experiences tensility and
its lower half as seen in cross section experiences pressure. If
this model has a Young's modulus E then for the entirety of the
cross section a bending moment is given in the following
expression: 1 M = z T = E S z 2 S = E - a / 2 a / 2 bz 2 z = E a 3
b 12 . ( 2 )
[0031] Accordingly, as shown in FIG. 4, let us assume that this
model is supported at two points spaced by a length L and also has
its center with a weight having a mass m (W=mg) suspended
therefrom.
[0032] Symmetry allows each supporting point to exert a supporting
reaction force W/2 upward. If balance in moment about an axis
perpendicular to the plane of the figure is considered for a
portion extending from a plane PQ, which is spaced from the model's
center 0 by a distance x larger than 0, to a supporting point, then
for plane PQ bending moment M is given by an expression (2) and,
with supporting reaction force W/2 contributing to (L/2-x)*W/2,
there can be obtained an expression (3): 2 E a 3 b 12 = ( L 2 - x )
W 2 . ( 3 )
[0033] From this expression, radius of curvature p is obtained as a
function of x. In general, a curve y=f(x) has a curvature
represented by .rho..sup.-1=y"/{1+(y').sup.2}.sup.{fraction (3/2)}.
Assuming that .vertline.y'.vertline.<<1, if its terms of
higher than the first degree can be neglected, then 3 y " = 6 W Ea
3 b ( L 2 - x ) . ( 4 )
[0034] is obtained. Herein, if y=0 and y'=0 are applied for x=0
then an expression (5) is obtained, as follows: 4 y = 6 W Ea 3 b (
Lx 2 4 - x 3 6 ) . ( 5 )
[0035] If the center descends by an amount e then y=e for x=L/2.
Therefore, from expression (5), Young's modulus E is obtained, as
represented by an expression (6): 5 E = WL 3 4 ea 3 b . ( 6 )
[0036] This is transformed to obtain amount e, as represented by an
expression (7): 6 e = WL 3 4 Ea 3 b . ( 7 )
[0037] It can be understood that amount e is in inverse proportion
to the cube of thickness a of LSI chip 7. More specifically, if LSI
chip 7 has large thickness a it is less flexible, which increases
the possibility that when printed circuit board 9 is bent the chip
cannot bend accordingly.
[0038] As such, in order for the entirety of a package to bend in
response, reducing LSI chip 7 in thickness can be effective.
[0039] Initially, reference will be made to FIG. BE to describe a
structure of a semiconductor device in the present embodiment. A
single wafer 1 is used to provide a plurality of LSI chips 7. Each
LSI chip has a circuit side 2 formed thereon and having a surface
(a lower surface, as seen in FIG. BE) provided with a solder ball 6
serving as an external connection electrode. Substrate 1 has a back
surface, opposite to the surface with the external connection
electrode, with resin 5 applied thereon.
[0040] Reference will now be made to FIGS. 1A-1E to describe a
method of manufacturing a semiconductor device in the present
embodiment.
[0041] FIG. 1A shows a cross section of wafer 1 used to produce a
plurality of semiconductor chips. Wafer 1 has circuit side 2
thereon provided with an electrode formed for example of aluminum.
Circuit side 2 also has a wiring pattern completed to allow its
surface to be later provided with solder ball 6 serving as an
external connection electrode and arranged in matrix.
[0042] As shown in FIG. 1A, a protection tape 3 is stuck on a
surface of circuit side 2 of wafer 1 (hereinafter referred to as
the back surface of wafer 1) in abrasing a side opposite that
having circuit side 2. Then, as shown in FIG. 1A, wafer 1 is set on
an abrasor 4 to have its back surface abrased.
[0043] Typically in producing a semiconductor device an ingot is
cut to have a wafer thickness and then abrased with a wafer lapper.
This wafer lapper may be used to abrase the back surface of wafer
1, since the wafer lapper can abrase a large number of wafers
simultaneously and thus contribute to high productivity. The wafer
is set on a turntable and an abrasive liquid containing an abrasive
is used to mirror-finish the wafer.
[0044] Note that the wafer may be ground before it is abrased. If
it is roughly ground the whole process time can be reduced. It
should be noted, however, that after it is ground it must be
abrased and thus mirror-finished, since grinding wafer 1 often
results in the wafer having its processed surface with small
scratches and wafer 1 thus reduced in thickness may crack at such
scratches when the wafer experiences force exerted to bend it.
[0045] The thickness of wafer 1 to be provided by abrasing the
wafer depends on the size of wafer 1, although for example a
thickness reduced to be as small as approximately 50 .mu.m is
sufficient to be in effect impervious to bending.
[0046] Then, as shown in FIG. 1B, abrased wafer 1 is removed from
abrasor 4 and surface protecting tape 3 is removed from the
wafer.
[0047] With reference to FIG. 1C, resin 5 is applied on the back
surface of wafer 1 to serve as a member reinforcing the back
surface of the wafer. In doing so, the wafer is printed or
spin-coated with the resin. One of the techniques is employed to
correspond to the resin to be used. For example, a highly viscous
resin would be appropriately applied if it is printed, since if the
resin is applied by a spinner it may not be distributed
satisfactorily. Initially, a mask is prepared. Initially, a mask is
designed to allow resin to be applied only on a wafer. The resin is
only required to have a thickness on the order of several tens
.mu.m. As such, the resin is applied on a mask prepared to be as
thick as targeted and thereon a squeegee is scanned to print the
resin.
[0048] In contrast, if less viscous resin is used, spin-coating
would be faster in applying the resin in reduced thickness and
uniformly. Wafer 1 is placed on a spinner and an appropriate amount
of resin is then supplied thereon. Then the spinner is turned to
cause centrifugal force to distribute and thus apply the resin on
the wafer.
[0049] Then, with reference to FIG. 1D, solder ball 6 is provided
to serve as an external connection electrode. In this step, a ball
mainly formed for example of tin/lead eutectic alloy is placed
together with flux and an electrode is formed by reflowing. The
external connection electrode is not limited to solder ball 6 and
it may be an electrode in a different form. In forming the
electrode in the different form it may for example be plated and
thus grown.
[0050] Finally, with reference to FIG. 1E, wafer 1 is cut along a
dicing line to provide individual semiconductor chips 7. Thus as a
semiconductor device completes semiconductor chip 7 with solder
ball 6 connected thereto. Although FIG. 1E shows only two
individual semiconductor chips cut apart, this cutting step in
effect provides a large number of semiconductor chips cut apart
from each other.
[0051] Note that while in the above exemplary method the abrasing
step is provided after the formation of a wiring pattern for
circuit side 2, this abrasing step may be provided for example
before or during the formation of circuit side 2.
[0052] Furthermore, the abrasing step can be eliminated if any
pre-process is used to previously prepare wafer 1 of approximately
several tens .mu.m in thickness.
[0053] The present invention can provide a semiconductor device
wherein semiconductor chip 7 has a surface provided with an
external connection electrode and a surface opposite that with the
external connection electrode, abrased to reduce semiconductor chip
7 in thickness to allow semiconductor chip 7 itself to flex in
response to bending-force. When a substrate with semiconductor chip
7 packaged receives force and thus bends, together with the
substrate the chip can accordingly bend to alleviate stress in
solder ball 6 or a solder connection so as to prevent the solder
connection from breaking. Furthermore, resin having a low elastic
modulus (a low Young's modulus) can be applied on the abrased
surface of semiconductor chip 7 to reinforce the chip without
having any effect on the bendability of the chip configured as
above. Resin 5 can protect semiconductor chip 7 to eliminate the
risk of semiconductor chip 7 chipping or being scratched and thus
cracking. As such, semiconductor chip 7 can be more readily handled
and thus enhanced in mechanical reliability.
[0054] Preferably, resin 5 is of material having a small elastic
modulus of approximately 1.5 to 5.0.times.10.sup.6 N/m.sup.2 since
resin 5 with such a small elastic modulus does not impair the
bendability of LSI chip 7. Such a value of elastic modulus is small
relative to that of LSI chip 7 and it is thus a negligible value
for the entirety of a package, and applying resin 5 on LSI chip 7
can prevent the chip from chipping or being scratched, to allow the
chip to be handled more readily. Resin 5 is applied in an amount
that can be set as desired in a range that does not affect on the
bendability of the entire package. Desirably, resin 5 is reduced in
thickness in a range that can prevent LSI chip 7 from chipping or
being scratched, to approximately several tens .mu.m as the package
can be decreased in thickness and its material cost can also be
reduced.
[0055] Specifically, resin 5 having the above elastic modulus can
be resin of rubber type, silicone type, epoxy type, polyimide type
or urethane type.
[0056] Furthermore the present invention can provide a method of
manufacturing a semiconductor device wherein after the initial half
of a wafer process is completed and before a wafer is diced the
wafer can be abrased and thereon resin can be applied to produce a
large number of packages simultaneously in a single process.
[0057] Second Embodiment
[0058] The present embodiment shows by way of example the FIG. 1E
semiconductor chip 7 bare-chip packaged on printed circuit board 9.
As a result, such a structure as shown in FIG. 2 is obtained.
[0059] The present embodiment can provide a semiconductor device
wherein semiconductor chip 7 has a surface provided with an
external connection electrode and a surface opposite that with the
external connection electrode, abrased to reduce semiconductor chip
7 in thickness to allow the chip itself to flex in response to
bending-force. As such, when printed circuit board 9 with
semiconductor chip 7 packaged thereon receives force and thus
bends, together with printed circuit board 9 semiconductor chip 7
can accordingly bend to alleviate stress in solder ball 6 or a
solder connection so as to prevent the solder connection from
breaking. Furthermore, applying resin of a low elastic modulus (a
low Young's modulus) on the abrased surface of semiconductor chip
7, can reinforce thus-configured semiconductor chip 7 without
affecting the bendability of the chip.
[0060] In the present invention a semiconductor chip has a surface
provided with an electrode and a surface opposite that with the
electrode, abrased to reduce the chip in thickness. As such, when
the chip itself receives force exerted to bend it, together with
the printed circuit board the semiconductor chip can accordingly
bend to reduce stress in a solder connection to prevent the solder
connection from being damaged. Furthermore, applying resin of a low
elastic modulus on the abrased surface of the semiconductor chip
can protect the chip to eliminate the risk of the semiconductor
chip chipping or being scratched. As such, the semiconductor chip
can be handled more readily. As a result, the entirety of the
semiconductor device can be mechanically more reliable.
[0061] Although the present invention has been described and
illustrated in detail, it is clearly understood that the same is by
way of illustration and example only and is not to be taken by way
of limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
* * * * *