U.S. patent application number 13/898615 was filed with the patent office on 2013-10-10 for semiconductor die collet and method.
This patent application is currently assigned to Texas Instruments Incorporated. The applicant listed for this patent is Texas Instruments Incorporated. Invention is credited to Dan OKAMOTO, Seiichi YAMASAKI.
Application Number | 20130264836 13/898615 |
Document ID | / |
Family ID | 39775149 |
Filed Date | 2013-10-10 |
United States Patent
Application |
20130264836 |
Kind Code |
A1 |
OKAMOTO; Dan ; et
al. |
October 10, 2013 |
Semiconductor Die Collet and Method
Abstract
A system comprises a collet is configured for holding a die
surface against the bearing surface and for simultaneously pushing
outward on the center region of the die so held.
Inventors: |
OKAMOTO; Dan; (Oita, JP)
; YAMASAKI; Seiichi; (Oita, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Texas Instruments Incorporated |
Dallas |
TX |
US |
|
|
Assignee: |
Texas Instruments
Incorporated
Dallas
TX
|
Family ID: |
39775149 |
Appl. No.: |
13/898615 |
Filed: |
May 21, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12844937 |
Jul 28, 2010 |
8465619 |
|
|
13898615 |
|
|
|
|
11690808 |
Mar 24, 2007 |
7790507 |
|
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12844937 |
|
|
|
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Current U.S.
Class: |
294/185 |
Current CPC
Class: |
H01L 2224/2919 20130101;
H01L 2224/75743 20130101; H01L 2924/01082 20130101; H01L 24/29
20130101; H01L 2224/2919 20130101; H01L 2924/01033 20130101; H01L
2924/07802 20130101; H01L 21/6838 20130101; H01L 2224/83192
20130101; H01L 24/83 20130101; H01L 2224/8385 20130101; H01L
2924/0665 20130101; H01L 24/75 20130101; H01L 2924/0665 20130101;
H01L 2924/3512 20130101; H01L 2924/00 20130101; H01L 2924/00
20130101; H01L 2924/00 20130101; H01L 2924/0665 20130101 |
Class at
Publication: |
294/185 |
International
Class: |
H01L 21/683 20060101
H01L021/683 |
Claims
1-8. (canceled)
9. A system comprising: a collet configured for retaining a
semiconductor die on a bearing surface using a vacuum force applied
to a portion of a first surface of the die, the collet also
configured for applying a pushing force in a direction opposite the
vacuum force to a portion of the first surface of the retained
die.
10. A system according to claim 9 whereby the pushing force causes
outward flexion of the retained die held by the collet such that a
handling tool may bring the outwardly flexed region of the second
surface of the die into contact with the die pad before the
periphery of the second surface of the die contacts the die
pad.
11. A system according to claim 9 further comprising means for
applying the pushing force using pressurized gas.
12. A system according to claim 9 further comprising a flexible
skin attached to the bearing surface of the collet.
Description
[0001] This application is a divisional of application Ser. No.
12/844,937 filed Jul. 28, 2010, which is a divisional of
application Ser. No. 11/690,808 filed Mar. 24, 2007, the contents
of both are herein incorporated by reference in its entirety.
TECHNICAL FIELD
[0002] The invention relates to electronic semiconductor devices
and manufacturing. More particularly, the invention relates to
semiconductor device manufacturing and packaging and to die
handling apparatus and related methods.
BACKGROUND OF THE INVENTION
[0003] In conventional semiconductor device assembly, it is known
to use adhesive to permanently mount a semiconductor die to a
mounting pad or substrate. Typical adhesive die attach processes
use curable adhesive, such as epoxy or polyimide, as die attach
material to affix the die to a die pad, leadframe, substrate, or
socket, for convenience referred to herein generally as the die
pad. It is common in the art to dispense die attach material in a
controlled amount on a die pad. Die handling equipment used for die
attach processes typically employs a pick-and-place tool to lift a
die from a wafer tape or other holding mechanism and place it on a
die pad. The portion of the die handling equipment that actually
makes contact with the die is referred to as a collet. The die is
placed on the collet, either by surface contact alone or with
assistance from a mechanical ejector pin guiding the die onto the
collet. A vacuum force exerted within the collet holds the die in
the collet while the tool moves it into the appropriate position
for placement on the pre-applied adhesive on the die pad.
[0004] Die handling presents technical challenges. Particularly for
thin dice, which are becoming increasingly common in the arts,
handling during die attach requires great care to avoid cracks or
other damage. Some examples of die attach-related failure
mechanisms known in the art include backside tool marks, scratches,
or microcracks, which can eventually lead to die cracking. Thinner
dice are in particular danger from microcracks, which can result
from excessive flexing of the die during handling. The contact
surfaces of die attach collets are sometimes made from relatively
soft plastic or elastomeric materials instead of metal in an effort
to avoid causing mechanical damage on the die surface. The practice
of using a vacuum to hold the die in the collet is another example
of efforts to avoid inflicting damage to fragile dice. The use of a
prior art vacuum collet, however, tends to cause a thin die to flex
forming a concavity during die placement, which can cause further
problems. Damage to the surface of the die can also occur,
particularly in the central region, due to contact with the
collet.
[0005] The amount and distribution of die attach material between
the die and the die pad can be crucial to the secure attachment of
the die to the die pad and to the long term reliability of the
completed assembly. Achieving the appropriate depth and uniform
distribution of the die attach adhesive layer, also called the bond
line, is a significant challenge. If the bond line is too thin, the
bond may be insufficient to hold the die to the die pad. If the
bond line is too thick, curing may be inhibited or prolonged, the
bond may tend to weaken over time, thermal performance may suffer,
or other problems may result. An uneven bond line resulting from
non-uniform adhesive distribution can result in similar problems or
in a combination of such problems. One of the most threatening
problems a non-uniform distribution of adhesive can create is the
formation of voids in the adhesive between the die and the die pad.
Voids can lead to failures due to insufficient adhesive coverage or
thermally induced stresses, for example. The formation of a
concavity in the die surface, caused by the flexing of a thin die
placed in a vacuum collet common in the arts, can induce these and
other problems.
[0006] Generally, in addition to the formation of the bond line, a
quantity of adhesive is pressed from between the die and the bond
pad during die placement. The formation of adhesive that builds
from the bond pad to the edges of the die is known as the die
attach fillet. The formation of the fillet can be adversely
affected by the excess, lack, or non-uniform distribution of
adhesive in the formation of the bond line. Excessive die attach
fillet may lead to die attach contamination of the die surface. Too
little fillet may reduce the strength of the attachment and lead to
eventual problems such as die lifting or die cracking. The
formation of a proper fillet may be impeded by excessive,
inconsistent, or unpredictable die flexion during placement of the
die on the adhesive by a die handling collet.
[0007] Due to these and other problems, it would be useful and
advantageous to provide semiconductor die handling apparatus and
manufacturing methods with improved die handling capabilities,
particularly for use with relatively thin and delicate dice.
SUMMARY OF THE INVENTION
[0008] In carrying out the principles of the present invention,
using methods and equipment compatible with established
manufacturing processes, improved semiconductor die handling
collets contribute useful advantages to the art. The invention
provides apparatus for the handling and placement of semiconductor
dice and superior die attach techniques, resulting in improved
semiconductor device assemblies.
[0009] According to one aspect of the invention, a method for
attaching a semiconductor die to a die pad includes steps for
positioning a die on a bearing surface of a collet and retaining
the die on the bearing surface of the collet using a vacuum force.
A pushing force is exerted on the die adjacent to the applied
vacuum force. The pushing force is used to oppose flexion of the
die in the direction of the vacuum force. In further steps, the die
is placed on the die pad, with die attach adhesive interposed
between the die and the die pad, the die is then released from the
collet.
[0010] According to another aspect of the invention, in a method
for attaching a semiconductor die to a die pad using a preferred
embodiment of a collet, a pushing force is applied to the die in
order to bow the central region of the die toward the die pad.
[0011] According to another aspect of the invention, a collet for
handling a semiconductor die includes a body having a bearing
surface for receiving the die. A chamber in the body has an open
side bounded by the bearing surface, with a vacuum groove included
in the bearing surface for holding a die against the bearing
surface. A port is provided for transmitting an expelled gas to the
chamber. The parts are arranged so that the vacuum force is adapted
for holding the die surface against the bearing surface and the
expelled gas is adapted for pushing the center of the die out from
the interior of the chamber.
[0012] According to yet another aspect of the invention, in a
preferred embodiment, a collet is provided wherein an expelled gas
may be applied for pushing outward on the center of a die held
therein such that the die extends outward beyond the plane of the
bearing surface.
[0013] According to another aspect of the invention, a preferred
embodiment of a collet includes a flexible skin attached to the
body of the collet and situated for supporting a die held by the
collet during handling.
[0014] According to still another aspect of the invention, a
preferred embodiment of a semiconductor die attach system includes
a collet having a die bearing surface. The collet is configured for
retaining the die on the bearing surface using a vacuum force and
also for applying a pushing force to an adjacent portion of the die
in opposition to inward flexion of the die in the direction of the
vacuum force. The system also includes a handling tool for moving
the collet to a die pad, and placing the die on the die pad.
[0015] According to another aspect of the invention, a collet
system features an arrangement whereby a pushing force may be
applied to cause outward flexion of a die held by the collet such
that a handling tool may bring the center region of the die into
contact with a die pad in advance of the periphery.
[0016] According to another aspect of the invention, a collet
system includes provisions for using pressurized gas for applying a
pushing force to the center region of a die held to the collet by a
vacuum force.
[0017] According to still another aspect of the invention, a
semiconductor device assembly of the invention includes a flexed
die with a cured bond line formed with the central region of the
die thinner than the periphery.
[0018] The invention has advantages including but not limited to
providing methods, apparatus, and systems offering improvements in
die handling capabilities useful in the manufacture of
semiconductor device packages. These and other features,
advantages, and benefits of the present invention can be understood
by one of ordinary skill in the arts upon careful consideration of
the detailed description of representative embodiments of the
invention in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The present invention will be more clearly understood from
consideration of the following detailed description and drawings in
which:
[0020] FIG. 1 is a bottom view of a die handling collet according
to an example of a preferred embodiment of the invention;
[0021] FIG. 2A is a cutaway side view of the die handling collet
according to the example of a preferred embodiment of the invention
of FIG. 1 shown in the context of a die attach system and
method;
[0022] FIG. 2B is a cutaway side view of the die handling collet in
a continuation of the example of a preferred embodiment of the
invention of FIG. 2A shown in the context of a die attach system
and method;
[0023] FIG. 2C is a cutaway side view of the die handling collet in
a continuation of the example of a preferred embodiment of the
invention of FIGS. 2A and 2B shown in the context of a die attach
system and method;
[0024] FIG. 3 is a bottom view of a die handling collet according
to an example of an alternative preferred embodiment of the
invention;
[0025] FIG. 4A is a cutaway side view of the die handling collet
according to the example of a preferred embodiment of the invention
of FIG. 3 shown in the context of a die attach system and
method;
[0026] FIG. 4B is a cutaway side view of the die handling collet in
a continuation of the example of a preferred embodiment of the
invention of FIG. 4A shown in the context of a die attach system
and method; and
[0027] FIG. 4C is a cutaway side view of the die handling collet in
a continuation of the example of a preferred embodiment of the
invention of FIGS. 4A and 4B shown in the context of a die attach
system and method for implementing a preferred embodiment of a
semiconductor device assembly of the invention.
[0028] References in the detailed description correspond to like
references in the various drawings unless otherwise noted.
Descriptive and directional terms used in the written description
such as first, second, top, bottom, upper, lower, side, and so
forth, refer to the drawings themselves as laid out on the paper
and not to physical limitations of the invention unless
specifically noted. The drawings are not to scale, and some
features of embodiments shown and discussed are simplified or
amplified for illustrating the principles, features, and advantages
of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0029] In general, the invention provides a die handling collet and
related systems and methods for improved die handling in
semiconductor device manufacturing processes, particularly die
attach processes. Referring primarily to FIG. 1 and FIG. 2A, a
bottom view (FIG. 1) and cutaway side view (FIG. 2A) of a collet 10
according to a preferred embodiment of the invention is described.
A body 12, preferably made from plastic, metal, or other suitably
rigid material, is capable of receiving a die 14 (FIG. 2A). A
vacuum groove 16 is provided at the edge of the body 12. The vacuum
groove 16 is incorporated into a die-bearing surface 18 of the body
12, preferably entirely around the periphery. The vacuum groove 16
is in communication with vacuum ports 20 for transmitting a vacuum
force, indicated by arrow 22, generated by a suitable mechanism
such as a pump (not shown). The vacuum groove 16 preferably
distributes the vacuum force around the periphery of the
die-bearing surface 18 for holding a die 14 during handling and
placement. A chamber 24 is incorporated within the body 12 and is
preferably encompassed by the die-bearing surface 18. One side of
the chamber 24 is open such that a die 14 placed on the bearing
surface 18 completes the enclosure. Within the chamber 24, a port
26 is provided for expelling pressurized gas, preferably air,
indicated by arrow 28. The expelled gas 28 pressurizes the chamber
24, exerting a pushing force on the adjacent surface of the die 14.
The pushing force preferably opposes the die flexion which tends to
occur due to the application of the vacuum force 22, preventing or
reducing the temporary formation of a concavity on the outer
surface of the die 14 due to flexing. Preferably, during die
attach, the chamber 24 is sufficiently pressurized to cause the die
14 to bow outward slightly in a position convex to the adjacent die
pad 32 or intervening die attach adhesive 30 (FIG. 2A).
[0030] Now referring primarily to FIG. 2B, the collet 10 is shown
in the context of further steps in a die attach method according to
preferred embodiments of the invention. As illustrated, using the
preferred embodiment of the collet 10 shown and described above,
the expelled air 28 within the chamber 24 is preferably used to
flex the die 14 in order to present a convex surface to the die
attach material 30 pre-applied to the die pad 32. The convex
surface of the die 14, as indicated by arrows 34, tends to expel
air from between the die 14 and die attach adhesive 30 during the
ultimate placement of the die, reducing the frequency and magnitude
of void formation. Although the use of a convex surface is
preferred, in an alternative embodiment, the die may be flexed by
the expelled air 28 by an amount adapted to counter any inward
flexion caused by the vacuum 22, and calculated to prevent the
outward flexion of the die 14. This implementation may be preferred
for example with particularly delicate dice, preventing or
attenuating flexion and presenting a substantially flat die surface
to the die pad 32 and the intervening die attach adhesive 30,
promoting a uniform thickness of die attach material 30. It should
be appreciated by those skilled in the arts that other alternative
embodiments are possible without departure from the invention, for
example, die attach processes using die adhesive film may also
advantageously use the invention. As depicted in FIG. 2C, as the
collet 10 brings the die 14 into position on the die attach
adhesive 30, the pushing and vacuum forces may be reduced or
eliminated, ultimately enabling the collet 10 to be removed after
the die 14 is placed.
[0031] An alternative preferred embodiment of a collet 40 of the
invention is depicted in a bottom view in FIG. 3, and in
corresponding cutaway side views in FIG. 4A through 4C showing an
example of a system and method for its use. As described elsewhere
herein, the collet 40 has a body 12 preferably made from plastic,
metal, or like material and is capable of receiving a die 14 as
shown. A vacuum groove 16 is incorporated into the die-bearing
surface 18 of the collet 40, preferably at the edge of the body 12
and around its periphery. The vacuum groove 16 is provided with a
vacuum force 22 through suitable vacuum ports 20. The vacuum groove
16 preferably evenly distributes the vacuum force 22 around the
periphery of the die-bearing surface 18 for holding a die 14 during
handling and placement. An interior chamber 24 is incorporated
within the die-bearing surface 18 of the body 12. A port 26 is
provided for expelling pressurized air or other gas 28 into the
chamber 24. As in the other preferred embodiment described, the
expelled air 28 pressurizes the chamber 24 to prevent the formation
of a concavity in the outer surface of an adjacent die 14 due to
flexion in response to the application of the vacuum force 22.
Preferably, during die attach the chamber 24 is sufficiently
pressurized to cause the die to bow outward slightly in a position
convex to the adjacent die attach adhesive 30 as shown in FIG. 4A
and FIG. 4B. In this alternative embodiment, the collet 40 also
includes a support skin 42. The support skin 42 is preferably
permanently attached to the die bearing surface 18 of the collet
body 12. The support skin 42 is made from a flexible material such
as, for example, a thin film of Teflon, Mylar, (both registered
trademarks of DuPont Corporation), polymer, or the like. In
operation, while the vacuum 22 exerted in the vacuum groove 16
holds the die 14, the pushing force of air 28 expelled into the
cavity 24 pressurizes the support skin 42. As a result, the center
region of the die 14 may be caused to bow outward in a shape convex
relative to the die attach adhesive 30. As with the above-described
embodiments, using this preferred method, the bowed center region
of the die 14 die contacts the die attach adhesive 30 first and
then spreads outward toward the periphery as it is moved toward the
die pad and as the pushing force on the die 14 is diminished. This
sequence avoids the trapping of air during die attach, helps to
form the die attach adhesive into a bond line 30 of uniform
thickness, and fosters the formation of suitable fillets 36.
Alternatively, for example in cases where the die 14 may be
particularly susceptible to damage from flexing, the outward
pressure 28 may be regulated to hold the die 14 substantially flat
relative to the die pad 32 and attach adhesive 30. Thus the
invention may be used for regulating the shape of the die surface
presented to the die attach locale, balancing against inward
flexion exerted by the vacuum force 22, but refraining from bowing
the die 14 outward in order to prevent inducing stress on the die
14 in cases where increased gentleness is required. In another
alternative embodiment, illustrated in the final position of the
die 14 in FIG. 4C, the bond line 30 is cured with a "smile" profile
as shown, preferably uniformly thinner in the central region of the
die 14 and progressively thicker approaching the periphery.
[0032] As shown and described herein, preferred embodiments of the
invention contribute one or more useful advantages to the art. The
invention provides advantages including but not limited to improved
die handling capabilities and reductions in damage during die
attach in microelectronic semiconductor device package assembly.
While the invention has been described with reference to certain
illustrative embodiments, the methods, apparatus, and systems
described are not intended to be construed in a limiting sense.
Various modifications and combinations of the illustrative
embodiments as well as other advantages and embodiments of the
invention will be apparent to persons skilled in the art upon
reference to the description, drawings, and claims.
* * * * *