U.S. patent application number 14/189874 was filed with the patent office on 2014-06-26 for integrated circuit package and method of manufacture.
This patent application is currently assigned to Texas Instruments Incorporated. The applicant listed for this patent is Texas Instruments Incorporated. Invention is credited to Donald C. Abbott, Brian E. Parks, Ubol A. Udompanyavit.
Application Number | 20140175626 14/189874 |
Document ID | / |
Family ID | 50432082 |
Filed Date | 2014-06-26 |
United States Patent
Application |
20140175626 |
Kind Code |
A1 |
Abbott; Donald C. ; et
al. |
June 26, 2014 |
INTEGRATED CIRCUIT PACKAGE AND METHOD OF MANUFACTURE
Abstract
An integrated circuit package has a leadframe having an open
space extending therethrough. An integrated circuit device is
attached to a portion of the upper surface of the leadframe. A
shunt is located within the open space such that it is not in
contact with any portion of the leadframe.
Inventors: |
Abbott; Donald C.; (Norton,
MA) ; Udompanyavit; Ubol A.; (Dallas, TX) ;
Parks; Brian E.; (Sherman, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Texas Instruments Incorporated |
Dallas |
TX |
US |
|
|
Assignee: |
Texas Instruments
Incorporated
Dallas
TX
|
Family ID: |
50432082 |
Appl. No.: |
14/189874 |
Filed: |
February 25, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13644647 |
Oct 4, 2012 |
8697496 |
|
|
14189874 |
|
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|
|
Current U.S.
Class: |
257/666 |
Current CPC
Class: |
H01L 2224/48247
20130101; H01L 23/3121 20130101; H01L 2224/48091 20130101; H01L
23/49531 20130101; H01L 2224/48091 20130101; H01L 2224/49171
20130101; H01L 23/49541 20130101; H01L 2224/05554 20130101; H01L
21/568 20130101; H01L 2224/49171 20130101; H01L 2924/00014
20130101; H01L 2224/48247 20130101; H01L 2924/00 20130101; H01L
23/4952 20130101; H01L 2224/48137 20130101 |
Class at
Publication: |
257/666 |
International
Class: |
H01L 23/495 20060101
H01L023/495 |
Claims
1-20. (canceled)
21. An integrated circuit package comprising: a lead frame having
an upper surface, an oppositely disposed lower surface and at least
one opening extending through the leadframe from said upper surface
to said lower surface; an integrated circuit device attached to a
portion of said upper surface of said leadframe; and a shunt
positioned at least partially in said opening, wherein, said shunt
is not in contact with any portion of said leadframe.
22. The integrated circuit package of claim 21 and further wherein
said integrated circuit device is electrically connected to said
shunt and to said leadframe.
23. The integrated circuit device of claim 22 and further wherein
said integrated circuit device is electrically connected to said
shunt and to said leadframe by wire bonds.
24. The integrated circuit package of claim 21 and further
comprising: a molding material encompassing at least portions of
said leadframe, said integrated circuit device and said shunt.
25. The integrated circuit package of claim 21 and further wherein
said shunt is formed from an alloy comprising copper, manganese,
and nickel.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional of and claims priority to
U.S. patent application Ser. No. 13/644,647, filed Oct. 4, 2012.
Said application incorporated herein by reference.
BACKGROUND
[0002] An integrated circuit package serves to physically and
electrically connect an integrated circuit device (housed within
the integrated circuit package) to a printed circuit board. One
type of integrated circuit package is known as a "flat no-leads
package". This type of package is a surface-mount technology that
connects an integrated circuit device to surfaces of the printed
circuit board without the use of through-holes. Perimeter lands on
the package bottom provide electrical connections to the printed
circuit board. Flat no-leads packages typically include a planar
copper leadframe substrate upon which the integrated circuit device
is mounted. The leadframe and the integrated circuit device are
typically encapsulated within a molding material. Flat no-lead
packages generally include an exposed thermal pad to improve heat
transfer out of the integrated circuit device (and into the printed
circuit board). There are various types of flat no-leads packages
in use, including QFN (quad-flat no-leads) and DFN (dual-flat
no-leads) variations.
[0003] For certain integrated circuit package applications, it is
required that a rectangular copper alloy slug or shunt be included
in the package with one surface exposed for soldering.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is a plan view of exemplary block of connected
leadframe sheets.
[0005] FIG. 2 is a plan view of one of the leadframe sheets of FIG.
1.
[0006] FIG. 3 is a plan view of an exemplary leadframe from the
leadframe sheet of FIG. 2.
[0007] FIG. 4 is a cross-section view of the leadframe of FIG. 3,
taken along the line 4-4 in FIG. 3.
[0008] FIG. 5 is a cross-section view similar to that of FIG. 4,
but showing the leadframe of FIG. 3 having tape applied to its
lower surface.
[0009] FIG. 6 is a plan view of the leadframe of FIG. 3,
illustrating a shunt supported on the tape shown in FIG. 5, an
integrated circuit device mounted on a die pad of the leadframe and
wirebonding between the integrated circuit device, the shunt and
the leadframe.
[0010] FIG. 7 is a cross-section view of the leadframe of FIG. 6,
taken along the line 7-7 in FIG. 6.
[0011] FIG. 8 is a perspective view of a completed integrated
circuit package.
[0012] FIG. 9 illustrates by flow diagram, selected steps in an
exemplary method for manufacturing an integrated circuit package
according to the present disclosure.
[0013] FIG. 10 illustrates by flow diagram, one embodiment of a
method of manufacturing an integrated circuit package.
[0014] FIG. 11 illustrates by flow diagram, another embodiment of a
method of manufacturing an integrated circuit package.
DETAILED DESCRIPTION
[0015] As discussed previously, for certain integrated circuit
package applications, it is required that a rectangular copper
alloy slug or shunt be included in the package with one surface
exposed for soldering. The copper alloy used in the shunt may, for
example, be of the type sold under the trademark MANGANIN.RTM., and
may, for example, have a composition of about 86% copper, 12%
manganese, and 2% nickel. Because of the relatively high cost of
this alloy, it is advantageous to have the leadframe formed from a
less expensive leadframe alloy, for example, the alloy sold under
the trade designation "CDA194". CDA194 is well suited and
characterized both thermally and mechanically for use in
leadframes. It is also formulated to facilitate stamping and
etching of leadframes.
[0016] In general terms, an integrated circuit package, along with
a method of manufacturing the package, are disclosed herein. The
disclosed package and method of manufacture provide the ability,
for example, to incorporate a slug or shunt made of a more
expensive copper alloy (e.g., MANGANIN.RTM.) into a package having
its leadframe manufactured from a less expensive leadframe alloy.
The alloy CDA194, as mentioned above, is widely used for leadframes
and is readily available from rolling mills. MANGANIN.RTM.,
however, is generally less widely used and available.
[0017] The process of manufacturing the package disclosed herein
begins by providing a leadframe, e.g., the leadframe 40, FIG. 3.
FIG. 1 illustrates a block 10 of connected leadframe sheets 22, 24,
26, and 28. FIG. 2 illustrates the leadframe sheet 22 in further
detail, it being understood that the remaining leadframe sheets 24,
26, and 28 may be substantially identical to the leadframe sheet
22. With reference to FIG. 2, the leadframe sheet 22 may include a
plurality (e.g., eighty-eight, as depicted in FIG. 2) of leadframes
30 including the individual leadframes 32, 34, 36, 38 and 40.
[0018] FIG. 3 illustrates the leadframe 40 in further detail, it
being understood that the remainder of the leadframes 30 may be
substantially identical to the leadframe 40. It is noted that, for
purposes of illustrative efficiency, the package and method of
manufacture will be described herein specifically in conjunction
with the exemplary leadframe 40. It is to be understood, however,
that the methodology described may be carried out on all of the
leadframes 30 while they are still connected to one another in the
leadframe sheet 22 and while the leadframe sheets 22, 24, 26, and
28 are still connected to one another in the leadframe block
10.
[0019] With reference now to FIG. 3, the leadframe 40 may include a
frame portion 42 having an upper surface 44 and an oppositely
disposed lower surface 46 (FIG. 4). A plurality of tabs 50,
including the individual tabs 56, 58, and 62, may extend inwardly
from the frame 42, as shown. The tops of the tabs 50 are the
targets for wire bonding connections to the integrated circuit
device (in a manner that will be described in further detail
herein). With reference again to FIG. 3, the right side (as viewed
in the orientation of FIG. 3) of the leadframe 40 may be occupied
by a die mounting pad 70 for mounting an integrated circuit device,
in a manner as will be described in further detail herein. The left
side of the leadframe 40 may include an open space 80 that extends
completely through the leadframe, i.e., the open space 80 extends
from the upper surface 44 to the lower surface 46 of the leadframe
40.
[0020] The leadframe 40 may be constructed from a relatively
inexpensive leadframe alloy, for example, the alloy sold under the
trade designation "CDA194". Alternatively, the leadframe 40 may be
constructed of copper or another copper alloy, other metal or metal
alloy.
[0021] Continuing with the description of the methodology, and with
reference now to FIG. 5, tape 90 may be adhered to the lower
surface 46 of the leadframe 40 such that it extends beneath the
entire extent of the leadframe. Tape 90 may include an upper
surface 92 and an oppositely disposed lower surface 94. To adhere
the tape 90 to the leadframe 40, the upper surface 92 of the tape
90 may be adhered to the lower surface 46 of the frame portion 42
in areas where the tape 90 underlies the frame portion 42. The tape
90 may, for example, be either a pressure sensitive adhesive tape
or a thermoplastic tape and may have a thickness "A", for example,
of about 2 mil-50 .PHI.m. It is noted that the relative thickness
of the tape 90 has been exaggerated in FIG. 5 for purposes of
illustrative clarity.
[0022] With reference to FIGS. 6 and 7, after the tape 90 has been
applied, a shunt 100 may be inserted into the open space 80 of the
leadframe 40. As can be appreciated from FIG. 6, the shunt 100 may
be located such that it does not touch any part of the leadframe
frame portion 42 and is supported only by the tape 90. The shunt
100 may be placed within the open space 80 of the leadframe 40
using conventional die mount, pick and place equipment. It is noted
that the shunt 100 may be formed in a large sheet of interconnected
shunts (not shown). The shunts may then be separated from one
another prior to insertion into the leadframes. The shunt 100 may,
for example, be formed from a relatively expensive material such as
a copper alloy sold under the trademark MANGANIN.RTM.. The shunt
may be pre-plated or post-plated, as desired.
[0023] With further reference to FIGS. 6 and 7, an integrated
circuit device 110 may be mounted to the leadframe 40, as shown.
More specifically, the Integrated circuit device 110 can be
attached to the die mounting pad 70 in a conventional manner, using
an adhesive material such as epoxy or silver filled epoxy.
[0024] Next, with continued reference to FIGS. 6 and 7, the
integrated circuit device 110 may be electrically connected to the
shunt 100 and the leadframe 40, for example, using bonding wires.
Bonding wires 102 and 104, for example, may extend between the
shunt 100 and the pads 112 and 114, respectively, on the integrated
circuit device 110. A bonding wire 106 may extend between the
integrated circuit device pad 116 and the top of the leadframe tab
56. In a similar manner, a bonding wire 108 may extend between the
integrated circuit device pad 118 and the top of the leadframe tab
58. For purposes of illustrative clarity, only four bonding wires
have been shown in FIG. 6. It is to be understood, however, that
many more bonding wires may be provided to establish the desired
connections between the integrated circuit device 110, the
leadframe 40 and shunt 100.
[0025] After wire bonding has been completed, in a manner as
described above, the leadframe 40, integrated circuit device 110
and shunt 100 may be encapsulated within a molding material (e.g.,
the molding material 122, FIG. 8) in a conventional manner. The
molding material may, for example, be a plastic material such as
epoxy or other conventional insulating material. The molding
material 122 may be formed in an injection molding process or it
may be applied as a coating.
[0026] Once the molding material has been applied and it has
hardened, it serves to secure the location of the shunt 100
relative to the leadframe 40. Accordingly, after the encapsulation
step has been completed, the tape 90 may be removed from the
leadframe 40. Thereafter, the individual leadframes in the
leadframe sheet 22 may be separated into individual integrated
circuit packages, such as the integrated circuit package 120, FIG.
8. After encapsulation and separation have been completed, in a
manner as described above, the tabs 50 may be electrically isolated
from one another in a conventional manner.
[0027] FIG. 8 schematically illustrates the completed integrated
circuit package 120 after encapsulation and separation have been
completed, in a manner as described above. As can be seen from FIG.
8, the molding material 122 may encompass the leadframe 40, the
shunt 100 and the integrated circuit device 110, except for the
bottom 101 of the shunt 100, the bottom 111 of the die pad and the
bottoms of the tabs 50 (e.g., the bottoms 156, 158, and 162 of the
tabs 56, 58, and 62, respectively). These areas are left exposed
(i.e., not covered by the molding material 122) in order to
facilitate later soldering to an underlying printed circuit board
or the like. Use of the tape 90, in a manner as previously
described herein, serves to prevent molding material from covering
these surfaces during the encapsulation process.
[0028] The bottoms of the tabs 50 (e.g., the bottoms 156, 158, and
162 of the tabs 56, 58, and 62, respectively) facilitate later
solder connection of the integrated circuit package 120 to
corresponding pads on an underlying printed circuit board or the
like. As can be appreciated, once the integrated circuit package
120 has been attached, for example, to an underlying printed
circuit board, a distinct electrical pathway will be established
from each pad on the integrated circuit device 110 (e.g., one of
the integrated circuit device pads 112, 114, 116, 118, FIG. 6) and
a corresponding pad on the printed circuit board. With reference,
for example, to the tab 58, electrical continuity will be
established between the corresponding printed circuit board pad and
the tab 58 via a solder joint extending between the printed circuit
board pad and the bottom 158 of the electrically conductive tab 58.
Continuity is also established between the top of the tab 58 and
the pad 118 of the integrated circuit device via the bonding wire
108. Accordingly, in this manner, a continuous and distinct
electrical pathway is established between the pad 118 of the
integrated circuit device 110 and a corresponding pad on the
underlying printed circuit board.
[0029] FIG. 9 is a flowchart illustrating an exemplary method of
manufacturing described herein. With reference now to FIG. 9, step
202 includes providing a sheet 22 (FIGS. 1-2) containing a
plurality of interconnected leadframes 30, each leadframe (e.g.,
the leadframe 40, FIG. 3) having a die mounting pad 70 and an open
space 80 extending therethrough. Step 204 includes applying tape 90
(FIGS. 5-6) to a lower surface of the leadframes 30. Step 206
encompasses providing a shunt sheet containing a plurality of
interconnected shunts (e.g., the shunt 100, FIG. 6). Step 208
includes separating the shunt sheet into individual shunts (e.g.,
the shunt 100, FIG. 6). Step 210 describes, using a pick and place
apparatus, installing one shunt 100 (FIG. 6) into the open space 80
of each leadframe 40, such that the shunt 100 is supported on the
tape 90 and does not touch any portion of the leadframe 40. Step
212 includes, using a pick and place apparatus, mounting an
integrated circuit device 110 (FIG. 6) onto the die mounting pad 70
of each leadframe. Step 214 includes wirebonding the integrated
circuit device 110 to portions of the leadframe 40 and to the shunt
100 (FIG. 6). Step 216 includes encapsulating the leadframe 40,
shunt 100 and integrated circuit device 110 in a molding material
122 (FIG. 8). Step 218 encompasses removing the tape 90 from the
lower surface of the leadframe 40. Finally, step 220 includes
separating the individual leadframe units from one another to form
a completed integrated circuit package 120 (FIG. 8). This
separating step may, for example, be accomplished by a sawing
process.
[0030] FIG. 10 is a flowchart depicting one embodiment of a method
of manufacturing an integrated circuit package. With reference now
to FIG. 10, step 302 includes providing at least one lead frame
having an upper surface, an oppositely disposed lower surface and
at least one open space extending through the at least one
leadframe from the upper surface to the lower surface. Step 304
includes attaching an integrated circuit device to a portion of the
upper surface of the at least one leadframe. Step 306 includes
applying tape to the lower surface of the at least one leadframe.
Step 308 includes placing a shunt at least partially in the open
space such that it is in contact with the tape. Step 310 includes
electrically connecting the integrated circuit device to the shunt
and to the at least one leadframe. Step 312 includes encompassing
at least portions of the at least one leadframe, the integrated
circuit device and the shunt with a molding material. Finally, step
314 includes, thereafter, removing the tape from the lower surface
of the at least one leadframe
[0031] FIG. 11 is a flowchart depicting another embodiment of a
method of manufacturing an integrated circuit package. With
reference now to FIG. 11, step 402 includes providing at least one
lead frame having an upper surface, an oppositely disposed lower
surface and at least one open space extending through the at least
one leadframe from the upper surface to the lower surface. Step 404
includes attaching an integrated circuit device to a portion of the
upper surface of the at least one leadframe. Step 406 includes
placing a shunt at least partially in the open space such that it
is not in contact with any portion of the at least one leadframe.
Step 408 includes electrically connecting the integrated circuit
device to the shunt and to the at least one leadframe. Finally,
step 410 includes, while maintaining the shunt not in contact with
any portion of the at least one leadframe, encompassing at least
portions of the at least one leadframe, the integrated circuit
device and the shunt with a molding material.
[0032] As can be appreciated, the package and method described
herein provide many advantages. The present method, for example,
uses a relatively inexpensive tape 90 to hold the shunt 100 in
place within the leadframe. Other applications use rivets to hold
the shunt in place or tape which ultimately becomes encapsulated
and incorporated in the finished device to secure the shunt on the
leadframe. This type of tape is expensive as it must be die cut to
a picture frame form. Further, the use of tape in this manner
provides additional interfaces where later delamination might occur
within the finished package. The use of rivets is disadvantageous
for several reasons. Riveted attachments, for example, tend to take
up more space--particularly since the rivets generally require tie
straps extending from the leadframe. Further, a more complex
leadframe and shunt result when rivets are used. Most
significantly, the use of rivets negatively impacts the hermeticity
of the overall package since additional paths for moisture ingress
are created (i.e., the tie straps to which the rivets attach, one
located at each end of the shunt). In the present process using the
tape 90, the shunt 100 is fully encapsulated on five sides with
only the bottom surface 101 exposed.
[0033] Another advantage provided by the package and method
described herein is that, since the tape 90 is removed after
encapsulation, it does not become part of the final package and,
thus, does not pose a risk of causing delamination between the mold
compound and the tape. The present package and method also allow
customization of the shunt 100; the shunt, for example, can be
formed from a different alloy than the leadframe 40 and/or the
shunt 100 can be selectively plated with any desired material
without the need to also plate the leadframe 40. Further, the size
and shape of the shunt 100 can be easily changed with no need to
change the configuration of the leadframe 40 (as long as the shunt
100 fits in the leadframe open space 80).
[0034] The foregoing description of specific embodiments has been
presented for purposes of illustration and description. The
specific embodiments described are not intended to be exhaustive or
to suggest a constraint to the precise forms disclosed, and many
modifications and variations are possible in light of the above
teaching. The illustrated embodiments were chosen and described in
order to best explain principles and practical application, to
thereby enable others skilled in the art to best utilize the
various embodiments with various modifications as are suited to the
particular use contemplated. It is intended that the scope of the
disclosure herein be defined only by the claims appended hereto and
their equivalents, except as limited by the prior art.
* * * * *