U.S. patent application number 13/417603 was filed with the patent office on 2012-07-05 for method of making a low profile flip chip power module.
Invention is credited to Demei Gong, Ming Sun.
Application Number | 20120167384 13/417603 |
Document ID | / |
Family ID | 39715644 |
Filed Date | 2012-07-05 |
United States Patent
Application |
20120167384 |
Kind Code |
A1 |
Sun; Ming ; et al. |
July 5, 2012 |
Method of Making a Low Profile Flip Chip Power Module
Abstract
A power module is proposed to package an electronic system
having flip chip power MOSFET devices. The power module includes a
front surface cover board and a multi-layer printed circuit
laminate bonded thereto. Notably, the front surface of the printed
circuit laminate includes recessed pockets each having printed
circuit traces atop its floor. Inside the recessed pockets are
power MOSFET and other circuit components bonded to the printed
circuit traces. As the circuit components are encased inside the
power module, it features a low profile, an increased mechanical
robustness and EMI/RFI immunity. Additionally, some circuit
components can be provided with a front-side bonding layer that is
also bonded to the front surface cover board to realize a
double-side bonding to the interior of the power module. Methods
for making the low profile power module are also described.
Inventors: |
Sun; Ming; (Sunnyvale,
CA) ; Gong; Demei; (Shanghai, CN) |
Family ID: |
39715644 |
Appl. No.: |
13/417603 |
Filed: |
March 12, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11678061 |
Feb 23, 2007 |
8159828 |
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13417603 |
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Current U.S.
Class: |
29/829 |
Current CPC
Class: |
H01L 25/16 20130101;
H01L 2224/0554 20130101; H01L 2924/15311 20130101; H01L 25/072
20130101; H01L 2924/00014 20130101; Y10T 29/53174 20150115; H05K
3/4611 20130101; H05K 2201/10674 20130101; H01L 2224/16225
20130101; H01L 2924/1461 20130101; H05K 1/141 20130101; H01L
2224/05573 20130101; H01L 2924/13091 20130101; H01L 2924/15153
20130101; H01L 2924/00014 20130101; H01L 2924/16195 20130101; H01L
2224/73253 20130101; H05K 1/183 20130101; H01L 2924/19105 20130101;
H05K 1/0203 20130101; H01L 2224/05571 20130101; H01L 2924/00014
20130101; H01L 2924/1461 20130101; H05K 3/4697 20130101; H01L
2924/00014 20130101; Y10T 29/49124 20150115; H05K 2201/1056
20130101; H01L 23/552 20130101; H01L 2224/0557 20130101; H01L
2224/0556 20130101; H05K 3/3436 20130101; H01L 2224/05599 20130101;
H01L 2924/00 20130101; H01L 2224/0555 20130101 |
Class at
Publication: |
29/829 |
International
Class: |
H05K 3/36 20060101
H05K003/36 |
Claims
1. A method of making a low profile power module that encases a
plurality of circuit components, the method comprising: A) forming
a multi-layer printed circuit laminate having: (1) a plurality of
bonded printed circuit layers each having a circuit forming means
thereon; and, (2) along the front surface of the multi-layer
printed circuit laminate: (2a) a plurality of recessed pockets each
having the circuit forming means atop its floor; and (2b) a
plurality of circuit components, located inside the plurality of
recessed pockets, each having a back-side component bonding means
that is conductively bonded to the circuit forming means; B)
providing an electrically conductive front surface cover board; and
C) physically and electrically bonding the front surface of the
multi-layer printed circuit laminate to a back surface of the front
surface cover board.
2. The method of making a low profile power module of claim 1
wherein forming a multi-layer printed circuit laminate further
comprising: A1) forming the plurality of bonded printed circuit
layers each having a circuit forming means thereon; A2) along the
front surface of the plurality of bonded printed circuit layers,
creating the plurality of recessed pockets by selectively removing
a corresponding plurality of material pockets from a corresponding
number of layers of printed circuit layers; A3) placing the
plurality of circuit components inside the plurality of recessed
pockets; and A4) conductively bonding the plurality of circuit
components, via their back-side component bonding means, to the
circuit forming means.
3. The method of making a low profile power module of claim 1
wherein forming a multi-layer printed circuit laminate further
comprising: A1) providing a number, according to the layer
requirement of the multi-layer printed circuit laminate, of printed
circuit layers each having a circuit forming means thereon; A2) for
each printed circuit layer, determining and pre-cutting out a
specific number of windows each of a specific geometry such that,
upon later lamination, the number of printed circuit layers would
form said plurality of recessed pockets; A3) stacking and
laminating the number of printed circuit layers hence
simultaneously forming said plurality of recessed pockets; A4)
creating, if necessary as specified by the multi-layer printed
circuit laminate, additional circuit forming means on each of the
number of laminated printed circuit layers; A5) placing the
plurality of circuit components inside the plurality of recessed
pockets; and A6) conductively bonding the plurality of circuit
components, via their back-side component bonding means, to the
circuit forming means.
4. A method of making a low profile power module that encases a
plurality of circuit components, the method comprising: A)
providing an electrically conductive front surface cover board; B)
forming a multi-layer printed circuit laminate having: (1) a
plurality of bonded printed circuit layers each having a circuit
forming means thereon; and, (2) along the front surface of the
multi-layer printed circuit laminate: (2a) a plurality of recessed
pockets each having the circuit forming means atop its floor; and
(2b) a plurality of circuit components, located inside the
plurality of recessed pockets, each having a front-side component
bonding means that is capable of being conductively bonded to the
front surface cover board and a back-side component bonding means
that is conductively bonded to the circuit forming means; and C)
physically and electrically bonding both the front surface of the
multi-layer printed circuit laminate and all the front-side
component bonding means to the front surface cover board.
5. The method of making a low profile power module of claim 4
wherein providing an electrically conductive front surface cover
board further comprises using a front surface cover board material
that is heat conductive whereby facilitate heat dissipation from
said plurality of circuit components.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of a pending
U.S. patent application entitled "Low Profile Flip Chip Power
Module and Method of Making" by Ming Sun with filing date of Feb.
23, 2007 and application Ser. No. 11/678,061 whose content is
hereby incorporated by reference for all purposes.
FIELD OF INVENTION
[0002] This invention relates generally to the field of electronic
packaging. More specifically, the present invention is directed to
the packaging of power semiconductor modules.
BACKGROUND OF THE INVENTION
[0003] A general trend of modern day electronic product, as
demanded by the market place, is product miniaturization with
vastly increasing functionality. With no exception, the same trend
also applies to the segment of power electronics. Hence, even in
the area of power electronics, there has been an ongoing need of
product miniaturization concurrent with the other requirements of
heat dissipation and electromagnetic interference/radio frequency
interference (EMI/RFI) shielding prominent in power
electronics.
SUMMARY OF THE INVENTION
[0004] A low profile power module is proposed to package an
electronic system that includes power Metal-Oxide-Semiconductor
Field Effect Transistor (MOSFET) devices. The power module includes
an electrically conductive front surface cover board and a
multi-layer printed circuit laminate physically and electrically
bonded to the back of the front surface cover board. The
multi-layer printed circuit laminate has numerous bonded printed
circuit layers for forming a multi-layer electrical
interconnection. Notably, the front surface of the printed circuit
laminate includes a number of recessed pockets each having numerous
printed circuit traces atop its floor. Located inside the recessed
pockets are numerous flip-chip power MOSFET devices and other
circuit components that are conductively bonded to the printed
circuit traces atop the recessed pocket floors. As the various
circuit components are encased inside the power module, it features
a low profile, an increased mechanical robustness and EMI/RFI
immunity.
[0005] Additionally, some of the various circuit components can be
provided with a front-side bonding layer that is then conductively
bonded to the front surface cover board to realize a corresponding
double-side bonding to the interior of the power module. In a more
specific embodiment, the power MOSFET flip chips have their
source-contacts and gate-contacts located on their back-side and
their drain-contacts located on their front-side as referenced to
the orientation of the power module. To facilitate heat dissipation
from these double-side bonded circuit components, the front surface
cover board is further made heat conductive as a heat sink. As the
front surface cover board is flat, an external heat sink can be
easily attached to the front surface cover board so as to
facilitate heat removal from the power module.
[0006] One method of making the power module includes: [0007] A)
Forming the multi-layer printed circuit laminate having the bonded
printed circuit layers, the front-surface recessed pockets and the
circuit components located inside and flip-chip bonded to the
printed circuit traces inside recessed pockets. [0008] B) Providing
an electrically conductive front surface cover board. [0009] C)
Physically and electrically bonding the front surface of the
multi-layer printed circuit laminate to the front surface cover
board. As a variation, some of the circuit components can
additionally be made front-side bondable hence conductively bonded
to the front surface cover board in this step.
[0010] One method of forming the multi-layer printed circuit
laminate further includes: [0011] A1) Forming the numerous bonded
printed circuit layers. [0012] A2) Along the front surface of the
numerous bonded printed circuit layers, creating the recessed
pockets by selectively removing a corresponding number of material
pockets from a corresponding number of layers of printed circuit
layers. [0013] A3) Placing the various circuit components inside
the recessed pockets. [0014] A4) Conductively bonding the various
circuit components, via their back-side component bonding pads, to
the recessed pockets.
[0015] An alternative method of forming the multi-layer printed
circuit laminate further includes: [0016] A1) Providing a number,
according to the layer requirement of the multi-layer printed
circuit laminate, of printed circuit layers. [0017] A2) For each
printed circuit layer, determining and pre-cutting out a specific
number of windows each of a specific geometry such that, upon later
lamination, the number of printed circuit layers would form the
desired recessed pockets. [0018] A3) Stacking and laminating the
number of printed circuit layers hence simultaneously forming the
desired recessed pockets. [0019] A4) Creating, if necessary as
specified by the multi-layer printed circuit laminate, additional
circuit forming features such as printed through holes and solder
masks on each of the now laminated printed circuit layers. [0020]
A5) Placing the various circuit components inside the recessed
pockets. [0021] A6) Conductively bonding the various circuit
components, via their back-side component bonding pads, to the
recessed pockets.
[0022] These aspects of the present invention and their numerous
embodiments are further made apparent, in the remainder of the
present description, to those of ordinary skill in the art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] In order to more fully describe numerous embodiments of the
present invention, reference is made to the accompanying drawings.
However, these drawings are not to be considered limitations in the
scope of the invention, but are merely illustrative.
[0024] FIG. 1 is a cross sectional illustration of the low profile
power module of the present invention;
[0025] FIG. 2A-FIG. 2J illustrate the steps under one embodiment to
make the low profile power module under the present invention;
and
[0026] FIG. 3A-FIG. 3J illustrate the steps under an alternative
embodiment to make the low profile power module under the present
invention.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0027] The description above and below plus the drawings contained
herein merely focus on one or more currently preferred embodiments
of the present invention and also describe some exemplary optional
features and/or alternative embodiments. The description and
drawings are presented for the purpose of illustration and, as
such, are not limitations of the present invention. Thus, those of
ordinary skill in the art would readily recognize variations,
modifications, and alternatives. Such variations, modifications and
alternatives should be understood to be also within the scope of
the present invention.
[0028] FIG. 1 is a cross sectional illustration of a low profile
power module 10 of the present invention. The low profile power
module 10 is proposed to package an electronic system that
includes, for simplicity of illustration, one or more power
Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) 64, one
or more Integrated Circuit (IC) 60 and one or more passive
component 62. While not specifically illustrated, the active
circuitry of the power MOSFET 64 is flip-chip, with its source and
gate contacts on its back side as referenced to the orientation of
the low profile power module 10. Thus, the source and gate contacts
of the power MOSFET 64 get electrically connected to back-side
solder bumps 24 through a pad opening 66. Similarly, the packaging
of the IC 60 is also of the flip chip type. It is remarked that the
power MOSFET drain 68 further has a front-side component bonding
layer 27, located on its front side as referenced to the
orientation of the low profile power module 10.
[0029] Globally, the low profile power module 10 includes an
electrically conductive front surface cover board 12 and a
multi-layer printed circuit laminate 14 physically and electrically
bonded to the front surface cover board 12. The multi-layer printed
circuit laminate 14 has numerous laminated and bonded traditional
printed circuit layers (PCB layer one 14a, PCB layer two 14b, PCB
layer three 14c and PCB layer four 14d) for forming a multi-layer
electrical interconnection. A few associated circuit forming
constituents of the PCB layers such as plated through-hole 20 (also
called "Via Hole" in the art) and solder mask 22 are illustrated.
However, to avoid unnecessary obscuring details, numerous
additional circuit forming constituents such as interconnecting
circuit traces interposed between the PCB layers 14a, 14b, 14c and
14d are not shown here except for printed circuit traces 26 that
will be presently described. As defined here, "circuit forming
constituents" is a set of pre-determined three-dimensional patterns
of interconnected conductive pads, printed circuit traces, planes,
conductive through holes, solder masks, ball grid arrays (BGA),
land grid arrays (LGA) for forming the inter-component electrical
connection of an electronic system. Notably, the front surface of
the multi-layer printed circuit laminate 14 includes a recessed
pocket 25 having printed circuit traces 26 atop its floor. Thus,
the various circuit components of power MOSFET 64, IC 60 and
passive component 62, being also located atop the floor of the
recessed pocket 25 at locations corresponding to the printed
circuit traces 26, are electrically bonded, via the back-side
solder bumps 24, to the rest of the electronic system embodied with
the low profile power module 10. As power MOSFET 64 is usually a
vertical device, its device current flows from one major surface of
the semiconductor substrate to an opposite major surface. It is
also important to point out that, with proper matching of the
thicknesses amongst PCB layer one 14a, PCB layer two 14b, back-side
solder bumps 24, power MOSFET 64 and front-side component bonding
layer 27, the now encased power MOSFET 64, between the recessed
pocket 25 and the front surface cover board 12, has its drain 68
electrically bonded to the front surface cover board 12, further
connected to the back surface of the multi-layer printed circuit
laminate 14 through plated through hole 20. However, wherever
lateral MOSFET instead of vertical MOSFET is used, this type of
double-sided conductive bonding is unnecessary so it is not
necessary to electrically connect the front surface cover board 12
to the back surface of the multi-layer printed circuit laminate 14
through plated through hole 20. In such case the MOSFET 64 may
still thermally contact the front surface cover board 12 to
facilitate thermal dissipation. The substrate of IC 60 usually
requires insulation from MOSFET drain 68 therefore is preferably
not in electrical contact with front surface cover board 12. To
enable further electrical connection to an external system, the low
profile power module 10 includes an external ball grid array 30
metallurgically attached to a number of corresponding bonding pads
19 and plated through holes 20 located on a back surface of the
multi-layer printed circuit laminate 14.
[0030] For those skilled in the art, by now it should become clear
that with proper choice of size and number of recessed pocket 25
the low profile power module 10 can be embodied to encase a
plurality of MOSFET, IC plus numerous other types of active and
passive circuit components such as, but not limited to, BIPOLAR,
IC, capacitors, inductors, resistors, diodes. As the various
circuit components are encased inside the power module, it features
a low profile, an increased mechanical robustness and EMI/RFI
immunity. Of course, the front surface cover board 12 can be made
heat conductive so as to facilitate heat dissipation from the
double-side bonded power MOSFET 64 and IC 60. As the front surface
cover board 12 is flat, additional external heat dissipating
apparatus, such as heat sink, cooling fan, re-circulating fluid
cooling module, Thermal Electric Module (TEM), can be easily
attached to the front surface cover board 12 so as to facilitate
heat dissipation from the double-side bonded power MOSFET 64.
[0031] As for its material, the front surface cover board 12 is an
electrically conductive material such as Copper, Aluminum, Ni/Au
plated other metals or laminate board, Carbon made conductive
materials and ions conductive materials. The front-side component
bonding layer 27 is made of an electrically conductive material
such as solder paste or electrically conductive epoxy filling the
gap between, for example, the front surface of power MOSFET 64 and
the front surface cover board 12.
[0032] FIG. 2A-FIG. 2J illustrate the steps under one embodiment
for making the low profile power module 10. In STEP Ia, the four
PCB layers 14a, 14b, 14c and 14d are stacked up and registered with
respect to one another. Although not specifically shown here, each
of the four PCB layers 14a, 14b, 14c and 14d has been pre-formed
with circuit forming constituents on it already. The four PCB
layers are then, typically under heat and pressure, laminated
together in STEP IIa. In STEP IIIa via holes 18 are drilled through
the laminate together with partial drillings to create various pad
openings 17. Next, the via holes 18 and pad openings 17 are
electroplated with a conductive material in STEP IVa to
respectively become plated through holes 20 and bonding pads 19. In
STEP Va solder masks 22 are printed to guard the plated through
holes 20 and the bonding pads 19 against a later overflow of solder
balls during their melt down to electrically bond with the plated
through holes 20 and the bonding pads 19.
[0033] In STEP VIa, the recessed pocket 25 is created, along the
front surface of the bonded PCB layers 14a, 14b, 14c and 14d, by
selectively removing a corresponding material pocket from a
corresponding number of PCB layers, in this case the PCB layer 14a.
The method of removal includes mechanical milling, partial
mechanical drilling and laser cutting. Notice the completion of
STEP VIa reveals the printed circuit traces 26 atop PCB layer two
14b.
[0034] In STEP VII, called die attaching in the art of IC
packaging, the various circuit components of power MOSFET 64, IC 60
and passive component 62 are first placed and mechanically
registered inside the recessed pocket 25. Then the various circuit
components are conductively bonded, via their back-side solder
bumps 24, to the printed circuit traces 26. As is well known in the
art, a temperature above 200 degree C., depending upon the type of
solder or epoxy used, is needed to form permanent die bonds.
[0035] In STEP VIII, the front surface cover board 12 is placed
atop the multi-layer printed circuit laminate 14 with the various
circuit components already conductively bonded to the floor of the
recessed pocket 25. The front surface of the multi-layer printed
circuit laminate 14, together with the front-side component bonding
layer 27 of power MOSFET 64, are then physically and electrically
bonded to the front surface cover board 12.
[0036] In STEP IX the partially completed low profile power module
is first flipped upside down. A number of solder balls 21 are then
placed upon their corresponding bonding pads 19 and plated through
holes 20 of the multi-layer printed circuit laminate 14.
[0037] In STEP X the number of solder balls 21 are metallurgically
bonded to their corresponding bonding pads 19 and plated through
holes 20 to form the external ball grid array 30 for further
electrical connection of the now completed low profile power module
10 to an external system. Notice the now completed low profile
power module 10 is flipped back to its original orientation.
[0038] As a simplified overview of the present invention, the above
STEPS Ia to X can be partitioned into a first portion (STEPS Ia to
VII) and a second portion (VIII to X). The first portion forms the
multi-layer printed circuit laminate 14 with the various circuit
components of power MOSFET 64, IC 60 and passive component 62
conductively bonded to the recessed pocket 25. The second portion
physically and electrically bonds the front surface of the
multi-layer printed circuit laminate 14 together with the
front-side of power MOSFET 64 to the electrically conductive front
surface cover board 12.
[0039] FIG. 3A-FIG. 3J illustrate the steps under an alternative
embodiment to make the low profile power module 10 under the
present invention. Except for STEPS Ib to VIb, the rest of the
STEPS VII to X are the same as were already elucidated under FIG.
2G-FIG. 2J. In STEP Ib, the four PCB layers 14a, 14b, 14c and 14d
and stacked up and registered with respect to one another in the
X-Y plane.
[0040] In STEP Ib, for each of the four PCB layers 14a, 14b, 14c
and 14d, a specific number of windows each of a specific geometry
are determined and pre-cut out with mechanical milling, partial
mechanical drilling and laser cutting such that, upon later
lamination, the four PCB layers would form the desired recessed
pocket 25. In this case, a precut window one 15a is made on PCB
layer one 14a and a precut window two 15b is made on PCB layer two
14b. Thus, in STEP IIIb, the four PCB layers 14a, 14b, 14c and 14d
are laminated with the simultaneous formation of the recessed
pocket 25.
[0041] In STEP IVb via holes 18 are drilled through the laminate
together with partial drillings to create various pad openings 17.
Next, the via holes 18 and pad openings 17 are electroplated with a
conductive material in STEP Vb to respectively become plated
through holes 20 and bonding pads 19. In STEP VIb solder masks 22
are printed to guard the plated through holes 20 and the bonding
pads 19 against a later overflow of solder balls during their melt
down to electrically bond with the plated through holes 20 and the
bonding pads 19.
[0042] While the description above contains many specificities,
these specificities should not be constructed as accordingly
limiting the scope of the present invention but as merely providing
illustrations of numerous presently preferred embodiments of this
invention. For example, other than the illustrated power MOSFET 64
and IC 60 modules, the present invention can be modified to package
numerous other types of semiconductor modules or even miniature
mechanical devices such as Miniature Electro Mechanical System
(MEMS) devices.
[0043] Throughout the description and drawings, numerous exemplary
embodiments were given with reference to specific configurations.
It will be appreciated by those of ordinary skill in the art that
the present invention can be embodied in numerous other specific
forms and those of ordinary skill in the art would be able to
practice such other embodiments without undue experimentation. The
scope of the present invention, for the purpose of the present
patent document, is hence not limited merely to the specific
exemplary embodiments of the foregoing description, but rather is
indicated by the following claims. Any and all modifications that
come within the meaning and range of equivalents within the claims
are intended to be considered as being embraced within the spirit
and scope of the present invention.
* * * * *