U.S. patent application number 09/725643 was filed with the patent office on 2002-05-30 for stacked power amplifier module.
This patent application is currently assigned to Nokia Mobile Phones Ltd.. Invention is credited to Pohjonen, Helena.
Application Number | 20020064029 09/725643 |
Document ID | / |
Family ID | 24915395 |
Filed Date | 2002-05-30 |
United States Patent
Application |
20020064029 |
Kind Code |
A1 |
Pohjonen, Helena |
May 30, 2002 |
Stacked power amplifier module
Abstract
Stacked substrates using passive integration components formed
in silicon or stainless steel substrates interconnect with active
elements mounted on the surface of the substrate to form a
miniaturized power amplification module. Metal filled vias pass
through the layers and carry electrical signals to and from the
active elements and passive components. The metal filled vias
function as thermal transfer heat sinks to transfer heat away from
the active elements and the module.
Inventors: |
Pohjonen, Helena; (Espoo,
FI) |
Correspondence
Address: |
WARE FRESSOLA VAN DER SLUYS &
ADOLPHSON, LLP
BRADFORD GREEN BUILDING 5
755 MAIN STREET, P O BOX 224
MONROE
CT
06468
US
|
Assignee: |
Nokia Mobile Phones Ltd.
|
Family ID: |
24915395 |
Appl. No.: |
09/725643 |
Filed: |
November 29, 2000 |
Current U.S.
Class: |
361/719 ;
257/E23.105; 257/E25.029; 361/704 |
Current CPC
Class: |
H01L 25/16 20130101;
H01L 2924/3011 20130101; H05K 1/0206 20130101; H05K 1/141 20130101;
H05K 1/16 20130101; H05K 1/0207 20130101; H05K 2201/0317 20130101;
H01L 2924/0002 20130101; H05K 3/4641 20130101; H01L 2924/0002
20130101; H01L 2924/09701 20130101; H05K 3/445 20130101; H01L
23/3677 20130101; H05K 2201/09563 20130101; H01L 2924/00
20130101 |
Class at
Publication: |
361/719 ;
361/704 |
International
Class: |
H05K 007/20 |
Claims
What is claimed is:
1. A power amplification module comprising: at least one thin film
passive integrated substrate having formed therein one or more
passive components; at least one active element for amplifying
electrical signals; means for mounting said at least one active
element on a surface of said at least one thin film passive
integrated substrate; means for interconnecting said at least one
active element to said one more passive components formed in said
at least one thin film passive integrated substrate thereby
defining a power amplification electrical circuit configuration;
means for connecting input/output electrical signals to and from
said integrated passive components and said active elements; said
connecting means further comprising heat sinking means for
transferring heat generated by said active element away from said
active element and said module for dissipation.
2. A power amplification module as defined in claim 1, wherein said
thin film passive integrated substrate comprises a flexible silicon
substrate.
3. A power amplification module as defined in claim 1, wherein said
thin film passive integrated substrate comprises a flexible
stainless steel substrate.
4. A power amplification module as defined in claim 1, wherein said
interconnecting means further comprises metal filled via holes
through said at least one thin film passive integrated
substrate.
5. A power amplification module, as defined in claim 1, wherein
said at least one active element comprises an active die.
6. A power amplification module as defined in claim 4 wherein said
metal filled via holes include a dielectric material for
electrically insulating said metal in said via from said
substrates.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to miniaturized
power amplifiers and deals more particularly with a power amplifier
module having passive components formed on a flexible silicon or
stainless steel substrate using thin film passive integration and
interconnected to active amplification components mounted on the
substrate using metal filled via holes through the substrate to
provide heat transfer and input and output terminals.
BACKGROUND OF THE INVENTION
[0002] Power amplifiers are one of the most power consuming
components in portable wireless devices particularly portable
cellular handsets due to cellular standard output power level
requirements. There are a number of sources of power losses related
to the power amplification function, for example the power
efficiency of the 2-to-3 amplification stages typically required to
produce the desired output power level; losses due to input and
output impedance mismatching, and losses in the supply voltage
stabilizing and control functions. Additionally, there are further
losses caused by harmonic frequency suppression, such as for
example, frequency filtering needed at input and/or output of the
amplification stages. High volume manufacturing, faster system
testing and design reuse requirements have led into the use of
pre-tested power amplifier modules including functionality of more
than one cellular standard. Low capacitance densities available
from active silicon (Si) and galliumarsenide (GaAs) or indium (In)
based integrated circuit technologies, and lossy passive components
due to thin (typically 0.2-1.5 .mu.m) metals and low resistive
substrates used in silicon technology limit full monolithic
integration of all supporting passive components together with the
active elements (transistors, MOSFETs or MESFETs) needed for power
amplification. Furthermore, full integration of all passive
components used in a power amplifier may not be cost effective.
[0003] Currently, power amplifier modules are generally
manufactured on laminate-like FR4 or BT laminate or ceramic (HTCC,
high temperature co-fired ceramics or LTCC, low temperature
co-fired ceramics) substrates to minimize various losses, and for
cost optimization. Additional active and passive elements are
mounted on top of these substrates. These prior art module
substrates have limited capability for miniaturization because when
using laminates, the required matching (capacitors and coils) and
power stabilizing passive components such as, capacitors, ferrites
and coils can be only partially embedded in the module substrates.
In the case of laminated substrates such as FR4 and BT, the
capacitance densities between different wiring layers are low
(typically 0.05-0.5 pF/sq mm) which results in producing large
(2-10 sq mm) area and inaccurate capacitors. Inductors or coils
needed in typical matching circuits are a few nanohenries in value
and their physical size is limited by the dielectric constant of
the substrate material used which dielectric constant for a ceramic
substrate is 6.5-9.5 and for a laminate substrate is 2.5-4.5. The
interconnection metal thickness of the substrates and dielectric
losses of the insulating layers also affect the total losses of the
power amplifier module. Coils requiring magnetic material such as,
ferrite core or isolator coils cannot be embedded in currently
known power amplifier substrates.
[0004] FIG. 1 shows a prior art castellated power amplifier module
10 on layered substrates 12, 14 wherein all the power amplifier
module components 16, 16 are surface mounted (SMT) components
located on a surface 18 of the substrate 12 and includes one or
more amplification stages. The size of the module 10 depends on the
size of the SMT components; the numbers of substrate layers, wiring
density and the type of substrate used which may be ceramic or
laminate. Electrical input and output signals are fed to the module
10 components along castellated electrical conductors 20, 20 along
the edges or sides of the module substrates. The amplifier module
package is typically inserted into a socket mounted on a printed
circuit board or the like forming the desired electrical
circuit.
[0005] FIG. 2 shows another prior art land grid array (LGA)
amplifier module 30 on layered substrates 32, 34 which may be
ceramic or laminate, wherein some of the matching components 36,
38, 40 (resistor, inductor, capacitor) are embedded into the module
substrate and some of the active devices required for the
amplification stages or energy management circuits such as DC-to-DC
converters may be flip chip 42 or wire bonded 44 on the surface 46
of the top substrate 34. Electrical input and output signals are
fed to the module 30 components by means of metal posts or pins 48,
48 under the module which is inserted into a socket mounted on a
printed circuit board or the like.
[0006] FIG. 3 shows another prior art ball grid array (BGA) module
60 on layered substrates 62, 63, 64 which may be ceramic or
laminate, wherein some of the matching components 66, 68, 70
(resistor, inductor, capacitor) are embedded into the module
substrate and some of the active components 72, 74 are flip chip or
wire bonded on the substrate. Electrical input and output signals
are fed to the module 60 components by means of an array of balls
76, 76 under the module which is inserted into a socket, soldered
or otherwise connected to a circuit board or the like.
[0007] The demand for module miniaturization and increased heat
transfer has led to solution attempts wherein some groups of
supporting passive components are integrated as separate chips on a
module substrate. FIGS. 4A and 4B show one side and an opposite
side, respectively of a prior art example of a partial integration
of a power amplifier module 80 wherein the main module substrate 82
is ceramic. A limited number of matching components 84, 86, 88
(resistor, inductor, capacitor) are passively integrated onto a
high resistive silicon substrate 90 using thin film techniques to
form an integrated passive chip 92. The chip 92 can be wire bonded
or flip chipped on the module substrate 82 along with power
amplifier chips 94, 94 and other SMT components 96, 96.
[0008] The use of hybrid assembly techniques such as illustrated in
FIGS. 1-3 or the stacking of active and integrated passive
substrates as illustrated in FIGS. 4A and 4B, together with SMT
components lead to relatively thick modules (typically 1.22-2.2
mm). Additionally, heat generated in the active devices of the
amplifier module must be conducted effectively out of the devices
and the module. Typical power amplifier module substrates like
glass fiber epoxies and Al.sub.2O.sub.3 have low thermal
conductivity (.about.1 and 20 W/mK respectively) compared to metals
(Cu 397 W/mK, Au 316 W/mK) or separate heat sink materials like AIN
(190 W/mK), Be (250 W/mK) or silicon carbide (270 W/mK). One
thermal transfer method uses metal posts that pass through the
module substrate from the metallized backside of the amplifier chip
to the system board to additional heat sinking metal plate(s). The
use of additional heat sink materials increases the cost of the
modules, and therefore is generally reserved for low volume and
high power applications.
SUMMARY OF THE INVENTION
[0009] The present invention at least obviates if not entirely
eliminates the disadvantages of prior art power amplification
modules by providing a power amplification module with a silicon or
stainless steel substrate having thin film passive integration
formed passive components stacked on a substrate carrying active
components.
[0010] In a broader aspect of the invention, a power amplification
module comprises at least one thin film passive integrated
substrate having formed therein one or more passive components and
includes at least one active element for amplifying electrical
signals. At least one active element is mounted on a thin film
passive integrated substrate surface and the active element is
interconnected to one or more passive components formed in the thin
film passive integrated substrate thereby defining a power
amplification electrical circuit configuration. Input/output
electrical signals connect to and from the integrated passive
components and active elements wherein the connecting means further
comprises heat sinking means for transferring heat generated by an
active element away from the active element and the module for
dissipation.
[0011] It is an object of the present invention therefore to
provide a miniaturized power amplification module for use in
wireless and cellular communication applications that overcomes the
problems associated with prior known power amplifier modules.
[0012] It is a further object of the present invention to provide a
power amplification module having one or more thin substrate layers
of silicon or stainless steel wherein passive integration
components are formed therein and interconnect with active elements
mounted thereon.
[0013] It is a still further object of the present invention to
provide connection means through the amplification module substrate
layers to carry input and output electrical signals to and from the
passive integrated components and the active elements wherein the
connection means provides thermal transfer from the active elements
and the module.
[0014] It is a yet further object of the present invention to
provide silicon or stainless steel substrates that are sufficiently
thin to be flexible to accommodate packaging contours and
shapes.
[0015] These and other objects and advantages of the present
invention will become more apparent from an understanding of the
following detailed description of presently preferred embodiments
of the invention when considered in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a diagrammatic representation of a prior art power
amplifier module on substrates connected as a castellated
module.
[0017] FIG. 2 is a diagrammatic representation of a prior art power
amplifier module on substrates connected as a land grid array (LGA)
module.
[0018] FIG. 3 is a diagrammatic representation of a prior art power
amplifier module on substrates connected as a ball grid array (BGA)
module.
[0019] FIGS. 4A and 4B are diagrammatic representations of opposite
sides respectively of a prior art power amplifier module partially
integrated in accordance with prior art techniques.
[0020] FIG. 5 is a diagrammatic representation of a stacked power
amplifier module embodying the present invention.
[0021] FIG. 6 is a cross sectional view of the stacked power
amplifier module showing a metal filled via passing through the
module.
[0022] FIG. 7 is a cross sectional view of the metal filled via of
FIG. 6 arranged as an input/output connection using a ball grid
connection.
[0023] FIG. 8 is a top plan cross sectional view of the metal
filled via of FIG. 6.
[0024] FIG. 9 is a diagrammatic representation of a stacked power
amplifier module embodying the present invention shown assembled
with a printed circuit board.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0025] Now considering the invention in further detail, a
diagrammatic representation of a stacked power amplifier module
embodying the present invention is illustrated in FIG. 5 and is
generally designated 100. The module 100 is built on a thin film
substrate such as silicon or stainless steel generally designated
102. A minimum number of dielectric layers and substrate layers
103, 104, 105 on which the required passive matching components
(resistors, capacitors, inductors, microstrip/striplines) are
integrated are stacked on the substrate 102 without the need of an
additional module substrate to carry the passive integrated
components. A dielectric coating on layers 103, 104, 105 isolate
the integrated passive components from the substrate 102. Active
devices such as a power amplifier chip 106 or other circuit
function devices 108 connect to the surface 110 of the layer 105 of
the module by wire bond or flip chip connection means. The passive
integrated matching components for example, 112, 114, 116 are
formed on the substrate layers. Although any insulating
substrate-like glass can be used for passive integration of the
matching passive components, silicon has good thermal conductivity
(145 W/mK) compared to GaAs (46 W/mK), and preferably, silicon is
used as the substrate for the thin film passive component
integration. If a silicon substrate is used, additional active
device functions such as for example, ESD (electrostatic discharge)
and PIN diodes and varactors may be embedded in the silicon
substrate.
[0026] Metal filled via holes 120, 120 pass generally
perpendicularly through the power amplifier module substrate and
stacked layers on which the passive components are integrated to
conduct input/output signals and power supply voltages to the
components of the power amplifier module. The via holes may be
formed using any suitable method such as for example, micro
machining techniques. FIG. 6 shows a cross sectional view of a
metal filled via passing through the module. The metal filled via
120 is surrounded by a dielectric material 122 to insulate it and
any electrical signals carried by it from the substrate layers
shown for example as 102, 104. The metal filled via 120 is exposed
at its upper end 124 to make contact with the components located on
the surface 110 of the module 100. The lower end 126 may terminate
in a ball grid contact 128 as illustrated in FIG. 7 to make
electrical and physical contact with a cooperating electrical
contact point. FIG. 8 is a top plan cross sectional view of the
metal filled via 120 and shows the dielectric 122 surrounding the
metal core 130. As illustrated in FIG. 5, one or more metal filled
vias 120 make contact with the active devices 106, 108 to
facilitate thermal transfer of heat from the devices and the module
in addition to carrying electrical signals and supply voltage
potentials.
[0027] FIG. 9 is a schematic representation of a stacked power
amplifier module generally designated 150 embodying the present
invention connected to a printed circuit board such as a system
motherboard generally designated 152 using a ball grid array (BGA)
interconnection arrangement. The power amplifier module 150 is
similar to the power amplifier module 100 illustrated in FIG. 5.
The module 150 includes wire bonded active devices 154 and flip
chip devices 156. Metal filled vias 158 interconnect the printed
circuit board 152 to the active device 154. Another metal filled
via 160 for example, interconnects the printed circuit board 152 to
a passive integrated capacitor 162 by means of a ball grid contact
164. A dielectric layer on top of the thin film passive components
protects the active devices and covers the passive components
except for the electrical contacts. Electromagnetic (EM) shields
not shown in the figure may be used to surround the chip(s) and/or
the entire amplifier module. In addition to BGA interconnection to
the motherboard, LGA (land grid array) interconnection techniques
can be employed equally as well with the power amplifier module of
the invention.
[0028] The power amplifier module of the present invention also
uses thin film techniques to coat and pattern magnetic materials
such as for example, soft ferrites for manufacturing cores for
coils serving as RF chokes. The RF chokes are used as loads for
stabilizing voltage power supply feeds to the power amplifier
module. The RF chokes are also used when required as isolators at
the power amplifier output.
[0029] The specific metal for the uppermost substrate of the module
is determined by the interconnection and assembly techniques
employed for any additional parts, for example, bare die power
amplifiers made using Si, GaAs, InP, SiC or some other material,
and other component dies, SMT or other components and parts such as
EM shields. The partial passive integration approach allows smaller
module size due to higher density of thin film integrated passive
components and small line width (2-10 .mu.m) of thin film
technology compared to soldered or conductive adhesive mounted
discrete passive components and typical module laminate or ceramic
substrates and their line width (>10-100 .mu.m) and typical
spacing (>10 .mu.m).
[0030] In a further embodiment of the power amplifier module of the
present invention, both the thickness of the active and passive
silicon substrates can be reduced to provide a further miniaturized
module for stacked systems requiring a thin total system assembly.
If the thickness of silicon is .about.<80 .mu.m, the silicon
substrate becomes flexible permitting its use directly as a module
substrate on the system motherboard thereby further reducing the
thermal resistance or temperature coefficient mismatch between the
system board and the module board, and which in turn increases
system reliability. Stainless steel is also suitable for use as a
passive integration material that can be reduced in thickness and
which provides good thermal conductivity and flexibility. Both
silicon and stainless steel substrates made sufficiently thin to be
flexible, can also act as matching media between possible different
temperature coefficients of the system board and the power
amplifier module. Such thin substrates have acceptable reliability
in bending and twisting conditions of the system board without any
additional relaxation media such as fill material needed to be
placed under the substrate during the system board
manufacturing.
* * * * *