U.S. patent application number 14/285079 was filed with the patent office on 2014-09-11 for lead-frame circuit package.
This patent application is currently assigned to FREESCALE SEMICONDUCTOR, INC.. The applicant listed for this patent is THIERRY DELAUNAY, GILLES MONTORIOL, FREDERIC TILHAC. Invention is credited to THIERRY DELAUNAY, GILLES MONTORIOL, FREDERIC TILHAC.
Application Number | 20140252570 14/285079 |
Document ID | / |
Family ID | 34982536 |
Filed Date | 2014-09-11 |
United States Patent
Application |
20140252570 |
Kind Code |
A1 |
MONTORIOL; GILLES ; et
al. |
September 11, 2014 |
LEAD-FRAME CIRCUIT PACKAGE
Abstract
A lead-frame circuit package comprises a die and a substrate
located thereon to route radio frequency signals to/from the die.
The package preferably comprises an exposed pad on the die to
receive a power amplifier device wherein the substrate is used to
provide high-Q elements such as RF chokes on signal paths to/from
the power amplifier device. In this manner, the design benefits
from the power capabilities and improved grounding of a lead-frame
conductor, whilst also achieving the routeing capabilities and
small scale advantages provided by a multi-layer printed circuit
substrate.
Inventors: |
MONTORIOL; GILLES;
(TOURNEFEUILLE, FR) ; DELAUNAY; THIERRY; (SAINT
ORENS, FR) ; TILHAC; FREDERIC; (TOULOUSE,
FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MONTORIOL; GILLES
DELAUNAY; THIERRY
TILHAC; FREDERIC |
TOURNEFEUILLE
SAINT ORENS
TOULOUSE |
|
FR
FR
FR |
|
|
Assignee: |
FREESCALE SEMICONDUCTOR,
INC.
Austin
TX
|
Family ID: |
34982536 |
Appl. No.: |
14/285079 |
Filed: |
May 22, 2014 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11816038 |
Aug 10, 2007 |
8736034 |
|
|
PCT/IB2005/001077 |
Feb 24, 2005 |
|
|
|
14285079 |
|
|
|
|
Current U.S.
Class: |
257/664 ;
257/666 |
Current CPC
Class: |
H01L 2924/10329
20130101; H01L 2924/12042 20130101; H01L 2924/15787 20130101; H01L
2924/01013 20130101; H01L 2924/14 20130101; H01L 23/49575 20130101;
H01L 24/48 20130101; H01L 23/49531 20130101; H01L 2224/73265
20130101; H01L 2924/014 20130101; H01L 24/29 20130101; H01L
2224/48247 20130101; H01L 2924/01029 20130101; H01L 2924/0132
20130101; H01L 2224/29111 20130101; H01L 2924/1433 20130101; H01L
24/73 20130101; H01L 2224/49171 20130101; H01L 2924/0132 20130101;
H01L 2924/01322 20130101; H01L 2924/30107 20130101; H01L 2924/30111
20130101; H01L 2924/181 20130101; H01L 2924/0001 20130101; H01L
2224/45144 20130101; H01L 2924/0132 20130101; H01L 2924/01322
20130101; H01L 2924/0106 20130101; H01L 2924/15747 20130101; H01L
2924/09701 20130101; H01L 2924/0001 20130101; H01L 2924/01027
20130101; H01L 2924/01023 20130101; H01L 2924/01079 20130101; H01L
2224/48137 20130101; H01L 2924/0132 20130101; H01L 24/49 20130101;
H01L 24/45 20130101; H01L 2924/0132 20130101; H01L 2924/01014
20130101; H01L 2224/32245 20130101; H01L 2224/49171 20130101; H01L
2924/01083 20130101; H01L 2924/15153 20130101; H01L 2924/3011
20130101; H01L 2924/01033 20130101; H01L 2223/6644 20130101; H01L
2224/16 20130101; H01L 2224/45144 20130101; H01L 2224/16245
20130101; H01L 2924/15787 20130101; H01L 2924/181 20130101; H01L
2224/48091 20130101; H01L 2924/01031 20130101; H01L 2924/00
20130101; H01L 2224/48247 20130101; H01L 2924/01079 20130101; H01L
2924/0105 20130101; H01L 2924/00012 20130101; H01L 2924/01014
20130101; H01L 2924/01033 20130101; H01L 2224/32245 20130101; H01L
2924/01082 20130101; H01L 2924/00 20130101; H01L 2924/0105
20130101; H01L 2924/00 20130101; H01L 2924/00014 20130101; H01L
2924/01079 20130101; H01L 2924/00012 20130101; H01L 2224/48247
20130101; H01L 2224/29099 20130101; H01L 2924/00 20130101; H01L
2924/00014 20130101; H01L 2924/00 20130101; H01L 2924/00 20130101;
H01L 2924/01032 20130101; H01L 2924/0105 20130101; H01L 2924/01031
20130101; H01L 2924/12042 20130101; H01L 2924/19041 20130101; H01L
2924/30111 20130101; H01L 2924/01075 20130101; H01L 2924/0105
20130101; H01L 2924/01082 20130101; H01L 2924/15747 20130101; H01L
2224/73265 20130101; H01L 2224/48091 20130101; H01L 23/64 20130101;
H01L 2924/01032 20130101; H01L 2924/1517 20130101 |
Class at
Publication: |
257/664 ;
257/666 |
International
Class: |
H01L 23/495 20060101
H01L023/495 |
Claims
1. A lead-frame circuit package comprising: a die; and a substrate
having a first side on which a first side of the die is attached
and a second side providing electrical connections, the substrate
for routing radio frequency signals to or from the die via the
electrical connections, wherein the substrate comprises reactive
components formed therein, the reactive components coupled, on the
first side of the substrate, to the die and, on the second side of
the substrate, to the electrical connections, the reactive
components providing impedance matching for the routing of the
radio frequency signals.
2. The lead-frame circuit package of claim 1 wherein the die
comprises an exposed pad located on a second side of the die
opposite the first side of the die, the exposed pad having a power
amplifier device attached thereon.
3. The lead-frame circuit package of claim 2 wherein the die is
grounded through the exposed pad.
4. A lead-frame circuit package according to claim 1 wherein the
substrate is a multi-layer substrate or high density integration
substrate to support signal routing to the power amplifier
device.
5. A lead-frame circuit package according to claim 1 wherein the
reactive components are arranged to provide electrical
characteristics equivalent to one or more radio frequency inductive
choke(s).
6. A lead-frame circuit package according to claim 1 wherein the
substrate is arranged to operably couple tracks to or from a
lead-frame using wire-bonding.
7. A lead-frame circuit package according to claim 1 wherein the
substrate is one of: organic, Low temperature Co-fired Ceramic
substrate, an integrated passive device.
8. A lead-frame circuit package according to claim 1 wherein the
lead-frame circuit package is one of: Quad Flat No-lead package,
Thin Quad Flat Pack or Small Outline package.
9. A lead-frame circuit package according to claim 1 wherein the
substrate is arranged to support flipped or non-flipped dice and/or
surface mount devices.
10. A lead-frame circuit package according to claim 1 wherein the
substrate is arranged to be used as a relay pad within a high
impedance integrated power amplifier implementation.
11. A wireless communication unit comprising a transmitter portion
adapted to transmit radio frequency signal and/or a receiver
portion adapted to receive radio frequency signals utilizing a
lead-frame circuit package comprising: a lead frame and a substrate
located on a first side of the lead frame to route radio frequency
signals to or from a power amplifier device, wherein the lead frame
comprises an exposed pad located on the first side of the lead
frame, the exposed pad having the power amplifier device thereon,
the power amplifier device having a ground connection through to
the lead-frame via a path that does not include the substrate.
12. The wireless communication unit of claim 11 wherein the
substrate is a multi-layer substrate or high density integration
substrate to support signal routing to the power amplifier
device.
13. The wireless communication unit of claim 11 wherein the power
amplifier device is grounded through the exposed pad.
14. A wireless communication unit according to claim 11 wherein the
substrate supports tracks arranged to provide electrical
characteristics equivalent to one or more radio frequency inductive
choke(s).
15. A wireless communication unit according to claim 11 wherein the
substrate is arranged to operably couple tracks to or from the
lead-frame using wire-bonding.
16. A wireless communication unit according to claim 11 wherein the
substrate is one of: organic, Low temperature Co-fired Ceramic
substrate, an integrated passive device.
17. A wireless communication unit according to claim 11 wherein the
lead-frame circuit package is one of: Quad Flat No-lead package,
Thin Quad Flat Pack or Small Outline package.
18. A wireless communication unit according to claim 11 wherein the
substrate is arranged to support flipped or non-flipped dice and/or
surface mount devices.
19. A wireless communication unit according to claim 11 wherein the
substrate is arranged to be used as a relay pad within a high
impedance integrated power amplifier implementation.
20. A lead-frame circuit package comprising: a die; and a
multi-layer substrate comprising a plurality of thin dielectric
layers, the multi-layer substrate having a first side on which a
first side of the die is attached and a second side providing
electrical connections, the multi-layer substrate for routing radio
frequency signals to or from the die via the electrical
connections, wherein the multi-layer substrate comprises high-Q
components formed therein, the high-Q components coupled, on the
first side of the multi-layer substrate, to the die and, on the
second side of the multi-layer substrate, to the electrical
connections, the high-Q components providing impedance matching for
the routing of the radio frequency signals.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is a divisional of U.S. patent application
Ser. No. 11/816,038, entitled "LEAD-FRAME CIRCUIT PACKAGE," filed
on Aug. 10, 2007, which is a National Stage Entry under 37 C.F.R.
.sctn.371 of PCT/IB2005/001077, filed Feb. 24, 2005, the disclosure
of which is hereby expressly incorporated by reference in its
entirety.
FIELD OF THE INVENTION
[0002] The preferred embodiment of the present invention relates to
a lead-frame circuit package. The invention is applicable to, but
not limited to, a lead-frame circuit package suitable for use with
a radio frequency power amplifier module or a front-end module.
BACKGROUND OF THE INVENTION
[0003] The present invention relates to radio frequency (RF) power
amplifier (PA) and front-end modules (FEM). Typical applications
targeted for such technologies are cellular phones, Personal
Digital assistants (PDA) and wireless connectivity applications
such as Digital video Broadcast (DVB-H and DVB-T), Zigbee, wireless
local area networks (WLAN) and Ultra wideband applications (UWB).
The substantially high transmission power associated with RF
communication (for example class 12 global system for mobile
communication (GSM) or general packet radio system (GPRS)
communication) where the transmit time is half of the total
communication time, forces the need to dissipate the energy in a
restricted area and increases the difficulty of miniaturization of
the package.
[0004] A power amplifier module for amplifying RF signals includes
a radio frequency amplifier including several RF transistors (PA
dice) adapted to accept an input radio frequency signal, biasing
signals and control signals (controller die) and to output an
amplified version of the input radio frequency signal according to
biasing and control signals.
[0005] The RF transistors are generally integrated in one or
several integrated circuits, such as a Gallium Arsenide (GaAs) IC,
Silicon BiCMOS, Silicon Germanium Hetero-junction Bi-polar
Transistor, or other CMOS-based technologies. The integrated
circuit also includes biasing circuitry, which provides the DC
voltage or current and a control circuit allowing the control of
the power delivered at the output.
[0006] The amplifier ICs are also interconnected to components such
as inductors, capacitors resistors or transmission lines used for
impedance matching and control of the RF transistors.
[0007] A front end module (FEM) is the association of the above
power amplifier module (PA) with the matching circuits. The
matching circuits are connected to the harmonic filtering circuits.
The filtering circuits are connected to the antenna switch. The
matching circuits can also be implemented using surface mount
devices (SMDs) on any of the following: [0008] (i) Substrate or
leads; [0009] (ii) Printed circuit board (PCB) tracks on or in the
substrate; [0010] (iii) Back and forth wire-bonding between a
substrate and the dice; or [0011] (iv) Integrated passive devices
(IPD) on substrate or leads; or [0012] (v) Any combination of the
above four implementations.
[0013] The harmonics filtering can be implemented using integrated
passive devices on substrate or leads and embedded devices in the
substrate. The switch uses a dedicated semiconductor process, such
as GaAs, CMOS on Silicon on Insulator (SOI).
[0014] As an operating frequency increases, a transistor's
characteristics change dramatically. Above 1 MHz, depending upon
the transistor, the input and output impedances decrease and become
increasingly more reactive. The voltage, current and power gain
decrease and there is a greater tendency for signals at the output
to feedback to the input through internal capacitance. This leads
to a loss of power gain, which is highly undesirable.
[0015] Power gain is often used in radio frequency (RF) circuits to
emphasize a difference between active and passive circuits. A
passive network may have a voltage gain or a current gain, but not
both at the same time.
[0016] In contrast, the majority of audio-frequency designs involve
only minor changes in impedance level and very few impedance
changing devices. Voltage gain is a meaningful term under such
conditions. At radio frequencies, however, impedance matching is
required as, impedance levels throughout a circuit change
dramatically. Thus, the only true indication of how good a
transistor operates is to calculate its power gain.
[0017] For power amplifiers used in RF mobile communication, the
power amplifier (PA) performance is often judged based on its Power
Added Efficiency (PAE), as it directly impacts, say, the mobile
communication unit's talk time. It is known that PAs require
excellent grounding in order to obtain an optimum performance in
PAE, as well as in gain and output power.
[0018] In a dual-band amplifier design, suitable for both low-band
and high-band use in digital cellular communication units compliant
with the Global System for Mobile (GSM) communications, a PA
typically exhibits a performance of 60% PAE in the low GSM band of
850-900 MHz, and 55% PAE in the high-band (global standard) direct
communication system (DCS)/personal communication system (PCS)
frequencies of 1800-1900 MHz.
[0019] European Patent Application titled: "Arrangement and method
for Impedance Matching" by Philippe Riondet, Gilles Montoriol, and
Jacques Trichet describes a method using wire-bonding and using on
chip capacitors for impedance matching of PA and FEM. A known power
amplifier packaging design utilises lead-frame inductors.
[0020] As illustrated in FIG. 1, such a design 100 has only been
implemented for a PA, in this case a dual-band amplifier, whereby a
first amplifier 110 is designed for GSM, and a second amplifier 105
is designed for DCS-PCS operation. Furthermore, due to space
constraints in being able to build an RF module using such
lead-frame technology, the only other component on the die is the
power amplifiers' associated control functionality 115. The whole
package is configured in a 7.times.7 mm plastic package.
[0021] It is known that it is very difficult to implement high-Q
inductors in a small size and at a low cost, as shown by the
inductive tracks 120 implemented on the lead-frame package.
Furthermore, implementing discrete inductors is impractical, due to
the size and cost of such components. Wire bonding has also been
shown to provide acceptable high-Q performance of inductors at very
low cost. Notably, the lead-frame package described in U.S. Pat.
No. 6,621,140 B1 has also been described as a mechanism to achieve
a high-Q inductor performance, whilst focusing on achieving the
best `Q`.
[0022] U.S. Pat. No. 6,750,546 B1, by Villanueva et. al. describes
an assembly process for a flip chip lead-frame package.
[0023] However, a power amplifier designer would ideally like to
implement a complete front-end module. Unfortunately, the
aforementioned use of high-Q lead-frame inductors 120 proposed in
U.S. Pat. No. 6,621,140 B1 occupies about 40% of the PA area,
thereby removing any practical possibility to implement a complete
front-end module. Furthermore, due to the extensive use of
inductive tracks that are required to manufacture a complete RF
front-end module, a lead-frame package provides poor signal
routeing capability.
[0024] PCT application--US2004/0232982 A1, by Ichitsubo et. al.,
describes an RF front-end module for wireless communication
devices, and is notably focused on the avoidance of using a printed
circuit board (PCB)/LTCC and surface mount technologies (SMTs).
[0025] However, it is noteworthy that none of the above citations
adequately address the aforementioned problem of implementing a RF
power module having an improved power performance. In particular,
none of the above citations disclose a mechanism that improves
power added efficiency, where sufficiently less die size is
required to implementing high-Q components, such as inductors,
capacitors and RF chokes.
[0026] In summary, a key parameter in the design of high
performance power amplifiers is the quality of the grounding.
Typically, the RF die grounding is realized by soldering the die
205, using tin lead solder, or gold tin eutectic solder), directly
on a metallic flange heatsink 220, as illustrated in the circuit
arrangement 200 of FIG. 2. The active die is operably coupled to
substantially co-located PCBS 210 via wire-bonds 215. This known
art allows the best thermal contact between the die active area 205
and the best electrical contact for the grounding. It is also well
known that a resistive or inductive grounding of the RF power
device generates fast degradation of power gain and power added
efficiency.
[0027] However, a similar structure 300 is illustrated in FIG. 3,
which has been widely used as a low cost structure. Here, an active
die 305 is directly coupled to surface mounted components on a PCB
310 via wire-bonds 315. A primary weakness of this structure is a
significantly worse grounding, as compared to the RF die grounding
of soldering directly on a metallic flange as shown in FIG. 2. This
remains the case even if there is a large number of via holes 320
underneath the active die 305.
[0028] Thus, a need exists for a low cost, lead-frame packaging
technology that allows the PA die to exhibit an improved
performance, whilst offering high routeability and ease of
implementing high-Q components.
STATEMENT OF INVENTION
[0029] In accordance with aspects of the present invention, there
is provided a lead-frame circuit package that comprises a
multi-layered substrate therefor, a multi-layer substrate and a
wireless communication unit having a lead-frame circuit package as
a front-end module, as defined in the appended Claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 illustrates a known RF power amplifier integrated
circuit that uses lead-frame inductors;
[0031] FIG. 2 illustrates a known integrated circuit structure;
and
[0032] FIG. 3 illustrates a second known integrated circuit
structure.
[0033] Exemplary embodiments of the present invention will now be
described, by way of example only, with reference to the
accompanying drawings, in which:
[0034] FIG. 4 illustrates a first example of a complete RF
front-end module, utilising lead-frame technology, and constructed
in accordance with the preferred embodiment of the present
invention;
[0035] FIG. 5 illustrates a diagram of a multi-layer substrate
employed in accordance with the preferred embodiment of the present
invention;
[0036] FIG. 6 illustrates a second example of a complete RF
front-end module, utilising lead-frame technology, and constructed
in accordance with the preferred embodiment of the present
invention;
[0037] FIG. 7 illustrates one example of an application to
facilitate the lead-frame packaging, in accordance with the
preferred embodiment of the present invention;
[0038] FIG. 8 illustrates a further cross-section example of a
standard multi-layer substrate and a HDI substrate, adapted for use
in accordance with the preferred embodiment of the present
invention; and
[0039] FIG. 9 illustrates a cross-section of a lead-frame package
with an exposed pad, in accordance with the preferred embodiment of
the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0040] The preferred embodiment of the present invention will be
described in terms of a lead-frame package for a radio frequency
(RF) power amplifier (PA) module capable of operation in digital
wireless cellular communication units, such as GSM, Edge, or
3.sup.rd generation (3G) cellular phones. However, it will be
appreciated that the inventive concepts herein described may be
embodied in any radio frequency amplifier device or apparatus.
[0041] In the context of the present invention, the term
`lead-frame packaging` encompasses, at least, any metal frame that
provides external electrical connection to a packaged integrated
circuit (IC) or chip, as they are commonly referred to.
[0042] Furthermore, in the context of the present invention, the
term `substrate` encompasses, at least, any organic or ceramic
printed circuit board (PCB) that provides internal (die to die
and/or die to surface mount technology (SMT) components) and
external electrical connection to the packaged chip.
[0043] It is also envisaged that a PCB may also embed some devices,
such as capacitors, inductors, filters etc. Furthermore, in the
context of the present invention, the term `high density
integration` (HDI), when applied to a substrate, encompasses, at
least, any high density interconnect.
[0044] For a mobile communication application, where cost is a
driving constraint, it is accepted that lead-frame packaging for a
PA die, with a back side exposed pad, has demonstrated superior
performance to the previously used multilayer substrates packages
(organic or ceramic). The performance improvement in power added
efficiency has been found to be between 5-7%. Thus, it is commonly
accepted that a lead-frame type of package with a backside exposed
pad, offers the best performance for a PA die technology.
[0045] In accordance with the preferred embodiment of the present
invention, a substrate is located on a die within a lead-frame
circuit package and used for several functions. The simplest
function is its use in re-routeing wire-bonding from the lead-frame
package to the die and/or the die to another die and/or a substrate
to another substrate. Thus, any combination of routeing is
envisaged within the lead-frame packaging.
[0046] In a case where the substrate is used to support die routing
or having embedded components, such as capacitors or inductors
located therein, a multi-layer substrate or HDI type of substrate
is generally needed. It is envisaged that the substrate could be
organic or ceramic.
[0047] In summary, the preferred embodiment of the present
invention proposes the use of a High Density integration (HDI)
printed circuit board (PCB) or Low temperature Co-fired Ceramic
(LTCC) substrate inside such a lead-frame package for Radio
Frequency modules/operation.
[0048] In this manner, a PA die has an improved performance using a
lead-frame packaging, whilst the use of a substrate allows
advantageous signal routing and increased track space to provide,
for example, choke inductance. This configuration resolves the
problem associated with using lead-frame packages, which are
renowned as providing poor routeing capability. As such, lead-frame
packages are typically unsuitable for high level integration around
the PA die and consequently unsuitable for designs of complete
front-end modules or complete radio modules.
[0049] Advantageously, this configuration of using a substrate on a
die within a lead-frame plastic package enables the PA module to
provide even more power added efficiency (PAE).
[0050] Power amplifiers (PAs) and front-end modules (FEMs) require
excellent grounding for an optimum performance in PAE, and also in
gain and power. In the context of the present invention, such
grounding is provided by utilising lead-frame packaging.
[0051] Preferably, the lead-frame package is configured with an
exposed pad that facilitates high routeing capability for
`in-package` systems. This enables a substantially equal
performance for the RF power amplifier versus known prior art
lead-frame packaged PAs and FEMs. The provision of a multi-layer
substrate to facilitate a substantial amount of the signal
routeing, as well as a number of inductive components such as RF
chokes, also enables the inventive concept to be used in
`systems-in-package` type applications. Thus, and advantageously,
the inventive concept of the present invention utilizes the
benefits known from using multilayer substrates together with
benefits provided by lead-frame technologies.
[0052] In accordance with a preferred embodiment of the present
invention, a first example of a complete RF front-end module 400 is
illustrated in FIG. 4. The complete RF front-end module 400
utilises lead-frame technology. In this case, and notably in
accordance with the preferred embodiment of the present invention,
a substrate 410 is arranged to provide a substantial number of the
high-Q components. Furthermore, the substrate is arranged to sit on
an exposed pad where all connections are wire bonded to the
substrate.
[0053] In alternative embodiments, other means of connecting wires
to the substrate may be used, such as bumped substrate or a
substrate with a back side pattern, allowing back side attach with
conductive glue or solder, for example tin lead solder. As soon as
the substrate or PCB is bumped it can be considered as a standard
bumped die and be flipped on either the lead-frame flag or the
leads. A similar approach can be implemented with a back side
pattern on the substrate or PCB, where solder is located similar to
any dice on a lead-frame flag or leads.
[0054] RF high-Q inductors 405 are configured by using primarily
wire bonds and leads to the substrate as bonding pad with
tuneability. In this context, `tuneability` means that by changing
the wire-bonding length or position of some wires, the inductor can
be tuned, i.e. all the parameters that will define the loop profile
of the wire-bonding may be adjusted to achieve the desired
performance.
[0055] In accordance with the preferred embodiment of the present
invention, a HDI substrate 410 is used, in effect, as a surface
mounted device (SMD) that contains, say, high-Q choke inductors and
a 2.sup.nd matching inductor for, say, a high-band PA. A HDI
substrate is a multi-layer organic PCB including a thin dielectric
layer (pregreg) on each side of a core dielectric layer.
[0056] A typical HDI substrate 500, adapted for use in the
preferred embodiment of the present invention, is illustrated in
FIG. 5. The pregreg layers preferably include small vias, generally
laser drilled instead of standard mechanical drilling. The
advantage of the HDI substrate is the small size that can be used
for a via, enabling higher density interconnections versus the
standard multi-layer PCB. Vias may be filled or not with copper to
allow maximum thermal dissipation.
[0057] It is also envisaged that the HDI substrate 500 could be
used to embed discrete components, such as capacitors 505, 510
and/or inductors 515 and/or filters and/or resistors 525. Such a
design will facilitate easy replacement of any SMT components on
either the substrate or leads, which will further decrease the
package size and simplify the assembly process flow.
[0058] Referring back to FIG. 4, a PA die sits on a standard
lead-frame or an exposed pad 415. It has been found that locating
the PA die on an exposed pad obtains an optimal performance. The
exposed pad provides excellent RF grounding of RF transistors, at
low cost, whilst achieving the best power gain and PAE, as
illustrated in, and described later with respect to, FIG. 9.
[0059] Another critical component in achieving a high PAE
performance in PA modules is the provision of high-Q inductors and
capacitors. It is proposed that high-Q surface mounted devices
(SMDs) are included within the lead-frame packaging and used to
provide some of the capacitors, inductors and RF chokes in the PA
design. Alternatively, high-Q capacitors can be realized using
Metal Insulator Metal (MIM) caps in Gallium Arsenide (GaAs).
[0060] The complete RF front-end module 400 in FIG. 4 also
comprises a controller device and other front-end die components
such as a harmonic filter and switch (not shown), which both are
arranged to sit on the exposed pad. In FIG. 4, a die 415, including
two RF amplifiers, sits on an exposed pad; together with the
biasing controller die 420, two harmonic filters 425 and an antenna
switch 430.
[0061] Referring now to FIG. 6, a second example of a complete RF
front-end module 600 is illustrated, where the RF front-end module
again utilises lead-frame technology, and is constructed in
accordance with the preferred embodiment of the present invention.
In this case, the multi-layer substrate is arranged to sit on
exposed pad and is operably connected to the exposed pad of the PA
die, via leads. A number of RF high-Q inductors 605 primarily use
wire bonds to connect to the PA die, with the high-Q performance
provided by routeing within the multi-layer substrate.
[0062] The HDI multi-layer substrate is preferably arranged to sit
on leads using, for example, chip on leads technique (COL), as
described in MicroLeadFrame.RTM. package from AMKOR.TM., or using
flip-chip technology, as described in U.S. Pat. No. 6,750,546 B1 or
U.S. Pat. No. 6,597,059 B1.
[0063] Notably, the controller and front-end die 610 of the
complete RF front-end module 600 are `flipped` on the multi-layer
substrate, thereby taking advantage of the HDI routeing capability.
Furthermore, in FIG. 6, the PA die 615 sits on an exposed pad for
best performance. Again, non-critical SMD components are preferably
included within the lead-frame packaging.
[0064] Referring now to FIG. 7, a diagram 700 of a multi-layer
substrate is illustrated, that is locatable on the exposed pad of
the lead-frame package, for example the lead-frame package
illustrated in FIG. 4 or FIG. 6. The multi-layer substrate
encompasses metal tracks to facilitate signal routeing as well as
microstrip lines to simulate the characteristics of an RF
choke.
[0065] Referring now to FIG. 7, one example of an application 700
to facilitate the lead-frame packaging is illustrated, that can be
used to support the inventive concept hereinbefore described. The
example application is an AMKOR.TM. packaging technology of flip
chip in micro lead-frame (MLF) (fcMLF), which is appropriate for
signal routeing of RF signals in RF products up to 20 GHz. Flip
chip in MLF facilitates the implementation of a flip chip die PA
705 (for example a Silicon Germanium (SiGe)) that can be located
close to a flip chip substrate (HDI or LTCC) that may be configured
to contain a substantial portion, if not most, of the routeing
tracks and/or supporting high-Q components.
[0066] The die 705 is located within a moulded plastic body 710.
The die 705 is attached to a copper lead-frame 715 via high lead,
tin or gold solder bumps 720. The moulded plastic body comprises
half-etched areas 725.
[0067] FIG. 7 also illustrates an exposed pad version 750, wherein
the application of the exposed pad version 750 using the inventive
concept hereinbefore described will be understood by a skilled
artisan.
[0068] Referring back to FIG. 6, one or more filters and/or the RF
switch would preferably be flipped on the substrate, as shown in
the example arrangement 600. In this manner, it is envisaged that a
RF module could be implemented that encompasses a flip chip
transceiver and a PA (wire bonded or flip chip) manufactured in
SiGe or GaAs.
[0069] Advantageously, this type of implementation may remove the
need for wire-bonding from the assembly process. Removing
wire-bonding allows a manufacturer to decrease the die size because
the bonding areas and bonding pad clearance are no longer needed.
All interconnects (solder bumps) are located on chip and then the
chip is flipped and soldered on with a dedicated metal pattern on
the PCB.
[0070] It is advantageous to have all of the bill of material (BOM)
bumped and flipped on the lead-frame, such as the: PA dice,
Controller die, Harmonic filtering dice, switch die, substrate(s),
thereby eliminating complex assembly processes in dealing with
mixed assembly process such as wire-bonding and flip. This results
in, say, a 20% cost reduction. In addition, the inventive concept
benefits from a reduction in package size, which is also smaller
than the mixed assembly process.
[0071] Referring now to FIG. 8, a further cross-section example of
a standard multi-layer substrate 800 is illustrated, as adapted in
accordance with the preferred embodiment of the present invention.
The multi-layer substrate 800 is a multi-layer organic PCB
including a plurality of thin dielectric layers (pregreg) 805 on
each side of a plurality of core dielectric layers 810. The pregreg
layers 805 preferably include small vias generated using standard
mechanical drilling 815. Electrical conductors 820 are illustrated
on each of the pregreg layers 805.
[0072] A further cross-section example of an HDI substrate 850 is
illustrated in FIG. 8, as adapted in accordance with the preferred
embodiment of the present invention. The HDI substrate 850 is a
multi-layer organic PCB including a plurality of thin dielectric
layers (pregreg) 855 on each side of a plurality of core dielectric
layers 860. The pregreg layers 855 preferably include small vias
generated using laser drilling 865. The advantage of the HDI
substrate is the small size that can be used for a via, enabling
higher density interconnections versus the standard multi-layer
PCB.
[0073] Referring now to FIG. 9, a cross-section of a lead-frame
package with an exposed pad is illustrated, in accordance with the
preferred embodiment of the present invention. Here, again, the die
905 is located on the exposed die pad 910 utilising a die attach
material 925. The lead-frame package comprises a copper lead-frame
915 and a moulded compound 920. Gold wire bonding 930 is used to
connect the die to the lead-frame packaging.
[0074] It is also envisaged that the inventive concept of the
present invention can be implemented using any active die
comprising surface mount technology (SMT) components.
[0075] Furthermore, it is envisaged that the inventive concept may
be implemented to use any passive substrate such as organic, LTCC,
Integrated Passive Device (IPD), with or without embedded
components. Typical passive devices, which include resistors,
inductors, capacitors, filters and baluns, are discrete components
that take up large amounts of space on a circuit board or add
complexity to an RF module. In contrast Integrated Passive Devices
are fabricated on a millimetre scale using volume manufacturing and
assembly methods similar to silicon processes. They can be
integrated directly onto a chip or module to eliminate the need for
discrete devices. They offer the added advantage of lower cost and
improved tolerances. Several technologies can be used such as
silicon, GaAs or glass.
[0076] It is also envisaged that the inventive concept of the
present invention may be utilised with any type of lead-frame
package such as Quad Flat No-lead (QFN) package, Thin Quad Flat
Pack (TQFP) or Small Outline (SO) package, with or without exposed
pads/flags package. A skilled artisan will also appreciate that the
multi-layer substrate used in the inventive concept of the present
invention can be used to route tracks between active and/or passive
dice and used to support flipped or non-flipped dice as well as
SMDs.
[0077] It is also envisaged that the multi-layer substrate may be
arranged for use as a relay pad for High Impedance Integrated Power
Amplifier (HIIPA) implementation, say using the impedance matching
methods for power amplifiers as described on page 3 of U.S. Pat.
No. 6,621,140 B1.
[0078] Although the preferred embodiment of the present invention
has been described with reference to use of a multi-layer
substrate, it is envisaged that a single-layer, high-dielectric,
substrate may suffice. However, it should be noted that such
substrates may be unsuitable for mobile communication applications,
as low-cost substrate material that is typically required for such
applications generally has a relatively low dielectric
constant.
[0079] It is within the contemplation of the present invention that
the inventive concept can be used in any RF module, such as a RF
power amplifier or RF modem, particularly to provide a low cost RF
package/module for use in wireless communication units. Thus, it is
envisaged that the inventive concept can be used within any
wireless communication technology, including: digital TV (Digital
Video Broadcasting (DVB) and Integrated Services Digital
Broadcasting (ISDB) units) second and/or third generation (3G)
cellular phones (such as 3.sup.rd Generation Partnership Project
(3GPP), Multimedia Broadcast Multicast Service (MBMS)/High Speed
Downlink Packet Access (HSDPA), 3GPP2, Bluetooth capable units,
Global System for Mobile communication (GSM), RF test equipment,
private mobile radio, etc.
[0080] Furthermore, it is envisaged that the inventive concept can
be used in any RF module within a wireless communication unit, such
as a transmitter portion adapted to transmit radio frequency
signals and/or a receiver portion adapted to receive radio
frequency signals utilising the aforementioned lead-frame circuit
package.
[0081] It will be understood that the use of a multilayer substrate
inside a lead-frame package, as described above, aims to provide at
least one or more of the following advantages: [0082] (i) The
design benefits from the power capabilities and improved grounding
of a lead-frame conductor, whilst also achieving the routeing
capabilities provided by a multi-layer printed circuit substrate at
low cost; [0083] (ii) The advantage (around 5% in PAE for a
front-end module), is almost equivalent to the increment expected
moving from one technology platform (i.e. active die) to another;
[0084] (iii) It allows integration of a substantial portion of a RF
front-end module on the substrate due to the substrate's routeing
capability; [0085] (iv) High-Q inductors can be implemented using
SMD technology within the substrate and therefore within the
lead-frame package; and [0086] (v) Alternatively, use of metal
layers of a multi-layer substrate allows high-Q inductors to be
used, taking up a very small size as compared to package leads.
[0087] In particular, it is envisaged that the aforementioned
inventive concept can be applied by a semiconductor manufacturer to
offer both RF devices and RF packages. For example, a semiconductor
manufacturer may employ the inventive concept in a design of a
stand-alone RF device, such as a RF power amplifier, or
application-specific integrated circuit (ASIC) and/or any other
sub-system element.
[0088] Whilst the specific and preferred implementations of the
embodiments of the present invention are described above, it is
clear that one skilled in the art could readily apply variations
and modifications of such inventive concepts.
[0089] Thus, a low cost packaging technology has been described
that allows the PA die to exhibit an improved PAE performance and
high routeability within a lead-frame circuit package, wherein the
aforementioned disadvantages with prior art arrangements have been
substantially alleviated.
* * * * *