Advanced Circuit Materials Enable New Technologies

Transcription

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Electronics Technology
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MARCH/APRIL 2010
2012
Electronic
Passengers
For
C4ISR/EW systems
UAVs
Audio and text
communications
Platform systems
Automotive
25
Video and imagery
Temperature rise—°C
Mission recording
Situational
awareness and C2
Lethality
VICTORY
data bus
(VDB)
FR-4
Unfilled HC
Modified PPO
SiO2-filled HC
BN-SiO2-filled PTFE
20
Power distribution
Threat detection
and reporting
Logistics
15
0.71°C/W
10
0.33°C/W
0.32°C/W
0.20°C/W
5
0.07°C/W
Platform sensors
Extra vehicle
network interface
0
12 | LINKING VEHICLES FOR VICTORY
5
10
15
20
25
30
Input power—W
Crew protection
Electronic warfare
0
16 | COTS GEAR FOR MILITARY TESTING
21 | MATERIALS FOR MILITARY CIRCUITS
35
Design &Technology
ART AGUAYO / SENIOR MARKET DEVELOPMENT MANAGER
Rogers Corp., Advanced Circuit Materials Div., 100 S. Roosevelt Ave., Chandler, AZ 85226;
(480) 961-8271, e-mail: [email protected], www.rogerscorp.com
Advanced Circuit
Materials Enable
New Technologies
circuit materials, the thermal conductivity
(TC) of the material is often the main differentiator when the thermal management
of a design is a concern. Selecting materials
with the higher thermal conductivity will
have the largest impact in reducing temperature from a PCB perspective.
How can the TC of a PCB material impact
the performance of a military system? To
better understand how PCB materials with
high TC values could benefit some designs,
Military circuit and system designers rely on higha study was performed by circuit-materials
supplier Rogers Corp. (www.rogerscorp.
performance circuit materials to achieve greater
com) on a number of different PCB matefunctionality from circuits that are smaller, lighter,
rials (Table 1). Samples of each material
0.020 in. (0.5 mm) thick with 50-Ω transand less expensive than their predecessors.
mission lines were evaluated with a 1.9ffective battlefield communications,
GHz signal source
25
advanced unmanned aerial vehicles
set to five different
FR-4
(UAVs), and high-resolution radar
power levels, with
Unfilled HC
20
all have one thing in common—they rea top level of 26 W.
0.71°C/W
Modified PPO
quire more (technology) with less (size,
Figure 1 details
SiO2-filled HC
cost, weight, and power consumption).
the results of these
15
BN-SiO2-filled PTFE
Circuit and systems designers are constantmeasurements.
ly breaking new ground to meet the needs
These
materials
10
0.33°C/W
of modern defense systems but, to do so,
represent a fairly
0.32°C/W
they have relied on an often-overlooked
wide range of com0.20°C/W
5
component: circuit materials. After all, immercial materials,
0.07°C/W
pressive advances in circuit materials techwith much different
0
0
5
10
15
20
25
30
35 material characternology have armed aerospace and defense
Input power—W
designers with the tools they need to meet
istics. For example,
demanding, modern requirements.
by comparing FR-4
A key requirement for military compo- 1. These plots compare the temperature rise as a function of input to a polyphenylenenents and systems in recent years has been power at 1.9 GHz for five different PCB materials.
oxide (PPO) circuit
the reduction in form factor, while also inmaterial, the impact
creasing functionality. Unfortunately, this
of reducing the loss tangent by a factor of 5
combination usually results in an increase
can be observed. When comparing modiin operating temperature, making thermal
fied PPO circuit materials with RO4350B
management an important concern for
materials from Rogers Corp.—with both
military circuit and system designers. One
considered low-loss RF circuit materials—
way that most electrical engineers have
the effects of using RO4350B and its higher
traditionally dealt with the problem of tem2. These photographs compare a sample
perature rises at the circuit-board level has
been by specifying printed-circuit materials
of RT/duroid 5880LZ PCB material before
with lower dissipation factors. But the dis(top) and after (bottom) 500 thermal
sipation factor is just one characteristic of a
shock cycles.
printed-circuit-board (PCB) material from
a list of parameters that can also provide inTable I: Comparing PCB materials
sights into how a material can impact that
Material
Dielectric
Dissipation
Thermal conductivity
need for more functionality from less size,
constant
factor
(W/m/K)
weight, and cost.
Epoxy/glass
4.5
0.02
0.4
In comparing materials with different
dissipation factors, for example, the lossModified PPO
3.65
0.004
0.4
tangent difference can be an order of magRO4350B® high3.66
0.003
0.7
nitude between two PCB materials, such
frequency laminate
as epoxy glass and polytetrafluoroethylene
RT/duroid® 6035HTC
3.50
0.0014
1.4
(PTFE) circuit laminates. For low-loss
Temperature rise—°C
E
DEFENSE ELECTRONICS • OCTOBER/NOVEMBER 2012
S21
Design &Technology
Frequency (GHz)
1
5
10
15
20
25
30
35
40
45
50
8 to 50 GHz
Average Dk
Dispersion (%)
3.60
3.55
Dielectric constant (Dk)
TC results in a close to 50% reduction in
temperature rise. For optimal thermal management, selection of a material with both
low loss tangent and high TC is desired.
In a quest for the best balance of low loss
and high TC, a material like RT/duroid
6035HTC from Rogers Corp. features a
low loss tangent of 0.0014 at 10 GHz and
a TC of 1.4 W/m/K. The laminate is based
on a PTFE resin with high-TC ceramic filler.
As the measured response of Fig. 1 shows,
the level of RF power to the PCB based on
the 6035HTC material has minimal impact
on temperature rise. The combination of
low-loss tangent and high TC is the reason
for this: While other PTFE materials are
available with lower loss tangents (as low as
0.009), their TC values are also much lower,
in the range of 0.2 to 0.3 W/m/K. This will
result in far inferior results in terms of thermal management compared to RT/duroid
6035HTC material.
Cost is also a consideration when select-
3.50
3.482
1.2%
3.45
3.40
0
5
10
15
20
25
30
35
40
45
50
Frequency—GHz
3. The change in dielectric constant with frequency for RO4350B LoPro laminate helps
determine the dispersion for the material from 8 to 50 GHz.
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Dk
3.58
3.53
3.51
3.49
3.49
3.48
3.48
3.47
3.47
3.47
3.47
ing a PCB material. In the case of the lowloss materials, the resin used in these materials is either a thermoset type (such as
epoxy, PPO, or butadiene) or PTFE based.
The materials using PTFE tend to be more
expensive. Processing these materials [such
as the use of plated-through holes (PTHs)
for connections through the PCB] and special handling requirements can also be pricier. Among the thermoset materials that
would present cost advantages, RO4350B
laminate has the best thermal performance.
While greater by a factor of 3 over RT/duroid 6035HTC material in terms of TC, it
still is significantly lower than other potential thermoset RF material choices.
The importance of reliable PCB performance on the battlefield cannot be overemphasized; mission success can depend on
an electronic function such as communications. Modern communications systems,
such as software-defined radios (SDRs),
are designed not only for reliable, highspeed communications, but to do so securely even in hostile operating conditions.
Such radios are used not only by personnel, but also on board satellite systems, airships, and on UAVs. All of these advanced
military systems have depended on new
developments in high frequency materials,
which have been critical in reducing weight
and size while also increasing functionality.
In the past, foam-based PCB materials
OCTOBER/NOVEMBER 2012 • DEFENSE ELECTRONICS
Design &Technology
Table 2: Materials used in airborne applications
have been developed to provide advantages
Material
Dielectric
constant
in weight, but such materials were difficult
to process using traditional PCB handling
methods (for example, no PTH capabiliRT/duroid 5880
2.2
ties). Ultimately, these materials were reRT/duroid 6002
2.94
moved from the market.
RT/duroid 5880LZ
1.96
For space and airborne applications,
Krytar Mil Ad Designs_Krytar.HalfPg.Mil.ad.mw&rf/DE 1/14/11 11:38 AM Page 1
Dissipation
factor
Density
(g/cm3)
Coefficient of thermal
expansion in the z-axis
(ppm/°C)
0.0009
2.2
237
0.0012
2.1
24
0.0019
1.4
42
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S24
many programs have relied on materials
based on PTFE/random glass (such as
RT/duroid® 5880 material from Rogers
Corp.) or PTFE/ceramic filler (RT/duroid
6002 material from Rogers Corp.) because
of either the low dielectric constant and
loss tangent (lower electrical loss) or low
Z-axis coefficient of thermal expansion
(CTE, for high PTH reliability) and stable
temperature performance. But increasing
system demands for lighter-weight materials motivated further PCB materials development for additional savings in weight.
This has resulted in the development of a
material such as RT/duroid 5880LZ from
Rogers Corp., which combines the benefits
of low dielectric constant with the low Zaxis CTE of the RT/duroid 5880 and RT/
duroid 6002 materials, but with a 30% reduction in density (see Table 2). The RT/
duroid 5880LZ material is suitable for lightweight antennas requiring a low dielectricconstant material. Bond layers for the material can be either thermoplastic or thermoset films (Table 3 shows three options for
use with RT/duroid 5880LZ).
The unique properties of RT/duroid
5880LZ are achieved through the use of a
select filler system, which also makes possible the excellent thermal cycling reliability
of PTHs formed in the material. To evaluate the thermal cycling reliability of PTHs
formed in RT/duroid 5880LZ, testing was
performed on 0.060-in.-thick material with
0.0198-in.-diameter viaholes. Samples were
exposed to 500 air-to-air thermal shock
cycles at −55 and +150°C. No failures were
found in any of the 125 PTHs tested.
The growing use of mobile data has impacted electronic design in commercial as
well as in military circles. According to a
report by a leading data firm,2 the amount
of mobile data is projected to practically
double every year through 2016. These demands fuel the need to develop faster electronic systems that can handle not only the
mobile data portion of a network but also
data from fixed sources, as networks move
towards serial data rates of 40 Gb/s.
These trends hold true in the case of both
Design &Technology
Table 3: Comparing bond-film
options for RT/duroid 5880LZ
Material
FEP film
Dielectric
constant
Dissipation
factor
2.1
0.003
2.28
0.003
450 (TP)
2929 bondply
2.94
0.003
475 (TS)
5/12/11 10:06 AM Page 1
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Employing multipurpose payloads including
EO/IR, EW, SAR and others, UAVs can now transmit
complex information directly to troops in the field
while simultaneously sending the information halfway around the world for analysis.
CTT, Inc. continues its expansion of GaAs- and
GaN-based solid-state amplifier products and
subassemblies designed to accommodate these
ever evolving requirements.
CTT’s UAV experience includes participation in
data and video communication links on programs
including Shadow, Hunter, Predator/Reaper,
Pioneer, Global Hawk and others.
Building on this experience, CTT is well positioned
to offer engineering and production technology
solutions – including high-rel manufacturing – in
support of your complete UAV system requirements.
More than twenty-five years ago CTT, Inc.
made a strong commitment to serve the defense
electronics market with a simple goal: quality,
performance, reliability, service and on-time
delivery of our products.
Lamination temperature
(°F)
(FPGAs) in military electronic systems has
made these systems more intelligent, but
also more reliant on the capability of processing more data faster.
As serial data rates have increased from
2.5 Gb/s in the early 2000s to 9.8 Gb/s, and
now to 40 Gb/s, the push has increased for
PCB materials with the loss and dispersion
characteristics that can support these data
rates. High-speed digital signals, which can
be viewed as a combination of fundamental
and harmonic frequencies, are extremely
broadband in nature and require PCB materials that can handle broadband signals.
For high-speed digital projects, designers
are turning to PCB materials that have traditionally been used in RF/microwave circuits, such as RO4350B LoPro copper foil
material in 0.004-in. thickness. This PCB
material provides very stable performance
over a wide bandwidth.
Figure 3 shows test results from 8 to 50
GHz for RO4350B LoPro material, where
the dielectric constant dispersion is only
1.2%. This low value ensures that the shape
of a high-speed digital pulse is preserved
through a PCB, since the pulse’s various
signal components (fundamental, harmonics) travel with minimal time differences
through the PCB’s signal path.
Another material characteristic that is
important for maintaining signal integrity
is loss. Materials are characterized in terms
of both dielectric and conductor losses. For
many applications, it is important to select
a material with minimal conductor losses,
since any gains made by choosing materials with low dielectric losses could be lost
by increased conductor losses. Figure 4
details the improvement in insertion loss
for RO4350B LoPro material. At 20 GHz
(the fundamental frequency of a 40-Gb/s
signal), reduction in insertion loss is about
30% over traditional RO4000® material,
helping protect the amplitude of the overall signal. For high-speed digital applications, the use of RO4350B with LoPro foil
enables circuit designers to not only preserve signal integrity but, with the 0.004-in.
thickness of the material, to accommodate
complex multilayer designs while keeping
overall thickness low.
These material advances represent just
a handful of the improvements made in
PCB materials in recent years. These have
been motivated by the needs of electronic
designers not only for military applications,
but in commercial, industrial, automotive,
and medical electronics industries to do
more with less: to achieve increased electronic functionality from smaller, lighter,
and less-expensive PCB materials. DE
References
1. Horn, Caisse, Willhite, “Measurement
and Modeling of the Effect of Laminate
Thermal Conductivity and Dielectric Loss
on the Temperature Rise of HF Transmission Lines and Active Devices,” DesignCon 2012.
2. “Cisco Visual Networking Index: Global
Mobile Data Traffic Forecast Update, 20112016,” February 2012.
4-mil
RO4350B LoPro
4-mil
RO4350B
1
-0.120
5
-0.389
-0.277
10
-0.658
-0.461
15
-0.908
-0.638
20
-1.121
-0.799
25
-1.335
-0.953
30
-1.551
-1.098
35
-1.764
-1.301
40
-2.004
-1.399
45
-2.149
-1.489
50
-2.274
-1.654
0
-0.5
Loss—dB/in.
commercial and military systems, with an
increasing amount of defense-related data
produced by remote sensors, surveillance
systems, and a growing number of military electronic systems in general. The increasing speeds of digital signal processors
(DSPs) and field-programmable
gate arrays
ctt.uav.ad.fp.11.09_CTT
UAV.half.pg.MW&RF
Loss (dB/in.)
Frequency
(GHz)
-1.0
-0.101
4-mil RO4350B
4-mil RO4350B LoPro
-1.5
-2.0
-2.5
0
5
10
15
20
25
30
35
40
45
50
Frequency—GHz
4. These plots of insertion loss versus frequency compare standard RO4350B laminate
with RO4350B LoPro material with low-profile copper conductor.
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