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Base Metal Electrode Capacitors Cut Costs in Automotive and High Voltage Applications

January 30, 2009 By Dennis Leave a Comment

By Gerald Koebrugge, Knuth Albertsen, Wiljan Coppens, and Wilma Derks; Ferro Electronic Materials Systems B.V., The Netherlands

Cross Section of an MLCC Showing Dielectric and Electrode Layers

Today’s automobiles contain an ever-increasing number of electronic gadgets. The need for safer, more comfortable, pollution-free, and cost-effective transportation has created a great opportunity for the electronic industry to develop new systems to fulfill these needs. In the last several years, the use of programmed fuel injection, antilock brake systems, cruise control, airbag systems, air conditioning, and advanced entertainment systems have become standard. In the near future, more technology, such as drive-by wire and hybrid electrical cars, will become commonplace.

This trend creates a challenge for the electronics industry to supply components that can operate in the harsh New X8R Material The X8R compositions are produced by mixing and milling dopant components and BaTiO3. Oxides and carbonates were used as dopant components for the solid state process routing. For the coated version, soluble dopant components were selected. Figure 1 presents the procedure for preparing the formulations.

Figure 1: Material Preparation (Left: Solid State/Right: Coating)

For the solid state process, BaTiO3 is mixed with the dopant components and the material is milled to the required particle size. For the coated version, BaTiO3 is milled to the target particle size, then the dopants are added underhood environment where they are exposed to high temperatures and a variety of chemicals. For devices using ceramic capacitors, this requirement can be met with X8R materials, which are rated for temperatures to 150°C. Noble metal PME X8R materials have been developed recently with special emphasis on reducing firing temperature and, therefore, lead content, making the material RoHScompliant. However, even though the material can be used to the solution and fixed to the BT.

Disc capacitors are then prepared from granulated powder and pressed in a dye.Electrode ink is applied on each side of the disc capacitor. with up to 95% silver electrodes, these parts are expensive for higher layer count and larger amounts of MLCCs due to the noble metals. Another challenge is the increased use of electronics which can add to vehicle weight because each device requires copper wire to connect the electronic system to the control unit. To reduce weight while increasing available power, many automakers are replacing the current 12 to 24 V system with 42 V systems. In addition, the use of buss systems will reduce weight even further. Because these systems employ a network with addresses for each electronic device, more electronics can be found under the hood and near the engine. As a result, the electronics must operate at higher temperatures. To extend the temperature range of electronics, X7R capacitors (rated at -55° to 125°C) must be replaced with X8R capacitors, which can operate at 150°C.

Noble metal X8R capacitors, based on palladium/silver (PdAg) electrode systems combined with Bi2O3-TiO2, are widely available. However, these parts are expensive and cost-prohibitive for widespread use
in automotive applications. To reduce costs, X8R multilayer ceramic capacitors (MLCCs) constructed of base metal electrodes (BME) are being developed for use in automotive applications. In particular, a barium titanate composition meeting X8R requirements for use with nickel electrodes has been developed that incorporates an improved coating process to help distribute dopants homogeneously over the surface of the BaTiO3 grains. The adhesion of this layer is strong enough to allow dispersion with yttrium-stabilized zirconia (YTZ) beads. MLCCs prepared from the coated powders demonstrate higher insulation resistance and voltage breakdown. The high voltage breakdown and stable DC bias performance of the material makes it applicable for high voltage X7R applications as well.

New X8R Material

The X8R compositions are produced by mixing and milling dopant components and BaTiO3. Oxides and carbonates were used as dopant components for the solid state process routing. For the coated version, soluble dopant components were selected. Figure 1 presents the procedure for preparing the formulations. For the solid state process, BaTiO3 is mixed with the dopant components and the material is milled to the required particle size. For the coated version, BaTiO3 is milled to the target particle size, then the dopants are added to the solution and fixed to the BT. Disc capacitors are then prepared from granulated powder and pressed in a dye.
Electrode ink is applied on each side of the disc capacitor. MLCCs are prepared from PVB-based green tapes, stacked on a Keko Pal (IX), and use a pure nickel inner electrode paste. The plates are isostatically pressed and cut
into individual MLCCs and the layer thickness of the tape was targeted for 8 to 10 μm after sintering. The firing atmosphere used for the disc capacitors and MLCCs during sintering had an oxygen partial pressure of about 1 x 10-10 bar at 1300°C. The fired parts were re-oxidized at 1000°C for two hours in moistened nitrogen.

After firing, the MLCCs were tumbled and copper terminations were applied. The capacity was measured with an Agilent 4278A LCR meter. This bridge was connected to a Vötsch VT7004 to measure the temperature dependence of the capacitance.

HALT (highly accelerated lifetime testing) was performed by monitoring insulation resistance at 140°C. A voltage of 50 V/μm was applied during this test to discriminate between different materials and to provide an indication of reliability at the severe application conditions. TEM studies were performed using a TECNAI F30ST TEM (FEI) with field emitter gun (FEG) operated at 300 kV. A 4 μl suspension of powder in alcohol was placed on a copper grid supporting a formvar carbon film. Subsequently, the grid was allowed to dry on paper. As a result, part of the suspension was left behind on the carbon film.

Figure 2: TEM Micrograph with Elemental Mapping for Three Different Areas


Coated Technology vs. Solid State:

The key factor in this study was the distribution of the dopants on the BaTiO3. Therefore, the material was examined by TEM in combination with EDX element mapping. Figure 2 shows the TEM scan for a material produced with solid state mixing and milling. In this experiment, EDX was performed on three different spots. The elemental spectra clearly demonstrate that for areas 2 and 3, Ba, Ti, and O are the important elements, whereas for area 1 (small grain near the coarser grain), Mn is present. The contribution of Ba and Ti in this spectrum is from the BaTiO3 neighbor. Even though the dopant particle is very fine, it is still a detectable isolated grain. Other dopant elements can also be detected on different spots as isolated grains. For coated materials, single grains of dopants cannot be found. Figure 3 shows a TEM micrograph of the coated material in combination with several elemental maps (over the marked area). The elemental map is represented by a distribution of intensities, as detected by EDX. The intensity is proportional to the concentration in mass percent.

Figure 3: STEM Micrograph of a Coated Material


The micrographs demonstrate the detectable dopant elements Mn, Si, and Y are well distributed over the surface
of the BaTiO3 grain. Dopant elements are mainly observed on the edge of the grain where the concentration of Ba and Ti is low. At higher Ba and Ti concentrations, signals from other elements become weak or disappear.
Milling resistance of the coating is important in applications of coated dielectric powders. During MLCC processing, the powders are dispersed in organic solvents by using ZrO2, which can damage or strip off the coating layer on top of the grains. Adhesion of the coating to the grain is very important to prevent the separation of the coating from the grain.

Figure 4 presents STEM micrographs of coated material in combination with elemental maps for Ba, Ti, Mn, Si, and Y after milling four hours in ethanol-toluene with binder and 1 mm YTZ balls. Again, the intensity is related to the concentration in mass percent.

Figure 4: STEM Micrograph of a Mill-Coated Material in Combination With Elemental Maps For Ba, Mn, Si and Y Over The Marked Area


The elemental maps demonstrate the coating remains on top of the grain. For most of the elements, the intensity appears at the edge of each grain. The presence of Zr is due to milling and indicates the intensity of milling during the dispersing process; however, the coating stays on the grains. Full BME-X8R compositions were prepared using both the solid state and the coating process. Figure 5 lists typical powder properties, and Figure 6 shows typical electrical properties for 40 nF MLCCs.

D50 [μm] 0.8
D90 [μm] 1.4
BET [m2/gr] 5.5
Figure 5: Typical Powder Properties AD202N

The data in Figure 6 indicates both insulation resistance (IR) and breakdown voltage (BDV) are higher for the coated material at room temperature, thus illustrating processing conditions affect material properties. It seems reasonable to assume the improved homogeneity of the coated material will also improve reliability under elevated temperature and voltage conditions.

Coated Solid state
K Value >2000 >2000
DF [%] 2.3 2.1
IR [GΩ] @ 25°C 93 78
RC [s] @ 25°C 3900 3200
VBD [V/μm] 157 129
HALT [h] 140°C,
50V/μm >100 >100
Figure 6: Typical Electrical Properties of 8μm MLCCs

Figure 7 shows a typical micrograph of an X8R MLCC produced from the coated materials and demonstrates a very dense ceramic is produced after firing at 1320° to 1350°C. Layer thickness is about 8 μm.

Figure 7: Cross Section of X8R Multilayer Capacitor


Figure 8: Typical TCC Curve for AD202N Multilayer Capacitor


The temperature dependence of the formulation is presented in Figure 8 on page 20. A flat TCC curve has been obtained for 10 μm 1206 MLCCs. Capacity varies by only a few percentage points over a wide temperature range (+7.5% from -55° to 125°C) and drops at temperatures above 130°C to about -11% at 150°C, meeting the X8R temperature specification.

Figure 9: Typical DC Bias Curve of AD202N (10 μm Part)


Figure 10: Aging Curve of AD202N


Electrical properties indicate the potential of this material. Typical K values are sufficiently high for use in 10 μm, 0603, 47 nF capacitors. The RC value at room temperature is higher than 3000 s.

The stable temperature behavior of the material makes
it acceptable not only for automotive applications but
also for other areas where use condition temperature
limits the suitablility of X7R capacitors. The higher
operating temperatures being seen in many electronic
applications require components that can withstand these
conditions.
In addition, a voltage breakdown above 120 V/μm
(150 V/μm for the coated version) implies the possibility
of using this material in high voltage applications.
This is supported by the DC bias behavior of
MLCCs with 10 μm dielectric thickness, as shown
in Figure 9. This curve indicates that 80% of the
initial capacity is available at 50 V (5 V/μm) and
50% of the capacity is available at 100 V
(10 V/μm). Aging tests, in Figure 10, indicate the
aging loss is about 1% from 24 to 240 hours.

Conclusions:
Higher operating temperatures in automotive electronic applications require the use of X8R MLCCs. To reduce costs, base metal (BME) compositions have been developed to replace precious metal compositions. Furthermore, the addition of specialty coatings improves some of the electrical properties such as IR and BDV. In addition, the BME-X8R material has promising dielectric properties and thermal stability. It may also be suitable for use in high voltage X7R applications.

References
1. Motoki, T., “Chip Monolithic Ceramic Capacitors
Drive Automotive Applications.” AEI, Dempa Publications,
Inc., August 2003.
2. Krueger, S. and Grace, R., “New Challenges for
Microsystems-Technology in Automotive Applications.”
MST News 1, 2001.
3. Paumanok Publications, Inc., “The Changing Environment
for Passive Components in Automotive Electronic
Subassemblies: 2000-2005.” Passive Component
Industry, March/April 2001, pp 7-11.
4. Symes, W., Chu, M., Davis, E., and Capurso, J., “Enabling
Thinner, High Performance, Lower-Cost MLCCs
that Meet Environmental Regulations.” Passive Components
Industry, July 2007, pg 26.
5. Koebrugge, G., Albertsen, K., Coppens, W., and
Derks, W., “BME-X8R for Automotive and High Voltage
Applications.” CARTS Europe 2006 Proceedings,
Germany.

Readers Who Viewed This Article Also Viewed The Following: (1) (1) Ceramic Capacitors: World Markets, Technologies & Opportunities: 2009-2014 ISBN # 1-893211-25-8 (December 2009) (2) (2) BME MLCC: Global Markets, Technologies & Opportunities: 2005-2010 ISBN # 1-893211-74-6 (2005) (3) MLCC In Automotive Electronic Subassemblies: 2004 Market Study (4)
End-Use Markets For Passive Components: 2007-2011 ISBN # 1-893211-52-5 (2007).

Filed Under: Feature Story, Raw Materials Tagged With: ,

Base Metal Electrode Capacitors Cut Costs In Automotive and High Voltage Applications

January 30, 2009 By Dennis Leave a Comment

By Gerald Koebrugge, Knuth Albertsen, Wiljan Coppens,
and Wilma Derks
Ferro Electronic Materials Systems B.V., The Netherlands

Cross Section of a Multilayered Ceramic Chip Capacitor Showing Electrode and Dielectric


Today’s automobiles contain an ever-increasing number of electronic gadgets. The need for safer, more comfortable, pollution-free, and cost-effective transportation has created a great opportunity for the electronic industry to develop new systems to fulfill these needs. In the last several years, the use of programmed fuel injection, antilock brake systems, cruise control, airbag systems, air conditioning, and advanced entertainment systems have become standard. In the near future, more technology, such as drive-by wire and hybrid electrical cars, will become commonplace.

This trend creates a challenge for the electronics industry to supply components that can operate in the harsh New X8R Material The X8R compositions are produced by mixing and milling dopant components and BaTiO3. Oxides and carbonates were used as dopant components for the solid state process routing. For the coated version, soluble dopant components were selected. Figure 1 presents the procedure for preparing the formulations.

Figure 1: Material Preparation (Left: Solid State/Right: Coating)

For the solid state process, BaTiO3 is mixed with the dopant components and the material is milled to the required particle size. For the coated version, BaTiO3 is milled to the target particle size, then the dopants are added underhood environment where they are exposed to high temperatures and a variety of chemicals. For devices using ceramic capacitors, this requirement can be met with X8R materials, which are rated for temperatures to 150°C. Noble metal PME X8R materials have been developed recently with special emphasis on reducing firing temperature and, therefore, lead content, making the material RoHScompliant. However, even though the material can be used to the solution and fixed to the BT.

Disc capacitors are then prepared from granulated powder and pressed in a dye.Electrode ink is applied on each side of the disc capacitor. with up to 95% silver electrodes, these parts are expensive for higher layer count and larger amounts of MLCCs due to the noble metals. Another challenge is the increased use of electronics which can add to vehicle weight because each device requires copper wire to connect the electronic system to the control unit. To reduce weight while increasing available power, many automakers are replacing the current 12 to 24 V system with 42 V systems. In addition, the use of buss systems will reduce weight even further. Because these systems employ a network with addresses for each electronic device, more electronics can be found under the hood and near the engine. As a result, the electronics must operate at higher temperatures. To extend the temperature range of electronics, X7R capacitors (rated at -55° to 125°C) must be replaced with X8R capacitors, which can operate at 150°C.

Noble metal X8R capacitors, based on palladium/silver (PdAg) electrode systems combined with Bi2O3-TiO2, are widely available. However, these parts are expensive and cost-prohibitive for widespread use
in automotive applications. To reduce costs, X8R multilayer ceramic capacitors (MLCCs) constructed of base metal electrodes (BME) are being developed for use in automotive applications. In particular, a barium titanate composition meeting X8R requirements for use with nickel electrodes has been developed that incorporates an improved coating process to help distribute dopants homogeneously over the surface of the BaTiO3 grains. The adhesion of this layer is strong enough to allow dispersion with yttrium-stabilized zirconia (YTZ) beads. MLCCs prepared from the coated powders demonstrate higher insulation resistance and voltage breakdown. The high voltage breakdown and stable DC bias performance of the material makes it applicable for high voltage X7R applications as well.

New X8R Material

The X8R compositions are produced by mixing and milling dopant components and BaTiO3. Oxides and carbonates were used as dopant components for the solid state process routing. For the coated version, soluble dopant components were selected. Figure 1 presents the procedure for preparing the formulations. For the solid state process, BaTiO3 is mixed with the dopant components and the material is milled to the required particle size. For the coated version, BaTiO3 is milled to the target particle size, then the dopants are added to the solution and fixed to the BT. Disc capacitors are then prepared from granulated powder and pressed in a dye.
Electrode ink is applied on each side of the disc capacitor.

MLCCs are prepared from PVB-based green tapes, stacked on a Keko Pal (IX), and use a pure nickel inner
electrode paste. The plates are isostatically pressed and cut into individual MLCCs and the layer thickness of the tape was targeted for 8 to 10 μm after sintering. The firing atmosphere used for the disc capacitors and
MLCCs during sintering had an oxygen partial pressure of about 1 x 10-10 bar at 1300°C. The fired parts were re-oxidized at 1000°C for two hours in moistened nitrogen. After firing, the MLCCs were tumbled and copper terminations were applied.

The capacity was measured with an Agilent 4278A LCR meter. This bridge was connected to a Vötsch VT7004 to
measure the temperature dependence of the capacitance. HALT (highly accelerated lifetime testing) was performed by monitoring insulation resistance at 140°C. A voltage of 50 V/μm was applied during this test to discriminate between different materials and to provide an indication of reliability at the severe application conditions. TEM studies were performed using a TECNAI F30ST TEM (FEI) with field emitter gun (FEG) operated at 300 kV. A 4 μl suspension of powder in alcohol was placed on a copper grid supporting a formvar carbon film. Subsequently, the grid was allowed to dry on paper. As a result, part of the suspension was left behind on the carbon film.

Figure 2: TEM Micrograph with Elemental Mapping for Three Different Areas

Coated Technology vs. Solid State:

The key factor in this study was the distribution of the dopants on the BaTiO3. Therefore, the material was examined by TEM in combination with EDX element mapping. Figure 2 shows the TEM scan for a material produced with solid state mixing and milling. In this experiment, EDX was performed on three different spots.
The elemental spectra clearly demonstrate that for areas 2 and 3, Ba, Ti, and O are the important elements, whereas for area 1 (small grain near the coarser grain), Mn is present. The contribution of Ba and Ti in this spectrum is from the BaTiO3 neighbor. Even though the dopant particle is very fine, it is still a detectable isolated grain. Other dopant elements can also be detected on different spots as isolated grains. For coated materials, single grains of dopants cannot be found. Figure 3 shows a TEM micrograph of the coated material in combination with several elemental maps (over the marked area). The elemental map is represented by a
distribution of intensities, as detected by EDX. The intensity is proportional to the concentration in mass percent.

Figure 3: STEM Micrograph of a Coated Material in Combination with


The micrographs demonstrate the detectable dopant elements Mn, Si, and Y are well distributed over the surface
of the BaTiO3 grain. Dopant elements are mainly observed on the edge of the grain where the concentration of Ba
and Ti is low. At higher Ba and Ti concentrations, signals from other elements become weak or disappear. Milling resistance of the coating is important in applications of coated dielectric powders. During MLCC processing, the powders are dispersed in organic solvents by using ZrO2, which can damage or strip off the coating layer on top of the grains. Adhesion of the coating to the grain is very important to prevent the separation of the coating
from the grain.

Figure 4 presents STEM micrographs of coated material in combination with elemental maps for Ba, Ti, Mn, Si, and
Y after milling four hours in ethanol-toluene with binder and 1 mm YTZ balls. Again, the intensity is related to the concentration in mass percent.

Figure 4: STEM Micrograph of a Mill-Coated Material in Combination


The elemental maps demonstrate the coating remains on top of the grain. For most of the elements, the intensity appears at the edge of each grain. The presence of Zr is due to milling and indicates the intensity of milling during the dispersing process; however, the coating stays on the grains. Full BME-X8R compositions were prepared using both the solid state and the coating process. Figure 5 lists typical powder properties, and Figure 6 shows typical electrical properties for 40 nF MLCCs.

D50 [μm] 0.8
D90 [μm] 1.4
BET [m2/gr] 5.5

The data in Figure 6 indicates both insulation resistance (IR) and breakdown voltage (BDV) are higher for the
coated material at room temperature, thus illustrating processing conditions affect material properties. It seems reasonable to assume the improved homogeneity of the coated material will also improve reliability under elevated temperature and voltage conditions.

Figure 6: Typical Electrical Properties of 8μm MLCCs
Coated Solid state
K Value >2000 >2000
DF [%] 2.3 2.1
IR [GΩ] @ 25°C 93 78
RC [s] @ 25°C 3900 3200
VBD [V/μm] 157 129
HALT [h] 140°C,
50V/μm >100 >100

Figure 7 shows a typical micrograph of an X8R MLCC produced from the coated materials and demonstrates a very dense ceramic is produced after firing at 1320° to 1350°C. Layer thickness is about 8 μm.

Figure 7: Cross Section of X8R Multilayer Capacitor

Figure 8: Typical TCC Curve for AD202N Multilayer Capacitor

The temperature dependence of the formulation is presented in Figure 8. A flat TCC curve has been obtained for 10 μm 1206 MLCCs. Capacity varies by only a few percentage points over a wide temperature range (+7.5% from -55° to 125°C) and drops at temperatures above 130°C to about -11% at 150°C, meeting the X8R temperature specification.

Figure 9: Typical DC Bias Curve of AD202N (10 μm Part)


Figure 10: Aging Curve of AD202N

Electrical properties indicate the potential of this material. Typical K values are sufficiently high for use in 10 μm, 0603, 47 nF capacitors. The RC value at room temperature is higher than 3000 s. The stable temperature behavior of the material makes it acceptable not only for automotive applications but also for other areas where use condition temperature limits the suitablility of X7R capacitors. The higher operating temperatures being seen in many electronic applications require components that can withstand these conditions.

In addition, a voltage breakdown above 120 V/μm (150 V/μm for the coated version) implies the possibility of using this material in high voltage applications. This is supported by the DC bias behavior of MLCCs with 10 μm dielectric thickness, as shown in Figure 9. This curve indicates that 80% of the initial capacity is available at 50 V (5 V/μm) and 50% of the capacity is available at 100 V (10 V/μm). Aging tests, in Figure 10, indicate the aging loss is about 1% from 24 to 240 hours.

Conclusions:
Higher operating temperatures in automotive electronic applications require the use of X8R MLCCs. To reduce costs, base metal (BME) compositions have been developed to replace precious metal compositions. Furthermore, the addition of specialty coatings improves some of the electrical properties such as IR and BDV. In addition, the BME-X8R material has promising dielectric properties and thermal stability. It may also be suitable for
use in high voltage X7R applications.

References
1. Motoki, T., “Chip Monolithic Ceramic Capacitors
Drive Automotive Applications.” AEI, Dempa Publications,
Inc., August 2003.
2. Krueger, S. and Grace, R., “New Challenges for
Microsystems-Technology in Automotive Applications.”
MST News 1, 2001.
3. Paumanok Publications, Inc., “The Changing Environment
for Passive Components in Automotive Electronic
Subassemblies: 2000-2005.” Passive Component
Industry, March/April 2001, pp 7-11.
4. Symes, W., Chu, M., Davis, E., and Capurso, J., “Enabling
Thinner, High Performance, Lower-Cost MLCCs
that Meet Environmental Regulations.” Passive Components
Industry, July 2007, pg 26.
5. Koebrugge, G., Albertsen, K., Coppens, W., and
Derks, W., “BME-X8R for Automotive and High Voltage
Applications.” CARTS Europe 2006 Proceedings,
Germany.

Readers Who Viewed This Article Also Viewed The Following: (1) Ceramic Capacitors: World Markets, Technologies & Opportunities: 2009-2014 ISBN # 1-893211-25-8 (December 2009) (2) (2) BME MLCC: Global Markets, Technologies & Opportunities: 2005-2010 ISBN # 1-893211-74-6 (2005) (3) MLCC In Automotive Electronic Subassemblies: 2004 Market Study (4)
End-Use Markets For Passive Components: 2007-2011 ISBN # 1-893211-52-5 (2007).

Filed Under: Feature Story Tagged With: ,

Passive Components in Automotive Electronics—Past, Present, Future

January 30, 2006 By Dennis Leave a Comment

By Ron Demko; AVX Corporation

The evolution of automobiles from their birth as simple horseless carriages to the current wide range of highly complex models has been nothing short of breathtaking. Today’s automobiles exhibit significantly greater performance, luxury, and safety compared to the automobiles offered just a few years ago.

Figure 1: Niobium vs. Polymer Capacitor Failure Resistance Comparison


The goal of the next generation cars will be to offer the consumer a blend of even higher levels of driving performance, more luxurious amenities, increased levels of safety, and better fuel efficiency. Without a doubt, we can safely predict that performance levels unheard of a few years ago will be possible through the use of advanced engine control units, various electronic stabilization packages, a broad array of sensors, and high speed communications bus structures.

Figure 2: Capacitor Burn Rate and Ignition Energy Comparison


Initial Electronic Content:
Many of us can recall the days of control cables, linkage rods, and belts on automobiles. Electronic content first emerged in the form of non-critical entertainment and comfort offerings. AM radios are the best example of this event. AM radios quickly evolved into the various forms of early audio options. Among them were FM radio, 8 track players, and cassette tape players. As these entertainment options were accepted by consumers, the auto manufacturers became efficient in large volume electronic manufacture. Automobile accessory manufacturers began to improve the electronics design, efficiency, reliability, and size through process improvements and the well-known transition from tube-based circuitry to semiconductors. Ceramic capacitors, as well as most other passive components, met that challenge by evolving from typically higher voltage leaded devices to intermediate voltage devices in axial and miniature radial packages. Ultimately SMT packages were offered when reliability performance levels could meet and exceed the requirements of the Big Three (Ford, DaimlerChrysler, and General Motors).

Figure 3: Progression of Low Inductance Capacitor Types


Somewhere along that semiconductor and system evolution process, common mode chokes and capacitive based
filters were used in OEM designs to improve the performance of these options through better voltage quality. More advanced noise filters began to emerge as aftermarket options for the home mechanic. In fact, a case can be made that the home mechanic audio market was so great and appeared so lucrative that the Big Three realized that major design efforts should be placed there. Advances in aftermarket audio choices reinforced automotive manufacturers’ commitment to audio and entertainment product development efforts. The audio and entertainment trend led to expectations for the cost reduction, electrical performance, and reliability demanded by the electronic divisions of the Big Three. In most cases, evolution of passive components centered upon improving the reliability of ever increasing electrical quantities in smaller SMT case sizes—e.g. more capacitance in smaller case sizes. Other efforts were placed upon improved electrical stability over temperature and increased voltage ratings for new breeds of power semiconductors.

Figure 4: 10nf/100nf Dual Capacitor Array vs. Discrete Capacitors Impedance Versus Frequency


Secondary Electronic Content Phase:
The next area of electronic content occurred in the offering of comfort options on automobiles. Developments like power windows, power locks, speed alarms, intermittent wipers, and air conditioning all began to involve some form of passive components for power stabilization, filtering, and sensor functions. Though the function of these systems still was not considered as critical to automobile operation, the manufacturers
placed increased reliability and performance demands on suppliers.

As time progressed, performance enhancement systems were developed and introduced at a later phase in this trend. Typically, these systems involved using redundant circuitry and systems to maintain overall automobile performance and accuracy. Further, designs were structured in such a way that an electronic system failure would not inhibit total vehicle operation.

Third Electronic Content Phase:
Eventually, semiconductor trends, costs, and process capability evolved so much that cost effective reliable VLSI ICs became available for designers. Additionally, low cost, reliable power semiconductors came onto the market.

These broad developments would forever change automotive electronics. Miniature, reliable VLSI chips are crucial
to the control of engine, power train, and vehicle stability functions. Next generation VLSI ICs will be called upon to improve automobile fuel economy through the control of advanced items such as variable displacement engines, variable CAM timing, variable compression ratios, direct injection, and variable advanced multi-speed transmissions. Most importantly, from this article’s perspective, the VLSI chips cause an exponential need for the implementation of efficient ceramic capacitors in designs. Efficient capacitors are needed for voltage stabilization and decoupling, as well as EMC control associated with the high operating speed and the small trench size associated with VLSI ICs. In fact, EMC control and compliance is a major goal driving many automotive electronic designs. Passive components and advanced passive components can be utilized to simplify and solve EMC design issues. As additional specialty ICs are created (stability, occupant sensor, IR control/ sensor, etc), there will be an additional need for high operating temperature range capacitors and high quality bulk decoupling capacitors. Power ICs allow designers the option to control loads and modules in a fast, direct method. These power ICs are driving the need for higher voltage capacitors exhibiting low inductance, as well the need for miniature higher power circuit protection devices.

Figure 5a: MLV Equivalent Model


Passive Trends:
One way to group the advances in passive components is by end application family. A simplified grouping of application types yields three general end sectors: 1. generalpurpose electronics, 2. high temperature and harsh environment solutions, and 3. EMI/Transient suppression solutions.

1. General Purpose Electronics
Examples of general-purpose electronics are modules, which do not expose electronics to excessive environmental demands. These can range from dashboard electronics to passenger compartment mounted ECU systems, or from RKE units to wiper control circuits. Other examples of emerging general-purpose circuits are internal mapping/in car navigation, speech recognition, biometrics, and interior seating controls. Regardless of the exact circuit there is always an overall desire to make the circuit smaller, cheaper, and more reliable. Passive components are addressing the designers’ general improved cost, size, and reliability goals through the introduction of new types of bulk decoupling capacitors, low inductance–efficient decoupling capacitors and high device density capacitor arrays.

Niobium Oxide Capacitors (OxiCap™) are lead-and halogen- free capacitors that offer automotive designers high reliability and fail-safe operation ideal for use in high reliability applications. The niobium oxide capacitor was
developed as a higher performance alternative to aluminum and other SMT technologies. These capacitors are capable of lead free reflow process temperatures of 260°C through a 3-pass operation. The OxiCap is based
upon a niobium oxide ceramic anode material that is processed through the same steps as Tantalum capacitors. OxiCaps exhibit high reliability (0.5%/1000hours) as a result of the Nb2O5 dielectric in combination with the
self-healing MnO2 cathode. Niobium Oxide capacitors are packaged in the same EIA case sizes as Tantalum
capacitors and are available in both standard and low ESR series. For instance, standard and
low ESR Oxicaps are available in B, C, D, E, V, and Y case sizes, from values of 100μf to 680μf and ESR values from
50 to 150mΩ. The typical applications OxiCap capacitors address are low voltage bulk decoupling around ICs and
DC:DC converter output filtering (typically on 5 volt lines).

As previously stated, OxiCap devices offer high reliability and fail-safe operation. OxiCap devices fail in a high
resistance mode, which in the great majority of cases will not impact the functional operation of the circuit. A
comparison of typical failure resistance distribution between Niobium-Oxide capacitors and polymer types is shown in Figure 1. The data illustrates a high resistance failure mode relative to other capacitor types.

Further, a failed OxiCap has a 95% reduced ignition failure mode compared to conventional tantalum capacitors, due to an ignition energy requirement nearly three orders Niobium also has a favorable burn rate of approximately one tenth that of Tantalum. Data comparing the burning rate and ignition energy between
Niobium Oxide, Tantalum, and Niobium Polymer is shown in Figure 2.

Low Inductance Decoupling Capacitors help designers meet stringent EMC requirements associated with today’s vehicles by lowering overall PCB impedances and minimizing PCB geometry. It is possible that a designer may actually reduce the number of decoupling capacitors used on a design with the use of low inductance capacitors. Additionally, low inductance decoupling capacitors offer designers a capacitor with a dramatically higher self-resonant frequency of operation— thereby actually extending the useful frequency range of the capacitor. The progression of advanced, low inductance decoupling capacitors is shown in Figure 3. Generally speaking, in addition to aspect ratio rules, the larger the number of connections to the capacitor terminals, the lower the capacitor inductance. If alternate termination connections are placed in close proximity to one another, the inductance is further minimized due to magnetic field cancellation. Figure 3 illustrates those rules—SMT capacitors offer favorable geometries over axial leaded capacitors. Standard EIA case size capacitors’ inductance can be minimized by a geometric optimization, terminating SMT capacitors on the long side vs. the short sides.

As process capability developed, multiple connections were alternately made to the terminations, thus improving magnetic field cancellation and further reducing capacitor inductance. Finally, geometric rules and I/O optimization were combined to create capacitors with inductances minimized in the low tens of ph (or lower). Presently, most of the automobile interest in low inductance capacitors is limited to reverse geometry capacitors (those terminated on the long side—typically like 0612, 0508, and 0306 sizes).

High Device Density Capacitor Arrays are a space-saving alternative to discrete capacitors in parallel bus and redundant system circuitry. Capacitor arrays will be used extensively in engine control units, entertainment systems, and smart modules. Four element capacitor arrays are typically available in 0508 and 0612 packages, with voltage ratings up to 100 volts. Both NPO and X7R dielectrics are available in values up to 470pf and 0.1μf respectively. An emerging trend is to use dual value capacitor arrays on analog circuitry. Alternatively, dual value arrays can be used to broaden the frequency response (Figure 4) of a decoupling capacitor on ICs sensitive to Vcc quality and EMI. Two-element array usage is expected to increase because it saves space in filtering drivers of multiplex bus communications within automobiles.

2. High Temperature and Harsh Environment Solutions Sensors and modules are examples of high temperature and harsh environment electronics, which are typically under- hood mounted. These assemblies experience significant periods of high temperature operation, large numbers of temperature cycling, as well as random vibration/shock. Specific modules and assemblies can range from engine, clutch, and gearbox controllers to turbocharger sensors. Hybrid automobiles also have a variety of high temperature and harsh environment electronics modules. Typically these are inverter/converter circuits, motor control, and water pump applications.

Long term reliability and performance are critical regardless of the exact circuit under discussion. Size and cost are important considerations as well. Miniature and highly reliable versions of 150°C rated ceramics and 175°C rated Tantalum capacitors have been developed to address high temperature applications. In addition, new termination material systems have been developed that greatly improve ceramic capacitor temperature cycling performance.

High Temperature X8R Ceramic Capacitors exhibit a temperature stability of +/-15% across their rated temperature range of –55 to +150°C. X8R capacitors have been available for some time in standard and automotive AECQ-200 qualified parts. Typically X8R capacitors were available in tin and conductive epoxy terminations for hybrid applications.

A significant new development is that AVX now offers RoHS-compliant X8R capacitors in a termination technology called FLEXITERM™ (available on other standard dielectric discrete and array capacitors as well). FLEXITERM™ is a flexible termination layer that helps maintain electrical integrity under external forces such as vibration, bending, and temperature cycling. This flexible termination is achieved by coating the copper termination of a ceramic capacitor with a conductive polymer, then plating with nickel and tin. The flexible, high conductivity termination material allows nearly three times the board flexure of standard ceramic capacitors, thus enhancing the components’ mechanical and temperature flexure performance to prevent system failures due to cracking.

Figure 5b: Dual MLV Array CAN Bus Implementation


At high temperatures, the mismatched coefficient of thermal expansion (CTE) between capacitors and PCBs can cause excessive forces at the connection interface of the dissimilar materials. This force can be significant in automotive applications where varying load conditions cause large temperature fluctuations and vibration. FLEXITERM’s flexible properties lessen the stress on the component, reducing the system failure risk. It is important to note that some manufacturers offer flexure protection by using an adapted internal electrode design, where an increased gap is made between the end of the electrode and the side of the chip. This design helps to reduce low resistance and short circuit failures due to the higher chance of the crack passing through one polarity group of electrodes and not the worst case scenario of shorting though both polarities. However, depending on how high the crack spreads through the component, an increasing loss of capacitance occurs due to the disconnection of electrodes. Another limitation of adapted internal designs is that higher capacitance values may not be offered for these components.

Figure 6: High and Low Speed CAN MLV Options


The X8R capacitors reduce the transfer of mechanical stress on the component; preventing damage during module manufacture, board flexing, vibration, and temperature expansion. It has been designed so that failure
due to board flexing/temperature cycling would be contained in the termination area and in open mode. This stops the current supply, removing the risk of damage or fire from a short circuit failure. With FLEXITERM™ the open circuit occurs in a small area of the termination with little or no degradation to the capacitor’s performance.

These capacitors can withstand over 4mm board flexure and AECQ 200 temperature cycling requirements for 3000 cycles without failures.

High Ttemperature Tantalum Capacitors are available in AVX’s new THJ series. These devices combine high temperature operation and higher basic reliability for optimal performance in automotive applications. Continuous operation at +175°C is possible with a 50% derating of voltage ratings. The level of reliability of THJ capacitors is 0.5%/100 hours at rated voltage, rated temperature, and 0.1Ω circuit impedance. THJ capacitors are available in A, B, C, and D case sizes in values up to 150μf and 35V ratings.

3. EMI and Transient Suppression Solutions:
EMI and transient suppression solutions are needed on virtually all automotive electronics. Examples range from air bag igniters to motor driver circuits. The most common circuits in need of both EMI and transient protection are multiplex bus communication networks within vehicles. There is a variety of SAE recommended practices for vehicle multiplexing, with one of the most common being CAN bus. Within a CAN bus, each node has an interface circuit that needs to be protected from transient events as well as filtered for EMI emissions and interference. Multilayer Varistors (MLVs) can provide both transient suppression and EMI filtering in a single component, based upon a predictable bi-directional zener clamping capability and a definable off state capacitance. Figure 5a shows the equivalent model for a MLV. Figure 5b shows how a dual element MLV (each element represented by a bi-directional zener contained within the blue box – which represents a single 0508 package) can be utilized as a single component solution to CAN bus protection. It is very significant to note that new versions of MLVs now offer lower leakage current than zener diodes, thereby allowing sensors to be more accurate and systems to consume less power. Additionally, new choices for CAN bus protection are now offered, based on CAN bus speed (Figure 6).

Summary:
There is strong evidence that automobile electronic content will continue to increase due to consumer demands and government regulatory requirements. At the same time, passive component usage will also increase due to increased general electronic content within vehicles. Given these trends, high performance passive components will need to continue to evolve in order to meet the demands of next generation semiconductors, sensors, and modules.

MLCC In Automotive Electronic Subassemblies: 2004 Market Study

End-Use Markets For Passive Components: 2007-2011 ISBN # 1-893211-52-5 (2007).

Companies Who Reviewed This Article Also Reviewed: (1) Value-Added & Application Specific Ceramic Capacitors (High Voltage, High Frequency and High Temperature): World Markets, Technologies & Opportunities: 2005-2010

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