High-Frequency Noise Suppression Using Ferrite-Plated Film

EMC Devices
High-Frequency Noise Suppression Using
Ferrite-Plated Film
YOSHIDA Shigeyoshi, KONDO Koichi, ONO Hiroshi
Abstract
Ferrite-plated ?lm is a ?exible magnetic sheet that can be deposited at ordinary temperatures. Its high electrical resistance and high
permeability up to the UHF band al ows the ?lm with a thickness of only a few microns to ef ectively suppress high-frequency elec-
tromagnetic noise without side ef ects. It can be formed directly onto electronic components and circuit boards and contains no or-
ganic substances such as polymers, so that it can withstand re?ow soldering process and may even be used inside IC chips or in
the inner layers of multi-layer boards. The active application of this device is currently under way based on the expectation that it wil
provide a simple solution to problems that are likely to become even more complex in the future, such as prevention of the high-
frequency noise of electronic devices and improvements to signal integrity.
Keywords
noise suppression sheet, ferrite-plated ?lm, high-frequency noise, EMI, autotoxemia, signal integrity
1. Introduction
FERRIX is attracting attention as a new noise solution for sup-
pressing the electromagnetic interference that may occur in
The composite-type noise suppression sheet (BUSTERAID)
very small areas of printed circuit boards with high-density
is used widely to solve the problem of high-frequency noise
mounting or largely integrated electronic devices such as SiPs
that has recently become an issue of increasing seriousness1).
(System in Packages). As a thin ?lm of only a few microns
The noise suppression sheet has been adopted rapidly as an
thickness, it can provide an excellent noise suppression effect
“attach and function” quick countermeasure without side ef-
and can be plated on a wide range of materials. In addition, the
fects, such as secondary electromagnetic interference. This is
thinness, excellent high-frequency permeability and steep
due to its loss characteristics, which feature frequency selec-
magnetic resonance characteristics of the ferrite-plated ?lm is
tivity and to its high electrical resistance. The mounting evalu-
also effective for improving the transmission/reception perfor-
ation method has come to be standardized by the International
mance of the rapidly spreading RFID systems. Therefore, the
Electrotechnical Commission (IEC)2).
?lm is also expected to become a signal integrity solution for
The thickness requirements for noise suppression sheets are
the UHF-band RFID systems that has been dif?cult to imple-
now reaching 10µm following the expansion of its application
ment using composite magnetic sheets.
to equipment with little excess space such as cellular phones
In this paper, we discuss the features of the ferrite-plated
and DSCs (Digital Still Cameras). It has already become dif-
?lm, its conducted noise suppression effects and the result of
?cult to provide a suppression capability (proportional to the
our investigations into variations in radiation noise by direct
product of sheet thickness and permeability µ) for the compos-
plating of the ferrite ?lm onto the surface of a printed circuit
ite sheets that are in use as the current mainstream choice. As a
board on which a microcomputer is mounted.
result, the ferrite-plated ?lms and the nano-granular thin ?lms
are both attracting attention as the next-generation noise sup-
2. Magnetic Properties Required for High-
pression sheets because of their excellent high-frequency per-
Frequency Noise Suppression
meability.
The ferrite-plated ?lm (BUSTERFERRIX) that we introduce
Fig. 1 shows a scheme diagram of the frequency spectra of
in this paper, is a newly developed thin-?lm magnetic material.
the permeability µ (complex permeability µ = µ’ – jµ”) of the
Its deposition process was developed by Professor Abe of To-
magnetic material (hereinafter referred to as the permeability
kyo Institute of technology3) and NEC TOKIN is currently
pro?le). In the following, we will describe the permeability
working with the aim of practical implementation. BUSTER-
of magnetic materials required for the suppression of
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EMC Devices
High-Frequency Noise Suppression Using Ferrite-Plated Film
rial. Consequently, since the magnetic materials should not
have a magnetic loss in the signal frequency domain and should
be accompanied with a signi?cant loss in the noise domain in
order to attenuate only the noise component, domain A in Fig.
1 is used for the noise suppression.
On the other hand, in the application to the magnetic cir-
cuitry of RFID, the magnetic shielding effect is obtained be-
fore the start of the frequency dispersion of permeability due to
magnetic resonance, as in domain B of Fig. 1, so the resonance
frequency f should be much higher than the signal frequency.
r
Therefore, to obtain a high noise suppression effect and mag-
netic shielding performance, it is required that; 1) the product
µ • f of the initial permeability (µ ) and resonance frequency
i
r
i
(f ) is large; 2) the resonance frequency f should be controlla-
r
r
ble over a wide frequency range, and; 3) the resonance loss
rises steeply.
Fig. 2 shows the permeability pro?le of ferrite-plated ?lm.
As the resonance frequency f is from ?ve times to more than
r
Fig. 1 Frequency distribution of magnetic permeability and domains
ten times higher than the bulk, the µ • f product becomes sig-
for different applications.
i
r
ni?cantly larger.
Fig. 3 shows diagrams of the cross-sectional structures of the
high-frequency noise and the improvement of signal integrity
ferrite-plated ?lm and composite noise suppression sheet, and
based on Fig. 1.
The noise suppression sheet and ferrite-plated ?lm suppress
high-frequency noise by means of frequency domain separa-
tion making use of the magnetic resonance that is controllable
according to the composition and shape of the magnetic mate-
Fig. 3 Microstructures of composite-type noise suppression sheet
Fig. 2 Examples of the permeability properties of ferrite-plated ?lm.
and plated ferrite ?lm, difference in their permeability (µ”) pro?les.
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Special Issue : Electronic Devices
the corresponding permeability (µ”) pro?les. Their compari-
son shows that the rise with the ferrite-plated ?lm is very steep,
suggesting that it is very convenient for signal integrity im-
provement for RFID systems as well as for high-frequency
noise suppression.
3. Conducted Noise Suppression
Effect of Ferrite-Plated Film
The ferrite-plated ?lm can be formed on a wide range of sub-
stances including polymer ?lm such as PET ?lm, FPC board
composed of polyimide, glass epoxy wiring board on which
Fig. 4 Conducted noise suppression effects Ploss of ferrite-plated ?lm
electronic components are mounted, and major electronic
and composite noise suppression sheet.
component surface materials such as semiconductor sealants.
In this section, we will describe one of the simpli?ed evalua-
tion methods of noise suppression effect when magnetic sheets
or ?lms are placed onto a micro-strip line.
The conducted noise suppression effect of the noise suppres-
sion sheet and ferrite-plated ?lm when it is placed on a trans-
mission line can be expressed as the power loss per unit line
length, P , using the following formula.
loss
P ?M • µ” • f • ? ------------------------ (1)
Fig. 5 Model mounting diagrams of ferrite-plated ?lm and composite
loss
Here, M is the coupling coef?cient between the high-fre-
noise suppression sheet.
quency ?ux produced by the current ?owing through the trans-
mission line and the noise suppression sheet, and ? is the
onto an actual circuit. Fig. 5(a) is the image of the composite
depth of magnetization caused by the high-frequency current.
noise suppression sheet and Fig. 5(b) is the image of the fer-
The coupling coef?cient M in formula (1) contains the effect
rite-plated ?lm.
of the gaps due to the adhesive tape or similar material be-
As seen above, the ferrite-plated ?lm can be formed directly
tween the transmission line and the noise suppression sheet. As
onto electronic components and circuits and can exhibit an ad-
a result, if the noise current ?owing through the transmission
equate noise suppression effect with a thickness of only 3µm.
line is weak, both M and ? become small and the noise sup-
It is therefore capable of suppressing the high-frequency con-
pression effect drops.
ducting noise of complicated structures with which the noise
Therefore, to obtain a high suppression effect with the com-
suppression sheet cannot be easily applied, for example an
posite-type noise suppression sheet, it is necessary to eliminate
electronic circuit board with high-density mounting, very
the gaps that degrade the coupling coef?cient. A composite
small electronic components or an internal layer of a multi-
sheet with a self-tacking property has been developed for this
layer circuit board.
purpose, but the use of adhesive tape is usually necessary to
ensure the attaching strength. On the other hand, the ferrite-
4. Radiated Noise Suppression Effect of
plated ?lm is formed directly onto the target components/cir-
Direct Plating onto a Printed Circuit Board
cuits so that it can render the coupling coef?cient M larger than
the composite sheet and is therefore very advantageous for ac-
We formed a Ni-Zn ferrite-plated ?lm of 3µm thickness di-
tual use in mounting. Fig. 4 shows the comparison of the con-
rectly onto a printed circuit board carrying a microcomputer
ducted noise suppression effect P between the case in which
chip with 20MHz clock operation using the spin spray process.
loss
a composite noise suppression sheet with 50µm thickness (µ =
Fig. 6 shows the permeability pro?le of the ferrite-plated ?lm.
i
50) is placed in close contact on a micro-strip line without us-
Ni and Zn composition control was utilized to achieve a per-
ing an adhesive sheet and the case in which a ferrite-plated
meability pro?le with which the magnetic loss becomes domi-
?lm of 3µm thickness (µ = 45) is formed directly on it.
nant at above 100MHz, which corresponds to 5 times the mi-
i
Fig. 5 shows images of the mounting of each magnetic ?lm
crocomputer’s clock frequency. We then placed the printed
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EMC Devices
High-Frequency Noise Suppression Using Ferrite-Plated Film
surface by means of the magnetic loss of the ferrite-plated
?lm.
The printed circuit board used in the test carried multiple
electronic components including capacitors in addition to mi-
crocomputer chips but we did not recognize any problem that
would affect their performance including operation malfunc-
tion due to the direct plating of the ferrite-plated ?lm. This was
because the ferrite-plated ?lm can be formed at the relatively
low temperature of about 80°C and presents high electrical re-
sistance and is also thermally stable.
Fig. 6 Relative permeability of ferrite-plated ?lm plated directly onto a
5. Conclusion
microcomputer circuit board.
Nowadays, it is hardly possible to achieve design perfor-
mance criteria of IT equipment that is under rapid progress
with such developments as the cellular phone without solving
the problem of high-frequency electromagnetic interference.
Noise suppression sheets are required to provide a high-fre-
quency magnetic shielding function for improving signal in-
tegrity by manipulating the ?ow of the ?ux induced by high-
frequency current as well as featuring a signi?cant magnetic
loss function for suppressing high-frequency noise (EMI or
“autotoxemia”).
Under these circumstances, the new applications of ferrite-
plated ?lm that features high electrical resistance and excellent
permeability are being increasingly adopted. These include di-
rect forming onto printed circuit boards as well as improve-
ments in the transmission/reception characteristics of UHF-
band RFID systems. Expectations for ferrite-plated ?lm as an
Fig. 7 Radiation noise spectrum of a microcomputer circuit board.
effective solution to the problem of high-frequency electro-
magnetic interference have thus increased to a very high lev-
circuit board with the ferrite-plated ?lm in a TEM cell, con-
el.
nected it to a spectrum analyzer via an placed, and measured
In closing this paper, we would like to express our deep grat-
and evaluated the radiated noise during operation of the micro-
itude to Professor Masanori Abe of Tokyo Institute of Technol-
computer.
ogy and Professor Emeritus Yutaka Shimada of Tohoku Uni-
Fig. 7 shows the spectra of the radiated noise. The radiation
versity for their guidance and assistance in the present
level dropped for the printed circuit board with the directly
developments.
plated ferrite ?lm plating compared to the printed circuit board
without the ferrite-plated ?lm. This effect became more no-
References
ticeable as the frequency increased, and was eventually recog-
1) Yoshida, S. et al.: Abstract of 1997 EMC Symposium, 4-1-1 (1997).
nizable as a clear difference at 1.5GHz or more.
2) IEC: New work item proposal for “Noise suppression sheet for digital
This result very much resembles the frequency dependency
devices and equipment," 51/652/NP (2001).
of the conducting noise suppression effect obtained by form-
3) Abe, M., KAGAKU TO KOGYO (Science and Industry), 75, 8, 342 (2001).
ing the ferrite-plated ?lm on a transmission line in the previous
section. Namely, it can be judged as the result that the forma-
tion of ferrite-plated ?lm almost all over the printed circuit
board surface made it possible to absorb the high harmonic
current propagated from the microcomputer chip to the board
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Special Issue : Electronic Devices
Authors' Pro?les
YOSHIDA Shigeyoshi
Deputy General Manager,
R&D Division,
NEC TOKIN Corporation
KONDO Koichi
Staff,
Materials Development Center,
R&D Division,
NEC TOKIN Corporation
ONO Hiroshi
Assistant Manager,
Materials Development Center,
R&D Division,
NEC TOKIN Corporation
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