Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2001-10-03
2003-09-09
Talbott, David L. (Department: 2827)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S266000, C361S795000
Reexamination Certificate
active
06617527
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printed circuit board and a manufacturing method of the printed circuit board, particularly, relates to a printed circuit board having a structure of transmission line, which is hardly affected by external noise, low in scattering of impedance and excellent in a transmission characteristic, and a manufacturing method of the printed circuit board.
2. Description of the Related Art
Recently, with entering into an informational age, equipment such as a communication terminal has been widely spread. Following this situation, equipment has been progressed in high frequency and a mobile terminal equipment of which radio frequency (RF) signal is in an order of GHz has been introduced in a market. Further, even in a memory subsystem of a personal computer, a higher speed processing has been advanced in a frequency of some hundreds MHz. In response to this trend, a printed circuit board being excellent in a transmission characteristic of which impedance is controlled in accordance with a higher frequency is demanded.
FIG. 5
is a cross sectional view of a printed circuit board according to the prior art.
FIGS.
6
(
a
) through
6
(
d
) are cross sectional views of a printed circuit board of the prior art for explaining a manufacturing process.
In FIG.
6
(
a
), a copper foil formed on an insulative resin substrate
10
composed of glass epoxy, for example, is wet etched through a photolithography process and an inner layer circuit pattern
11
having a predetermined shape is obtained.
In FIG.
6
(
b
), a surface treatment such as blacking process is applied on a surface of the inner layer circuit pattern
11
. Insulative resin layer is formed on the insulative resin substrate
10
so as to cover the inner layer circuit pattern
11
by using a screen printing process or a curtain coating process, or by sticking a sheet material of insulative resin on the insulative resin substrate
10
. Consequently, an insulative layer
12
is obtained. A thickness of the insulative layer
12
is 20 to 90 &mgr;m. A blind hole, which reaches to the inner layer circuit pattern
11
, or a through hole, which passes through the insulative resin substrate
10
, is provided at a predetermined position on the insulative resin layer
12
.
In FIG.
6
(
c
), after roughening a surface of the insulative layer
12
with oxidizing agent, a copper layer is formed over the insulative layer
12
by the electroless plating method or electrolytic plating method, and then a conductive layer
13
is obtained. With respect to a degree of roughness on the surface of insulative resin layer
12
, an average roughness Ra in the center line is approximately 0.1 to 20 &mgr;m. Further, a thickness of the conductive layer
13
is from some &mgr;m to some tens &mgr;m.
In FIG.
6
(
d
), an outer layer circuit pattern
14
having a predetermined shape is obtained by forming the conductive layer
13
through the wet etching process by the photolithography. Consequently, a printed circuit board having two layers of circuit patterns can be obtained. Further, in a case of multi-layering circuit patterns, it is accomplished by repeating the above-mentioned processes shown by FIGS.
6
(
b
) through
6
(
d
).
An impedance of transmission line in the printed circuit board mentioned above is mainly defined by a thickness and permittivity of insulative resin layer, a thickness and width of conductive layer of the transmission line and a configuration of grounding. Particularly, a strip line and an impedance of micro strip line are affected by a thickness of insulative resin layer and a line width of transmission line.
FIGS.
7
(
a
) and
7
(
b
) are ideal structures of transmission line and show a micro strip line and a strip line respectively.
In the micro strip line shown by FIG.
7
(
a
), an impedance Zo1 of transmission line, which is composed of a first circuit pattern
1
for grounding, a first insulative resin layer
2
and a second circuit pattern
3
for signal formed over the insulative resin layer
2
, can be given by a following formula (1).
Zo1
=
60
ϵ
r
0.475
+
0.67
LN
5.98
h1
W
0.8
+
t
[
Ω
]
(
1
)
where “&egr;r” is a permittivity of the first insulative resin layer
2
, “h1” is a thickness of the first insulative resin layer
2
, “w” is a width of the second circuit pattern
3
for signal and “t” is a thickness of the second circuit pattern
3
respectively.
In the strip line shown by FIG.
7
(
b
), an impedance Zo2 of transmission line, which is composed of a first circuit pattern
1
for grounding, a first insulative resin layer
2
and a second circuit pattern
3
for signal formed over the insulative resin layer
2
, a second insulative resin layer
4
formed on the first insulative resin layer with covering over the second circuit pattern
3
and a third circuit pattern
5
for grounding, can be given by a following formula (2).
Zo2
=
60
ϵ
r
0.475
+
0.67
LN
5.98
h1
W
0.8
+
t
×
1
1
+
h1
h2ϵ
r
/
ϵ
r2
+
h1
[
Ω
]
(
2
)
where “&egr;r2” is a permittivity of the second insulative resin layer
4
and “h2” is a thickness of the second insulative resin layer
4
respectively. The other symbols are the same as those of the formula (1).
An RF of mobile communication terminal equipment such as a mobile telephone is mostly in a GHz band. An RF signal received by an antenna installed in the equipment flows through a circuit pattern for signal on a printed circuit board and is stepped down to some hundreds MHz in an intermediate frequency section. Finally the RF signal is stepped down to some tens MHz in a base-band. In order to obtain excellent receiving sensitivity of equipment, a transmission characteristic in a printed circuit board from an antenna to an intermediate frequency section is most important.
In order to prevent external noise deteriorating a transmission characteristic, a grounding line is provided in parallel to a circuit pattern for signal, which is a transmission line of printed circuit board. As shown in
FIG. 5
, a second circuit pattern
14
a
is formed above a first circuit pattern
11
a
for grounding being isolated by an insulative resin layer
12
provided between the first and second circuit patterns
11
a
and
14
a
. Circuit patterns
14
b
1
and
14
b
2
are provided along both sides of the second circuit pattern
14
a
in a predetermined distance.
On the contrary, the construction shown in
FIG. 5
is insufficient in a shielding effect, so that equipment installing the printed circuit board is easily affected by an external noise and causes inferior receiving sensitivity.
Generally, an electromagnetic field in a high frequency can penetrate into a shallower depth from a surface of conductive material due to a skin effect. Consequently, a high frequency current flows through a surface layer of metal. A skin thickness &dgr; of surface layer, where a high frequency current flows through, is given by a following formula (3).
δ
=
2
μ
σ
ω
=
1
π
f
σ
μ
[
m
]
(
3
)
where “&mgr;” is a permeability of conductive material, “&sgr;” is a conductivity of the conductive material and “&ohgr;” is an angular frequency of an electromagnetic field respectively.
A circuit pattern for signal to be a transmission line is composed of a copper layer. If a signal frequency is 1 GHz, a skin depth is approximately 2 &mgr;m. Consequently, it is apparent that a signal current just flows through a skin layer of circuit pattern.
FIGS.
8
(
a
) and
8
(
b
) are ideal drawings showing a current distribution of signal in a printed circuit board of the prior art. FIG.
8
(
a
) shows a current distribution of signal in a lower frequency. FIG.
8
(
b
) shows a
Ozeki Masahiro
Ryu Hiroyuki
Shindoh Motoshi
Alcala José H.
Connolly Bove & Lodge & Hutz LLP
Talbott David L.
Victor Company of Japan , Limited
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