Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2001-06-22
2002-06-04
Le, N. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S762010, C029S828000
Reexamination Certificate
active
06400168
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high-frequency probe having a signal line which has a fore end pressed against a signal electrode of a device-under-test (abbreviated to DUT hereafter) to be measured, and a rear end connected to a connector for connection to an external measuring instrument.
The present invention especially relates to a high-frequency probe for use in measurement of a DUT, which is placed on a device stage establishing electrical connection with a ground electrode of the DUT and serving as a ground electrode and which has a number of signal electrodes arrayed with a narrow pitch. More particularly, the present invention relates to a tip portion structure of a high-frequency probe and a method of fabricating a probe tip portion, which can provide contact with the signal electrodes and electrical characteristics with higher reliability and more stability.
2. Description of the Related Art
Hitherto, as illustrated in
FIGS. 1A and 1B
, a high-frequency probe
100
of the above-mentioned type comprises a body block
110
, a tip portion
120
, and a connector
130
. A coaxial cable
111
penetrating the body block
110
is connected to the connector
130
for electrical connection which connects an external measuring instrument and the tip portion
120
brought into contact with signal electrodes of a DUT to be measured.
Further, as illustrated in
FIG. 2
, the tip portion
120
comprises a signal contact lead
121
and two ground contact leads
122
, each of which has resiliency. The ground contact leads
122
are arranged side by side on both sides of the signal contact lead
121
and on substantially the same plane normal to a direction in which the conductors bend due to resiliency. Thus the signal contact lead
121
and the ground contact leads
122
are formed in a coplanar structure.
Usually, the signal contact lead
121
at the center serves as a contact lead for a signal and is brought into contact with a signal electrode
211
of a DUT
210
. On the other hand, the ground contact leads
122
on both sides of the signal contact lead
121
serve as ground contact leads and are brought into contact with ground electrodes
212
of the DUT
210
.
In case that the probe tip portion has such a conductor array structure, the DUT is limited to a coplanar type device wherein signal electrodes and ground electrodes are arranged on the same plane and with the same pitch as conductors arranged in a tip portion of a high-frequency probe.
A large surface area is required in the device of the above-mentioned type having two ground electrodes arranged on both sides of one signal electrode and on the same plane. For compound devices obtained from a wafer of gallium arsenide (GaAs), in particular, the wafer cost is higher than that of a silicon wafer. Therefore, a reduction in the number of devices obtained from one piece of wafer considerably pushes up the device cost. Accordingly, a mass-produced device is constructed such that ground electrodes are not disposed on the same plane as a signal electrode, and uses its backside surface as a ground electrode. In addition, a chip area is reduced and a wafer thickness is thinned to cut down the device cost and to ensure a desired high-frequency characteristic.
In a case that the conventional high-frequency probe described above is employed to measure a DUT of such a structure that the backside surface entirely serves as a ground electrode, any contact between electrodes of the DUT and contact leads of a probe tip portion cannot be achieved. Accordingly, the measurement is performed for the DUT mounted on a board. In this case, the board has measuring electrodes arranged with the same pitch as the contact leads of the high-frequency probe, and the high-frequency probe can be connected to the board.
Also, in the probe having the above tip portion structure, pressing forces are applied to the electrodes of a DUT in an unstable condition because the probe contact leads are pressed against the DUT electrodes with any one electrode serving as a fulcrum. Such an unstable condition may damage the contact lead ends of the probe due to application of an excessive pressure.
The conventional high-frequency probe described above has therefore problems as follows.
The first problem is that the measurement is very difficult or impracticable when the signal electrode and the ground electrodes of the DUT to be measured are not arranged on the same plane.
The reason is because the contact leads of the probe are arranged side by side on the same plane for making contact with the DUT electrodes. Further, because the contact leads of the probe has the pitch in match with the array pitch of those DUT electrodes, the contact leads cannot contact with DUT electrodes having other structures not in match with that pitch.
The second problem is that, in a case of the DUT not having a coplanar structure, a measuring board must be prepared and the measurement requires time and labor.
The reason is because the above-described high-frequency probe has the signal contact lead and the ground contact leads which are of the coplanar structure. In other words, for a measuring DUT of any structure different from the coplanar type, a measuring board is necessary and the DUT being measured requires to be mounted and dismounted to and from the measuring board. For the DUT having a structure wherein a number of signal electrodes are arrayed with a narrow pitch, particularly, a lot of time and labor are taken for wiring job.
The third problem is that a sufficient contact pressure is not obtained in a case that the contact lead of the probe is pressed against the electrode of the DUT for measurement. Thus resulting is in instability in measurement of electrical characteristics, and the contact lead of the probe is susceptible to damage.
The reason is because the above-described high-frequency probe has the structure wherein the contact lead contacts the signal electrode of the DUT under measurement and bends at a freely-suspended end. Also, because a pressing force is exerted on the contact lead of the probe to bend its end about a fulcrum positioned on the contact lead, it is difficult to adjust the pressing force. Stated otherwise, the pressing force must be somewhat moderated in view of such a risk that damage may occur at the end of the contact lead if the pressing force is intensified to make stable measurement.
The fourth problem is that the DUT has an increased area and the product cost is increased.
The reason is because, for measuring a DUT by the above-described high-frequency probe, ground electrode of the DUT requires to be arranged on both sides of a signal electrode thereof on the same plane in the same positional relationship as that between a signal contact lead and ground contact leads of the probe. In other words, because a surface area of the DUT is increased, the number of DUTs produced from one piece of wafer is reduced. The fourth problem is particularly remarkable in a case that the DUT is a compound device of gallium arsenide being more expensive than silicon.
Meanwhile, U.S. Pat. No. 5,506,515 discloses a simplified structure of the tip portion of the high-frequency probe of the above-described type. The disclosed structure of the tip portion of the high-frequency probe is illustrated in FIG.
3
. In the figure, a coaxial cable
140
has a cross section surface at its end and comprises a coaxial inner conductor, a coaxial outer conductor, and a dielectric interposed between both the conductors, which are in a concentric relation.
Specifically, the coaxial cable
140
comprises three concentric parts, i.e., a coaxial inner conductor
141
at the axial center, a coaxial outer conductor
142
at an outer periphery, and a dielectric
143
interposed between both the conductors
141
and
142
. The end of the coaxial cable
140
is cut perpendicularly to the coaxial direction to provide a cross section portion
144
. A central contact lead
151
is fixedly connected to the coaxial inner conductor
Hayakawa Satoshi
Inoue Hirobumi
Matsunaga Kouji
Nikaidou Masahiko
Tanehashi Masao
Deb Anjan K
Foley & Lardner
Le N.
NEC Corporation
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