Blade-like connecting needle

Details Blade-like connecting needle Blade-like connecting needle

2002-02-12

2004-04-06

Karlsen, Ernest F. (Department: 2829)

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of individual circuit component or element

C324S754090

Reexamination Certificate

active

06717426

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a blade-like connecting needle for use on a probe card as a probing equipment or a contact probe for connecting a measuring unit to a semiconductor wafer for making measurement on the semiconductor wafer, and more particularly to a blade-like connecting needle for use on a probe card, which is capable of stably and greatly reducing a measurement waiting time that serves as an important factor in measuring a small current.
2. Description of the Related Art
One conventional probe card is shown in the plan in view of
FIG. 10
among the accompanying drawings, and a portion of the conventional probe card for connection to a semiconductor wafer is shown at an enlarged scale in
FIG. 11. A
current measurement signal electrode and a guard electrode which extend from a measuring unit are connected downwardly to respective pads A and B shown in
FIG. 11
via pogo pins. The pad A is electrically connected to pads F and G, but insulated from the pad B, which is positioned outwardly of the pad A. A signal line connected to the pad A extends via a cable to a needle mount area D, where it is connected to a probe needle of certain shape. The probe needle is connected to desired electrodes on a semiconductor wafer. The needle mount area D generally has single-core needles, coaxial needles, or blade-like connecting needles.
FIGS. 12 through 15
of the accompanying drawings show conventional blade-like connecting needles at an enlarged scale in the needle mount area D on the probe card shown in FIG.
11
.
FIGS. 14 and 15
show in perspective one of the conventional blade-like connecting needles as viewed from respective opposite sides. Signal lines
114
(
FIG. 12
) from the measuring unit are connected to blade signal lines
111
shown in
FIG. 15
, which are connected to signal patterns
120
on tip ends of the blade-like connecting needles. The signal patterns
120
are connected by soldering to respective probes
116
that are held in contact with desired electrodes on a semiconductor wafer. In
FIGS. 14 and 15
, guard patterns
112
(
112
a
,
112
b
,
112
c
) are disposed to cover substantially entirely two faces
112
b
,
112
c
and a portion of one face
112
a
of the blade-like connecting needle. The guard pattern
112
b
, which may be viewed as a bottom surface of the blade-like connecting needle, is fixed by soldering to the needle mount area guard pattern
113
(
FIG. 12
) on a probe card
117
. The blade-like connecting needles are held in one-to-one correspondence to channels of the measuring unit. If counter measures against problems associated with small currents and noise are required, the patterns
112
are provided between the blade signal lines
111
and another potential, and connected to the respective pads B (FIG.
11
). The guard patterns
112
may extend from one side of a blade body
115
which is made of an insulating material, on which the signal line
111
is placed, to an opposite side of the blade body
115
. The guard patterns
112
serve to prevent a current from flowing from or into the signal lines
111
to another potential via the surface of the probe card substrate insulator
117
, for example.
Preferably, an active guard whose potential is maintained at the same level as the potential of the signal line
111
is usually used as the guard, no signal current leaks from or into the signal line via the guard patterns to or from another potential. Any dielectric absorption due to the insulator between the signal line and the guard does not occur because the potential difference is nil. Therefore, the measurement of a small current can instantaneously be started when a certain voltage is applied to the signal line.
Even when a passive guard for fixing the guard potential to a certain fixed potential at all times is employed, some advantageous effect can be expected. As shown in
FIG. 12
, as “another patnetial” to a particular signal line, the lower guard pattern belonging to an adjacent signal line channel, and, in addition, many signal lines, guard patterns, and patterns providing other potentials are present at a high density.
As can be seen from
FIG. 12
, the signal line
111
is disposed and exposed on the surface of the blade body
115
in the conventional structure. If a small current on the order of fA is to be measured, a measurement waiting time is long because of a dielectric absorption current caused by the insulator between the signal line and the other potential pattern having a different potential. In the presence of a capacitive coupling to other potential patterns, a longer measurement waiting time is needed due to the time required to charge the capacitance. The capacitive coupling should desirably be eliminated in view of possible fluctuations of other potentials and a possible superposition of noise.
Japanese laid-open patent publication No. 8-330369 discloses an attempt to place the needle mount area D in a lower trenched position for preventing different potential present in other parts of the system from being directly “seen” by the signal line, and to position guard patterns on side faces of the trench. The disclosed attempt provides good results. However, since the disclosed attempt requires complex processing on the probe card substrate insulator
117
, it is difficult and costly to produce a high-density blade package.
The above characteristics will be described on the basis of an equivalent circuit. An equivalent circuit of the structure shown in
FIG. 12
is illustrated in FIG.
16
. For the sake of brevity, a dielectric absorption term is modeled by a linear approximation. As also shown in
FIG. 15
, a signal line terminal
60
in
FIG. 16
corresponds to the signal line
111
, a guard terminal
62
to the guard patterns
112
(
112
a
,
112
b
,
112
c
), and a terminal
64
having a different potential to an adjacent channel pattern. For an active guard, since the signal line terminal
60
and the guard terminal
62
are always held at the same potential, they may be considered as being short-circuited. Thus, only the other potential terminal
64
corresponding to the adjacent channel pattern may be considered from the terminal
60
. It is assumed that the terminal
64
of differing potential has a certain constant potential and the potential of the signal terminal
60
changes stepwise with respect to the potential of terminal
64
. Since the charging and discharging of a capacitive component C
3
is finished instantaneously, it does not pose any problem on a settling time. However, the time constant of a resistive component R
4
and a capacitive component C
4
, which represents a dielectric absorption term, generally shows a large value of several tens of seconds, it takes a very long period of time to measure a small current until an error current value falls into an allowable range. For example, when the terminal voltage of the conventional blade changes by 10 V, it occasionally takes several tens of seconds until the error current value due to the dielectric absorption term falls into a range of the order of fA. Required settling times differ greatly depending on the position of the blade-like connecting needle and the manufacturing lot thereof because of variations in insulator materials. In addition, since the insulator characteristics greatly vary depending on the environmental conditions (temperature and humidity), pollution, etc., the insulator may have poor weather resistance and poor environment resistance. The conventional probe card (a combination of a probe card blank board, wiring cables, and blade-like connecting needles) has been problematic because its specification needs to have a large margin against material variations and environmental conditions. Japanese patent application No. 2000-036636 (Japanese laid-open patent specification No. 2001-231195) reveals an invention relating to a probe card blank board that is improved to solve the above problems and provide substantially ideal characteristics. Therefore, blade-like

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