Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
1999-10-14
2001-07-17
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S763010, C324S765010, C324S711000, C324S538000
Reexamination Certificate
active
06262580
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to a method and a testing system for measuring contact resistance. More particularly, the invention relates to a method and a testing system used for measuring contact resistance of pins of an integrated circuit.
2. Description of the Related Art
In the conventional method for measuring a contact resistance, for example, an open/short circuit method, a voltage of a device is measure while applying the device with a direct current. In
FIG. 1
, the circuit diagram for a conventional method to determine whether the contact is good or poor is illustrated. In the circuit, a current flows into an integrated circuit chip
100
from a voltage input source
120
. The testing device
150
(a probe) extracts a certain amount of the current from a signal pin
110
, while the voltage difference is measured across the signal pin
110
and the voltage input source
120
. Using the voltage input source
120
as a reference standard, that is, assuming the voltage input source
120
is at a level of 0 volt, if the signal pin
110
has a voltage level between −0.3 volt to −1.5 volt, the signal pin
110
is determined to be a good contact. Otherwise, beyond this range, the signal pin
110
has a bad contact.
As shown in
FIG. 1
, the voltage difference across the signal pin
110
and the voltage input source
120
is equivalent to a voltage across a diode
130
of about 0.7 volt. If the voltage input source
120
has a voltage level of 0 volt, the pin signal
110
then has a voltage of −0.7 volt that falls within the normal operating range (−0.3 to −1.5 volt).
Typically, the amount of the extracted current is as small as about 100 micro-amperes (&mgr;A). Thus, even if the signal pin
110
is in bad contact with the probe
150
to form a non-Ohmic contact, that is, there is a voltage drop across the contact, or when the contact resistance is high, the open/short circuit test might still pass. As a result, the integrated circuit fails in the function test.
For example, while the extracted current is 100 micro-amperes, and the contact resistance is 900 Ohms (&OHgr;), the voltage drop is only 0.09 volt. The variation is about 12.86%. Plus the original voltage difference of 0.7 volt, the total voltage difference is 0.79 which is still within the tolerable range. Therefore, the signal pin with a contact resistance as high as 900 Ohms passes the open/short circuit test. However, this high contact resistance may cause error results while performing the function test.
As described above, the conventional circuit or method to measure the contact resistance has a very low sensitivity according to the contact resistance. Therefore, even with a bad contact of the pin, it can still pass the open/short circuit test but fails in the function test to cause an error.
SUMMARY OF THE INVENTION
The invention provides a testing system for measuring a contact resistance of a signal pin on an integrated circuit comprising the signal pin, a voltage source pin and an internal circuit. The testing system comprises a testing circuit and a tester. The testing circuit comprises an RC circuit coupled to the signal pin and the voltage source pin and two switches to control the on/off states of the testing circuit. The tester comprises a voltage source and a channel, wherein the voltage source is coupled to the RC testing circuit and the channel is coupled to the signal pin.
In the above structure, an RC circuit is coupled to both the tester and the integrated circuit. With the addition of the RC circuit, even if the contact resistance is very small, the voltage level with this contact resistance experiences an RC effect which can be easily observed. Therefore, the problems occurring in the conventional circuit are resolved.
The invention further provides a method of testing the contact resistance of a pin on an integrated circuit. An RC circuit is provided. A diode with a voltage level equivalent to a voltage drop across an internal circuit of the integrated circuit is added to the RC circuit. A testing signal is input to the RC circuit with the diode. A reference voltage level V
1
of a reference response signal to the testing signal is obtained. The integrated circuit is coupled with the RC circuit via the signal pin and a voltage source pin on the integrated circuit. The testing signal is input to the voltage source pin through the RC circuit. A voltage level V′ of a response signal obtained at the signal pin is measured. The voltage level V′ is compared to the reference voltage level V
1
to obtain a difference in voltage that reflects the magnitude of contact resistance of the signal pin.
In addition, the method may also include steps of inputting the testing signal to the RC circuit without the diode and obtaining the voltage level V″ of the response signal. The voltage level V″ gives an indication of the operating status of the internal circuit.
Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
REFERENCES:
patent: 5557209 (1996-09-01), Crook et al.
patent: 5631572 (1997-05-01), Sheen et al.
patent: 5696451 (1997-12-01), Keirn et al.
patent: 6008664 (1999-12-01), Jett et al.
patent: 6097203 (2000-08-01), Parker et al.
patent: 6104198 (2000-08-01), Brooks
patent: 11101849A (1997-09-01), None
Brown Glenn W.
Hamdan Wasseem H.
Thomas Kayden Horstemeyer & Risley LLP
United Microelectronics Corp
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