This invention relates to a probe device for testing high speed integrated circuits such as amplifiers, microprocessors, signal processors and memories as well as circuit boards which may include integrated circuits and/or other electronic elements.
Testing of integrated circuits (IC""s), also called chips or dies is an important part of the design and manufacture of the circuits. Advantageously, initial testing is performed while the chips are still held together as parts of a semiconductor slice or wafer. If the testing shows that the design or the process employed to manufacture the chips is faulty then the design or manufacturing process can be altered to produce the desired result.
The development of higher speed integrated circuits has required the development of new testing techniques. In particular, the use of ordinary wire probes to make connection between the chip and the testing apparatus can no longer be employed because the wire probe inductance produces undesirable large voltage transients as the probe currents change during testing and capacitive and inductive coupling between probe wires generate extraneous signals that confuse the test results. There are essentially six separate functions that should be performed to accurately and reliably test high speed integrated circuits:
1. The probe wires carrying high speed signals should be shielded from one another as much as practicable to minimize coupling between the probe wires.
2. The probe wires carrying high speed switching currents should be low inductance to minimize current induced voltage transients.
3. The probe tips should have mechanical compliance to allow each individual probe tip to move independently of the others to assure reliable contacts in the presence of unavoidable small variations in the placement of the probe tips and unavoidable nonplanarity of the slice or probe mounting during testing.
4. The probe tips that contact the circuit to be tested should be small in size so that chips with closely spaced test pads may be tested.
5. The probe apparatus should be mechanically durable for long lasting reliable operation.
6. The connections between the probe assembly and the testing apparatus should be effected with minimal degradation of the testing signals.
Satisfactory solutions to many of the above requirements that have enjoyed considerable commercial success are disclosed in U.S. Pat. No. 4,871,964 issued Oct. 3, 1989 and U.S. Pat. No. 5,373,231 issued on Dec. 13, 1994 and assigned to the same assignee as the present invention. However, when the application requirements are not so stringent we seek a less expensive structure.
The invention disclosed here describes apparatus that meets the above requirements and is advantageous in that it is simple and inexpensive to construct and is an extension of a well-developed technology. Possible disadvantages are that the probe assembly may not be as high speed and the probe tips may be less mechanically compliant than the aforementioned solutions. However, for a large number of probe testing applications the new apparatus is expected to be superior due to lower cost and it is expected to be very rugged and allow smaller probe tip separation.
Although this invention is primarily directed toward testing of integrated circuits while still part of a semiconductor slice, the apparatus may also be adapted for testing larger structures such as printed circuit boards or ceramic substrates that may include packaged or unpackaged integrated circuit chips.
This invention describes novel electronic probe apparatus for testing integrated circuits in which a prior art epoxy probe card is modified to include electronic components such as capacitors, inductors, resistors, transformers and/or active elements such as transistors, amplifiers or analog to digital converters. In addition, some of the probe wires are surrounded with an insulating layer and an outer conductive sheath to form coaxial cables for the transmission of high speed signals. The probe apparatus may include novel probe structures consisting of an electrically insulating shank with an electrically conductive tip for testing those parts of a chip that require very low capacitance and/or high impedance testing. A relatively large area conductive layer over the top and/or the bottom of the probe card serves as a ground plane to reduce the coupling between adjacent probe wires and to reduce the coupling between the probe wires and any external circuitry.