Bare or unpackaged semiconductor dice are used extensively in the manufacture of electronic devices. Known-good-die (KGD) is a collective term that connotes unpackaged dice having the same quality and reliability as the equivalent packaged product. The demand for known-good-die has led to the development of test procedures for testing unpackaged semiconductor dice.
For test and burn-in of an unpackaged die, a carrier replaces a conventional single chip package in the testing process. The carrier typically includes an interconnect element that allows a temporary electrical connection to be made between the die and external test circuitry. In addition, such a carrier must allow the necessary test procedures to be performed without damaging the die. The bond pads on a die are particularly susceptible to damage during the test procedure.
Recently semiconductor manufacturers have developed carriers for testing discrete, unpackaged die. Different types of carriers are disclosed in U.S. Pat. No. 4,899,107 to Corbett et al. and U.S. Pat. No. 5,302,891 to Wood et al., which are assigned to Micron Technology, Inc., and in U.S. Pat. No. 5,123,850 to Elder et al., and U.S. Pat. No. 5,073,117 to Malhi et al., which are assigned to Texas Instruments.
One of the key design considerations for a carrier is the method for establishing a temporary electrical connection with contact locations on the die. These contact locations are typically pads such as bond pads or test pads located on the face of the die. With some carriers, the die is placed face down in the carrier and biased into contact with an interconnect. The interconnect contains the contact structure that physically contacts and forms an electrical connection with the die pads. Exemplary contact structures include wires, needles, and bumps. The mechanisms for making electrical contact include piercing the native oxide of the die pad with a sharp point, breaking or burnishing the native oxide with a bump, or scrubbing the native oxide with a contact adapted to move across the die pad.
These different contact structures are designed to establish an electrical connection with the bond pads of a die under test. Preferably this connection is low-resistance and ohmic. Low-resistance connotes a resistance that is negligible. An ohmic connection is one in which the voltage appearing across the connection is proportional to the current flowing for both directions of current flow. In the past it has been difficult to establish a low-resistance ohmic connection with bond pads while minimizing damage to the pads. A bond pad may only be about 1.mu. thick and is thus relatively easy to damage. In general, each of the above noted contact structures will displace the bond pad metallization and damage the pad.
In addition to forming a low-resistance ohmic connection, it is also desirable for a contact structure to be compliant in nature. Sometimes an arrangement of bond pads may present a sloped or irregular surface topography. This may be due to the mounting arrangement of the die in the carrier or to the uneven topography of the bond pads across the surface of the die. It is thus advantageous to form the interconnect with compliant contacts adapted to conform to the vertical location of the bond pad. In a similar manner, it is desirable for the contact to possess a resiliency which permits it to return to its original position for reuse.