Unpackaged or bare semiconductor dice are used to construct multi chip modules (MCMs) and other electronic devices. Unpackaged dice must be tested and burned in during the manufacturing process to certify each die as a known good die. This has led to the development of temporary packages that hold a single bare die for testing and burn-in. The temporary packages provide the electrical interconnection between the test pads on the die and external test circuitry. Exemplary temporary packages are disclosed in U.S. Pat. Nos. 5,302,891; 5,408,190 and 5,495,179 to Wood et al., which are incorporated herein by reference.
Typically, this type of temporary package includes an interconnect having contact members that make a temporary electrical connection with the test pads on the die. The temporary package can also include a force applying mechanism that presses the die against the interconnect. For example, in the above cited patents the force applying mechanism can include a clamp mechanism that attaches to a package base, and a spring that presses the die against the interconnect.
Typically, the interconnect for the temporary package includes a substrate wherein the contact members are formed. One type of interconnect is formed of silicon and includes raised contact members formed as etched pillars having penetrating projections. The penetrating projections are adapted to penetrate into the bond pads on the die to form a temporary electrical connection for testing. A conductive layer overlies each raised contact member and is in contact with a conductor (e.g., metal trace) formed on the substrate. The conductors can be wire bonded, or otherwise electrically connected, to corresponding external contacts on the base of the temporary package. This type of interconnect is described in U.S. Pat. No. 5,483,741 to Akram et al., which is incorporated herein by reference.
Another type of interconnect includes a substrate and microbump contact members mounted on the substrate. The substrate in this case can be silicon, or a low CTE material such as ceramic or glass. The microbump contact members and conductors can be in the form of a flexible tape similar to two layer TAB tape. This type of interconnect is described in U.S. Pat. No. 5,487,999 to Farnworth, which is incorporated herein by reference.
In general, the electrical characteristics of the interconnects can have an affect on the die test procedure. In particular, the electrical characteristics of the contact members and the conductors can have a profound affect on the test procedure. Significant electrical parameters include the resistivity of the contact members, the resistivity of the conductors, the contact resistance at the interface of the contact members and conductors, and the capacitance between the conductors and the substrate. In order for the interconnect to provide valid test data, the value of these electrical parameters must fall within relatively narrow ranges.
Defects in the interconnect can also have an affect on the electrical characteristics of the interconnect. For example, an insulating layer that insulates the conductors from the substrate can be defective allowing current to leak from one or more conductors into the substrate. The substrate can also include cracks that propagate through the insulating layer creating undesirable electrical paths in the assembled temporary package.
These types of defects can be present as a result of the fabrication process for the interconnect. Also, since the interconnects are designed to be reused many times, defects can arise as a result of continued usage of the interconnects. For example, the interconnects are repeatedly stressed by the force applying mechanism of the temporary package which biases the die and interconnect together. In addition, the interconnects are repeatedly subjected to thermal cycling in a burn-in oven.
In view of the foregoing, it would be desirable to have a method for evaluating the electrical characteristics of interconnects used to test bare semiconductor dice.
Accordingly, it is an object of the present invention to provide a method for testing interconnects for bare semiconductor dice using test structures formed on the interconnect.
It is yet another object of the present invention to provide an improved interconnect for testing semiconductor dice having various test structures formed thereon for evaluating various electrical characteristics of the interconnect.
It is a still further object of the present invention to provide a method for fabricating test structures for interconnects for bare semiconductor dice.
Other objects, advantages and capabilities of the present invention will become more apparent as the description proceeds.