A new test technology for package, module and PCB interconnects

This paper discusses an application of a new testing method, Thermal Transmission line Testing (T/sup 3/) for dense packaging interconnects based on measurements of transient thermal signatures along the circuits. The T/sup 3/ methodology has several advantages over current electrical test systems that require numerous built-in module test points and special interconnect probe fixtures designed to reduce their influence on the measurement. The T/sup 3/ system consists of a low power laser, providing a heating pulse to the circuit, together with an IR camera which detects and measures the thermal pulse propagating down the interconnect conductor. The measurement is non-contact, requiring no special interconnect probes. Furthermore, the thermal tests are locally self isolating, meaning that it doesn't matter if the circuit under test is properly terminated or not, since the low power thermal signal decays rapidly. The application of the T/sup 3/ interconnect evaluation technology discussed is the estimation of the contact resistance of TAB Inner Lead Bonds (ILB) and a comparison of these estimates with the subsequent pull test analyses of the leads. A negative trend of ILB contact resistance with bond pull strength is indicated.