A new test technology for package, module and PCB interconnects

This paper discusses an application of a new testing method, Thermal Transmission line Testing (T³) for dense packaging interconnects based on measurements of transient thermal signatures along the circuits. The T³ 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 T³ 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 T³ 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