Electrical approach to nondestructive analysis on WB-PBGA with TDR technology

Time Domain Reflectometry (TDK) is a powerful measurement technique that uses the reflection of a pulse sent down a transmission line to characterize the impedance of that line. The voltage of a reflection will vary depending on the distance to the fault and on the amount of energy reflected. In this paper we develop a simple and effective electrical nondestructive analysis (NA) system for the evaluation of the interconnection of wire-bonded plastic ball grid array (WB-PBGA) package. An open-end fixture (OEF) was employed to connect fast rising edge signals to the package which was monitored for its time delay and reflection voltage parameters. This technology represents a valuable new method for the NA of WB-PBGA packages, and it has enabled the rapid and efficient detection and location of faults. Comparative TDR measurements accurately predicted the location of opens and short circuits in the copper traces of the substrate, bond wire, and solders balls. The TDR analysis was verified by using X-ray analysis. The paper establishes the use of a TDR system incorporating an open-end fixture for locating opens and shorts in WB-PBGA packages.