Low-cost electrical measurement systems for reliability testing

As widely known the implementation of lead-free processes induced some thermo-mechanical disadvantages. Although a lot of components do have lead-free interfaces, they are not qualified for the standard lead-free reflow soldering process due to the high peak temperatures during the soldering process. Those components have to be processed by special soldering processes like selective soldering, manual soldering or with low melting solder pastes, which leads to quite expensive and time-consuming processes. Affected components are inductors, capacitors, blue tooth antennas, relays, active components like older microprocessors and high brightness LEDs. Supported by leading members of the German organization ZVEI, we set up together with nine industrial partners and two Fraunhofer Institutes the public funded project TDMA - Thermal induced Damage Mechanisms on electronic Assemblies and deduction of operational alternatives. As an initial investigation the project partners chose some 30 different critical components and developed two test boards for processing these components (see Fig. 1) with four different solder pastes and four different soldering profiles. After an initial 100% inspection according to the production processes the test boards have been brought into temperature cycling tests (1,000 cycles -40°C / +125°C). During inspection stops after 100, 250, 500 & 1,000 cycles all boards have been inspected optically, electrically, by X-ray inspections and partly by Scanning Acoustic Microscopy (SAM) to find and investigate structural damages of components and/or solder joints. In addition, to get immediately informations about electrical degradation the project team at the Technische Universität Dresden developed together with the industrial partners three measurement systems for that task discussed in the next sections.