Reliability investigation of SMT-boards for the automotive industry

One important demand for car electronics is a high reliability! Especially a high range of surrounding conditions (especially temperature) is a challenge for electronics in automotive! The solder joints are one important part! The following questions are exists: • Which materials (PCB-Finish, Solder Paste,…) are fulfill this challenges ? • What about different types of packages? • Which test procedures are able to characterize the reliability? The Ishikawa Diagram (see Figure 1) visualizes the dependencies between the responses (especially the reliability and the shear force in this case) and the related factors. A main goal of this research work is the determination of these dependencies. The investigation was conducted in a cooperation between the companies Hella, Heraeus and the Technical University of Dresden. A test layout was designed on the basis of typical components for this application and put into effect both as a circuit board (with relevant materials for high temperature applications) with 3 surfaces, in the case of chemical Tin with two circuit board thickness, and also in the form of thick film applied to ceramic substrates. Solder pastes with a flux system designed for the lead-free soldering process, three lead-free alloys and also a conductive adhesive of silver were used as joining materials, i.e. filler materials. A Sn63 alloy was used as reference. In total 784 circuit boards and 224 aluminum substrates were assembled with 238 components each, making a total of 239,904 components, in order to use these for further tests. The test criteria were four different high temperature exposures (HT exposure) and exposure in a warm, humid environment 85/85 up to N=1000. For the evaluation, 0 Ohm resistances, shear strengths and metallographic sections were examined on selected and predetermined components after cyclical sampling. The recorded data were statistically evaluated and the results are discussed. The main tool for this evaluation is the Analysis of Variance (ANOVA).