Fatigue measurement setup under combined thermal and vibration loading on electronic SMT assembly

In the past vibration experiments have been conducted in the field of automotive, railway transportation, aerospace and other applications where electronics face dynamic mechanical loads. The tests were used to either qualify components or systems, analyse interconnect reliability or to research the fatigue behaviour of the involved interconnect materials. Dominant investigation has been in solder alloys. Field conditions of the named applications usually introduce coupled mechanical and thermal loads to electronics systems. Great efforts have been made to enable these conditions in the experimental environment and extract reasonable reliability results. However, experimental methodologies considering coupled vibration and temperature loads for qualification purpose, accelerated reliability testing or fatigue analysis lack for well-defined load conditions, ability of in-situ load measurement or unwanted behaviour of the experimental setup (e. g. deflection change or rigging due to temperature changes). In recent work we introduce an experimental setup which overcomes these drawbacks. A test vehicle and an associated mount as well as an in-situ measurement approach were developed and tested. This novel setup offers test vehicle clamping options which represent system conditions including rigging for qualification purposes or enable fatigue research which rely on constant rigging-free load conditions. The specimen is a standard PCB with mounted SMT components. Typically vibration will be done as a sine dwell with frequencies in the range of 50 Hz…1 kHz. The setup may be used for isothermal vibration experiments at room, lower or higher temperatures (e.g. -40°C or 125°C) but it enables vibrations experiments at temperature cycling conditions as well. A low weight mount and PCB design targeting temperature cycling with reasonable gradients of about 1 K/min. Combined with integrated PCB heaters even local component heating is enabled. Dependent on the temperature condition either optical or capacitive contact-free in-situ displacement or deflection measurements can be utilised. The latter is very important for small or low weight specimens since acceleration sensors usually add to much mass and strain gages are difficult to mount. Using the contact-free measurement systems high spatial and time measurement resolution can be achieved