Long-term and ageing tests
Long-term and ageing tests
In everyday use, printed circuit boards are exposed to various stresses such as heat and humidity. For many applications it therefore makes sense to test the longevity of the products.
During the reliability analysis in our laboratory, accelerated ageing processes are used to simulate how those influences actually affect the individual product properties of the printed circuit boards.
Development is a priority at KSG: we work with the supplier industry in numerous projects to adapt production processes and the materials used. The aim is to identify the complex relationships between the thermo-mechanical fatigue behaviour of through-hole plating and the manufacturing technologies as well as the process parameters and the materials used.
That is how manufacturing processes and technologies are optimised. A particularly efficient test method used by KSG since 2011 is in-situ resistance measurement in the temperature shock test. This results in rapid temperature changes – for example between -40 and +150°C within 30 seconds.
During the relocation of printed circuit boards from the cold chamber to the hot chamber of the automatic test chamber, thermo-mechanically produced cracks in the through-hole plating are enlarged. This procedure can also be used for microvias. The resulting increase in resistance is detected and linked to a failure criterion, e.g. 5 percent increase in resistance. This means that a very large number of holes can be checked very accurately and the results are always available.
The preparation of the microsections is no longer used to locate failed parts, but only for spot-testing depth.
In order to investigate and prevent migration phenomena under simulated operating loads, two high- performance insulation resistance measuring systems from LWS are available.
For SIR and CAF assessments, climate stresses in the range of 10-98 °C/10-90 percent relative humidity can be created. The measurement of leakage currents and insulation resistances for the evaluation of printed circuit board layouts under humid warm stress conditions with bias voltages between 10 and 1000V can be performed on 180 measuring channels in each case.
So a statistically validated number of printed circuit boards can be tested simultaneously for several test variants. The main causes of migration in addition to the PCB structure are the cleanliness of the manufacturing processes and the printed circuit board surfaces.
High-performance, microscopic methods with different imaging modes are used to characterise electrically detected defects for cause analysis.