SMTA International Conference Proceedings


The Necessity of Temperature Humidity Bias Testing with High Voltages = 1000 V

Authors: Erik Biehl, Joachim Hink, Cindy Chak, Noel Jones, Sebastian Maass
Company: Robert Bosch GmbH, Automotive Electronics, Robert Bosch Company Ltd., Robert Bosch Pty. Ltd.
Date Published: 9/17/2017   Conference: SMTA International


Abstract: At present there is an increase in the use of partial or full drive electrification in vehicles. Together with electrification, higher current and voltage is also anticipated for the printed circuit board (PCB) of the control unit. Around 500 V is currently being used in the area of hybrid and fully electric vehicles and there is a reasonable expectation that operating voltages will race up to the 1000 V range over the coming years. Operation time is also likely to increase since the control units of today’s vehicles are only under voltage during driving. In the future cars with electric drive may have applied voltage during parking/standby. This shift will increase operation time from 6000 – 8000 h to 87,600 – 131,400 h (10 – 15 years voltage always on e.g. guard circuit) over the life of the product.

Today all temperature humidity bias testing of PCBs e.g. IPC-TM 2.6.25A “Conductive Anodic Filament (CAF) Resistance” are related to voltages of up to 100 V. Voltages greater than 100 V are not fixed in any of the standards as a testing voltage. However, IPC-TM 2.6.25A does also state, that the bias voltage shall be two times higher than the operation voltage of the PCB for a correlation between testing and field. The life time equation from IPC 9691A indicates that isolation distances need to be increased according to voltage that is used. This equation is only valid for the failure mechanism from the formation of conductive anodic filaments (CAF).

This study introduces an approach with increased voltages up to 1000 V and test durations for existing test conditions such as 85º C / 85% RH to accommodate for this increase in demand from the product application and to take into account additional failure mechanisms that could become prevalent from the increased loading conditions.



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