Lifetime Estimation of a Bluetooth Module for Ubiquitous Systems

Information processing has been thought of as a key to ubiquitous systems. Operating systems composing ubiquitous systems are also important since ubiquitous systems do not provide desired performance when the operating systems fail. Bluetooth module becomes a critical item for these operating systems. Thus, accurate reliability estimation of the module under various environmental conditions is required for profitable ubiquitous system development. This paper shows quantitative reliability evaluation results of a Bluetooth module through extending previous qualitative methods limited to structure reliability tests and solder joint reliability tests for Bluetooth modules. Accelerated life testing (ALT) of the modules using temperature difference in temperature cycling as an accelerated stress was conducted for quantitative reliability evaluation under field environment conditions. Lifetime distribution parameters were estimated using the failure times obtained through the ALT, and then Coffin-Manson model was implemented. Results of the ALT showed that the failure mode of the modules was open and the failure mechanisms are both crack and delamination. The ALT reproduced the failure mode and mechanisms of failed Bluetooth modules collected from the field. Further, a quantitative reliability evaluation method with respect to various temperature differences in temperature cycling was proposed in this paper. BIO lifetime of the module for the temperature difference 70°C using the proposed method would be estimated as about 4 years.