Ultra small hearing aid electronic packaging enabled by chip-in-flex

There has been enormous worldwide effort to increase the volumetric efficiency of electronic packaging. Much of this effort has been driven by the telecommunications industry that has succeeded in reducing cell phone size while simultaneously increasing functionality. The hearing aid business has always had the need to use extremely small electronic packaging because hearing aids pack electronics into the ear canal. In fact, in 1952 the first commercial device to make use of transistors was the hearing aid. In recent years hearing aid microelectronic packaging has been moving from ceramic hybrid-based packaging to flexible circuit based technologies. The introduction of wireless systems in hearing aids has sharply increased component count from less than 20 per device in 2005 to more than 70 in 2010. Due to the size and shape of a multitude of types of hearing aids, flexible circuits need to be folded and bent to fit inside hearing aid cases. All available space is essentially used. Additionally, more powerful processors and more memory are enabling sophisticated algorithms that are able to greatly improve sound quality. There continues to be a strong marketing desire to add more features to hearing products while at the same time making them smaller and less visible. These added features are further increasing component count and are the driving force behind the need to make smaller electronic assemblies. This paper will examine the use of embedded die packaging (or chip-in-flex) to drive significant further size reduction in custom and standard hearing instruments over what can be achieved using chip-on-flex or ceramic hybrid based technologies. The performance improvement, size reduction, changes in supply chain, impact on wafer test, impact on device test and challenges of working with wafers instead of die will be discussed. This paper will also discuss the results of extensive reliability testing including accelerated aging, thermal shock, pad integrity, drop- tests, moisture sensitivity, ESD testing, light sensitivity and hearing aid assembly solder simulation testing.