Fan-Out Wafer Level Packaging - A Platform for Advanced Sensor Packaging

As mobile devices have become ubiquitous, also a large number of integrated sensors have entered our daily life. And with every new generation of mobiles the number of sensors increases, forming a growing market. Applications range from consumer to automotive and industrial up to biomedical. Especially in the era of Internet of Things (IOT), of smart manufacturing or of autonomous driving highly integrated and low cost sensor packaging solutions are required. Fan-out Wafer Level Packaging (FOWLP) is currently the hottest packaging trend in microelectronics - offering opportunities for a miniaturized system integration with multiple die packaging and 3D integration as well as packaging of stress sensitive components or sensors where a direct access to the sensing surface is needed. MEMS pressure sensors are used in a wide variety of applications with a still growing market share. Packaging challenges come from the stress sensitive and fragile membrane and the necessity for direct media access to this membrane. Low pressure compression molding as used for FOWLP seems to be a suitable choice for encapsulation. The access to the sensor membrane then can be managed by removing the RDL above the membrane. However, depending on membrane type, a protection of the membrane during processing might be mandatory, especially during assembly, molding and debonding. Here, different approaches to protect such delicate structures will be introduced. Gas sensors used for air quality measurement as well as early fire detection have similar demands as MEMS sensors. The integration of particle and humidity barrier protection layers will be also discussed here. Another challenging market are bio-medical sensors. Point of Care devices for medical applications are becoming more and more widespread. Besides the described challenges for biomedical sensor also the question arises when the sensor die will be functionalized for detection of e.g. biomarkers as this functionalization is typically not temperature stable. The planar FOWLP packaging approach offers also the direct integration of a microfluidics on top. Optical sensors as e.g. proximity or image sensor are also a suitable application for FOWLP also due to the planar packaging and direct accessibility of component surfaces. 77 GHz automotive radar modules are another example which is already introduced in volume manufacturing using the advantage of very short and low inductance interconnects in FOWLP as well as the possibility of integrating antennas on package. Packaging cost could be lowered when moving from wafer to large area panel level packaging. One example here is the fingerprint sensor packaged on panel from Nepes which is ready for high volume manufacturing. An example of gas sensor packaging on panel will also be given in the paper. In summary the paper will present the potential of Fan-out Wafer Level Packaging for advanced sensor packaging and show FOWLP examples for a wide variety of sensors including MEMS based acceleration and pressure sensors, capacitive micro-machined ultrasonic transducers (CMUTs), gas sensor and bio-medical sensors.