**4. Conclusions**

In this study, an innovative approach for FOWLP of CMUT sensors by using inkjet-printed redistribution layers was pursued. Two realizations of the proposed FOWLP were shown and the performance of the packaged sensors with sensitive membranes was compared to bare dies performance. The reliability of the printed RDLs was assessed by using a thermal cycling test. The effects of multilayering and incorporating an insulating ramp between the die and mold were investigated. The cross-sectional analysis of the failed samples manifested the bottlenecks of the printed lines. Consequently, the challenges and opportunities of printed RDLs were addressed. The proposed approach for FOWLP of MEMS by using inkjet printing could eventually lead to a new platform for cost-effective heterogeneous integration. In this study, an innovative approach for FOWLP of CMUT sensors by using inkjet-printed redistribution layers was pursued. Two realizations of the proposed FOWLP were shown and the performance of the packaged sensors with sensitive membranes was compared to bare dies performance. The reliability of the printed RDLs was assessed by using a thermal cycling test. The effects of multilayering and incorporating an insulating ramp between the die and mold were investigated. The cross-sectional analysis of the failed samples manifested the bottlenecks of the printed lines. Consequently, the challenges and opportunities of printed RDLs were addressed. The proposed approach for FOWLP of MEMS by using inkjet printing could eventually lead to a new platform for cost-effective heterogeneous integration.

**Author Contributions:** Investigation: A.R., M.D., C.S., L.R. and J.Z.; Methodology: A.R., M.D., C.B.; Writing—original draft: A.R., M.D., C.S.; Writing—review & editing: A.R., M.D., C.S., J.Z. and K.-F.B.; Supervision: M.S.-R., S.R., T.B., and K.-F.B. All authors have read and agreed to the published version of the manuscript **Author Contributions:** Investigation: A.R., M.D., C.S., L.R. and J.Z.; Methodology: A.R., M.D., C.B.; Writing original draft: A.R., M.D., C.S; Writing—review & editing: A.R., M.D., C.S., J.Z. and K.-F.B..; Supervision: M.S.- R, S.R., T.B., and K.-F.B. All authors have read and agreed to the published version of the manuscript

**Funding:** This project has received funding from the Electronic Component Systems for European Leadership Joint Undertaking under grant agreement No 737487. This Joint Undertaking receives support from the European Union's Horizon 2020 research and innovation program and Belgium, Netherlands, France, Germany, Austria, Spain, Czech Republic, Norway. **Funding:** This project has received funding from the Electronic Component Systems for European Leadership Joint Undertaking under grant agreement No 737487. This Joint Undertaking receives support from the European Union's Horizon 2020 research and innovation program and Belgium, Netherlands, France, Germany, Austria, Spain, Czech Republic, Norway.

**Acknowledgments:** Credit for the LDV measurements goes to Steffen Kurth. **Acknowledgments:** Credit for the LDV measurements goes to Steffen Kurth.

**References**

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results. **Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
