PRINTED FLEXIBLE CIRCUIT Introduction to Water­Repellent Polymer Substrate Electronic industries are continually striving towards the use of flexibility and stretchability substrates like polyethylene terephthalate (PET) and thermoplastic polyurethane (TPU) with good water repellent characteristics or also known as hydrophobicity to improve the functionality of printed circuit for electronic packaging. This book focuses on the hydrophobicity performance of flexible substrate PET and TPU with the presence and absence of ceramic coating (Ti02). A low-cost self-fabricated contact angle measurement tool is also invented to fulfill the hydrophobicity analysis by using the Process Design and Development (PDD) concept involving the Pugh Method followed by a One-Sample T-Test to verify the accuracy measurement of the selected design. The knowledge gained would be beneficial to extend the use of flexible substrate PET and TPU and Ti02 coating in electronic applications