Composite coating structure in an implantable electronic device

• Published in: Soldering & surface mount technology Vol. 21; no. 3; pp. 24 - 29
• Main Authors: Kokko, Kati, Harjunpää, Hanna, Heino, Pekka, Kellomäki, Minna
• Format: Journal Article
• Language: English
• Published: Bradford Emerald Group Publishing Limited 26.06.2009; Emerald
• Subjects: Adhesives; Applied sciences; Coatings technology; Design. Technologies. Operation analysis. Testing; Electronics; Environmental protection; Epoxy coatings; Exact sciences and technology; Failure analysis; Flipchips; Humidity; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Integrated circuits; Joining; Joining materials; Medical equipment; Physics; Polymers; Protective coatings; Radiation; Scanning probe microscopes, components and techniques; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Semiconductors; Silicones; Studies; Temperature; Testing, measurement, noise and reliability; Coatings technology; Adhesives; Flipchips; Joining materials; Scanning electron microscopy; Failure analysis; Electronic component; Adhesive joint; Flip-chip; Durability; Reliability; Coatings; Medical application; Composite material; Coated material; Crack
• ISSN: 0954-0911; 1758-6836
• DOI: 10.1108/09540910910970385

Purpose - The purpose of this paper is to investigate the influence of composite coating structure on the reliability of adhesive flip chip joints. The need for conformal coating is considered, especially for medical applications, and medical sterilization is also considered.Design methodology approach - Two test lots were assembled and one of them was sterilized using gamma sterilization. Both test lots were coated first with epoxy and then with Parylene C, resulting in a composite coating structure. The reliability was studied using a constant humidity test and the failure analysis was performed with cross-sections and scanning electron microscopy analysis. These results were compared to earlier research results on conformal coatings.Findings - The reliability of both test lots proved to be good. The composite coating structure shields the joints from humidity and improves the reliability compared to non-coated test samples. When the conformal coating was compared to the pure Parylene C coated test lot, the reliability was almost the same. This leads to the conclusion that the epoxy layer in the composite coating structure has no value when long-term reliability is considered. Gamma sterilization does not greatly affect reliability. The epoxy coating under the Parylene C layer cracked during reliability testing.Originality value - The paper shows the influence of composite coating structure on the reliability of adhesive flip chip joints, particularly important in medical applications.