Characterization and Application of a Novel Permanent Bonding Material

Microelectronic and microelectromechanical systems platforms maintain a variety of industry standards for permanently bonding one substrate or component to another. Examples include: direct, anodic, solder, eutectic, thermocompression, direct metal-to-metal, ultrasonic, and adhesive bonding techniques. This paper focuses on bonding improvements for polymeric adhesives that enable new possibilities for device packaging. Adhesive bonding is a powerful technique that uses a polymeric intermediate layer to create a bond between two surfaces or wafers. Four main markets that use the adhesive bonding approach are: three-dimensional integrated circuits (3-D ICs), microelectromechanical systems (MEMS) and IC integration, wafer-level packaging (WLP), and biomedical microelectromechanical systems/micro total analysis systems (BioMEMS/μTAS). The main advantages of adhesive bonding include greater design flexibility, surface planarization, low bonding temperature, and tolerance to particles. Various polymeric materials have been developed to satisfy the need for permanent adhesive bonding applications, but moisture absorption, limited thermal stability, and the long-term reliability of many of these polymers still cause manufacturers to withhold the processes from high-volume production. Benzocyclobutene (BCB), a widely used bonding adhesive, suffers from high bond temperature, long curing process, and high cost of ownership, and presents challenges to achieve void-free adhesive bonding with simultaneous high post-bonding alignment accuracy. This paper introduces a novel permanent bonding material with low moisture absorption and high thermal stability. Developmental efforts include details of material and process optimization along with reliability and performance results. Attributes of these materials include improved rheological properties that result in better planarization and improved bond quality and low temperature bonding process requirements that enable high throughput. In addition, void-free bonding with high post-bonding alignment accuracy can be achieved using this permanent bonding material. The reliability performance will be presented in detail.