Evaluation of interposers in the ACF bonding process

Current mobile phones are more or less information and entertainment devices with the ability to communicate with other devices through wireless networks. In addition, it is more and more a mobile office for business user offering access to needed files and services in company´s intranet to conduct daily business. To be able to perform these tasks, mobile phone needs very high performance and high functionality combined with small size and low energy consumption. It is also very important to optimize the total system cost. Utilizing different functional blocks as modules gives the designer and product marketing higher freedom to increase product variety and tailoring by using common building blocks to create a product. One of the key challenges is the physical interconnection between the modules, when number of connections increases and high performance with low interference is required. An interesting option for this interconnection dilemma is to use anisotropic conductive film (ACF) to connect the modules. ACF offers minimal form factor, high-density and low cost, as well as high reliability. Successful execution of board-to-board (flexible or rigid) interconnection using ACF needs careful consideration of design issues, materials selection, and process development. Sufficient thermal transfer to the ACF during the process is needed for proper curing. An interposer is used between the bonding head and the materials to be bonded to eliminate any issues with planarity. As the interposer has definite effect on the thermal transfer to the ACF, we have studied effects of different interposer materials and thickness to the quality of the ACF interconnection