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Novel processes to enable deposition of metal coated polymer micro-spheres for flip-chip interconnections
conference contributionposted on 07.08.2015, 10:46 by Junlei Tao, David Whalley, Changqing Liu, Fengshun Wu, H. Kristiansen
Electronics packaging with Anisotropic Conductive Adhesives (ACAs) has been successfully implemented in flat screen assembly and smart cards for more than two decades, but novel processes are required to enable any significant further increases in interconnection density. This paper will report work to further develop two promising methods which can potentially extend the application of the types of conductor particles used in ACAs to enable ultra-fine pitch interconnections by selectively depositing these metal-coated polymer particles onto targeted bond pads. These two methods are electrophoretic deposition (EPD) and magnetic deposition (MD). To allow EPD the particles were positively charged by being immersed in a HCl solution, and then were selectively deposited onto the bumps on a silicon test chip. However the HCl immersion results in etching of the nickel layer, which is believed to significantly impact the conductivity and reliability of the interconnections formed, even though a connection forms between the particles and pads which is quite strong. In the MD process the Ti/Ni/Au bond pads on the test chips were permanently magnetized so that the particles were attracted to the pads, and the results proved that a sufficient density of the Ni/Au coated polymer particles became adhered to the pads providing a simple, low cost, and ultra-fine pitch method.
The authors would like to acknowledge the financial support of the EPSRC IeMRC, the Marie Curie International Research Staff Exchange Scheme (IRSES) project entitled “Micro-Multi-Material Manufacture to Enable 1158 Multifunctional Miniaturised Devices (M6)” (Grant No. PIRSES-GA-2010-269113) and the EC 7th FP Project “Functional Joining of Dissimilar Materials Using Directed Self-assembly of Nanoparticles by Capillary-Bridging - HYPERCONNECT”.
- Mechanical, Electrical and Manufacturing Engineering