As an isotropic conductive adhesive, that is, a hybrid Cu paste composed of Cu powder, solder powder, and a fluxing resin system, has been quantitatively characterized. The mechanism of an electrical connection based on a novel concept of electrical conduction is experimentally characterized using an analysis of a differential scanning calorimeter and scanning electron microscope energydispersive X-ray spectroscopy. The oxide on the metal surface is sufficiently removed with an increase in temperature, and intermetallic compounds between the Cu and melted solder are simultaneously generated, leading to an electrical connection. The reliability of the hybrid Cu paste is experimentally identified and compared with existing Ag paste. As an example of a practical application, the hybrid Cu paste is used for LED packaging, and its electrical and thermal performances are compared with the commercialized Ag paste. In the present research, it is proved that, except the optical function, the electrical and thermal performances are similar to pre-existing Ag paste. The hybrid Cu paste could be used as an isotropic conductive adhesive due to its low production cost.Keywords: Hybrid Cu paste, fluxing resin, isotropic conductive adhesive, solder wetting. Manuscript received Sept. 1, 2010; revised Dec. 14, 2010; accepted May 20, 2011. This work was supported by the IT R&D program of MIC/IITA (2006-S-056-01, Anisotropic Conductive material for IT Components).Yong-Sung Eom (phone: +82 42 860 5547, email: yseom@etri.re.kr), Kwang-Seong Choi (email: kschoi@etri.re.kr), Seok-Hwan Moon (email: shmoon@etri.re.kr), and Jong-Tae Moon (email: jtmoon@etri.re.kr) are with the Convergence Components and Materials Research Laboratory, ETRI, Daejeon, Rep. of Korea.Jun-Hee Park (email: jhpark@ledpack.co.kr) is with the LED Pack Co., Daejeon, Rep. of Korea.Jong-Hyun Lee (email: pljh@snut.ac.kr) is with the Department of Materials Science & Engineering, Seoul National University of Technology, Seoul, Rep. of Korea.http://dx.doi.org/10.4218/etrij.11.0110.0520
I. IntroductionEver since an Ag filled conductive paste was first introduced in U.S. Patent [1], isotropic conductive adhesives (ICAs) have continuously been developed for electrical interconnections in semiconductor packaging. In general, a conductive paste as a composite material is composed of polymeric resins and metallic filler. For a high electrical conductivity, flaked Ag powder is widely used by many researchers [2], [3]. Lu and others reported that the conductivity of Ag paste was achieved by a mechanical contact between Ag particles due to the shrinkage of the polymer matrix during the cure processing [2]. Also, Jiang and others attempted to use nano-sized Ag particles and micro-sized Ag flakes mixed with an epoxy resin for an increase in electrical conductivity [3]. The high conductivity was achieved using a dramatic reduction of interfaces between conductive fillers due to a low temperature sintering of the nano Ag particles. However, it is well known that Ag powder is still to...