Tomasz Falat

Carbon nanotubes and silver flakes filled epoxy resin for new hybrid conductive adhesives

Combining conductive micro and nanofillers is a new way to improve electrical conductivity. Micrometric silver flakes and nanometric carbon nanotubes (CNTs) exhibit high electrical conductivity. A new type of hybrid conductive adhesives filled with silver flakes and carbon nanotubes (DWCNTs or MWCNTs) were investigated. High electrical conductivity is measured as well as improved mechanical properties at room temperature. Small agglomerates and free MWCNTs dispersed in the silver/epoxy composites improve the electrical conductivity and a synergistic effect between MWCNTs and micro sized silver flakes is observed in hybrid composites. Glassy and rubbery storage moduli of the hybrid composites increase with increasing silver loading at fixed CNTs volume fraction. High value of the storage modulus, measured in DWCNTs/μAg hybrid composites at rubbery state, is caused by strong agglomeration of DWCNTs bundles. The electrical and mechanical properties are consistent with the morphologies of the hybrid composites characterized by SEM.

Nano-silver inkjet printed interconnections through the microvias for flexible electronics

In the recent years the huge demand for miniaturized, highly functional and also more and more reliable electronic equipment is observed. The development of electronic industry strongly depends not only on the scale of electronic components miniaturization but also depends on miniaturization and kind of printed circuit boards (PCBs). Nowadays, the flexible substrates plays more and more important role in electronics. Organic flexible electronics are being developed for computer displays, radio frequency identification tags, sensors and actuators, solar cells and for much other devices. The use of polymer-based substrates, coupled with an inkjet printing technique opens up the possibility of cost-effective processing in high volumes by use of roll-to-roll processing. Double-sided circuits requires the electrically conductive interconnections between both layers. The big challenge is the manufacturing of surface layouts and vertical interconnections in flexible substrates in the same process without an involvement of other technologies. In the current paper the idea of through-hole microvias metallization by using the inkjet printing technique is presented.

Numerical Approach to Characterization of Thermally Conductive Adhesives

Thermally conductive adhesives (TCA) and electrically conductive adhesives (ECA) are one of the major concerns of the contemporary micro-electronics. They are especially important in application where e.g. effective heat dissipation is the key factor for reliability issues. Currently there is a lot of ongoing research in order to improve the basic thermal property of adhesives, which is mainly heat conductance. According to the literature data the heat conductance can vary from 0.1 up to 60 W/m-K. It depends not only on the filler material, its content and configuration but also on thermo-mechanical properties of matrix. On the other hand numerical simulation becomes nowadays an inevitable tool for rapid non-destructive and low-cost experiments. The basic problem of numerical experiments is accuracy. Nevertheless the error can be minimized by combining the numerical and traditional experiments. This can be achieved by means of partial validation of numerical results by traditional experiments or by precise and appropriate material properties measurement. In fact, the above approach was applied in current work in order to simulate the influence of curing temperature and time on the thermal conductance of polymers. Thermally conductive adhesives belong to polymer materials. In order to apply numerical simulation it is required to have an appropriate description of the thermal and mechanical behavior of polymers. Most often polymers are described by cure dependent or independent linear viscoelastic model (Jansen, 2004). Having this model, which parameters in fact can be measured experimentally, it is possible to simulate the stress and strain field caused by polymer curing and shrinkage phenomena and finally assess the thermal conductance accordingly. Current paper focuses on a problem of numerical simulation of TCA in order to recognize the trend dependence of thermal conductivity due to viscoelastic model of polymers and filler particles contact area

Molecular dynamics study of the chiral vector influence on thermal conductivity of carbon nanotubes

Current paper focuses on the influence of chiral vector on thermal conductivity of carbon nanotubes. The non-equilibrium molecular dynamic technique was implemented in commercially available software. The eleven single-walled CNTs of various chirality (from zigzag to armchair) was investigated. Moreover, the influence of length on CNTs thermal conductivity was examined.

Influence of nano silver filler content on properties of ink-jet printed structures for microelectronics

The influence of nano silver filler content on properties of ink-jet printed structures for microelectronics were investigated. Samples were prepared by using ink with different nano silver filler content: 44 %, 41 % and 38 %. The electrical measurements were performed during and after heating process. It was shown, that filler content does not have a strong influence on sintering time, but it changes the final resistivity of printed and sintered structures. The enhancement of sintering process by UV exposure was also investigated. Preliminary results are promising and the further study will be conducted.

An accurate method for thermal conductivity measurement of thermally conductive adhesives

In the following paper the measurement method of thermal conductivity is described. These method was especially designed for measuring the thermal conductivity of the thermally conductive adhesives. The principal information about the experimental setup, mathematical model of experiment and the change of its uncertainty (calculated using type B method presented in ISO Guide for measurements) depended on measurement parameters are described. The obtained uncertainty from the model was compared with the real measurements of polymer composites filled with silver microflakes.

The study of carbon nanotube's length in reference to its thermal conductivity by molecular dynamics approach

Current paper focuses on the influence of carbon nanotube (CNT) length on its thermal conductivity. The powerful technique which is molecular modeling was used. The non-equilibrium molecular dynamics was implemented in commercially available software. The eight single-walled carbon nanotubes from 50 nm to 400 nm was investigated. The obtained results show the trend of increasing thermal conductivity for longer nanotubes.

An approach to measurement and evaluation of the thermal conductivity of the thermal adhesives in electronic packaging

In the following paper the measurement method of thermal conductivity is described. This method was especially designed for measuring the thermal conductivity of the thermal adhesives. The principal informations about heat transfer are given, and the experimental setup, mathematical model of experiment and its uncertainty with 95% of probability are shown. The thermal conductivity of polymer based material filled in 0.5% with carbon nanotubes is measured.

Thermally Conductive Adhesives for Microelectronics - Barriers of Heat Transport

Thermally conductive adhesives consist of the polymer base material matrix and the conducting filler dispersed randomly. It is commonly believed, that similarly as in the case of electrically conductive adhesive, with content of filler above the percolation threshold, the heat conduction depends mainly on the filler material bulk thermal conductivity. In fact, the heat transport inside an adhesive formulation is strongly constricted by the existing thermal contact resistance between filler particles. Additionally, the heat transport is limited by a bond resistance. The adhesive bond resistance in comparison to the total resistance of the thermally conductive adhesive joint becomes an important factor especially in case of microelectronic packaging where the adhesive layer thickness can be of the order of micrometers.

Structure of the Thermal Interface connection made of sintered nano silver

Continuous miniaturization of semiconductor devices enables integration in packages on increasingly smaller surfaces. Increasing power and minimization of dimensions results in diametrical increase of thermal flux density. Current works are focused on high performance TIMs (Thermal Interface materials). The main role of such TIMs is efficient dissipation of heat from electronic device to the surface. Within the frame of the study thermal interconnections made of sintered nano silver pastes were evaluated in terms of the application as layers that effectively remove the heat from semiconductor structures. Structure of TIM interconnections between silicon die and ENIG (Electroless Nickel Immersion Gold) on copper/FR4 substrate was the object of the study. X-Ray CT analyses have shown that voids presence, contact surface and interconnection thickness strongly depends on nano-filled paste composition and technique of application. The results will be compared with results of further studies (i.e. electrical and thermo-mechanical measurements).