13 October 2013
Year: 2013Price: 10.00
Photonic sintering by means of a xenon flash is based on the photothermic effect. Advantages of photonic sintering of printed structures are a) short process times within milliseconds and b) the selective coupling of the energy into the printed structure in dependence of the material especially on thermal sensitive substrates.
The absorption of light, or in general of electromagnetic radiation, causes heat. Absorption of light in printed metal structures is high, as many metallic nano-particles are black due to their small size. The effect of surface plasmon resonance (SPR) leads to effective conversion of optical energy into thermal energy.[1] [2] [3] SPR is the resonance vibration of the free electrons of the nano-particles, which are excited by electromagnetic waves. The SPR effect is not only dependent on the dielectric properties of the material itself but on the size, form and coating of the nano-particles. For example, 30 to 75 nm sized silver nano-particles that are typical in inks show a SPR at wave lengths of 423 to 454 nm.[4] For copper nano-particles between 4 and 10 nm size this resonance wave length is 557 to 570 nm,[5] and for manganese nano-particles this resonance wave length is between 240 and 310 nm.[6] SPR
The absorption of light, or in general of electromagnetic radiation, causes heat. Absorption of light in printed metal structures is high, as many metallic nano-particles are black due to their small size. The effect of surface plasmon resonance (SPR) leads to effective conversion of optical energy into thermal energy.[1] [2] [3] SPR is the resonance vibration of the free electrons of the nano-particles, which are excited by electromagnetic waves. The SPR effect is not only dependent on the dielectric properties of the material itself but on the size, form and coating of the nano-particles. For example, 30 to 75 nm sized silver nano-particles that are typical in inks show a SPR at wave lengths of 423 to 454 nm.[4] For copper nano-particles between 4 and 10 nm size this resonance wave length is 557 to 570 nm,[5] and for manganese nano-particles this resonance wave length is between 240 and 310 nm.[6] SPR
has not been evaluated with nano particles of CuNiMn alloys (constantan) so far.
The sintering of copper and copper alloyed nano-particles is a challange due to their affinity to oxidation. Copper nano-particles of diameter 20 to 50 nm covered with polyvinylpyrrolidone (PVP) onto polyimid (PI) foil could be sintered by means of a xenon flash. The PVP covering layer with an optimum thickness of 2 nm inhibit surface oxidation and furthermore reduces surface oxides during the flash sintering process. The necessary energy for sintering the copper nano-particles to electrical conductivity of 1 % (compared to bulk material) is in the range of 12.5 to 32 Jcm-2. It is unclear if a single or multiple flash process is better as a decrease of the electrical properties was observed in some cases.[7] [8] With commercial equipment for photonic sintering, using pulses of more than 1000 Hz having a spectral range from 200 to 1000 nm, electrical conductivities of copper up to 10 % and of silver up to 25 % (compared to bulk conductivities) are achieved onto temperature sensitive substrates like polymer foils. Simulations with silver show a total process time from heating to cooling down of less than 2 milliseconds: after 0.2 ms a temperature of 600 °C is reached for the duration of 0.8 ms and cooling under 100 °C will take place within the next 0.8 ms.[9]
The sintering of copper and copper alloyed nano-particles is a challange due to their affinity to oxidation. Copper nano-particles of diameter 20 to 50 nm covered with polyvinylpyrrolidone (PVP) onto polyimid (PI) foil could be sintered by means of a xenon flash. The PVP covering layer with an optimum thickness of 2 nm inhibit surface oxidation and furthermore reduces surface oxides during the flash sintering process. The necessary energy for sintering the copper nano-particles to electrical conductivity of 1 % (compared to bulk material) is in the range of 12.5 to 32 Jcm-2. It is unclear if a single or multiple flash process is better as a decrease of the electrical properties was observed in some cases.[7] [8] With commercial equipment for photonic sintering, using pulses of more than 1000 Hz having a spectral range from 200 to 1000 nm, electrical conductivities of copper up to 10 % and of silver up to 25 % (compared to bulk conductivities) are achieved onto temperature sensitive substrates like polymer foils. Simulations with silver show a total process time from heating to cooling down of less than 2 milliseconds: after 0.2 ms a temperature of 600 °C is reached for the duration of 0.8 ms and cooling under 100 °C will take place within the next 0.8 ms.[9]
