Flexible
metal electrodes are essential for flexible electronics,
where the main challenge is to obtain mask-free patterned metals directly
on substrates such as poly(dimethylsiloxane) (PDMS) at low cost. This
work highlights a feasible strategy named femtosecond laser-activated
metal deposition for electroless deposition of metals (Cu, Ni, Ag,
and Au) on PDMS, which is suitable for maskless and low-cost fabrication
of metal layers on PDMS and even on other materials of different natures
including polyethylene terephthalate, paper, Si, and glass. The electrical
conductivity of the PDMS/Cu electrode is comparable to that of bulk
Cu. Moreover, robust bonding at the PDMS/Cu interface is evidenced
by a scotch tape test and bending test of more than 20,000 cycles.
Compared with previous studies using a nanosecond laser, the restriction
on absorbing sensitizers could be alleviated, and catalysts could
originate from precursors without polymer substrates under a femtosecond
laser, which may be attributed to nonlinear absorption and ultrashort
heating time with the femtosecond laser. Implementing a human–machine
interface task is demonstrated by recognizing hand gestures via a
multichannel electrode array with high fidelity to control a robot
hand.
This study provides a comparison of the influence of Pd(P) thickness on reactions during soldering with the Sn-3Ag-0.5Cu alloy. Soldering was carried out in an infrared-enhanced conventional reflow oven, and a multiple reflow test method (up to ten cycles) was performed. With increasing Pd(P) thickness, the (Cu,Ni) 6 Sn 5 grew more slowly at the solder/Ni(P) interface, while the Ni 2 SnP/Ni 3 P bilayer became predominant after the first reflow. These three intermetallics, i.e., (Cu,Ni) 6 Sn 5 , Ni 2 SnP, and Ni 3 P, gradually coarsened as the number of reflow cycles increased. Furthermore, an additional (Ni,Cu) 3 Sn 4 layer appeared between (Cu,Ni) 6 Sn 5 and Ni 2 SnP, especially for the case of a thicker Pd(P) layer (0.2 lm). The attachment of the (Ni,Cu) 3 Sn 4 to the Ni 2 SnP, however, was fairly poor, and a series of microcracks formed along the (Ni,Cu) 3 Sn 4 /Ni 2 SnP interface. To quantify the mechanical response of the interfacial microstructures, shear testing was conducted at two different shear speeds (0.0007 m/s and 2 m/s). The results indicated that the interfacial strength and the Pd(P) thickness were strongly correlated.
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