Foldable printed circuit boards on paper substrates
Wiki entry by : Dongwoo Lee, AP225 Fall 2010.
Paper in this Wiki : Adam C. Siegel, Scott T. Phillips, Michael Dickey, Nanshu Lu, Zhigang Suo, George M. Whitesides, Foldable printed circuit boards on paper substrates. Advanced Functional Materials 20, 28-35 (2010).
The authors illustrate the fabrication methods and properties of the paper based flexible electronic circuits. The advantage of this research is that one can create the low-cost, multi-functional, 3D-structured circuits with the everyday product, paper. Fig 1. shows the schematic of the fabrication process for the printed circuit. A laser cutted stencil makes patterned conductive paths to connect electronic components since metal is deposited on the designated region. Then, conductive epoxy was used to make connections between the components and the metal lines. Even though the fabrication method is quite simple, circuits created showed good enough performances in terms of flexibility as shown in the fig. 2. By using the general concept, the authors showed several possible applications, such as circuit on origami paper with 3D shape. (fig 3)
Soft Matter Discussion
It is beneficial to integrate soft and hard material since the the composite can be used for developing the cutting-edge devices such as wearable electronics and flexible display. The paper introduces a cheap method to fabricate the paper based electronics and its characteristics. The main advantage of this method is that the process is very low cost compared to the polymer based electronics for the flexible circuits. One problem of this method is the fatigue property. As can be seen in the fig. 2, the standard deviation is large, meaning that the device is not reliable to use. One may be able to solve this problem introducing more flexible electrically conductive material in the folding area. For example, one can make conductive liquid be trapped in the edge lines(folding lines) so that the conductivity is remained for several number of folds. One of the limitation of this method is in scaling. In the work, they chose the conductive material as Tin, zinc, silver and indium which are ductile. However, it was found that ductile material becomes brittle when its thickness is approximately a few nano-meters. Also, smoother papers should be used for the small paper based electronics since the roughness of the paper effects on the conductivity, as described in the paper. Even though there are some future works to be done for real application of this method, the general idea of this paper is simple and quite creative and is expected to be used in everyday products soon.