Contact Resistance Characteristics of Elastomeric Complex Structure Contacts for Gold and Tin Printed Circuit Board
Characteristics of conductive elastomer which is composed of silicone rubber and dispersed carbon black particles shows conductive and elastic properties in one simple material. This material has been widely applied to contacts of switches and connectors of a liquid crystal panels. However, since surface state of the contact is very soft, it is difficult to remove contaminant films of contaminated opposite side contact surface and to obtain low contact resistance owing to break the film. This study has been conducted to clear structures of the elastomer which indicates removal characteristics for contaminant films and low contact resistance. As specimens, six different types of the elastomer contacts composed by different type of dispersed such materials as carbon and metal fibers, metal mesh, and plated surfaces were used. The opposite contacts were Au and Sn plated contact surface on a printed circuit board (PCB). The elastomeric contacts contained hard materials showed lower contact resistance than only dispersed carbon particles in the elastomer matrix for both contaminated PCB contact surfaces.
Contact Resistance Characteristics at Low Temperature
The application of cryogenics to the fields of electrical engineering has great possibility. However, performance of contacts used in the application may be estimated to deteriorate due to contaminant films. It is important subject to clarify the electrical conduction mechanisms of contacts covered with contamination films to obtain low contact resistance characteristics at the low temperature as well as at the normal temperature. From these standpoints, electrical conduction mechanism and contact resistance at low temperature were examined. Schottky current was observed in oxide film covered contacts over a range from 300 K to 77 K. The contact resistance at the low temperature increased by approximately 100 times or more over that of normal temperature due to Schottky conduction. For clean surface, the contact resistance passes through a minimum at low temperature due to thermal contraction of true contact area. In conclusion, Schottky conduction was found predominantly. Therefore, if the contaminant films exist at the contact surface, contact resistance increased remarkably at low temperature. Moreover, even for contacts of clean surfaces, contact resistance has a limiting value unlike resistance of metal conductors. These results give a serious problems in the performance of contacts for the cryogenic application.
A New Vacuum Pressure Infiltration CFRP Method and Preparation Experimental Study of Composite
In order to prepare a carbon-fiber-reinforced polymer composite (CFRP) with ideal microstructure and properties, a new vacuum pressure infiltration CFRP method is proposed based on an analysis of existing CFRP preparation process methods. Research on composite material preparation systems was carried out by using this new method principle. The system mainly includes a fiber pre-forming module, a vacuum heating infiltration module, a hot-press curing molding module, and a data acquisition control module. Under the conditions of natural curing at 0 MPa + 6 h + 25 °C, vacuum heating curing at –0.05 MPa + 30 min + 80 °C, and hot-press curing at 0.7 MPa + 5 min + 50 °C, a two-dimensional (2D) CFRP with excellent microstructure and properties was successfully prepared. Observing the microstructure of the prepared composite material, it can be found that the inside of the composite material was sufficiently and uniformly infiltrated, and common preparation defects such as holes and delamination were effectively controlled. Through the performance test, the bending strength of the material reached 790 MPa.