Abstract
The electrical interconnect is an essential component of most electrical system configurations. The ability of the interconnect interface to reliably transmit power and / or data throughout the system is critical to its overall performance. Degradation of the mechanical or electrical properties of the interface can reduce the system performance or in severe cases, make it inoperable. There are several factors which can inhibit the performance of the interconnect, one of most severe is long term exposure to elevated temperatures. This effect can also be accelerated when combined with other severe environmental conditions such as high vibration and physical shock, which are often found in down hole oil and gas well drilling applications. This type of exposure can significantly degrade the essential properties of a reliable electrical interface such as contact resistance, mechanical stability, and electrical isolation. This paper will present options for design features and material properties that can be incorporated into an interconnect design that will mitigate these adverse effects. Specifically, this paper addresses the material properties of the contact interface and its surface treatment, the mechanical and electrical properties of the insulating material, the robustness of the mating features and the contact retention system.
Two key features of the contact interface that are discussed are the stability of its electrical resistance and the robustness of its mechanical retention. Long term exposure to high temperatures typically induces stress relaxation in the compliant members of the contact interface that are required to produce a stable, low resistance interface, while allowing for a high level of mate / unmate durability. Stress relaxation can also reduce the mechanical stability of the contact interface where metal or plastic retention features are utilized. In the case of retention through epoxy bonding, imparting thermal stress at the bonding surface can result in loss of adhesion and / or retention.
The surface treatment of the contact interface has also been shown to be a contributing factor in its electrical stability in high temperature applications. Typically, the interface is plated with a hard gold over nickel finish, which provides a noble interface that is corrosion resistant, but with the hardness required to withstand many mate / unmate cycles. A small percentage of nickel or cobalt are typically alloyed with the gold to produce the required hardness. In most applications, it has minimal impact on the overall resistance of the contact interface. In high temperature applications, however, it can tend to diffuse through the gold to the contact interface. Since these materials have a higher resistivity, they can negatively affect the resistance of the interface. The impact of this effect is reviewed in this paper.
Finally, results of the evaluations on high temperature insulating materials and bonding epoxies are presented in this paper. The mechanical and dielectric stability of the insulating materials and the adhesion properties of the epoxy used for contact retention were the primary concerns for their evaluation. The verification tests that included at temperature exposure were conducted at +260°C to simulate extreme use cases for most down hole applications.
An improved model for the parallel hot wire: Application to thermal conductivity measurement of low density insulating materials at high temperature