Electroplating and Friction Corrosion in the Use of Automotive Connectors

Corrosive gases, high humidity, and strong oscillations are the three major conditions that cause oxidation and frictional corrosion, leading to connector failure. These environmental factors can have a significant impact on the contact surfaces between tin and lead tin, with 90% of connector surfaces falling under this category. Usually, people use electroplating of precious metals, such as gold or silver plating, because these metals do not undergo oxidation. The thickness of these coatings ranges from 0.5 µ m to 1.27 µ m. However, unfortunately, due to the presence of these precious metals and their processing, this type of electroplating process is expensive, so people try to use these electroplating materials as little as possible. In automotive electronic wiring harness applications, only about 10% of connection points use this type of metal. As a result, some major connector suppliers, such as FCI, have provided alternative electroplating solutions (such as pure tin electroplating, tin Teflon, NXT, and lamination technology) that not only meet OEM cost requirements, but also have the same performance in their products. Due to the need to meet high standards of automotive specifications, the compression terminal technology (connector to circuit board) originating from the telecommunications market has attracted much attention. Due to the thinness of automotive PCBs compared to PCBs used in the telecommunications industry, the operating temperature (125oC) is much higher, and the usage environment is subject to vibration, it is not an easy task to introduce this technology into automotive systems. This technology brings significant process cost-effectiveness by pressing a solderless pin into a metal PCB board hole. To meet strict automotive application conditions, FCI press fit terminals are specially designed to provide fully controllable force when inserted into the PCB, minimizing resistance and deformation, ensuring a stable interface with the PCB. Due to its cost-effectiveness compared to wave soldering and fully automated process that reduces PCB costs, FCI butterfly solutions (and related application tools) are increasingly favored by automotive manufacturers. In addition to superior performance (compatibility with SMT processes and excellent maintenance of component integrity), it also improves additional process quality due to the absence of thermal shock and tin bridge risks to the PCB. In addition, FCI found that under the conditions of using the correct electroplating process and pins in compression applications, the resistance of contacts remains relatively small when they are constrained by various external conditions, such as rapid temperature changes, relative humidity changes, long-term exposure to dry environments, and gas corrosion. However, as the number of pins increases, the pressure becomes significant, so great care should be taken when inserting the connector into the base. FCI has developed a new electroplating process called "NXT". Based on the chemical properties of amorphous nickel, it can provide a very smooth and uniform electroplating surface, which can significantly reduce the thickness of the gold coating (by about 80%). In safety critical applications, this technology can support extremely low signal currents. Multi pin connectors pose another challenge to the connection electroplating system. For ergonomic considerations, the insertion force of the connector should be as small as possible, but as the circuit count increases, the force required to insert the connector will increase proportionally. However, electrical performance typically indicates that each contact obtains high contact pressure (often resulting in high insertion force), which contradicts the goal of obtaining low connector insertion force. To solve this problem, people have developed a new type of contact surface. Teflon microparticles undergo the same treatment in a regular tin bath and are selectively electroplated onto the contact surface. Micro particles can reduce the insertion force of a typical tin plated terminal by more than 40%. This solution allows the connector to have more pins and does not require the insertion of auxiliary devices - enhancing ergonomics and improving connector stability. In addition, measurements have shown that when terminals are susceptible to vibration, tin Teflon surfaces have better anti friction and corrosion properties than any other tin plated contacts.