Contents
10 Electromechanical Components
Plastic molded or encapsulated components are of increasing importance due to rising requirements for smaller, lighter, and more compact designs with cost efficient pricing. Wherever mechanics and electronic meet, electromechanical components can be used in a multitude of applications, such as in automotive, communications, appliance, and consumer electronics engineering. In automotive applications such components are used in ever increasing volumes. In hybrid housings electronic components are integrated into components for increasingly more complex engine management functions. Strip-molded contact parts are for example used for seat adjustment, and airbag sensors; assembled contact parts are important functional components among others for memory mirror positioning units.
Electromechanical components usually consist of stamped circuit patterns (lead frames) which are coated in the contacting areas with functional surface layers. They serve as the electrical connections of the component to the outside wiring. The lead frames are over-molded with plastics or mounted into plastic molded parts. In addition electronic components can be added to increase the level of product integration. Utilizing the metal–plastic compound the mechanical stability of the plastic is combined with the conduction of electrical energy and electronic signals through the lead frame. In this way protective enclosures for electronic controls of machinery are created which at the same time serve as connecting points to the outside wiring. This can be achieved through hybrid frames and housings. Over-molding of contact components or assembly of different single parts in plastic enclosures can also be used to manufacture electromechanical components.
For achieving the highest possible functionality of the end product a close cooperation between the manufacturer and the end user in the early phases of development and design of new custom tailored electromechanical compo- nents is recommended. Innovative and cost-efficient designs can be realized through the combination of the know-how of the manufacturer in for example contact, coating, stamping, plastics processing, and assembly technologies and the mostly rather complex requirement profile given by the end user.
Besides the contact components the plastic materials are the critical building blocks for electromechanical components. Plastics used are mostly technical thermoplastics and heavy-duty plastics which fulfill the requirements for high mechanical strength, temperature stability, and fatigue strength (Table 10.1). For the final selection of a plastic material economical considerations and the avoidance of environmentally hazardous ingredients such as for example flame retardants must be considered. The application of the most suitable contact material coating and the selection of carrier materials are covered in chapters 5, 7, and 9.
10.1 Hybrid Frames and Housings
Hybrid frames and housings serve as the connecting points between mechanics and electronics (Fig. 10.1). They allow the transmission of signals or electrical energy. The connection to the current paths inside the housing is mostly done by bonding with aluminum wires. The over-molded lead frames are typically manufactured from aluminum clad strip materials which are well suited for bonding. The connectors integrated into the housing for transferring the current paths to the outside are coated with tin, silver, or gold, depending on specific requirements.
Fig. 10.1: Component with hybrid housing for use in automobiles
10.2 Continuous Strip Over-Molding
In strip form over-molded contact parts reduce the complexity of assembly of the finished product. This complexity constantly increases with adding additional subcomponents (Fig. 10.2).
The strip over-molded contact parts can be tested for various quality parameters during manufacturing to continuously ensure the ever increasing reliability requirements of the end components.
Combining stamping and molding techniques in an automated production line allows the stamped contact parts to be molded into plastics as a complete functional unit. This also allows to reduce manufacturing tolerances to levels below those achievable with conventional assembly methods.
Fig. 10.2: Examples of strip over-molded contact components
Fig. 10.3: Examples of assembled contact components
10.3 Assembled Contact Components
For applications and materials which do not allow strip over-molding, semi or fully automated assembly processes can be utilized. Different single parts like printed circuit boards, stamped parts, or contact components are assembled together with plastic molded parts on specialized equipment to complete functional components with low tolerances and high levels of functionality (Fig. 10.3). This also allows to integrate components which otherwise are difficult to mount onto circuit boards or carriers, such as capacitors, coils, or sensor elements into the functional component assembly. Contact parts used in these components are already tested on the assembly machine for quality parameters and functionality.