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 electronics 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 components 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, 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. The Plastics used, are mostly technical thermoplastics and heavy-duty plastics which fulfill the requirements for high mechanical strength, temperature stability and fatigue strength (Table 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 Contact Carrier Materials, Surface Coating Technologies and Applications for Bonding Technologies.

Table 1: Frequently Used Plastic Materials and their Properties

Type of Plastics: Poly-condensate Sub-Type: Thermo- plastics Abbrev.	Properties
	Density [g/cm3]	Reinforcement Materials	mechanical	electrical	thermal	resistant against
PPS	1.34 - 1.64	glass fibers, graphite fibers	very high mechanical strength and stiffness even at high temperatures, low toughness, very low creep, better properties with addition of 40% glass fibers	excellent isolation properties, very low dielectric losses	usable up to 240°C, short term up to 270°C, low combustibility, self-extinguishing, non-dripping	up to 220°C no known solvents, conc. sodium hydroxide, conc. hydrochloric and sulfuric acid, good hydrolysis resistance
PA6 PA66 PA610 PA11 PA12 A amorph	1.12 - 1.14 1.13 - 1.14 1.06 - 1.08 1.04 1.01 - 1.02 1.06 - 1.12	glass fibers, graphite fibers, mineral powders, glass beads, chalk, lubricants such as graphite, MoS2	depending on the PA type, crystalline structure and water content; high mechanical strength, stiffness, and toughness; higher mech. strength through stretching; very tough after water absorption; high fatigue strength, good impact toughness, abrasion resistant, good sliding properties through addition of graphite and MoS2; increased mechanical strength with glass and graphite fiber addition	depending on water content, good surface resistance reduces static surface charge, high dielectric losses, good resistance against creep currents	upper use temperature 80 – 120°C depending on type, short term up to 140 – 200°C, mostly boil resistant, can be sterilized, narrow softening range	aliphatic and aromatic hydrocarbons, gasoline, oils, greases, some alcohols, esters, ketenes, ether, many chlorinated hydrocarbons, weak alkaline solutions
PBT	1.29	glass fibers, glass beads, minerals, talcum	very high toughness at low temperatures, good stiffness and mechanical strength, good long term stability, low abrasion at good sliding properties	good isolation properties, good dielectric strength, little effect of humidity	good thermal stability, use temperature 60 – 110°C, short term higher, with glass reinforcement up to 200°C, low tendency to turn yellow, very low thermal expansion, burns with sooty flame and drips	aliphatic and aromatic hydrocarbons, fuels, oils, greases
LCP	1.40 - 1.92	glass fibers, minerals	very high precision and dimensional stability, high stiffness at low wall thickness, low thermal expansion coefficient; reinforced, better sliding ability, electrically conductive and suitable for electroplating types	dielectric losses depend on surface coating, good electrical conductivity; depending on type suitable for anti-static applications	use temperature 200 – 250°C, good high temperature stability, very low thermal expansion, resistant to soldering temperatures < 250°C, difficult to combust and self-extinguishing	good resistance against widely used organic solvents, i.e. acetone, methanol, chlorine gas, acetic acid
PPA	1.26 - 1.85	glass fibers, minerals	high impact strength with good mechanical strength and stiffness, very high dimensional stability at high temperatures, very low humidity absorption	very low electrical losses	use temperature up to 185°C, standard types with UL94-HB classification, special flame protective types	very good resistance against typically used organic solvents, i.e. acetone, methanol, etc., water based solutions (DI water, 10% ammonium hydride, typical liquids used in the automobile such as brake fluid, motor oil, etc

Hybrid Frames and Housings

Hybrid frames and housings serve as the connecting points between mechanics and electronics (Figure 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.

Figure 1: Component with hybrid housing for use in automobiles

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 (Figure 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 enables to reduce manufacturing tolerances to levels below those achievable with conventional assembly methods.

Figure 2:Examples of strip over molded contact components

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 (Figure 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.

Figure 3: Examples of assembled contact components