WHAT'S THE BIG DEAL ABOUTautomotive connectors? Just snap 'em together and you're up and running, right?
Not exactly, although that would be the ideal situation. Modern automobiles are increasingly dependent on electronics for governing the engine; controlling braking, steering, and safety functions; and running entertainment, navigation and other convenience features. High-speed digital electron- ics require that components, and the connectors that link them, be not only physically joined but also tight in electronic noise emissions to prevent interference, as well as easy to install and good value for money.
Putting the importance of connectors into perspective, Richard Black, president of the automotive division of connector maker Molex Incorporated (Lisle, IL), cites industry surveys that show, "From internal electrical audits performed at the factory to warranty work at dealerships, electrical connectors are the number-one source of electrical problems." Many of these stem from non-mating of connectors at the factory, which is still mainly a manual assembly-line task, to LNAs, or loose, not attached, contacts.
|Electronic filtering elements within connectors can open up circuit board space for more electronic functions.|
In manual connector mating, many situations require an installer to establish a successful connection of many tens of wires while reaching behind an assembly . The installer may take additional time to engage a connector-position-assurance feature, much like a "latch" that positively seats and locks the connector halves.
Positive, mate. To improve mating reliability and reduce the time and expense of manual connector joining, Molex has developed positive engagement connectors that allow direct docking of pre-wired modules as the components mounting them are joined to one another (see figure at left). Here, a lead-in on one of the connector halves captures the other "floating" half, on a dash panel, say, and ensures a reliable mate. The floating feature allows up to 3 mm of movement in the lateral (x-y) directions to account for non-alignment.
The connector is used on the Dodge/Plymouth Neon to effect a connection having 75 circuits when the center dash stack is installed by a robot arm in the body. It is also used on the Chrysler LH instrument cluster. The system is also designed to accept the terminal contact configurations approved by the U.S. Car Consortium, a government-industry group. The organization is looking to reduce the roughly 50-odd types of contacts now used to perhaps four or five in all future automotive applications.
|Fretting corrosion in tin, the most common contact surface finish, is induced by small contact movements. This effect can be countered by high normal force or lubricants to prevent oxide formation.|
The self-aligning connectors also eliminate the need for a service loopthe extra inches of wiring harness (and attendant weight and cost) that an installer needs to have available to allow maneuvering the harness into position before mating.
Black says that future applications in the design stage include keyless entry, other trim panels, and seats. When asked if any engine compartment uses are planned, he notes the general attitude is wait-and-see. "Industry wants to see it work first," he adds, "They like to see technology somewhere else" rather than be true leaders in this area.
Black also stresses that because auto electronic control modules are doing more and more functions, more circuits are needed. The trend in modules is from 8- to 16-bit microprocessors, with 32-bit units in the wings, at higher and higher processing speedsprime conditions for noise, EMI, and RFI. "You don't want emissions to confuse other components, particularly safety related items such as airbag electronics and antilock brakes.
To this end, the company has developed engine-control connectors with built-in shielding and grounding that handle microprocessor noise. "For filtering and shielding, the best way is to filter on the I/O connector," Black says. He notes a power control module connector supplied by Molex to Delphi Delco that LC (inductance/capacitance) filters 160 circuits.
Material needs. Effecting positive connections is possible only if the contact terminals themselves are sound. Contact material performance and cost must be tuned to the operational environment. Connectors can hold a variety of wire gauges and insulation configurations, whose ends are terminated by crimping, soldering, or techniques such as insulation displacement, says Y. V. Murty, former manager, interconnection surface sciences, with AMP (Harrisburg, PA). "The open end of the connector offers a separable interfacea convenience feature for assembly, repair, and retrofit," he notes. Impacting choice of contact materials and coatings are connector temperature, contact configuration and loads, and frequency of disconnections and reconnects, as well as airborne contaminants, including rotating machinery lubricants.
|Automotive connector manufacturers must accommodate conditions in four operational temperature zones in a car.|
|1||85C||audio, body electronics, airbag electronics, instrument clusters|
|105C||communication, navigation, adaptive cruise control, collision avoidance|
|125C||engine controls, brake electronics, ignition module, electronic motor controls|
|155C||(As per Class 3)|
The U.S. Car Consortium divides electrical wiring systems into four classes based on the operational temperature requirements for passenger cars and linked to the associated systems that would be found in those temperature areas (see table). Thermal design, and subsequent testing, must take into account not only temperature but thermal cycling as well. For cycling considerations, the NEMI (National Electronics Manufacturing Initiative) standard is that 1,000 one-hour cycles between -55 and 125C equals a 10-20 year operating life. This requirement is expected to be raised to 2,000 cycles by 2001, according to Murty.
Mechanical-design factors include the level of connector normal force (which is between the two halves of an individual contact) and its consistency for stable contact resistance. Other parameters are insertion/withdrawal forces and vibration. Contact resistance also depends on the base material and finish coatings.
Resistance is governed mainly by the surface finish used. Gold is highly corrosion resistant and easily electroplated, but high in cost and its cyanide electroplating solutions are an environmental concern. While gold operates reliably at normal forces of only 100 grams, it is relatively soft and subject to wear, limiting the number of connect/disconnect cycles. Palladium has higher hardness, but is also a precious metal.
The most common automotive connector finish is tin. Contacts with tin finishes are designed to operate in the 85-105C range. Above that, gold finishes are preferred. However, tin finishes fail by fretting wear, due to formation of an insulating, brittle oxide film, producing an open circuit (see figure). Such action can be countered by high normal contact forces (around 400 grams), as well as "floating" the connector to avoid mechanical contact displacements that cause oxide flaking and build up. In addition, anti-fretting lubricant can be used to seal the surface from oxygen and displace any oxide away from the contact surface.
In concluding, Murty advises connector manufacturers to be in close contact with their materials suppliers to more easily tailor designs to user specifications.
|Insert, mold, and forget|
|FCI develops and offers insert-molded components for various electrically-actuated devices located around door-modules and passenger-cabin applications, including central door locking (shown), power windows, and sunroofs.|
By David J. Bak,Editor-in-Chief, Global Design News
Westland, MI-In today's autos, increasing demand for greater numbers of electrical devices, and the resulting decrease in available packaging space has many OEMs and Tier 1 suppliers looking for new approaches to electrical connector/component reliability. Their focus? Precision insert molding.
By combining the processing advantages of plastics with the mechanical and conductive properties of metal, precision insert molding encapsulates multiple parts as one. Of half a billion FCI APEX automotive connectors, virtually none have failed from shock, vibration, moisture, or dirt. Insert molding also provides the following benefits:
Smaller size, less weight. Precision insert molding can eliminate certain costly harnesses and integrate the connector function directly into the component. FCI's central door locking module is a good example. Manufactured for Germany's Mannesmann VDO, the part integrates a 10-inch electrical lead frame into a complex plastic housing.
Improved functionality. Thanks to microelectronics, automotive circuitry is increasingly integrated in a distributed manner. This leads to production of active devices, or devices with built-in logic. Such products are driving the use of insert mold technology within the auto industry.
For example, FCI's air mass sensing system is geared for engine-compartment use. A plastic housing with integrated lead frame permits direct wire bonding, yet resists shock, vibration, and extremes of temperature. The sensing circuit resides inside the housing, sealed against the engine compartment environment.
Other active device opportunities for precision insert molding include motion sensors for automotive alarm and airbag deployment, and emission control monitors.
Simulation opportunities. Under development at FCI, software promises more accurate plastic delivery systems, improved cavity design, reduced shrinkage or warping, and less movement of encapsulated metal parts.
These programs combine conventional mold-flow programs with finite-element analysis that looks at forces exerted on elements within the system and determines stress levels. "Overlapping these two specialized software tools," states Richard Kakkuri, FCI advanced product development manager, "allows a math model that will predict the behavior of integrated metal components during the mold process. As the plastic fills the die, we can see if a circuit, for example, will move or break."