Turn-Key Potting Benefits OEM Electronics Producer

 

Although it is still early afternoon as the 1991 sedan eases onto the freeway, the driver switches on his headlights. It is the law in Canada. A sophisticated electronic module immediately senses the presence of daylight, automatically reduces wattage to the headlights by 20 percent and switches off the unnecessary tail lights, prolonging the life of the lamps. The electronic circuitry that controls the process is only one of a wide variety of electronic and Electro-mechanical systems and components manufactured by Lectron Products, a major supplier to the Big Three automakers. This particular module, however, presented the Rochester Hills, Michigan, manufacturer with a special set of problems.

Due to the part's under-bonnet location, the automaker specified that not only must the part itself meet strict quality standards, but it also must be able to withstand the rigors of an environment where it would be subjected to water, salt, oil, gasoline and extreme temperature fluctuations. A two-part reactive polyurethane, manufactured by Biwax Corp., Des Plaines, Illinois, had already been tested and approved as the specified potting material. Lectron turned to Thermal Innovations Corp., Manasquan, N.J., for a engineered design proposal on how best to employ the new potting material.

Thermal Innovations responded by custom-designing an automated turn-key potting system that combined in its own Seal-Cure high-purity, special infrared pre-heat oven and infrared curing oven; an automatic meter, mix and dispense system manufactured by Sealant Equipment and Engineering; the Biwax polyurethane potting material and a series of index conveyors to join them together in a closed-loop system. The idea was to combine the state-of-the-art technology in each area into a relatively simple cost-effective potting process that could be operated by a few people and produce high quality modules.

Production Steps

In the first step of the operation, modules are loaded manually onto the conveyor for delivery to the pre-heat oven. Modules are heated to approximately 70°C to remove any moisture retained by the PC boards and to help ensure uniform flow of the potting material around the board's intricate electronic components. This pre-heat oven is rated at 7.2kw and is approximately 5.5 ft. long.

Schematic diagram showing production line layoutAfter pre-heating, the modules are automatically indexed and positioned underneath the automatic meter, mix and dispense machine, a See-Flo® 7. After a sensor indicates that a module is in place, the machine automatically dispenses a 100-cc shot of the mixed potting material. The module then moves along the conveyor to the curing oven, an infrared Seal-Cure oven which is the heart of the system. The oven heats and accelerates the two-component (resin/catalyst) chemical reaction at much lower ambient temperatures than conventional convection ovens. The infrared oven transmits electromagnetic waves through the air which are directed at the target module and absorbed. The special quartz infrared emitters can be fine-tuned to accommodate the potting material's absorption characteristics as well as the thickness of the material. This ability to control energy output ensures that the material, rather than the heat sensitive electronic components, warms and cures quickly. The Sure-Cure oven fully cures the potted assembly in just 3 minutes with total energy efficiency. This particular final cure oven is rated at 14.4 kW and is approximately 10 ft. long. The module never reaches a temperature above 65°C. After the curing process, modules are conveyed through a forced ambient air cooling section so that an un-gloved operator can immediately unload the system.

SeeFlo 7 Dispensing SystemSystem Components

The Lectron system uses a central command electrical control panel for temperature zone control, conveyor indexing speed and automatic dispensing. The system is easily monitored and was designed to plant specifications. However, Thermal Innovations has the capability to design and install sophisticated computer-controlled systems that can be integrated into the most complicated computerized manufacturing, inventory and information systems. The potting material, Biwax 82.643, has been custom formulated to meet and exceed automotive requirements and for use in infrared curing operations. The material is a two-part reactive polyurethane that exhibits many beneficial characteristics, such as long pot life, low exotherm, low viscosity, non-abrasiveness, 1:1 ratio, high-low temperature stability and environmental resistance. It will cure at room temperature in the event of power failure. In this application, the material needs to be fairly elastomeric when cured, so that it protects delicate electronic components.

The See-Flo® 7 meter, mix and dispense machine was selected for its compatibility with the potting material and its ability to be interfaced with an automated turn-key system. The part A and B material components are supplied to the inlets of the metering cylinder assemblies by gravity feeding from double-stacked 55-gallon drums. Precision volumetric metering is accomplished by positive displacement, double-acting balanced metering cylinders. When the signal to dispense is received from the central command control panel, the air powered system reciprocates, forcing a pre-determined volume (100-cc shot) of metered material through the non-moving (static) mixer nozzle assembly. The disposable static motionless mixer produces a high-quality and air-free blending of dual-component materials. The volume of mixed material in the system is kept to minimum by blending immediately in the nozzle prior to dispensing. When the dispense cycle is completed, the No-Flush spool valve direction is reversed, creating a Snuf-Bak action at the tip and ensuring a positive No-Drip® cut-off of the mixed material.

Benefits

Currently the system is producing approximately 200 potted modules/hr. Rather than a normal cure time of 13-15 minutes, 3 minutes in the Seal-Cure oven is sufficient. This greatly reduces oven bottlenecks and work-in-process inventory. The oven is also much more energy efficient than its convection counterpart, so savings are realized in that area as well. Benefits in labour area are obvious; the system was designed specifically for a single operator and comparatively simple operation. Low oven temperatures and reduced need for solvent use in the dispensing equipment make the system safer and more user-friendly. Installation is quick and easy, as all components are pre-wired and pre-tested. A single exhaust system ties directly into existing plant systems, and wiring is simplified. The system also is compact and offers good use of floor space. "The entire potting operation is proving what cooperation and communication among industry resources can accomplish in a relatively short time," Biwax's Les Schober says. "Thermal Innovations, Sealant, Lectron and Biwax all contributed, and each of us learned the benefits of the team effort approach." Thermal Innovations' Nick Fusilli puts it another way. "We want Manufacturers everywhere to become aware that the resources are available for turn-key systems just like the Lectron project. We're working together to keep one step ahead not only of our own competitors, but also of our own customers' needs. New Material, new ways to dispense them, new curing processes -- all of these things can come together in one integrated system if you are working with suppliers who have established relationships among the various disciplines.