Everywhere these days, one invariably runs into electronics. They are fast becoming an integral part of our daily language, as well as our lives. In fact, we’re in the midst of what might be called “The Electronic Age.: Almost every industry has been revolutionized by electronics – defense/aerospace, automotive, medical, recreational, telecommunications, home appliance and computer.

The products manufactured in these areas are by-products of electronic technology; they are made better, cheaper, and much more reliable with electronic components. Our future is undoubtedly tied to electronics. To assure greater response to industry’s needs of high technology, many corporations have committed groups of scientists, researchers, development engineers, production and marketing professionals, and technical sales specialists to resolve problems and create new frontiers for design and industrial process engineers.

Component Protection

Protection is of vital importance in the electronic industry. An electronic circuit board houses delicate 1 mil gold wire transistors, glass diodes, capacitors, resistors, semiconductors, and silica chips, which make that particular device function property. Consequently, any damage to the components could cause the device to fail. Damage often occurs because of short-out or component breakage. Reliable protection against the following environmental conditions is of importance:

Moisture. This will cause an electronic component to short itself out, resulting in premature failure of the component and the device it is in.

Thermal shock. Electronic components must often withstand the effects of extreme temperature fluctuations, ranging from - 40°C to 125°C. Thermal shock is a problem not only in certain climatic regions, such as Alaska or the Sahara Desert, but also in particular applications, such as in an automotive electronic ignition module that is subject to extreme engine heat. Temperatures too hot or too cold can cause component cracking (under extremely cold conditions) or melting of electrical connections within the component (due to extreme heat).

Chemicals. Electronic components can be subject to corrosive materials like salt, solvents, gas, and oils. In most cases, the problem is similar to that of moisture seepage “frying” the component. In some cases the component will not short-out immediately. The damage happens more gradually through corrosion. The end result, however, is the same; life expectancy of the component is shortened.

Mechanical shock. Particularly in automotive applications, mechanical shock can reduce the effectiveness of an electronic component. Delicate wiring and glass diodes are vulnerable to vibration and breakage.

Security (keeping technology a secret). One area that is seldom discussed, but nonetheless understood, is security. Advanced technology carries with it the daily threat of industrial theft or espionage. This is seen particularly within the video game industry. Small electronic components carry the high-tech memory patters on silica chips that make each particular game different.

A related area of concern is after-market replacement sales. While this does not strictly represent a security “problem,” in the same sense that piracy and industrial theft do, manufactures of aftermarket products lose money when “do-it-yourselfers” dissect electronic components in an effort to repair or copy them, rather than replace them.

Structural integrity is critical to ensure a sound, solid component with durability and reliability. Insulation from moisture, vibration, thermal cycling, and corrosion must be recognized as an important consideration in designing and producing electronic components.

A Solution

With all these problems facing the manufacturers of electronic components, the need for parallel protection and security technology is great. Potting and encapsulating electronic components with flowable two-part silicones, epoxies, polyesters, and urethanes represent a possible solution. Material supplies, in conjunction with meter/mix/dispense equipment manufacturers, can profile a “one-two combination” for potting and encapsulating electronic components.

Potting and encapsulating are the terms used for filling components with one-or two-art flowable materials. Typical applications may include modules, relays, power supplies, amplifiers, transformers, ferrite cores, connectors, circuit boards, capacitors, fly-back transformers, ignition coils, thermostats, high-voltage transformers, and video games modules. Whether silicones, epoxies, or urethanes are used, meter/mix/ dispense equipment injects these directly into the electronic component without harming the delicate wiring or memory patters within. This precision equipment guarantees the material to be completely air-free and mixed on ration within guidelines of the material manufacturer’s specification. This is accomplished in a variety of ways, depending on the application.

Selecting Materials

There are basically three groups of flowable materials from which to choose; silicone elastomers, epoxies, and urethanes. Each has its individual characteristics and can be used in a number of situations, depending on the application and requirements.

If five individual electrical engineers had the same product to manufacture and they had to specify which type of material to use. Without consulting each other, there would be a good chance that the material specified in each case would be totally different. Several properties should be examined:

Surface Adhesion. The material must bond to the walls of the housing and adhere to the components.

Low Shrinkage. During the curing process the material hardens, and depending on the physical part size and the area of mixed material used, one can expect various degrees of shrinkage. Too much shrinkage, however, could actually crush the delicate electronic components within the particular device. Such as glass diodes. Stress should be minimized during the material cure cycle.

Volatile Materials. During the curing process, dangerous gaseous by-products can be produced. When the resin and catalyst materials are mixed, there is a chemical, or perhaps an exothermic, reaction. Occasionally, fumes or gases emitted into the working environment pose hazardous working conditions for the person performing the operation. Adequate air ventilation hoods should be installed over the application area. The major dangers to avoid are severe skin and eye irritation, inhaling vapors, and the use of flammable explosive materials.

Tensile, Flexural, and Compressive strength. These are a prime consideration in certain applications. An electronic device may be expected to resist high levels of compression without cracking or damage to its components. Flexibility refers to how well a component can withstand structural forces and still retain its shape; resiliency will become even more important as electronic components replace products in high-stress, abnormal service conditions.

Electrical Insulation and Conductivity. The material selected should retain its properties over a wide range of frequencies. It should complement. And not hinder, the flow of electricity through components.

The material should also offer some kind of insulation against outside electrical interference. While the manufacturers of electronic components are probably aware of outside interferences and design their components accordingly, the main concern is that these flowable sealants not interrupt the components’ function while providing the necessary protection.

Chemical Resistance. As was mentioned earlier, salt, solvents, gases, oils, and many other industrial chemicals pose a threat to electronic componentry. This is why the sealants selected must be, themselves, in a cured state, resistant to chemicals. Of course, each material is vulnerable to certain chemicals that render its protective properties useless. The epoxies, urethanes, and silicones must be individually tested against these chemicals before a specification can be written.

Cost. One of the most discussed considerations in selecting sealant materials is the expense. Many electronic component manufacturers have turned to fillers to lower unit cost. The two fillers most commonly used in the industry are silica sand and glass beads.Fillers are often used in conjunction with flowable materials to pot or encapsulate electronic components. It is preferred that the filler be poured into the electronic device before potting and sometimes preheated to 220°F to insure total impregnation by lowering the mixed material viscosity and allowing the air to escape.

Fillers lower cost by minimizing volumetric area. These cost advantages can easily be seen, for example, if the average material cost is about $1.75 per pound, the average material cost for silica sand is about .03¢ per pound, and the filler consume 75% of the device’s area.

Fillers also give a higher electrical insulation factor; minimize shrinkage; protect module from extreme temperature fluctuations; reduce the coefficient of thermal expansion and contraction; improve thermal conductivity; and make application easy.

Application Equipment

More and more manufacturing and industrial processes are incorporating such applications as potting, encapsulating, and structural bonding into their operations. Good, reliable, sophisticated meter/mix and dispense methods are required to keep pace with production. In addition, the material manufacturers are responding to these present needs and are actually anticipating what the needs may be in the future by developing new and different types of epoxies, urethanes, silicones, and other flowable two-part adhesives. As a result, the responsibility that falls to the meter/mix and dispense industry is heavy. Not only must equipment suppliers stay abreast of industry’s present needs, but we also much engineer to future needs if our equipment is to complement specified material and electronic products.

Industrial engineers should always keep in mind that equipment suppliers and material manufacturers present themselves as something of a “package deal.” Sealant material is practically useless without meter/mix and dispense equipment; meter/mix and dispense equipment is worthless without the material.

From the point of view of the equipment industry, a major concern is obtaining the appropriate information about the material and its intended application. Equipment supplies must have this information so that they can fit the proper meter/mix system to particular needs.

These aren’t just inconsequential details. Others in the equipment industry will confirm. This information is vital to determine exactly what type of system is required.

Equipment should be modular in design to permit the user of meter/mix and dispense equipment to customize it to a particular application or material.

Because of flow characteristics, for example, some materials must be heated; others must be cooled. Some applications require the operator to visually fill the electronic component; other require a precise metered shot of mixed material. Also, one may receive the A and B materials in 55-gal drums, 5-gal pails, or 1-gal cans. A wide variety of optional supply equipment, therefore, is necessary; pressure supply tanks, fluid transfer pumps, and material ram assemblies accommodate most application needs.

Machine proportioning and mixing provides several advantages over pre-mixing by hand by providing complete control of materials from container to application. Machines are more accurate and can provide consistent material quality vs. pre-mixing by hand.

Equipment can keep pace with higher production requirements and supply mixed material on demand only when required from a "no-drip" dispense valve that "snuffs back" the material into the nozzle.

Pot life. This is the workable time a mixture can be used or applied at t given temperature before it hardens and cures. Depending on which material is used, pot life can range from a few seconds to several hours. Mixed materials can be purged automatically or manually with pure resin or with a non-flammable solvent (methylene chloride) from the manifold, mixer, hose, and gun before it cures.

In light of the chemical dumping problems in industry, more manufacturers are turning to resin purge and/or solvent flushing in a closed loop fashion, which allows the solvent to be reused. After the solvent flush operation is completed, the solvent is air-purged from the mix manifold, hose, and gun. This assures no solvent contamination of the A and B materials, which must be freshly mixed.

Mixing. The A and B materials are mixed together on ratio and completely air free by either dynamic power mixing or no-moving-parts static mixing.

Static mixing uses ribbon-like baffles and chambers to fold and refold the two streams of material under pressure. Some resigns with high cohesive viscosities resist a high-quality mixture through a static mixer. In these few cases, an air-operated, high shear dynamic power air mixer is appropriate.

The mixer is located downstream of the mix manifold and sometimes, with fast pot life material, at the dispense nozzle. Mixer position is often determined by the pot life. The shorter the pot life, the closer the mixer must be located to the application point.

Today’s dispense equipment is capable of handling a wide variety of material viscosities, ranging from water (150 centipoise) to paste consistency (1 million centipoise), and even material with micro-balloon contents.

Bench-top Proportioning Equipment. Bench-top proportioning equipment provides a simple and economical method of potting and encapsulating small electronic components. The unit works on an air-operated, positive-displacement principle designed to meter and mix two-part compounds such as epoxies, urethanes, and silicones, and it will dispense them in precise, air-free, metered shots. The system is ideal for intermittent or production line use because of its variable shot and variable flow rate characteristics. The unit itself may measure in the vicinity of around 24” high x 15” wide x 9” deep and is compact enough to fit any place where space is limited. Few moving parts makes this machine easy to clean and service, while interchangeable metering rods foster quick, low-cost ration changes. In addition, shot size can be easily adjusted by the operator by simply rotating a threaded control screw.

Two-part materials are supplied to the dispenser either by pressure tanks, pumped directly from original containers, or by gravity feed. Positive displacement metering rods force precise quantities of compounds through the mixer, which has no moving parts. The uniformly blended compound is then dispensed through a “dripless” dispensing gun, remote nozzle, or pencil-type applicator.

Applications of this type of unit would include automotive electronic ignition modules; solenoid values for irrigation sprinklers; sonar buoys/underwater detection devices; and optic sensors/electric eye modules.

Floor-standing Proportioning Equipment. This manual unit stands on the floor enabling operators to walk around to manually pot and encapsulate. These units provide the flexibility of taking the dispense gun to the application. This allows the operator to visually fill each component, giving a high degree of flow control at the application point.

These units are classified as either fixed ratio or variable ratio. They incorporate single-acting or double-acting balanced metering cylinders. The equipment is designed according to the “positive displacement” principle of metering. Shot after shot is consistently accurate whether in demanding assembly line applications or in the intermittent use.

Floor-standing proportioning equipment can be operated in manual, semi-automatic, or automatic mode, using one dispense gun or several. It uses a single air or hydraulic powerhead motor, which drives the metering cylinder simultaneously. Ratio check controls are provided for quality control purposes.

Typical applications include television fly back transformers; video game central modules; electronic ignition coils; mercury relay switches; Geo-phones; turn signal devices; impedance coils; telecommunications switching relays; and submersible pumps (oil and water).

The Future

As electronic technology increases, the need for protection of these components must increase. The sealant and meter/mix and dispense equipment industries are in a very benevolent situation. They can be the people who expand the electronic industry’s capability. However, electronic component engineers/designers must be aware of how potting and encapsulating can ultimately enhance their component’s capabilities and reliability. To view potting and encapsulating as merely anew market for sealants and dispensing equipment is short-sighted. Potting and encapsulating offers tremendous potential growth opportunities for the electronics industry. It falls upon the adhesive industry and the equipment manufacturers to educate the electronics industry to capabilities and subsequent benefits. Lines of communication must be kept open. New ideas, applications, and technology must be continually explored, researched, exchanged, and modified to meet the demands of the electronics industry.

Vacuum Impregnation. Ideal for the manufacture of high-voltage electronic components, vacuum impregnation equipment is designed and engineered to dispense precise, metered shots of flowable single – or plural-component materials into intricate spaces under a controlled vacuum environment. Dispensing in a vacuum eliminates all possible air voids and air entrapment, thereby producing high-quality, void-free products.

Normally, special vacuum chambers are manufactured and designed to each customer’s specifications. This automatic equipment can be supplied with mixed material from a variety of meter/mix and dispense systems according to application requirements.

Vacuum impregnation can assure a higher degree of integrity and reliability. This new, state-of-the-art equipment technology can create a higher quality electronic component, one that will last longer, handle greater stress factors, and be more competitive on an international basis.

A manufacturer of reed-relays, for example, turned to vacuum impregnation to improve product quality and production rates. The manufacturer was dispensing a 1 cc shot of hand-mixed material with syringes into a 1” x ½” x ½” metal case, which had a wire-wrapped coil inserted. The major problem was air entrapped under the coil which shorted out the unit. Cosmetically, the unit was a mess.

A special vacuum chamber was designed and manufactured to drastically improve the process. The equipment was controlled by a programmable controller, which operated the index table, the meter/mix and dispense equipment, and the vacuum levels. A tray was designed to hold 120 parts at a time, which were to be placed on an index table and evacuated to 29 inches of mercury. Four Micro-Shot dispense heads metered precise 1 cc shots of mixed material into the relay housing.

At first the relay would not accept the epoxy because of mixed material viscosity. A closed loop liquid recirculating heat system was installed on the meter/mix and dispense unit and a heat line jacketed the dispense nozzle. One the material temperature reached
120°F., the reed-relays accepted the material.

By using vacuum impregnation and automatic meter/mix and dispense equipment, a high-quality, air-free impregnated product was ensured. The production rate and cosmetics of the component also were greatly improved.