March/April 1999 Issue WHN

De-Mystifying Vacuum Impregnation

Straightforward answers about the "Black Magic"

process of sealing electronic assemblies

Todd Weldon

Megatech

For many electrical engineers, vacuum impregnation, otherwise known as "sealing," is a mysterious, little known process for sealing porous metals, such as in die cast or powdered metal applications. It is routinely used

However, the connection is rarely made that impregnation sealing is just as effective for electronic assemblies, such as those that include wiring and plastics. All engineers know that plastic components must be protected before assembly to ensure optim

Such oversight occurs simply because too few individuals fully understand either the process or the benefits of sealing. Yet, this lack of information could affect the quality of their parts and ultimately lead to a failing or poorly performing product

In order to provide engineers with the knowledge of an additional option to improve reliability, Wayne Fisher, vice president of Magna-Tech/TechnaSeal, agreed to help demystify sealing technology. Located in Muncie, Indiana, Magna-Tech/TechnaSeal, has t

What electronic parts can be sealed?

Microscopic voids in electronic components can cause failures in all types of parts, parts that could be better sealed and protected by vacuum impregnation. These include pin connectors, switches, wire assemblies, capac

"This process is for sealing all types of electronic components," Fisher stated. "Traditionally, it's mainly been used for things you might find under the hood of a vehicle, such as a connector, wire assemblies, wire harnesses — these types of

Why do electronic components need to be sealed?

Tiny holes or cracks are inherent in all molded electronic components, especially where the metal pins meet the plastic case. These voids can allow moisture or other corrosive particles to penetrate the plastic, shorten

"Nothing will frustrate a customer more than an intermittent problem that fails in the field, but then miraculously starts to work when examined by a repair technician," noted Fisher.

The automotive industry has its own particular need for sealing because specifications often demand that components like fuel pumps, wiring harnesses or encapsulated coils meet leak requirements to protect them from road salt and moisture, leaks from tr

Finally, most electronic parts must also be protected from heat, whether from an engine manifold or from the hot temperatures inside today's high-powered Pentium computers. Heat can cause plastic and metal to flux at different temperatures, looseni

Batch Processing Basket which lowers sealed parts into the rinse tank to wash off residual resins.

Why aren't traditional methods of sealing good enough?

"If you seal with an O-ring made of rubber, over time it is going to get dry and brittle, and then crack. A good seal will not do that," Fisher said. "Likewise, if someone puts a dollop of silicone around the connectors

"Ultimately, top coats and other external sealants tend to affect the finish of the product. In contrast, if a vacuum sealing process is performed correctly you should be able to have two products on your desk and look at them under shop or office light

What, exactly, does vacuum sealing entail?

Vacuum impregnation is not an outside coating, but instead seals the part internally using a vacuum pressure chamber to impregnate liquid resin into minute cracks. The heart of the process takes place relatively quickly

Customers provide the sealing house with parts that are molded, finished and ready for assembly. The parts are placed in batches into baskets and then into a vacuum pressure chamber where vacuum is drawn. This evacuates the chamber and opens fine leak p

The chamber is then pressurized, forcing a liquid resin into the components. After passing through several rinses to clear excess resin from external surfaces, the remaining resin inside the part is left to catalyze into a polymer — a result of the

"At room temperature, the resin will cure in a matter of hours. Alternatively, we can cure the resin at 150° F, which speeds up the process to completely dry the product in about one hour," said Fisher. "There have been cases where parts were dropp

What makes vacuum sealing so effective?

The seal is made with an anaerobic resin composed of methacrylate monomers, which is formulated differently than that of metal sealants. It is purposely designed to seal at the interface between two dissimilar materials

The resin is also formulated to withstand a wide range of temperatures from -40°C to +150°C. It is effective in plugging holes on the surface as well as for what is known as "through porosity" — cracks and holes that travel all the way th

What are the benefits of sealing?

Vacuum impregnation permanently seals parts in a way that cannot crack or degrade, with better quality control and higher production rates than other sealing methods. There is no shrinkage, it stops corrosion, and meets

This adds up to financial savings for OEMs and automobile manufacturers alike by reducing labor costs and the number of faulty parts. Initially, 100 percent of parts are tested to demonstrate the effectiveness of the process, but soon, only 5 percent or

There are definite cost savings because of the decreasing scrap and increasing salvage quantities. Most importantly, though, manufacturers profit because the proper seal on an electronic part can prevent the failure of a larger component. For example, t

"The thing that horrifies automotive engineers is the idea of a warranty claim," Fisher pointed out. "Somebody's going to have to answer for it. What if it was a 25 cent connector that failed because moisture passed through the seal? Now they have

Why is outsourcing the sealing process more effective than doing it in-house?

In some traditional methods of sealing, employees must handle each part, sometimes numbering millions a year, to shoot epoxy onto the surface. Mistakes can easily be made — applying too much alters the shape of the

In order for this process to be carried out in-house, a manufacturer would have to make a capital investment in vacuum pressure chambers, rinsing basins, and furnaces; spend time learning the process; and then purchase the resin supply, all at a conside

It is also difficult for an OEM to match the level of quality control that can be achieved by a company that specializes in sealing. For example, Magna-Tech/TechnaSeal meets certified performance standards, including ISO 9002 and QS 9000 — the stan

"We may be the last people to see these parts before they go to assembly," Fisher said. "To do business with GM, Ford, Chrysler, and Japanese manufacturers, we've always had to have quality control systems. If they send us 1000 pieces to be sealed,

Is sealing cost-effective?

For pennies a part, vacuum impregnation is more cost-effective than other sealing processes. One OEM of lamp assemblies is switching to vacuum impregnation, cutting sealing costs nearly in half because of time and labor

"They had this state-of-the-art plant with a little antique machine to shoot epoxy that looked like it was from the World War II era," recalled Fisher. "They determined that their internal cost was in the 10-cent per piece range what with material cost,

What is the final payoff for sealing?

One hundred percent "First Time Capability" is the standard by which many manufacturers measure success. This means they can warrant that their product will perform flawlessly right from the start. By employing proper s

"Given the fact that vacuum impregnation can help manufacturers meet their quality goals, it should no longer be looked upon as a value-added process, but rather a value-guaranteed process," Fisher said. "The bottom line is that engineers need to know t

For more information on vacuum impregnation sealing for electronic components, contact MagnaTech/ TechnaSeal at 3416 South Hoyt Avenue, Muncie, IN 47302; or call (765) 284-5050; or fax (765) 286-0557. Visit MagnaTech/TechnaSeal on the web at: www.techna