Original Date: 05/01/2000
Revision Date: 01/18/2007
Information : Encapsulation and Impregnation
Northrop Grumman Defensive Systems Division (DSD) builds a number of assemblies that require encapsulation or impregnation. An encapsulated or impregnated assembly is typically an electrical device (e.g., high voltage power supplies, ignitors, modulators, transformers) requiring a protective coating of material to fill all spaces between components and around the exterior surfaces. In most applications, the encapsulant material is silicone, epoxy, or urethane. In the past, process yields were relatively low (50% to 60%) especially on start-up items, and required 100% inspection by quality assurance (QA). Voids in the encapsulant were common. Process traceability was very difficult because it relied too much on manually generated logs and operator memory. Northrop Grumman DSD has implemented a number of improvements for encapsulation and impregnation.
The current practice institutes these changes: Statistical Process Control (SPC) is used in critical areas to ensure that the manufactured product maintains certain build criteria from lot to lot. These parameters include cleanliness testing, viscosity measurements, adhesion testing, and hardness readings.
Grit blasting was replaced by plasma etching to prepare the part surfaces before encapsulation, resulting in cleaner parts with better adhesion.
Design for Manufacturability is instituted by Operations on all new product types. This approach ensures that the development, design, and manufacturability of new products enable the company to continue producing quality encapsulated and impregnated assemblies efficiently.
Northrop Grumman DSD has empowered its operators by training them to perform 97% of the in-process inspections.
The Encapsulating Team developed a handbook, Encapsulation for Dummies, for operators and design groups as a source of information on these processes and failure analysis.
Since implementing these changes, Northrop Grumman DSD has greatly increased its process yields on encapsulated and impregnated items; eliminated voids; and reduced analysis costs. Empowerment has also increased operator awareness, resulting in higher quality products and quicker isolation of problems.
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