Presentation on theme: "2005 TRFA Conference Epoxy, Urethane, Silicone: Choice Of Encapsulant for High Reliability Magnetic Components Robert O. Sanchez Design Engineer Sandia."— Presentation transcript:
2005 TRFA Conference Epoxy, Urethane, Silicone: Choice Of Encapsulant for High Reliability Magnetic Components Robert O. Sanchez Design Engineer Sandia National Laboratories Albuquerque, New Mexico (505) Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.
2005 TRFA Conference Introduction Magnetic components such as transformers, solenoid coils, and inductors are required for various DOE and DOD programs. Component application requirements, materials compatibility, small package size requirements, resistant to severe environmental shock, high voltage, and material aging affects are all considered when designing a magnetic component.
2005 TRFA Conference Background Sandia National Laboratories - Research and Development - Weapon Programs Lockheed Martin Corporation Department of Energy Sandia Suppliers
2005 TRFA Conference Magnetic Component Description Transformers - Vary in size from 0.25 in 3 to 1.25 in 3 Inductors - Vary in size from in 3 to 2 in 3 Coils - Vary in size from 0.25 in 3 to 0.75 in 3 Design for Weapon Application - Severe Environments
2005 TRFA Conference Encapsulated Magnetic Component Types Sandia Has More than 100 Designs of Weapon Magnetic Components that have been Fielded in Subassemblies.
2005 TRFA Conference High Voltage Transformer Design 6KV Power Transformer - Ferrite 2616 Pot Core - Wire 42 AWG Polyester Insulated - Wire 34 AWG Polyester Insulated - Kraft Paper Insulation - Solder - Phenolic Microballoon filled Polysulfide Stress Relief Medium - Encapsulation
2005 TRFA Conference 1200 Volt Flyback Transformer
2005 TRFA Conference Epoxy, Urethane, Silicone: Choice Of Encapsulant for High Reliability Magnetic Components Howard W. Arris Materials Process Engineer Sandia National Laboratories Albuquerque, New Mexico (505) sandia.gov Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.
2005 TRFA Conference Introduction Sandia has developed a number of encapsulation formulations Commercially available formulations sometimes utilized Use commercial available constituents- minimize variability Formulations can be generally categorized into epoxies, urethanes, silicones Choice of encapsulant determined by: component type, operating parameters, 40 years manufacturing experience Epoxy and silicone formulations utilize fillers to alter material properties
2005 TRFA Conference Introduction Component design, fabrication techniques, core materials, component functionality- dictate encapsulant, epoxy, urethane, foam, silicone Development of formulations consists of: - Identifying component types for each formulation - Completing component evaluations
2005 TRFA Conference Epoxy for Power Transformers Complete impregnation is required Voids in encapsulant can cause HVB during testing and operation Filled formulations, process at elevated temperatures to reduce viscosity Sufficient pot life to facilitate impregnation of secondary winding Note: It is important to balance TIME/TEMPERATURE/VISCOSITY
2005 TRFA Conference Epoxy for Power Transformers Failure modes after encapsulation may include cracking of encapsulant or ferrite cores, and breakage of windings Encapsulation stresses due to cure shrinkage, CTE differences can lead to component failure The only encapsulants that have been used successfully for this type of component are filled epoxy formulations
2005 TRFA Conference Urethanes and Silicones for Pulse Transformers Obtaining complete impregnation of pulse transformers is not as critical as with power transformers Sandia pulse transformers vary in size from 1in 3 to.25in 3 Typical design might consist of: 5 turn primary winding of 28AWG and a secondary winding of 75 turns of 38AWG on a torroidal core Core materials: molypermalloy powder or ferrite (ferrite cores are stress sensitive)
2005 TRFA Conference Urethanes and Silicones for Pulse Transformers Urethane encapsulants historically used, more recently filled silicone resin Silicone formulations filled with glass micro balloons (GMB) - GMB helps reduce high CTE Urethane formulation has outstanding electrical properties; however, a short pot life Silicone formulation has long pot life; however, we must account for high CTE during cure and “poisoning” associated with silicone
2005 TRFA Conference Polyurethane Foam for Low Voltage Magnetics Low voltage magnetics include: pulse transformers, current viewing resistor transformers, inductors, and coils Utilize various core types, materials, winding configurations, package configurations Obtaining complete impregnation of low voltage transformers is not required Cure stress of encapsulant must be minimized
2005 TRFA Conference Polyurethane Foam for Low Voltage Magnetics Polyurethane foams induce least amount of stress during encapsulation and cure of all of our resin systems Foams are used to facilitate packaging requirements and mitigate shock during testing and use lb/ft 3 most commonly used, Toluene Diisocyanate foams used for 30 years Mold design enabling complete flow are critical to robust package
2005 TRFA Conference Polyurethane Foam for Low Voltage Magnetics Environmentally conscious foams, ploymeric diisocyanate developed, component evaluations started Foam components are manufactured at one of our production facilities, formulations and processing will not be presented here
2005 TRFA Conference Formulations
2005 TRFA Conference Epoxy Encapsulation Formulations Epoxy formulations used for high voltage power transformers historically filled with mica, more recently aluminum oxide and fused silica investigated 4X Mica, (Mineralite Corp.), T-64 Al 2 O 3, ALCOA (Aluminum Corporation of America), Teco-Sil- 44CSS, SiO 2, (C-E Minerals) Use of filler reduces CTE (coefficient of thermal expansion) -reduces stress on encapsulated units Striking a balance between filler loading levels, pot life, viscosity are critical to this application
2005 TRFA Conference Epoxy Encapsulation Formulations Aluminum Oxide and Silica loading levels were determined experimentally Units are encapsulated, cured, and sectioned to analyze impregnation into the secondary winding Examined under 20x magnification Impregnation on these units was excellent
2005 TRFA Conference Epoxy Encapsulation Formulations The following processing temperatures have been determined to be optimum for this formulation and these components 828 epoxy 71°C Mica, Al 2 O 3 or SiO 107°C Curing agent 54°C Molds with transformers vacuum dried at 71°C,.2-3 Torr, 2 hours minimum
2005 TRFA Conference Epoxy Encapsulation Formulations Filler Loading Levels Parts By Weight Mica60 Al 2 O SiO 2 120
2005 TRFA Conference Epoxy Formulations (New) Two Part Formulation Part “A” Formulation IngredientParts By Weight 828 Epoxy50 Arcol PPG KF Total 65.05
2005 TRFA Conference Epoxy Formulations (New) Part “B” Formulation IngredientParts By Weight EMI 2,4 2 MHHPA40 Total42 Filler loading levels Mica60 OR Al 2 O 3 200
2005 TRFA Conference Epoxy Formulations (New) The following process parameters have been determined to be optimum for this component and resin formulations Fillers are dried at 107°C, 4 hrs., then stabilized at 71°C 828 Epoxy, MHHPA, and PPG-1025 preheated to 60°C EMI 2,4 at room temperature Molds with transformers vacuum dried at 71°C,.2-3 Torr, 2 hours minimum
2005 TRFA Conference Epoxy Processing Typical loading levels may be as high as 40 volume percent- resulting in high viscosity formulations Processing temperature is essential to obtaining complete impregnation Time/Temperature/Viscosity Low processing temperature produces a high viscosity formulation resulting in voids or incomplete impregnation High processing temperatures results in shortened pot life that may lead to incomplete impregnation
2005 TRFA Conference Epoxy Processing Determining optimum processing parameters requires experience and the understanding of the effect of Time /Temperature/Viscosity 5-10°C can drastically affect formulation viscosity Heat loss must be minimized to maintain optimum viscosity Molds are filled and degassed at 1-3 Torr for 2-3 minutes Molds are returned to atmosphere and the cure is initiated
2005 TRFA Conference Urethanes and Silicones for Pulse Transformers Conap EN-7™- Urethane MaterialParts by weight EN-4 part “A”100 EN-7 part “B”18.8 Processed at room temperature Molds are filled and degassed at 1-3 Torr for 2-3 minutes
2005 TRFA Conference Urethanes and Silicones for Pulse Transformers Silicone MaterialParts by weight Sylgard™184 part “A”100 (Dow Corning) Sylgard™184 part “B” 10 GMB, D32/ (3M product) Processed at room temperature Molds are filled and degassed at 1-3 Torr for 2-3 minutes
2005 TRFA Conference Summary Encapsulation of magnetic components is essential if they are to survive the environmental requirements. Selection of the encapsulant, either epoxy, urethane, or silicone is dependent on the type of transformer. Choice of the correct formulation is critical in providing high reliability components.
2005 TRFA Conference Acknowledgements Sandia National Laboratories Manny O. Trujillo - Formulation, Process Development Patrick Klein - Materials Characterization Scott Campin - Materials Characterization Mil-Spec Magnetics Shelly Gunewardena- CEO Tony Gunewardena - President