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`
`September 24-26, 1996
`Rosemont Convention Center
`Rosemont (Chicago), Illinois USA
`
`ELECTRICAL
`MANUFACTURING & COIL
`WINDING ASSOCIATION,
`INC.
`
`Petitioners' Exhibit 1011, pg. 1
`
`

`

`Published by:
`Electrical Manufacturing & Coil Winding Association, Inc.
`P.O. Box 278
`Imperial Beach, CA 91933
`
`Copyright 1996
`
`The opinions expressed in these papers are those of the authors and not necessarily
`those of the EMCWA. All papers are printed as submitted by the authors.
`
`Additional copies of the Proceeding may be purchased, while the supply lasts, at $50.00
`per copy from Electrical Manufacturing & Coil Winding Association, Inc., P.O. Box 278,
`Imperial Beach, CA 91933
`
`© 1996 Electrical Manufacturing & Coil Winding Association, Inc.
`
`Electrical Manufacturing & Coil Winding 1996
`
`ISBN 0-941783-16-2
`
`Petitioners' Exhibit 1011, pg. 2
`
`

`

`THERMOPLASTIC ENCAPSULATION: A RAPIDLY
`EXPANDING TECHNOLOGY FOR SENSORS, SOLENOIDS,
`STEPPER MOTOR STATORS, TOROIDS AND TRANSFORMERS
`
`Rakesh S. Puri
`James F. B. Patterson
`Thomas D. Boyer
`
`DuPont Engineering Polymers
`Wilmington, Delaware
`
`ABSTRACT
`
`From anti-skid braking systems (ABS) through
`hydraulic control systems to distribution transform(cid:173)
`ers, a common problem is how best to protect
`wound coils against operating environments. In(cid:173)
`creasingly, the answer is thermoplastic encapsula(cid:173)
`tion using engineering polymers ranging from nylon
`to liquid crystal polymers. In addition to providing
`excellent coil protection, these thermoplastic resins
`eliminate the volatile organic compounds (VOCs)
`commonly associated with potting processes and
`make possible the high productivity required in the
`encapsulation of automotive sensors and small
`toroids for printed wiring boards.
`
`This paper reviews the more significant engineering
`polymers used in encapsulation, the molding and
`tooling techniques required, and typical end - use
`applications.
`
`INTRODUCTION
`
`Electrical coils and components are encapsulated for
`physical protection, electrical insulation and heat
`dissipation. Until recently, the polymers most com(cid:173)
`monly used for encapsulation were thermoset resins
`such as epoxies, phenolics and polyesters. Today,
`however, engineering thermoplastics, such as
`nylons, PET polyesters and PBT polyesters, are
`beginning to take the lead.
`
`The development of pretested IEC 85 and UL 1446
`Electrical Insulation Systems using thermoplastics
`for encapsulation has facilitated the shift from
`thermoset to thermoplastics. Such systems speed
`the listing process and reduce the time and costs of
`testing.
`
`COST COMPARISONS
`
`Higher material costs for thermoplastics are often
`outweighed by savings in manufacturing costs.
`Injection molding allows dramatically faster produc(cid:173)
`tion cycles and the elimination or reduction of
`secondary operations. Yields are higher, and
`molded-in functional and assembly features can
`eliminate the need for additional parts.
`
`Yields are increased because thermoplastics are
`tougher in thin sections than thermosets, so thermo(cid:173)
`plastic encapsulations are less likely to break during
`manufacturing.
`
`The number of parts required and assembly labor
`costs are reduced by integrating the functions of
`brackets and connectors into a one-piece encapsu(cid:173)
`lation molding. Increasingly, designers are taking
`advantage of these integral parts to reduce produc(cid:173)
`tion costs.
`
`ENVIRONMENTAL CONSIDERATIONS
`
`Compared with typical thermoset encapsulation
`resins, engineering thermoplastics generally offer
`increased productivity, more toughness to permit
`designs with thin sections, recyclability and elimina(cid:173)
`tion of emissions during encapsulation.
`
`Unlike impregnation with some varnishes or potting
`with epoxies and some other thermosetting materi(cid:173)
`als, thermoplastic encapsulation produces no
`environmentally harmful emissions or volatile
`organic compounds (VOCs).
`
`467
`
`Petitioners' Exhibit 1011, pg. 3
`
`

`

`Molders can recycle sprues and runners by grinding
`them up for reuse. In tests, parts of typical thermo(cid:173)
`plastics containing up to 50% ground scrap routinely
`meet UL standards. Thermoset scrap usually can't
`be recycled back into the molding process.
`
`Heat-conductive grades of PET polyester can be
`used to substantially reduce core and "hot spot"
`temperatures of encapsulated components. Since
`they are electrically conductive, they would often be
`molded over a conventional insulating resin.
`
`THERMOPLASTICS FOR ENCAPSULATION
`
`Most thermoplastic encapsulated components today
`are produced with nylon and polyester resins. All the
`materials for encapsulation described in this paper
`are reinforced with glass. Newer materials have
`been developed to extend the performance range of
`standard nylons and polyesters.
`
`Encapsulated components rated for service up to
`Class F ( 155°C) in UL 1446/1 EC 85 Electrical
`Insulation Systems (EIS) typically use PA 66 nylon,
`PET polyester or PST polyester. One PET polyester
`is now recognized in a UL EIS for Class H (180°C).
`Solenoids requiring the Class H recognition are in
`commercial production with this PET.
`
`Glass-reinforced (GR) PA 612 nylon is increasingly
`used for encapsulation of fine-gauge sensor wind(cid:173)
`ings. This resin permits low speed, low pressure
`molding to avoid damage to delicate windings
`because it has a slower crystallization rate and a
`higher flow rate at low injection pressure than either
`GR PA 66 nylon or PET polyester.
`
`High temperature nylons (HTN) provide greater
`thermal resistance and better dimensional stability
`than GR PA 66 nylon while delivering toughness and
`chemical resistance typical of the nylon family. HTNs
`melt at about 300°C, while PA 66 nylon melts at
`255°C. One resin has recently achieved a UL
`relative thermal index (RTI) of 150°C (electrical),
`1 ooc higher than the highest-rated PA 66 nylon
`available.
`
`Compared with PET or PST polyesters, HTN resists
`short-term exposures to higher temperatures and
`provides better resistance to chemical attack, hot
`humid environments and thermal cycling.
`
`Applications for HTN are under development in
`the encapsulation of sensors, solenoids and
`transformers.
`
`LCPs are possible candidates for encapsulations
`that must withstand frequent or long-term exposure
`to temperatures greater than 175°C. They also offer
`outstanding dimensional stability.
`
`For thermoplastic encapsulation of larger parts than
`those technically or economically feasible with
`injection molding, a new sheet material can be
`compression molded over the part. Called thermo(cid:173)
`plastic moldable composite sheet, it consists of a
`stable matrix of glass fibers impregnated with a
`thermoplastic resin such as PET. One of the first
`applications being developed involves encapsulation
`of distribution transformers operating above 10 kVA
`that have thermal cycles from ambient temperature
`to 200°C.
`
`THERMOPLASTIC ENCAPSULATION
`TECHNIQUES
`
`In most cases, electrical components are encapsu(cid:173)
`lated with thermoplastic in an insert injection molding
`operation. The coil or component is inserted in the
`mold, and the melted thermoplastic is injected while
`lead wires or terminals are clamped off from the
`thermoplastic flow.
`
`The object being encapsulated can be supported in
`the mold with stationary pins, or with hydraulically
`actuated pins that are retracted before the melted
`material solidifies. When pins are retracted during
`molding, the spaces they occupied pack with poly(cid:173)
`mer so there are no holes to fill in a secondary
`operation.
`
`Although some encapsulation is done with horizontal
`molding equipment, the preferred process uses
`vertical clamp machines that allow gravity to hold the
`insert in place as the positioning pins are operated
`before molding begins.
`
`Maximum productivity can be achieved with shuttle
`or rotary table molding presses with two or more
`lower mold halves. While one encapsulation is being
`carried out, an operator or robot can remove finished
`parts and insert coils or components at the loading/
`unloading station(s).
`
`ENCAPSULATION OF SENSORS
`
`Sensors for measuring speed, position, fluid level
`and other variables are widely used in automobiles
`and appliances as well as in industrial controls. They
`
`468
`
`Petitioners' Exhibit 1011, pg. 4
`
`

`

`often are encapsulated to provide electrical insula(cid:173)
`tion and protection against moisture, dirt and me(cid:173)
`chanical damage.
`
`Low-pressure, slow-speed encapsulation molding is
`often selected for sensors because they usually
`contain delicate windings that can be damaged by
`high molding speed and high injection pressure.
`
`Automotive wheel speed sensor
`
`SSI Technologies Inc. encapsulates the automotive
`wheel speed sensor shown in Figure 1 in glass(cid:173)
`reinforced PA 612 nylon. The metal parts in the
`mounting flanges are molded-in inserts.
`
`The sensor shown was redesigned for molding in a
`tool with retractable pins to support the coil bobbin
`during encapsulation. The change provided major
`improvements in productivity and part quality.
`
`Previously, the bobbin insert was held by a steel
`fixture (hand tooling) placed by hand in the encapsu(cid:173)
`lation tool. Holes remained in the encapsulation
`
`when the fixture was removed after molding as
`potential sites for moisture penetration. Significant
`labor was required to load and unload this fixture . In
`addition, the fixture caused the tool to wear, resulting
`in molded parts with flash.
`
`The sensor is now produced in a tool equipped with
`hydraulically actuated pins that support the bobbin
`during molding, then retract so that the spaces they
`occupy fill with polymer to help seal the encapsula(cid:173)
`tion. The retractable pin system also meets the need
`for consistently accurate positioning of the sensor
`coil. This is crucial because of the strong effect of
`the coil position on the sensor's output signal.
`
`Figure 2a shows the mold with positioning pins
`extended. Figure 2b shows the pins retracted. The
`
`Figure 1 a: Automotive wheel speed sensor, front
`view.
`
`Figure 2a: Sensor mold, positioning pins extended.
`
`Figure 1 b: Automotive wheel speed sensor, rear
`view.
`
`Figure 2b: Sensor mold, positioning pins retracted.
`
`469
`
`Petitioners' Exhibit 1011, pg. 5
`
`

`

`timing of pin retraction during the molding cycle is
`controlled by synchronizing it with the linear position
`of the molding machine's screw. Each mold cavity
`has eight pins, four in each half. The ends of the
`pins fit into bosses molded in the top and bottom of
`the coil bobbin (Figure 3). These bosses prevent
`horizontal movement of the insert, while the hydrau(cid:173)
`lic pins prevent vertical movement.
`
`Figure 3: Sensor bobbin with four of eight positioning
`bosses visible.
`
`The new production technique reduced labor for
`molding and finishing by more than 50%. Elimination
`of the fixture required for the old tool eliminated the
`need to load the bobbin/lead cable assembly into the
`fixture, so the new process can run with one opera(cid:173)
`tor instead of two.
`
`Previously, one operator loaded bobbin/lead cable
`assemblies in a fixture while another placed a
`loaded fixture in the tool and removed a molded
`sensor. With the new tooling, the operator unloads a
`sensor and then loads a bobbin/lead cable assembly
`directly in the tool. While one half of the tool is in the
`molding position, the other is open for unloading and
`loading.
`
`With the improved tooling, these sensors no longer
`require visual inspection and deflashing because
`there is no molding flash . With the old tool, loading
`the fixture caused wear of mating surfaces that led
`to flash-causing polymer leaks. The new tool isn't
`subjected to this wear, and in addition, flash is
`suppressed because molding pressures are as
`much as 40% lower because gates are larger than in
`the tooling previously used.
`
`(AWG 42) magnet wire (AWG 42) used for the
`sensor coil. The material is particularly well suited to
`retractable-pin tooling because its relatively slow
`crystallization rate aids in filling the space left by the
`pins as they are retracted. This material also has
`good thermal shock resistance, a key advantage in
`meeting automotive thermal cycling requirements .
`
`ENCAPSULATION OF SOLENOIDS
`
`Solenoids are generally made by encapsulating coils
`wound on bobbins. The use of bobbins that have
`been molded to achieve full crystallization is crucial.
`Incompletely crystallized bobbins are apt to
`shrink and/or distort during encapsulation. Full
`crystallization is achieved by using mold tempera(cid:173)
`tures of at least 1 oooc for PET polyester and at least
`80°C for GR PA 66 nylon.
`
`Ideally, coils should be precision- or level-wound so
`that the encapsulation polymer will flow smoothly
`over the winding's surface. Random winding can
`disrupt polymer flow and cause bunching of magnet
`wire.
`
`Blocking out moisture
`
`Bobbin flange design can affect the mechanical
`connection between bobbin and encapsulation. A
`tight seal is important because it helps keep mois(cid:173)
`ture away from the windings.
`
`One way to improve the seal is to use a bobbin
`flange with tapered rather than square ends. The
`thin, tapered ends melt more readily during encapsu(cid:173)
`lation, providing a melt bond when PET polyester is
`used. On other surfaces, melt bonding can be
`enhanced by the use of fine melt ribs.
`
`Another way to improve the link is to provide
`grooves in the bobbin flanges to achieve a mechani(cid:173)
`cal lock between the encapsulation and flange.
`
`Figure 4a (next page) shows the grooved design of
`the flanges on a bobbin used in a solenoid valve for
`an automotive suspension leveling system. The
`valve is mounted on a compressor located under(cid:173)
`neath an automobile where it is exposed to moisture
`and salt spray that could corrode inadequately
`protected windings .
`
`The GR PA 612 polymer selected for the sensor
`allows filling of the mold at relatively low pressure
`and slow rate. This minimizes stresses on the fine
`
`Thanks to the grooves and good molding practice,
`the solenoid valve meets the suspension system
`manufacturer's rigorous leak-test requirements. The
`
`470
`
`Petitioners' Exhibit 1011, pg. 6
`
`

`

`manufacturer, Multicraft Electronics, reports that it
`has developed technology to achieve a melt bond
`between encapsulation and flange to meet future
`needs for an even tighter moisture barrier.
`
`In addition to meeting moisture penetration require(cid:173)
`ments, Multicraft's solenoid also stands up in severe
`vibration and thermal cycling tests. Both the coil
`bobbin and encapsulation are molded from glass(cid:173)
`reinforced PA 66 nylon resins. The various stages in
`producing the encapsulated valve are also shown in
`Figure 4a.
`
`The leveling system's bobbin also illustrates the
`potential for the integration of additional functions
`into the bobbin design. It has an integrally molded
`valve seat that simplifies manufacturing, and its bore
`serves as the guide for the armature. The sectioned
`component in figure 4b shows the integral valve
`seat.
`
`Figure 4a: Stages of production, solenoid valve for
`automotive suspension levelling system.
`
`Figure 4b: Bobbin of solenoid valve has an integrally
`molded valve seat.
`
`471
`
`Figure 5: Encapsulated box-frame and laminated
`solenoids.
`
`Solenoids for appliances and other applications
`
`The box-frame and laminated solenoids shown in
`Figure 5 are used in a range of equipment, including
`appliances and vending machines. The manufac(cid:173)
`turer, Dormeyer Industries, switched from thermoset
`polyester to PET polyester thermoplastic for encap(cid:173)
`sulation to lower production costs and to reduce
`lead-wire leakage.
`
`Costs were lower owing to higher yields, faster mold
`cycles and reduced tooling wear. The PET
`polyester's toughness allowed reducing encapsula(cid:173)
`tion thickness by 40% to cut material requirements.
`Taking advantage of this toughness, Dormeyer can
`provide parts with integral mounting brackets when
`users require them.
`
`Use of a pre-approved UL 1446 Electrical Insulation
`System saved time and testing costs in achieving UL
`recognition.
`
`Automotive Emissions Control Solenoid Valve
`
`The solenoid valve shown in Figure 6 (next page)
`vents the fuel vapor canister in an automotive
`evaporative emissions control system. The system
`features on-board diagnostics that alert drivers to
`malfunctions that increase emissions.
`
`Petitioners' Exhibit 1011, pg. 7
`
`

`

`Figure 6: Canister vent solenoid
`valve with encapsulation covering
`both the bobbin and the valve
`body
`
`The valve's design is quite innovative. The encapsu(cid:173)
`lation encases both the bobbin assembly and the
`valve body, securely joining them and sealing their
`interface. The flux-concentrating steel components
`for the solenoid are also covered by the encapsula(cid:173)
`tion. In addition, terminal housing and a mounting
`bracket are molded integrally with the encapsulation,
`thus reducing part and assembly costs.
`
`A new grade of GR PA 66 with especially high melt
`flow is used for the encapsulation so very low
`injection pressures can be employed. Normal
`pressures caused distortion of the valve body during
`overmolding. The bobbin and valve body are also
`molded from GR PA 66.
`
`Figure 7: Encapsulated automotive anti-theft an(cid:173)
`tenna coil with empty and wound bobbins.
`
`Figure 8: Encapsulated toroidal choke coil.
`
`Integrally molded hooks secure the antenna on a
`circuit board, thus avoiding the need for separate
`fasteners. An insert-molded header connects the coil
`to system circuitry.
`
`The finished unit withstands repeated thermal
`cycling from -40°C to 85°C at 95% relative humidity
`and vibration from 1 0 to 500 Hz at acceleration
`forces of up to 1 OG, according to Standex.
`
`ENCAPSULATION OF SPECIALIZED COILS
`
`Toroidal choke coils
`
`Automotive Anti-Theft System Antenna Coil
`
`Figure 7 shows an antenna coil made by Standex
`Electronics for an automotive anti-theft system.
`Vehicle starting is controlled by radio-frequency
`identification codes received by the antenna, which
`surrounds the ignition lock. The coil form, a wound
`coil and an encapsulated coil are shown in Figure 7.
`
`This component is encapsulated with GR PA 612
`nylon. The material permits encapsulation molding at
`low injection pressure and slow fill rate to avoid
`damage or displacement of the delicate fine-gauge
`winding. The tooling is tunnel-gated, which mini(cid:173)
`mizes surface defects and eliminates secondary
`finishing, including degating.
`
`Another recent application for GR PA 612 nylon from
`Standex involves the encapsulation of small board(cid:173)
`mounted toroidal choke coils for power filtering.
`Figure 8 shows a choke coil before and after encap(cid:173)
`sulation.
`
`Encapsulation protects the coils against physical
`damage, dust and moisture penetration. The mold
`design provides total part coverage with no holes in
`the encapsulation.
`
`Standex reports that these units can be soldered to
`circuit boards using surface-mount technology.
`The encapsulation is designed so that automated
`equipment can pick up and place coils on circuit
`boards.
`
`472
`
`Petitioners' Exhibit 1011, pg. 8
`
`

`

`Previously, Standex potted the coils in thermoset
`epoxy in a molded thermoset case. The epoxy took
`up to 24 hours to cure. The change from epoxy to
`GR PA 612 provided a significant cost reduction.
`
`ENCAPSULATION OF MOTOR STATORS
`
`The use of encapsulation technology to insulate
`motor stators offers substantial savings in cost
`compared with the use of paper, film or molded
`insulation parts. The origin of such savings is evident
`in the case of the NEMA 23 stepper motor produced
`by Pacific Scientific Motor and Controls Division
`shown in Figures 9 and 10.
`
`The motor's encapsulated stator is a key element of
`a "design for manufacturing". The PET polyester
`
`Figure 9: Stepper motor sectioned to show details of
`encapsulation.
`
`Figure 1 Oa: Wound stator of stepper motor, ready for
`overmolding.
`
`Figure 1 Oc: Encapsulated stator after machining.
`
`Figure 1 Ob: Stator after overmolding.
`
`Figure 1 Od: Completed stepper motor
`
`473
`
`Petitioners' Exhibit 1011, pg. 9
`
`

`

`encapsulation replaces an aluminum rear end bell
`and an electrical connector housing required with
`the previous design, which was potted in thermoset
`epoxy. The patented encapsulation design and
`technology also permitted elimination of eight
`connectors and a circuit board. Figure 9 shows a
`motor that has been sectioned to show details of the
`encapsulation.
`
`Electrical connections are provided by fusing pins in
`a header to the winding leads. The header is re(cid:173)
`tained in the encapsulation and enclosed by the
`integral housing.
`
`The stator is wound using slot liners of PET polyes(cid:173)
`ter. Figure 1 Oa shows the wound stator ready for
`overmolding. It is placed in the bottom half of the
`mold (see Figure 11) which is then indexed under
`the top of the mold. A round core in the mold leaves
`a bore for the rotor. Molding takes only 45 seconds
`compared with 2 hours for epoxy potting.
`
`Molding pressure and speed are carefully controlled
`to avoid damage to windings and ensure proper
`packing of the mold to achieve void-free parts.
`
`Next, the molding sprue and gate shown in Figure
`1 Ob are removed and the bore is precisely honed to
`produce a 0.003 in. (76 J..l.m) gap between the rotor
`and stator. Then the end bells are machined so they
`are perpendicular to the rotor (Figure 1 Oc). A groove
`is machined in the integral front end bell to retain the
`snap ring that holds the rotor in place. Much of the
`honing and machining is automated. Figure 1 Od
`shows an assembled motor.
`
`coils and laminations. In tests conducted by DuPont,
`transformers encapsulated in PET polyester and
`overmolded with conductive PET polyester operated
`at significantly lower temperatures .
`
`Figure 11 : Wound stator of stepper motor in mold.
`
`Encapsulating larger transformers
`
`Encapsulation of larger transformers can be accom(cid:173)
`plished with thermoplastic compression molding
`sheet composites. The composite sheets are
`heated, placed in tooling in a molding press and
`formed under pressure around the transformer.
`These sheets are reinforced with glass fibers that
`are 0.5 in. (inches) (12.7 mm [millimeters]) long and
`randomly oriented in parallel with the sheet's sur(cid:173)
`faces. Both insulating and conductive types are
`available.
`
`ENCAPSULATION OF TRANSFORMERS
`
`SUMMARY
`
`Encapsulation techniques for transformers and
`chokes are much the same as for solenoids and
`sensors. Connectors or terminals can be molded in.
`Coil forms with stepped configurations or tapered
`flanges are used to help ensure a secure bond with
`the encapsulation material, and coils are wound with
`smooth surfaces to ease thermoplastic flow.
`
`Thermoplastic encapsulation of electrical coils and
`components is growing very rapidly because of the
`cost, performance and environmental benefits
`available with thermoplastics. New encapsulation
`materials, advances in encapsulation technology
`and the development of UL 1446/IEC 85 EIS's are
`supporting this growth.
`
`PET polyesters rather than PAs are preferred for
`encapsulating transformers for continuous operation
`because they have higher relative thermal indices.
`
`Conductive PET polyester has carbon additives
`that provide thermal conductivity of 1.5 W/m·K
`(watts/meter·degrees Kelvin) . This material can
`be used in overmoldings that remove heat from
`
`REFERENCES
`
`"Improved Thermoplastic Encapsulation of a Wheel
`Speed Sensor Using Retractable-Pin Tooling",
`Griswold, S.K., T.J. Bryan and J.F.B. Patterson, from
`New Applications of Plastic Components in Vehicle
`Design (SP-1166), SAE International, 400 Common(cid:173)
`wealth Drive, Warrendale , PA 15096-0001, 1996.
`
`474
`
`Petitioners' Exhibit 1011, pg. 10
`
`