CA2343660A1 - A circuit device having a protective coating formed by injection molding a reactively cured material - Google Patents

Abstract

Circuit devices can be protectively encapsulated in a rubber material. The coating may be applied by injection molding a mixture of reactive components that form the insulating rubber once cured. The injection of the liquid components minimizes injury to the circuit components, while achieving a high degree of defect free coating. The coated circuit devices are then resistant to water and other environmental effects. Heat distribution is controlled. The exterior may be further metallized and grounded to limit electromagnetic interference.

Description

wi ' ' CA 02343660 2001-04-11 A CIRCUIT DEVLCE HAVING A PROTECTIVE COATING FORMED BY
INJECTION MOLDING A REACTIVELY CLfRED MATERIAL
The Applicants hereby claim the benefit of their provisional application, Serial Number 60/206626 filed May 24, 2000 for "A Circuit Device Having A Protective Coating Formed By Injection Molding A Reactively Cured Polyurethane."
1. Technical Field The invention relates to electronic circuit device construction and particularly to protective coatings for electronic circuit devices. More particularly the invention is concerned with an electronic circuit device coated by a reactive injection molding process.

2. Background Art I5 Encapsulating circuit devices in an electrically in ulating material is a known method to protect a circuit device from water and other substances, and to distribute heat evenly in the circuit device. Other desired results are electrical insulation, physical damage protection, packaging ease and reduced total package cost. The selection and application of coating materials must be done carefully to compliment the circuit device's mechanical, electrical and environmental conditions. There are three commonly applied methods to encapsulate electronic circuit devices. The first is potting wherein one forms a container (a pot) including th.e circuit device and then fills the container with an insulating material that hardens around the circuit. The potting materials are commonly silicone based rubbers. The problem is the container is typically a metal casting or similar container resulting in a final circuit device that is bulky, and heavy. The cost of the casting is also significant. There is therefore a need to protect a circuit device from water and other materials without potting it in a metal container.
There is little exposed surface to release solvents or other outgased components by using either method. The potting material is poured on the circuit device, enabling it to flow by the force of gravity over, around and between the circuit device elements.

Care must be taken that there are no voids (bubbles) left in the pot which alter the performance of the circuit device with respect to a sta~~dard, provide an electrical discharge path or act as a water or similar access channel or reservoir. To achieve this, the potting material is necessarily quite fluid, but that l;enerally means the potting material takes a longer time in curing. Potting a circuit: device in a container then requires a relatively long cure time. There is then a need to reduce the coating time for the circuit device. There is a similar need for a coating pro<:ess with a short curing time.
Another encapsulation method is injection molding. More recently the use of high-pressure plastic injection molding for encapsulation has been used where the circuit device characteristics allow. The key difference between potting and the current injection molding methods is pressure. Potting is done at: atmospheric pressure while injection molding is done at a very high pressure. Depending upon the electrical application, voids are the significant problem in encapsulation. Voids result from the inability of the encapsulant to flow and fill the entire cavity. Additionally air may be trapped while mixing the potting components. Voids can cause electrical breakdown, particularly under high voltages. Voids can cause poor thf:rmal conductivity leading to circuit component failures. Potting materials can have poor adhesion, thereby providing conduction or water retention channels that limit circuit device integrity.
Voids can also be an aesthetic issue in some circuit devices.
Techniques to minimize and ideally eliminate voids have been developed, including: preheating the materials and circuit device to workable limits, thereby reducing viscosity, vibrating the potted circuit device to induce air migration, applying vacuum to the mixed materials or the potted circuit device to assist in air migration, and heating the potted circuit device to its full cure. The general observation is that injection molded circuit devices have a greater susceptibility to voids due to high material viscosity and low flow rates.
The ability of the encapsulant to adhere to circuit device components reliably is of great value, particularly where the coated sections are thin and the coating increases mechanical integrity. Surface arc tracking is a significant problem in high voltage applications. The encapsulant formulation is key to blocl;ing surface arc tracking, and has been demonstrated particularly in the injection molded circuit devices.

..r _ _ ____~ -d: CA 02343660 2001-04-11 Cure time and overall cycle time issues are insignificant problems in standard injection molded circuit devices. Potting compounds typically have long cure times and need to be "accelerated" or "catalyzed" to shorten their cure time. The cure times are usually very long, necessitated by having to have a reasonable process "working time"
prior to curing. Therefore the option is to have a long ambient cure time of up to a day or more, or to bake the circuit device at a non-destructive temperature for several hours to permit in-process handling and then allowing the circuit device to finish cure at ambient temperature. In either case, the circuit device, the' molds and other equipment are dedicated for an extended time period. This is expensive.
With any encapsulant, the physical shrinkage of the encapsulating material must compliment the physical limits of the circuit device and its components.
Current injection molding methods use high durometer materials leading to high forces on the circuit components either during injection or subsequent shrinkage. The forces resulting from injection molding of these materials, either during the initial molding or during shrinkage, can destroy circuit board components. There may be implosions of void-containing components such as capacitors; thermal damage to insulation, or coatings; fracture of sintered structures such as magnetic cores; distortion or tearing of interconnections such as foils, or leads; and mechanical dislocation of components. There may be large voids throughout the cavity. There may be poor, or no adhesion to components or substrate thereby forming electrical discharge paths along these internal channels. The entire package may be distorted due to shrinkage differentials.
The Applicants have developed a molding process using reaction injection molding or RIM molding. RIM molding simultaneously rnixes and injects two viscous materials that react to form a solid or resilient substance. RIM Molding, was initially developed to produce moderate-to-large, low-to-medium density parts for the automotive trim and interior market; it has since expanded to include relatively large consumer and commercial items. It has however not been widely applied to small items, presumably because of material arid process alternatives. Notably it has not been used with electronic products, and specifically not as a substitute for potting.

Disclosure of the Invention A protected electronic circuit device can be formed from a circuit device carrier supporting an electronic circuit device with two or more connection leads; and an electrically insulating, coating material closely covering and adhering to the circuit device. Connections for electrical input and output from the circuit are left extending through the coating. The coating material comprises a reactive combination of two or more fluid components. It is not necessary for the coating material to be further enclosed by an adjacent container. The protected circuit can be formed by positioning a carrier body with at least one electronic circuit device composed of two or more electronic components in a mold; supplying the mold with a curable, insulating coating material to coat and cover the electronic circuit device; curing the coating material; and ejecting the coated circuit device carrier body from the mold.
An object of the invention is to provide an overall snnaller coated circuit device.
Another object of the invention is to provide an overall lighter weight coated circuit device. An object of the invention is to speed up the manufacturing process in making coated circuit devices, and to enable a mass production process for the protective coating of circuit devices. Another object of the invention is to enable the use of low viscosity materials) (under 300 centipoise), to minimize void formation in the coating.
Other objects of the invention are to enable a reasonably :rapid coating process time of potentially less than two minutes, to increase production speed, and to enable high material flow rates with injection times of less than a few seconds while eliminating mechanical damage to circuit devices. A further object of the invention is to enable low molding temperatures (under 150°F). An object of the invention is to enable molding with a low (under 6.895 x 104 Pascals (10.0 pounds per square inch)) cavity pressure to reduce or eliminate component damage. An object of the invention is to reduce overall production coating cost.
Brief Description of the Drawings FIG. 1 shows a coated circuit device.

FIG.s 2, 3 and 4 show respectively top, side and bottom views of a preferred circuit device.
FIG. 5 shows a group of circuit devices grouped in a ladder form.
FIG. 6 shows an open mold.
FIG. 7 shows an open mold with two circuit sets inserted unto position.
FIG. 8 shows a partial, cross sectional, end view of a mold closed around two circuit devices.
FIG. 9 shows a top view of a molded set of two groups of circuit devices prior to prior to flash trimming and circuit device separation.
FIG. 10 shows a side view of the molded set of circuit devi<;es from FIG. 9.
FIG. 11 shows a coated circuit device with an exterior EMI barrier coating.
Best Mode for Carrying Out the Invention The preferred coated circuit device 10 consists of a circuit device 12 populated with circuit components that is then coated with a protective coating 14.
FIG.s 2, 3 and 4 show respectively, top, side and bottom views of a preferred uncoated circuit device 12. In the preferred embodiment a common circuit device support (board 16) holds' a series of similarly constructed circuit devices 12. Each circuit device 12 is supported on a separable portion of the circuit device support board 16. The separable circuit device 12 sections may be divided later one from another. In this manner, a plurality of coated circuit devices can be molded at once, thereby sharing common set up, mold and cure times. FIG. 5 shows a group of six circuit devices 12, similar to the one seen in FIG.s 2, 3 and 4, grouped on a common circuit board 16 in the form of a ladder. Six examples of the preferred circuit device 12 are positioned parallel arnd adjacent one another on the common circuit board 16 base forming the rungs of the ladder. Two side rails 18, 20 complete the ladder by coupling the ends of the six circuit devices 12. Slots 22 through the circuit board 16 extend between each of the adjacent circuit devices 12.
In the preferred embodiment, the electrical input contacts 24 and output contacts 26 for the circuit are formed on ends of the circuit devices 12, adjacent the side rails 18, 20. The contact points 24, 26 lie in a region that is not protectively coated in the final coating ' CA 02343660 2001-04-11 process. This leaves the contact points 24, 26 free of the coating material l4 and ready for electrical connection. In the preferred embodiment, foamed on the common circuit board 16 between the side rails 18, 20 and the contact points 24, 26 are score lines 28, 30. The score lines 28, 30 enable subsequent, rapid removal of the side rails 18, 20.
The circuit board 16 may also be formed with registration holes) 32 to enable accurate location of the circuit board 16 assembly in the mold 34.
Depending on the geometric form of the preferred circuit, and supporting circuit board, a mold is designed to enclose the circuit device within a chamber to receive, shape and hold the coating material in contact with those portions of the circuit device that are desired to be coated. Once the circuit device is coated, and the coating material is cured, the mold is opened and the coated circuit device is removed. Excess coating material, if any, is then trimmed, and any final circuit completion steps are taken.
A preferred mold was designed and built to hold two sets of the six rung ladders of circuit devices 12 as shown in FIG. 5. FIG. 6 shows an open view of the mold 34 for the two sets of six step ladders. The mold 34 had an upper half 36 hinged to a lower half 38. The mold halves 36, 38 included respective surface walls 40, 42 that when properly closed, define therebetween two retention chambers 44, 46 to receive and hold the two sets of the six step ladder structures (twelve circuiit device boards), and related coating material delivery channels 48, 50 and exit cha~lnels 52, 54. The delivery channels 48, 50 (also termed runners) for the coating material 14 lead to the two retention chambers 44, 46. The lower mold half wall 42 defines two cavities each including five lower baffle walls 56. The lower baffle walls 56 define six separate subchambers 58 in each of the retention chambers 44, 4Ei. Each subchamber 58 then encloses a volume surround a respective side of one of the circuit devices 12.
The upper mold half 36 is similarly formed with two cavities 62, 64 each with five similar upper baffle walls 66. The upper mold half 36 further includes four parallel seal channels 68. The four seal channels 68 extend perpendicular to the ladder rungs and run parallel and adjacent the ladder side rails 18, 20, overlapping the ends of each of the sets of the circuit devices 10: As shown, in each seal channel 68 is an inserted, compressible rubber end seal 70. Elongated rectangular blocks of rubber may be used as the end seals 70.

The upper mold half 36 includes an inlet 72 for the coating material 14. The inlet 72 leads to a mixing labyrinth 74 formed between the mold halves, and designed to assure good mixture of the injected coating materials 34. The serpentine labyrinth 74 mixer is comprised of a series of turbulence inducing corners. Thereafter the gates and channels guiding the injected coating material 14 are generally formed so as to not induce turbulence and cavitation in the circuit device retention chambers 44, 46. The outlet of the mixing labyrinth 74 leads by two equal delivery channels 48; 50 to the two retention chambers 44, 46. The delivery channels 48, 50 include low turbulence, fan type entrances 76, 78 coupled along the side lengths of the first two circuit device subchambers 58. The fan type entrances 76, 78 help provide a turbulence free flow of the coating material 14 as it enters the retention chambers 44, 46. At the opposite end of the circuit device retention chambers 44, 46 are similar fan shaped low turbulence exits leading to exit channels 52, 54. The exit channels 52, 54 receive the overflow of any excess coating material 14. The exit channels 52, 54 lead to a vacuum coupling (not shown) on the exterior of the upper mold half 36. The final exit channel is designed with an extended length to act as a volumetric accumulator (cushion) for any excess injected material. The two mold halves 36, 38 further include registration pins 80 (two located at the top of each for each retention chamber 44, 46) to mate with the registration holes 28, and thereby properly locate the sets of circuit device 12 in the retention chambers 44, 46. The two mold halves 36, 38 nnay also include registrations and locking features known in the art to assure the two mold halves 36, 38 stay in proper alignment during the molding process. The preferrc°d mold 34 is also electrically heated.
FIG. 7 shows an open mold with two circuit sets inserted in place. The registration holes 28 mate with the registration pins 80 to assure proper positioning.
When the mold compresses around the sets of the circuit device 12 ladders, the four rubber end seals 70 press against the ladder side rails 18, 20 and the ends of each circuit device 12 to cover the circuit device 12 contacts 24, 26. FIG. 8 shows a partial, cross sectional, end view of a mold 34 closed around two circuit devices 12. With the mold 34 closed, the lower half baffle walls 56 and the upper half baffle walls 66 approach each other between each of the circuit devices 12, but do not close with one another, or the circuit devices 12; thereby leaving an open channel extending along the length of the adjacent subchambers 58. Since the lower baffle walls 56 and the upper baffle walls 66 do not close with the circuit board slots 22 between adjacent circuits sets, the coating material 14 is free to flow from one subchamber 58 into the: next.
The coating material 14 is selected to be sufficiently fluid so that it may be injected safely around the circuit components, and thereafter cure to provide an insulating and protective coating. For practicality, it is convenient to form the coating material 14 by mixing two or more reactive fluid components just prior to injection into the mold chambers 44, 46. During injection the mixture coats or fills all of the relevant areas, and volumes. By using reactive,. fluid components, the mixture starts reacting during the injection stage, which may be quite rapid, arnd when in final position, the components finish reacting to cure as a solid. It is understood that fluid here means capable of flowing, and solid means either a rigid or a resilient substance that does not flow at the normal operating conditions of the circuit device. The coating material should have a sufficiently high dielectric constant, given the operating voltages and separations of the circuit components to resist discharge between circuit components through the coating material. The coating material should also have sufficient heat tolerance as to not deteriorate under the heating load o:f the operating circuit. The preferred coating material is a reactively cured polyurethane based rubber (RIM).
These materials are typically formed by combining an isomer component and a resin component. The Applicants' preferred coating material was a reactive combination of a resin material, ELASTOLIT # M50872R (BASF Corporation), and isomer material, .
WUC 3092 T Isocyanate (BASF Corporation). These two materials combine to form a Shore-A 70 durometer urethane material. The resulting coating material has a specific gravity of 1.05 grams per cubic centimeter, a flexural modulus at 23°
Celsius of 1100 pounds per square inch, a tensile strength of 1060 pounds Viper square inch, an elongation of 220 percent at breakage, and an instant hardness of 70 Shore A. The cured coating material 14 had a measured dielectric value of about 1.772 x 104 volts per millimeter (450 volts per mil). The preferred material at the time of mixing has a warm viscosity of about 200 or 300 centipoise, and a cold viscosity of about 700 centipoise at 35° to 40.5° Celsius (95° to 105° Fahrenheit). The preferred F~IM material components are _g_ heated to about 35° to 40.5° Celsius (95° to 105°
Fahrenheit) prior to mixing and injecting the combination into the mold. Depending on the final use of the coated circuit, care may have to be used to avoid coating material formulations including components that may outgas over time and interfere with the final operational environment. The Applicants found that lamp ballasts otherwise properly coated with a material including a small portion of triethlenediamine (tertiary amine) negatively effected the aluminized polycarbonate lamp housings, and the formulation had to be changed.
The chosen circuit device is placed in an injection mold. The mold may be heated to an appropriate temperature: The mold in the preferred embodiment is heated to 65.5°C (150°F). Controlled heating helps assure a consistent product, and speeds the curing process. In the preferred embodiment the delivery channels and exit channels are positioned in the mold so as to be protected from being; coated, or rapidly cleared if filled. In the preferred method, a vacuum is drawn on the mold to remove air from around the circuit devices, and to speed the flow of the coating material through the mold. The two or more reactive components forming 'the reactively cured coating material are mixed and rapidly fed into the mold to fill. the space around and coat portions of the circuit device components as desired. In the preferred method, the coating material components are each fed under pressure (injected) into a mixing head and then into a mixing labyrinth where the coating mateo~ial components (isomer and resin) are adequately mixed. The emerging mixture of the components (isomer and resin) forms the raw RIM material that reactively cures to form the final coating material.
The raw coating mixture then enters the main mold cavity to spread around the enclosed circuit device. Coating material is then simultaneously introduced through a divided channel to the two lead ballasts via "butterfly venturi's". These regulate the rates of flow of coating materials by proportioning them to compliment the circuit device restrictions and providing complete and simultaneous filling of the entire retention chambers. The coating material flows laterally across the paralleled circuit devices via the inter-connecting webs and exits via similarly configured retention chambers and commonly exit via a long perimeter exit channel. The pressure differential between the injection pressure and the ambient exit or applied vacuum pressure (as the case may be) causes the curing coating material to flow through, over and around the circuit device. Preferably the circuit device is configured provide reduced flow resistance. Flow resistance can result in injection turbulence in the coating material leading to coating defects such as bubbles, unfilled cavities, poorly adhered coating, and uncoated sections. In the prefewed embodiment, the curing coating material is pushed or drawn across the circuit device to an exit port allowing the escape of entrained or enclosed gases. The long coating material exit channel has vacuum drawn on it (and effectively the entire mold) by an external pump. The exit charnel allows for low mold pressures (typically less than 6.895 x 104 Pascals (10.0 pounds per square inch)) that assists the coating material inflow. A long exit channel is preferred as it compensates for possible variations in coating material injection volume (purposely or otherwise) while allowing the material to cure in place. The long exit channel negates the possibility of excess coating material reaching the mold exterior and being subsequently ingested into the vacuum pump, if any, a potential operational difficulty for regular production.
The cure time for the injected coating material should be greater than the time needed to fully inject the mold cavity, but thereafter may have any conveniently short cure time. After filling the mold, the coating material is allowed to cure.
Preferably, this is rapid, and may even be completed within only a few seconds after injection is completed. The mold is opened and the coated circuit devices) are ejected from the mold. FIG. 9 shows a top view of a molded set 70 of two groups of circuit devices 12 prior to separation. FIG. 10 shows a side view of the molded set of circuit devices of FIG. 9, prior to separation.
Once the ladder is cured, and ejected from the mold, the side rails 18, 20 are broken off at the score lines 28, 30 and removed. The web of cured RIM
material is cut adjacent where the subchambers are segmented by the pairs of baffle walls to separate the individual circuit devices 12. The individual circuit devices 12 may also be conductively coated (metallized, for example flash aluminized, or other conductive coating, for example an Indium Tin Oxide coating). The conductive coating 74 can then be electrically grounded in a fixture to form an electromagnetic interference (EMI) radiation barrier. FIG. 11 shows a coated circuit device 76 with an exterior EMI barrier coating 74 overcoating the RIM injected coating material.
In production of an actual example, a circuit device mold assembly was oriented on a support stand and coupled to receive the injected raw material. Raw Material Canisters, containing the first part of the reactive coating material (isomer) and the second part of the reactive coating material (resin) was coupled to a mixing head.
External gas pressure was supplied to the raw material sources to assist material delivery from the canisters. The raw material mixture ways supplied under pressure to two hydraulic pump-driven tandem cylinder units that ingested and then metered the raw materials from the canisters. As known in the art, a control system that inter-relates all of the process components and elements may be coupled to the system.
The preferred mold attitude was set at an inclination of approximately 45°
upwards from the material inlet end (mixing chamber) toward the exit channel.
The upward sloping mold enhanced the purging of any entrapped cavity air by flowing coating material through the upper ends of the top mold ballast cavities. The 45°
inclination of the mold had a further ergonomic benefit to the operator in materials handling and visibility.
The empty, closed circuit device mold was preheated to its preferred operating temperature, which in one example was 65.5°C (150°F). The preheated mold was opened and two six ballast circuit device board assemblies were placed into position and the mold was closed. A hydraulic pump system vvas initiated to evacuate the retention chambers through the exit channels. A vacuum was then drawn on the mold to induce a negative pressure. With the gas assist, the two tandem hydraulic cylinders are retracted, ingesting a capacity charge of both moldin;~ material components. The vacuum pump was started. The molding cycle was first started without a circuit device in position. This was to initially fill (prime) the material delivery system and verify molding integrity.
After the initial priming, two sets of six circuit devices 12 were positioned in the mold 34 with the circuit device 12 lead contacts facing up. The upper mold half was closed, thereby pressing the rubber seals along the lengths; of the circuit device 12 lead contacts. A vacuum of approximately 6.895 x 104 Pasc;als (10.0 pounds per square inch) was drawn on the exit channel 46. The RIM materials were then mixed immediately adjacent the input in a mixing head, and them injected under pressure into the mold. The hydraulic control circuit device was then started, forcing the two material components through the serpentine mixing cJhamber in the correct mix proportions. The mixed (and now curing) coating material was forced through the two butterfly venturi (at either ends of the mold) and is proportionally distributed laterally and upwardly through the two mufti-ballast mold cavities. The coating material passed through the serpentine mixing labyrinth 74 and then into the first circuit device subchambers to flow below, through and over the first two circuit devices. The coating material then passes between the ends of the lower baffle walls and upper baffle walls and through the circuit board slots 22 between the first a.nd the second sets of circuit devices. The coating material 14 then flowed into the second subchamber. The coating material continued until it reached the exit channels. Aided by the vacuum;
the coating material accumulates and moves through the exit butterfly chambers and into the long perimeter exit channel. During this period the coating material delivery cycle ceases, the vacuum to the mold is interrupted and the coating material is allowed to cure. The mold was opened and the two molded ballast panel assemblies were removed. The average molding cycle time was approximately 1.5 minutes total. The individual circuit devices were then cleaned of any excess coating material, and divided one from another. Mold release, if any is necessary, may be applied to the mold as required between operational cycles. Delivery cylinder replenishment is automatic within the control cycle. These production steps may be repeated as necessary.
The two circuit device retention chambers had a total volume of approximately 180 cubic centimeters (I 1 cubic inches). The mold fill time was approximately 2.0 or 3.0 seconds for a flow rate of approximately 130 grams per second. The mixing head pressure was approximately 1.723 x 10' Pascals (2500 pounds per square inch).
The coating material was fed under a pressure of approximate°1y 6.895 x 104 Pascals (10.0 pounds per square inch). Peak gauge pressure on the retention chamber during filling has been measures at approximately 3.447 x 104 Pascals (5.0 pounds per square inch).
The gel time for the coating material was approximately 30 to 70 seconds. Once the coating material was injected, it was allowed to cure for about one minute.
The mold was then opened and the circuit devices surrounded by t:he cured RIM material were released. The circuit devices were gang sliced with rotary blades plunged along the length of the web formed between the adjacent circuit devices where the upper and lower baffle walls formed deep grooves. The ladder rail portions were then separated by cutting or breaking them away, leaving the individual coated circuit units.
No clean up of the mold was necessary. It is suggested that a mold release such as a silicon spray or an aerosol wax spray be intermittently used. Because o:Fthe rapid mold filling, it has been found that the circuit device components can cause turbulence in the flowing coating material. This turbulence can lead to down stream voids in the cured coating material that are cosmetically undesirable, and may lead to reduced shielding and insulation. It is suggested that the circuit device components be located on the circuit device board so that there are few or no flat surfaces on the; forward and trailing sides of components with respect to the coating material flow. ;3uch flat surfaces have been found to induce turbulence and therefore result in unfilled cavities. The Applicants I S found that in general round surfaces should face directly towards the inflow or outflow, and that flat surfaces were best oriented to parallel the coating material flow direction.
The coated circuit devices have been tested by initially weighing them and then soaking them in water for a 24 hour period. An insignificant increase in weight of 1 percent was noted. The circuit devices were then operal:ed, and no change in circuit device operation was detected.
The resulting circuit device has a protective coating covering all of the circuit device elements except the input and output connections. The coating was found to fill virtual the entire mold cavity, and regions around the circuit device components with no significant voids detected to date. The coating provided a~ homogeneous material, with no apparent visual or physical variations detected to date. The coating had a shrinkage compatible with circuit device components with no significant distortion. The coating is resilient, offering excellent impact protection and some mounting flexibility. The coating is aesthetically acceptable with a consistent matte finish. The coating is resistant to water and other materials, insulates the circuit device elements and helps distribute heat. The assembly is small and light weight in comparison to similar circuit device constructions potted in a can. The construction avoids the cost, increased size, weight, and other limitations of using a pot to hold the circuit device. The conductively coated format allows for EMI noise reduction by electrical grounding. The assembly is inexpensive with regard to both materials and production time in comparison to potted circuit devices.
The RIM molding process yielded an economical manufacturing process alternative with high capacity, good repeatability and high yield. The process equipment has relatively low equipment and tooling costs. The process yields an aesthetically acceptable, uniform and repeatable circuit device. The urethane sheathing provides excellent circuit device impact and deformation properties with some mounting resilience, as well. The integral mold seals and the use of low molding pressure result in little or no mold flash. No significant internal voids have been observed in any circuit device. An occasional external upper mold corner has shown air entrapment, but this problem has been solved by process adjustment. No mechanical damage to the circuit components has occurred, including any injury to fine wires and foil features. While there have been shown and described what are at present considered to be the preferred embodiments of the invention, it will be apparent to those skilled in the art that various changes and modifications cain be made without departing from the scope of the invention defined by the appended claims.

Claims (29)

1. A method of enclosing an electronic circuit device comprising the steps of:
a) positioning a carrier body with at least one electronic circuit device composed of two or more electronic components in a mold;
b) supplying the mold with a curable, insulating coating material to coat and cover the electronic circuit device;
c) curing the coating material; and d) ejecting the coated circuit device carrier body from the mold.

2. The method in claim 1, wherein the insulating coating material is a reaction cured coating material.

3. The method in claim 1, wherein the insulating coating material is injected into the mold.

4. The method in claim 3, wherein a vacuum is applied to the mold while the insulating coating material is injected into the mold.

5. The method in claim 1, wherein the coating material is supplied at a temperature less than a temperature destructive of any of the components of the circuit device board.

6. The method in claim 1, wherein the coating material is supplied at a pressure less than a pressure destructive of any of the components of the circuit device body.

7. The method in claim 1, wherein the carrier body includes two or more segmented electronic circuit devices, and the mold defines for each electronic circuit device a mold volume substantially segmented from similar mold volumes associated with adjacent electronic circuit devices thereby forming substantially segmented coated electronic circuit devices whereby each coated electronic circuit device may be readily divided from the remaining coated electronic circuit devices along such segmentations into separate coated circuit device carrier bodies.

8. The method in claim 1, wherein the coating material is a reactive coating material.

9. The method in claim 1, wherein the coating material at injection has a viscosity less than 300 centipoise.

10. The method in claim 1, wherein the coating material has a curing time of less than 2 minutes.

11. The method in claim 1, wherein the injection time is less then five seconds?

12. The method in claim 8, wherein the reactive coating material is a reactive polyurethane.

13. A method of protectively coating a plurality of electronic circuit device bodies comprising the steps of:
a) forming a single carrier with a plurality of segmented circuit devices;
b) coating the carrier with an insulating coating; and c) dividing the coating and carrier along the circuit device segmentations to form separate coated circuit device bodies.

14. A coated electronic circuit device made by the process in claim 1.

15. The electronic circuit device made by the process in claim 14 further having an exterior conductive coating.

16. The electronic circuit device made by the process in claim 15 wherein the exterior conductive coating is a metallization layer.

17. The electronic circuit device made by the process in claim 15 wherein the exterior conductive coating is an indium tin oxide layer.

18. A protected electronic circuit device comprising:
a) a circuit device carrier supporting an electronic circuit device with two or more connection leads; and b) an electrically insulating, coating material closely covering and adhering to the circuit device, while leaving connections for electrical input and output from the circuit extending through the coating, the coating material comprising a reactive combination of two or more fluid components, wherein the coating material is not further enclosed by an adjacent container.

19. A protected electronic circuit device comprising:
a) a circuit . device carrier supporting an electronic circuit device while leaving connections for electrical input and output from the circuit extending through the coating; and b) a molded insulating, coating covering the circuit device, but not covering the connection leads, wherein the coating material is not further enclosed by an adjacent, mold shape defining container.

20. The coated circuit device in claim 19, wherein the coating material is infused around at least one of the electronic components.

21. The coated circuit device in claim 19, wherein the coating material is a reactive coating material.

22. The coated circuit device in claim 21, wherein the reactive coating material is a reactive polyurethane.

23. The coated circuit device in claim 21, wherein the reactive coating material has a dielectric constant in excess of 400 volts per mil.

24. The coated circuit device in claim 19, wherein the carrier body includes two or more segmented electronic circuit devices coated with coating material, and positioned between two or more of the adjacent segmented circuit devices are substantially segmentations formed in the coating material, whereby the coated circuit device carrier body is readily divided along such segmentations into separate coated circuit device carrier bodies.

25. The coated circuit device in claim 19, wherein the reactive coating material is further coated with a deposited conductive layer.

26. The coated circuit device in claim 19, wherein the deposited conductive layer is grounded.

27. The coated circuit device in claim 26, wherein the deposited conductive layer is a deposited metallization layer.

28. The coated circuit device in claim 26, wherein the deposited conductive layer is an indium tin oxide (ITO) layer.

29. The method in claim 1 wherein the mold includes an extended vacuum line, and the coating material cure time is less than the time to flow transport the coating material across the mold, and into the vacuum line.