US3889285A

US3889285A - Canister diode having improved environment protective insulation

Info

Publication number: US3889285A
Application number: US444199A
Authority: US
Inventors: Marcel F Milewski; Curtis E Weiser
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1974-02-20
Filing date: 1974-02-20
Publication date: 1975-06-10
Anticipated expiration: 1992-06-10
Also published as: CA1012254A

Abstract

A top hat or canister type diode is provided with improved insulation between its canister electrode and the oppositely poled electrical lead by the use of a hot melt adhesive material having a relatively high dielectric constant used to coat and electrically seal the insulator between the diode electrodes. By inserting a relatively rigid paper stiffener member, the hot melt material will be retained in the proper position with respect to the diode electrodes. The degree of improvement in the insulation between the canister and the oppositely poled electrical lead can be conveniently controlled by merely changing the diameter of the paper disc and the quantity of hot melt resin.

Description

United States Patent 1 Milewski et al.

[ June 10, 1975 [75] Inventors: Marcel F. Milewski, Allen Park;

Curtis E. Weiser, Detroit, both of 21 Appl. No.: 444,199

[52] U.S. Cl. 357/72; 357/74; 357/76;

357/80; 357/81 [51] Int. Cl. H011 3/00; H011 5/00 [58] Field of Search 317/234, 3, ll, 1, 4

[56] References Cited UNITED STATES PATENTS 10/1964 Ruben 317/234 E 12/1969 Dulin 317/234 E 2/1973 Suenaga et al. 317/234 E l/l974 Sawano et al. 317/234 E Primary Examiner-Andrew .1. James Attorney, Agent, or FirmRobert A. Benziger; Keith L. Zerschling [57] ABSTRACT A top hat or canister type diode is provided with improved insulation between its canister electrode and the oppositely poled electrical lead by the use of a hot melt adhesive material having a relatively high dielectric constant used to coat and electrically seal the insulator between the diode electrodes. By inserting a relatively rigid paper stiffener member, the hot melt material will be retained in the proper position with respect to the diode electrodes. The degree of improvement in the insulation between the canister and the oppositely poled electrical lead can be conveniently controlled by merely changing the diameter of the paper disc and the quantity of hot melt resin.

5 Claims, 6 Drawing Figures CANISTER DIODE HAVING IMPROVED ENVIRONMENT PRGTECTIVE INSULATION" BACKGROUND OF TI-IEINVENTION 1. Field of the Invention A i l i i I The present invention is directedto the field of man ufacturing processes for canistertype diode elements and particularly 'to' that portion ofthat abovenoted field which is concerned withthe provision of adequate forms of insulation to such diodes. More particularly still, the present invention is directed to a diode having environmental protective insulation and its method of manufacture.

2. Description of the Prior Art The canister or top hat form of diode, more completely described hereinbelow with reference to FIG. 2, finds great utility in the electric current rectification apparatus of an automotive vehicle generating system. In such use, a plurality of, typically six, diodes are coupled to suitable heat dissipation means and are electrically coupled to the various phases of the electrical alternator such that a DC voltage of approximately constant magnitude will appear across selected output electrodes. For the purposes of achievingthe optimum packaging requirements with minimum cost, such alternator rectifiers are typically mounted at one axial end of the alternator.

As is well known, automotive vehicle alternator's are mounted to the engine block of the automotive vehicle engine and, so disposed, are exposed to the adverse enviroriment which exists under the hood to an automotive vehicle. Such environment includes extremes in temperature and the regular and periodic exposure in water, slush, and salt spray resulting from the passage of the vehicle along the highways where accumulations of such materials can be expected. The exposure to extremes in temperature coupled with the temperature sensitivity of the semiconductor elements, used as the current rectification element within the canister type diodes, necessitates that the canister type diodes and their heat sink mounting structure be exposed to a relatively constant flow of cooling air. However, the exposure to a flow of cooling air necessarily requires that the diodes also be exposed to the aforenoted conditions of water, slush, and salt spray and splash. Over the expected useful life of an automotive vehicle having such as alternator rectifier, particularly in localities where various forms of salt are applied to ice accumulations on the highways in order to melt those accumulations, the alternator rectifier diodes are exposed to a significant amount of splash. The splash normally includes electrically conductive foreign matter such as the salt in both solid and solution form. Continued use of the automotive vehicle in those localities where'regular ex posure of the vehicle to such conditions results in accumulation of foreign matter on various surfaces of the diodes used in the alternator rectifier. Under most adverse conditions; the accum ulat'ionof this foreign matter results in formation of a relatively low resistance bridge between the anode andic athode electrodes of the canister type diode resulting in'shorting out of the diode. Such shorting out constitutes an electrical system failure for the vehicle and necessitates a relatively expensive and certainly inconvenient replacement of the alternator rectifier. i

The requirements of the electrical system of the automotive vehicle in terms of current and voltage, necessitate the use of these canister type diodes. Their use further necessitates their exposure under less than advantageous conditions and it is therefore an object of the present invention to provide such diodes with an improved form of environmental protective insulation substantially more resistant to the effects of accumulation of foreign matter resulting from road splash. As used herein, the term road splash" is intended to mean and encompass all forms of foreign matter which may become air-or waterborne through the passage of the automotive vehicle over the roadways in the normal fashion and which may result in deposition of material on the surfaces of the automotive vehicle. Such road splash encompasses water, salt, slush, mud, gravel, and dust, which may be forced or drawn into contact with the various components of the automotive vehicle as a result of passage of that vehicle along a roadway.

Examination of vehicle alternator rectifier assemblies which have required replacement due to shorting out of one or more diodes has indicated that this susceptibility to failure occurs primarily with those diodes in which the canister corresponds to the cathode electrode. In such diodes, the anode electrode corresponds to an electrical lead extending from the diode. In order to eliminate this problem, it has been the practice to take completed alternator rectifier assemblies prior to being mounted within an alternator, and to completely coat that portion of the alternator rectifier assembly corresponding to the electrically more positive terminal, and particularly those diodes having their cathode electrodes formed as the diode canister, with an environmental stable sealant material. One material which the alternator rectifier can be dipped into or coated with an electrical insulating enamel. This material dem onstrates a high dielectric constant and also is relatively inert when exposed to the environment. This solution to the problem is not considered to be the best possible solution in view of the fact that the material with which the alternator rectifier assembly is coated results in a lowering of the heat dissipation properties of the heat sink and also results in increased cost of assembly and materials since the dipping operation is wasteful of the glyptol and constitutes a further processing step. It is therefore a specific object of the present invention to provide a canister type diode having additional environmental protective insulation between its cathode and anode electrodes.

The presently utilized alternator rectifier assembly achieves significant cost economics and efficiencies through the use of automated assembly equipment. In order to continue the production efficiencies and cost economies associated with the use of this automated equipment, any technique for providing environmental protective insulation to a canister type diode must be fully compatible with the use of this automated equipment in the manufacture and assembly of the alternator rectifier. In particular, the environmental protective insulation for the canister type diode must in no way interfere with or impede the operation of this automated machinery. It is therefore a further object of the present invention to provide a method of adding envi ronmental protective insulation to a canister type diode which does not interfere with the automated assembly of that diode and other components to produce an alternator rectifier. In order to maintain the cost economies associated with the use of automated equipment, it is a further object of the present invention to provide a method of providing environmental protective insulation to a canister type diode as may be implemented by automated equipment.

Another proposed solution has been to add a heat shrinkable cap to the affected diodes. This solution is expensive both in terms of material and in terms of manufacturing. It is therefore a further object to provide improved environmental protection which does not require heat shrinkable materials.

SUMMARY OF THE PRESENT INVENTION The present invention contemplates the addition of a composite layer of stiffener material and heat flowable sealant to a canister type electronic device, typically a diode, in proximity to the glass seal thereof in order to surround and sealingly engage the rim of the canister and the protecting electrode lead. The electrode lead is normally centrally positioned with respect to the canister. The heat flowable sealant functions as an environmental protective insulator between the canister and its centrally located electrode and the provision of a layer of stiffener material provides a support vehicle which maintains the heat flowable sealant in the proper relation with respect to the canister type diode during heating. As used in the context of this description, the term heat flowable sealant and heat flowing environmental protective material shall mean any material which is relatively rigid at the normal operating temperatures and over expected operating temperature ranges of the associated electronic device, softens upon heating to temperatures lower than would be destructive to the associated solid state electronic device, bonds readily when softened to the material forming the electrodes and to the material forming the insulator of the solid state electronic device, has high dielectric constant, is not heat degradible at maximum temperature, is relatively inert to expected environmental conditions and is compatible with solder in its liquid phase. The preferrable heat flowable sealants will have high viscosity at the maximum temperatures expected to be encountered. As used herein, the term stiffener material" shall mean any material which is chemically compatible with the heat flowable sealant and will have sufficient strength to support the weight of the heat flowable sealant at the flowing temperature of the heat flowable sealant.

The canister type diodes, as received from a vendor, are positioned in a fixture such that the glass seal and its centrally positioned electrode are generally upwardly directed. The environmental protective insulation is then added in the form of a sandwich with the stiffener member positioned between a pair of wafers of the heat flowable sealant. This composite is apertured for insertion over the projecting electrode so that it may rest under its own weight upon the glass seal surface of the canister. The temperature of the heat flowable material is then elevated so that it becomes semiliquid and may flow under its own weight to sealingly engage the projecting electrode and the edges of the canister. The stiffener member prevents substantial quantities of the heat flowable material from flowing down the sides of the canister. The canister type electronic device may then be cooled and the heat flowable sealant may return to its more rigid form. The processing of the canister type diodes to produce for example a finished alternator rectifier assembly proceeds in accordance with the conventional processing steps. Since such processing normally includes a heating step, this heating step may be utilized to cause sealing flow of the heat flowable sealant.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates an electrical schematic diagram of an alternator having an alternator rectifier for converting three phase AC into a DC output.

FIG. 2 illustrates a conventional canister type diode operatively associated with a heat sink means in a sectional view.

FIG. 3 is an elevational end view of the canister type diode of FIG. 2.

FIG. 4 illustrates the canister type diode of FIG. 3 including the environmental protective insulation composite of the present invention in association with a heat sink means at an intermediate processing step.

FIG. 5 is an elevational end view of the diode of FIG. 4.

FIG. 6 is a sectional view of the diode of FIG. 4, including the environmental protective insulation and in cooperative association with a heat sink means, subsequent to the heating step.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing wherein like numbers designate like structure throughout the various views thereof, FIG. 1 illustrates a representative electrical schematic for an alternator 10 as may be used in an automotive vehicle and of a rectifier assembly 12 used to convert the polyphase AC output of alternator 10 to a DC signal appearing across terminals l4, l6. Alternator 10 is typically comprised of a plurality of stationary stator coils 18a, 18b, 18c, sequentially excited by a variable magnetic field produced for example by rotating a DC energized field coil 20. In the illustrated embodiment, field coil 20 receives a regulated voltage from a voltage regulator 22 which is in electrical series circuit relation with the positive terminal of battery 24. As illustrated, this system is usable by a vehicle having a negative ground and therefore the negative terminal of battery 24 is shown connected to ground. Semiconductor rectifier assembly 12 includes a plurality of pairs of series connected

diodes

26 and 28, 30 and 32 and 34 and 36.

Diodes

26, 30 and 34 have their cathodes connected to output terminal 14 which will be considered to be the positive terminal.

Diodes

28, 32 and 36 have their anodes connected to the ground terminal 16. The common anode/cathode 38 of

diodes

26, 28 is connected to receive the alternating voltage signal produced across coil 18a. The common anode/cathode 40 of

diodes

30, 32 is connected to receive the alternating voltage signal produced across coil 18b. The common anode/cathode 42 of

diodes

34, 36 is connected to receive the alternating voltage signal produced across coil 186. As illustrated in FIG. 1, the stator field structure of alternator 10 is connected in a Y configuration. This configuration is merely exemplary and a delta configuration is also contemplated. The electrical polarity of

output terminals

14, 16 and of battery 24 could also be reversed and such reversal is also contemplated. The alternator 10 of FIG. 1 is illustrated as being a threephase alternator and greater or lesser number of phases for such alternators are also in common usage.

In the fabrication of alternator rectifier assembly 12, the normal practice is to form two heat sink plates which disposed to be coplanar and are electrically insulated from each other. The heat sink plates may then comprise the positive and negative rectifier electrodes. The heat sink plates would typically include an electrical terminal and would correspond electrically to a common cathode for

diodes

26, 30 and 34 and a common anode for

diodes

30, 32 and 36. A plurality of canister type diodes having the canister formed as the cathode electrode are suitably connected as for example by soldering to the heat sink plate comprising the positive electrode and including positive terminal 14. A similar number of canister type diodes having the canister formed as the anode electrode are similarly mounted to a second heat sink plate comprising the negative electrode and including the negative electrical terminal 16. This mounting arrangement assures a maximum heat exchange contact between the metal canister of the diode and the metal plate which forms the heat sink corresponding to a common electrode. The necessary electrical circuitry to interconnect the diode pairs and to provide terminals for eventual communication to the alternator phases is then added. This circuitry is typically in the form of electrical conductors encapsulated within a dielectric material and having apertures for receipt of the noncanister electrodes of the diodes. This circuitry is disposed in parallel spaced relation to the heat sink plates.

Referring now to FIGS. 1 and 2 and particularly to FIG. 2, a typical canister type diode 26 is illustrated in a sectional view. In this configuration, the canister housing 44 of canister type diode 26 comprises the cathode electrode of the diode. Canister 44 is directly bonded by suitable electrically conductive bonding material such as solder 45 to plate 46. In this instance heat sink plate 46 comprises the electrically positive rectifier electrode which includes positive terminal 14. A body of semiconductor pn type material 48 is situated within the interior of canister 44 and is electrically coupled to and supported within the canister 44 by a conductive element 50. Semiconductor material 48 is electrically bonded to the conductor member 50. A further electrode member 52 is bonded to semiconductor 48 on a side thereof opposite to that occupied by electrically conductive member 50. The anode electrode lead of the diode extends from the electrically conductive body 52 and projects away from canister 44. This anode electrode is denoted as 38 since it corresponds to the common anode/cathode electrode 38 of the pair of

diodes

26, 28 of FIG. 1. A glass seal plate 54 is added to the canister and is gripped by an overlapping lip 56 of the canister 44 and extends to the anode electrode 38. In those instances where diode 26 is situated in an alternator rectifier assembly and used in an automotive vehicle where it is subjected to road splash, foreign matter which may be relatively electrically conductive when compared with glass seal 54 may accumulate on the surface of glass seal 54 to form an electrically conductive bridge extending from anode electrode 38 to the lip 56 of canister 44. This electrically conductive bridge will effectively short out diode 26 such that the voltage signal appearing across alternator coil 18a in this instance will be directly applied to positive terminal 14. Conversely, the DC battery voltage will also be applied directly to one side of the alternator coil 18a.

One common alternative construction for a top hat or canister form of diode is to place the semiconductor pn junction material directly on the base portion of the canister and to arrange the outwardly projecting electrode to extend through the glass seal means to the exposed face of the semiconductor material. This improves the ability of the canister to extract undesired heat from the semiconductor material.

FIG. 3 illustrates a top view of diode member 26 and shows the generally circular configuration in which the great majority of canister type diodes are commercially available. It will be appreciated that while the hereinabove contained discussion is directed to a single diode 26 it applies to each of the

diodes

26, 30, 34 having their cathode electrode forming as the canister portion as well as the

diodes

28, 32, 36 having their anode electrode formed as the canister portion. In fabricating an alternator rectifier 12, it is typically the fashion to have automated machinery receive a large plurality of diodes having sized polarities, to electrically sort and test the diodes on an individual basis so that those diodes having their canisters formed as the cathode electrodes may be situated on heat sink plates intended to function as positive electrodes while those diodes having their anode electrodes formed as the canister may be situated on heat sink plates intended to function as negative electrodes. The desired plurality of diodes, three diodes as illustrated in FIG. 1, will be situated on the surface of a plate comparable to that fragmentarily illustrated as plate 46 in FIG. 2 along with a selected amount of electrically conductive bonding material typically solder in paste or preshaped form. The diodes will be held in place upon the plate by the operation of a suitable fixture or by the force of gravity. This composite will thereafter be passed through a furnace to elevate the temperature thereof to the melting temperature of the solder which will then form the desired electrical and mechanical bond between the canister portions 44 of the diodes and the surface of the heat sink plate.

One arrangement for forming the complete alternator rectifier assembly 12 requires the association of the necessary diodes, properly oriented with respect to a pair of electrode heat sink plates and positioned for proper cooperation with means comprising the necessary circuitry to interconnect the various pairs of diodes and to provide a plurality of electrical terminals for eventual communication to the alternator coils and to the DC circuitry. Having been so associated, this composite structure, now including the electrode/heat sink plates a plurality of diodes positioned on each of the plates and interconnecting circuitry, which may be in the form of an encapsulated circuit, with sufficient amounts of paste solder or solder preform provided at the various electrical interconnection points may then be passed through a heating furnace or oven to raise the solder temperature to its melting temperature in order to accomplish the necessary electrical and mechanical bonding. Upon cooling of this structure to a convenient handling temperature, the alternator rectifier assembly 12 may thereafter be mounted in an alternator housing and electrically connected to receive the AC signals from the alternator windings and to provide a DC voltage across the

terminals

14, 16.

Referring now to FIGS. 4, 5 and 6, the present invention contemplates providing envivonmental protective insulation to a conventional canister type of electronic device such as the diode illustrated in FIGS. 4 and 6 as diode 26. The diode is substantially as described hereinabove with reference to FIG. 2. As such it includes a canister body 44 and a semiconductor pn junction material 48 mounted therein and electrically communicated to and supported within the canister body 44 by electrically conductive member 50. A second electrically conductive member 53 is positioned'on a face of the semiconductor pnjunction material 48 in opposition to electrically conductive member 50 and an electrical lead, in this case anode 38, extends outwardly and upwardly relative to FIG. 4, from electrically conductive member 52. Seal means 54 is sealingly received by the lip 56 of canister 44 surrounding and sealingly engaging the electrical lead 38.

The environmental protective insulation according to the present invention comprises a plurality of wafers of heat flowable environmental protective material and of support material. The plurality of wafers, in the form of a sandwich with the stiffener member 58 situated between a pair of wafers of heat flowable sealant 60 is disposed on the exterior surface of seal means 54. As illustrated, the presently preferred support or stiffener material is a thin paper layer denoted as numeral 58 which is sandwiched between a pair of wafers of the heat flowable environmental protective material 60. These materials may be provided, in the case of a circular cross section canister, in the form of circular discs of material which have a centrally located aperture arranged to receive the electrical lead, in the illustrated diode, anode 38. Square, rectangular, triangular or irregularly shaped wafers may also be used if, for example, the noncircular shape more readily lends itself to the particular manufacturing process or to suit a particular application. The sandwich of wafers, 58, 60 may be provided as individual wafers separately arranged on the glass seal means 54. The sandwich may also be provided in composite form by suitably coating both sides of the stiffener member 58 with the selected heat flowable sealant 60. It would also be possible to apply the heat flowable sealant to both sides of a relatively continuous strip of stiffener member material and to thereafter sever, punch, or otherwise separate the desired sandwich configuration from the strip for placement on the electronic device.

The presently preferred form of the heat flowable environmental protective material is a hot melt adhesive No. 70-0073 available from National Starch and Adhesive Company. This material combines a plurality of desirable attributes. This material may be easily handled at room temperature and may be formed as relatively rigid wafers. This material demonstrates an affinity to bond to the glass seal 54, to the metal of the canister 44 and to the paper support material whose importance is discussed hereinbelow. In selecting a particular heat flowable material, care must be taken to assure that the material is compatible with the solder-in its, the solders liquid phase and for its ability to withstand the expected environmental conditions. A further consideration which must be made in selecting the suitable heat flowable environmental protective material is the temperature/viscosity relationship of the material. In the case of formation of apparatus including mechanical and electronic components such as the "alternator composite'assembly, the heat flowable material must "retainsufficient'stiffness, that is, it must be sufficiently viscous, so that substantial portions of it will not flow away from the upper, relative to FIG. 4, surface of the canister of the electronic device.

The material identified hereinabove as hot melt adhesive 70-0073 demonstrates the desired affinity to bond, the necessary compatibility with the solder in its liquid phase, and has a good temperature/viscosity relationship. More importantly, this material demonstrates good resistance to the environmental hazards which were discussed hereinabove and described as road splash. It will be appreciated that the oven temperature and the residence time of the device within the oven may be determined by factors other than the parameters of the heat flowable sealant. In the illustrated situation, the use of a heating oven to flow the solder for assembly of an alternator rectifier established the oven conditions for which a suitable heat flowable sealant was selected. Different oven conditions might render the exemplary material unsuited by causing excessive or inadequate softening and flow. Thus, the range of suitable material will vary depending on the further manufacturing processes to which the electronic device is to be exposed and the potential for utilizing one or more steps of the further manufacturing processes as the heating step to complete the bonding of the environmental protective insulation to the electronic device. lt will also be appreciated that selection of an adequate heat flowable sealant may be easily made by selecting a material according to the various criteria set forth hereinabove.

The fabrication of the alternator rectifier assembly utilizing the environmentally protected electronic devices of the present invention would proceed generally as described hereinabove. A pair of heat sink plates would be disposed in coplanar electrically insulated relationship. A plurality of electronic devices having their canister formed as an anode electrode would be disposed on a first of these plates and a similar plurality of electronic devices having their canisters formed as a cathode electrode would be properly disposed on the other of these plates. The normal disposition of the electronic device would be such that the glass seal means 54 and the projecting, noncanister, electrodes would'be generally upwardly directed. The environmental protective insulation according to the present invention would then be placed upon the glass seal rectifier assembly 12, it is advantageous to select a heat means surface so that the projecting electrode passes through the apertures provided therefor in each of the layers of the environmental protective insulation. Thereafter, the necessary electrical circuit means would be disposed so as to properly interconnect the noncanister electrodes to form the diode pairs and to interconnect these diode pairs with terminals for eventual electrical communication with the alternator phases. The composite assembly thus described, and prior to heating may be held in loosely assembled relationship through the use of proper fixturing tools and this may be aidedby the reliance upon the force of gravity. Additionally, the sandwiches comprising-the environmental protective insulation may also provide fixturing aids in supporting the necessary circuitry upon the surface of the various electronic devices. This composite assembly would thereafter be passed through a heating oven to elevate the temperature of the electrically conductive bonding material 45 and the heat flowable sealant 60 to esabli'sli'the elc tric' al and mecli'anicalbonding of the various componeintsiin thiscomposite assembly into a unitary alternator rectifiepassembly and to concomitantly cause sufficientdlow'of the heat flowable sealant so as to permitthe heat flowable sealant on either side of the stiffener member 58 to bond itself and to form an environmentally protective insulating bond between the heat flowable sealant and the lip 56 of the canister 44 on the one side and the projecting electrode on the other side.

When the temperature of the heat flowable material is elevated sufficiently to cause this material to flow, the presence of the interstitial layer of stiffener material such as paper 58 provides a support surface which will maintain substantial quantities of the flowable ma terial 60 on the upper surface of the paper. The paper should be selected so as to be sufficiently rigid to support the weight of this slight amount of heat flowable material under the expected temperature conditions. For the flowable material mentioned hereinabove, it" has been found that ordinary writing paper suitably perforated for passage of electrode 38, has sufficient stiffness where the paper support layer beyond the lip 56 by about 30 percent of the radius of the lip 56. Consufficiently stiff at this dimension to retain adequate quantities of heat flowable material in proximity to the electrode nevertheless permits substantially quantities versely, it has been found that tissue paper, hil 25 of the flowable material 60 to flow down the sides of canister 44 in an unpredictable fashion. Stiffener mernber 58 is preferably slightly smaller than the wafers of heat flowable sealant.

With reference now to FIG. 6, it can be seen that the effect of passage of the composite assembly through the heating oven will result in sufficient flow of the flowable material 60 to fill the voids created about electrode 38 by the apertures in the wafers and will also flow into substantially complete contact with the upper surface of glass seal means 54. In addition, sufficient means flowable material will flow about the edge of support member 58 so as to completely surround the seal the upper, relative to FIG. 6, surface of the canister diode 26.

Referring now to FIG. 5, a top elevational view of the discs which are slightly larger in diameter than the diameter of diode 26. This dimension has been selected in order to provide a direct distance path between anode 38 and the canister 44 which is several times larger than a similarly defined path for the prior art diode of FIG. 2. By extending the support layer 58 be-v yond the lip 56, the environmental protective insulation includes a surface portion which may be somewhat protected by its geometry from the effect of road splash. While accumulations of foreign matter on the upper, relative to FIG. 6, surface 62 of the heat flowable material, the lower surface 64 will be generally shielded from direct splash and will therefore further inhibit the formation of a diode shorting bridge of foreign matter.

The environmentally protected electronic device according to the present invention thus obtains the objectives set forth hereinabove. By the comparatively simple expedient of placing wafers of heat flowable materialjin a relatively rigid state, and of a supporting material such as ordinary writing paper in contact with the glass seal surfaceofthe-canister type electronic device andby'subsequentlyperforming the normal alternator rectifier assembly steps including the step of passing the composite assembly including a plurality of diodes and suitable heat sink/electrode plates and electrical circuits through a heating oven, the diodes are provided with additional insulation to prevent shorting out of the diode while the rectifier assembly is soldered together. The provision of the support or stiffener material assures that sufficient quantities of the heat flowable material will be retained on the surface thereof to provide the desired degree of additional environmental protective insulation. By merely changing the diameter of the support paper and by changing the total quantity of heat flowable material in its rigid or wafer form, placed above the support layer when in the cool and nonflowable state, the total distance between the anode electrode 38 and the canister 44 may be controlled. Assuming the accumulation of road splash deposits is some direct function of time of exposure to road splash, the time period and hence useful life of the diode prior to accumulation of a destructive amount of road splash may be conveniently and easily controlled and extended.

The use of a heat flowable material and its support layer is fully compatible with the normal manufacturing process for the alternator rectifier assembly and merely requires the addition of these elements to the diodes prior to the addition of the electrical circuitry which will interconnect the diode pairs and the diode pairs with the various phases of the alternator output.

We claim:

1. In combination with a solid state electronic device of the type having a body of semiconductor pn junction material retained with a canister housing, at least two electrically distinct terminals in electrical communication with different regions of the semiconductor body, and an insulating means disposed within the canister housing, forming a wall thereof, to seal the semiconductor body within the housing while electrically insulating the terminals, the improvement comprising:

heat flowable environmentally protective insulating material disposed across the exterior surface of the insulating means and sealingly engaging the electrical terminals and arranged to increase the direct distance path between the terminals whereby the time period required for the accumulation of foreign matter on the surface of the insulating means to short out the device may be extended, and stiffener member embedded within the heat flowable material operative to retain substantial quantities of heat flowable material, when heated, in proximity to the electrodes.

2. The environmental protective insulated device of claim 1 wherein said stiffener member comprises a wafer of paper selected to have substantial rigidity.

3. The environmental protective insulated device of claim 1 wherein said heat flowable environmental protective insulating material comprises upper and lower wafers of heat flowable material hving an interstitial layer of stiffener material, the upper and lower wafers being fused into a substantially unitary mass and being fused to the terminals of the device whereby the exterior surface of the insulating means of the device is sealed from the atmosphere.

3,889,285 r l 1 :12 4. The environmental protective insulated device of r 5. The environmental protective insulated device of claim 3 wherein the stiffener member comprises a layer claim 4 wherein the=zheat flowable material comprises of paper selected to have a rigidity commensurate with I supporting a predeterminable mass of said heat flowv able material thereon against the force of gravity. 5 I l a hot melt adhesive. I

Claims

1. IN COMBINATION WITH A SOLID STATE ELECTRONIC DEVICE OF THE TYPE HAVING A BODY OF SEMICONDUCTOR PN JUCTION MATERIAL RETAINED WITH A CANISTER HOUSING, AT LEAST TWO ELECTRICALLY DISTINCT TERMINALS IN ELECTRICAL COMMUNICATION WITH DIFFERENT REGIONS OF THE SEMICONDUCTOR BODY, AND AN INSULATING MEANS DISPOSED WITHIN THE CANISTER HOUSING, FORMING A WALL THEREOF, TO SEAL THE SEMICONDUCTOR BODY WITHIN THE HOUSING WHILE ELECTRICALLY INSULATING THE TERMINALS, THE IMPROVEMENT COMPRISING: HEAT FLOWABLE ENVIRONMENTALLY PROTECTIVE INSULATING MATERIAL DISPOSED ACROSS THE EXTERIOR SURFACE OF THE INSULATING MEANS AND SEALINGLY ENGAGING THE ELECTRICAL TERMINALS AND ARRANGED TO INCREASE THE DIRECT DISTANCE PATH BETWEEN THE TERMINALS WHEREBY THE TIME PERIOD REQUIRED FOR THE ACCUMULATION OF FOREIGN MATTER ON THE SURFACE OF THE INSULATING MEANS TO SHORT OUT THE DEVICE MAY BE EXTENDED, AND A STIFFENER MEMBER EMBEDDED WITHIN THE HEAT FLOWABLE MATERIAL OPERATIVE TO RETAIN SUBSTANTIAL QUANTITIES OF HEAT FLOWABLE MATERIAL, WHEN HEATED, IN PROXIMITY TO THE ELECTRODES.

4. The environmental protective insulated device of claim 3 wherein the stiffener member comprises a layer of paper selected to have a rigidity commensurate with supporting a predeterminable mass of said heat flowable material thereon against the force of gravity.

5. The environmental protective insulated device of claim 4 wherein the heat flowable material comprises a hot melt adhesive.