EP0231363A1 - Electrical circuit fabrication apparatus and method - Google Patents

Abstract

A wire (11) used to repair or replace circuit elements, such as printed circuits, includes heat resistant insulation surrounded by a hot melt adhesive. The wire is easily attached to the surface of printed circuit boards by applying a hot iron (19) to the adhesive coating layer of the wire and by fusing the adhesive, which thereby adheres to the surface. from the menu. The hot iron includes a grooved tip so that when the iron tip is pressed onto the wire, the tip wraps around the wire, quickly melting the adhesive and bonding fairly quickly. The coating is applied by vertically moving insulated metal wire through a length of molten adhesive and then through a die.

Description

ELECTRICAL CIRCUIT FABRICATION APPARATUS AND METHOD

FIELD OF THE INVENTION This invention relates to methods and apparatus for making corrections and changes in electrical circuits, and particularly to printed circuit boards, through the use of jumper wires, and to the structure and fabrication of the jumper wires. This invention also relates to devices and methods for holding and cleaning hot irons used in circuit fabrication or correction. This patent application is a continuation-in-part of U. S. Patent Application Serial No. 759,467, filed July 26, 1985.

BACKGROUND OF THE INVENTION Printed circuit boards often are found to contain errors, or require changes due to improvements in the circuits. The circuit board changes can be made by changing the art work for the board. However, this can be very expensive.

Even if the changes are fairly extensive, often it is far less costly to hand-apply jumper wires in selected locations on the board. The new connections usually are made by inserting one bare end of an insulated jumper wire into a plated hole in the board, gluing the wire onto the surface of"the board along a predetermined path, and inserting the other bare end into another plated hole. Then the board is passed through a wave soldering bath which solders all of the wires and component terminals in the plated holes. Alternatively, the terminals can be hand-soldered in place.

The board surfaces onto which the jumper wires are glued most often are coatings of "solder resist" materials, usually epoxy resins. The adhesives used to glue the jumper wires onto those surfaces vary; they include silicone rubber, acrylics, epoxies, and hot-melt adhesives. The adhesives are applied manually. The prior methods of applying adhesives suffer various disadvantages. For example, the wire usually must be held in place for a substantial amount of time to allow for sufficient curing or cooling of the adhesive to properly secure the wire to the printed circuit board. Usually

SUBSTITUTE SHEET this is a time-consuming process and may result in a poor bond if sufficient cooling or curing time is not allocated. Another disadvantage of prior methods is that they are messy. This increases labor costs for the process due to. increased set-up and clean-up time. Also, the prior methods usually are awkward to use. This further reduces worker productivity.

When hot-melt adhesives are used, sometimes they are melted in a pot kept near the work station where it is used, and the adhesive is taken from the pot when needed. There are several problems with this technique. One problem is that a considerable amount of time is required each day in order to melt the material in the pot to get it ready to use. Also, the material does not last long in the molten state and must be replaced relatively frequently; that is, the adhesive does not have a very long "pot life" .

Some prior adhesives are toxic or give off toxic fumes when used, thus posing a health hazard to workers and necessitating the use of special safety procedures and/or equipment.

Another problem in using hot-melt adhesives is that the tool used to apply the adhesive should be cleaned frequently in order to prevent the build-up of hardened adhesive on it. Cloths can be used for this purpose, but they are relatively slow and inefficient to use since they must be replaced frequently as the surface becomes covered with waste adhesive, and since a clean area on the cloth may take a considerable length of time to find. Also, if a hot iron is used to melt the adhesive, the cloth may smolder or burn due to contact with the iron.

A cleaning problem similar to that experienced with hot-melt adhesive melting irons is found in using soldering irons. Wet sponges usually are used to wipe the excess solder and flux materials off of the iron tip. However, the sponge dries out and becomes charred and must be replaced relatively frequently.

A problem with some jumper wires which have thin coatings of high-temperature-resistant plastics such as polytetrafluorethylene (e.g. DuPont "Teflon") for insulation is that they are not very resistant to cuts and abrasion.

This endangers the integrity of the circuits in which they are used.

OBJECTS OF THE INVENTION It is an object of the present invention to provide an improved method for securing jumper wires to circuit elements such as printed circuit boards which overcome the aforementioned problems and disadvantages. Another object is to provide an improved wire for use in such a method, and to provide an improved circuit element such as a printed circuit board utilizing the wire and the method.

It is a more specific object of this invention to provide such a method and wire which are relatively easy and fast to use, and with which circuit corrections or changes are made relatively efficiently at a moderate cost.

Another object of the present invention is to provide a device for use in cleaning the tip of a hot iron used to melt or apply circuit-fabrication material such as adhesives or solder, in which cleaning can be done relatively rapidly and easily, and in which a fresh cleaning surface can be obtained with similar rapidity and ease. It is a more specific object to provide a relatively simple and inexpensive cleaning device which also serves as a holder for the hot iron. A still further object is to provide such a device and cleaning material for use in the device in which combustion of the cleaning material during cleaning is retarded.

A further object of this invention is to provide a method and apparatus for producing the improved wire of the invention.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present

TITUTE SHEET invention, wire to be secured to a circuit element such as a printed circuit board comprises an electrical conductor with an inner coating of insulation and outer coating of adhesive, preferably a hot-melt adhesive.

In one embodiment of the invention, the wire can be pre-cut to desired lengths and the insulation stripped at the ends to form pre-fabricated jumper wires. The pre-fabricated jumpers also can be pre-bent to a desired shape, thus making them ready to use.

In use, the adhesive-coated wire is electrically connected at its ends to terminals of the circuit element, and the wire is secured to the surface of the element by simply heating and pressing the adhesive coating against the surface.

The adhesive coating advantageously serves the dual purpose of providing a quantity of adhesive convenient to every spot along the length of the wire, while also serving as a protective coating for the relatively thin insulation in the wire.

Preferably, the adhesive is heated and pressed against the surface by means of a heating device such as a hot iron with a tip shaped to straddle the wire and press it against the surface of the circuit element.

The adhesive coating and iron tip are dimensioned so that only a relatively small amount of adhesive is melted by the hot iron, thereby enabling the adhesive to be melted relatively quickly and harden with similar speed.

In straddling the wire, the hot iron preferably contacts the surface of board to heat it locally. To this end, the hot iron tip, in its preferred form, has an elongated groove which is deeper than the diameter of the insulator layer but shallower than the diameter of the adhesive layer.

It is preferred that the melting temperature of the adhesive be relatively high so that there will be a minimum

SUBSTITUTE SHEET amount of softening of the adhesive bonds of the jumper wires ^_, to the printed circuit board when it is passed through a wave soldering device which heats the board significantly. It also is preferred to use a relatively high iron temperature so as to ensure good adhesion of the adhesive to most of the epoxies and other materials used to coat printed circuit boards.

The electrical insulation on the wire should be able to withstand the temperature of the heating device without melting. Therefore, it is preferred that the insulation be made of a thermoset material; that is, a material which in its finished form does not soften with reheating. An irradiated, cross-linked polymer, such as polytetrafluoroethylene (PTFE) , (e.g., DuPont "Teflon"), is a preferred thermoset material used for the insulation. PTFE also can withstand the relatively high temperatures of the hot iron and the adhesive coating process of the invention.

The adhesive coating is applied to the PTFE-coated wire by heating a container of the adhesive to a fluid state, and passing the wire through the fluid material and a die. Preferably, the surface of the PTFE insulation is etched to improve adhesion of the adhesive coating, and the wire is moved vertically through the fluid container to ensure uniformity in the thickness of the adhesive coating.

The hot iron tip cleaning problems are solved, in accordance with the present invention, by providing a cleaning element with an easily-renewable cleaning surface. The surface can be renewed by simply removing one layer of a layered cleaning element to expose a fresh layer.

The cleaning element preferable for use with the grooved hot iron tip is one composed of plural strands of fibrous material, preferably of a size to fit into the groove of the iron. Preferably, the cleaning material is wound on a form such as a spool. Ordinary cotton string comprises an excellent and inexpensive stranded fibrous material. It is simply wound on the spool, and unwound to expose a fresh layer when needed.

Alternatively, especially for cleaning soldering irons, the cleaning surface comprises a roll of cloth tape with a pressure-sensitive adhesive backing which is simply peeled off of the roll and torn off to expose a fresh surface.

A combination iron holder and iron cleaner also is provided.

If it is desired to dampen the cleaning material with water, a water reservoir is provided in which to store water in contact with the cleaning material.

The cleaning material is treated with a combustion retardant to prevent the material from burning or smoldering due to contact with a hot iron.

Various other objects, advantages, and features of the present invention will be described in or will become readily apparent from the following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Figure 1 is a perspective view of an insulated electrical wire embodying the present invention;

Figure 2 is a side elevation view of a heating device for use with the wire of Figure 1;

Figure 3 is a schematic perspective view illustrating of the use of the wire of Figure 1 and the heating device of Figure 2 to repair a printed circuit board;

Figure 4 is an enlarged side elevation view of the tip of the heating device of Figure 2 being brought into contact with the wire of Figure 1;

Figure 5 is a side elevation view similar to Figure 4 after the tip of the heating device has been removed from the wire;

SUBSTITUTE SHEET Figures 6, 6A and 6B are, respectively, enlarged side elevation, bottom plan, and end elevation views of the preferred embodiment of the tip of the heating device of Figure 2;

Figure 7 is a cross-sectional view of the tip of the heating device of Figure 6 shown as it melts the adhesive which coats the electrical wire of Figure 1;

Figure 8 is an enlarged perspective view of an alternative embodiment of the tip of the heating device of the invention;

Figure 9 is an enlarged side elevation view of the tip of Figure 8 being brought into contact with the wire of Figure 1;

Figure 10 is an enlarged side elevation view of an alternative embodiment of the tip of the heating device of the invention being brought into contact with the wire of Figure 1;

Figure 11 is a side elevation view similar to that of Figure 9 showing the tip of Figure 10 after it has been pressed against the wire of Figure 1 and then removed;

Figure 12 is an enlarged view of an alternative embodiment of the tip of the heating device of the invention;

Figure 13 is a bottom plan view of the device shown in Figure 12;

Figure 14 is a schematic perspective of the equipment used for coating insulated wire with a hot-melt adhesive outer coating;

Figure 15 shows graphs plotting the viscosity versus temperature for two hot-melt adhesives used to coat the wire of the invention;

Figure 16 is a perspective view of one embodiment of a device for holding and cleaning a heating device tip in accordance with the present invention;

Figure 17 is a cross sectional view taken along line 17-17 of Figure 16;

SUBSTITUTE SHEET Figure 18 is a perspective view of an alternative heating device holder/cleaner device;

Figure 19 is a cross sectional view taken along line 19-19 of Figure 18;

Figure 20 is a partially schematic cross-sectional view of the cleaning action of the cleaning device of the invention;

Figure 21 is a cross-sectional view of another embodiment of the holder/cleaner device; and

Figure 22 is a perspective view of a material used in the device of Figure 21.

GENERAL DESCRIPTION _ Figure 1 shows the special jumper wire 10 of the present invention. The wire 10 includes an inner conductor 12, a coating of insulation 14, and a coating of hot-melt adhesive 16 over the insulation 14.

Figure 2 shows an electrical heating iron 19, like a soldering iron, with a handle 17, a receptacle 18, an electrical heating element 26, and a specially-shaped tip 23. As it is shown in Figures 6 and 7, the tip 23 is flattened to give it a shape like a screwdriver blade. The lower edge of the tip has an elongated groove 41 (Figures 6-6B) to fit over the outside of the wire 10 so that the iron tip embraces the wire, and the sides 44 of the tip on opposite sides of the groove 41 straddle the wire as shown in Figure 7 when the tip is pressed down on top of the wire.

In Figure 3, a jumper wire 11 having the structure of the wire 10 in Figure 1 and the heating device 19 of Figure 2 are shown in use for repairing or changing a printed circuit board 28.

First, if the jumper wire 11 has not been pre-cut to the proper length, one end of the wire 10 is stripped of insulation, bent over, and inserted into a plated hole 25 in the board 28. Then the heated tip 23 of the device 19 is pressed down onto the wire 10 near the hole 25, held there for a second or two, and released. The wire then is bent to form corners 13 and 15, and the hot iron 19 is used again in the same way at appropriate points along the wire to secure it to the surface of the board 28. Then, when the correct length of the jumper wire has been determined, the wire is cut, and the remaining end is stripped of insulation, bent over and inserted into another plated hole 27. Then, the jumper wire ends are soldered into the holes 25 and 27 by the use of a soldering iron or gun, or preferably, in a wave soldering device which solders all of the junctions on the board 28 simultaneously.

If the jumper wire 11 has been pre-cut to the proper length and its ends stripped before use, the stripping and cutting steps described above are not necessary. Also, the bends of the wire at 13 , 15 and at the ends of the jumper wire can be pre-for ed by the use of bending dies. Then the user need only apply and attach the wire to the board.

Portions of printed conductors on the board 28 are shown at 29, 31 and 33. The conductors 29 and 31 make electrical contact with the jumper wire 11 at the plated holes 25 and 27. However, the jumper wire 11 crosses over the conductor 33 and others like it without making electrical contact, both because of the insulation on the wire, and because of the insulating epoxy solder-resist coating over at least some of the conductors on the board.

The iron tip 23 heats and very quickly melts the hot-melt adhesive 16, which flows in the manner shown in

Figure 7, and adheres to the surface of the printed circuit board 28. Some of the adhesive cools quickly to form a bond. Then, after being held in place briefly, the iron tip 23 is removed and the remaining melted adhesive cools, forming a solid adhesive bond between the wire and the board surface.

The jumper wire process and equipment described above are quick and easy to use, and have other advantages which will be discussed in the detailed description which follows.

DETAILED DESCRIPTION

A. Wire Structure

The wire 10 shown in Figure 1 includes an inner conductor 12 which, for example, may be a .010 inch diameter copper wire. It may have a very thin (.0002-.0005 inch) electroplated coating of silver on the outer surface.

In order for the insulation 14 to be able to withstand the high temperatures it will be subjected to during the use of this invention, the insulation is preferably is a thermoset, heat resistant polymer material. Preferred materials are irradiated, cross-linked polymers such as polytetrafluorethylene (PTFE) and may include other thermoset polymers such as polyvinylchloride and polyolefins such as polyethylene. Such an insulation layer 14 is such typically about .005 inch thick, and in the preferred embodiment its outer surface is etched chemically, e.g. by a caustic chemical solution, in order to promote adhesion between it and the adhesive 16. The thickness of insulation layer 14 is preferred to be approximately 45% to 55% of the diameter of conductor 12.

The hot-melt adhesive layer 16 should be just thick enough to supply enough melted adhesive to make a good bond. For example, an adhesive thickness of about .005 inch thick, that is, one approximately equal to the thickness of the insulation layer 14, is preferred. For reasons discussed below, a preferable hot-melt adhesive is "Hysol" brand type

XPA-1245 or type 7901. Both materials are polyamides sold by the Dexter Corporation.

B. Heating Device

The heating device 19 illustrated in Figure 2 may be a conventional soldering iron but with the typical pointed soldering tip replaced by the special tip 23.

The device of Figure 2 may be used to help route

SUBSTITUTE SHEET - li ¬

the wire by pressing the hot tip against the wire near a desired bend to fasten the wire to the board at the point of contact. As the iron is used to hold the wire down, it is bent at the contact point of the iron tip to the board 28 to change the direction of the wire. This is desirable because bending and fastening of the wire are done in the same step.

The preferred tip 23 is illustrated in Figures 4 through 7. As it is shown in Figure 6, the tip preferably has screw threads 35 at one end and is threaded into a threaded hole in the receptacle 18 (Figure 2) . Therefore, the tip 23 may be used in conjunction with many different types of irons such as soldering irons which use replaceable tips. The tip 23 is elongated and relatively thin at its lower end so as to facilitate accessibility to the printed circuit board 28 in areas congested with many components and/or conductors.

The tip 23 is cylindrical at its upper threaded end 35, and tapers outwardly in the dimension shown in Figure 6 , and tapers inwardly in the dimension shown in Figure 6B. The angle 0 of taper is approximately four degrees.

As it is shown in Figure 6 , the metal at each end of the groove 41 is cut away to form rounded edges 37. This enables one to tilt the tip 23 sideways while using one of the rounded edges 37 as a pivot, thus holding the wire down and allowing one end of the melted adhesive area to cool and harden faster than if the iron tip were held in contact with the wire over the full width of one tip. The rounded edges 37 prevent the metal from digging into the insulation 14 on the wire.

The depth of the groove 41 preferably is between 65% and 85% of the total diameter of the wire 10 with the adhesive coating intact, and is about equal to the diameter of the insulated wire plus the thickness of the adhesive coating. The groove 41 forms ridges or legs 44 (Figure 7)

SUBSTITUTE SHEET with bottom edges 43 (Figure 6) .

When the hot iron tip 23 has melted through the adhesive 16, the bottom edges of the ridges 44 abut against the epoxy "solder-resist" coating 47 on the printed circuit board 28, as it is shown in Figures 4 and 7. This creates some heating of the board material so as to enhance adhesion. The tip 23 is shown in Figure 7 with melted adhesive which has spread outwardly from the ridges 44 as indicated at 45. This spreading action is believed to enhance rapid cooling and hardening of the adhesive.

The preferred range of temperatures for the tip 23, when using Hysol XPA adhesive is from around 550°F. to 650°F. A temperature of approximately 600°F. is preferred.

The iron need be applied for only one or two seconds, in most cases. One reason for such speed, it is believed, is that the mass of the melted adhesive is small relative to the mass usually used with prior methods. The coating of adhesive is just thick enough to ensure that the spaces between the ridges 44 and the wire 10 are filled, or a little more than filled, with adhesive. Another reason, it is believed, is that the bond extends over a relatively long section of the wire and thus covers a substantial area so that the holding power of the adhesive quickly becomes adequate to secure the wire to the board without being held down so that the iron can be removed to allow the adhesive to further cool and harden rapidly.

An alternative tip 22 for the heating device is shown in Figures 10 and 11. The tip 22 is cylindrical in shape and is surrounded by a coil spring 24 which can be used to press the wire against the printed circuit board before, during, and after melting of the hot-melt adhesive in the unusual circumstances in which the foregoing arrangement does not give fast enough cooling of the adhesive. The spring 24 is fixed at one end to the heating element 26 (Figure 2 ) of the heating device 19. At its

SUBSTITUTE SHEET opposite end, the spring extends beyond the end of the tip 2. As it is shown in Figure 11, the spring 24 presses the wire 10 downwardly against the printed circuit board 28. As the heating device 19 is pushed downwardly further, the spring 24 is further compressed so that the tip 22 is pressed against the wire to heat a local region of the adhesive layer 16.

After the adhesive has been melted, the heating device 19 is lifted slightly from the wire 10, as shown in Figure 11, so that the tip 22 is lifted from the wire, but the spring 24 continues to hold the wire against the printed circuit board 28. This allows time for cooling and setting of the adhesive 16 without allowing the wire to spring upwardly and pull free of the circuit board 28.

Another tip 32 of the heating device 19 is shown in Figure 8. The tip 32 includes three hemispherical feet 34. As it is shown in Figure 9, these feet allow the tip 32 to straddle the wire 10 as it is pressed against the printed circuit board 28. The feet also serve to position the tip properly over the wire 10 during the bonding process.

Another tip 40 for the heating device 19 is shown in Figures 12 and 13. The tip 40 is substantially the same as the tip 23 described above. One end (not shown) has threads and is threaded into a hole in a hexagonal body member 38 which is, in turn, threaded into the heating element of the device.

The tip 40 has a concave, cylindrical groove in it.

The groove 42 separates elongated ridges 44 which serve as legs which straddle the wire 10 as the tip is pressed against the printed circuit board 28. As with the preferred embodiment of Figures 6 and 7, the tip 40 straddles the wire 10 and presses against the printed circuit board 28 to locally heat the board for a better bond. The spring 24 is not required. The groove 42 is aligned with two corners of the hexagonal member 38. This assists in the orientation of

SUBSTITUTE SHEET the groove 42 with the wire by giving the user an alignment reference plane.

C. Adhesive Material

The temperature of the usual wave solder bath is around 500°F or a little higher. In the usual wave soldering process the bath metal brief touches only the bottom side of the printed circuit board - the one without components attached. However, portions of the upper side of the board sometimes reach temperatures over 300°F. Therefore, in order to prevent the jumper wire from coming loose during wave soldering, the melting temperature of the adhesive should be as high as possible, but at least 300°F to 350°F. Accordingly, the two preferred adhesives for use in this invention are those having the highest melting points and having the ability to adhere to glass-filled epoxy printed circuit board surfaces and epoxy solder-resist coatings.

The approximate viscosity-temperature curves of the preferred Hysol adhesives used in the present invention are illustrated in Figure 15. Both are seen to be advantageous in that the viscosity is relatively high at temperatures just below the "melting point" temperatures. The melting point of the Hysol 7901 adhesive, as determined by the standard "ring and ball" test specified in ASTM E28-67, is around 340°F. The melting point of the XPA 1245 adhesive, using the same procedures, is approximately 392°F. The XPA 1245 material is preferred because of its higher melting point and its higher viscosity at temperatures above the melting point. However, adhesives with even higher melting points, say, up to 550°F, are even better.

The maximum melting point temperature of the adhesive is not particularly critical. However, it has been found that an iron tip temperature of at least 500° to 650° should be used in order to obtain an adequate chemical reaction between the adhesive and certain epoxy resins used as solder-resist materials to ensure a good bond. Although

SUBSTITUTE SHEET higher iron temperatures can be used, this can cause problems. Therefore, a melting point below 550°F is preferred.

It should be pointed out that the viscosity- temperature curves of Figure 15 are only estimates, and that the actual values may differ significantly from those shown. Therefore, the "melting point" for each material, which is fairly well defined, should be used as the most reliable measure of the holding power of the adhesive at elevated temperatures.

D. Adhesive Coating Process

Figure 12 shows machine 48 used for coating the wire 10 of Figure 1 with hot-melt adhesive. The adhesive- free wire 60 preferably has PTFE-insulation which is etched in a caustic chemical solution to promote the adhesion of the adhesive layer 16 to the insulator layer 14. Any of several caustic chemical solutions known in the art may be used for the etching process.

The coating machine 48 consists essentially of a take-up reel 74 driven by a variable speed motor (not shown) , a supply reel 58, a melting pot 50 with an adhesive supply reservoir 52 and a die 66 through which the adhesive-free wire 60 passes in a vertical direction.

The adhesive is placed in pellet form in the melting pot 50 and is melted by an electric heater which is part of the melting pot assembly. The melted adhesive is stored in the adhesive supply reservoir 52 at a constant temperature of around 400°F, which is monitored by means of thermocouple 54. Reservoir 52 also serves as the coating chamber. Nitrogen gas is fed into the melting pot 50 through a tube 56 to minimize the oxidation of the molten adhesive.

The adhesive-free electrical wire 60 is mounted on the supply reel 58 and routed over a guide pulley 62 to the adhesive supply reservoir 52. The wire 60 passes upwardly through a guide 64 into the reservoir 52 where it is coated

SUBSTITUTE SHEET wi^'tir molten adhesive. The wire 60 then exits the reservoir 52 through the die 66 which is provided to determine the thickness of the adhesive layer on the wire.

The orifice size of the die 66 is adjustable to vary the thickness of the adhesive and to accept various sizes of wire.

After coating, the wire 10 travels a distance sufficient to allow the adhesive to harden. The distance L depends on the thickness of the adhesive, the speed of the wire, and the ambient air temperature, among other things. The wire 10 then is routed over a precision pulley 70. The precision pulley 70 is integral with a counter mechanism 71 which counts the number of revolutions of the pulley 70 in order to measure the length of wire coated.

The wire 10 then passes over a level-winding pulley 72 and is level-wound on the take-up reel 74. The reel 74 is driven at a variable speed and pulls the wire 10 through the coating machine 48 at a relatively constant speed.

By moving the adhesive-free wire 60 vertically rather than horizontally through the die 66, unevenness of the adhesive coating due to the effects of gravity are avoided. The result is an even adhesive coating economically applied.

E. Tip Cleaning

A device 76 for cleaning the tip of the heated iron 19 is shown in Figures 16 and 17. The device 76 also serves as a holder for the heating iron.

The cleaner/holder device 76 has a frame made of aluminum or other suitable metal. The frame comprises a single sheet of metal forming a base plate 78 and an upwardl - bent end portion 82, a cleaning device 79, and an iron holder 88 secured to the base plate at one end by means of a bolt and washer combination 89. The cleaning device 79 includes a form or spool 80 into which is wound several

SUBSTITUTE SHEET layers of an elongated fibrous material such as cotton string.

The spool 80 is wedged between the tapered helical spring forming the iron holder 88 and the upper edge 85 of the end-portion 82 of the base to releasably hold the spool in place so that the iron tip 23 can be wiped across the cleaning surface 84 formed by the string wound on the spool 80.

The spool 80 has a cylindrical core and flanges 92 to hold the string wound in it in place. The spool 80 can be an ordinary fishing-line spool, for example. It is held by tabs 83 at the ends of the upper edge 85 of the end portion 82.

The cotton string preferably is treated with a combustion-retardant solution. A suitable solution consists of 2% borax and 2% boric acid by weight dissolved in water.

The cleaning process is shown in Figures 17 and 20, as well as Figure 16. The tip 23 is moved over the cleaning surface 84 in a direction 87 (Figure 17) in which the groove 41 is aligned with the strands 106 of the string as shown in Figure 20, so as to allow the strands 106 to enter the groove 41 of the tip 23 to clean out any residual adhesive. The bottom edges 43 of the ridges 44 and the outside surfaces of the ridges are also cleaned by adjacent strands of string.

Of course, the surface 84 also can be used to clean other adhesive melting iron tips such as thoses illustrated in Figures 8 through 13, regardless of the shape of the tip. In accordance with the present invention, a fresh cleaning surface can be exposed by means of one of two alternative methods. First, the spool 80 can be rotated a little to expose a clean portion of the surface 84. When there is no more clean area, the second method can be used; namely, unwinding the string on the spool until a fresh layer of string has been exposed. Either method is simple

SUBSTITUTE SHEET and quick.

Other cleaning surfaces can be used. For example. Figure 21 shows a cleaning surface formed by a roll 97 of adhesive tape which has a relatively soft, absorbent cloth backing. When a clean wiping surface is needed, the user can either rotate the spool 80, or the user can peel off all or part of one layer of tape 97. The upper front edge 85' of the base portion is sharpened and/or serrated to facilitate cutting- off a length of tape.

Figure 22 is an enlarged section of the tape 97 of

Figure 21. The adhesive material is shown at 99 and the soft cloth backing at 101. A tape of the type described is so-called

"athletic" tape which is used to wrap ankles, knees and other parts of athlete's bodies for support purposes. Since the adhesive tape 97 needs the adhesive primarily to hold the roll together without unwinding, tape with a relatively weak adhesive may be used. The cloth 101 should be treated with fire- retardant materials of the type described above.

It is believed that the embodiment of the invention shown in Figures 21 and 22 is especially suitable for cleaning the tips of soldering irons. If the adhesive melting iron of Figures 2-7 is to be cleaned using the tape form of cleaning surface, the groove in the iron tip can be cleaned especially well if corduroy cloth is used for the tape 97. The ridges of the cloth preferably extend circumferentially around the roll, and the tip 23 can be wiped against the cloth in the direction shown by arrow 87 in Figure 17 to clean out the groove in the tip.

It is believed by many that a cleaning surface for soldering irons should be wet in order to do the best cleaning. Accordingly, a water reservoir 93 is mounted on the base plate 78 (Figure 17) for the roll of string 80 to be immersed in. The string will stay wet all the way around as water is absorbed from the reservoir 93 into all fibers of the string.

SUBSTITUTE SHEET The same kind of reservoir 93 also can be used with the tape of Figure 21. As desired, the fire-retardant chemicals can be added to the water in the reservoir 93, if desired, rather than soaking the string before the spool of string is mounted on the base plate 78.

If desired, water in the reservoir 93 can be replenished automatically by use of any of a multitude of known water replenishment devices, such as those used to water pets, chickens, etc. Water can be added by such means through an inlet tube 95.

An improved cleaner/holder device 94 is illustrated in Figures 18 and 19. The device 94 has a frame consisting of a single aluminum sheet punched and bent to form a generally U-shaped structure. The frame has a lower base portion 96, an angled front portion 100, and a top portion 98. The top portion 98 has a rectangular hole 102 which is slightly wider than the length of the spool 80 , but whose other dimension is slightly smaller than the diameter of the flanges 92 of the spool 80. The weight of the spool forces the edges of the flanges 92 against the edges of the hole 102. This acts as a brake to hold the spool in place while an iron tip is being wiped across its surface 84.

The front portion 100 of the frame has a circular hole into which an elongated cylindrical bushing 86 is fitted. Bushing 86 is constructed of a heat-resistant material and, as it is shown in Figure 19, is secured in place by circular retaining clip 104. Bushing 86 serves as the holding device to hold the heating device 19 when it is not in use.

As with the embodiments shown in Figures 16, 17, 21 and 22, a water reservoir 93 can be provided to keep the cleaning surface damp. Also, the tape form of the cleaning surface shown in Figures 21 and 22 also can be used with the holder shown in Figures 18 and 19.

Each of the embodiments shown in Figures 16-21 has

SUBSTITUTE SHEET rubber feet 19 on the base plate to keep the device from slipping on a surface on which it rests while a hot iron is being pushed against the cleaning spool 80.

While the present invention has been particularly shown and described with reference to preferred embodiments, various changes and modifications in form and details may be made without departing from the spirit and scope of the invention. It is intended that the appended claims be interpreted as including the foregoing as well as various other changes and modifications. CLAIMS:

SUBSTITUTE SHEET

Claims

1. An electrically conductive wire, said wire comprising, in combination, an electrical conductor, a coating of insulation on said wire, and a coating of normally solid, inactive adhesive on said insulation, said adhesive being adapted to be activated by the application of a tool thereto at each of a plurality of locations along its length so as to cause said wire to adhere to a substantially planar support surface at each of said locations in response to the application of said tool.

2. A wire as in Claim 1 in which said adhesive is a hot-melt adhesive and said tool is a heating tool.

3. A wire as in Claim 1 in which said support surface is an epoxy resin surface of an electrical printed circuit board.

4. A wire as in Claim 2 in which said adhesive is a polyamide resin with a melting point of from approximately 300°F to approximately 550°F.

5. A wire as in Claim 2 in which said adhesive has a melting point of from approximately 340°F to 400°F.

6. A wire as in Claim 1 in which the thickness of said adhesive coating is approximately equal to the thickness of said insulation.

7. A wire as in Claim 1 in which the thickness of said adhesive coating is approximately sufficient to fill the interstices between said insulated wire and said planar surface when an applicator which straddles and envelops said wire is applied thereto.

8. A wire as in Claim 2 in which said insulation is relatively easily strippable, and said adhesive coating is adapted to melt and create a bond between said wire and said surface when contacted by said heating tool at a temperature substantially higher than the melting point of said adhesive for a time of one or two seconds.

9. A pre-fabricated jumper wire, said jumper wire comprising, in combination, a length of wire, pre-cut to a

SUBSTITUTE SHEET desired dimension, said wire having an inner conductor and a coating of insulation which is stripped away at at least one end of said wire, and a coating of adhesive over the remaining insulation on said wire, said adhesive being adapted to be activated by the application of a tool thereto at a plurality of locations along its length to cause said wire to adhere to a substantially planar surface.

10. A jumper wire as in Claim 9 in which both ends of said length of wire have the insulation stripped away, and said wire is pre-bent to a desired shape so as to follow a desired path when attached to said planar surface.

11. A wire as in Claim 9 in which said adhesive is activated by the application of a heated tool thereto.

12. A wire as in Claim 11 in which said adhesive is a hot-melt polyamide adhesive material.

13. A wire comprising an electrical conductor, an electrical insulator layer surrounding said conductor, and a hot-melt adhesive coating surrounding said insulator layer for bonding said wire through heating to a non-adhesive surface, in which said insulator layer is polytetrafluorethylene (PTFE) which has been etched in a caustic solution to promote adhesion with said adhesive layer, and in which said adhesive layer has a lower melting point than said insulator layer.

14. A wire as in Claim 1 in which said adhesive layer has a melting point between approximately 300°F and 550°F.

15. A wire as in Claim 1 in which said adhesive layer has a melting point between approximately 340°F and

400°F.

16. A wire as in Claim 1 in which said insulator layer has a thickness equal to approximately 45% of the diameter of said electrical conductor.

17. A wire as in Claim 1 in which said adhesive layer has a thickness approximately equal to the thickness of said insulator layer.

18. A method of securing wires to an electrical circuit member, said method comprising the steps of providing a wire comprising a length of conductor having an electrical insulator layer thereon and an adhesive layer surrounding the insulator layer, electrically connecting the ends of the conductor to said circuit member, said adhesive being normally inactive and being activated by application of an applicator thereto, and applying an applicator to said wire to fasten it to said circuit member.

19. A method as claimed in Claim 18 wherein the adhesive layer is a hot-melt adhesive.

20. A method as claimed in Claim 18 wherein the support is a printed circuit board.

21. A method as claimed in Claim 20 including the step of pressing the hot-melt adhesive against the printed circuit board by means of a heating device having a tip which straddles the wire to heat and compress the adhesive.

22. A method as claimed in Claim 21 wherein the tip comprises an elongated groove positioned over the wire, the depth of the groove being greater than the diameter of the insulator layer and less than the diameter of the adhesive layer.

23. A method as claimed in Claim 19 including heating said adhesive layer by the application of a heated member having a temperature of from approximately 550°F to approximately 650°F.

24. A method as claimed in Claim 20 wherein the adhesive layer is pressed against the printed circuit board by means of a heating device having a heated tip and a spring element, and the spring element presses against the wire as the heated tip is moved toward and into contact with the wire and continues to press against the board as the heated tip is pulled away from the wire.

25. A method as claimed in Claim 20 including the

SUBSTITUTE SHEET step of electrically connecting the ends of the conductor to terminals on said printed circuit board by soldering.

26. A printed circuit board having a non-printed electrical wire interconnector thereon, the wire interconnector comprising an insulator layer surrounding a conductor and an adhesive layer surrounding the insulator layer along substantially its entire length, the conductor being electrically connected to the printed circuit board at its ends and mechanically coupled to the printed circuit board between its ends by the adhesive layer.

27. A printed circuit board as claimed in Claim 22 wherein the adhesive layer is a hot-melt adhesive.

28. A printed circuit board as claimed in Claim 23 wherein the adhesive layer has a melting point of between approximately 300°F and approximately 550°F.

29. A printed circuit board as claimed in Claim 24 wherein the conductor is electrically connected at its ends by solder.

30. A printed circuit board as claimed in Claim 23 wherein the insulator layer is a thermoset material.

31. A heating device for heating an insulated electrical wire which has been coated with an adhesive layer comprising a handle, a heating element and a heating tip extending from said heating element, said tip having a bottom side which is elongated in one direction, and an elongated groove forming ridges on opposite sides of said groove in order to straddle said wire during heating.

32. A heating device as in Claim 1 in which said heating element is adapted to maintain said tip at a temperature between approximately 550°F and approximately 650°F.

33. A heating device as in Claim 1 in which said elongated groove of said tip has a depth greater than the diameter of said insulation but less than the diameter of said adhesive layer, and in which said ridges are dimensioned to

SUBSTITUTE SHEET touch a planar surface on which said wire is resting while said tip straddles said wire after melting the adhesive in the vicinity.

34. A heating device as in CLai 1 in which said tip has a rectangular cross section with one dimension much greater than the other, said elongated groove running the length of said one dimension.

35. A heating device as in Claim 31 in which said tip is provided with a coiled spring coaxial to said tip, said spring being secured to said heating device above said tip and extending beyond the length of said tip.

36. A device as in Claim 31 in which the end edges of said groove are beveled to allow said tip to be rocked about one of said edges while resting on said wire without damaging said wire.

37. A device for cleaning the tip of a heated iron for melting solid materials used for joining objects together, said device comprising, in combination, a support, a cleaning surface comprising a plurality of elongated fibrous strands mounted on said support member and extending in substantially the same direction.

38. A device as in Claim 37 including a plurality of layers of said strands, each upper layer being removable from the next lower layer to expose a fresh cleaning surface.

39. A device as in Claim 38 in which said support member comprises a form for holding a strand of fibrous material wrapped around it, and said cleaning surface comprising a single strand of cotton string wound on said form in a plurality of turns.

40. A device as in Claim 39 in which said holder comprises friction brake means for impeding the movement of said support member.

41. A device as in Claim 37 in which said iron has a grooved tip for melting hot-melt adhesive on wires,

SUBSTITUTE SHEET - 26 -

and said strands are of a size such that the material of a least one of said strands enters the groove of said tip when said tip is pressed against said one strand with said groove aligned with said one strand.

42. A device as in Claim 37 in which said fibrous strands contain a combustiσn-retardant material.

43. A device as in Claim 42 in which said combustion-retardant material is selected from the group consisting of boric acid, borax, and a combination of boric acid and borax.

44. A device as in Claim 39 in which said support member is a cylindrical spool.

45. A hot iron support and cleaning structure comprising a base, a holding member mounted on said base for holding said hot iron when not in use, cleaning means including a form with a fibrous material on it, said form being movably mounted on said base for cleaning said hot iron, and gripping means for holding said form stationary when contacted by said hot iron for cleaning movement.

46. A device as in Claim 53 wherein said holding member comprises a resilient means mounted on said base, said gripping means comprising said holding member mounted to urge said form against a portion of said base to act as a friction brake.

47. A device as in Claim 45 in which said form is a rotatable spool, and said gripping means comprises a plate with a hole in it, said hole being slightly narrower in one dimension than the diameter of said spool, and slightly larger in another dimension than the length of said spool, with said plate being positioned so that, when said spool is inserted into said hole, gravity pulls it against an edge of said hole to brake it.

48. A device as in Claim 45 in which said cleaning means comprises a cylindrical spool wound with a roll of adhesive tape with a cloth backing useful for cleaning said hot iron, said gripping means including a plate extending near and contacting said form, said plate serving as a cutting edge for cutting off removed sections of tape.

49. A device as in Claim 48 in which said hot iron is adapted to heat a hot-melt adhesive and has a handle, a heating element, and a tip with an elongated, grooved lower edge.

50. A cleaning device for cleaning the tips of hot irons comprised of a surface of continuous fibrous material wrapped in a plurality of layers about a support member, the upper one of said layers being removable to expose a fresh layer.

51. A device as in Claim 50 in which said fibrous material contains a combustion-retardant material.

52. A device as in Claim 50 in which said fibrous material is soaked in a solution selected from the group consisting of boric acid, borax and a combination of boric acid and borax.

53. A device as in Claim 50 in which said fibrous material comprises absorbent cotton string.

54. A device as in Claim 50 in which said fibrous material comprises absorbent corduroy material.

55. A device as in Claim 50 in which said fibrous material comprises adhesive tape with an absorbent cloth backing.

56. A device as in Claim 50 including a reservoir mounted so that a liquid contained therein is in contact with said fibrous material to wet it.

57. A method for cleaning hot irons comprising the following steps: providing a cleaning element consisting of a plurality of layers of fibrous material, passing the tip of said iron over the outermost layer of said element to clean said tip, and removing said outermost layer when it is no longer clean so as to expose a clean layer of said element.

58. A method for preparing said cleaning element

SUBSTITUTE SHEET in Claim 57 including the steps of soaking said fibrous material forming each of said layers in a fire-retardant solution at a time selected from the group consisting of before or after said material is placed on its support form, or during use.

59. A method of coating insulated electrical wire with a hot-melt adhesive, said method comprising: melting said adhesive in heated chamber, passing uncoated insulated electrical wire though said melted adhesive in said chamber, withdrawing said electrical wire vertically from said heated chamber through a die to insure uniform coating, and cooling said coating to solidify it.

SUBSTITUTE SHEET