GB2148079A - Soldering device - Google Patents

Abstract

An improved soldering iron incorporates a ceramic resistant heating element having the resistant element formed of a metal or alloy which has a temperature coefficient of resistance greater than that of platinum. This is used in combination with a heat conducting body which has a thermal conductivity substantially less than that of pure or almost pure copper. The heat conducting body is, in fact, more effective when its thermal conductivity is 20% or less that of pure copper. <IMAGE>

Description

SPECIFICATION Soldering Device Background of Invention A soldering device is improved by utilizing a ceramic heater having a resistance element printed or screened thereon in combination with a heat conducting body which is formed of a thermal conducting material wherein the thermal conductivity of the material is substantially less than that of pure or nearly pure copper.

Resistant heater soldering irons have been known for many years. The basic components of these soldering irons included a resistant heater element in combination with a heat conducting body which has a low thermal conductivity. The heat conducting body could include a soldering tip formed as a part thereon or as an independent part which is threaded on or was frictionally held in engagement with the heat conducting body. It was recognized many years ago that the heat conducting body should be formed of a material having good heat conductive qualities.

Copper, because of its availability and its excellent thermal conductivity was recognized early on as the material of choice for the formation of the heat conducting body.

The heat of these soldering irons is generated by passing an electrical current through a resistance heating element. The resistance element utilized is in the form of a wire. Normally, the wire was coiled in one mannerorthe other so as to increase the length of the wire coil which could be located in a particular volume in order to yield the desired heat output needed for functioning of the soldering iron.

Many different sizes and shapes of coils have been utilized throughout the years. For the most part, all of the different geometric shapes for the resistance coils have been based upon initially coiling the resistance wire in a tight spiral and then further shaping the spiral into other orientations.

Because of the electrical conductivity of the heat conducting body, it is necessary to electrically insulate the resistance heating element from the heat conducting body by the use of dielectric materials such as mica plates or the like. In certain instances, the resistance element was wound around ceramic cores and the like in order to provide physical supportforthe resistance element.

More recent technology has embedded the coils or other geometric shapes of the resistance wire directly into ceramic matrices in order to protect the same.

Nickel alloyed with chromium to form a series of proprietary alloys known as nichrome has become the material of choice for use in formation of the resistance element. Many formulations of the nichrome alloy have been utilized in a variety of shapes and structures depending upon the particular soldering iron manufacturer. It is because of the ability of nichrome wire to maintain its structural integrity when heated to high temperatures by the passage of an electrical current through itthat nichrome has become the material of choice for formation of the resistance elements.

Nichrome, however, has several disadvantages.

When exposed to air at high temperatures, eventually the integrity of the alloy is deteriorated, leading to failures of the heating element. To overcome this disadvantage, certain manufacturers have attempted to embed the nichrome into a dielectric material which will protect it from the air and hopefully increase its longevity. Unfortunately, unless the air is totally excluded, hot spots will develop along the coil of the nichrome resistance heater, and at these hot spot areas deterioration will occur, decreasing the lifetime of the resistance element.

Additionally, to get sufficient watt density, a sufficient mass of nichrome wire must be utilized.

With the advent of electronics and the reduction in scale of electronic components, the large soldering irons of the past are no longer useful for electronic assembly work. For use with modern of electronic components, a soldering iron of a reduced scale compared to soldering irons of years past is necessary. This presents problems in the manufacturing of these soldering irons because of the inability to wind a sufficient amount of nichrome wire into a small enough size to fit into these irons yet still maintain a sufficient watt density to produce sufficient heat for the soldering process.

In order to overcome the disadvantages of utilizing wire coils for the resistance heating elements, certain manufacturers have recently introduced resistance heating elements which do not utilize coils of nichrome or other suitable wire. In their place a pattern for a resistance heating element is screened or otherwise formed on a green piece of ceramic using a paste, powdered metal or the like as a precursor for the element. The resistance element pattern is then covered with further green ceramic or left exposed, and the totality of the structure then calcined to both vitrify the ceramic as well as form the powder, paste or other form of the resistance material into a continuous resistance element. For the purposes of this specification these will hereinafter be referred to as ceramic resistance heating elements.

In considering the material from which to form the resistance heating element, several criteria have to be kept in mind. They must exhibit a fast heat rise time, have good dielectric strength and must be capable of a long and useful lifetime. By incorporating the resistance element right into the body or matrix of the ceramic or dielectric covering, the resistance element is essentially shielded from the air, and thus deterioration of the same by the air is inhibited.

Present technology has not lent itself to the use of nichrome as the material for formation of those ceramic resistance heating elements as described in the preceding. It has not been possible to incorporate a sufficient mass of the nichrome to provide sufficient electrical resistance for the generation of the necessary heat. Further, a suitable nichrome based material for formation of the resistant element pattern having a sufficient temperature coefficient of resistance (TCR) is not presently available. Known nichrome alloys have a TCR generally in the range of 1200 to 1800 ppmrC whereas a material having a TCR greater than this is needed to form the small size ceramic resistance heating elements of the small mass soldering irons.

Because of the above factors, other materials have been chosen as the basis of the resistance element of these ceramic resistance heating elements. Suitable resistance elements can be formed based upon the use of tungsten as the resistance metal.

Unfortunately, it has been found that when ceramic resistance heating elements having tungsten as their resistance element are utilized in conjunction with the normally used heat conducting bodies, the soldering irons so produced have exhibited very poor heat recovery properties. Once the ceramic resistance heating element has heated up the heat conducting body, and heat has then been withdrawn from the heat conducting body by actual soldering operations and the like, the tungsten based heating elements are extremely hesitant in reheating the heat conducting body.

It has previously been considered that formation of the heat conducting body out of very good thermal conductors is necessary for transfer of the heat from the heating element to the soldering tip and to the actual soldering joint. A dichotomy thus exists. With the use of nichrome wire heating elements, performance of the soldering iron increases by increasing the thermal conductivity of the heat conducting body, while at the same time, when these same excellently performing heat conducting bodies are coupled with tungsten based ceramic resistance heating elements, poor performance characteristics of the soldering iron are exhibited.This has tended to deter the acceptability in the market place of soldering irons which incorporate ceramic resistance heating elements which have as their resistance heating material compositions containing tungsten and the like which are screened onto a green ceramic and then calcined or sintered to form the final ceramic resistance heating element.

Brief Description of the Invention In view of the above, it is a broad object of this invention to provide a soldering iron device which can utilize as its heating element a resistance heater not based on the use of nichrome with the soldering device exhibiting rapid heat recovery characteristics on actual use of the soldering device. It is a further object of this invention to provide a heating device which seemingly goes contrary to existing technology in its use of a heat conducting body formed of a material which has a thermal conductivity which is decreased with respect to the state of the art use of material having a high thermal conductivity.Additionally, it is an object of this invention to provide a soldering device which, because of its engineering principles and manufacture practices utilized to produce the same, is capable of a long useful life, yet is economically available to the consumer.

These and other objects, as will become evident from the remainder of this specification are achieved in a soldering device having a heat conducting body, a heater and means for supplying current to said heater an improvement which comprises: said heater including an insulating member and an electrical resistance member; said electrical resistance member encapsulated in said insulating member and electrically connected to said means for supplying current, said electrical resistance member being formed of a material having a temperature coefficient of resistance in parts per million per degree Celsius greater than the temperature coefficient of resistance 0 to 1 000C of platinum of about 3850 parts per million per degree Celsius.Said heat conducting body being sized and shaped so as to abut with said heater in association with said electrical resistance member so as to absorb heat discharged from said electrical resistance member upon passage of current through said electrical resistance member and said heat conducting body formed of a heat conducting material which has a thermal conductivity at least less than about 50% of that of at least 99.5% pure copper.

Preferably, the electrical resistance member would be formed of a material which contains as its primary electrical current conducting resistance element an element chosen from the group consisting of tungsten, ruthenium, rhodium, platinum, paladium or silver. Based on economic considerations, more preferably, tungsten would be used.

Preferably, the heat conducting body would be formed of a material having a thermal conductivity which would be about 20% of that of essentially pure copper. More preferredly, the thermal conductivity would be approximately 10% that of pure copper. Suitable for use as the heat conducting body would be alloys of copper. Preferredly, these alloys would contain copper in a range of about 60% to about 95% with those having the preferred thermal conductivity of 20% that of pure copper or less generally being alloys of copper containing approximately 90% plus or minus several percent of copper.

Brief Description of the Drawings The invention disclosed in this invention will be better understood when taken in conjunction with the drawings wherein a typical soldering iron embodying the principles of this invention is shown.

In the drawings: Fig. 1 is a side elevational view in section of such a typical soldering iron; Fig. 2 is an isometric exploded view of certain components located near the right hand side of Fig.

1; Fig. 3 is an alternate embodiment for certain of the structures illustrated in Fig. 2.

The invention described in this specification and illustrated in the drawings utilizes certain principles and/or concepts as are set forth in the claims appended to his specification. Those skilled in the pertinent arts to which this invention pertains will realize that these principles and/or concepts are capable of being utilized in a variety of embodiments differing from the exact illustrative embodiment utilized herein. For this reason, this invention is not to be construed as being limited to only the illustrative embodiment but is only to be construed as being limited to the claims appended to this specification.

Detailed Description of the Invention Before describing this invention in detail, certain physical properties of material related to this invention need be described. Prior to describing these however, certain definitions with regard to the same need be set forth. The temperature coefficient of resistance, abbreviated by the capital ietters TCR as noted above is, by definition an indication of resistance at a specific reference temperature. It normally bears the units ohms/0C/ohm. It thus refers to the change in resistance of a given conductor resulting in a particular change in temperature about a reference temperature divided by the conductor's resistance at the reference temperature.

Because the electrical resistance cancels out, the only unit associated with the TCR is the0 unit. This will be expressed as 0C for this application.

The TCR value can conveniently be converted into several specific ratios, percentages or parts per million. For use in this specification, the TCR's will be expressed as parts per million for the resistance temperature change of from 0 to 100 C.

For certain pure metals, the temperature coefficient of resistance as well as the thermal conductivity are listed in reference manuals. For the purposes of this specification, the values listed with regard to the TCR have been extracted from the Electronics Engineers'Handbook, Second Edition, Fink and Christiansen, Copyright 1982, published by McGraw Hill Books. TCR values listed are from Table 6.1, entitled Physical Properties of Pure Metals of that volume. Other reference books, at least with respect to paladium, list values differing from that listed in the Electronics Engineers'Handbook referred to above, and for the purposes of this specification and the claims appended hereto, differentiation with respect to numerical values of the TCR's are based on those listed in the Electronics Engineers'Handbook.In this book, paladium is listed as having a TCR of 4200 parts per million (ppm)/"C which is greater than that of platinum, listed as 3920 ppm/0C, both at 0 two 1000C reference. Palladium is therefore considered to have a higher TCR than platinum forthe purposes ofthis specification and claims. Insofar as this may differ in other reference books, the other reference books are considered subservient to the values listed in the Electronics Engineers'Handbook, Second Edition.

The TCR values of other elements which need be considered with respect to this specification and the claims appended thereto are as listed in Table 6.1 of the referred to Second Edition of the Electronic Engineers Handbook and are as follows: Rhodium 4400 ppm/OC Ruthenium 4100 ppm/ C Silver 4100 ppm/ C Tungsten 4800 ppm/ C As noted previously, nichrome generally has a TCR in the range of from about 1200 to 1800 ppmffC.

As is evident from comparing to all of the elements listed above, the highest value noted for nichrome is sufficiently less than the values of all of the other referred to elements presented above. The TCR of the final sintered resistance element as utilized herein would vary depending upon the alloys present in the material from which the resistance element is formed. For the purposes of this specification, the exact compositions from which these resistance elements are formed need not be discussed. Commercial ceramic resistance heating elements are available with the TCR parameters provided by the manufacturer of the same.As for instance, for the purposes of this specification, a ceramic resistance heating element is available from the Kyoto Ceramic Co., 52-11 Ibnoue-cho, Higashina, Yamashina-ku, Kyoto 607, Japan, under the name of Plate Heater, Serial Number TH-81 809.

Such a resistance heating element can be purchased specifying the TCR of the resistance element located therein. For the purposes of this specification and the claims appended thereto, TCR's at least equal to that of elemental platinum of 3920 ppmfC are considered to be the minimum usable.

US patent 4,035,613 and British laid open Application 2,064,396 refers to the formation of these ceramic resistance heating elements. British "396" also references Japanese patent publication No. 10,527/1977 and West German laid open patent No. 2,548,019. The contents of this patent and the laid open applications are herein incorporated by reference with respect to production of ceramic resistance heating elements.

With regard to the heat conducting body as hereinafter identified, the thermal conductivity of the same need be specified. The value given for copper in Table 6.1, Physical Properties of Pure Metals of the Electronics Engineers'Handbook, Second Edition, as referred to above, when converted to the BTU/sq.ftlft./hr./0F unit system, by multiplying a value listed in that Table by .588 is found to be 234 BTU/sq.ft./ft./hr/0F. For alloys other than pure copper for which an understanding of the same is needed for this specification, reference is made to a handbook published by the Bridgeport Brass Co., Bridgeport, Connecticut, Copyright 1957, entitled Bridgeport Brass and CopperAlloy Handbook. Listed on Pages 74 and 75 of that book are thermal conductivities in the BTU based unit system for specific alloys useful for this invention, as well as other alloys utilized for comparative purposes.

For the purposes of this specification, it is considered that copper of a 99.5% degree purity or better would be considered as essentially pure copper, with a thermal conductivity exceeding that of 200 in the BTU unit system. This is based on temperature measurements near ambient and not at elevated soldering temperatures which are normally around 470 C. The thermal conductivity for all material pertinent to this specification would accordingly decrease at higher temperatures.

However, for reference purposes, the thermal conductivity taken at or near ambient temperature is sufficient in order to differentiate those materials which are useful for the practice of this invention. In referring to the thermal conductivity, as compared to pure, or essentially pure, copper, the conductivities at or near ambient temperature are utilized for the basis of comparison. At higher temperatures, such as that at or below the optimum soldering temperature of about 470 C, the same ratios would be maintained, or essentially the same ratios would be maintained, among the materials, with the exact numerical values, however, differing because of the increase temperatures.

Referring now to the Figures of the drawings, in Fig. 1, there is shown in side view, a soldering iron which is constructed utilizing the principles of this invention. Several component parts of the soldering iron are essentially standard in the art and will not be discussed in extreme detail because of their similarity to existing components.

In Fig. 1 is shown a soldering iron 10 which includes a handle portion 12 having a rubber grip 14 located thereon. A three element electrical cord 16 is fed through the rear of the handle 12 with the individual electrical wires 18, 20 and 22 separated from each other within the interior of the handle 12.

A spacer unit 24 is used to thread the individual wires 18,20 and 22 within the interior of the handle 12 and to separate the same.

An insulative insert 26 has a first portion 26a and a second portion 26b. The first and second portions 26a and 26b fit together tQ form a cylindrical member which is frictionally slid into the handle 12 through the opening 28. The portions of the insert 26a and 26b are appropriately keyed to fit with one another in a standard manner and a detailed consideration of the keys and the like is not needed for the understanding of this invention. The insulative insert 26 is formed of a thermal insulating material that is a very poor heat conductor and as such serves to help shield the transfer of heat from the working portions of the soldering iron 10 to the user of the iron 10.

Extending outwardly from the handle 12 to the right in Fig. 1 is a metal tube 30 preferredly formed of a material such as stainless steel or the like. When other components as hereinafter described are assembled within the interior of the tube 30 the tube 30 is inserted between the two component pieces of the insulative insert 26 and the totality of the package is then pressed into the handle 12 with frictional engagement between the tube 30 and the insulative insert 26 as well as frictional engagement between the insulative insert 26 and the handle 12 holding the totality of the components together. The spacer 24, of course, would be appropriately positioned around the particular wires 18,20 and 22 prior to insertion of the combined unit formed of the tube 30 and the components located therein and the insulative insert 26 into the handle 12.As such the spacer 24 is partially located within the interior of the insulative insert 26 with the remainder located within the interior of the handle 12 toward the cord end ofthe handle 12.

A heat conducting body 32 having a threaded projection 34 located on one end thereof is located within the end of the tube 30. The threaded portion 34 serves to receive soldering tips by threading appropriate tips onto it. It further serves to transfer heat to the soldering tips during actual soldering operation. By use of the threaded portion 34 a variety of shapes and configurations of soldering tips can be utilized with the soldering iron 10.

The heat conducting body 32 is essentially divided into three portions. The first of these is the forward portion 36 from which the threaded portion 34 extends. The forward portion 36 is utilized to attach the heat conducting body 32 to the tube 30 by spot welding the tube 30 at several places to the forward portion 36 after the heat conducting body 32 has been inserted into the tube 30.

A middle portion 38 of the heat conducting body 32 tapers downwardly from the diameter of the forward portion 36 to a smaller diameter of the rearward portion 40.

Two longitudinally extending slots 42 and 44 are formed in both the rearward portion 40 and the middle portion 38 of the heat conducting body 32.

This allows the insertion of two identical ceramic resistant heating elements 46 and 48 respectively into the slots 42 and 44 of the heat conducting body 32 so as to locate the forward end of each of the elements 46 and 48 in intimate contact with the mass of the heat conducting body 32. As constructed each of the ceramic resistant heating elements 46 and 48 include a resistant element shown by the phantom lines 50 in their forward end.

Appropriate electrical leads 52 and 54 for the element 46, and 56 and 58 for the element 48 lead from the resistant element 50 to the rear of the ceramic resistance heating elements 46 and 48. It is evident that the resistant element 50 of each of these units 46 and 48 is located in the forward end with the remainder of the elements 46 and 48 serving only to conduct the electrical leads 52,54,56 and 58 rearwardly and further to form the ceramic resistant heating elements 46 and 48 in an elongated configuration such that they may be supported at their rear end near the handle portion 12 of the soldering iron 10 yet have the resistant element 50 located distal from the grip 14 so as to place the resistant element 50 distal from the user's hand to insure comfortable utilization of the soldering iron 10.

Insofar as the resistance elements 50 are only located in the forward end of the elements 46 and 48 it is only necessary for the heat conducting body 32 to extend a short distance within the tube 30. The heat conducting body 32 is thus in intimate contact with the portion of the ceramic resistant heating elements 46 and 48 wherein the resistant element 50 is located, but is not needlessly oversized to extend further within the tube 30 requiring both a greater heat input to raise itto working temperature and also contributing to excess mass and thus the weight of the soldering iron 10.

The two ceramic resistance heating elements 46 and 48 are wired in parallel with respect to wires 18 and 20. Wire 18 connects to leads 52 and 56 and wire 20 connects to leads 54 and 58. Wire 22 is appropriately contacted against the tube 30 to serve as a ground wire for the tube 30 and the heat conducting body 32 and a soldering tip attached thereto. Two small ceramic tubes 60 and 62 are inserted over the end of the wires 18 and 20 and portions of the leads 52 and 58 attaching thereto to electrically isolate these from one another within the interior of the handle 12. The totality of the heat conducting body 32, the elements 46 and 48, the ceramic tubes 60 and 62 are drawn into the interior of the tube 30 to complete construction of the soldering iron 10.

In Fig. 3 an alternate embodiment of the invention is shown which utilizes a cylindrical ceramic resistance heating element 64. In conjunction with a heat conducting body 66. The body 66, instead of having the slots as outlined above, has a cylindrical bore 68 formed therein which is sized so as to accept the ceramic resistance heating element 64 and form an intimate contact with the same. The cylindrical ceramic resistance heating element 64 is formed with an appropriate resistant element (not shown) in its interior as with the elements 46 and 48. it, of course, is located only along that portion of the element 64 which fits within the bore 68.

The material chosen for the resistant elements 50 in the elements 46 and 48, for example, is selected so as to have a TCR O to 1000C equal to or greater than that of the TCR of platinum which is currently indicated to be 3920 ppm/ C. Appropriate resistance elements can be formed from the metals tungsten, platinum, palladium, ruthenium, rhodium or silver to achieve these results. For economic considerations tungsten would be the preferred member of the group. Ceramic resistance elements utilizing tungsten as a resistant element therein are available from the Kyoto Ceramic Company of the address listed above. These elements can be purchased having specific TCR's such as a TCR greater than the TCR of platinum noted above.

For a typical soldering iron such as the soldering iron 10 above the ceramic resistant heating element will be specified so as to draw approximately 30 watts of power at a typical line voltage of 110 or less volts and typical amperage of slightly greater than .3 amps. Such heaters when energized at 110 volts conveniently heat to the slightly greater than 4700C optimum soldering temperature.

In contrast to soldering iron technology based on the use of nichrome as the resistant element it is deemed disadvantageous to form the heat conducting bodies 32 or 66 of pure or essentially pure copper. Typically, such conducting bodies utilizing nichrome technology would be formed either of pure copper or copper doped with small amounts of alloying elements such as tellerium or chromium. Atypical alloy for utilization in prior heat conducting bodies might consist of 99.5% copper and .5% tellerium. This alloy would have a slightly depressed thermal conductivity with respect to pure copper of about 204 Btu/sq. ftlftlh PF @ 680F as is listed on page 75 of the above referred to Bridgeport Brass company catalog.A similar chromium based alloy containing approximately .5% chromium in 99.5% copper would have a slightly higher thermal conductivity of about 220 Btu's etc.

As noted above it is considered disadvantageous to utilize such good thermal conducting metals to form the heat conducting body of this invention.

Instead alloys are chosen which have depressed thermal conductivity with respect to that of at least 99.5% pure copper. As, for instance, a thermal conductivity of at least 50% less than that of 99.5% copper is considered advantageous with it being preferred to use alloys having conductivities in the range of 10 to 20% of that of 99.5% pure copper.

There are commercial alloys available containing copper in a range of approximately 90% plus or minus several percent which have thermal conductivities which are depressed to a level of from 10 to about 20% of that of 99.5% pure copper.

Some of these alloys and their thermal conductivity would have the following components.

Alloy 1 Copper 90.85% Aluminum 7.15% Silicon 2.0% Thermal Conductivity 20 Btu/sq ftlftlhrffF (W 680F Alloy 2 Copper 90.1% Aluminum 8.9% Iron 1.0% Thermal Conductivity 35 Btu/sq ft/ft/hrPF gS 680F Alloy 3 Copper 89.15% Nickel 10.0% Iron .085% Silicon 1.25% Thermal Conductivity 22 Btu/sq ftlft/hrfF @ 680F Other alloys having copper in a range of about 60 to about 95% are known which exhibit thermal conductivities in the range of about 50% less than that of 99.5% pure copper.As, for example, certain brasses, such as a brass composed of 61.25% copper, 3.4% lead and 35.35% zinc exhibit a thermal conductivity of 67 Btu/sq ftlft/hr/0F g 68 F.

Additional brass alloys with thermal conductivities in the range of 60 to 70 Btu/sq ftlftlhrPF ( 680F are commercially available from the Bridgeport Brass company noted above.

For comparative purposes a first soldering device was constructed as follows. A heating element having a TCR greater than that of platinum was mated with a heat conducting body having a thermal conductivity less than 50% that of 99.5% pure copper. The resistance element located within the ceramic resistance heating element was formed of a paste containing tungsten which exhibited a TCR of 4440 ppm/ C after firing of the green element. The resistance of this element at 230C was measured as 71.2 ohms with an applied voltage of 110.6 volts and .330 amps. The heat conducting body was formed of alloy 1 listed above. During operation this first soldering device drew 36.50 watts.

This was compared to a second soldering device which was constructed utilizing the same ceramic resistance heating element coupled to a heat conducting body having the size and dimensions of the first heat conducting body except that it was formed of an alloy containing 99.5% copper and .5% tellerium. The two test devices were both equipped with identical soldering heating tips having a thermal couple located thereon and were energized so as to heat the same. When the soldering temperature of 4770C was reached the soldering tips were cooled with an air stream located approximately .5 mm away from the same to withdraw heat from the soldering tips. When the tips had cooled down to 1 820C the air stream was removed and the time necessary to reheat the soldering tips to 4770C was recorded.

The recovery time of the test device utilizing the conducting body formed of the 99.5% copper, .5% tellerium was 9 minutes whereas the recovery time of the testing device utilizing the heat conducting body formed of 90.85% copper, 7.15% aluminum and 2.0% silicon was only 5 minutes. A similar test conducted utilizing a conducting body having a 99.5% copper, .5% chrome alloy indicated a 7 minute recovery time.

It is evident from the above tests that by coupling a heat conducting body which is essentially deficient with respect to the thermal conductivity of essentially pure copper with a ceramic resistance heating element having a TCR for its resistance element greater than that of platinum, a decrease in recovery time necessary to reheat the heat conducting body to optimum soldering temperature is observed. The recovery time of the device constructed as per this specification exhibited better heat recovery time than even that of a typical nichrome heating element which, when tested using the same protocol, exhibited a heat recovery time of 5.75 minutes.

Claims (17)

1. In a soldering device having a heat conducting body, a heater and means for supplying current to said heater an improvement which comprises: said heater including an insulating member and an electrical resistance member; said electrical resistance member encapsulated in said insulating member and electrically connected to said means for supplying current; said electrical resistance memberformed of a material having a temperature coefficient of resistance measured in parts per million per degree Celsius greater than the temperature coefficient of resistance 0 to 1 000C of platinum which has a temperature coefficient of resistance of about 3850 parts per million per C;; said heat conducting body sized and shaped so as to abut against said heater in association with said electrical resistance member so as to absorb heat discharged from said electrical resistance member upon passage of current through said electrical resistance member; said heat conducting bodyformed of a heat conducting material which has a thermal conductivity at least less than about 50% of that of at least 99.5% pure copper.

2. The device of claim 1 wherein: said electrical resistance member is formed of a material containing as its primary electrical current conducting resistant element a chemical element selected from the group consisting of tungsten, ruthenium rhodium, platinum, palladium or silver.

3. The device of claim 2 wherein: said chemical element is tungsten.

4. The device of claim 1 wherein: said heat conducting body is formed of a material having a temperature coefficient of resistance less than about 20% of said copper.

5. The device of claim 4 wherein: said heat conducting member is formed of a material having a temperature coefficient of resistance of about 10% that of said copper.

6. The device of claim 1 wherein: said heat conducting member is formed of an alloy containing less than 95% copper.

7. The device of claim 6 wherein: said alloy contains less than 92% copper.

8. The device of claim 7 wherein: said heat conducting member is formed of an alloy containing from about 60% copper to about 92% copper.

9. The device of claim 2 wherein: said heat conducting body is formed of a material having a temperature coefficient of resistance less than about 20% of said copper.

10. The device of claim 9 wherein: said heat conducting member is formed of a material having a temperature coefficient of resistance of about 10% that of said copper.

11. The device of claim 2 wherein: said heat conducting member is formed of an alloy containing less than 95% copper.

12. The device of claim 11 wherein: said alloy contains less than 92% copper.

13. The device of claim 12 wherein: said heat conducting member is formed of an alloy containing from about 60% copper to about 92% copper.

14. The device of claim 3 wherein: said heat conducting body is formed of a material having a temperature coefficient of resistance less than about 20% of said copper.

15. The device of claim 14 wherein: said heat conducting member is formed of a material having a temperature coefficient of resistance of about 10% that of said copper.

16. The device of claim 3 wherein: said heat conducting member is formed of an alloy containing less than 95% copper.

17. The device of claim 16 wherein: said alloy contains less than 92% copper.