CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.

61/617,538, filed March 29, 2012, which is incorporated herein by reference in its entirety for all purposes.

FIELD OF THE INVENTION

This invention relates generally to a method of manufacturing a soldering tip, and more particularly to a method of manufacturing a soldering tip with magnetic induction. BACKGROUND OF THE INVENTION

Tips for soldering and desoldering irons have been made by cutting a metal rod to a desired tip shape and then plating the tip shape with one or more metal layers to improve the durability and/or improve solder wettability. The metal rod is often made of copper because of its excellent heat conducting properties, and the iron and chrome are plated on the tip-shaped copper core. An alternative to plating has been to cover the tip- shaped copper core with a stainless steel cap.

A drawback of prior art manufacturing methods is that some tip shapes can be complex and difficult to manufacture by conventional cutting or milling methods, thereby increasing manufacturing costs. Conventional iron and chrome plating processes can have a significant environmental impact. Also, problems with thermal conductivity can arise between the tip-shaped copper core and a stainless steel cap, thereby reducing the work performance of the soldering desoldering tip. Accordingly, there is a need for a method of making a tip for soldering and desoldering irons which is cost effective, environmentally friendly, and results in a tip with good work performance.

SUMMARY OF THE INVENTION

Briefly and in general terms, the present invention is directed to a method of making a soldering tip.

In aspects of the present invention, the method comprises placing a heat- conducting material in a soldering tip cap, heating the soldering tip cap with magnetic induction applied to the soldering tip cap, and filling inner spaces of the soldering tip cap with the heat-conducting material.

The features and advantages of the invention will be more readily understood from the following detailed description which should be read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 A-1C are cross-sectional views showing an exemplary soldering tip cap being filled by melting a bar of a heat-conducting material in the soldering tip cap.

FIGS. 2A-2C are cross-sectional views showing an exemplary soldering tip cap being filled by melting powder particles of a heat-conducting material in the soldering tip cap.

FIGS. 3 and 4 are cross-sectional views showing an exemplary soldering tip within a magnetic induction coil. FIG. 5 is a diagram showing an exemplary setup for controlling a magnetic induction coil and for subjecting a vacuum to a soldering tip cap within the magnetic induction coil.

FIG. 6 is a graph showing of an exemplary power profile for a magnetic induction coil.

FIGS. 7 and 8 are exemplary flow diagrams showing a method of making a soldering tip.

FIG. 9 is a cross-sectional view of an exemplary soldering tip cap suitable for desoldering operations.

FIG. 10 is an x-ray image showing an exemplary soldering tip cap filled with heat-conducting material, and showing void defect that arises during filling with the heat-conductive material.

FIG. 11 is an x-ray image showing an exemplary soldering tip cap filled with heat-conducting material with no void defects.

FIG. 12 are x-ray images showing an exemplary soldering tip cap filled with heat-conducting material, and showing void defects that arises during or after cooling of the heat-conductive material.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the word "soldering" refers to a process involving the application and/or removal of molten metal to a work piece. A non-limiting example of a molten metal is solder. Non-limiting examples of a work piece are circuit boards and metal objects. As used herein, the term "soldering iron" refers to a tool used to apply and/or remove molten material from a work piece. As used herein, the term "soldering iron" encompasses dcsoldcring tools which remove molten metal from a work piece.

As used herein, the term "soldering tip" refers to the working tip of a tool used to apply and/or remove molten material from a work piece. As used herein, the term "soldering tip" encompasses desoldering tips that remove molten metal from a work piece by suction or by other methods.

As used herein the terms "magnetic induction" and "electromagnetic induction" are used interchangeably and refer to a process in which electrical eddy currents are induced in a component. Due to the electrical resistance of the component, the eddy current lead to Joule heating of the component. If the component is made of ferrous material, additional heating occurs through magnetic loss or hysteresis heating, which arises from the rapid flipping of magnetic domains inside the material.

As used herein, any term of approximation such as, without limitation, "near", "about", "approximately", "substantially", "essentially" and the like mean that the word or phrase modified by the term of approximation need not be exactly that which is written but may vary from that written description to some extent. The extent to which the description may vary will depend on how great a change can be instituted and have a person of ordinary skill in the art recognize the modified version as still having the properties, characteristics and capabilities of the modified word or phrase. For example and without limitation, a feature that is described as "substantially equal" to a second feature encompasses the features being exactly equal and the features being readily recognized by a person of ordinary skilled in the art as being equal although the features are not exactly equal. Referring now in more detail to the exemplary drawings for purposes of illustrating embodiments of the invention, wherein like reference numerals designate corresponding or like elements among the several views, there is shown in F G. 1Λ an exemplary soldering tip cap 10. Heat-conducting material 12 is placed in soldering tip cap 10. Soldering tip cap 10 becomes hot when magnetic induction is applied to soldering tip cap 10. Due to its increased temperature, soldering tip cap 10 melts heat- conducting material 12.

As shown in FIG. IB, as heat-conducting material 12 melts, spaces 14 between heat conducting material 12 and soldering tip cap become filled. Heat-conducting material 12 has filled in space 14A at the closed end of cavity 16. In the illustrated embodiment, cavity 16 is conical, and space 14A is located at the narrow end of the conical cavity.

As shown in FIG. 1C, as heat-conducting material 12 continues to melt, inner spaces 14 between heat conducting material 12 and soldering tip cap 10 become filled. Cavity 16 of soldering tip cap 10 is filled completely. In other embodiments, cavity 16 is partially filled.

In FIGS. 1 A-1C, heat-conducting material 12 is in the form of a bar. Examples of a bar include without limitation, a block, a rod, and a wire made of the heat- conducting material. For example, and not limitation, heat-conducting material 12 can be a copper wire that is 0.S mm in diameter and 5 mm long, or copper rod that is 3.12S mm in diameter and 3.5 mm long. Heat-conducting material 12 can take other forms. In some embodiments, as shown in FIGS. 1 A and IB, bar 12 includes forward segment 12a and rear segment 12b. Placing of the bar in cavity 16 includes placing forward segment 12a through the open end of cavity 16 and into contact with forward portion 10a of soldering tip cap 10. As shown in FIGS IB and 1C, forward segment 12a melts before rear segment 12b.

In FIGS. 2A-2C, heat-conducting material 12 is in the form of powder particles. It should be understood mat the powder particles and soldering tip cap 10 are not drawn to scale in the figures. As eddy currents are induced in soldering tip cap 10 by magnetic induction, soldering tip cap 10 heats up and melts powder particles 12. As powder particles 12 melt, spaces 14 between powder particles 12 and soldering tip cap 10 become filled in with the heat-conducting material.

In some embodiment, the powder particles of heat-conducting material 12 are mixed and the mixture is introduced into cavity 16.

Whether in the form of a bar, powder particles, or other shape, heat-conducting material 12 can be copper, a copper alloy, silver, and a silver alloy. Heat-conducting material 12 can have other compositions.

In some embodiments, heat-conducting material 12 has a thermal conductivity that is greater than the base material of soldering tip cap 10.

As shown in FIG. 3, heating by magnetic induction can be accomplished by placing soldering tip cap 10 within exemplary magnetic induction coil 18. Magnetic induction coil 18 is an electrical conduit that is powered at a frequency and voltage which induce electrical eddy currents in soldering tip cap 10 and thereby cause soldering tip cap 10 to increase in temperature. In some embodiments, magnetic induction coil 18 is powered at a frequency and voltage which induce electrical eddy currents in soldering tip cap 10 and heat-conducting material 12. Magnetic induction coil 18 is powered at a frequency and voltage that minimizes induction heating of heat-conducting material 12 so that melting of heat- conducting material 12 occurs primarily due to contact with soldering tip cap 10.

In some embodiments, heat-conducting material 12 is melted primarily due to contact with soldering tip cap 10 which has become heated above the melting temperature of heat-conducting material 12. Magnetic induction coil 18 is powered at a frequency and voltage that cause soldering tip cap 10 to heat up to at about or above the melting temperature of heat-conducting material 12.

In the above embodiments, the frequency used to power magnetic induction coil 18 can be at about 400 kHz or about 13.56 MHz. Other frequencies can also be used.

Referring to FIG. 3, magnetic induction coil 18 is a continuous electrical conduit including a plurality of loops 18A-18G. Soldering tip cap 10 is contained entirely with magnetic induction coil 18.

In some embodiments, the inner diameters of the loops differ according to the outer diameters of the outer surface of soldering tip cap 10. The size of the inner diameters of the loops in relation to the outer diameters of the outer surface of soldering tip cap 10 can facilitate uniform heating and minimize void defects (for example, FIGS. 10 and 12) during the filling process, so that a defect-free soldering tip (for example, FIG. 11) is produced.

In FIG. 3, exemplary soldering tip cap 10 has forward portion 10A and rear portion 10B. Rear portion 10B is wider than or has a larger diameter than that of forward portion 10A. Loop 18F located adjacent to rear portion 10B has an inner diameter larger than that of loops 18A-18C located adjacent to forward portion 10A. The inner diameter of loop 18A is designated Dl for example. The outer diameter of forward portion 10A is designated D2 for example. As shown in FIG. 4, in some embodiments, soldering tip cap 10 is carried on base member 20 which can rotate relative to magnetic induction coil 18. Base member 20 can be coupled to a motor, which when activated, causes soldering tip cap 10 and any heat- conducting material contained in it to rotate about central axis 22 of soldering tip cap 10. Rotation of soldering tip cap 10 within magnetic induction coil 18 can facilitate uniform heating and minimize void defects (for example, FIGS. 10 and 12) during the filling process, so that a defect-free soldering tip (for example, FIG. 11) is produced.

As shown in FIG. S, in some embodiments, magnetic induction coil 18 can be located within vacuum chamber 24. Vacuum chamber 24 allows soldering tip cap 10 to be subjected to a vacuum while it is heated, while heat-conducting material 12 is melted, and while spaces 14 are filled. Pressure inside vacuum chamber 24 is controlled through the use of various switches or valves, pressure gauges, pumps, tanks, and gas supplies. Subjecting soldering tip cap 10 and heat-conducting material 12 to a vacuum can minimize void defects (for example, FIGS. 10 and 12) during the filling process, so that a defect-free soldering tip (for example, FIG. 11) is produced. In some embodiments, magnetic induction coil 18 is subjected to a vacuum from about -25 psi to about -28 psi.

In some embodiments, soldering tip cap 10 and heat-conducting material 12 are subjected to a vacuum prior to heating in order to replace the atmosphere in the vacuum chamber with a gas mixture of 10% hydrogen gas and 90% nitrogen gas. Other gas mixtures can be used. Upon application of the vacuum, the gas mixture is introduced in the vacuum chamber, followed by healing by magnetic induction in a pre-heating step. During the pre-heating step, the pressure in the vacuum chamber with the gas mixture can be from about 1 psi to about 2 psi. The pre-heating step using the gas mixture can remove oxide films from soldering tip cap 10. After the pre-heating step, soldering tip cap 10 and heat-conducting material 12 are subjected to a vacuum again to substantially remove the gas mixture. Next, during a main-heating step, magnetic induction coil 18 can be powered at a higher level which causes heat-conducting material 12 to melt and fill spaces 14 within cavity 16 of soldering tip cap 10. As shown in FIG. 5, in some embodiments, magnetic induction coil 18 can be powered using a matching box connected to an output tuner and high frequency power supply. A chilling machine can be coupled to magnetic induction coil 18. The output tuner adjusts the frequency used to power magnetic induction heating coil 18. The matching box allows for further, fine tuning of the frequency used to power magnetic induction heating coil 18.

As shown in FIG. 6, in some embodiments, exemplary power profile 30 is used to power magnetic induction coil 18 containing soldering tip cap 10 which carries heat- conducting material 12. Power profile 30 includes pre-heating segment 30A, followed by main-heating segment 30B, and followed by cooling segment 30C. In pre-heating segment 30A, magnetic induction coil 18 is powered at about 200 watts for about 60 seconds in order to heat soldering tip cap 10 in a gas mixture. The gas mixture is selected to remove an oxide film from soldering tip cap 10. The gas mixture can be about 10% hydrogen gas and about 90% nitrogen gas. Other gas mixtures and ratios can be used. The gas mixture pressure can be about 1 psi to about 2 psi. In main-heating segment 30B, magnetic induction coil 18 is powered at about 250 watts for about 65 seconds, during which a vacuum is applied to soldering tip cap 10 and heat-conducting material 12 for the purpose of degassing or removing gas. Heat- conducting material 12 melts and fills spaces 14 in cavity 16 of soldering tip cap 10. Degassing prevents the formation of air pockets and facilitates filling of all spaces 14. Any air pockets (as indicated by arrows in FIG. 10) would decrease thermal conductivity of a finished soldering tip.

In cooling segment 30C, magnetic induction coil 18 is powered at a lower level, at about 200 watts for about 5 seconds, followed by a rampcd-down or gradual decrease from about 200 watts to about 70 watts over a period of about 130 seconds. Cooling segment 30C prevents shrinking or overly rapid shrinking of heat-conducting material 12 which has filled cavity 16 of soldering tip cap 10. Shrinking or rapid shrinking of heat- conducting material 12 can lead to formation of voids and/or air pockets within heat- conducting material 12, as shown for example by arrows in FIG. 12. Any voids or air pockets would decrease thermal conductivity of a finished soldering tip.

After cooling segment 30, power to magnetic induction coil 18 is discontinued. Soldering tip cap 10 and heat-conducting material 12 can cool further.

In some embodiments, power profile shapes and power levels different from FIG. 6 can be used depending on the configuration and size of soldering lip cap 10. Referring again to FIG. 6, heating of soldering tip cap 10 includes powering magnetic induction coil 18 to first power level PI, and followed by powering magnetic induction coil 18 from first power level PI declining to second power level P2. In some embodiments, first power level PI is maintained for first time duration Tl, and first power level PI declines to second power level P2 over second time period T2 greater than first time period Tl .

FIGS. 7 and 8 illustrate an exemplary method of making a soldering tip cap. Although reference is made to the numerals of the soldering tip cap shown in previous figures, it should be understood the method can be implemented to make soldering tip caps having configurations other than those described above.

In block 40, heat-conducting material 12 is placed in soldering tip cap 10. Next, in block 42, soldering tip cap 10 is heated with magnetic induction applied to the soldering tip cap. In block 44, heat-conducting material 12 fills inner spaces 14 of the soldering tip cap 10 with heat-conducting material 12. Spaces 14 are filled by molten heat-conducting material 12 which later solidifies. Spaces 14 can be filled during block 42, after block 42, or during and after block 42.

In some embodiments, the method further comprises controlling the cooling rate of heat-conducting material 12 after spaces 14 have been, as shown in block 46

In some embodiments, the method further comprises forming soldering tip cap 10, as shown in block 48.

As shown in FIG. 7, in some embodiments, block 48 includes sintering process performed on metal particles to form soldering tip cap 10 with cavity 16. As shown in FIG. 8, in block 50, an alloy is selected to be the base material of soldering tip cap 10. The selected alloy has properties that provide solder wettability and good durability so that the finished soldering tip has a long functional life. A non- limiting example of an alloy is Fe + 7%Cu + 0.3%Ni + 0.1 %Ag. In block 52, metal particles of the selected alloy are kneaded with a binder. The binder can be a mixture of plastic material and wax. The binder facilitates subsequent injection into a mold.

In block 54, the kneaded material is granulated into pellets. Granulation enhances moldability of the material for subsequent molding.

In block 56, the granulated material, which includes the selected alloy and binder, is injected into a mold at high temperature and pressure. The molding process forms what is referred to in the art as a "green compact" of the alloy and binder. The mold is configured to provide cavity 1 in soldering tip cap 10. Optionally, the mold is configured to provide one or more ribs 11 (FIGS. 3 and 4) protruding outside of cavity 16.

In block 58, the binder is removed from the green compact. This can be accomplished by aqueous degreasing for reduced environmental impact. Other types of degreasing, such as heat degreasing and solvent degreasing can be used. In block 60, the degreased green compacted is sintered so that the powder particles are bonded directly to each other. The bonding is achieved at least in part by diffusion of atoms to points of contact between boundaries of the powder particles. Sintering is performed in an oven carefully controlled at a sintering temperature. The sintering temperature can be from about 80% to about 90% of the melting temperature of the alloy of the green compact.

Thereafter, the method can proceed to block 40 (FIG. 7). In some embodiments, after block 46 (FIG. 7), injection molding gate 13 is removed from soldering tip cap 10, as shown in block 70. Removal can be performed by cutting, milling, or other machining methods.

In some embodiments, after block 70, a protective coating is applied to soldering tip cap 10, as shown in block 72. The protective coating can include aluminum and can be applied using an aluminum diffusion process, includes masking, application of aluminum and a binder on soldering tip cap 10, baking, and grinding. The masking is applied to soldering tip cap 10 where any solder plating is to be applied later.

In some embodiments, after block 72, solder plating is applied to the soldering tip cap 10, as shown in block 74. Plating includes removing the previously-applied mask, and dipping soldering tip cap 10 while in a heated state in a solder bath, which can be 100% tin.

In the above embodiments, the soldering tip cap can have other configurations. As shown in FIG. 9, soldering tip cap lOd can have a configuration useful for desoldering operations. Soldering tip cap 1 Od has annular cavity 16d that surrounds suction tube 17. During desoldering operations, solder is suctioned into suction tube 17 in order to remove solder from a work piece.

Applicant has found that the above embodiments of the present invention can eliminate void defects shown by arrows in FIGS. 10 and 12 and thereby product defect- free soldering tips, as shown in FIG. 11.

While several particular forms of the invention have been illustrated and described, it will also be apparent that various modifications can be made without departing from the scope of the invention. It is also contemplated that various combinations or subcombinations of the specific features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims.