Patent Application
20100243712
The present application relates generally to an apparatus and components used in the application of heat. More particularly, the present application relates to a thermode and methods of assembling and manufacturing a thermode.
Thermodes are devices used for local application of heat, typically in soldering and heat staking applications and the like. Heat is produced by direct resistance heating of the tip of the thermode. The ‘soldering gun’ is a common example.
The main advantage of thermodes is very rapid temperature change (can be >1000° C./sec) and generally with precise control over the temperature. Also, since the resistance element is typically in direct contact with an item to be heated, efficient heat transfer occurs and rapid heating of the item is possible. Since the tip has little thermal mass, rapid cooling to ambient is typically also possible. Forced air cooling can assist with very rapid cooling as well.
There are several styles of thermodes in common use. These thermodes differ mainly by the shape of the tip and the direction of current flow relative to the item to be heated.
A thermode typically includes the following elements:
Important factors for a good heating process include sufficient pressure and good planarity of the thermode with the item to be heated. These factors ensure good and consistent thermal transfer and accurate temperature control. When soldering plated leads or ribbon wire, planarity is preferably better than half the thickness of the solder plate.
Thermodes are typically produced by welding a tip to a copper shank. This welded construction can result in a number of deficiencies, such as: variations in fit-up and weld penetration lead to variable device resistance with poorer welds resulting in unwanted heating; poor fit-up resulting in residual stress in the tip leading to premature failure due to stress cracking; poor fit-up resulting in poor planarity of the working surface relative to the mounting features; elements made of difficult to weld material are stressed, develop a large heat-affected zone and/or have incomplete welds which leads to unwanted hot-spots and premature failure due to stress cracks near the weld; and/or the welding process itself plus the addition of features to facilitate assembly adds extra machining steps as well as an additional process step.
Further, in the common fold up configuration, if the tip is connected to L-shaped conductors, this can result in a diagonal current flow through the tip and a diagonally distributed hot spot across the working surface of the tip, which can result in uneven heating.
Still further, mounting in known thermodes is generally complex. The thermode must typically be constrained by three datum surfaces in order to achieve controlled planarity between the working surface and the item to be heated.
Thermode lifetime is also limited by a host of mechanisms including: metal fatigue from repetitive thermal and mechanical stress; liquid metal embrittlement; liquid metal corrosion; galvanic corrosion; thermocouple detachment—particularly with tip material which is difficult to weld such as titanium; and thermocouple wire breakage from handling, thermal embrittlement, flux corrosion and other factors.
Although some suppliers have developed single-piece fold up and blade thermodes in order to eliminate welded construction, these designs typically have complex clamping arrangements and involve removable fasteners and other parts. These arrangements also typically involve the tip being subject to stress and strain, which potentially shortens the lifetime of the tip.
As such, there is a need for an improved thermode that is intended to overcome at least some of the issues in conventional thermodes.
According to an aspect herein, there is provided a thermode comprising: a shank; a tip; and a transition zone between the shank and the tip, the transition zone configured to provide resistance gradients to improve containment of heat in the tip.
In a particular case, the shank and tip are formed as a single piece. The formation of the shank and tip may be formed by, for example, wire EDM.
In another particular case, the transition zone is configured to provide resistance gradients to improve containment of heat in the tip by having a greater thickness at the shank that the thickness at the tip.
In another particular case, the thermode may further comprise a cooling jet integrated within the shank such that the cooling jet directs cooling airflow to the tip. In this case, the thermode may also include a cooling connector connected with the cooling jet in the shank, the cooling jet connector configured to connect with a matching connector on a thermode clamping system,
In yet another case, the thermode may further include a mount adjoining to and extending from the shank, wherein the mount has a greater width than the shank.
In yet another case, a galvanic lead may be provided to the tip to electrically bias the tip. This biasing of the tip is intended to reduce corrosion of the tip.
In still another case, the thermode may include a thermocouple attached to the tip in close proximity to a working surface. In this case, the thermocouple may include a galvanic lead to electrically bias the tip.
According to another aspect herein, there is provided a clamping arrangement for a thermode comprising: a clamp for clamping the thermode, wherein the clamp operates with a single actuator; an integrated heating connection for connecting to heating elements of the thermode; and an integrated cooling connection for connecting to cooling elements of the thermode.
In a particular case of the claiming arrangement the heating connection may include electrodes to provide electrical power connections to the thermode and the cooling connection may include a central pneumatic manifold arranged to separate the electrodes and provide pneumatic connections to the thermode, and the clamping arrangement may further include a support structure to hold the electrodes and the central pneumatic manifold.
In this particular case, the clamp may include one fixed jaw and a moveable jaw and the movable jaw may be configured to move by operation of the single actuator. In this case, the support structure may include datum surfaces adapted to maintain alignment of a tip of the thermode with the clamping arrangement for accurate positioning of the tip on a working surface. In particular, the fixed jaw and the moveable jaw may include a rounded point contact to establish compression of the thermode to the datum surfaces.
According to another aspect herein, there is provided a method for manufacturing a single piece compact thermode comprising: machining a first profile into a workpiece; machining a second profile into the workpiece and parting off an unfinished thermode having separate halves or terminals and shank; bonding the two halves of the terminals and shank together; and attaching a thermocouple,
In a particular case, the method may include plating the thermode. In this case the plating the thermode may include plating the shank with a conductive material, plating the tip with a protective material, or the like.
In another particular case, the method may including providing and retaining a keeper bar to facilitate handling and to maintain mechanical stability during the process.
In another particular case, the attaching the thermocouple may include swaging the thermocouple to a tip of the thermode.
Other aspects and features will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.
Embodiments will now be described, by way of example only, with reference to the attached Figures, wherein:
The thermode (20) includes: a shank (22); a tip (24); a transition zone (26), which joins the shank (22) and the tip (24); and a mount (28), which supports the shank (22). As shown in
The thermode (20) of
In this embodiment, the thermode also includes a gradient transition zone. The applicants herein have identified that known thermode designs typically incorporate an abrupt transition between the tip and the shank. This abrupt transition may be the most appropriate for welding purposes but it has been determined that an abrupt transition compromises the ability to optimize current distribution and thermal management. In this situation, poor thermal management allows heat to be stored in the shank of the thermode resulting in some process drift in high duty-cycle repetitive operation. The use of a single piece construction allows for the creation of an appropriately contoured transisition zone.
This embodiment also includes an integrated cooling jet, intended to allow for faster cooling of the tip.
This embodiment is also intended to be plug compatible with various commercially available thermode tip assemblies, which are composed of a tip welded to a two piece shank. In a particular case, the mount is composed of two ⅛″ square electrodes separated by a 1/64″ insulator which are at least ½″ long resulting in a 3.18×7.0×12.7 mm mount which is clamped to fixture the thermode and conduct heating current. This single-piece design is intended to provide compatibility with tooling common to the industry. This tooling can include existing tooling or, in some cases, a similar but non-standard electrode arrangement.
It will be understood that the single-piece construction and other elements above can be applied to the construction of fold up, blade and peg styles of thermodes. The fold up style above may sometimes be referred to as “modified fold up” because the tip is at right angles to the conventional orientation. A single piece thermode embodiment intended to be equivalent to the conventional roll-up style can be produced in a similar fashion but may require some additional machining (see
Analysis of conventional thermodes has also revealed that thermocouple leads are generally poorly supported. Typically, thermocouples are attached directly to the thermode tip, which can result in the thermocouple circuit experiencing common mode voltages conducted to it by the tip, which, in some cases, leads to inaccurate temperature readings. This is particularly relevant when soldering solar modules, which produce voltages when exposed to stray light.
In the present embodiments, a thermocouple is attached to the tip of the thermode. Preferred locations are inside the tip typically at the mid-point (as shown in
In some embodiments, a galvanic protection wire (not shown) may also be attached to the tip, for example, by spot welding or swaging. This galvanic protection wire may alternatively be incorporated into the thermocouple, for example, if it is a three-wire type (e.g. jacketed or shielded). This galvanic protection wire may be used to apply an electrical bias to the tip, which can be used to control and minimize corrosive action between the tip material and the material with which the tip is in direct contact. A reduction in corrosive action can improve the life of the thermode.
As shown in
The shank (22), tip (24), transition zone (26) and integrated cooling jet (36) can be provided in a single piece. The mount (28) can have a wider width at a terminal end thereof than at a shank adjoining end thereof. The width of the mount (28) can increase from the shank adjoining end to the terminal end. In this case, the shank (22) and the mount (28) are actually provided as an integral shank-mount.
A terminal (30) is provided at the terminal end of the mount (28). The pneumatic connector (32) is also provided at the terminal end of the mount (28). The pneumatic connector (32) is configured as a pneumatic port with a seal.
This type of thermode is designed to use an improved clamping arrangement (described in further detail below), which may incorporate both heating (electrical) and cooling (pneumatic) connections; and may use a single fastener/actuator to facilitate ease of replacement and minimize downtime. The clamp is intended to provide an increased surface area as compared to conventional designs. The clamp is also intended to provide improved electrical conductivity, improved thermal management and an improved mechanical datum. The clamp provides a planar datum, which is intended to help ensure that planarity between the thermode tip and the item to be heated is maintained. In this embodiment, the planarity is controlled by a single surface while in conventional thermodes three surfaces must typically be aligned to provide planarity.
The compact thermode design of
In this embodiment, the thermode is produced by machining a single piece of metal. Preferred metals combine moderate resistivity, good mechanical strength and good corrosion resistance. Presently preferred metals include: low resistance grades of Titanium such as commercially pure Ti in ASTM grades 1, 2, 3 or 4; alloys of Ti with moderate resistivity such as ASTM grades 12, 15, 17 or 9; other alloys of titanium may be used, particularly for thermodes with relatively small tips; stainless steels particularly those alloys with no or negligible nickel content and relatively high carbon and phosphorous content such as stainless 416, 420 or 430; and other commonly used metals such as inconel and tungsten steel.
At 102, a first profile (typically the most complex profile) is machined into a piece of material (workpiece) to form the initial thermode shape. The machining may be conducted, for example, by a wire electrical discharge machining (EDM) tool. In practice, the method may actually be performed such that a plurality of thermodes may be machined at this stage, In particular, the first profile may be formed on a blank from which multiple thermodes can be struck—for example, as many as can be accommodated within the envelope of a wire EDM tool.
In a particular case, the manufacturing sequence may preferably incorporate the use of a keeper bar. The keeper bar is used to: hold and fixture the workpiece during manufacture to improve fixturing and prevent tool marks; hold critical dimensions until all manufacturing operations are complete; and, in some cases, hold multiple workpieces in a grouping so that several/many thermodes can be machined at one time with one setup to minimize manufacturing costs. The keeper bar is preferably attached to the main body of the workpiece in such a way that the contact areas which also serve as a datum for locating the thermode when in use can be formed in the same machining operation as the tip, in order to ensure the best parallelism between these surfaces.
At 104, a second profile is machined on the workpiece to complete the thermode shape. In the case where multiple thermodes are machined at the same time, individual unfinished thermodes may also be parted off. In either case, it is preferred to retain a keeper bar to facilitate handling and help maintain mechanical stability.
At 106 (optional), the workpieces may be plated. For example, tips or tips and shank may be plated with a protective material. In another example, terminals or terminals and shank may be plated with a conductive material.
Plating may be applied to various parts, for example: a highly conductive non-oxidizing metal to reduce contact resistance in the electrode clamping area such as gold plate; a protective barrier for increased corrosion resistance and/or reduced solder wetting of the tip such as TiN, DLC, etc; the tip may also be protected by a barrier layer formed through heating or self heating which causes a reaction with an atmosphere with the resulting layer being composed of an oxide or nitride of one or more components of the base metal.
At 108, the two halves of the terminals and shank are bonded together, for example, using a high temperature epoxy or other suitable method. At 110, another optional element, the two halves may also be pinned together for additional strength.
At 112, also optional, additional machining may be performed, such as: to provide cooling jet air passages; to prepare the tip for thermocouple attachment or strain relief; and/or to mark the part with part numbers or serialization information.
At 114, the keeper bar is parted from the work-piece.
A thermocouple is attached at 116. For example, the thermocouple can be spot-welded or swaged to the tip. Leads for the thermocouple can be strain-relieved by attachment to the shank with means such as high temperature tape, spot welded metal tab or bolt-on wire clamp. Leads for the thermocouple can be trimmed to length and a connector can be attached. As noted above, a galvanic protection lead can be attached separately from or together with the thermocouple.
As noted with regard to
It will be understood that some of the method elements may be optional or varied and that some method elements may be performed in a different order than that listed depending on various factors such as the quantity of thermodes to be produced and the like.
As shown in
In the embodiment shown, the clamp assembly or system comprises the following elements:
In this embodiment, the clamp provides an increased surface area as compared to conventional designs to provide improved electrical conductivity and thermal management. Conventional thermodes provide a contact area with dimensions of approximately 3.18 mm×12.7 mm and a fixed contact area of approximately 40 mm̂2 while embodiments herein are intended to provide a contact area of 6 mm×12 mm or an area of 72 mm̂2 but which can be increased for larger thermodes.
The clamp also provides a planar datum, which is intended to help ensure that planarity between the thermode tip and the item to be heated is maintained.
A mounting arrangement such as that shown in
Generally speaking, embodiments herein are intended to comprise one or more of the following elements or features:
It will be understood that, for the compact thermode and clamping arrangement described herein, it may be possible to provide a kit including a clamping arrangement for the compact thermode that allows a conventional thermode device to be converted for use of the clamping arrangement and compact thermode described herein.
Embodiments described herein are also intended to provide advantages over existing approaches, which may include: minimize part count; simplified manufacturing process; lower cost; improve reliability; and improved serviceability with rapid replacement.
In the preceding description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be apparent to one skilled in the art that these specific details are not required in order to practice these embodiments.
The above-described embodiments are intended to be examples only. Alterations, modifications and variations can be effected to the particular embodiments by those of skill in the art without departing from the scope of the application.
This patent application claims the benefit of U.S. Patent Applications 61/164,163, filed Mar. 27, 2009, and 61/222,523, filed Jul. 2, 2009, which are hereby incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61164163 | Mar 2009 | US | |
| 61222523 | Jul 2009 | US |
