Patent Description:
Solder tubes may be utilized for a variety of soldering applications, including radio systems, wire harnesses, as an EMI shield to ground termination, wire to wire splicing, etc. For example, soldering tubes may be used for terminating electrical joints within a heat shrink termination device. The ends of exposed electrical wiring may be placed within the solder tube and soldered together. The solder tube alloy preform may provide a precise, controlled amount of solder to hold the wires securely in place while an outer plastic sleeve may provide enclosed protection from the elements and further electrical contact.

Solder tubes may be created using a progressive stamping die. For example, five to eight press strokes / cycles may be needed before a single tube is produced. Some conventional implementations of solder tubes provide a flux coating on the exterior of the solder tube to facilitate the soldering process. After the solder tube is made, it may be de-greased and then subjected to an exterior flux coating process. The exterior flux coating may be applied in the range of <NUM>% to <NUM>% by weight.

To provide a visual verification that a reflow temperature for the solder has been reached, a thermochromic dye may be added to the exterior flux coating. During reflow soldering that melts the flux, when a correct reflow temperature is reached, the thermochromic dye will change color (e.g., become colorless). The color change of the thermochromic dye will show the operator that the solder alloy of the solder tube has reached a correct temperature to melt the solder alloy such that an acceptable solder joint may be formed. <FIG> illustrates one such example of a thermochromic dye in a flux coating on a solder tube that is red prior to the reflow process /soldering. <CIT> describes a heat-recoverable soldering device comprises a heat-recoverable member having a fusible solder insert and associated with the solder insert, a solder flux composition which undergoes a visible color change at a critical temperature. Solderable substrates are positioned within the device and heated until a critical temperature has been reached as indicated by a color change in the flux. The critical temperature depends on the material of the particular heat-recoverable member and the solder used. It is that temperature which is required to effect a solder joint between the substrates and recovery of the heat-recoverable member.

<CIT> (describing all the features of the preamble of claim <NUM>) describes a wire for use in a brazing or soldering operation having an elongated body of a metallic material. The elongated body has an outer surface. A channel is formed along a length of the body. The channel has an opening. A flux solution is deposited within the channel and along the length of the body. The flux solution covers a portion of the outer surface. A portion of the flux solution is exposed through the opening in the channel.

<CIT> describes a solder preform with predisposed flux to be located adjacent to a gap formed between multiple solderable surfaces such that upon heating, the flux wicks into and prepares the solderable surfaces prior to the solder melting and wicking into the freshly prepared gap.

<CIT> describes a brazing wire including a first metal alloy wrap defining an encasing perimeter around a core and having a longitudinal seam extending over a length of the first metal alloy wrap, and a second metal alloy wrap disposed within the core of the first metal alloy wrap. The second metal alloy wrap defines an encasing perimeter around a core and has a longitudinal seam extending over a length of the second metal alloy wrap. The brazing wire further includes a corrosive flux material disposed within the core of the second metal alloy wrap.

Implementations of the disclosure are directed to solder preforms with an internal flux core including a thermochromic indicator.

A solder preform according to the present invention is defined in claim <NUM>.

Further preferred embodiments of the present invention are defined in the appended claims. In some implementations, the second end is secured to the first end using an interlocking joint.

In some implementations, each of the first opening and the second opening are cut along an entire height of the solder tube, wherein during reflow soldering, flux core flowing out of the first opening of the first end coats an inside of the solder tube and flux core flowing of the second opening of the second end coats an outside of the solder tube. In some implementations, the second end is secured to the first end using an interference fit with one or more stakes.

In some implementations, the flux core of the solder tube comprises between <NUM> wt. % and <NUM> wt. % of the solder tube. In some implementations, the flux core of the solder tube comprises greater than <NUM> wt. % of the solder tube. In some implementations, the solder alloy comprises greater than or equal to <NUM> wt. % of the solder tube.

In particular implementations, the solder tube has a height ranging from <NUM> to <NUM>, an inner diameter ranging from <NUM> to <NUM>, and an outer diameter ranging from <NUM> to <NUM>, and wherein the second end overlaps the first end a distance ranging from <NUM> to <NUM>. In some implementations, the solder tube has a height to wall thickness of greater than <NUM>:<NUM>.

Other features and aspects of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the features in accordance with various embodiments. The summary is not intended to limit the scope of the invention, which is defined solely by the claims attached hereto.

The technology disclosed herein, in accordance with one or more embodiments, is described in detail with reference to the following figures. The drawings are provided for purposes of illustration only and merely depict typical or example embodiments of the disclosed technology. These drawings are provided to facilitate the reader's understanding of the disclosed technology and shall not be considered limiting of the breadth, scope, or applicability thereof. It should be noted that for clarity and ease of illustration these drawings are not necessarily made to scale.

The figures are not intended to be exhaustive or to limit the invention to the precise form disclosed. It should be understood that the invention can be practiced with modification and alteration, and that the disclosed technology be limited only by the appended claims.

As used herein, the term "thermochromic indicator" refers to a thermochromic dye, thermochromic pigment, or other thermochromic component that may provide a visual indication of when a soldering temperature has been reached. For example, the thermochromic indicator may be a visible color at room temperature.

According to the present invention, as the thermochromic indicator is heated at or above the alloy reflow temperature, the visible color may dissipate until the thermochromic indicator is colorless.

As noted above, solder tubes coated with a solder flux including a thermochromic dye may facilitate the soldering process by providing a visual indication of when correct soldering temperatures have been reached. This design, however, may have a number of problems.

First, if the amount of required flux is greater than about <NUM> wt%, it may become increasingly difficult to both obtain the required amount of flux by wt. % and uniformly coat the solder tube on its inner section and outer section.

Second, during manufacture it may be very difficult to achieve a consistent inner diameter (ID) dimension across solder tubes because of the amount of flux that gets into the center of the tube. In some instances, the center of the tube may become plugged with flux.

Third, the post flux curing step may present a variety of potential defects. The flux-coated surface of the tube may become tacky. Tubes may stick together and clump into one mass. The flux coating may chip off easily, leaving exposed areas. Because solder tubes may be handled several times after flux coating and before final packaging, there is the potential for damages occurring on multiple occasions. Further, if solder tubes rub against each other during shipment, the flux coating may turn into a flux powder/dust.

Fourth, because of the dust that may be created from shipping the solder tubes and how they may be bowl fed, they may cause increased downtime of production lines because of the cleaning of the bowls needed due to the build-up of flux powder.

In view of the foregoing issues, there is a need for an improved solder tube design. To this end, implementations of the disclosure are directed to solder tubes with an internal flux core including a thermochromic indicator. Additional implementations of the disclosure are directed to other solder preforms with an internal flux core including a thermochromic indicator.

<FIG> illustrate a solder tube <NUM>. <FIG> shows a perspective view of solder tube <NUM>, <FIG> shows a side view of solder tube <NUM>, and <FIG> shows a cross sectional top view of solder tube <NUM>. <FIG> show the top and bottom sections of <FIG>, respectively. As depicted, solder tube <NUM> has a cylindrically shaped solder alloy body, including an overlap joint with an outer end <NUM> circumferentially overlapping an inner end <NUM>. In implementations, the body may have a circular cross section or an elliptical cross section. During formation, the solder tube <NUM> may be cut off at each of the ends <NUM> and <NUM> (e.g., heightwise along the solder tube). This allows an internal flux core <NUM> with a thermochromic indicator to flow out of the solder tube <NUM> through outer end <NUM> and inner end <NUM> during reflow soldering. In other implementations, only one of the ends <NUM> or <NUM> is cut such that the flux core <NUM> flows through only one of the ends.

In some implementations, the solder tube <NUM> may be perforated in one or more locations (e.g., either at the ends or some other location of the tube) to allow flux to flow out through the one or more perforations in addition to the ends during reflow soldering. The perforations may be of a suitable size and shape such that sufficient flux flows out of the perforations at a sufficient rate. The perforations may be formed after the solder alloy has been formed into a tube, or beforehand. In some implementations the solder alloy tube may be manufactured such that the flux only weeps out through perforations. For example, in such implementations, the solder tube may not have any overlapping ends (i.e., it is formed as a closed cylinder).

Each perforation may extend through the entire wall of the solder tube such that flux flows out of both an inner and outer side of the tube. Alternatively, the perforation may be formed such that flux only flows out through one of the inner side or outer side of the tube. The perforations may be suitably shaped (e.g., as an ellipse or polygon), deep, positioned, and/or numbered such that flux sufficiently covers the inner and/or outer surface of the tube and substrate during reflow soldering. For example, perforations may be circumferentially distributed throughout the solder tube (e.g., on the outer and/or inner side).

Although in some implementations the solder tube could be manufactured such that the flux only weeps out through perforations (e.g., without having any overlapping ends), it has been observed in some instances that perforations by themselves may not be sufficient for allowing the flux to weep out onto the substrate. Without being bound to any particular theory, this may be attributed to the softness of the solder alloy metals, which may have a tendency to smear over the perforations, thus not allowing the flux to escape to the extent of design depicted in <FIG>.

Referring again to <FIG>, flux core <NUM> flowing out of inner end <NUM> may flow onto the soldered substrate through the interior of the tube whereas flux core flowing out of outer end <NUM> may flow onto the soldered substrate through the exterior of the tube. During a reflow soldering process, the flux core <NUM> with the thermochromic indicator (e.g., dye or pigment) may weep out onto the substrate uniformly from cut ends <NUM> and <NUM>. As the solder tube <NUM> is heated and the flux begins to melt, the flux may uniformly flow out of ends <NUM> and <NUM> to spread on the metal (e.g., wires) to be soldered, coating it with the thermochromic indicator color, cleaning the metal surface, and keeping the metal surface clean until the molten solder alloy reaches it, and promoting the spreading of the solder on the surface of the metal. By virtue of the illustrated implementations, improved wetting of the solder to the substrate may be achieved as compared to the conventional non-overlapping, flux-coated solder tube design. This in turn may facilitate the formation of a better solder joint. In experiments, the embedded flux was observed to spread better as compared to the conventional design.

In the illustrated example, the overlapped joint is formed by staking in two locations <NUM> (e.g., through the center of the overlapping joint to be formed) to form an interference fit to prevent joint separation of the two cut ends <NUM> and <NUM>. It should be appreciated that in other implementations the overlapped joint may be staked in one location or more than two locations to prevent joint separation. For example, the number of stakes may vary depending on the height of the solder tube <NUM>. Additionally, other methods may implemented as an alternative to or in addition to staking to prevent separation of or otherwise hold the overlapped joint in place. For example, in some implementations the overlapped joint may be created by spot soldering. As another example, <FIG> illustrates one example design for interlocking an outer end <NUM> with an inner end <NUM>. The interlocked mechanical joint may have two separate cut off ends, allowing the flux core <NUM> to weep out and spread onto the substrates that are to be solder together. Although <FIG> depicts a "puzzle piece" interlock mechanism, other interlock mechanisms could be implemented.

In implementations, the flux core <NUM> may comprise between about <NUM> wt. % and <NUM> wt. % of the solder tube <NUM>. The flux of flux core <NUM> may be a "no-clean" flux whose flux residue after reflow, may not need to be cleaned from the substrate to ensure reliability. Alternatively the flux may be a water soluble flux or some other type of flux.

Flux core <NUM> includes a thermochromic indicator that may be added to the flux prior to formation of solder tube <NUM>. For example, a thermochromic dye or pigment may be added to a flux before it is processed into the center of the solder alloy, and then formed into solder tube <NUM>. Depending on its chemical makeup, the thermochromic indicator may come in a variety of different colors. For example, the dye or pigment may be red, orange, pink, etc. The thermochromic indicator may be any suitable thermochromic component that, when heated, provides a visual indication that the solder alloy of solder tube <NUM> has reached a correct soldering temperature. During reflow soldering, the color of the thermochromic indicator coating the substrate may vanish at a desired reflow soldering temperature based on the chemistry of the thermochromic indicator component. When color is found to be non-existent during reflow (e.g., melting) of the alloy, this may provide an indication that the solder alloy has maintained a suitable temperature for a sufficient amount of time. As should be appreciated, the thermochromic indicator and color may be selected depending on the melting properties (e.g., solidus and/or liquidus temperatures) of the solder alloy.

The solder tube <NUM> may be comprised of any suitable solder alloy such as a tin-silver-copper (SAC) alloy, a Sn alloy, a SnAg alloy, a Bi alloy, an In alloy, or some other solder alloy. In some implementations, the solder tube <NUM> may be comprised of a single metal. The solder alloy or metal may make up <NUM> wt. % or greater of the solder tube. The solder tube may have a height to wall thickness ratio of greater than <NUM>:<NUM>.

In implementations, the solder tube may have an inner diameter (ID) ranging from <NUM> to <NUM> and an outer diameter (OD) ranging from <NUM> to <NUM>, where the ID And OD measurements are taken perpendicular to the center of the overlap joint, from side to side as depicted in <FIG>. In implementations, the solder tube may have a height H ranging from <NUM> to <NUM>. In implementations, the solder tube overlap joint may have a distance D ranging from <NUM> to <NUM>. The illustrated solder tube <NUM> may be used in a variety of applications, including cable splicing in wire harnesses and cable assemblies. For example, it may be placed within a plastic tube, wires may be inserted within tube <NUM>, and then the assembly may be reflowed such that the solder creates an electrical connection while the plastic protects the connection from environmental hazards.

<FIG> is a photograph illustrating a cross section of a solder tube after being cut apart. As illustrated, a flux core with a thermochromic indicator is embedded in the solder alloy and distributed substantially and uniformly. The thermochromic indicator in this example is colored red.

A variety of advantages may be achieved from the internal flux core solder tube design described herein. First, the internal flux may have a higher level of flux by wt. % (e.g., up to about <NUM> wt. %, or in some cases even greater than <NUM> wt. %) as compared to the conventional exterior flux-coated design. Second, because the flux is contained within the walls of the tube, the ID and OD dimensions of the tube may have tighter tolerances, along with eliminating the problem of flux obstructing the inner portion of the tube. Third, as no post flux curing step is needed, this may eliminate the aforementioned issues of having a tacky flux-coated surface, parts sticking together, the flux coating chipping off, and the coated flux turning into dust/powder from parts rubbing together during shipment. Moreover, by removing the dust/powder problem, production lines may no longer need to stop to clean bowls having a build-up of flux powder, thereby allowing them to operate for longer periods of time. These and other advantages that may be realized from the solder tube design described herein will be appreciated from the disclosure.

While implementations of the disclosure have thus far been described in the context of solder tubes having an internal flux core including a thermochromic indicator, the techniques described herein could also be applied to a variety of other solder preforms that would benefit from having an embedded flux core with thermochromic indicator that flows out of the solder preform in a controlled manner to provide a visual indication during reflow soldering. By foregoing an external coating of flux with thermochromic indicator on other preforms shapes, chipping off of the external flux coating may be avoided. Additionally, the dust that may be created from shipping and handling such a product may be avoided.

The flux coating may chip off easily, leaving exposed areas. Because solder tubes may be handled several times after flux coating and before final packaging, there is the potential for damages occurring on multiple occasions. Further, if solder tubes rub against each other during shipment, the flux coating may turn into a flux powder/dust.

For example, <FIG> illustrate a solder washer <NUM>. <FIG> shows a perspective view of solder washer <NUM>. <FIG> shows a cross-sectional view of solder washer <NUM>. As depicted, solder washer <NUM> has a flat, circularly shaped alloy body, with a central hole, an ID section <NUM>, and an OD section <NUM>. In some implementations, solder washer <NUM> may have a height to wall thickness ratio of less than or equal to three (e.g., a height to wall thickness ratio of <NUM>:<NUM>). Although solder washer <NUM> has a circular body shape with a central circular hole in this example, in other implementations its body and/or central hole may have some other elliptical shape or a non-elliptical shape. For example, the washer hole and/or body may have a rectangular shape.

Embedded in solder alloy body <NUM> is an internal flux core <NUM> with a thermochromic indicator. In this example, the solder alloy body <NUM> is open along the sidewall(s) of ID section <NUM> and the sidewall(s) of OD section <NUM>. As such, the internal flux core <NUM> flows out of solder washer <NUM> via the walls of ID section <NUM> and OD section <NUM> during reflow soldering. In other implementations, the side wall(s) of only one of the ID section <NUM> or OD section <NUM> is/are open.

In some implementations, solder washer <NUM> may have a thickness of between <NUM> and <NUM>; an ID between <NUM> and <NUM>; and an OD between <NUM> and <NUM>. Solder washer <NUM> may be manufactured using a stamping die. In some implementations, solder washer <NUM> may be stamped or cut from a solder. For example, a preform with internal flux core <NUM> may be formed, and the washer <NUM> may be cut or stamped from the preform. This process of cutting out the washer may expose the internal flux core <NUM> via the side walls of ID section <NUM> and OD section <NUM>. For example, a solder ribbon with internal flux core <NUM> may be formed, and the solder washer <NUM> may be stamped from the solder ribbon.

In other implementations, a solder washer having an overlapping joint similar to solder tube <NUM> may be formed in a similar manner to how solder tube <NUM> is formed.

<FIG> illustrate a solder disc <NUM>. <FIG> shows a perspective view of solder disc <NUM>. <FIG> shows a cross-sectional view of solder disc <NUM>. As depicted, solder disc <NUM> has a flat, circularly shaped alloy body <NUM> and outer section <NUM>. In some implementations, solder disc <NUM> may have a height to wall thickness ratio of less than or equal to three (e.g., a height to wall thickness ratio of <NUM>:<NUM>). Although solder disc <NUM> has a circular body shape in this example, in other implementations its body may have some other elliptical shape.

Embedded in solder alloy body <NUM> is an internal flux core <NUM> with a thermochromic indicator. In this example, the solder alloy body <NUM> is open along the sidewall(s) of outer section <NUM>. As such, the internal flux core <NUM> flows out of solder disc <NUM> via the sidewall(s) of outer section <NUM> during reflow soldering. In some implementations, the side wall(s) of solder disc <NUM> may be open along its entire diameter. In other implementations, the side wall(s) of solder disc may be open along a portion or portions of the disc's diameter.

In some implementations, solder disc <NUM> may have a thickness between <NUM> and <NUM>, and an OD between <NUM> and <NUM>. Solder disc <NUM> may be manufactured using a stamping die. In some implementations, solder disc <NUM> may be stamped or cut from a solder. For example, a preform with internal flux core <NUM> may be formed, and the solder disc <NUM> may be cut or stamped from the preform. This process of cutting out the disc may expose the internal flux core <NUM> via the side walls of outer section <NUM>. For example, a solder ribbon with internal flux core <NUM> may be formed, and the solder disc <NUM> may be stamped from the solder ribbon.

In some implementations, a solder preform formed by cutting a segment of solder ribbon may be used. <FIG> illustrate a solder ribbon segment <NUM>. <FIG> shows a top perspective view of solder ribbon segment <NUM>. <FIG> shows a cross-sectional view of the solder ribbon segment <NUM>. As depicted, solder ribbon segment <NUM> has a solder alloy body <NUM> that is flat and rectangular in shape. In some implementations, solder ribbon segment <NUM> may have a square shape.

Embedded in solder alloy body <NUM> is an internal flux core <NUM> with a thermochromic indicator. In this example, the solder alloy body <NUM> is open along an end <NUM> along its height. As such, the internal flux core <NUM> flows out of solder ribbon segment <NUM> via end <NUM> during reflow soldering. In implementations, the opening at end <NUM> may be formed by cutting solder ribbon segment <NUM> from a solder ribbon. For example, solder ribbon segment <NUM> may be cut from a spool of solder ribbon. In some implementations, solder ribbon segment <NUM> may be open along both ends such that the internal flux core <NUM> flows out of both ends during reflow soldering. In some implementations, solder ribbon segment <NUM> may have a thickness between <NUM> and <NUM>.

In some implementations, the solder preform described herein may be assume an irregular shape to tailor it to a specific application. <FIG> illustrate an irregularly-shaped solder preform <NUM>. <FIG> shows a top perspective view of solder preform <NUM>. <FIG> shows a cross-sectional view of the solder preform <NUM>. As depicted, solder preform <NUM> has an irregularly-shaped, flat solder alloy body <NUM>. Embedded in solder alloy body <NUM> is an internal flux core <NUM> with a thermochromic indicator. During reflow soldering, the internal flux core <NUM> flows out of an opening of the solder preform <NUM>.

In some implementations, the flux core with thermochromic indicator of the solder preforms described herein may comprise between about <NUM> wt. % and <NUM> wt. % of the solder preform. In some implementations, the flux core may comprise between about <NUM> wt. % and <NUM> wt. % of the solder preform. In other implementations, the flux core may comprise greater than <NUM> wt. % of the solder preform, ribbon, or wire. The flux core may be a "no-clean" flux whose flux residue after reflow, may not need to be cleaned from the substrate to ensure reliability. Alternatively the flux may be a water soluble flux or some other type of flux.

In some implementations, the solder alloy body of the solder preforms described herein may comprise any suitable solder alloy such as a tin-silver-copper (SAC) alloy, a Sn alloy, a SnAg alloy, a Bi alloy, an In alloy, or some other solder alloy. In some implementations, the solder alloy body may be comprised of a single metal. The solder alloy body may make up <NUM> wt. % or greater of the solder preform, ribbon, or wire.

In some implementations, the solder preforms described herein may be configured to melt at a temperature between about <NUM> and <NUM>. The color of the thermochromic indicator of the flux core may be configured to vanish at a temperature between about <NUM> and <NUM>. The thermochromic indicator may be configured to become colorless once a peak reflow soldering temperature is reached. The peak reflow soldering temperature may be between about <NUM> and <NUM>.

Claim 1:
A solder preform (<NUM>) comprising:
either the preform being in shape of a solder tube, the tube comprising a cylindrically shaped solder alloy body, the solder alloy body comprising a first end (<NUM>), a second end (<NUM>), and at least one opening located at the first end or the second end, the second end circumferentially overlapping, or interlocking with, the first end;
or the preform being in the shape of a solder washer with a central hole, the washer comprising a solder alloy body with an inner diameter sidewall and an outer diameter sidewall, and at least one opening located at the inner diameter sidewall or the outer diameter sidewall;
the solder preform being characterised by the following:
a flux core (<NUM>) embedded in the solder alloy body, the flux core comprising a thermochromic indicator, such that during reflow soldering, the flux core comprising the thermochromic indicator is configured to flow out of the at least one opening of the solder alloy, and the thermochromic indicator is configured to become colorless at or above a reflow temperature of the solder alloy,