Patent Description:
Selective soldering can be used in many soldering applications, for example <CIT>, <CIT> and <CIT> disclose soldering components of a Printed Circuit Board (PCB). <CIT> discloses a mounting device for controlling a mounted member in a wave solder machine, wherein the mounted member is a hot air knife used on a solder pot for debridging solder on a PCB after wave soldering.

<CIT> discloses a method of wave soldering an element characterized by covering at least a portion of the solder wave with a non-oxidizing gas.

Selective soldering can, in general, be differentiated into two methods: multi-wave dip soldering and point-to-point soldering.

In multi-wave dip soldering processes, typically a large solder pot, or soldering assembly <NUM> is used (as shown in <FIG>) having a solder plate <NUM> that includes nozzles <NUM> to which liquidus solder is pumped. The soldering assembly <NUM> is typically closed with a cover plate, which has been removed in <FIG> in order to illustrate the nozzles <NUM> more clearly. <FIG> shows that the nozzles <NUM> are provided in a cavity <NUM> defined by side walls <NUM>. An upper part of the sidewalls <NUM> defines a lip <NUM> on which a cover plate is seated. The cover plate will include openings to expose the nozzles <NUM>. As can be seen in <FIG>, the depth of the cavity <NUM> defined by the height of the sidewalls <NUM> is selected so that the top of each nozzle <NUM> will be generally at the same level as the cover plate. The cover plate serves to maintain a low oxygen environment around the nozzles during soldering. The PCB (not shown) is lowered towards the nozzles, such that connector leads/pins (for example in a Cu - Copper - panel) are dipped into the liquidus solder present in the nozzle to form solder connections/joints at corresponding locations on the PCB. That is, multiple solder connections can be formed simultaneously. Each multi-wave dip soldering assembly has a specific nozzle plate with the nozzles being located at the required solder positions. The nozzles may have different shapes depending on the connectors to be soldered and the free space on the assembly. <FIG> illustrates a typical nozzle <NUM> used in a multi-wave dip soldering process. For connectors with a high risk of bridging, a laser-cut screen <NUM> (provided separately from the nozzle itself) may be provided in the nozzle <NUM> to help avoid bridging of solder.

In point-to-point soldering processes, typically a small solder pot, or soldering assembly, generally containing only one nozzle, is used. The nozzle comprises a body portion having an inlet at its lower end and an outlet for dispensing liquidus solder. In contrast to multi-wave soldering where the connectors pins are dipped into the nozzle, solder overflows from the outlet and a pin is dragged through or dipped into the flowing solder (or conversely the nozzle may be moved relative to the pin).

As noted above, multi-wave dip soldering processes suffer from the problem of bridging of solder between soldered pins or connectors, or between a soldered pin an another part of the PCB or other apparatus not being soldered. This can cause short circuiting. The known use of a nozzle screen, such as is illustrated in <FIG>, provides a partial solution to this bridging, and may thus be referred to as a de-bridging screen. However, such de-bridging screens can be delicate both in manufacture and in use, and are damaged easily (for instance if a pin or other part to be soldered is misaligned). Furthermore, screens (and hence the whole nozzle) must be designed specifically to match a product to be soldered, with holes to match the connectors to be soldered. This requires additional expense and production delay in exchanging nozzles if a solder pot is to be used to soldered different PCBs.

In addition, current methods of manufacturing the soldering components are limited with regards to the nozzle geometry that can be produced. This can lead to sub-optimal nozzles. The trend in the industry is that components are getting smaller. This miniaturization result in a smaller pitch between the pins. For pitches smaller than <NUM> it is not physically possible to make a screen because the distance has become too small, owing to it not being feasible to laser cut screens with smaller than <NUM> dimensions. It is a known problem of screens that flux residue from a PCB can clog a screen with small holes. During cleaning the screen may be damaged owing to its fragility. For these small pitches another de-bridging technology is required.

As used herein, when referring to 'solder' in use within a nozzle, it is to be understood that the solder is in a liquid state.

It would be advantageous to produce a soldering system that helps overcome the above described problems. Particularly, it would be advantageous to reduce occurrences of bridging during multi-wave dip soldering processes. It would be advantageous to provide a nozzle for multi-wave dip soldering processes that is more robust, less fragile and less sensitive for contamination and clogging. It would be advantageous to provide a nozzle for multi-wave dip soldering processes that is better able to accommodate different pins or components to be soldered.

According to a first aspect of the present disclosure there is provided a soldering nozzle for directing solder during a multi-wave soldering operation, the soldering nozzle comprising: a solder outlet for dispensing solder therefrom and to receive a plurality of parts to be soldered; and a de-bridging gas outlet arranged to direct de-bridging gas between a plurality of soldered parts after they exit the solder outlet.

According to a second aspect of the present disclosure there is provided a solder pot comprising: a solder plate; and at least one nozzle as described above, the at least one nozzle being provided on the solder plate such that liquidus solder and de-bridging gas can be supplied to the nozzle.

According to a third aspect of the present disclosure there is provided a solder pot comprising: a soldering nozzle for directing solder during a multi-wave soldering operation, the soldering nozzle comprising a solder outlet for dispensing solder therefrom and to receive a plurality of parts to be soldered; and a de-bridging gas outlet located relative to the soldering nozzle such that de-bridging gas is directed between a plurality of soldered parts after they exit the solder outlet.

According to a fourth aspect of the present disclosure there is provided a system for soldering a component, comprising: a supply of liquid solder; a solder pot as described above; and a pump configured to pump solder from the solder supply to the at least one nozzle of the soldering assembly.

According to a fifth aspect of the present disclosure there is provided the use of a soldering pot in a multi-wave soldering operation, the soldering pot comprising a nozzle including a solder outlet for dispensing solder therefrom and a de-bridging gas outlet arranged to direct de-bridging gas between a plurality of soldered parts after they exit the solder outlet.

For the avoidance of doubt, any of the features described herein apply equally to any aspect of the invention.

In its most general form, a soldering assembly is disclosed including at least one nozzle for directing solder during a soldering operation. The soldering assembly may be a soldering assembly for use in multi-wave soldering process (typically including more than one nozzle).

Referring to <FIG>, this illustrates a soldering nozzle <NUM> according to an example of the present invention for directing solder during a multi-wave soldering operation. The nozzle <NUM> comprises a solder outlet <NUM> to which solder may be pumped. PCB leads, connectors, or other components to be soldered may be dipped into the solder outlet <NUM>, as is conventional for a multi-wave soldering process, and in this respect nozzle <NUM> may be functionally the same as nozzle <NUM> illustrated in <FIG>. However, in accordance with an example of the present invention, nozzle <NUM> further comprises at least one de-bridging gas outlet <NUM>. <FIG> illustrates an example in where a plurality of de-bridging gas outlets <NUM> are arranged along one side of the solder outlet <NUM>. After parts to be soldered are dipped into solder within the solder outlet <NUM> and then exit the solder outlet, the or each de-bridging gas outlet <NUM> is arranged to direct de-bridging gas between the soldered parts to remove solder in unwanted locations between the soldered parts, where otherwise there would be a risk of solder bridges forming.

The de-bridging gas may comprise nitrogen blown between soldered parts or leads to remove the solder when it is still liquidus. Other inert gases may also be used, and suitable inert de-bridging gases will be known to the skilled person. Other gases such as carbon dioxide may be suitable in some situations. The de-bridging gas may be heated to above the solder liquidus temperature. In some situations heating may not be required if solder adhering to the PCB is expected to remain above the liquidus temperature for long enough. After the PCB of other part being soldered is dipped in the solder, the de-bridging gas is blown underneath the board.

As de-bridging is performed by blowing de-bridging gas towards a PCB after parts to be soldered have been dipped in the solder outlet, there is no requirement for a screen across the solder outlet to perform de-bridging. The de-bridging gas may be blown continuously (at least during a particular soldering operation). In some alternatives, the de-bridging gas may be jetted intermittently when the PCB is located relative to the gas outlets <NUM> such that a location for which de-bridging is required is presented to a gas outlet <NUM>. In some examples each of a plurality of gas outlets may be blowing de-bridging gas at the same time, or they may be separately controlled.

Referring now to <FIG> a soldering system <NUM> suitable for implementing multi-wave soldering including a nozzle according to <FIG> will be described. Other than the nozzle, the soldering system <NUM> may be similar to conventional multi-wave soldering processes. The soldering system <NUM> comprises a robot <NUM> (also referred to as an actuating means or translation means) arranged to pick up a PCB <NUM> from a conveyor, lift the PCB <NUM> into a shuttle <NUM> in the direction of arrow <NUM>. The shuttle <NUM> then moves the PCB <NUM> to solder pot <NUM> in the direction of arrow <NUM>. In <FIG> a cover plate <NUM> is visible which as described above closes off the top of the solder pot <NUM> except for openings where one or more nozzles are exposed (not clearly visible in <FIG>) in order to maintain a low oxygen environment during soldering.

The shuttle <NUM> then aligns the PCB <NUM> with solder pot <NUM> (and nozzle <NUM>, though not visible in <FIG>) and lowers parts to be soldered into solder outlet <NUM> in the direction of arrow <NUM>. The shuttle <NUM> then lifts the PCB <NUM> such that it clears the solder outlet <NUM>. The de-bridging gas outlets <NUM> direct the de-bridging gas between the solder parts to prevent solder bridges forming. As noted above, the de-bridging gas outlets <NUM> may be continuously blowing de-bridging gas. As the shuttle <NUM> lifts the PCB <NUM> clear of the solder outlet <NUM>, the solder parts move into the gas flow from outlets <NUM> such that de-bridging occurs. In some examples, after the PCB <NUM> is clear of the solder outlet <NUM> is may be transferred by the robot <NUM> such that the solder parts move through the gas flow.

<FIG> illustrates an example of a nozzle <NUM> in which there is an array of de-bridging gas outlets located along one long side of a generally rectangular solder outlet. However it will be appreciated that this may vary. Firstly, the shape of the solder outlet may be dictated mainly by the shape and disposition of parts to be soldered in a multi-wave soldering process. Secondly, there may be only a single de-bridging gas outlet, or if there is a plurality then they may be arranged differently, for instance being provided on two sides of the solder outlet. In one example the de-bridging gas outlets are arranged on a downstream side of the nozzle, in the sense that after parts to be soldered are dipped into the solder outlet and then removed, they pass over the de-bridging gas outlets as they are transported out of the solder pot.

The flow rate, direction and temperature of the de-bridging gas defines if a bridge will be removed or not. Typically, the de-bridging gas is blown in between two leads. A flow rate will be configured to remove the solder bridge, and the flow rate may depend on the pitch between leads. For instance, to remove a bridge the flow rate may be <NUM>-<NUM> litres/minute. The flow rate may be proportional to the size of the nozzle, and in particular the size of the or each gas outlet <NUM>. The gas temperature may be well above the melting point of the solder. However, in some examples the solder is expected to remain above the solder liquidus temperature at the time it is exposed to the de-bridging gas flow and so lower temperature gases may be used. Furthermore, where an array of de-bridging gas outlets are provided, it may be that all operate simultaneously to jet de-bridging gas towards a PCB to remove solder bridges across the whole PCB. Alternatively, in some examples the de-bridging gas outlets may be separately controlled to adjust or stop the flow of de-bridging gas.

Referring now to <FIG>, this illustrates a soldering nozzle <NUM> according to another example of the present invention for directing solder during a multi-wave soldering operation. The nozzle <NUM> is similar to the nozzle <NUM> illustrated in <FIG>, and comprises a solder outlet <NUM> to which solder may be pumped. However, in place of an array of de-bridging gas outlets, a single elongate orifice <NUM> is provided, which acts as an air knife to direct a continuous jet of de-bridging gas across some or all of the width of the solder outlet <NUM>. Other variations will be apparent to the skilled person, for instance an air knife broken into two or more sections or a combination of an array orifices with an air knife linearly arranged along a nozzle. In further examples it may be that a sequential (in the direction of PCB movement) series of de-bridging orifices or slots may be provided.

The nozzle incorporating the de-bridging gas outlets may be integrally formed. Suitably, it may be manufactured by 3D printing the nozzle. However, the present invention is not limited to the use of 3D printing. This makes it possible that provide substantially any required shape to define the channels for solder and de-bridging gas within the body of the nozzle itself. The nozzle will have a connection (nipple or threaded tube) to connect tubing for de-bridging gas supply, as well as a connection to a source of solder.

To 3D print the nozzle, the nozzle may include a plurality of stacked layers, for instance of stainless steel or titanium, provided so as to at least partially define the required channels. In this example, the stacked layers are deposited during an additive manufacturing, or 3D printing, process. That is, during construction, successive layers of stainless steel or titanium are deposited to build up the nozzle structure.

As an example of an additive manufacturing or 3D printing process, a thin layer (for example, of <NUM> to <NUM> microns thickness) of metal powder (for example stainless steel or titanium) is laid down on top of a build-plate. The powder is melted or welded together in predetermined positions, for example by a laser or welding means. The predetermined positions may be defined by a 3D CAD model, for example. The build-plate is lowered by a distance substantially corresponding to the thickness of the thin layer and these steps are repeated. Once the required number of layers have been added, the non-melted/welded powder is removed to reveal the component inside. The component may be heat treated to improve the mechanical properties or post-processed (for example turning, milling, tumbling or shot peening).

The construction of a nozzle in this way allows different shapes and models to be produced that would generally not be possible with milling, drilling or casting processes. As such, nozzles with improved functionality may be produced. In addition, the use of materials within the printed nozzles may be more efficient.

Previously, it would have been expected that a 3D printed component, such as the nozzle of this disclosure, would have a rough surface (as a result of the addition of successive layers). As such, there would be an expectation that the roughened surface of the nozzle (in particular, the surface defining the channel) may affect the nozzles ability to produce a consistent, laminar flow of solder. However, surprisingly, this has found to not be an issue for the 3D printed nozzle.

In a further example, the entire solder pot assembly may be 3D printed. That is, the solder pot may include a plurality of stacked layers of stainless steel or titanium.

The multi-wave soldering nozzles of <FIG> and <FIG> incorporate an integral de-bridging gas outlet, which may for instance be suitably formed through 3D printing the nozzle. However, according to other example embodiments, it is not essential that the de-bridging gas outlet is integrally formed with the solder nozzle, only that it be provided proximal to the nozzle at a location such that when the soldered parts of the PCB are lifted clear of the solder outlet (or as the PCB is moved downstream), de-bridging gas is blown across the solder parts to perform de-bridging. Suitably this may be achieved by providing a de-bridging gas outlet (which may be referred to as an air-knife) to a cover plate, at or close to an opening for a nozzle. However, the de-bridging gas outlet may be supported or positioned independently of the cover plate. The de-bridging gas outlet may be fixed in position relative to the solder nozzle.

Referring now to <FIG>, these illustrate a portion of a solder pot in accordance with a further example of the present invention in which a cover plate includes an opening for a nozzle and a de-bridging gas outlet. Solder nozzle <NUM> is shown, including solder outlet <NUM>. As the nozzle <NUM> does not incorporate a de-bridging gas outlet, it may be generally similar to nozzle <NUM> of <FIG>, though no screen <NUM> is required. Nozzle <NUM>, and particularly solder outlet <NUM>, is shown exposed within opening <NUM> of cover plate <NUM>. Cover plate <NUM> closes off the solder pot cavity as described above in connection with <FIG>, though only the portion surrounding opening <NUM> is shown in <FIG>. It will be appreciated that cover plate <NUM> may include further openings associated with further nozzles.

<FIG> further show a de-bridging gas outlet <NUM> in the form of an air knife with a single elongate gas outlet. It will be appreciated that alternatively two or more discrete gas openings may be provided. In the example of <FIG> the de-bridging gas outlet <NUM> is 3D printed and secured to the cover plate <NUM> with screws <NUM>. However, it will be appreciated firstly that 3D printing is only one suitable fabrication technique and secondly that alternative fixation techniques will be well known to the skilled person. Indeed, in some examples the de-bridging gas outlet <NUM> may be integrally formed with the cover plate <NUM> itself. It can be seen that the de-bridging gas outlet <NUM> is directed towards the solder outlet <NUM> so that gas will be blown across parts of the PCB as they are lifted clear of the solder outlet <NUM>, or moved downstream from the solder outlet <NUM> over the de-bridging gas outlet <NUM>.

Claim 1:
A soldering nozzle (<NUM>,<NUM>) for directing solder during a multi-wave soldering operation, the soldering nozzle (<NUM>,<NUM>) comprising:
a solder outlet (<NUM>,<NUM>) for dispensing solder therefrom and to receive a plurality of parts to be soldered; and
a de-bridging gas outlet (<NUM>) arranged to direct de-bridging gas between a plurality of soldered parts after they exit the solder outlet (<NUM>,<NUM>),
characterised in that
the solder outlet (<NUM>,<NUM>) and the de-bridging gas outlet (<NUM>) are integrally formed.