Patent Application
20060186183
1. Field of Invention
The present invention relates generally to apparatus for manufacturing printed circuit boards and for assisting the process of soldering metals to integrated circuit boards, and more particularly to a wave soldering machine having an improved wave solder nozzle adapted to better control the flow of solder when performing a solder application on a printed circuit board.
2. Discussion of Related Art
Generally speaking, in a wave soldering machine, a printed circuit board (PCB) is moved by a conveyor on an inclined path past a fluxing station, a preheating station, and finally a wave soldering station. At the wave soldering station, a wave of solder is caused to well upwardly (by means of a pump) through a wave solder nozzle and contact portions of the PCB to be soldered. The efficiency of the soldering process is affected by a number of concerns, one of which is the ability to control the flow of solder material at the point of contact with the PCB and after the PCB moves away from the solder wave. Inconsistency of flow of solder material may cause inaccurate soldering applications.
Specifically, and with reference to
One disadvantage with the inert solder wave nozzle 10 is that it is difficult to control the velocity of solder material being generated from the backside of the wave. It is known that optimum soldering results when the velocity VB of the PCB 18 traveling over the wave is equal or substantially equal to the velocity VS of the solder material flowing over the back guide 14 of the wave solder nozzle 10. Typically, the velocity of the solder wave is greater than the velocity of the PCB 18. The difference in the velocities of the PCB and solder wave results in a phenomenon called “bridging,” which is the undesirable interconnection of solder material between adjacent metallic pads of the PCB.
Solder wave nozzles adapted to operate within an oxygenated atmosphere are configured to reduce the velocity of solder material on the backside of the wave so that the velocity of solder material equals or substantially approximates the velocity of the PCB. Examples of such solder wave nozzles can be found in U.S. Pat. Nos. 3,921,888, 3,989,180 and 4,886,201. One disadvantage with known air nozzle designs is increased solder dross production.
Embodiments of the invention provide improvements to wave solder nozzles, such as those described above.
A first aspect of the invention is directed to a wave solder nozzle adapted to deliver solder material to perform a wave soldering operation on a printed circuit board in an inert atmosphere. The wave solder nozzle comprises a front plate and a back plate coupled to the front plate. The front plate and the back plate define a channel through which solder material flows. The nozzle further comprises an exit trough extending from the back plate. The exit trough has a weir provided at one end of the exit trough. The exit trough is constructed and arranged to control the flow of solder material from the wave solder nozzle. A surface of the exit trough is wettable to improve the flow of solder material out of the wave solder nozzle.
In an embodiment of the invention, the wettable surface is located on a chamfered edge of the weir. In another embodiment, the wettable surface is fabricated from iron. In yet another embodiment, the wettable surface is fabricated from iron having less than 3% carbon. In a further embodiment, the wettable surface is fabricated from iron having approximately 0.2% carbon.
A second aspect of the invention is directed to a wave soldering machine to perform a wave soldering operation on a printed circuit board in an inert atmosphere. The wave soldering machine comprises a housing and a conveyor coupled to the housing. The conveyor is configured to deliver a printed circuit board to the housing. The wave soldering machine further comprises a wave soldering station coupled to the housing. The wave soldering station comprises a reservoir of solder material, and a wave solder nozzle in fluid communication with the reservoir. The wave solder nozzle comprises a front plate and a back plate coupled to the front plate. The front plate and the back plate define a channel through which solder material flows. The nozzle further comprises an exit trough extending from the back plate. The exit trough has a weir provided at one end of the exit trough. The exit trough is constructed and arranged to control the flow of solder material from the wave solder nozzle. A surface of the exit trough is wettable to improve the flow of solder material out of the wave solder nozzle. The wave soldering machine further comprises a controller to control the operation of the wave soldering machine.
In an embodiment of the invention, the wettable surface is located on a chamfered edge of the weir. In another embodiment, the wettable surface is fabricated from iron. In yet another embodiment, the wettable surface is fabricated from iron having less than 3% carbon. In a further embodiment, the wettable surface is fabricated from iron having approximately 0.2% carbon.
A third aspect of the invention is directed to a method of improving the flow of solder material out of a wave solder nozzle of a wave soldering machine in an inert atmosphere. The method comprises: delivering solder material to a wave solder nozzle; performing a wave soldering operation on a printed circuit board; and improving the flow of solder material over the wave solder nozzle by providing a surface of the wave solder nozzle with a wettable material.
The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:
This invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” “having,” “containing,” “involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.
For purposes of illustration, and with reference to
The wave soldering station 40 includes a wave solder nozzle, generally indicated at 42 in
To prevent the bridging phenomenon and the unwanted build up of solder dross, one would expect that a system configured to combine an air nozzle design and an inert atmosphere would result in optimal performance. However, when inerting the atmosphere (e.g., an atmosphere with less than 100 ppm of O2) of an air solder wave nozzle, the surface tension of the solder material greatly increases, thereby causing an inconsistent flow of solder material over the backside of the nozzle. Particularly, with existing air nozzles, solder material, e.g., lead-based (tin/lead), lead-free, etc., has a tendency to bead up on the nozzle, thus negatively affecting the laminar flow of solder material over the nozzle.
Referring to
The back plate 50 of the wave solder nozzle 42 is formed with an exit trough 58, which extends generally perpendicularly from the back plate. The exit trough 58 is configured to vary the angle of the solder material 54 flowing over the exit trough. An adjustable weir or exit wing 60 is provided at the end of the exit trough 58 to control the level of solder material 54 flowing from the wave solder nozzle 42. Specifically, the weir 60 may be adjusted upwardly and downwardly to raise and lower the height of the solder wave, respectively. The wave solder nozzle 42 may be constructed, for example, in a manner similar to the construction of the wave solder nozzles disclosed in U.S. Pat. Nos. 3,921,888, 3,989,180 and 4,886,201, which are owned by Speedline Technologies, Inc., the assignee of the present invention, and incorporated by reference herein.
The provision of the exit trough 58 and the weir 60 control the flow of the solder material 54 from the nozzle 42. Specifically, the flow of solder material 54 may be controlled (e.g., by controller 46) so that the velocity VS of the solder material is equal or substantially equal to the velocity VB of the PCB 18.
As discussed above, the wave solder nozzle 42 shown in
Referring to
To enable the operation of the solder wave nozzle 42 within an inert atmosphere, the exit trough 58 in general, and the weir 60 in particular, may be fabricated from a material that enables the solder to wet on surfaces to better the flow of material. As shown in
In one embodiment, the wettable material is iron. Preferably, the wettable material is fabricated from iron impregnated with less than 3% carbon. Most preferably, the wettable material is fabricated from iron impregnated with approximately 0.2% carbon. Other materials and alloys may further be chosen, and include: grey cast iron; cast iron; stainless steel; chrome-plated steel; nickel; titanium; and copper. For example, it is contemplated that stainless steel treated with a very strong acid will provide sufficient wettability to enable molten solder material 54 to flow evenly over the weir 60. Notwithstanding, low carbon iron demonstrated the best results.
In one embodiment of the invention, the chamfered edge 64 is electroplated with pure iron or low carbon iron (e.g., 1018 steel). Other suitable methods may also be employed.
In another embodiment of the invention, a method of improving the flow of solder material out of a wave solder nozzle of a wave soldering machine is further disclosed. The method includes: delivering solder material to a wave solder nozzle; performing a wave soldering operation on a printed circuit board; and improving the flow of solder material over the wave solder nozzle by providing a surface of the wave solder nozzle with a wettable material. This method may be achieved by employing nozzle 42 described above.
Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.
