[02] In the manufacture of a circuit boards, conductive solder paste, epoxy or ink is selectively printed on a substrate such as a ceramic substrate or a fiberglass circuit board. A metal or plastic stencil or screen is often used for this printing operation and particularly where solder traces or bumps are printed on the substrate.

In prior operations of this type, the circuit board to receive solder bumps is placed on a vacuum printing nest or the circuit board is clamped thereto. The nest is attached to a slide which, following alignment, is shuttled under a metal stencil, foil or screen which is preferably made of brass or stainless steel. Once under the stencil, the stencil moves down to make contact with the circuit board and solder paste is deposited on the stencil and is squeezed through the holes in the stencil by a wiping blade which is moved across the upper face of the stencil. When the printing is complete, the stencil is lifted off of the circuit board, and the circuit board, nest and slide, being connected together, are shuttled back to an operator where the circuit board is removed and the process is repeated.

[03] However, after the wiping blade is drawn across the stencil to distribute solder into the holes in the stencil, the solder paste tends to flow over the edges of the blade to accumulate on the periphery of the stencil. Most commonly, solder paste collects in the form of two parallel lines just outside the wiping area of the blade.

[04] There have been attempts in the prior art to address the foregoing concerns. For example, it is most common for the operator to simply stop the printing operation so that the accumulated solder paste can be manually pushed back into the center of the stencil and thus within the wiping area of the blade. This is typically done with a hand-held wiping blade. This operation is undesirable because not only does it add to down time of the printing process but it is also messy, labor and time intensive and requires undesirably operator contact with the toxic solder paste.

[05] In view of the foregoing, there is a need for an automated, reliable method maintaining the solder paste within the wiping area of the stencil. There is also a demand for a stencil wiping device that obviates the need to stop the stencil printing process due to accumulation of solder paste on the edges of the stencil just outside of the wiping area of the blade. Further, there is a demand for a stencil wiping device that enables continuous stencil printing without minimal operator contact with the toxic solder paste. There is still a further demand for a stencil wiping device that greatly reduces the labor associated with stencil printing.

SUMMARY OF THE INVENTION [06] The present invention preserves the advantages of prior art stencil wiping devices for printed circuit boards. In addition, it provides new advantages not found such currently available devices and overcomes many disadvantages of such currently available devices.

[07] The stencil cleaning apparatus, in accordance with the present invention, includes a mounting base with a main blade affixed thereto. The main blade includes wiping edge, a leading side and a trailing side. A first deflector blade is connected to the mounting base and includes a deflector edge which is in substantially in the same plane as the main wiping edge and disposed in spaced apart relation to the trailing side of the main wiping edge at one of the outside edges of the main wiping edge. A second deflector blade is also provided on the opposing side of the main wiping edge.

The deflectors are angled relative to the main blade so that material, such as solder paste, being wiped by the main blade and which accumulates over the outside edges of the main blade, are deflected by the deflector blades toward the center of the main blade for continued wiping with no printing down time or contact with the toxic solder paste by the operator.

[08] In accordance with the present invention, the stencil wiping blade with solder paste deflector is used by first mounting it to the appropriate stencil printing equipment.

A circuit board to be printed upon is brought into communication from below with a stencil having a series of holes and patterns therethrough. Solder paste is then applied to the top of the stencil for subsequent wiping into the aforesaid holes and patterns which represent circuit board traces, solder bumps, and the like. The wiping blade of the present invention is then drawn over the top of the stencil thus spreading the solder paste across the top of the stencil and into the holes and patterns. As the stencil is wiped, excess solder paste migrates over the two outside edges of the wiping blade to accumulate in two longitudinally running mounds of solder paste. However, with the present invention, as soon as the solder paste flows over the outside edges of the main wiping blade, the inwardly angled deflector blades immediately re-direct the solder paste back towards the center of the main wiping blade, namely to a location within the wiping area of the opposing main blade.

[09] It is therefore an object of the present to provide a stencil wiping device that is more efficient and faster than prior art stencil wiping devices.

[10] Another object of the present invention is to provide a stencil wiping device that is less expensive to operate than prior art stencil wiping devices.

[11] It is a further object of the present invention to provide a stencil wiping device that can effectively re- direct accumulated solder paste on the periphery of the stencil without shutting down stencil printing operation.

[12] It is a further object of the present invention to provide a stencil wiping device that is much less labor and time intensive than prior art stencil wiping devices.

BRIEF DESCRIPTION OF THE DRAWINGS [13] The novel features which are characteristic of the present invention are set forth in the appended claims.

However, the invention's preferred embodiments, together with further objects and attendant advantages, will be best understood by reference to the following detailed description taken in connection with the accompanying drawings in which: [14] Fig. 1 is a perspective view of the stencil wiping blade with deflector of the present invention ; [15] Fig. 2 is a top view of the stencil wiping blade assembly with solder paste deflectors of Fig. 1; [16] Fig. 3 is a bottom view of the stencil wiping blade assembly of Fig. 1; [17] Fig. 4 is a left side elevational view of the stencil wiping blade assembly of Fig. 1; [18] Fig. 5 is a front elevational view of the stencil wiping blade assembly of Fig. 1; [19] Fig. 6 is a close-up perspective view of the stencil wiping blade assembly of Fig. 1 in operation; and [20] Fig. 7 is a side elevational view of stencil wiping blade assembly with a pair of stencil wiping blades working in conjunction with one another in a print station.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT [21] Referring to Fig. 1-5, the stencil wiping blade device 10 of the present invention includes mounting base 12 with a wiping blade 14 affixed thereto. As best seen in Fig. 4, the mounting base 12 includes a main body 16 with a seat 18 that runs along the length of the mounting base 12 for receiving the wiping blade 14 therein. The wiping blade 14 includes a trailing side 20 and a leading side 22 where the trailing side 20 of the blade 14, preferably, communicates with the seat 18 of the mounting base 12. The wiping blade 14 is sandwiched between a clamp 24 and the seat 18 of the mounting base 12 and secured in place by a number of fasteners 26 to secure the entire wiping blade 14 in place relative to the mounting base 12.

[22] Preferably, the blade 14 of a given device 10 are approximately in the range of 2 to 28 inches long and approximately 1.0 inch high but may be of any desired length and height to accommodate the given stencil to be printed from. Also, the blade 14 is preferably of a thickness of approximately 0.030 of an inch to approximately 0.010 of an inch to accommodate most printed circuit board stencils.

The thickness of the blade 14 may also be modified to suit the needs of the particular stencil 32.

[23] Also, the mounting base 12 includes a number of brackets 28 with threaded holes 30 therein for facilitating the installation of the stencil wiping blade device 10 of the present invention into existing stencil printing equipment, generally referred to as 36 in Fig. 7. The brackets 28 are preferably positioned at an angle relative to the main body 16 of the mounting base 12 to facilitate orienting the wiping blade 14 at an angle relative to stencil 32. As is known in the prior art, it is preferred that the wiping blade 14 be oriented at an angle less than 90 degrees in the direction of the blade path over the stencil 32 to ensure smooth wiping of the solder paste 34 by the blade 14. For example, the blade 14 may be positioned at an angle of 40 degrees relative to the stencil 32 for optimal wiping.

[24] While the foregoing mounting base 12 and structure for affixing the wiping blade 14 thereto is the preferred, many other structures may be employed to mount a wiping blade 14 to stencil printing equipment 36. For example, the blade 14 may be permanently affixed to the mounting base 12.

[25] In accordance with the present invention, unique deflector members 38 are affixed to the mounting base 12 which also carries the wiping blade 14. The deflector members 38 each include a deflector blade 40 with a deflector edge 42 at its distal end which, as seen in Fig.

4, lies in substantially the same plane as the wiping edge 15 of the wiping blade 14 to ensure that when the wiping edge 15 of the blade 14 touches the stencil 32 so does the deflector edge 42. The trailing deflector members 38 are shown to also include a clip portion 44 with a number of apertures (not shown) to receive fasteners 46 for connection to the mounting base 12. An intermediate panel 48 is also provided which connects the clip portion 44 to the deflector blade 40 of the deflector member 38. It should be understood that this structure is a preferred structure but other deflector member structure members may be employed as long as they include a deflector blade 40 positioned as described below.

[26] Each of the deflectors 38 are positioned in a spaced apart rearwardly from the trailing side 20 of the wiping blade 14. As best seen in Fig. 3, a bottom view of the present invention, the deflectors 38 are not only spaced apart from the wiping blade 14 but are also angled inwardly toward the middle region 50 of the wiping blade 14 which is within the wiping area 50 of the wiping blade. Thus, the opposing edges 52 of the wiping blade 14 are positioned between the opposing edges 52 of the deflectors 38.

[27] Referring now to Fig. 6, the use of the deflectors 38 in conjunction with the wiping blade 14 can be seen. Fig. 6 illustrates only one side of the stencil wiping blade 14 with one of the deflectors 38 of the present invention. For ease of illustration only one side will be addressed below but it should be understood that the opposing side of the device 10 operates in identical mirror image fashion to what is shown in Fig. 6. Also, the device 10 is shown mounted to block 60 of printing equipment 36 which will be discussed in detail below.

[28] When the solder paste 34 has been applied to the top surface of a stencil 32 and is ready for printing to a printed circuit board (not shown), the wiping blade 14 is brought into contact with the top surface of the stencil 32.

The wiping blade 14 is then drawn across the top surface of the stencil 14, in the direction indicated by the arrow, to "squeegee"the solder paste 34 into the desired apertures and patterns 54 in the stencil 32 for stencil printing. The wiping blade 14 is oriented so that the angled between the stencil 32 and the leading edge 22 is less than 90 degrees to facilitate printing. While not optimal or preferred, angles less than 90 degrees may be used. During wiping, excess solder paste 34 will tend to flow beyond the edges 52 of the wiping blade 14. However, the deflector 38 captures the excess solder paste 34 and, due to the inwardly facing angle of the deflector 38, the solder paste 34 is re- directed onto the portion of the stencil 32 which can be reached by the opposing wiping blade 14 on subsequent passes. If the deflector 38 of the present invention was not employed, the excess solder 34 would accumulate outside the broken line 56 of Fig. 6 whereby it would be inaccessible by the opposing wiping blade 14 on subsequent passes.

[29] For actual use of the stencil wiping blade device 10 of the system, it can be easily mounted into a typical stencil printing system 36 which employs a pair of blades 14a and 14b that travel in opposite direction to one another to ensure complete printing. Typically, a pair of wiping blades 14a and 14b are employed in conjunction with one another. For example, as shown in Fig. 7, the pair of stencil wiping blade devices l0a and 10b are both independently mounted to actuating devices 58a and 58b, such as pneumatic cylinders 58a and 58b which are, in turn, mounted to a main support block 64. Other actuating devices, such as hydraulic cylinders and motorized linkages may also be employed and still be within the scope the present invention. The blades devices 10a and 10b are respectively mounted to blocks 60a and 60b of the actuating devices 58a and 58b by the brackets 28 on the mounting base 12a and 12b of the devices 10a and 10b. Fasteners, 62, such as threaded fasteners secure the wiping devices 10a and 10b to their respective actuating devices 58a and 58b.

[30] The blades 14a and 14b are oriented so that blade 14b is used to wipe to the left while blade 14a is used to wipe to the right. Thus, one of the stencil wiping blades 14a and 14b are used at a time to wipe solder 34 (as shown in Fig. 6) across the stencil 32 with deflectors blades 40a and 40b. In Fig. 7, the right stencil wiping blade 14b is shown in contact with the stencil 32 and is used to wipe in the right to left direction as indicated by the arrow. During this time, the left blade 14a is elevated and does not touch the stencil 32. For wiping, the stencil 32 may be moved relative to fixed wiping blades 14a and 14b or the blades 14a and 14b may be moved relative to a fixed stencil 32.

When the right blade 14b has completed its wiping pass, it is lifted off of the stencil 32 and the left blade 14a now is lowered to contact the stencil 32 to carry out a return wiping pass. The number of passes can be modified to suit the characteristics of the stencil and circuit board to be printed upon.

[31] Fig. 7 shows the blades 14a and 14b equipped with the deflectors 38a and 38b of the present invention. As a result, essentially continuous back forth wiping of the stencil 32 can be carried out with no down time or dangerous operator interaction with the undesirable excess solder paste 34 on the peripheral edges of the stencil 32.

[32] The stencil wiping device 10 of the present invention is shown with a single wiping blade 14. However, it is also possible to employ a number of parallel blades (not shown) in each device 10, depending on the needs of the particular application at hand.

[33] The blade 14 of the device, preferably, made of metal to be precise and resilient and long wearing while still being effective in wiping solder paste 34 from a stencil 32.

For example, steel is well-suited as a material for blade 14 The blade 14 may be made of other materials, such as rubber or plastic.

[34] It would be appreciated by those skilled in the art that various changes and modifications can be made to the illustrated embodiments without departing from the spirit of the present invention. All such modifications and changes are intended to be covered by the appended claims.