Background and Summary Apparatus and methods for reworking workpieces such as PCBs are well known.

Illustrative apparatus include the BGA 2000 or BGA 3000 Systems, available from OK Industries, USA World Headquarters, 4 Executive Plaza, Yonkers, New York 10701, which may include features for solder removal, solder stenciling, component alignment, component placement, and reflow, such as an oven for heating the component and solder. After solder is removed from a PCB, such as by desoldering with a solder wick and heated iron and a vacuum that is commonly used to pull off solder, an arm-mounted stencil is moved into position above a location on the PCB where it is desired to reapply a soldered pattern. The stencil is lowered to contact the surface of the PCB and solder paste, and solder is applied to the PCB, usually manually by a squeegee-type device.

It may happen that the stencil and the surface of the PCB are not coplanar. As a result, more solder may be applied by a relatively raised portion of the stencil. This may yield negative results, such as soldered points flowing being connected by solder overflow. It is desirable to provide a stenciling apparatus and a method of stenciling that ensures coplanarity between a stencil and a workpiece such as a PCB.

According to one aspect of the present invention, an apparatus for solder stenciling is provided and includes a stencil, a ball joint including a ball and a socket, and an arm fixing the stencil to one of the ball and the socket.

According to another aspect of the present invention, a solder stenciling apparatus is provided and includes a stencil, an arm attached at a first end to the stencil, and a joint, the arm being attached at a second end thereof to the joint, the joint permitting the arm to pivot in all directions about a pivot point.

According to yet another aspect of the present invention, a method for solder stenciling on a workpiece is provided. According to the method, a stencil is aligned relative to a position on a workpiece. Planarity of the stencil is adjusted such that the stencil and the workpiece are coplanar. Solder is applied to the workpiece through the stencil. The stencil is removed from the workpiece.

Brief Description of the Drawings The features and advantages of the present invention are well understood by reading the following detailed description in conjunction with the drawings in which like numerals indicate similar elements and in which: FIG. 1 is a schematic, perspective view of a rework assembly including an adjustable solder stenciling assembly in a raised position according to an embodiment of the present invention; FIG. 2 is a schematic, perspective view of a rework assembly including an adjustable solder stenciling assembly in a lowered position according to an embodiment of the present invention; FIG. 3 is a schematic, perspective view of a joint for a soldering assembly according to an embodiment of the present invention; FIG. 4 is a schematic, side, partially cross-sectional view of a joint for a soldering assembly according to an embodiment of the present invention; and FIG. 5 is a schematic, perspective view of a rework assembly according to a second embodiment of the present invention.

Detailed Description A printed circuit board (PCB) rework apparatus 21 according to an embodiment of the present invention is shown in FIGS. 1 and 2. Various rework apparatus are known, such as the Ball Grid Array and Chip-Scale systems including the BGA 2000 or BGA 3000 Systems, available from OK Industries, USA World Headquarters, 4 Executive Plaza, Yonkers, New York 10701, which may include features for solder removal, solder stenciling, component alignment, component placement, and reflow, such as an oven for heating the component and

solder. The rework apparatus 21 apparatus preferably includes a frame member 23 including a rigid frame portion 25 relative to which a workpiece, preferably a PCB 27, is positioned and, preferably, locked, such as by clamps 29, and an articulatable arm 31 that is preferably at least vertically movable in the Z direction relative to the frame 25.

An apparatus 33 for solder stenciling is attached to the articulatable arm 31. The solder stenciling apparatus 33 includes a stencil 35, an arm 37 attached at a first end 39 to the stencil, and a joint 41. The arm 37 is attached at a second end 43 thereof to the joint 41. The joint 41 preferably permits the arm 37, and thus the stencil 35, to pivot in all directions about a pivot point 45 (FIG. 4). Pivotability of the stencil 35 about the pivot point 45 facilitates attaining optimal coplanarity between the stencil and the surface of the PCB 27. The arm 31 preferably also permits horizontal linear and rotational movement of the solder stenciling apparatus 33 relative to the frame 25 in the X and Y directions.

A preferred joint 41 is shown in perspective in FIG. 3. As seen in FIG. 4, the joint 41 is preferably a ball joint including a ball 47 and a socket 49, the second end 43 of the arm 37 is preferably attached to one of the ball and the socket, preferably the ball. If desired or necessary, the arm 37 may be movable relative to the joint 41 or telescopic to facilitate vertical movement of the stencil relative to the PCB 27. Preferably, the articulatable arm 31 permits the majority of the vertical movement of the stencil 35, except for that portion of vertical movement that results from pivoting of the stencil about the pivot point 45.

In the embodiment of the apparatus 21 shown in FIGS. 1 and 2, the articulatable arm 31 may be manually movable, but is preferably drivable by any suitable drive assembly 51, such as an electric motor drive and gear, chain, or belt drive arrangement, or a manual drive and gear, chain, or belt drive, such as with knobs 51K to move horizontally rotationally and vertically relative to the rigid frame portion 25 to properly position the stencil 35 relative to the PCB 27. The articulatable arm 31 may be in the form of a platform that is movable up and down along a track 51Z in direction Z, out and in along another track (not shown) in direction X, and left and right along another track (not shown) in direction Y by the drive assembly 51, and on which the solder stencil apparatus 33 is fixed or movably mounted for movement in directions X and Y. The arm 37 may permit movement in the direction Z, if desired or necessary. If desired or necessary, the PCB 27 may be movable in the X, Y,

and/or Z directions, either manually or by a suitable drive mechanism (not shown), prior to stenciling.

An optical alignment assembly 53 is preferably provided for aligning the stencil 35 relative to a position on the PCB 27, such as a PCB land pattern, on which it is desired to stencil a pattern. The optical alignment assembly 53 is preferably an optical system such as is used in aligning chips for attachment to PCBs, and preferably includes vision system lamps for illuminating an area, and a device for varying a magnification level at which the area is viewed. The optical alignment assembly 53, or a part thereof, is preferably movable to a position between the stencil 35 and the PCB 27 when the stencil is in an upper-most position and movable out of the position to permit lowering of the stencil to the PCB. Part of the optical alignment assembly 53 is preferably mounted on a pivotable arm 53A (FIG. 1), and part 53P is preferably slidably mounted on a track 53T to facilitate movement of part of the optical alignment assembly. A precision optics package suitable for use in connection with the present invention may include the MP-2000 Micro Placer System available from OK Industries, USA World Headquarters, 4 Executive Plaza, Yonkers, New York 10701, and which also includes a X, Y, and theta rotation controls that are suitable for use as the drive assembly 51. A suitable movable optical alignment assembly and drive assembly is provided with the OK CSP-3500 Rework System, available from OK Industries, USA World Headquarters, 4 Executive Plaza, Yonkers, New York 10701. The optical alignment assembly 53 preferably aligns the stencil 35 relative to a position on the PCB 27 using an optical beam splitter, such as a prism, that views the workpiece and a bottom of the stencil simultaneously. Points on the stencil and the workpiece are aligned using alignment devices such as micrometers so that holes on the stencil align with solder pads.

After stenciling, a component is placed on the stenciled PCB, preferably using the optical alignment assembly 53 together with a suitable pick-up device, such as a vacuum pick- up device. The vacuum pick-up device may be mounted on the arm on which the stencil 35 is mounted. The PCB and component are then preferably heated, such as in an oven, to join the component to the PCB by means of the stenciled pattern. The BGA 2000 or BGA 3000 Systems, available from OK Industries, USA World Headquarters, 4 Executive Plaza,

Yonkers, New York 10701, are illustrative of rework apparatus having features which are suitable for use in connection with the present invention.

When the stencil 35 is lowered onto the PCB 27, any lack of coplanarity between the stencil and the PCB is compensated for by the ability of the stencil to pivot about the pivot point 45. A clamp, preferably a knobbed set screw 57 extending through an internally threaded opening 59 in the socket 45, is preferably provided to lock the stencil 35 in a proper coplanar relationship with the PCB 27 to minimize any tendency of the stencil to move during application of solder, which is ordinarily done manually by means of a metal squeegee (not shown). An end 61 of the set screw 57 preferably contacts a surface 63 of the ball 47 to lock the ball relative to the socket 49.

The arm 37 may support the stencil 35 at multiple, such as two, attachment points 65 or, as seen in FIG. 5, an arm 137 may support a stencil 35 at a single attachment point 165.

The stenciling apparatus 133 shown in FIG. 5 is a more manual embodiment of the invention, and may be preferable for smaller stenciling operations, or operations to be performed on more irregular surfaces than are conveniently handled using an apparatus such as is shown in FIGS. 1 and 2. The single arm 137 facilitates access to the stencil 35, which may be more difficult as the number of attachment points 65 (FIGS. 1 and 2) increases. The stenciling apparatus 133 is preferably part of an apparatus including a frame member 123 having a rigid frame portion 125 and an articulatable arm 131 to which a joint 41 is attached. The stenciling apparatus 133 is substantially identical to the stenciling apparatus 33.

A method for solder stenciling on a workpiece such as a PCB 27 according to the present invention will be described with reference to FIGS. 1 and 2. According to the method, the stencil 35 is aligned relative to a position on the PCB 27, preferably by using an optical alignment assembly 53 and a drive assembly 51, or, if preferred, manually. The stencil 35 is preferably aligned relative to the workpiece 27 by moving the articulatable arm 31 to which the stencil is attached relative to the fixed main frame 25.

Planarity of the stencil 35 is adjusted by pivoting the stencil about the pivot point 45 such that the stencil and the PCB are coplanar. After adjusting planarity, the stencil 35 is locked in a coplanar position, such as by a clamp such as a set screw 57. Solder is applied to

the PCB 27 through the stencil 35, such as by manually applying the solder with a squeegee.

The stencil 35 is removed from the PCB 27, preferably by being raised by the drive assembly 51.

It is, of course, possible to embody the invention in specific forms other than those described above without departing from the spirit of the present invention. The embodiments shown are merely illustrative and should not be considered restrictive in any way. The scope of the present invention is given in the appended claims, rather than the preceding description, and all variations and equivalents which fall within the range of the claims are intended to be embraced therein.