CLEANING ASSEMBLY AND METHOD FOR A PASTE MATERIAL PRINTER

A cleaning assembly 114 and cleaning method for a screen printer 100 for paste material printing is disclosed herein. In a described embodiment, the cleaning assembly 114 comprises an image capturing device having a fiducial camera 124 arranged to move to respective fiducial positions for performing fiducial recognition of a number of fiduciary markers 202,204 on the PCB 200 and on a stencil 112 of the screen printer 100; and a cleaning device in the form of a cleaning blade 128 that is arranged to clean the stencil 112 during the movement of the image capturing device 124.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a perspective view of a screen printer100for solder paste printing, the screen printer100comprising a conveyor system102for conveying substrates such as printed circuit boards (PCBs) (not shown) into a printing chamber104of the screen printer100. The screen printer100includes a pair of pivotable covers106, shown in open positions inFIG. 1, to allow access to the printing chamber104and the pair of pivotable covers106is normally closed during operation of the screen printer100. The screen printer100further includes a number of protective panels108.

FIG. 2is a bottom perspective view of the screen printer100with a number of parts, including the protective panels108, omitted to show a set of mounting frames110for supporting a stencil112and a fiducial recognition and cleaning assembly114.

FIG. 3is an end view of the screen printer100ofFIG. 2, in direction A inFIG. 2.

The stencil112has a print pattern116defined by a plurality of apertures118through which paste material is deposited onto respective solder pads of a PCB200. In this embodiment, the paste material is solder paste. The stencil112is substantially planar and includes a top side120on which the solder paste is dispensed and a bottom side122which engages the PCB200, and have sides extending generally in respective X-axis and Y-axis of the PCB200.

FIG. 4is a simplified schematic diagram of the PCB200. For the sake of simplicity, it does not show any artwork or solder pads, which would normally be present. The PCB200includes a first fiduciary marker202and a second fiduciary marker204which are reference points for determining orientation and alignment of the PCB200vis-a-vis the stencil112based on corresponding fiducial markers on the stencil112.

The fiducial recognition and cleaning assembly114includes an image capturing device and in this embodiment, it is a fiducial camera124mounted to guide tracks (not shown) in a usual manner for moving the fiducial camera124to respective fiducial positions for recognition of the fiduciary markers202,204on the PCB200, as well as corresponding fiducial markers on the stencil112in order to ensure an accurate alignment between the PCB200and the stencil112during the printing operation. Specifically, the fiducial camera124is arranged to move between the stencil112and the PCB200i.e. below the stencil112and above the PCB200.

FIG. 5is a close-up view of portion B ofFIG. 3and it should be appreciated that the fiducial camera124is arranged to point downwards to capture images of the fiduciary markers202,204of the PCB200, and to point upwards to capture the images of the corresponding fiducial markers on the stencil112. Also, the fiducial camera124includes a camera body126. In this embodiment, the fiducial recognition and cleaning assembly114includes a cleaning blade128mounted to the camera body126via a support frame130(to which the camera body126is coupled) so that movement of the cleaning blade128is synchronized with the movement of the fiducial camera124. The cleaning blade128has a longitudinal axis which is aligned to the X-axis of the PCB200and substantially orthogonal to the Y-axis of the PCB200.

The fiducial recognition and cleaning assembly114includes an actuator132for moving the support frame130and, thereby, the cleaning blade128towards the stencil112to contact with the bottom side122of the stencil112. In this way, the cleaning blade128is arranged to clean or scrape the bottom side122of the stencil112during the movement of the fiducial camera124.

An operation of the fiducial recognition and cleaning assembly114will now be described, with particular reference toFIG. 6, which is a simplified control block diagram of the screen printer100illustrating a processor134controlling the various parts of the fiducial recognition and cleaning assembly114.

A new print cycle begins with loading of the PCB200by the conveyor system102into the printing chamber104. A PCB stopper (not shown, and controlled by the processor134) extends to stop the PCB200at a predetermined position below the stencil112. For the purposes of this operation, the stencil112has already been used for an earlier printing cycle and is not yet cleaned. The PCB stopper is next retracted and the PCB200is lifted by the conveyor system102to a vision recognition height. The processor124then activates the actuator132to move the support frame130and, thereby, the fiducial camera124from a resting or parked position to a first fiducial position to capture an image of the first fiduciary marker202on the PCB200, as well as the corresponding first fiducial marker on the stencil112. Contemporaneously, the cleaning blade128contacts the bottom side122of the stencil112as the fiducial camera124is being positioned to the first fiducial position, i.e. at a cleaning position. Accordingly, the cleaning of the bottom side122of the stencil112by the cleaning blade128may begin as the fiducial camera124moves from its resting position to the first fiducial position.

After the fiducial camera124has successfully captured the first fiducial markers on the PCB200and the stencil112, the processor124controls the actuator132to move the fiducial camera124in the direction of arrow C (seeFIG. 4), from the first fiducial position to a second fiducial position for recognizing the second fiduciary marker204on the PCB200, as well as the corresponding second fiducial marker on the stencil112. Contemporaneously with the movement of the fiducial camera124, the cleaning blade128scraps off any residual solder paste as a result of the earlier print cycle from the bottom side122of the stencil112. After capturing the images of the second fiduciary marker204on the PCB200and the corresponding second fiduciary marker on the stencil112, the fiducial camera124(together with the cleaning blade128) moves to its standby position. It should be appreciated that the cleaning of the bottom side122of the stencil112by the cleaning blade128continues as the fiducial camera124moves to its standby position, because the cleaning blade128still maintains contact with the bottom side122of the stencil112.

Based on the captured images of the fiducial markers, the PCB200is repositioned to align with the stencil200if necessary. Thereafter, the PCB200is further lifted by the conveyor system102to contact with the stencil200to begin solder paste printing136in a usual manner. After printing, the PCB200is lowered to a transport height for the conveyor system102to convey it to an output section for a next process. The screen printer100is now ready for printing the next PCB200.

In the standby position, and preferably also during the transportation of the PCB200to the output section, the cleaning blade128may be cleaned or wiped by a static rubber squeegee to remove the scraped solder paste and keep the cleaning blade128clean.

The above steps are repeated with the cleaning of the stencil200being carried out simultaneously or concurrently with the movement of the fiducial camera124, for example, between the first and second fiducial positions. In this way, the cycle time is reduced substantially as opposed to conventional wiping or cleaning. Indeed, due to the reduced cycle time, it is possible (although not necessary), for the stencil200to be cleaned by the fiducial recognition and cleaning assembly114during each print cycle (i.e. during the fiducial recognition stage) and this may greatly reduce solderability and bridging issues. Further, the cleaning may reduce solder paste volume variation, thus improving the quality of the paste printing. Further, it has been found that this cleaning process may be particularly useful when manufacturing PCBs for smart phone applications since this may result in faster cycle time, better quality printing and reduced use of consumables for cleaning the stencil112.

The described embodiment should not be construed as limitative. For example, the references to “screen printer” or “stencil printer” may be used interchangeably. Similarly, references to “stencil” or “screen” may also be used interchangeably. Alternatively, the described embodiment may be adapted for stencil printers, not just screen printers. Also, the printing may be performed on other types of substrates (such as a ceramic substrate) not just PCBs. Likewise, not just solder paste but other types of paste material may be used, such as epoxy materials. Also, the actuator132may not be necessary if the guide tracks supporting the fiducial camera124are configured to lift the fiducial camera124upwards in order for the cleaning blade128to engage the bottom side122of the stencil112.

It is envisaged that the cleaning blade128(or generally the cleaning device) need not be mounted to the camera body126. For example, the cleaning blade128may be independently supported and separated from the camera body126and the cleaning of the stencil112is performed by the cleaning blade128during the movement of the fiducial camera124to achieve the cycle time reduction.

Further, the cleaning blade128may be arranged between an extended position and a retracted position. For instance, the cleaning blade128may extend from a retracted position to contact the bottom side122of the stencil122as the fiducial camera124is positioned between the first and second fiducial positions, while the extended cleaning blade128may retract to the retracted position in its standby position.

Instead of one cleaning blade128, there may be more than one cleaning blade128, and it is preferable to use twin cleaning blades so that the scraping of residual solder paste from the bottom side122of the stencil112may be more effective. The cleaning of the stencil112by the cleaning blade128may also be performed during the movement of the fiducial camera124from its standby position to the first fiducial position and/or from the second fiducial position to its standby position and this may provide a better cleaning coverage. In other words, broadly, it is envisaged that the cleaning of the stencil112may be performed concurrently during the movement of the fiducial camera124.

Also, besides using the cleaning blade128, other types of cleaning methods may be employed. For example, it is envisaged that, as an alternative or in addition, vacuum from a local venturi system may be used for cleaning the apertures if needed, or a conventional wiping device may be used too which wipes/cleans the stencil concurrently as the movement of the fiducial camera124.

The PCB may have more than two fiduciary markers202,204and it would be appreciated that cleaning is thus performed during the movement of the fiducial camera124from any one of the fiduciary markers to another fiduciary marker.

Having now fully described the invention, it should be apparent to one of ordinary skill in the art that many modifications can be made hereto without departing from the scope as claimed.