Screen printing apparatus

Abstract

A screen printing apparatus for and method of printing deposits of material onto a workpiece, the apparatus comprising: an inspection station for determining a positional relationship of features on upper and lower surfaces of the workpiece, the inspection station comprising: an imaging system for determining a positional relationship of features on upper and lower surfaces of the workpiece, the imaging system comprising at least two spaced imaging units for imaging features on an upper surface of the workpiece, at least two spaced imaging units for imaging features on a lower surface of the workpiece, and a processing unit for determining a positional relationship of the imaged features on the upper and lower surfaces of the workpiece; and a printing station for printing deposits of material onto the workpiece, the printing station comprising: a workpiece support assembly comprising a workpiece support member for supporting the workpiece at a printing zone; a printing screen disposed above the workpiece support member; a transport mechanism for transporting the workpiece to the printing zone; and an alignment system for aligning the upper surface of the supported workpiece and the printing screen in relation to one another, the alignment system comprising at least two spaced workpiece imaging units for imaging features on a lower surface of the workpiece, and an alignment stage for moving the workpiece support member and the printing screen in relation to one another such as to align the upper surface of the workpiece and the printing screen in relation to one another by reference to positions of the imaged features on the lower surface of the workpiece as imaged at the printing zone and the positional relationship of the imaged features on the upper and lower surfaces of the workpiece as determined at the inspection zone.

1 .- 39 . (canceled) 
   
   
       40 . A method of determining a positional relationship of features on upper and lower surfaces of a workpiece, comprising the steps of:
 supporting the workpiece at an inspection zone;   imaging at least two spaced features on an upper surface of the workpiece and at least two spaced features on a lower surface of the workpiece; and   determining a positional relationship of the imaged features on the upper and lower surfaces of the workpiece.   
   
   
       41 . The method of  claim 40 , further comprising the step of:
 transporting the workpiece to an inspection zone.   
   
   
       42 . A printing station for printing deposits of material onto a workpiece, comprising:
 a workpiece support assembly comprising a workpiece support member for supporting the workpiece at a printing zone;   a printing screen disposed above the workpiece support member;   a transport mechanism for transporting the workpiece to the printing zone; and   an alignment system for aligning an upper surface of the supported workpiece and the printing screen in relation to one another, the alignment system comprising at least two spaced workpiece imaging units for imaging features on a lower surface of the workpiece, and an alignment stage for moving the workpiece support member and the printing screen in relation to one another such as to align the upper surface of the workpiece and the printing screen in relation to one another by reference to positions of the imaged features on the lower surface of the workpiece as imaged at the printing zone and a previously-determined positional relationship of imaged features on the upper and lower surfaces of the workpiece.   
   
   
       43 . The printing station of  claim 42 , wherein the workpiece support member includes at least one recess for receiving at least one component on the lower surface of the workpiece. 
   
   
       44 . The printing station of  claim 42 , wherein the workpiece support member comprises a support plate on which the workpiece is in use supported. 
   
   
       45 . The printing station of any of  claims 42 , wherein the workpiece support assembly further comprises a vertical stage for raising and lowering the workpiece support member and the printing screen in relation to one another. 
   
   
       46 . The printing station of  claim 45 , wherein the vertical stage is operable to position the workpiece support member and the printing screen in relation to one another between a workpiece-receiving configuration in which the workpiece can be received above the workpiece support member, a workpiece-alignment configuration in which the supported workpiece can be aligned relative to the printing screen, and a workpiece-clamping configuration in which the workpiece is clamped. 
   
   
       47 . The printing station of  claim 45 , wherein the vertical stage is configured to raise and lower the workpiece support member in relation to the printing screen. 
   
   
       48 . The printing station of  claim 42 , wherein the alignment system further comprises at least two spaced screen imaging units for imaging features on a lower surface of the printing screen, and the alignment stage is configured to align the workpiece support member and the printing screen in relation to one another by reference to positions of the imaged features on the lower surface of the printing screen. 
   
   
       49 . The printing station of  claim 42 , wherein the alignment stage is configured to move the workpiece support member in relation to the printing screen. 
   
   
       50 . The printing station of  claim 42 , wherein the maximum spacing between the supported workpiece and the printing screen is less than about 20 mm. 
   
   
       51 . The printing station of  claim 50 , wherein the spacing is less than about 10 mm. 
   
   
       52 . The printing station of  claim 51 , wherein the spacing is less than about 5 mm. 
   
   
       53 . The printing station of  claim 52 , wherein the spacing is less than about 3 mm. 
   
   
       54 . The printing station of  claim 53 , wherein the spacing is less than about 2 mm. 
   
   
       55 . The printing station of  claim 42 , wherein the transport mechanism comprises a belt feed unit. 
   
   
       56 . The printing station of  claim 55 , wherein the belt feed unit comprises first and second belt drives for engaging opposed lateral edges of the workpiece. 
   
   
       57 . The printing station of  claim 56 , wherein the belt drives are configured to engage a lower surface of the workpiece. 
   
   
       58 . The printing station of  claim 42 , wherein the imaging units comprise camera units. 
   
   
       59 . A screen printing apparatus incorporating the printing station of  claim 42 .