AUTOMATIC REFERENCE PRINT HEIGHT DETECTION FOR SOLDER PASTE SCREEN PRINTERS
Original Publication Date: 1998-Sep-01
Included in the Prior Art Database: 2002-Jul-12
One specific problem associated with printing solder paste onto printed circuit board pads is repeatedly maintaining a gasket between the stencil through which the paste is deposited on the pad itself. All stencils are not the same, different manu- facturers use different "glues" which bond the sten- cil to the frame that surrounds it. It is the glue thick- ness variation that is the cause of the problem from set-up to set-up or simply from print to print. If a gasket is not formed, paste can be allowed to bleed outside the preferred printable area and cause sol- dering defects such as shorts (solder bridges) on tine pitch components and solder balling. One other effect of not having an adequate stencil to pad gas- ket is a variable separation speed i.e. as the squeegee wipes across the stencil rolling the paste into the apertures the stencil will separate from the board in an uncontrolled manner, this may lead to paste release issues and show itself as "dog earring" etc.