DIEs, which will be further processed to Flip Chips or wafer level packages receive their electrical connections (bumps) already on the wafer level. During the wafer bumping process e.g., soldering deposits are applied to the wafer using soldering paste, which are re-soldered in a subsequent soldering process into wafer bumps.

Steel stencils or screens are frequently used for the printing of solder paste print.

Furthermore the cleaning of the soldered wafers is also necessary to avoid problems during the subsequent processing of the isolated chips (solderability, underfill process, moulding). At the same time the used wafer passivation should be compatible with the cleaning process.

Further Information:

• Cleaning of stencils and screens
• Stencil underside in printers