Wafer Bump Stencils

The screen printing of solder balls onto the wafer represents an extremely economical method for the production of solder bumps for contacting the wafer to an interposer or circuit carrier.
 
Stencils required for this differ from standard SMT stencil due to their complexity, with several hundred thousand apertures, and the required positional precision.
 
Very thin metallic foils are used, which must exhibit extremely small thickness fluctuations. This is extremely difficult to realise by electro-chemical procedures.  Laser cutting of highly exact polished foils offers crucial advantages in this regard.
 
Special lasers are optimised to cut the large number of apertures quickly and cleanly. It is imperative that any thermal effect of laser cutting is minimised.

LPKF Laser & Electronics AG are constantly working on improvements to the finishing techniques of Wafer Bump Stencils.