Wafer bumping services are offered as a preparatory step for flip-chip bonding or as bumping
service alone. The types of solder bumping available include high lead solder, eutectic solder and
lead free solder. Lead free bump, which is composed of tin-silver alloy, can meet the WEEE
directives. Additionally, it can eliminate alpha particle sources.This service is currently offered for 6and 8wafers, and soon 12" wafers. About 11,000 bumps on a die with 120Ã‚Âµm bump pitch with lead free solder, and a 100Ã‚Âµm bump pitch.
Evaporation, stencil printing, and
plating are the three most com-
mon technologies used for depos-
iting the wafer bump.
In stencil printing, solder paste is
printed on to the UBM by screening it
through a stencil which contains
apertures that align with the wafer
bond pads. Then The solder paste is trans-
ferred to the bond pads by pushing a
bead of solder across the stencil.
Evaporation has the drawback that it has for UBM. High costs and low through-
put limit the use of evaporation for
bump deposition in high-volume
-Electroplating can accommodate tight
bump pitches and give high yield.
It is the most versatile process, relative
to bump size, pitch, and geometry, and
is increasingly used in wafer bumping.
Horizontal fountain-cell and vertical
rack plating tools architectures have been used for these methods. Vertical plating tools have a capacity
advantage over horizontal plating tools,
particularly for 300-mm wafers. The horizontal architecture includes much of the process control and ancillary
equipment, such as chemical delivery, re-
sulting in a high level of tool complexity
Try this link too: http://dom.semi.org/web/wFiles.nsf/Looku...MWG-03.pdf