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Disclosed is a method for a mold pattern to enable solder printing onto 300-mm wafers down to 100-micron pitch. Benefits include improved functionality and improved reliability.
English (United States)
This text was extracted from a Microsoft Word document.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately
50% of the total text.
Method for a mold
pattern to enable solder printing onto 300-mm wafers down to 100-micron pitch
Disclosed is a method for a mold pattern to enable solder
printing onto 300-mm wafers down to 100-micron pitch. Benefits include improved
functionality and improved reliability.
� � � � � Screen printing stencils are limited by the web spacing between
the apertures. The web spacing cannot be decreased below 45 microns as the
stencil begins to deform under the tension and printing forces. As the pitch of
the flip-chip interconnect shrinks, the apertures must also shrink to maintain
the minimum web spacing. This approach results in less solder volume deposited
on the wafer, which limits the die-to-package joint capability.
� � � � � Conventionally,
nickel stencils are electroformed with a minimum web spacing of 45 microns (see
Figure 1). No conventional solution exists that meets production requirements.
� � � � � The disclosed method is a 300-mm silicon wafer drilled to
aperture shapes, pitch, and size for a product similar to nickel stencils. A
silicon wafer with laser-drilled holes in a bump design is attached to a metal
support frame and used as a model to print solder in screen-print style.
� � � � � Silicon wafers can be laser drilled or deep reactive ion etched
(DRIE) to the tighter tolerances in the required pitches and aperture sizes
(see Figure 2). They can be used in place of the nickel web to force the solder
to the wafer for printing. Reliability requiremen...