Epithas® Ni/Au Process for Under Bump
These under bump metallization steps
produce optimum results on copper
and copper alloys:
Cleaner – Epithas MCL-10 acid soak cleaner
removes surface soils and contamination and
wets the surface to enhance solution transfer.
(Also available: MCL-067 CMOS-compatible,
low-foaming acid soak cleaner.)
Micro-etch – removes copper surface oxide
and roughens the copper, which enhances
Acid rinse – ensures that the copper surface is
oxide-free and residual copper has been removed.
Pre-dip – minimizes acid dilution of the
subsequent activator bath.
Activator – MCT-14 is an extremely stable
activator for copper and copper alloys. It is
well-suited for activating isolated copper pads
for subsequent nickel deposition. The MCT-14
immersion reaction bath displaces copper and
seeds it with palladium. The palladium initiates
the subsequent autocatalytic nickel plating step,
electroless nickel. The electroless nickel is an
autocatalytic process. The nickel layer acts as a
diffusion barrier that is solderable or aluminum
Electroless nickel – NPR-18 electroless nickel
is mildly acidic plating bath formulated for fine
line circuitry encountered in silicon wafer plating.
Bath formulation allows deposition of electroless
nickel without bridging. Highly stable, easy to
use. 6-8% phosphorus content as plated.
Immersion gold – TDS-20 cyanide-free
immersion gold bath was engineered specifically
for surface mount applications and wafer plating.
Neutral pH; will not corrode the underlying nickel
surface. Provides excellent solder joint reliability,
including small solder balls. The thin gold coating
maintains long-term solderability and prevents
nickel oxidization, and passivation.
Auto-catalytic gold – TMX-15 neutral pH
autolytic gold bath is cyanide-free, and was
designed specifically for surface mount
applications and wafer plating. Will not
corrode the underlying nickel surface, thus
it provides excellent solder joint reliability.
We recommend TDS-20 immersion gold as the
under-layer, and NPR-18 electroless nickel with
TMX-15 electroless gold.