CMOS-compatible UBM for Silicon Wafers / SOI Wafers
These under bump metallization steps produce optimum results on silicon wafers / SOI wafers:
CMOS-COMPATIBLE PROCESS FOR ALUMINUM METALLIZATION
- Cleaner – Epithas CACL-067 acid soak cleaner for pretreatment of silicon wafers, including SOI wafers, prior to the Epithas Ni/Au process.
- Micro-etch – LEC-19 removes naturally-occurring oxidation from aluminum and aluminum alloy surfaces. Pretreatment for electroless nickel on aluminum for silicon wafers, including SOI wafers.
- Zincate – MCS-30 acid immersion zinc for silicon wafer plating; minimizes the dissolution of aluminum, assures thin, uniform zinc deposit for subsequent electroless nickel plating.
- Electroless Nickel – NPR-18CM was developed for wafer plating applications with fine line circuitry. Highly stable bath; allows bridge-free deposition of electroless nickel. Low temperature operation for improved resist tolerance. 6-8% phosphorus as plated. 100 hour salt spray performance (ASTM B117). Adhesion is superior to electroplated nickel.
CMOS COMPATIBLE PROCESS FOR COPPER METALLIZATION
- Cleaner – Epithas CACL-067 acid soak pretreatment for silicon wafer plating, including SOI wafers
- Activator – MCT-14 is a highly stable activator for copper and copper alloys. Immersion reaction bath deposits palladium only on the copper surface. The palladium initiates the subsequent autocatalytic nickel plating step, electroless nickel.
- Electroless Nickel – NPR-18CM – for wafer plating, including SOI wafers, involving fine line circuitry.
Read Under Bump Metallization: Some Economical Alternatives by Mario Orduz, published in US Tech.