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Pretreatment of Aluminium Micropads for Electroless Nickel Plating

I am currently plating aluminium pads on semiconductors with electroless Nickel. The pretreatment is a double dip zincate technique. The pads are about 100 µm in diameter and have a thickness of 0.8 µm AlCu0.5%. I am wandering that this pretreatment leads sometimes to a completely dissolved aluminium pad on the semiconductor. The reaction of electroless nickel cannot appear at these positions. Neighbouring pads seems to be okay.

Can this be a problem of the semiconductor or local potential differences ? Has anyone observed similar behaviour and what can I do to avoid this problem ?

Lothar Henneken
- Stuttgart, Germany
2001

Your etching solution or zincation concentration is too high / or the etching time or zincation time too long. For your pretreatment process, I think 1 micro Al thickness is min. required. Your Al has only 0.8 micro, therefore, it is necessary to dilute the etching solution or zincation solution, or shorten the pretreatment time.

Good luck,

Yin Xiong
UTAC - Singpaore
2001

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