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Chip Scale Review January • February • 2017

[ChipScaleReview.com]

the resulting gold thickness on the front and

backside of the part from each plating bath.

The alkaline pH bath has a large discrepancy

between the gold thickness on the front versus

the backside of the parts. The frontside is three

times thicker than the backside. Whereas, the

part plated with the acid sulfite gold chemistry

has the same thickness on the front and back

of the part even though the backside was not

facing an anode or controlled by a separate

power supply.

Summary

The versatility and unique features of a

newly formulated acid sulfite gold plating

bath have been discussed. A proprietary

stabilizer enables this bath to operate at an

acidic pH, whereas, the competitive sulfite

gold baths operate at an alkaline pH. The

acidic pH plating bath is more compatible with

photoresist than the alkaline pH baths. Gold

deposited from this plating bath is smooth with

low roughness even though the bath does not

contain any heavy metal grain refiners. This

bath is non-toxic and does not require any

complicated waste treatment because the bath

is free of harmful components such as cyanide,

thallium, and arsenic. The unique chemistry of

this bath enables excellent step coverage and

bath efficiency over two metal turnovers. In

addition, the stress of the gold deposit is very

low at 5-10MPa compressive. This acid sulfite

gold plating bath can be used for a wide range

of applications.

As discussed, pattern plating ranging from 5

to 30+ microns of gold has been demonstrated.

In addition, the excellent throwing power of

this bath has been demonstrated by uniform

gold plating across the backside and in vias.

Also, this bath has been successfully operated

on four production plating tools, numerous

research tools, and various wet benches

demonstrating the versatility of this chemistry.

This plating bath is commercially available as

Elevate® Gold 7990. Future research on this

plating bath will include additional studies to

understand the performance of this chemistry

over 5MTOs.

Acknowledgements

The authors wish to thank the research

team at Technic including Scott Bateson

and Tom Tyson for their work on this

project and Bob Foreman, General

Manager, 1 Zone, LLC, for his valuable

contributions to this paper.

References

1. P. A. Kohl, “Deposition of Gold”

in Modern Electroplating, 5th ed.;

Hoboken, Ontario, Canada: John

Wiley & Sons, 2010, 115-130.

2. T. A. Green. “Gold electrodeposition

for microelectronic, optoelectronic

and microsystem applications,” Gold

Bulletin, vol. 40, pp. 105-114, 2007.

3. S. Dimitrijevic et al., “Non-cyanide

electrolytes for gold plating – a

review,” Int. J. Electrochem. Sci., vol.

8, pp. 6620-6646, 2013.

4. R. J. Morrissey, “A versatile non-

cyanide gold plating system,” Plat.

Surf. Fin., vol. 80, p.75, 1993.

Biographies

Therese Souza received her BS in

Chemistry from Providence College and is a

Senior Research Chemist at Technic Inc.

Contact author: Lynne Michaelson

received her BS in Materials Science &

Engineering from the U. of Michigan, and

her PhD in Materials Science & Engineering

from Massachusetts Institute of Technology.

She is a Senior Materials Scientist at Technic

Inc.; email

LMichaelson@technic.com

R&D Altanova 3601 So. Clinton Ave. South Plainfield, NJ 07080

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5.309 mil

1.012 mil

High Aspect Ratio Load

Board Drilling & Plating

• 0.4mm pitch

• 4.75mm thick

• 37:1 Aspect Ratio

• 1 mil plating

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