Letter 31028

Seeking 100um patterned plating on glass, small volume  

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Good morning,

We have a requirement for a plating process of some form to provide a stand-off of 100um (4 mils) +/- 10um on 150mm (6") round glass (borofloat) wafers. The wafers are 700um thick and coated with a custom anti-reflective coating (ARC). We need to build up a spacer layer to provide a hermetic seal. Thus, we wish build up a series of oval (race-track-like) rings on one side of the wafer; the other side must remain clear and undeposited. On top of this ring, we will print a low-melting temperature sealing glass (frit) for hermtic sealing to a semiconductor device. The frit burnout and bonding processes will take place over several hours at 400-450C. Thus, the plated metal must be stable at these temperatures, cannot by too porous and must have intimate (strong) adhesion to the glass substrate. We can provide a patterned seed layer of arbitrary composition (we have a CHA evaporator). The ARC layer has a top coat of silicon dioxide and is likely to be fairly robust to most chemistries. The pattern is a repetative series of rings and can easily be interconnected with a contact point provided, thus electro-plating or electroless-plating can be considered. We have considered using 100um of plated nickel, but have been told that the material is too "stressy" and that it will cause our wafer to curl or bow. The CTE of the borofloat is about 3.2 ppm/C over these temperature ranges. Since we are a semiconductor foundry, we are looking for a firm that is comfortable with our severe cleanliness requirements (the glass will be used for an optical component in the telecom industry). Testing would involve pull-testing sealed parts, and evaluating hermeticity through temperature/humidity cycling. Our volumes are likely to be small at this point, needing a half-dozen to a dozen parts for testing purposes and needing perhaps five-to-ten parts per month.

Thank you for your time,

Kevin A. Shaw, PhD
MEMS Semiconductor foundry - Ithaca, New York, USA

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