Wafers FAQ

Do the AC signal lines require a signal and ground contact on the wafer or just one pad?
It is best to provide ground-signal pairs at the wafer in order to minimize ground inductance at the probe-to-wafer interface. Ground-signal-ground is even better. Ground inductance must be closely watched for the high-speed paths, both for insertion loss and for crosstalk to neighboring lines that might share ground return paths. This is particularly important for characterization measurements such as Vector Network Analyzer (VNA) measurements. 

Limited frequency ranges may mitigate these issues. In functional testing applications, it is not unusual to see several digital lines share a ground. 

Some of our pads have a pitch of only X microns. Is this going to pose any problems? 
Our minimum pad pitch is continually being reduced as our process improves. Of course, wider pitches and pads are easier to probe and are more tolerant to operator errors. 

See your local Cascade Microtech representative for the latest specifications on minimum pad pitch and other important probe card parameters. 

How hard are the different metals in contact pads? 
Published hardness numbers vary considerably, but some average numbers are listed below. Note that pure copper and aluminum are very soft, but a few % alloy kicks them into the 400 range.