When you’re doing RF measurements you need to make sure you are measuring your device and not the test setup. Enter calibration substrates. FormFactor delivers a set of standardized Impedance Standard Substrates that are ready to go out of the box; ready to handle standard pitches. This however, doesn’t always work well for more complex designs on your device – a GSSG or any number of different combinations that isn’t a standard GSG layout, such as an array or non-regular pitch.

Now we can deliver custom calibration substrates that can address specific layouts for calibration that match the layout of the device under test (DUT).

The custom calibration substrates provide several advantages when compared to standard calibration substrates:

1. Superior calibration accuracy – The ability to match DUT layout improves RF calibration for better yield and the reduced site-to-site variation in probe cards eliminates the need for complex correlation between engineering and production measurements. In addition, verification standards can be placed on the ISS to confirm calibration stability in situ (offset open and offset short).

2. Versatile and cost-effective – Custom calibration substrates are capable of non-50 Ω loads to match the impedance of the device, such as for PAs, LNAs, and TIA Also, you can reduce calibration time by calibrating a multi-site probe card in a single touchdown instead of calibrating each site in series.

3. It’s a complete probing solution set – The probe, calibration substrate, and calibration coefficients are delivered at the same time, which greatly improves speed and efficiency to first data.

In general, calibration substrates need to provide a long lifetime – preferably lasting longer than a single probe card. In addition, it needs stable contact resistance (CRES) in order to deliver repeatable RF calibration. And certainly it needs to deliver accuracy.  We have characterized our custom calibration substrates and have shown that a single tile will last for the lifetime of the DUT, as well as providing stable CRES with minimal maintenance.

It used to be common to do a correlation between the engineering probe and the probe card. With custom calibration substrates it’s much simpler now because we do a full calibration. In fact, with our larger customers it’s becoming standard practice to use the custom calibration substrates given the advantages that they provide.

For more details on our custom calibration substrates, visit our website or download the technical brief (PDF).