Here are the highlights from Session Two – High Temperature Probing of the 20th annual IEEE Semiconductor Wafer Test Workshop (SWTW)
Keith Breinlinger, FormFactor, “Addressing the Operating Challenges of Full Wafer Contactors”:
Keith started by providing a real good analogy of the challenge of wafer probing in terms of contacting the edge of each sheet of papers in a sixteen high foot stack. He used the new full wafer probe cards SmartMatrix (DRAM) and the TouchMatrix (NAND FLASH) as the basis of his presentation.
FormFactor uses the concept of a Super Bond Pad where all the probe marks for an entire wafer at the extreme hot and cold operating temperatures are graphically overlaid to provide a measure of the performance of the card. With the SmartMatrix cards he showed improvement over time for all the dual (hot & cold) temperatures cards shipped that showed they are now capable of 34 µm x 43 µm bond pads with an operating range of 100 C.
He also identified two options that FormFactor is now providing in terms of probe card materials:
- Si wafer matched coefficient of thermal expansion (CTE) for use as a dual temperature card. These cards are typically ready to probe after about 30 minutes soaking at the desired temperature – i.e. the probe movement error is within the acceptable range. These cards typically reach thermal equilibrium after a full hour.
- Single temperature material with two classes:
- Class I – “Zero Soak” – the material is insensitive to changes in temperature (i.e. a CTE approaching zero). Typically the probes will move less than 2 µm over time and less than 0.5 µm movement at wafer change (when the wafer chuck is no longer under the probe card heating it). Therefore, probing can start immediately without a long soak period.
- Class II – “Quick Soak” – probing can start after about 10 minutes temperature soak. And this material reaches equilibrium after 20 to 30 minute temperature soak. It will typically moves 5 to 7 µm at wafer change.
Lou Molinari, ESA Corporation/Probe Solutions, “The Thermal Frontier … High Temp probing System Solutions and Analysis”:
Probe Solutions is a division of ESA Corporation to help develop new solutions in the probe space.
Most solutions in regards to thermal issues are addressing the probe card design but not operational environment. Design issues address the fixed cost but they can’t be changed once the design is finished. Where the environment impacts the operating cost (i.e. the loss of revenue) and should also be addressed.
As such they developed the Environmental Probe Card Control Unit (PCECU) heater. This heater is mounted either on or in the probe card tray. The probe cards sits on the tray when it is loaded in to the wafer prober. In their modeling and initial testing they have found that the probe card reaches thermal equilibrium approximately 50% faster by using the PCECU heater. Therefore, the heater the test cell is operational faster after a probe card change reducing the operation cost.
Jerry Broz, General SWTW Chair, “Remembering Good Friends of SW Test”:
Jerry took time during this session to once again pay tribute to those key individuals lost to the test community in the past year.
Note: I will post the link for the slides once they become available.