Cold Testing / Probing of Semiconductor Die
Historically semiconductor wafers were very seldom probe tested at sub zero degrees Centigrade for production. Any cold probe testing of bare die was usually done only during early product qualification for packaged parts or for an application that required very high reliability levels.
The difficulty in the past was controlling moisture build up and ice formation around the probe tips used to contact the bare die. This meant that cold probing at bare die level was a slow process constantly interrupted by the need to defrost and re-calibrate equipment and was not viable for mass production of wafers.
Therefore to assign a level of reliability and apply specification for parts in production release the common route today for most IDM manufacturers is to perform a “guardbanded” probe test at 25°C where the electrical limits are inset based on the specific design rules used during the product build to simulate performance under cold conditions. The guardbanded probe is still considered to be a reliable benchmark of performance at cold today and is sufficient and accepted for the majority of bare die applications.
However for bare die applications which are specialist such as cryogenics or those which require additional die reliability guarantees or KGD certification then today the situation has improved. Due to enhanced equipment development it is now possible to probe wafers reliably and continuously in a precision cold environment. The major issue of moisture and ice formation is eliminated by probing wafers in a dry moisture free environment. In addition the process can also be automated so that full production runs can be probed and characterised in one sitting which makes the process viable for volume die use.
Cold Probe Testing - Capabilities
- Testing of both bare die & Hybrid substrates
- Precision cold probing down to -65ºC
- Temperature accuracy ±0.5°C (Post calibration)
- Temperature stability ±0.1°C
- Moisture-free environment
- Efficient cooling system permits reliable measurement of devices with high power output and associated heat generation
- Fully automated multiple wafer handling
- Lot characterisation
- Customisable output data and logging