Unique Solution to Probe Constraints for High Current Limit Testing at Probe
If one is not careful, high current testing at probe can be an accident waiting to happen. Not only does each probe needle need to be precisely placed, but their current carrying capabilities need to be accounted for in all situations. In the early stages test development of one particular device, not all of these factors were properly accounted for. At first, it seemed as though alignment issues were causing various wafers to have several rows of continuity failures. Upon further investigation, however, it was noticed that not only were the probe cards aligned properly, but a handful of probe needles appeared to have reduced in length over the course of the wafer probe. After removing said needles from the probe card, severe warping was observed. This warping is typically caused by excessive current attempting to be sourced/sank through the needle.
After the HW was determined to be designed as intended, the Si design was then explored to ensure that each probe pad would only see the maximum 500mA current specified per probe needle. In fact, the design showed that where 4 probe pads were expected to supply up to 2A of current, only 2 probe pads were actually sourcing/sinking current. As a result, clever utilization of space was adopted to integrate 2 probe needles onto one probe pad. This turned a situation where 4 probe pads required 4 probe needles, to a situation where now only 2 probe pads were needed to encompass 4 probe needles. Such a novel technique was able to save time and money as well as eliminate the need for a Si re-design.