In wafer testing, a palladium alloy needle usually adopts as a testing medium, which delivers the electric signals of the detected welding pad to the testing machine by directly contacting, to check the status of the electric circuit on the wafer chip. Each needle applies a current of 150mA
~2A, and under a contact pressure of 2~5gram and a resistance of 1~2 ohm to finish the scrub motion on the welding pad. However, improper probing conditions cause a needle softening or burning from electrothermal effect. This study implements a series of conductive experiments simulating the contact situation to observe the electrothermal reactions in probing. A digital video camera was first used to record the conduct process, and then a great deal of colored image was captured in a specified time interval. By analyzing the RGB components of the images, an
image-electric energy model was developed for the palladium alloy cobra needle. Experimental results show that the needle begins turning into yellow when the electric energy up to 3.84 Joules.As the input energy increases, the needle turns to orange-red when the energy reaches 13.44
Joules. Understanding the electrothermoal reaction of the needle is helpful for setting the proper probing parameters to obtain the optimal performance.
