The method for measurement of the real Overdrive

Electrical testing method is the most efficient and cost-effective method to determine whether semiconductor chips are defective. In the wafer state, an interface device called a probe card is needed to physically contact with the pad for electrical test. Recently, the environment for wafer test is getting more challenging. This is because of decrease in pad-size due to device shrinkage, and increase in the number of pins due to multi parallelism of a probe card. First of all, it is important to make good probe cards, but it is also important to set the correct parameters of the probe card on the production line. There are many parameters to physically or electrically control the probe card. The Over drive (O/D) is an important parameter that controls the contact of the probe card pin with the wafer pad. The programed O/D can be easily known through the monitor of prober machine, but it is difficult to know how much contact is actually made between the tip and the pad. In this paper, we propose a new method to measure real O/D without using sensor. In this study two types of pins are used, one is the normal pin and the other is the plastic deformation pin. We will attempt to infer the real O/D through the amount of the plastic deformation of a pin. Precise control of the O/D and the planarization in this way, can improve the contact quality. From the amount of deformation, depending on the applied force, we can infer the real O/D amount. It can be seen by comparing the scrub size and height differences of two pins and the real O/D is calculated by using the plastic deformation pin. Based on this real O/D data, by controlling O/D and leveling in the direction of reducing contact resistance, we can avoid the test failure and improve the yield.