Novel analysis model for investigation of contact force and scrub length for design of probe card

摘要

Fabrication defects in IC chips are generally identified using a multi-layer needle probe card. To prolong the life of the card, the needles in each layer should experience a similar contact force and should produce a scrub mark of minimal length. To facilitate the probe card design process, this paper proposes an analytical model for evaluating the contact force and scrub mark length of a single-needle probe as a function of the overdrive distance. The model is based on Castigliano's displacement theorem and takes account of both the material and the geometric properties of the needle. The validity of the analytical model is confirmed by performing a series of finite-element simulations at overdrive distances ranging from 30 to 70 μm. In addition, experimental probe card tests are performed using a tungsten needle probe and an aluminum pad. A good agreement is found between the experimental and analytical results for overdrive distances in the range 50 ± 10 μm. Overall, the results presented in this study confirm that the proposed analytical model provides an accurate and convenient means of determining the optimal needle probe design given maximum permissible values of the contact force and scrub mark length, respectively.