Refined Wire Bond Pad Cratering Testing Method

Wire bonding is crucial in semiconductor packaging to create electrical connections from the die to the package using fine wires typically made up of copper or gold. However, unoptimized first bond parameters, specifically mechanical force and ultrasonic energy, can cause cracks in the interlayer dielectric (ILD) within the die, leading to electrical discontinuities and device reliability issues. Thus, Joint Test Action Group (JTAG) communication and leakage failures during electrical testing often signify ILD cracks which are further verified by destructive pad cratering test through chemical etching. Generally, good units yield clear bond pads, while those with ILD cracks exhibit dimples due to unevenness from metal layer separation. However, recent leaded quad flat package lots presented inconclusive pad cratering results due to abnormal brownish bond pads, attributed to their unique die structure where the barrier metal rests on a softer metal layer, M7, instead of the typical ILD which is harder. Due to reduced support, the barrier metal is more prone to minor cracks or pinholes, allowing the etching chemical to penetrate, dissolve the M7 layer underneath, and expose subsequent layers. This vulnerability led to the refinement of the current pad cratering testing method through modifications of testing parameters such as the etching solution, soaking temperature and duration, and incorporating ultrasonic cleaning along with its solution. Results obtained demonstrated the effectiveness in detecting the presence of ILD cracks and were further verified through cross-section analysis and attribute measurement system analysis (MSA). This refinement resulted in a remarkable 74% reduction in scrap cost compared to the baseline method.