The presence of gold within a Sn/Pb solder joint accelerates diffusion between the Sn and Ni of the Ni- V/Cu underlying bump metallurgy (UBM), generating early failures. A concentration of 1.2 wt% gold in the solder joint can accelerate time to failure by a factor of 400 [3]. The EDS x-ray microanalysis detection limit for gold in tin / lead solder of about 1.2 wt% gold was found to be above the concentration range of interest (0.1 – 0.5 wt% gold). Due to the reliability impact that even a low concentration of gold can have on solder joints employing Ni-V/Cu UBM, a method using differential scanning calorimetry (DSC) was developed to accurately measure gold concentrations of less than 1 wt% in solder bumps.

Determination of metal bridging failures on plastic encapsulated devices is difficult due to the metal etching effects that occur while removing many of the plastic mold compounds. Typically, the acids used to remove the encapsulation are corrosive to the metals that are found within the device. Thus, decapsulation can result in removal of the failure mechanism. Mechanical techniques are often not successful due to damage that results in destruction of the die and failure mechanism. This paper discusses a novel approach to these types of failures using a silicon etch and a backside evaluation. The desirable characteristics of the technique would be to remove the silicon and leave typical device metals unaffected. It would also be preferable that the device passivation and oxides not be etched so that the failure location is not disturbed. The use of Tetramethylammonium Hydroxide (TMAH), was found to fit these prerequisites. The technique was tested on clip attached Schottky diodes that exhibited resistive shorting. The use of the TMAH technique was successful at exposing thin solder bridges that extruded over the edge of the die resulting in failure.