Jaspreet S. Gandhi

Die-attach materials for high-density memory stacked die packaging

In this paper, several die attach adhesives (A to E) from different suppliers are investigated. The objective is to better understand the comprehensive properties of adhesives and to choose the right adhesive for a high-density memory stacked die packaging with improved packaging reliability. Differential scanning calorimetry (DSC) is used to investigate curing behavior and curing kinetics. Thermogravimetric analysis (TGA) is utilized to characterize the thermal and thermooxidative stability. The adhesion of die attach adhesives is determined at different temperatures. Dynamic mechanical analysis (DMA) and the test of fracture toughness of adhesives are carried out. In addition, the failure mode of adhesives after a die shear test is also discussed. The results show that adhesive A is more suitable for high-density memory stacked die packaging. This fundamental study can also help select die attach materials for other types of electronic packaging.

Adhesion improvement for polymer dielectric to electrolytic-plated copper

Copper is one of the common metals used in the semiconductor backend process and wafer level packaging. A photo definable polymer layer is usually used to passivate the Cu metal. Acceptable adhesion between the polymer layer and Cu is a very important factor to achieve high reliability for the IC component. The purpose of this paper is to investigate how to improve the adhesion strength between spin-on polymer dielectric material and electrolytic-plated Cu. Because adhesion strength is affected by the type of metal surface treatment prior to polymer coating, it is important to find a practical method for Cu surface treatment wafer process. Three types of treatment methods, including plasma, thermal, and wet process, were tried on the plated Cu surface. X-ray photoelectron spectroscopy (XPS) results are reported for the surface properties after treatment. Adhesion strength between the polymer layer and the Cu surface is reported as measured by manual tape, nano-indentation scratch, and four-point bending methods. Our results show that cleaning the Cu surface with dilute acetic acid significantly increases the adhesion between Cu and the polymer layer. We also report results for the change in Cu surface properties as a function of time after clean.

Investigation of thermo-mechanical stresses and reliability of 3D die-stack structures by synchrotron x-ray micro-diffraction

In this work, thermo-mechanical stresses and reliability of 3D die-stack structures developed for the Hybrid Memory Cube (HMC) technology are investigated using experiments and modeling analysis. Synchrotron x-ray micro-diffraction measurements are used to directly measure the stress distribution around Cu vias in different die levels. High resolution stress mappings are obtained and verified by finite element analysis (FEA). The FEA is applied to estimate the stress effect on device mobility changes and the warpage of the integrated structure.