The Formation of Nano-voids in electroless Cu Layers

Abstract

The electrical reliability of multilayer high density interconnection printed circuit boards (HDI-PCBs) is mainly affected by the thermo-mechanical stability of stacked micro via interconnections. Here, a critical failure mode is the stress related crack between the electrolytically filled via and the target pad, commonly known as target pad separation. The junction includes two Cu-Cu-interfaces, one between the target Cu pad and the thin electroless Cu layer and the second between electroless Cu and electrolytic Cu. In this paper we will show that state-of-the-art electroless Cu plating processes are able to provide solid, completely recrystallized and highly reliable stacked via junctions. Defect free interfaces were achieved by using ionic Pd-activators and electroless Cu baths with a cyanide based stabilizer system. Cyanide free electroless Cu baths tend more to the formation of nanometer sized defects, discovered via Transmission Electron Microscopy (TEM). In this case a precise adjustment of single stabilizer components is mandatory to achieve defect free layers. The defects are hollow and were identified as “nano voids”. A critical density of these nano voids weakens the interface, predefines the crack path and reduces the overall reliability of the junction. A precise localization of the nano voids within the junction was enabled by detecting the Ni-containing electroless Cu layer via TEM-Ni mapping. Slower volume exchange of the electroless Cu solution within the blind micro via (BMV) substantially increases the nano void density. The ability of nano voids to migrate and coalesce at elevated temperatures was investigated as well.

Research and Implementation of Robot Vision Scanning Tracking Algorithm Based on Deep Learning

“…Artificial neural network is a hierarchical network formed by widely connecting many simple computing units, which mimics the structure of biological neural networks and mimics the characteristics of biological neurons that can excite and inhibit, learn, and forget, providing a new solution for solving highly nonlinear and complex problems in machine learning. Firstly, the structure of artificial neural network will be briefly introduced [ 17 ].…”

Existing States of Co-Deposited Hydrogen in Electrolessly Deposited Copper Films from EDTA Complex Bath

“…We assume that these nanovoids were formed by the coagulation of superabundant Vac-H clusters and that a large amount of molecular hydrogen is formed by the combination among hydrogen atoms trapped in the vacancies. 15,16,20 The results of TDS measurements suggest that about 75% of the co-deposited hydrogen in the Cu film existed as molecular hydrogen in these nanovoids for a long time. According to an estimation by Graebner and Okinaka, 14 the pressure of hydrogen gas bubbles (molecular hydrogen in nanovoids) in the electrolessly deposited Cu film with a hydrogen concentration of 0.2 at % from the EDTA complex bath is calculated to be 70 MPa, which is comparable to the yield stress of bulk Cu.…”

“…7,8 The co-deposited hydrogen atoms in the Cu films have been recognized as a cause of residual stress generation, 9 ductility loss, [10][11][12][13] and void formation. 9,[14][15][16] These hydrogen-induced phenomena observed in the electroless Cu films have been analyzed and reported in detail by Okinaka and Nakahara et al [10][11][12][13][14]17,18 Since hydrogen generation is inevitable in electroless Cu deposition, previous investigations have been conducted to reduce the hydrogen co-deposition by using additives in the Cu plating bath. 9,11,19 However, the existing states of co-deposited hydrogen in the electroless Cu films and the detailed mechanism of their effects on the microstructure of Cu films have not yet been fully clarified.…”

Quantification of the Nano-Voids in Electroless Deposited Copper Layers Using SiNx TEM Grids

“…In the electroless plated copper layer, nano-voids are considered a cause of via-crack failure. 6 The electroless deposited copper layer with such defects has less ductility; thus, it is more vulnerable to external impacts such as thermal stress, causing malfunctions of the PCB. [7][8][9] Transmission electron microscopy (TEM) is a popular tool for analyzing nano-voids in electroless copper deposited layers by virtue of its high spatial resolution.…”