Density Interconnect Printed Circuit Boards Research Articles

3-((2-ethoxyethanethioyl)thio)propane-1-sodium sulfonate as a new accelerator for copper electroplating: Electrochemical and theoretical calculation studies

Superfilling of blind holes is essential for a high density interconnect printed circuit board (PCB), for which accelerators are essential for its high quality. However, the mechanical properties of copper obtained by electroplating with accelerators commonly used in industry still need to be further improved. It has been reported that 3-N,N-dimethylaminodithiocarbamoyl-1-propanesulfonic acid (DPS) can improve the copper crystal orientation and optimize the microstructure of copper plating by utilizing its CS bond. Based on this behavior, in this paper, 3-((2-ethoxyethanethioyl)thio)propane-1-sodium sulfonate (ETPS), an organic compound containing dithioester (─C(═S)─S─) special functional groups is proposed as a new accelerator for brightening coating. According to the experimental results, it is found that with ETPS as the accelerator, the superfilling of blind holes can be achieved with the reduced grain size and enhanced Cu (1 1 1) crystal surface for the copper electroplating layers; the copper microstructure with fine grains could contribute to improve the mechanical properties of copper plating. Molecular dynamics calculations have demonstrated that the inclusion of CS double bond can enhance the adsorption of ETPS on the surface of copper, leading to the accelerated deposition process of copper. This work will promote the research and development of new accelerators in the future.

Effect of electroless Cu depositions for micro-via structure and thermal cycling reliability

Micro-via plays an important role in high density interconnect printed circuit boards, which provides electrical conduction among different ICs. Recently, it has been found that the micro-vias suffer reliability problems like cracking and delamination due to the poor quality of the electroless Cu layer. In this work, we compared two different electroless Cu depositions, a traditional electroless Cu deposition method that uses Ni as a stress-regulating additive and a newly developed “OPC-FLET” Cu deposition method without Ni additive. These two Cu depositions were comprehensively investigated by using SEM and TEM characterizations. It is found that the traditional electroless Cu method can induce nanovoids in the deposition layer, whereas the OPC-FLET method can create a nanovoid-free electroless Cu layer. The OPC-FLET method is regarded as a more reliable method for micro-via preparation due to its flawless structure. According to the EDS analysis results, the incorporation of Ni can be regarded as the main culprit for the nanovoids, which can speed up the electroless Cu reaction and thus induce abundant hydrogen bubbles. Meanwhile, 5 times reflowing processes (220 °C, 5 min) were implemented to observe the effects of nanovoids on the micro-via structure and a thermal cycling test ranging from −55 °C to 150 °C was also conducted to investigate the reliability of these two micro-via structures.

Nanovoid Formation at Cu/Cu/Cu Interconnections of Blind Microvias: A Field Study

Abstract A key factor for a high electrical reliability of multilayer High Density Interconnection Printed Circuit Boards (HDI PCBs) is the thermomechanical stability of stacked microvia interconnections. With decreasing via sizes and higher numbers of interconnected layers, the structural integrity of these interconnections becomes a critical factor and is a topic of high interest in current research. The formation of nanovoids and inhibited Cu recrystallization across the interfaces are the two main indications of a weak link from the target pad to the filled via. Based on TEM/EDX measurements on a statistically relevant number of stacked and blind microvias produced in the industrial field, different types of nanovoid phenomena are revealed at the Cu/Cu/Cu junction. The types of nanovoids were categorized relating to the time of appearance (before or after thermal treatment), the affected interfaces or layers and the impact on the Cu recrystallization. The main root causes for each void type are identified and the expected impact on the thermomechanical stability of the via junction is discussed.

The Formation of Nano-voids in electroless Cu Layers

ABSTRACTThe 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.

HDI PCB Rogowski Coils for Automated Electrical Power System Applications

This paper presents and discusses the results of analysis and experimental studies of the metrological characteristics of Rogowski coils made in high density interconnect printed circuit boards technology. The purpose of the research and analysis was to determine the possibility of their use in the metering units of automated electrical power systems. Particular emphasis is placed on the formation of the resonant characteristics as well as to provide suitable resistance to external interfering electromagnetic fields. This allows, inter alia, the use of Rogowski coils for detection of interfering transmissions power line communication high-frequency conductive currents. Based on the obtained results, conclusions and recommendations for practice are formulated.

Effects of Voiding on the Degradation of Microvias in High Density Interconnect Printed Circuit Boards Under Thermomechanical Stresses

Printed circuit boards (PCBs) are made of several dielectric layers stacked on top of each other. These layers could be standard PCB core board or high density interconnect (HDI) layers. Microvias allow signal and power transmission between the HDI layers of the PCBs. The presence of voiding in filled microvias has raised concerns in industry about how they affect the degradation of microvias during the life cycle of the product. Voids can vary widely in shape and size and have been observed in both stacked and single-level microvias. This paper examines whether the presence of voids alone is responsible for the degradation of microvias, or if parameters such as void size and void shape have an influence as well. Both voided and nonvoided microvias were tested together using liquid-to-liquid thermal shock as the accelerated testing method to understand their different behaviors under thermomechanical stresses.

A Parameters Optimization of the CO<sub>2</sub> Laser Drilling Process for HDI Microvia Fabrication

The blind via holes formation by laser drilling is one of the key technologies for demanding high density interconnect printed circuit boards. In this paper , the drilling conditions of drilling the blind via holes and the quality of the drilled holes are examined using a CO2 laser source against the FR4 board without copper foil.We chose laser energy,pulse shot,pulse width and diameter of beam as the experimental parameter . The results showed that laser energy and beam diameter played a more important role on changing the blind vias’ diameter than pulse shot and pulse width .While the pulse shot and pulse width take more important role in changing the depth of vias.

Electrically Mediated Copper Electrodeposition for Interconnect Packaging and High Density Interconnect Printed Circuit Board Applications

not Available.

An innovative “ChemicalVia” process for the production of high density interconnect printed circuit boards

The ChemicalVia process, patented by CERN, provides a new method of making microvias in high‐density multilayer printed circuit boards of different types, such as sequential build‐up (SBU), high density interconnected (HDI), or laminated multi‐chip modules (MCM‐L). The process uses chemical etching instead of laser, plasma or other etching techniques and can be implemented in a chain production line. This results in an overall reduced operation and maintenance cost and a much shorter hole production time as compared with other microvia processes.

Chemical and mechanical adhesion mechanisms of sputter-deposited metal on epoxy dielectric for high density interconnect printed circuit boards

Strong chemical reactions between metal and polymer substrates significantly enhance adhesion of the metal to the polymer. This study investigated the adhesion of three types of thin film metals, including Cu, NiCr, and Cr, to a fully epoxy-based polymer. Before depositing these thin film metals, the epoxy surface was treated with either an Ar or O/sub 2/ plasma etch. It was found that NiCr and Cr produced higher peel strengths than Cu, but NiCr and Cr did not produce different peel strengths than each other. It was also found that O/sub 2/ plasma etch produced significantly higher peel strengths than Ar plasma etch for Cu and Cr, but not for NiCr. An XPS (X-ray photoelectron spectroscopy) study was performed to investigate the reactivities and possible chemical adhesion mechanisms of the metal thin films with the epoxy. It was determined that Cr reacted more strongly than Ni in forming metal oxide at the metal-epoxy interface. Cu was not seen to react strongly in forming oxide with the epoxy. Thermodynamic information supported the relative amounts of oxides found by XPS. Thermodynamic information also suggested that O/sub 2/ plasma etch did not produce significantly higher adhesion than Ar plasma etch on the NiCr samples due to the large Ni component of the NiCr thin film. An AFM (atomic force microscopy) study was performed to investigate possible mechanical adhesion mechanisms. Implications of the AFM results were that the main adhesion mechanism for all samples was chemical and that the Cu oxide that was available on the Cu samples was beyond the detection limits of the XPS equipment.

Electrical design and simulation of high density printed circuit boards

High density interconnect printed circuit board technology enables significant board size and layer count reduction. Thinner inner layer dielectric materials, reduced line widths, and closer spaced components inherent in high density board technology require a change in electrical design methodology. Most notably, the thinner dielectric thickness significantly impacts the electrical performance of the circuit board with respect to crosstalk, board capacitance, via inductance, and controlled impedance. Via inductance is significantly reduced as mechanically drilled through hole vias are replaced with microvias. Distributed capacitance will tend to increase because of the thinner dielectric layer and crosstalk between signal traces run on adjacent layers may also increase. Using either FR-4 type epoxy (diel, cnst.=4.0) or higher performance materials (diel, cnst.=2.8) conventional controlled impedance structures such as a stripline, microstrip, and coplanar waveguide are possible to design using current manufacturing capabilities. A 50 /spl Omega/ impedance can be achieved by a microstrip or a coplanar waveguide using either dielectric material. The stripline can only achieve approximately 35 /spl Omega/ with the higher performance material and 25 /spl Omega/ with the FR-4 type epoxy material. A 500 mW radio frequency receiver and transmitter module operating at 467 MHz was successfully fabricated using a three layer build-up high density circuit board. The circuit board construction had one build-up layer fabricated with a liquid epoxy material. The circuit board electrical design incorporated microstrip, stripline, and coplanar waveguide controlled impedance structures. The results of the electrical performance measurements indicated that transmitted power, receiver sensitivity, and frequency specification performance were similar to a six layer board manufactured with conventional technology.