Method for performing parallel stochastic assembly

info:eu-repo/semantics/publishe

Solid state diffusion in Cu-Sn and Ni-Sn diffusion couples with flip-chip scale dimensions

The formation and growth rate of intermetallics of frequently used metallisation systems for flip-chip bumping have been studied and are reported for many years. However, no data are available on diffusion couples with flip-chip processing methods and actual flip-chip scale dimensions. In this paper, the interdiffusion coefficients and activation energies of Cu-Sn and Ni-Sn intermetallic formations are measured on flip-chip bumps with 40 µm bond pad diameter. Also the morphology of the metallurgical reactions is described. Furthermore, the ideal case of a binary diffusion system is seldom present in real-life. In practice, the presence of additional alloying elements has an impact on the intermetallic stoichiometry and even on intermetallic growth and morphology. It is shown that small quantities of Cu in a Ni-Sn system can have a beneficial effect on the Ni consumption but larger quantities result in extreme scalloping of the intermetallic interface.status: publishe

Microstructural investigation of Co-P by TEM

The microstructure of electrodeposited Co-P films was investigated using transmission electron microscopy (TEM). The use ofultramicrotomy for sample preparation made it possible to obtain cross sections parallel to the growth direction of the film.Co-P films deposited under constant current conditions are amorphous and no nonuniformity could be identified at a scale ofa few to a few tens of nanometers. This is in contradiction with the often made assumption that Co-P electrodeposited underconstant current conditions has a columnar microstructure. Co-P layers electrodeposited in pulsed current conditions showa clear multilayer structure. © 2004 The Electrochemical Society. All rights reserved.status: publishe

Filling of microvia with an aspect ratio of 5 by copper electrodeposition

The filling of microvias with a diameter of 5 µm and a depth of 25 µm (aspect ratio of 5) by copper electroplating was investigated. Filling experiments were evaluated by analyzing cross-sections of filled vias with scanning electron microscopy and focused ion beam. The fill-up evolution shows a bottom-up mechanism, also known as superfilling mechanism. The evolution of potential with time (chronopotentiometric measurements) was recorded during the fill-up process of vias and is interpreted based on potentiodynamic polarization measurements. The bottom-up fill mode is affected by the concentration of leveler inside the vias. A differential plating rate that is responsible for bottom-up plating, develops along the profile of the via on depletion of the leveler inside the vias. Since the depleted via is less inhibited, the local electrodeposition rate increases in the via. At the top part and outside the via, the electrodeposition rate is strongly inhibited due to a higher leveler concentration comparable to the one in the bulk electrolyte, what results in a low local electrodeposition rate. In this paper, the contribution of levelers to the bottom-up mechanism during the electrodeposition of copper in microvias is investigated. The observed microstructure supports the superfilling mechanism.status: publishe

Challenges for capillary self-assembly of microsystems

Within the currently rising trend of heterogeneous microsystem integration and packaging, capillary self-assembly emerges as an innovative technique to enhance, complement and eventually replace pick-and-place assembly. Vast literature and experimental data support such claim. Still, the technique needs to overcome some important limitations in order to fully express its potential and earn wide industrial recognition. In this paper, we review and illustrate what are in our opinion the challenges ahead for making part-to-substrate capillary self-assembly reliable andseriously competitive with long-established assembly techniques. After setting self-assembly methods in the context of microsystemassembly and integration technologies, we focus on the standard embodiment of capillary self-assembly, and we describe in details the main, often novel technological steps required for its effective and reproducible performance. This preludes to an outline of what are presently, in our view, the major failure modes affecting the overall yield of the capillary self-assembly technique. Consequently, we propose solutions to face and overcome these challenges, which need to be met to foster the success of this technique.info:eu-repo/semantics/publishe

Establishing solder interconnects in capillary die-to-substrate self-assembly

In this work, we seamlessly include the establishment of multiple lead-free solder interconnects as an integral part of capillary die self-assembly. We demonstrate the mechanical and electrical functionality of electrodeposited indium bumps as interconnects between substrate binding sites and assembled dies. Our results open interesting perspectives for widespread use of the technique for 3D die integration.info:eu-repo/semantics/publishe

Conformal dip-coating of patterned surfaces for capillary die-to-substrate self-assembly

Capillarity-driven self-assembly of small chips onto planar target substrates is a promising alternative to robotic pick-and-place assembly. It critically relies on the selective deposition of thin fluid films on patterned binding sites, which is anyway normally non-conformal. We found that the addition of a thin wetting sidewall, surrounding the entire site perimeter, enables the conformal fluid coverage of arbitrarily shaped sites through dip-coating, significantly improves the reproducibility of the coating process and strongly reduces its sensitivity to surface defects. In this paper we support the feasibility and potential of this method by demonstrating the conformal dip-coating of square and triangular sites conditioned with combinations of different hydrophobic and hydrophilic surface chemistries. We present both experimental and simulative evidence of the advantages brought by the introduction of the wetting boundary on film coverage accuracy. Application of our surface preparation method to capillary self-assembly could result in higher precision in die-to-substrate registration and larger freedom in site shape design.status: publishe

Conformal dip-coating of patterned surfaces for capillary die-to-substrate self-assembly

Capillarity-driven self-assembly of small chips onto planar target substrates is a promising alternative to robotic pick-and-place assembly. It critically relies on the selective deposition of thin fluid films on patterned binding sites, which is anyway normally non-conformal. We found that the addition of a thin wetting sidewall, surrounding the entire site perimeter, enables the conformal fluid coverage of arbitrarily shaped sites through dip-coating, significantly improves the reproducibility of the coating process and strongly reduces its sensitivity to surface defects. In this paper we support the feasibility and potential of this method by demonstrating the conformal dip-coating of square and triangular sites conditioned with combinations of different hydrophobic and hydrophilic surface chemistries. We present both experimental and simulative evidence of the advantages brought by the introduction of the wetting boundary on film coverage accuracy. Application of our surface preparation method to capillary self-assembly could result in higher precision in die-to-substrate registration and larger freedom in site shape design.info:eu-repo/semantics/publishe

Challenges for capillary self-assembly of microsystems

Within the currently rising trend of heterogeneous microsystem integration and packaging, capillary self-assembly emerges as an innovative technique to enhance, complement and eventually replace pick-and-place assembly. Vast literature and experimental data support such claim. Still, the technique needs to overcome some important limitations in order to fully express its potential and earn wide industrial recognition. In this paper, we review and illustrate what are in our opinion the challenges ahead for making part-to-substrate capillary self-assembly reliable and seriously competitive with long-established assembly techniques. After setting self-assembly methods in the context of microsystem assembly and integration technologies, we focus on the standard embodiment of capillary self-assembly, and we describe in details the main, often novel technological steps required for its effective and reproducible performance. This preludes to an outline of what are presently, in our view, the major failure modes affecting the overall yield of the capillary self-assembly technique. Consequently, we propose solutions to face and overcome these challenges, which need to be met to foster the success of this technique.status: publishe