8 research outputs found
RLC effects in fine pitch anisotropic conductive film connections
The resistance, capacitance and inductance of Anisotropic Conductive Film (ACF) connections determine
their high frequency electrical characteristics. The presence of capacitance and inductance in the ACF joint
contributes to time delays and crosstalk noise as well as simultaneous switching noise (SSN) within the
circuit. The purpose of this paper is to establish an experimental method for estimating the capacitance and
inductance of a typical ACF connection. This can help to provide a more detailed understanding of the high
frequency performance of ACF assemblies.
Design/methodology/approach
Experiments on the transient response of an ACF joint were performed using a digital oscilloscope capable
of achieving the required ns resolution. An equivalent circuit model is proposed in order to quantify the
capacitance (C) and inductance (L) of a typical ACF connection and this model is fitted to the experimental
data. The equivalent model consisted of two resistors, an inductor, and a capacitor.
Findings
The capacitance and inductance of a typical ACF connection were estimated from the measured transient
response using Kirchhoff's Voltage Law. The method for estimation of R, L, and C from the transient
response is discussed, as are the RLC effects on the high frequency electrical characteristics of the ACF
connection.
Research limitations/implications
There was decay time deviation between the calculation and the experiment. It may be resulted from the
skin effect in the high frequency response and the adhesive surrounding joint as well. The main reason may
be the capacitance dielectric lost. Further research work will be done to test the dielectric lost in the ACA
joint.
What is original/value of paper
This paper presents a new method to characterise the high frequency properties of ACA interconnections
and will be of use to engineers evaluating the performance of ACF materials in high frequency applications
Microstructures and properties of new Sn-Ag-Cu lead-free solder reinforced with Ni-coated graphene nanosheets
© 2015 Elsevier B.V. All rights reserved. This paper deals with microstructures and properties of SAC305 lead-free solder reinforced with graphene nanosheets (GNS) decorated with Ni nanoparticles (Ni-GNS). These Ni-coated GNS nanosheets were synthesized by an in-situ chemical reduction method. After morphological and chemical characterization, Ni-GNS were successfully integrated into SAC305 lead-free solder alloy with different weight fractions (0, 0.05, 0.1 and 0.2 wt.%) through a powder metallurgy route. The obtained composite solders were then studied extensively with regard to their microstructures, wettability, thermal, electrical and mechanical properties. After addition of Ni-GNSs, cauliflower-like (Cu,Ni)6 Sn5 intermetallic compounds (IMCs) were formed at the interface between composite solder joint and copper substrate. Additionally, blocky Ni-Sn-Cu IMC/GNS hybrids were also observed homogenously distributed in the composite solder matrices. Composite solder alloys incorporating Ni-decorated GNSs nanosheets showed slightly reduced electrical resistivity compared to the unreinforced SAC305 solder alloy. With an increase in the amount of Ni-GNS, the composite solders showed an improvement in wettability with an insignificant change in their melting temperature. Mechanical tests demonstrated that addition of 0.2 wt.% Ni-GNS would result in 19.7% and 16.9% improvements in microhardness and shear strength, respectively, in comparison to the unreinforced solders. Finally, the added Ni-GNS reinforcements in the solder matrix were assessed with energy-dispersive X-ray spectroscopy, scanning electron microscopy and Raman spectroscopy
Microstructural evolution of 96.5Sn–3Ag–0.5Cu lead free solder reinforced with nickel-coated graphene reinforcements under large temperature gradient
In this study, 96.5Sn–3Ag–0.5Cu (SAC305) lead-free composite solder containing graphene nanosheets (GNS) decorated with Ni nanoparticles (Ni-GNS) was prepared using a powder metallurgy method. A lab-made set-up and a corresponding Cu/solder/Cu sample design for assessing thermo-migration (TM) was established. The feasibility of this setup for TM stressing using an infrared thermal imaging method was verified; a temperature gradient in a solder joint was observed at 1240 K/cm. Microstructural evolution and diffusion of Cu in both plain and composite solder joints were then studied under TM stressing conditions. Compared to unreinforced SAC305 solder, the process of diffusion of Cu atoms in the composite solder joint was significantly reduced. The interfacial intermetallic compounds (IMCs) present in the composite solder joint also provide a more stable morphology after the TM test for 600 h. Furthermore, during the TM test, the Ni-GNS reinforcement affects the formation, migration and distribution of Ni–Cu–Sn and Cu–Sn IMCs by influencing the dissolution rate of Cu atoms
Performance of Sn–3.0Ag–0.5Cu composite solder with TiC reinforcement: physical properties, solderability and microstructural evolution under isothermal ageing
This paper is focused on the effect of TiC nano-reinforcement that was successfully introduced into a SAC305 lead-free solder alloy with different weight fractions (0, 0.05, 0.1 and 0.2 wt%) through a powder-metallurgy route. Actual retained ratios of TiC reinforcement in composite solder billets and solder joints were quantitatively analysed. The obtained SAC/TiC solders were also studied extensively with regard to their coefficient of thermal expansion (CTE), wettability and thermal properties. In addition, evolution of interfacial intermetallic compounds (IMCs) and corresponding changes in mechanical properties under thermal ageing were investigated. Only about 10%–30% of initial TiC nanoparticles added were found retained in the final composite solder joints. With an appropriate addition amount of TiC nanoparticles, the composite solders exhibited an improvement in their wettability. A negligible change in their melting point and a widened melting range were found in composite solders containing TiC reinforcement. Also, the CTE of composite solder alloys was effectively decreased when compared with the plain SAC solder alloy. In addition, a growth of interfacial IMCs in composite solder joints was notably suppressed under isothermal ageing condition, while their corresponding mechanical properties of composite solder joints significantly outperformed those of non-reinforced solder joints throughout the ageing period
Effects of bandwidth limitations on the localized state distribution calculated from transient photoconductivity data
The possible effects of experimental bandwidth limitation on the accuracy of the energy distribution
of the density of localized states (DOS) calculated from transient photoconductivity data by the
Fourier transform method is examined. An argument concerning the size of missing contributions to
the numerical Fourier integrals is developed. It is shown that the degree of distortion is not
necessarily large even for relatively small experimental bandwidths. The density of states calculated
from transient photodecay measurements in amorphous arsenic triselenide is validated by
comparing with modulated photocurrent data. It is pointed out that DOS distributions calculated
from transient photoconductivity data at a high photoexcitation density are valid under certain
conditions. This argument is used to probe the conduction band tail in undoped a-Si:H to energies
shallower than 0.1 eV below the mobility edge. It is concluded that there is a deviation in the DOS
from exponential at about 0.15 eV below the mobility edge
Retained ratio of reinforcement in SAC305 composite solder joints: effect of reinforcement type, processing and reflow cycle
Purpose
This paper aims to systematically study the effect of reinforcement type, processing methods and reflow cycle on actual retained ratio of foreign reinforcement added in solder joints.
Design/methodology/approach
Two kinds of composite solders based on SAC305 (wt.%) alloys with reinforcements of 1 wt.% Ni and 1 wt.% TiC nano-particles were produced using powder metallurgy and mechanical blending method. The morphology of prepared composite solder powder and solder pastes was examined; retained ratios of reinforcement (RRoR) added in solder joints after different reflow cycles were analysed quantitatively using an Inductively Coupled Plasma optical system (ICP-OES Varian-720). The existence forms of reinforcement added in solder alloys during different processing stages were studied using scanning electron microscope, X-ray diffractometry and energy dispersive spectrometry.
Findings
The obtained experimental results indicated that the RRoR in composite solder joints decreased with the increase in the number of reflow cycles, but a loss ratio diminished gradually. It was also found that the RRoR which could react with the solder alloy were higher than that of the one that are unable to react with the solder. In addition, compared with mechanical blending, the RRoRs in the composite solders prepared using power metallurgy were relatively pronounced.
Originality/value
Present study offer a preliminary understanding on actual content and existence form of reinforcement added in a reflowed solder joint, which would also provide practical implications for choosing reinforcement and adjusting processing parameters in the manufacture of composite solders
Study of self-alignment of μBGA packages
In this paper, a detailed study of the self-alignment
of BGA packages is presented. Complete self-alignment can be
achieved even for a misalignment of the package of larger than
50% off the test board pad centres. A small residual displacement
of the package from perfect alignment after reflow is observed.
The reason for this displacement is the action of gas flow viscous
drag on the package during reflow. The use of eutectic SnPb solder
paste slightly reduces self-aligning ability, due to the increase in
the solder volume, which reduces the restoring force. Exposure of
the solder paste to a 25 C and 85% RH humidity environment
also has a detrimental effect on the self-alignment of the BGA
package, due to solvent evaporation and moisture absorption in
the paste causing solderability degradation. The self-alignment of
the package is also affected when there is slow spreading of molten
solder on the pad surface. This is attributed to the reduction of
restoring force due to the decrease in effective wetting surface area
of the board pad
Thermo-migration behavior of SAC305 lead-free solder reinforced with fullerene nanoparticles
In this work, SAC305 lead-free solder reinforced with 0.1 wt. % fullerene nanoparticles was prepared using a powder metallurgy method. A lab-made setup and a corresponding Cu/solder/Cu sample for thermo-migration (TM) test were designed and implemented. The feasibility of this setup for TM stressing was further verified with experimental and simulation methods; a temperature gradient in a solder seam was calculated as 1070 K/cm. Microstructural evolution and mechanical properties of both plain and composite solder alloys were then studied under the condition of TM stressing. It was shown that compared to unreinforced SAC305 solder, the process of diffusion of Cu atoms in the composite solder seam was remarkably suppressed. After the TM test for 600 h, Cu/solder interfaces in the composite solder seam were more stable and the inner structure remained more intact. Moreover, the addition of fullerene reinforcement can considerably affect a distribution of Cu6Sn5 formed as a result of dissolution of Cu atoms during the TM test. Hardness data across the solder seam were also found notably different because of the elemental redistribution caused by TM