Substrate Surface Finish Research Articles

Design of an Environmental Barrier Coating Bond Strength Test Coupon

Abstract The bond strength of an environmental barrier coating (EBC) to a substrate such as a silicon carbide fiber/silicon carbide matrix (SiC/SiC) ceramic matrix composite (CMC) is a function of coating application parameters, matrix surface roughness, and environmental exposure, which results in the formation of a thermally grown oxide layer (TGO) layer. Current estimates of the EBC bond strength to a substrate are made assuming that the applied force divided by pull tab area is a representative metric. Although this is an expedient method for rapid strength estimates, the process of bonding the EBC to a pull-tab creates thermo-elastic residual stresses that are superimposed with the applied tensile load. Minimization of these stresses via test specimen design should give the most realistic estimate of EBC bond strength. We examine the residual stresses imposed on the EBC by cooling of an adhesive layer bonded to various metal and ceramic tabs. The results are extended to examine the stress distribution in a TGO layer formed on a Plasma Spray-Physical Vapor Deposited (PS-PVD) Yb2Si2O7 (ytterbium disilicate) EBC. An EBC/substrate coupon that overhangs a titanium or Kovar® pull tab is recommended in order to minimize thermal stresses, avoid edge effects, and provide an acreage strength measurement. The test method is sensitive to changes in substrate surface finish and oxidation time.

The role of additively manufactured niobium alloy C103 substrate's surface finish and corner geometry on the silicide diffusion coating's performance

Nb-based C103 is an increasingly relevant material for aerospace applications due to recent advances in additive manufacturing (AM). AM enabled complex component geometries, along with the associated surface roughness, are a challenge to the survival of environmental barrier coatings (EBCs), like R512E. EBCs are necessary to provide protection for the oxidation susceptible C103 substrates in elevated temperature, oxidizing environments. This work leveraged cyclic thermal exposures to understand the role of AM surface finish on the residual stress, the oxidation protection mechanisms, and the survivability of the R512E coated C103, with insight into the corner geometry-dependent performance supported by finite element modeling (FEM). The experimental characterization indicated that the rough surface finish from AM resulted in increased voids within the build layers in the diffusion formed coating, which in conjunction with tensile residual stress along the substrate interface, negated the coating protection during thermal cycling. Conversely, the coating applied to prepared surfaces indicated survivability throughout the exposures. Furthermore, the coating's experimental corner-dependent performance was consistent with the FEM results, highlighted by increased damage around sharp corners with improved coating performance at a fillet corner. These experimental and model results inform the surface and corner preparation requirements to leverage the benefits of AM in R512E coated C103 for elevated temperature applications.

Diamond-Like Carbon (DLC) and AlCrN films onto Ti-6Al-4V substrates by Laser-Powder Bed Fusion (L-PBF): Effect of substrate heat treatment and surface finish

This paper focuses on the performance of thin-film coatings onto additively manufactured Ti-6Al-4V. Specifically, because metal parts obtained by laser-powder bed fusion (L-PBF) often require post-process heat treatments and surface finishing to meet end-user specifications, we studied how the resulting changes to mechanical strength and surface roughness affect the performance of films deposited by physical or plasma-enhanced chemical vapor deposition (PVD, PE-CVD). L-PBF Ti-6Al-4V substrates were heat-treated either below or above the β-transus and finished by grinding with different grit sizes, and then were coated with PVD AlCrN or a PE-CVD DLC-based film.Scratch adhesion on harder surfaces treated below the β-transus was higher with both coating types, whilst the substrate finishing had a negligible effect. Conversely, in ball-on-disc sliding wear tests, substrate roughness had a dominant effect: rough surfaces always resulted in earlier cracking and delamination of the coatings. Substrate hardness had a minor effect only with the AlCrN film. Moreover, the DLC-based films, because of the low-friction conditions they establish through a graphitized tribofilm as well as their higher H/E ratio, survived severe contact conditions better than the stiffer AlCrN. The results were interpreted in the light of the plasticity indices of the coated systems and their tribochemical interactions.

Solder Joint Degradation and Electrochemical Metallic Ion Migration Property of Solder Joints with Surface Finish

To confirm the degradation property of solder joints by substrate surface finish, chip resistors are reflow soldered to organic solderability preservative (OSP) and electroless nickel immersion gold (ENIG) finish substrate in a nitrogen atmosphere using the type 6 Sn-3.0Ag-0.5Cu (SAC305) solder paste. To confirm the electrochemical metallic ion migration (ECM) sensitivity with and without photo solder resist (PSR) ink-coated printed circuit board (PCB), comb patterned test vehicles were prepared by the hot air reflow soldering process in nitrogen atmosphere, and the SAC305 solder paste was printed on the conductor of the ECM test PCB. The ECM test was conducted under high temperature and high humidity conditions of 85℃ and 85% RH, respectively. As a result of measuring the void content of the 2012 chip resistor, the average void content of the OSP substrate was higher than that of the ENIG substrate. The thermal shock test (TST) indicated that the degradation rate of the OSP substrate was higher than that of the ENIG substrate. Microstructure analysis showed that the OSP substrate had more crack propagation and thicker intermetallic compound (IMC) thickness than the ENIG substrate. The ECM test revealed that the substrate with PSR-coated PCB coupon generated more dendrites than that without PSR-coated coupon. Because the PSR coated substrate decreased the moisture absorption into the substrate, moredendritesweredeterminedtobe generated.

Cold plasma studies on the influence of surface microstructured thickness in the secondary electron emission from tungsten coatings

The Secondary Electron Emission (SEE) from the Plasma Facing Components, (PFCs) affects the plasma sheath and edge structure of magnetically confined toroidal plasmas with effects on the Scrappe Off Layer (SOL), heat transport and incident plasma heat flux to the divertor targets. It is also behind the performance degradation in aerospace devices as Hall thrusters. In future reactor prototypes using tungsten (W) components, much more demanding and longer term conditions for the exposed PFCs are expected. These scenarios will exacerbate the material degradation of the exposed surfaces that will change its morphology, thus modifying its plasma material interaction behavior. In such scenario, specific studies on the influence of the microstructure in the tungsten SEE yields become necessary. In these laboratory experiments, the SEE emission of different microstructured tungsten coatings exposed to helium Glow Discharge (GD) plasmas has been analyzed by using a previously developed laboratory technique. It enables the characterization of the I-V characteristics of the biased sample and, at the same time, the acquisition of the electron incident flux by using a gridded probe adjacent to the exposed sample. Different microstructured W coated samples differing in coating thickness (2500 nm and 500 nm) and primal substrate surface finishing (translated in final differences within the W coating topologies) were analyzed, also including cold rolled tungsten and original stainless steel (SS) substrate (material in which the microstructured tungsten film was deposited) as benchmarks for comparison. The overall results have shown that the presence of a 2500 nm thick microstructured W coating decreases the SEE yield of tungsten (cold rolled) up to a factor 40% at electron mean energies of 100-175 eV. Conversely, 500 nm coatings did not reduce the SEE yield even showing an increase at 25-100 eV. The final increase/decrease in the obtained SEE yields seems to be more influenced by the microstructured coating thickness (where the role of intrinsic differences in oxygen content of the surfaces is discussed) rather than other questions possibly derived by the differences in surface topology (ordering, directionality and/or roughness of the microstructure features).

Effect of substrate surface finish and particle velocity on fatigue performance of cold spray coated A6061 aluminum alloy

Cold spray coatings made with powder of the same material as the substrate can be used to improve fatigue performance and/or to repair damaged parts. The effects of substrate surface finish and particle impact velocity on the bond strength and fatigue performance of Al-6061-T6 substrates coated with Al-6061 powder by using high pressure cold spray (CS) were investigated. To evaluate the effect of particle velocity, coatings were prepared by using both nitrogen (N2) and helium (He) as carrier gases. A new method for substrate surface preparation was introduced by low angle spraying (LAS) with the same powder prior to coating. The bond bar specimens in polished, semi-polished, grit-blasted (GB) and low angle sprayed (LAS) conditions were coated and tested for bonding strength. The microstructural characteristics and microhardness profiles of the coated samples were also evaluated. Fatigue tests on uncoated and coated samples were conducted under fully-reversed axial loading in load-controlled condition. The failure mechanism was identified by evaluating the fracture surfaces using scanning electron microscopy. The results showed that both bonding strength and fatigue performance of the coated specimens prepared by using He-gas were significantly higher than those prepared by using N2. Among the N2-sprayed coatings, the bonding strength of on LAS substrates were significantly higher than that of the other surface conditions, and the bonding strength of coatings on GB substrates was superior to that of polished and semi-polished samples. However, the fatigue performance of LAS-coated samples was inferior compared to uncoated samples due to cracks initiating in the coating and propagating into the substrate. The fatigue behavior of GB-coated specimens was similar to the uncoated samples due to delamination of the coating which resulted in stopping the cracks that initiated in the coating.

Effects of Solder Powder Particle Size and Substrate Surface Finish on Degradation Properties of Solder Joints

In this study, the degradation characteristics of solder joints composed of powder-size Sn-3.0Ag-0.5Cu and the substrate surface finish are compared. Reflow is performed at a N2 ambient to apply an organic solderability preservative (OSP), electroless nickel/immersion gold (ENIG) substrates, and solder pastes of Type 6 (5-15 ㎛) and Type 7 (2-11 ㎛). Subsequently, a thermal shock test (TST) is performed for 1,500 cycles at a temperature of -40 ℃ to 125 ℃ (dwell time of 10 min) to analyze the deterioration characteristics. After N2 reflow is performed, the void content of the OSP substrate/solder joints is higher than that of the ENIG substrate/solder joints, and the shear strength of the ENIG substrate/solder joints is higher than that of the OSP substrate/solder joints. After 500 TST cycles, the shear strength at the OSP substrate/Type 7 solder joints does not decrease, whereas the shear strength at the ENIG substrate/Type 7 solder joints decreases by approximately 25%. Cross-sectional analysis shows that Cu6Sn5 and (Ni,Cu)3Sn4 intermetallic compounds (IMCs) emerged in the OSP and ENIG interfaces, respectively. The increasing rate of IMC thickness at the Type 7 solder joints is higher than that at the Type 6 solder joints. Fracture analysis shows that the OSP and ENIG joints fractured in the solder and solder/IMC interfaces, respectively. The IMC of the OSP and ENIG joints exhibit scallop and needle shapes, respectively. The ENIG joints fractured at the solder/IMC interface because of a stress concentration in the needle-type IMC. After 1500 TST cycles, the shear strength of all samples decreases by more than 50%. Cross-sectional analysis shows a crack at the solder joints of all samples after 1,000 cycles. The decrease in shear strength is caused by these cracks.

Influence of Silicon Substrate Surface Finish on the Screen‐Printed Silver Metallization of Polysilicon‐Based Passivating Contacts

Passivated contact based on a thin interfacial oxide and a highly doped polysilicon layer has emerged as the next evolutionary step to increase the efficiencies of industrial silicon solar cells. To take maximum advantage from this layer stack, it is vital to limit the losses at the metal polysilicon interface, which can be quantified as metal polysilicon recombination current density (J0met) and contact resistivity. In cell concepts, wherein a large variety of silicon substrate surface finish can be obtained, it is essential to know how the surface finish affects theJ0metand contact resistivity. Herein, commercially available fire through silver paste and the metal‐polysilicon recombination current densities and contact resistivity are used for three different silicon substrate surface finishes, namely: planar or saw damage etched (SDE), chemically polished in acidic solution and alkaline pyramidal textured. Contact resistivity values below 3 mΩ cm2withJ0metin order of the recombination current density of the doped region (J0pass) are obtained for samples with planar surface for both 150 and 200 nm n+polysilicon layer thicknesses. The results presented in this work show that the samples with flat substrate morphology outperform the samples with textured surfaces.

Optical characterization of nickel plated non-ferrous sheet metals

The surface coating is an essential way to improve properties of materials in modern industries for optical application. The high reflectance can be used in the technology of solar cooking, solar cell, defence, and optical application. Electroplating is one of the processes to produce a high reflective coating on metal substrate through reduction of cations by direct electric current. In this research paper, nickel plating successfully deposited on copper using electroplating. Nickel plating deposited on copper sheets under various conditions. The properties of nickel plating depend on the deposition parameters which include substrate surface finish, temperature, deposition time, power etc. The effect of the nickel plating process parameter enhances the optical properties of the sheet, particularly the high reflectance. The macrostructure and optical characterization of nickel plating are characterised by scanning electron microscopy along with energy dispersive spectroscopy techniques. X-ray diffraction is used for phase composition and provides unit cell information of Ni plating. The process parameters are selected and optimised for high reflectivity in less duration. The hardness of the nickel plating coating is also investigated using micro hardness. The surface characteristic, reflectivity and hardness improves significantly after nickel plating on copper sheets.

Highly durable amphiphobic coatings and surfaces: A comparative step-by-step exploration of the design variables

The design and production of amphiphobic surfaces with enhanced durability is increasingly considered a hot topic. It is well known that the material's repellence against liquids is regulated by morphological and chemical features of the working interfaces under different conditions. In this work the approach to the fabrication of highly repellent surfaces against both water and low surface tension oils is presented for a better understanding of the role played by different variables, e.g. the substrate surface finishing when multicomponent hybrid coatings with a different structural organization and chemistry are deposited. As suggested by biomimetic criteria, hierarchical features, when coupled with low surface energy moieties, are able to provide liquid repellence for different practical scopes. This work has been focused on coating processes applied to aluminum alloys with different surface roughness by deposition of nanostructured ceramic oxide (Al2O3, SiO2 and TiO2) and fluoro-polymers (fluoroalkylsilane or acrylic resin). It was found that the relevance of the substrate/coating variables involved in maximizing the static and dynamic liquid repellency follows the order: morphology of the inorganic layer > substrate roughness at microscale > nature of organic fluoropolymer. Both flower- and spherical-like inorganic nanostructures actually promote a significant improvement of the repellence with respect to the organic layer alone, with Al2O3flower-like nanostructure being the most performant. Generally speaking, most hybrid-coated surfaces showed a good ability to withstand severe environments, the different response depending on the composition of the inorganic layers and not from the overall coating morphology. The step-by-step comparison of results suggests that the perspective for the application of such a kind of surfaces is related in a complex way to textural and chemical variables influencing the final performances which could stay unchanged or vary depending on the exposure environment and conditions.

CMP Pad Conditioning and Applications to Type 1 Impregnated Felt Polishing Pads

Pad conditioning is the process of “dressing” the surface of the polishing pad, generally with a highly engineered diamond abrasive disc. Conditioning not only refreshes the pad surface, the cutting characteristics of the conditioner determine the structure of the asperities that are in contact with the wafer. By tuning the cutting characteristics of the conditioner, polish performance can be manipulated over a wide range. With the most advanced pads, specific conditioning protocols are typically required to obtain the designed performance. Optimization of these protocols is enabled by an understanding of the pad surface statistics.Figure 1 illustrates the two types of polishing pads that will be compared in this talk. Suba 800 is an example of a Type 1 pad. Type 1 pads consist of a “non-woven” needled polyester felt impregnated with polyurethane. The pores in a Type 1 pad are formed from the spaces between the impregnated fibers and have a length scale of 100s of microns. The pores in a Type 1 pad tend to be interconnected. VP5000 is a Type 3 pad. Type 3 pads consist of discrete pores in a matrix of polyurethane. The matrix properties can be varied over a wide range and pore sizes range from single to 10s of microns. Type 3 pads should be isotropic in terms of their physical property and porosity distribution. Type 3 pads typically exhibit Shore D hardness in the range of 20-70. Type 1 pads are measured on softer hardness scales or in terms of compressibility.Pad conditioning of Type 3 pads in semiconductor wafer CMP is at a technically mature stage, and the knowledge base can be directly applied to substrate polishing with Type 1 pads. The decoupled Gaussian-Exponential model which has been successfully used in Type 3 pads can be directly applied to Type 1 pads. As Figure 2 illustrates, Type 1 pads exhibit an exponential porosity signature, but with a decay length about an order of magnitude larger than a typical Type 3 pad, consistent with the difference in length scales of the pores of the two pad types. The core of the distribution (accounting for most of the total surface) can be modeled as a Gaussian.Figure 3 provides examples of both Suba 400 and Suba 800 and differences in both the intrinsic porosity (exponential decay constant, Eτ) and Gaussian core width are evident. At least part of the difference in the porosity signature is due to the Suba 800 receiving a double impregnation of polyurethane, compared to a single impregnation for Suba 400, resulting in a comparatively shallower pore structure. The difference in the Gaussian core width is most likely the result of a different buffing process or media used to impart a surface finish at the factory.Figure 4 illustrates the range of texture that can be developed on the DuPont Suba 800 impregnated felt pad, one of the Type 1 pads most widely used in substrate polishing applications. As the figure illustrates, the hwhm of the Gaussian core can be driven from about 10 to 50 µm, while maintaining the deep background porosity that characterizes this pad. The ability to drive the texture into rougher and smoother regimes, compared to a new pad, implies a potential to drive the substrate process into previously unattainable performance spaces. Initial feedback from the field indicates that smoother pad surfaces can contribute to improved substrate surface finish. Rougher surfaces may contribute to improved throughput through polish rate increase.Figure 5 illustrates how key pad roughness metrics of Suba 800 are correlated with a basic conditioner diamond design parameter. Most roughness measurements are highly correlated, although one of the most widely used roughness parameters, the average roughness Ra, does not correlate well at all in this case. This is an excellent example where pad height distribution modeling provides critical insight into the drivers of the textural changes that effect polish performance, and how that performance might be manipulated through conditioning design.Signatures of surface textural degradation from the stress of polishing and accumulation of debris can be observed on Type 1 pad surfaces. It is well known that restoration of the pad surface structure through conditioning is a primary mechanism of stability in Type 3 pads. Data from the field indicates improvements in process performance and consumable life with Type 1 pads when conditioning has been implemented versus processes with no pad conditioning. The examples given here will be expanded upon and additional applications will be discussed. Figure 1

Correction to: Influence of Substrate Surface Finish Metallurgy on Lead-Free Solder Joint Microstructure with Implications for Board-Level Reliability

Correction to: Influence of Substrate Surface Finish Metallurgy on Lead-Free Solder Joint Microstructure with Implications for Board-Level Reliability

Influence of Substrate Surface Finish Metallurgy on Lead-Free Solder Joint Microstructure with Implications for Board-Level Reliability

Solder joints can experience fatigue cracking at the interface between the solder and substrate during thermal cycling due to the difference in thermal expansion between joined components. In order to strengthen the interfacial region and prevent cracking, two Cu pad surface treatments were studied on Sn-3Ag-0.5Cu solder, and on matte Sn plate and Ni plate coatings. The resulting intermetallic microstructures were characterized using scanning electron microscopy and energy-dispersive spectroscopy. Mechanical testing was performed using nano-indentation on the solder joints. The matte Sn plate on Cu sample formed an uneven distribution of Ag3Sn particles and a planar Cu6Sn5 interfacial intermetallic. The Ni-plated sample formed a needle-like Ni-rich interfacial intermetallic and uniform dispersion of Ag3Sn particles. The rough intermetallic compound (IMC)/solder interface and even IMC particle distribution cause the Ni-plated sample to experience reduced damage under board-level thermomechanical cycling because the interfacial structure reduces the Sn matrix recrystallization that contributes to fatigue cracking. In contrast, the matte Sn-plated sample exhibited an Ag3Sn particle-free zone adjacent to a planar Cu6Sn5 IMC layer which allows for rapid Sn recrystallization and fatigue crack propagation.

Nano-finishing of MEMS-based platforms for optimum optical sensing

The surface finish of the microelectromechanical systems substrate, particularly the ones that are deployed in chip-based optofluidic systems, is of utmost importance, and the overall surface finish helps in preventing light scattering and associated losses. The proposed system is made up of a microchannel with a coating on its interior which acts as a cladding layer and possesses an air-like refractive index. The water-based solutions with refractive indices higher than the coating, when confined within such channels, act as waveguides with a refractive index difference which would allow grazing incidence at the solution film interface. The microchannel is fabricated over a piece of Si along <100> direction with the help of lithography and wet etching technique. After wet chemical etching of silicon, multiple pyramidal hillocks with overall large surface roughness is observed which are not appropriate for loss-free light transmission and cause various optical losses. So the overall optimization of surface roughness created by the etching processes is critical from an optical standpoint. Roughness in the microchannel surface mainly arises due to wet etching through tetra methyl alcohol, potassium hydroxide, potassium ferricyanide and isopropyl alcohol. In this work, we have obtained surface finish upto ~1.33 nm at an etch rate of 141 nm/min which is obtained by tweaking the composition of the participating reagents in the etchants and also the etching temperature. The surface roughness obtained is quite small in comparison to the wavelength range of the visible spectrum and thus losses were greatly avoided. The low refractive index films over silicon substrate were characterized by field emission scanning electron microscopy, energy dispersive analysis of X-ray, atomic force microscopy, 3D optical profilometry and ellipsometry. The transmission results show that transmission loss was reduced by 27.42% for the coated samples with 33 nm surface roughness as compared to surface with 250 nm roughness.

(Invited) X-Ray Metrology of AlN Single Crystal Substrates

X-ray based techniques were used to characterize AlN single crystal substrates at different stages of production, providing essential information about substrate orientation, surface finish, structural perfection, and heteroepitaxy. X-ray topographs acquired on a commercial diffractometer confirmed that iterative diameter expansion of AlN boules, without the introduction of low angle grain boundaries, was successfully achieved. As a result, high-quality, macrodefect-free, 2-inch AlN substrates were demonstrated.

Effect of soft substrate topography on tribological behavior of multifunctional DLC coatings

In this study, the influence of soft substrate surface finishing (5 distinct conditions) on tribological properties of hydrogenated amorphous carbon (a-C:H) films is investigated. Low carbon steel substrates were plasma-nitrided and DLC-coated in a single PECVD batch. Topographical evolution was investigated through white light interferometry (WLI) and scanning electron microscopy (SEM). The substrate topography leads to a negligible impact on bonding structure and mechanical properties of a-C:H films, which were analyzed by Raman spectroscopy (RS) and nano-indentation. The nitriding and deposition process resulted in two groups of samples regarding the topographic features: (A) Rough—Sq coated ≈ 0.17–0.23 µm; (B) Smooth—Sq coated ≈ 0.08–0.11 µm. Tribological performance of multifunctional coatings under incremental normal load reciprocating dry sliding tests in ambient air revealed friction coefficients of 0.09 (Rough) and 0.05 (Smooth). Wear scars were analyzed by WLI, SEM and RS. The results suggest that rougher substrates inhibit tribolayer formation and stability, leading to higher friction coefficients.

Effect of the Soldering Atmosphere on the Wettability Between Sn4.0Ag0.5Cu (in wt.%) Lead-Free Solder Paste and Various Substrates

The “degree of wetting,” which is related to the contact angle (θ) between the molten solder and the substrate, is a useful parameter on the solderability process control. The contact angle, however, is strongly dependent on the type of substrate surface finish and used atmosphere (inert or non-inert). Furthermore, the surface tension, being an important parameter on the solderability process and performance, can also be achieved if the contact angle is known. In this study, the SAC405 [Sn4.0Ag0.5Cu (in wt.%)] solder paste contact angle was measured, by the “sessile drop” method, as a function of the temperature, surface pad finish and used atmosphere. The results are discussed, and the contact angles obtained for the different conditions are compared and discussed. Then, the surface tension (experimental) was obtained from the measured contact angle and compared with the obtained by using computation models (theoretical). The experiments performed in high vacuum conditions, i.e., low oxygen content, over a temperature range, allowed the evaluation and understanding of the surface oxides layers role on the solder wettability. The present study shows that in the soldering process, even in an inert atmosphere, usually used in industry, occurs the formation of superficial oxides, over the liquid solder and/or at the pad surfaces, that strongly affects the solder paste wettability, specially with Sn and OSP (organic solderability preservative) finishing. Differences in contact angle of ≥ 10° were determined between the two types of used atmospheres. The experimental surface tension and theoretical surface tension obtained, for the NiAu substrate type, present good correlation. The lower contact angle values were obtained for the NiAu and OSP finish types, independently of the atmosphere type.

Ball impact responses of Sn-1Ag-0.5Cu solder joints at different temperatures and surface finishes

The purpose of this paper is to measure and analyze the Sn-1Ag-0.5Cu solder joints under high speed ball impact test (BIT) conditions. In this study, the ball impact test was conducted at impact velocity of 300 mm/s on package-level solder joints with 0.3 mm ball diameter, bonded individually on substrate pads of Ni/Au, OSP and Ni/Pd/Au surface finishes at elevated temperature of 25, 50, 75, 100 and 125 °C, respectively. The experimental results show that Ni/Pd/Au surface finish at room temperature has higher intermetallic compound (IMC) strength performance than Ni/Au and OSP. These three different substrate surface finishes, however, tend to have quite similar IMC strength performance at elevated operation temperature. The board-level drop test reliability of TFBGA 14 mm × 14 mm 409 L for these surface finishes were also performed at room temperature. The trends of BIT results are in good agreement to board-level drop test reliability. A three-dimensional finite element analysis (FEA) model was established to analyze the transient structural responses in the solder joint for determining the maximum impact toughness capacity. The effects of temperature on solder joint material yield stress and IMC strength on the impact characteristics were investigated.

The effect of coating architecture and defects on the corrosion behaviour of a PVD multilayer Inconel 625/Cr coating

This paper investigates the effect of substrate surface finish and deposition conditions of PVD multilayer Inconel 625/Cr coatings on their ability to act as a corrosion-barrier. The corrosion-barrier performance of the coatings was characterized by potentiodynamic testing and salt-spray testing followed by image analysis of the exposed surface; further coating properties were investigated through XRD, SEM, EDX and scratch testing. The results show that multilayering produced the expected improvement in scratch resistance however it did not affect corrosion behaviour. Interrupting the deposition process did not decrease the defect density. Defect density was observed to reduce with decreasing substrate surface finish. The corrosion barrier performance of the multilayer Inconel 625/Cr coating (bp100nm) was greatly improved for coatings deposited on a polished substrate. For the multilayer Inconel 625/Cr coating system used in this work multilayering and process interruption did not prevent defects from limiting the corrosion barrier effectiveness of the coatings. Corrosion barrier performance was successfully enhanced by the use of low roughness substrates to minimise the defect density.

Mechanical strength of ground WC-Co cemented carbides after coating deposition

Manufacturing of hardmetal tools often involves surface grinding, ion etching and final coating. Each stage throughout the manufacturing chain introduces surface integrity changes which may be critical for defining the final mechanical behavior of the coated tools. Within this context, an experimental test program has been developed to assess the influence of a coating (TiN) deposition on surface integrity and transverse rupture strength of a previously ground fine-grained WC-Co grade substrate. Four different substrate surface finish conditions (prior to ion etching and coating) were evaluated: as sintered (AS), ground (G), polished (P), and ground plus high temperature annealing (GTT). Surface integrity and fracture resistance characterization, complemented with a detailed fractographic analysis, were performed on both uncoated and coated samples. Results show that the surface integrity after grinding has been partly modified during the ion etching and film deposition processes, particularly in terms of a reduced compressive residual stress state at the substrate surface level. Consequently, the grinding induced strength enhancement in hardmetals is reduced for coated specimens. Main reason behind it is the change of nature, location and stress state acting on critical flaw: from processing defects existing at the subsurface (uncoated G specimens) to grinding-induced microcracks located close to the interface between coating and substrate, but within the subsurface of the latter (coated G specimens). This is not the case for AS and P conditions, where flexural strength does not change as a result of ion etching and coating. Finally, fracture resistance increases slightly for GTT specimens after coating process, possibly caused by a beneficial effect of the deposited film on the residual stress state at the surface.