MPa Shear Strength Research Articles

Redox-triggered debonding of mussel-inspired pressure sensitive adhesives: Improving efficiency through functional design.

Debondable pressure-sensitive adhesives (PSAs) promise access to recyclability in microelectronics in the transition toward a circular economy. Two PSAs were synthesized from a tetravalent thiol star-polyester forming thiol-catechol-connectivities (TCC) with either biorelated DiDopa-bisquinone (BY*Q) or fossil-based bisquinone A (BQA). The PSAs enable debonding by oxidation of TCC-catechols to quinones. The extent of debonding efficiency depends on the interaction modes, which are determined by the chemical structure differences of both TCC-motifs. BY*Q-TCC-PSA debonds with exceptional loss of 99% of its approx. 2 MPa shear strength. For BQA-TCC-PSA, a debonding efficiency of only approx. 60% was found, irrespective of its initial shear strength, which could be tuned up to approx. 7 MPa. The efficiency of debonding for BY*Q-TCC-PSA after TCC-oxidation is linked to the loss of synergistic interactions without strongly affecting the bulk glue properties, outperforming the purely catechol-based BQA-analogue.

Low carbon multi-binder composite using lithomargic soil, biomass, and calcined seashell powder for sustainable bricks

Bricks are manufactured using clays, which are fired at temperatures ranging from 1000 to 1200 °C. Due to the lack of quality clay, it is necessary to find alternate soils and waste materials for manufacturing bricks. The use of agricultural, aqua-cultural, and industrial wastes in the manufacturing of construction bricks leads to low-carbon material. This addresses the problem of agro-aqua-industrial waste disposal. The present study focuses on the utilization of biomass (BM) and slaked seashell powder (SSP) in compressed soil bricks made with locally available lithomargic soil (LS). The proposed soil bricks are prepared with 85% processed lithomargic soil, 12.5% biomass and 2.5% seashell powder. The reaction of multi-binder materials has been activated by one-part activation. The cast soil blocks are temperature cured at 100 °C, 250 °C, 500 °C & 750 °C to understand the effect of temperature on the hydration process of binder material. The compressed soil bricks are tested for compressive strength, initial rate of absorption, water absorption test, chloride content, sulphate content, microstructure analysis and thermal conductivity. The strength of soil bricks in bonding and in masonry, 3 prism and 4 prism tests were also conducted. Overall results indicate that bio-based alkali-activated brick masonry is superior for real-time adaptation because it reaches 10 MPa to 11.2 MPa compressive strength and 0.98 MPa to 1.2 MPa shear strength with curing at 500 °C.

Joining Si3N4 ceramic to Invar using Mo mesh and Cu foil interlayer

Si3N4/Invar joints with Mo mesh and Cu foil as interlayers, individually and together, were vacuum brazed using Ag27.5Cu4.5Ti active filler at 1153 K for 10 min with following configurations: Si3N4/Ag26.7Cu4.5Ti + Mo/Invar, and Si3N4/Ag26.7Cu4.5Ti + Mo/Cu/Ag–Cu/Invar. The correlation between the microstructure of the brazing seam and shear strength of the joints are investigated. Ti segregated at Si3N4/filler interface and metallurgical bonding is established by formation of TiN and Ti5Si3 reaction products. Vickers microharndess profiles unveiled varying degrees of hardness across the brazing seam, resembling the layered structure. Individually introducing Mo mesh as interlayer suppressed the Fe2Ti and Ni3Ti intermetallic compounds (IMC) within the brazing seam, resulting in shear strength of 191.7 MPa. Hybrid combination of Mo mesh with Cu foil as interlayers, yielded 235.5 MPa shear strength in brazed Si3N4/Invar joints. This improvement is attributed to simultaneous favorable effects of Mo such as reduced residual stress near the Si3N4/filler interface and Cu, which prevents Fe2Ti and Ni3Ti IMC in the brazing seam, thereby enhancing the plastic flow.

Experimental investigation on microstructure and properties of Al alloy-PEEK joint with different surface structure obtained by hot-pressing

In this study, selective laser melting (SLM) additive manufacturing was used for the fabrication of Al alloy with the surface structure based on the construction of mechanical interlocking mechanism to complete the joining with polyetheretherketone (PEEK). The application of hot-pressing process provided a direct joining between Al alloy-PEEK at 460 °C for 40 min. This work characterized the forming of both cylindrical and trapezoidal structures, indicating that the structures were formed completely, and the gaps were clear. Although some dimples or micropores were generated in the forming solid, these defects in the forming were beneficial for the flowing and filling of PEEK during hot-pressing joint. The microstructure of Al plate fabricated by SLM showed typical parallel columnar grains perpendicular to the deposition direction and stacked and fish scale like feature in the deposition direction, respectively. The microstructure characterizations of Al alloy-PEEK joints showed that both materials were joined without gaps and formed a strong mechanical interlocking, guaranteeing a firm bond with maximal tensile shear strength up to 81 MPa for trapezoidal structure. By comparison, the joint with cylindrical structure possessed a low 65 MPa shear strength due to weak cuneiform anchor interlocking. Fracture surface was investigated in more detail. The result showed that the joint with cylindrical structure mainly showed interfacial failure and pulling-out, tilting deformation and fracture of the supporting, while the joint with trapezoidal structure exhibited a separation between the top surface of the supporting and the PEEK and brittle cohesive fracture of the PEEK between the gaps.

Ultra-high temperature brazing of C/C composite using pure Ni as filler based on eutectic reaction

To increase service temperature of brazed C/C-C/C joint, pure nickel was used as filler in ultra-high temperature brazing based on Ni-C eutectic reaction (1326 °C). The bond seam was composed of C-rich Ni(S.S.) matrix (FCC) and precipitating flake graphite; intimate interface and smaller contact angle (40°) confirmed good wettability; deep infiltration up to 120 μm occurred preferentially along perpendicular fibber bundle. As a result, 21.7 MPa shear strength was obtained. Fracture occurred within C/C side, rather than within bond seam or along initial interface. These results demonstrated that using pure Ni foil as filler even without strong/moderate carbide forming elements was feasible.

Regulating the glass network structure of SiO2f/SiO2 composite joints by in-situ silica diffusion

To expand the application of SiO2f/SiO2 composites, joining is one indispensable process. However, it is hard to take care of the property of the composites and simultaneously form a robust joint. Here, a B2O3–ZnO glass filler with a loose network structure was designed to realize the self-joining of SiO2f/SiO2 composites. Results revealed that silica has a relatively rapid diffusion rate in B2O3–ZnO glass which is beneficial for the fast replacement of the glass network former. After brazing, silica diffused into the brazing seam, became a new network former and thus regulated the glass network structure. As a result, the maximum working temperature of the joint increased 200 °C compared with pristine B2O3–ZnO glass. The joints own 23.3 MPa shear strength at room temperature and remain 22.3 MPa at 600 °C. This work offers a way to achieve the joining of SiO2f/SiO2 composites and break through the original maximum working temperature of the glass filler.

Fully recyclable multifunctional adhesive with high durability, transparency, flame retardancy, and harsh-environment resistance

Recyclable/reversible adhesives have attracted growing attention for sustainability and intelligence but suffer from low adhesion strength and poor durability in complex conditions. Here, we demonstrate an aromatic siloxane adhesive that exploits stimuli-responsive reversible assembly driven by π-π stacking, allowing for elimination and activation of interfacial interactions via infiltration-volatilization of ethanol. The robust cohesive energy from water-insensitive siloxane assembly enables durable strong adhesion (3.5 MPa shear strength on glasses) on diverse surfaces. Long-term adhesion performances are realized in underwater, salt, and acid/alkali solutions (pH 1-14) and at low/high temperatures (-10-90°C). With reversible assembly/disassembly, the adhesive is closed-loop recycled (~100%) and reused over 100 times without adhesion loss. Furthermore, the adhesive has unique combinations of high transparency (~98% in the visible light region of 400-800 nm) and flame retardancy. The experiments and theoretical calculations reveal the corresponding mechanism at the molecular level. This π-π stacking-driven siloxane assembly strategy opens up an avenue for high-performance adhesives with circular life and multifunctional integration.

Influence of Ag particle shape on mechanical and thermal properties of TIM joints

PurposeThe purpose of this paper is to develop and test the thermal interface materials (TIM) for application in assembly of semiconductor chips to package. Good adhesion properties (>5 MPa shear strength) and low thermal interface resistance (better than for SAC solders) are the goal of this research.Design/methodology/approachMechanical and thermal properties of TIM joints between gold plated contacts of chip and substrate were investigated. Sintering technique based on Ag pastes was applied for purpose of this study. Performance properties were assessed by shear force tests and thermal measurements. Scanning electron microscopy was used for microstructural observations of cross-section of formed joints.FindingsIt was concluded that the best properties are achieved for pastes containing spherical Ag particles of dozens of micrometer size with flake shaped Ag particles of few micrometers size. Sintering temperature at 230°C and application of 1 MPa force on the chip during sintering gave the higher adhesion and the lowest thermal interface resistance.Originality/valueThe new material based on Ag paste containing mixtures of Ag particles of different size (form nanometer to dozens of microns) and shape (spherical, flake) suspended in resin was proposed. Joints prepared using sintering technique and Ag pastes at 230°C with applied pressure shows better mechanical and thermal than other TIM materials such as thermal grease, thermal gel or thermally conductive adhesive. Those material could enable electronic device operation at temperatures above 200°C, currently unavailable for Si-based power electronics.

Formulation design of a new type of epoxy resin-based insulating adhesive and research on its high temperature resistance

A series of new epoxy resin adhesives were prepared by low viscosity bisphenol A epoxy resin E-44 and E-51as the matrix, low molecular polyamide 650# and phenolic modified JT-3008 as the curing agent, silicon micro powder and calcium carbonate as the fillers. The gelation time, surface drying time and shear strength of the samples were deeply tested. The thermal decomposition temperature and high temperature resistance of the samples were determined by TG analysis. Meanwhile, the surface fracture morphology was observed by SEM. The results showed that a new kind of heat epoxy resin insulation adhesive with long gelation time and convenient construction and meeting the requirements of production adjustment was successfully obtained through the optimization design of the formula,. The new epoxy resin insulation adhesive showed excellent mechanical properties with 18.00 MPa shear strength, which can be used at 380 ℃ for a short period of time and 130 ℃ for a long time. The new adhesive developed in this paper can be widely used in high voltage switchgear and other insulation materials, which has good application prospects.

Formulation design of a new type of epoxy resin-based insulating adhesive and research on its high temperature resistance

A series of new epoxy resin adhesives were prepared by low viscosity bisphenol A epoxy resin E-44 and E-51as the matrix, low molecular polyamide 650# and phenolic modified JT-3008 as the curing agent, silicon micro powder and calcium carbonate as the fillers. The gelation time, surface drying time and shear strength of the samples were deeply tested. The thermal decomposition temperature and high temperature resistance of the samples were determined by TG analysis. Meanwhile, the surface fracture morphology was observed by SEM. The results showed that a new kind of heat epoxy resin insulation adhesive with long gelation time and convenient construction and meeting the requirements of production adjustment was successfully obtained through the optimization design of the formula,. The new epoxy resin insulation adhesive showed excellent mechanical properties with 18.00 MPa shear strength, which can be used at 380 ℃ for a short period of time and 130 ℃ for a long time. The new adhesive developed in this paper can be widely used in high voltage switchgear and other insulation materials, which has good application prospects.

Microstructural evolution, fracture behavior and bonding mechanisms study of copper sintering on bare DBC substrate for SiC power electronics packaging

Robust bonding of Cu quasi-nanoparticles sintering for Ag coated chip and bare copper substrate was achieved. The effect of temperature, pressure and time on the sintering bonding strength and microstructural evolution was deeply studied. 36.5 MPa shear strength was achieved when applied 5 MPa pressure. By increasing to 30 MPa, it shows the best die shear strength of 116 MPa, accomplished with a sintering temperature of 250 °C for 3 min. Temperature also influenced the shear strength a lot. Between 210 °C and 230 °C can already provide strength over 30 MPa. When increased to 270 °C, the strength was extremely enhanced to over 120 MPa. Inspection on the fracture behaviors and cross-section of sheared off samples was conducted by SEM, EDS, and XRD. It is found that low bonding performance is due to both of the incomplete burnt out of organics and incomplete Cu QNPs sintering. In addition, high bonding is account for the positive effect of pressure and temperature on promoting the necking growth, sintering networking formation, pores isolation and brittle-ductile fracture transformation. The recommended sintering profile is 250 °C, 3 min, 20 MPa. Finally, the feasibility for SiC MOSFET power electronics DA was verified by testing its static characteristics at both room temperature and 150 °C.

Glass to aluminum joining by forming a mechanical pin structure using femtosecond laser

The joining of dissimilar materials is a widely used procedure with applications in many industries. While laser welding of such materials has gained traction interest recent years, this has intrinsic limitations, especially considering harsh requirements including surface roughness and weak bonding strength. This paper proposes a novel method to join Al6082 and SiO2 using a femtosecond laser to substantially reduce the requirements of material surface roughness and improve bonding strength. The proposed method involves drilling, ejection, filling and solidification, which results in forming a mechanical pin structure with some adhesive regions between Al6082 and SiO2, ensuring the two materials lock tightly. Besides, a significant tolerance of approximately 2 mm for focal positions was identified, overcoming the limitation of sensitivity of focus position in laser welding. Furthermore, over 100 MPa shear strength of Al6082-SiO2, which was comparable to the tensile strength of the aluminum alloy, was achieved. The proposed method provides a novel technique to improve the quality of products and facilitate the manufacturing process for joining dissimilar materials.

Reactive wafer bonding with nanoscale Ag/Cu multilayers

Reactive bonding using nanoscale multilayers based on the high specific surface/interface energy is a promising low-temperature and low-pressure wafer-bonding process. Herein, Si wafers were bonded using nanoscale Ag/Cu multilayers in N2 or the ambient atmosphere. A flawless joint composed of Ag-rich and Cu-rich face-centered cubic (fcc) phases was achieved in N2 with 22.2 MPa shear strength. However, a peculiar “fcc-(Ag)+voids/Cu2O/fcc-(Ag)+voids” three-layer sandwich structure with 11.1 MPa shear strength was formed due to significant out segregation of Cu toward the bonding-interface in the ambient atmosphere. The bonding mechanism and the role of oxygen were unveiled based on CALPHAD (CALculation-of-PHAse-Diagram) thermodynamic modeling.

Investigation of functional core-rim composite part production by inserted powder injection moulding

In this study, the use of Cu and Ni interlayers have been investigated for functional core-rim composite part production with WC-Co 9 wt-% feedstock/steel. For this purpose, different experiments have been performed and joining condition, shear strength and microstructure of the intermediate region have been examined. It has been found that AISI 4340 insert/WC-Co have been joined and 85.8 MPa shear strength achieved, but high speed steel insert has not joined. Moreover, it has been determined that better results are obtained with Ni interlayer. Under the same conditions, when the 40 µm Ni interlayer has been used between AISI 4340 core and WC-Co rim, shear strength has been increased approximately twice and has been 162.7 MPa.

Cladding thick Al plate onto strong steel substrate using a novel process of multilayer-friction stir brazing (ML-FSB)

Friction stir brazing (FSB) using a pinless tool together with a braze was developed to extend bond area over friction stir lap welding. When using a large pinless tool of Ø40 mm to clad 10 mm thick 5083Al plate to 16Mn steel by FSB with Zn braze, the thermomechanical effect was sufficient to achieve wetting on Al side by dissolving Al into molten Zn, but joint could not be formed due to poor wettability on steel side. To enhance mechanical disruption of oxide film on the steel, multilayer FSB (ML-FSB) process was proposed by adding a thin (3 mm thickness) and soft aluminum sheet as interlayer. The first FSB pass created bonding between the thin interlayer and steel substrate with 4.7 μm thick FeAl3 without Zn residue, having 55 MPa shear strength. The second FSB pass created bonding between the thin interlayer and thick 5083Al clad with a diffusion zone with a little Zn, having 50 MPa shear strength. This work provided a new way to fabricate “thick clad” layered composite with “strong substrate”, and suggested that mechanical route for strong substrate and metallurgical route (eutectic reaction) for Al for removing oxide film should be preferential and available in FSB.

Improvement of the Bond Strength of Ag Sinter-Joining on Electroless Ni/Au Plated Substrate by a One-Step Preheating Treatment

Ag sinter-joining technology has become one of the leading candidates to replace conventional high-Pb soldering technology for wide bandgap (WBG) power modules. In many cases of die-attach applications, Ni/Au plating is an inevitable choice for both die-back faces and substrates. In this study, a preheating treatment of the Ni/Au plating was utilized to increase the bond strength of the Ag sinter-joined structure of Cu-to-Cu to the electroless Ni/Au plating. Our research determined that the microstructure of the Ni/Au plating can be modified by performing an optimized preheating treatment. The thickness of the Ni underlayer was fixed at 5 μm, and the Au was plated with two different thicknesses of 0.1 μm and 0.3 μm. Ni/Au plated Cu substrates and Cu chips were preheated at various temperatures from 150°C to 350°C and then bonded with hybrid Ag particles at a low temperature of 250°C with a pressureless sintering process. Without the preheating treatment, average shear strength was 14.2 MPa (as plated Au), however, after a 1 h preheating treatment at 250°C, the interface microstructure change resulted in a 26.3 MPa shear strength, an increase of about 85%. The same improvement effect was also confirmed for the Au plating layer with a thickness of 0.3 μm. Energy dispersive x-ray spectrometry (EDS) and x-ray diffraction (XRD) analysis indicated that the preheating treatment influences the grain structure of the Au plating layer and removes defects, resulting in an increase of bond strength for the Au plated joint structure.

Laser brazing of a nickel-based superalloy using a Ni-Mn-Fe-Co-Cu high entropy alloy filler metal

In this study, we demonstrate the successful brazing and superior mechanical performance of laser brazed Inconel® 718 using a Ni-Mn-Fe-Co-Cu high entropy alloy filler metal with a nominal Ni:Cu:Co:Fe:Mn molar ratio of 1:1:1:0.25:1.75. A maximum 220 MPa shear strength is achieved. The high entropy alloy experiences the hardness increases 3–4 times after brazing. If the brazing temperature is higher than 1200 °C, the bonding strength suffers due to excessivediffusion between the base metal and the filler metal. The hardness behavior is attributed to a combination of the cocktail effect and lattice distortion induced by brazing.

Thermal stability of low-temperature sintered joint using Sn-coated Cu particles during isothermal aging at 250 °C

In this paper, we investigate the microstructural stability of a Cu–Cu joint sintered with microscale Cu particles and Sn-coated Cu (Cu@Sn) particles during an isothermal aging. Using Cu particles and Cu@Sn particles as die attach materials, pure Cu discs were bonded at 200 °C for 20 min with an applied pressure of 10 MPa in a formic acid atmosphere. After the bonding, the Cu sintered joint showed a loosely sintered structure, while the Cu@Sn sintered joint exhibited a microstructure comprised of a Cu3Sn network with a dispersion of Cu particles. The isothermal aging test was conducted at 250 °C in an air atmosphere. Debonding of the Cu sintered joint happened after the aging for only 100 h, due to a severe oxidation of the sintered Cu layer and Cu substrate. On the other hand, the Cu@Sn sintered joints showed better thermal stability. The joint presented nearly 20 MPa shear strength after the aging for 1000 h. The Cu3Sn IMC network suppressed the oxidation of Cu both in the sintered layer and on the substrate, thereby maintaining the microstructural integrity of the Cu@Sn sintered joint.

Pressureless sintering bonding using hybrid microscale Cu particle paste on ENIG, pure Cu and pre-oxidized Cu substrate by an oxidation–reduction process

To investigate the properties of the oxidation–reduction bonding (ORB) process with different kinds of microscale Cu particles, we characterized the microstructure and shear strength of ORB-produced joints using microscale flake-shaped Cu particles, spherical Cu particles, and their hybrid particle pastes. The Cu–Cu joints were bonded with the ORB process at 300 °C for 60 min without pressure, and 31.2 MPa shear strength was achieved by using the hybrid particle paste comprising 75 mass.% flake-shaped Cu particles and 25 mass.% spherical Cu particles. Moreover, ORB joints were also fabricated with pre-oxidized Cu and electroless nickel/immersion gold (ENIG)-finished Cu substrates. The bonded ENIG-finished Cu joint has a shear strength that is similar to that of the bonded pure Cu joint. On the other hand, the bonded pre-oxidized Cu joint shows a shear strength of 28.1 MPa, only 10% less than the shear strength of the bonded pure Cu joint. This result reveals that the shear strength of an ORB joint is insensitive to the surface condition of the substrate, which makes the ORB process acceptable in practical large-scale production.

Availability of in-situ reinforced active-transient liquid phase bond with good wettability for 70 vol.% SiCp/A356 composite using Al-Mg-Ga-Ti interlayer

For transient liquid phase bonding of as-cast 70vol.% SiCp/A356 composite, Al-24Mg-16Ga-1Ti (wt.%) active braze was designed by adding Ti as melting point increaser (MPI) for Al into Al-Mg-Ga active alloy near eutectic composition to produce in-situ reinforcement by precipitating a fine and dispersive Ti-containing intermetallic compound as reinforcement within the solid-solution bond seam after isothermal solidification. Bonding was performed at three temperature levels of quasi-melting (450°C), just fully melting (500°C), and over melting (550°C) for the braze under 0.5–1.75MPa in argon. The braze was able to produce fine (less than 1μm) and dispersive Ti-containing precipitated phase (Al-2Mg-1Ga-0.5Ti, at.%) as in-situ reinforcement only at 500°C under medium pressure (1–1.5MPa), increasing bond seam microhardness by 30Hv over the matrix. The braze robustly showed good wettability for each temperature due to the matrix dissolution and detectable amorphous reaction products containing Mg and Ga on SiC surface. Higher temperature caused coarsening of needle-like Si-containing Al-Si-Ti precipitated phase while higher pressure produced blocky Al3Ti with a shell of Mg and Ga. Sound joint produced at 500°C under 1.5MPa with 118.6MPa shear strength (98.8% parent composite) fractured completely within the composite.