Solid-liquid Interdiffusion Research Articles

Interfacial Reactions in the Cu/Ga/Co and Cu/Ga/Ni Samples

To fundamentally understand the solid–liquid interdiffusion joining processes between a Cu electrode and Co and Ni barrier layers using a Ga solder, the interfacial reactions in the Cu/Ga, Co/Ga, Ni/Ga, Cu/Ga/Co and Cu/Ga/Ni samples have been systematically examined. The reaction phases at the Cu/Ga interface in the Cu/Ga, Cu/Ga/Co and Cu/Ga/Ni samples reacted at 200°C, 350°C and 500°C are all the same, and are γ3-Cu9Ga4 and CuGa2, γ2-Cu9Ga4 and γ1-Cu9Ga4 respectively. No Co/Ga interfacial reaction phase was found in either the Co/Ga or Cu/Ga/Co samples reacted at 200°C, and the reaction phase is CoGa3 when reacted at 350°C and 500°C. The reaction phase in the Ni/Ga couples reacted at 200°C and 350°C is the Ni3Ga7 phase while it is Ni2Ga3 at 500°C. In the Cu/Ga/Ni samples, no Ni/Ga interfacial reaction phase is observed at 200°C, and the Ni3Ga7 and Ni2Ga3 phases formed at 350°C and 500°C have 8.5 at.%Cu and 14.0 at.%Cu solubilities. The growth rates of the reaction phases have been determined, and the Ga consumption rates in the Cu/Ga/Co and Cu/Ga/Ni samples at 200°C, 350°C and 500°C were calculated. It is observed that the consumption rates increase with the square root of the reaction time, and the consumption rate constants are 39.2 μm/h0.5 and 77.3 μm/h0.5, respectively.

Interfacial reactions in the Co/In/Cu and Ni/In/Cu samples

Abstract To provide fundamental understanding for the solid-liquid interdiffusion process using indium-based solders, interfacial reactions in the Co/In, In/Cu, Ni/In, Co/In/Cu and Ni/In/Cu samples at the Co/In, In/Cu and Ni/In interfaces are systematically determined. CoIn3 phase is formed in the Co/In couples reacted at 200, 350 and 500 °C. Cu11In9 and a two-phase mixture region are observed in the In/Cu couples reacted 200 °C, and δ-Cu7In3 and η'-Cu2In phases are found at 350 and 500 °C. In the Ni/In couples, the In7Ni3 phase is formed at 200 and 350 °C, while InNi and In3Ni2 phases are found at 500 °C. Except for the formation of an unknown ternary phase in the Co/In/Cu sample reacted at 350 °C, the reaction phases in the sandwich-type ternary samples are the same as those in the binary couples, and no significant cross- interactions are observed both in Co/In/Cu and Ni/In/Cu samples. The indium consumption rates are faster in the Ni/In/Cu samples. Their consumption rates are estimated based on the indium accumulation in the reaction phases.

Highly reliable joining for high‐temperature power modules: Ni–Sn DSLID with an Al sheet

Highly reliable operation at high temperatures is required for next-generation power modules in electric vehicles. We propose a joining concept involving nickel–tin (Ni–Sn) double solid–liquid interdiffusion with an aluminium (Al) sheet (Ni–Sn DSLID/Al), which enables the production of modules with high thermal reliability. The use of Ni–Sn DSLID/Al joint as bonding layers for a large thermal coefficient mismatch [silicon (Si) chip: 3.9 × 10−6 K−1, copper electrode plate: 16.5 × 10−6 K−1] effectively decreased the compressive stress to 250 MPa in the Si chip, compared with that of a conventional Ni–Sn SLID joint (500 MPa) after joining. Moreover, the stress was relaxed when heating to 200°C during thermal cycling (from −40 to 200°C), due to the plastic and creep deformations of the inserted Al sheet. In addition, Ni–Sn DSLID/Al joint suppressed crack propagation during thermal cycling and exhibited higher thermal durability than Ni–Sn SLID and Sn–10% antimony solder joints up to 500 cycles, due to the higher resistances of the plastic and creep deformations of the inserted Al sheet. The present concept demonstrates great potential for use in fabricating joints for next-generation power modules.

Internal Stress Evaluation on SiC Dices after SLID Process

Thin layers of intermetallic (IMC) were prepared using Solid-Liquid Inter-Diffusion (SLID) process. 3μm of Tin was deposited on SiC dice, then soldered on a copper substrate at different temperature: 250-300-330-370°C and different soldering times: 5sec-300 sec - 15 min - 1h. The composition of the IMC was identified using energy dispersive X-Ray spectroscopy (EDX). Two types of intermetallic layers were identified: Cu3Sn and Cu6Sn5. The samples were tested using die shear test. Then the internal stress was measured by X-Ray Diffraction (XRD). XRD spectrum obtained spotted only pure copper present underneath the intermetallic layer. The results showed that the level of residual stress is related to the amount of voids in the solder.

Solid-Liquid Interdiffusion (SLID) Bonding of p-Type Skutterudite Thermoelectric Material Using Al-Ni Interlayers.

Over the past few years, significant progress towards implementation of environmentally sustainable and cost-effective thermoelectric power generation has been made. However, the reliability and high-temperature stability challenges of incorporating thermoelectric materials into modules still represent a key bottleneck. Here, we demonstrate an implementation of the Solid-Liquid Interdiffusion technique used for bonding Mmy(Fe,Co)4Sb12 p-type thermoelectric material to metallic interconnect using a novel aluminium–nickel multi-layered system. It was found that the diffusion reaction-controlled process leads to the formation of two distinct intermetallic compounds (IMCs), Al3Ni and Al3Ni2, with a theoretical melting point higher than the initial bonding temperature. Different manufacturing parameters have also been investigated and their influence on electrical, mechanical and microstructural features of bonded components are reported here. The resulting electrical contact resistances and apparent shear strengths for components with residual aluminium were measured to be (2.8 ± 0.4) × 10−5 Ω∙cm2 and 5.1 ± 0.5 MPa and with aluminium completely transformed into Al3Ni and Al3Ni2 IMCs were (4.8 ± 0.3) × 10−5 Ω∙cm2 and 4.5 ± 0.5 MPa respectively. The behaviour and microstructural changes in the joining material have been evaluated through isothermal annealing at hot-leg working temperature to investigate the stability and evolution of the contact.

Evolution of microstructure of Lead free cu/Sn solders and copper oxide phase precipitation in Cu3Sn intermetallic during thermal cycling

Intermetallic layers were formed after Solid Liquid Interdiffusion (SLID). Cu-Sn interdiffusion leads to the formation of two intermetallic layers: Cu6Sn5 and Cu3Sn. In this work, Sn solder was subjected to thermal cycling from −65 to +250 °C at 10 °C/min. After few cycles we noticed the appearance of a new –pillar– shaped phase made of copper oxide. The Intermetallic layers were mechanically tested using die-shear testing. The die-shear resistance appears to be increasing when the number of thermal cycles increases. The microstructure was observed using Backscatter Electron detector (BSD) and Scanning Electron Microscopy (SEM). The composition of the phase was measured using Energy Dispersive x-ray spectroscopy (EDX). It appears that a new copper oxide phase forms after few cycles. As the number of cycles increase, the size and the number of the copper oxide phases increase.

A Brief Review on High-Temperature, Pb-Free Die-Attach Materials

High-Pb solders have been used as die-attach and interconnect materials for decades in discrete power components. Because of the known harmful effects of Pb to human health and the environment, as well as the demand of the wide-band-gap SiC/GaN power devices serving under high power density and high junction temperature, alternative Pb-free solders/materials and solutions have been studied intensively. Pb-free alternatives to replace high-Pb solders are still in their infancy. The exemption of using high-Pb solders has been extended to 2021, although it may be terminated anytime if a new technology or material were to be accepted industry-wide. The potential high-temperature Pb-free materials, including solders (AuSn/AuSi/AuGe, ZnAl and BiAgX®), Ag-sintering material, and transient liquid-phase bonding (TLPB) material, are reviewed in this paper with an emphasis on BiAgX® solders. The extremely high cost of Au-based solders limits their applications, although they have been used in high-temperature electronics. Zn-Al has a high melting temperature, good mechanical properties, and good thermal performance. However, the high reactivity makes Zn-Al solders only available in wire and preform. BiAgX® solder (available in paste, wire and preform) has been developed to replace the high-Pb solders for use in low-power discrete components, with relatively low cost and better reliability than the high-lead counterpart. Ag-sintering material and TLPB material form joints by atomic diffusion (either solid diffusion for sintering or solid–liquid interdiffusion for TLPB). The challenges in mass-production and the cost have restricted their success to be widely used in industry. Although it is likely that none of these materials/technologies are ideal to satisfy all the requirements of the variety of high temperature Pb-free die attach applications in terms of processing/reliability/cost, each solution has the potential to satisfy a niche within this broader categorization.

Perspectives of High-Temperature Pb-Free Bonding Materials

Abstract High lead solders have been used as die-attach and interconnect materials in discrete power packages. Due to the demand of SiC devices serving the high-power market and the harmful effects of Pb to human health and the environment, alternative Pb-free solders, novel bonding materials, as well as solutions have been studied extensively in recent years. The exemption of using high-Pb solders has been extended again to 2021, although it could be terminated at any time if a new technology or material were to be accepted by the industry. This paper presents potential materials and technologies for high-temperature Pb-free die-attachment, focusing on alternative solders. Sintering materials and transient liquid phase bonding (TLPB) materials have been briefly covered as well. AuSn, AuSi, and AuGe solders have shown to be exceptionally high in cost, which limited their application. BiAg- and BiCu-based solders—the BiAgX® family including solder paste, solder wire, and solder preform—improved wetting and exhibited remelting temperatures of 262°C and 270°C, respectively. The acceptable reliability performance on temperature cycling and thermal aging, as well as low material cost, has made them the most competitive candidates for low-power discrete die-attach devices. SnSbAgCu, with well-designed compositions in recent studies, offers a remelting temperature above 320°C. SnSbAgCu is targeted in markets for mid-to-high power devices. Reliability testing for other recently designed SnSbAgCu pastes for various die-attach vehicles is being studied. ZnAl has a remelting temperature above 380°C and an extremely low material cost (comparable to or even lower than the high-lead solders). Although the bonding process is stringent, the excellent thermomechanical behavior and the superior thermal/electrical conductivity have allowed ZnAl to be a potential candidate for high-temperature/high-power die-attach that is competitive with AuSi and AuGe solders. Sintering materials form bonds through solid state interdiffusion, while TLPB materials create a joint through solid-liquid interdiffusion, in which the remelting temperature is enhanced by forming massive IMCs. The desired high thermal/electrical/mechanical/melting performances, as well as the relatively low processing temperature (<350°C), are shining the sintering materials (especially Ag-sintering materials). The intrinsic high porosity (>20%) and the evolution of pores from pressureless sintering may overshadow the reliability. In addition, the immaturity of the processing (time/temperature/pressure/atmosphere/equipment availability, etc.) may deter the industrial adoption of sintering materials. So far, none of these materials or technologies is ideal to satisfy all the requirements of the variety of high-temperature, Pb-free die-attach applications in terms of processing, reliability, and cost. However, each material and solution has the potential to be a niche within this broader categorization.

Void Formation and Intermetallic Growth in Pulse Electrodeposited Cu-Sn Layers for MEMS Packaging

Electrodeposited copper (Cu)-tin (Sn) based solid–liquid interdiffusion (SLID) bonding is becoming popular in wafer-scale packaging of inertial Micro-Electro-Mechanical-Systems (MEMS) sensors due to its inherent advantages of lower cost, low processing temperatures and less stringent surface uniformity requirements. However, eliminating micron-size voids within intermetallic compounds (IMCs) and bond interfaces has remained a challenging task. The present study focuses upon IMC growth and void formation at varying temperatures and times. Stacks of varying thickness of Cu and Sn were fabricated by electrodeposition, and the samples were annealed at temperature ranging up to 300°C. Scalloped shaped Cu6Sn5 (η-phase) and comparatively uniform Cu3Sn (e-phase) intermetallics were observed. Experimental results show that the growth of metastable Cu6Sn5 dominates IMC formation at lower temperatures but as temperature increases, Cu3Sn dominates over the Cu6Sn5 growth. This IMC growth transition from Cu6Sn5 dominant growth to Cu3Sn dominant growth depends on the annealing temperature and has a critical time duration. The IMC thicknesses are compared with those obtained by numerical simulation models. For given annealing temperatures, intermittent voids formed in the IMC layers show increasing size and decreasing void fraction trends with increasing annealing times. The results suggest that Cu-Sn SLID bonding performed at 275°C yields reliable bonding since the void growth is minimal. Based on these results, a test vehicle containing a kelvin structure and daisy chains (having large number of Cu-Sn bonded structure), was fabricated, resulting in electrical resistances lower than 30 m-ohms and 6 ohms, respectively.

Material Shear Strength Assessment of AU/20SN Interconnection for High Temperature Applications

AbstractWhen a power module is under a continuous electrical load, a temperature effect is induced by the current load in the module configuration. The joint material therefore has long-term temperature and mechanical loadings under supplied power. A long-term temperature load can change the material and mechanical properties, including voiding, cracking, creeping and fracturing. Au/20Sn eutectic alloy, a highly temperature resistant material, is typically used for electric interconnections in high-power modules. The Au/20Sn is converted into AuSn and an Au5Sn intermetallic compound (IMC) by solid liquid inter-diffusion (SLID) bonding to form joints with high melting points. In this study, a test vehicle based on an actual power module was designed and fabricated to investigate and understand the material properties and mechanical behavior of Au/20Sn solder under a temperature load. The joint microstructure exhibited variation under different thermal treatment conditions such as temperature and load durations. The shear strength test was conducted to examine the mechanical strength of the joints under different thermal load conditions. The failure mode of the joint was further determined using fracture morphology after the shear test. Finally, the shear strength of Au/20Sn was identified to investigate the high temperature resistance of joints under different temperatures. The mechanical strengths of joints under different temperature loads are expressions of different mechanical characteristics and can be used to determine reliability at an intended high application temperature.

The nucleation-controlled intermetallic grain refinement of Cu-Sn solid-liquid interdiffusion wafer bonding joints induced by addition of Ni particles

In this study, Ni particle was validated as an effective grain refiner for the Cu-Sn solid-liquid interdiffusion (SLID) wafer bonding joints, which induced a dispersive non-interfacial nucleation of intermetallic grains, effectively preventing the grain mergence phenomenon. With increasing the Ni particle addition, there were significant reductions in both the (Cu, Ni)6Sn5 grain size and the Cu3Sn layer thickness, 6 wt% addition of Ni particles even led a formation of the intermetallic joints only consisted of (Cu, Ni)6Sn5 grains with an average grain size of 1.3 μm. (Cu, Ni)6Sn5 grain refinement could notably enhanced the shear strength of the intermetallic joints.

Design of diffusion barrier and buffer layers for β-Zn4Sb3 mid-temperature thermoelectric modules

The purpose of this work was to investigate the feasibility of using sputtered Ti/W-Ti/Ti multilayer as diffusion barrier and buffer layers between β-Zn4Sb3 thermoelectric (TE) material and Ag interconnect layer for mid-temperature TE module applications. Interdiffusion at the interface was examined by both scanning electron microscope and Auger electron spectroscopy. After penetrating the Ti buffer layer, Ag, Zn and Sb were successfully blocked by the W-Ti diffusion barrier layer. We also proved that the TE sample with diffusion barrier and buffer layers showed phase stability after high temperature aging. Also, the sheet resistance decreased as the temperature increased and it indicated good electrical properties at high working temperatures. In addition, the solid-liquid interdiffusion method was used to join the TE module, and the bonding remained stable at the TE module working temperature.

Behavior of stress generated in semiconductor chips with high-temperature joints: Influence of mechanical properties of joint materials

High-temperature joint materials are indispensable to realizing next-generation power modules with high-output performance. However, crack initiation resulting from stress concentration in semiconductor chips joined with high-temperature joint materials remains a critical problem in high-temperature operation. Therefore, clarifying the quantitative influence of joint materials on the stress generated in chips is essential. This study investigates the stress behavior of chips joined by Ni–Sn solid–liquid interdiffusion (SLID), which results in a high-temperature joint material likely to generate cracks after joining or when under thermal cycling. The results are compared with those fabricated using three types of solders, Pb–10%Sn, Sn–0.7%Cu, and Sn–10%Sb (mass %), which are conventional joint materials with different melting points and mechanical properties. Using Ni–Sn SLID results in the generation of high compressive stress (500 MPa) without stress relaxation after the joining process in contrast to the case of solders in which the compressive stresses are low (<300 MPa) and decrease to still lower levels (<250 MPa). In addition, no stress relaxation occurs during thermal cycling when using Ni–Sn SLID, whereas stress relaxation is clearly observed during heating to 200 °C using solders. Different stress behaviors between Ni–Sn SLID and other joint materials are illustrated by their mechanical strength and resistance against plastic and creep deformation. These results suggest that stress relaxation in a chip is key in suppressing crack initiation in highly reliable modules during high-temperature operation.

In–Bi low-temperature SLID bonding for piezoelectric materials

Purpose This paper aims to demonstrate low-temperature bonding for piezoelectric materials at temperatures well below the relevant Curie temperatures so as to avoid depolarization of the piezoelectric material during bonding. Design/methodology/approach Au-coated test samples of lead zirconate titanate (PZT) are bonded to a WC-based resonant backing layer with In–Bi eutectic material in which the In–Bi metal system is a preform or thin, evaporated layers. The bonded samples are characterized using electrical impedance spectroscopy and cross-section microscopy. The first technique verifies the integrity of polarization and reveals the quality of the bondline in a non-destructive manner, particularly looking for voids and delaminations. The latter technique is destructive but gives more precise information and an overview of the structure. Findings Successful low-temperature (115°C) bonding with intact PZT polarization was demonstrated. The bondlines show a layered structure of Au/Au–In intermetallic compounds (with Bi inclusions)/Au, capable of withstanding temperatures as high as 271°C before remelting occurs. For bonded samples using In–Bi preform, repeatable bonds of high quality (very little voiding) were obtained, but the bonding time is long (1 h or more). For bonded samples using evaporated thin films of In–Bi, bonding can be performed in 30 min, but the process needs further optimization to be repeatable. Originality/value Low-temperature solid-liquid interdiffusion (SLID) bonding is a novel technique, merging the fields of low-temperature solder bonding with the SLID/transient liquid phase (TLP) approach, which is normally used for much higher temperatures.

Continuous-wave operation of m-plane GaN-based vertical-cavity surface-emitting lasers with a tunnel junction intracavity contact

We have achieved continuous-wave (CW) operation of an optically polarized m-plane GaN-based vertical-cavity surface-emitting laser (VCSEL) with an ion implanted current aperture, a tunnel junction intracavity contact, and a dual dielectric distributed Bragg reflector design. The reported VCSEL has 2 quantum wells, with a 14 nm quantum well width, 1 nm barriers, a 5 nm electron-blocking layer, and a 23λ total cavity thickness. The thermal performance was improved by increasing the cavity length and using Au-In solid-liquid interdiffusion bonding, which led to lasing under CW operation for over 20 min. Lasing wavelengths under pulsed operation were observed at 406 nm, 412 nm, and 419 nm. Only the latter two modes appeared under CW operation due to the redshifted gain at higher temperatures. The peak output powers for a 6 μm aperture VCSEL under CW and pulsed operation were 140 μW and 700 μW, respectively. The fundamental transverse mode was observed without the presence of filamentary lasing. The thermal impedance was estimated to be ∼1400 °C/W for a 6 μm aperture 23λ VCSEL.

Wafer-Level AuSn/Pt Solid–Liquid Interdiffusion Bonding

In this paper, wafer-level AuSn/Pt solid–liquid interdiffusion bonding for hermetic encapsulation of microelectromechanical systems (MEMS) is evaluated. Although AuSn is used for bonding of ICs, the implementation of AuSn diffusion bonding in MEMS applications requires thorough understanding of its compatibility with the complete layer stack including adhesion, buffer, and metallization layers. Partitioning of the layer stacks is possible in MEMS devices consisting of several silicon wafers since the device wafer carrying functional structures and the encapsulation wafer have different restrictions on process integration and applicable metal deposition techniques. In this paper, CMOS/MEMS compatible sputtered platinum is utilized on the device wafer as a contact metallization for Au–Sn metallized cap wafer. The role of the platinum layer thickness as well as the nickel and molybdenum buffer layers on mechanical reliability were tested. The mechanical shear and tensile tests were performed for samples after bonding as well as after high-temperature storage and thermal shock tests. The results were rationalized based on the combined microstructural, thermodynamic, and fracture surface analyses. High-strength and thermodynamically stable bonds were achieved, exhibiting shear strength up to ~180 MPa and tensile strength up to ~80 MPa. Platinum was consumed completely during bonding and was observed to dissolve mainly into the (Au,Pt)Sn phase. Thicker platinum layer (200 versus 100 nm) increased the (Au,Pt)Sn phase thickness and resulted in higher strength. The molybdenum buffer layer under the platinum metallization increased the tensile strength significantly.

Characterization of low temperature Cu/In bonding for fine-pitch interconnects in three-dimensional integration

This study presents the results for Cu/In bonding based on the solid–liquid interdiffusion (SLID) principle for fine-pitch interconnects in three-dimensional integration. The microbumps were fabricated on Si wafers (55 µm pitch, 25 µm top bump diameter, 35 µm bottom bump diameter). In was electroplated directly on Cu only on the top die microbumps. Two different In thicknesses were manufactured (3 and 5 µm). The interconnects were successfully fabricated at a bonding temperature of 170 °C. High temperature storage was carried out at 150 and 200 °C for different times between 2 and 72 h directly after the interconnect formation in order to investigate the temperature stability. The microstructure was analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The intermetallic compound (IMC) found in the microbumps after electroplating was CuIn2. The intermetallic interlayer consists of Cu11In9 and a thin layer of Cu2In after bonding and isothermal storage.

Cu-Sn Intermetallic Compound Joints for High-Temperature Power Electronics Applications

Cu-Sn solid–liquid interdiffusion (SLID) bonded joints were fabricated using a Sn-Cu solder paste and Cu for high-temperature power electronics applications. The interfacial reaction behaviors and the mechanical properties of Cu6Sn5 and Cu3Sn SLID-bonded joints were compared. The intermetallic compounds formed at the interfaces in the Cu-Sn SLID-bonded joints significantly affected the die shear strength of the joint. In terms of thermal and mechanical properties, the Cu3Sn SLID-bonded joint was superior to the conventional solder and the Cu6Sn5 SLID-bonded joints.

Accelerated Metastable Solid–liquid Interdiffusion Bonding with High Thermal Stability and Power Handling

Emerging high-performance systems are driving the need for advanced packaging solutions such as 3-D integrated circuits (ICs) and 2.5-D system integration with increasing performance and reliability requirements for off-chip interconnections. Solid–liquid interdiffusion (SLID) bonding resulting in all-intermetallic joints has been proposed to extend the applicability of solders, but faces fundamental and manufacturing challenges hindering its wide adoption. This paper introduces a Cu-Sn SLID interconnection technology, aiming at stabilization of the microstructure in the Cu6Sn5 metastable phase rather than the usual stable Cu3Sn phase. This enables formation of a void-free interface yielding higher mechanical strength than standard SLID bonding, as well as significantly reducing the transition time. The metastable SLID technology retains the benefits of standard SLID with superior I/O pitch scalability, thermal stability and current handling capability, while advancing assembly manufacturability. In the proposed concept, the interfacial reaction is controlled by introducing Ni(P) diffusion barrier layers, designed to effectively isolate the metastable Cu6Sn5 phase preventing any further transformation. Theoretical diffusion and kinetic models were applied to design the Ni–Cu–Sn interconnection stack to achieve the targeted joint composition. A daisy chain test vehicle was used to demonstrate this technology as a first proof of concept. Full transition to Cu6Sn5 was successfully achieved within a minute at 260°C as confirmed by scanning electron microscope (SEM) and x-ray energy dispersive spectroscopy (XEDS) analysis. The joint composition was stable through 10× reflow, with outstanding bond strength averaging 90 MPa. The metastable SLID interconnections also showed excellent electromigration performance, surviving 500 h of current stressing at 105 A/cm2 at 150°C.

Gigahertz scanning acoustic microscopy analysis of voids in Cu-Sn micro-connects

Gigahertz scanning acoustic microscopy (GHz-SAM) is applied to the characterization of bulk voids in the Cu-Sn material system, often used in micro-connects. An increased demand for the development of miniaturized interconnect technologies, such as micro-connects, means that fast characterization methods are required for the assessment and detection of reliability impacting defects. This study attempts to formulate an analytical technique aimed at detecting micro-structural defects in Cu-Sn micro-connects, such as micro-bumps for 1st level interconnects and solid-liquid interdiffusion bonds for nano- and microelectromechanical systems. To study the potential of the analytical method, a specific electroplating chemistry was used that increases the probability of defect formation in the electroplated Cu film. The chemistry is known under certain electroplating overpotentials to promote hydrogen bubble induced voids within the Cu. The samples containing voids were inspected by GHz-SAM with a highly focused acoustic lens operating at 1.12 GHz. To validate the results, GHz-SAM micrographs were compared with focused ion beam prepared cross-sections of the selected samples. Advances in acoustic transducer technology operating in the GHz frequency band allow for micron sized defect examination of materials with enhanced lateral resolution and sub-surface sensitivity.