Wire Bond Reliability Research Articles

Wire Bond Ability Enhancement of 8 Leads Small Outline Integrated Circuit and 14 Leads Thin Shrink Small Outline Package Using AuPd Coated Cu Wire Bonding for Automotive Devices

Paper present a study enhancement of wire bonding process in the integrated circuit package with 2N AuPd coated Cu wire (2N-AuPdCu) for Automotive devices. Wire bonding is the electrical connection between pad and leadframe. In present, Au wire is recently use for interconnection while the gold price still exorbitant and caused concern to the wire bonding cost. Cu wire is a lower price and considered to be an alternative for the interconnection but still concern in term of corrosion and reliability. Recently, 4N AuPd coated Cu wire (4N-AuPdCu) material have been introduced for automotive device but still encounter the reliability problem. The 2N AuPd coated Cu wire was developed version for more reliability enhancement and consider to use for alternative wire of automotive device. In the experiment, Au wire, 4NAuPdCu wire and 2N AuPd coated Cu wire were used for wire bonding process on 8 leads Small Outline Integrated Circuit Package (8L-SOIC) and 14 leads Thin Shrink Small Outline Package (14L-TSSOP) to compare wire bond ability. Analysis, this package tested wire bond ability and reliability. The results performed well in wire bond ability and reliability for 2N AuPd coated Cu wire when comparing with Au wire and 4N AuPd coated Cu wire. Therefore, 2N AuPd coated Cu wire can enhance the quality and reliability for 8L-SOIC package and 14L-TSSOP package for automotive device.

Exploration of Interfacial Materials Chemistry Control to Improve Cu Wire-Bonding Reliability

Exploration of Interfacial Materials Chemistry Control to Improve Cu Wire-Bonding Reliability

Evaluation of Copper and Gold Wire Bonds in PEM Devices

Abstract The shift from gold to copper wire bonds used in plastic encapsulated microcircuits (PEMs) has been gradual for the last few years. Many agencies and critics question the long-term robustness and reliability of copper wire bonds; however, PEM manufacturers have been thoroughly evaluating and optimizing the copper wire bond process over the last few years to produce highly reliable products. When the manufacturing process is optimized and closely controlled and monitored, copper wire bonds can be a reliable and stronger alternate to gold wire bonds. This paper details a copper wire bond study that specifically compares copper wire against gold wire bonds following combined environmental life stress test conditions. In this study, bond pull testing indicates good performance of both copper and gold wire bonds. The methods used in this analysis (destructive physical analysis, wire pull testing, and environmental testing) were effective techniques for evaluation of bond wire integrity, detection of manufacturing defects, and overall assessment of copper and gold wire bond processes. Based on wire bond testing in this analysis, the reliability and integrity of optimally developed copper wire bonds appear to be superior to or even stronger than gold wires in the same package type. Equivalent reliability was demonstrated for both copper and gold wire bonds in this test.

Bond Wire Fatigue of Au, Cu, and PCC in Power LED Packages.

Bond wire failure, primarily wire neck breakage, in power LED devices due to thermomechanical fatigue is one of the main reliability issues in power LED devices. Currently, the standard testing methods to evaluate the device's lifetime involve time-consuming thermal cycling or thermal shock tests. While numerical or simulation methods are used as convenient and quick alternatives, obtaining data from material lifetime models with accurate reliability and without experimental fatigue has proven challenging. To address this issue, a mechanical fatigue testing system was developed with the purpose of inducing mechanical stresses in the critical region of the bond wire connection above the ball bond. The aim was to accelerate fatigue cracks at this bottleneck, inducing a similar failure mode as observed during thermal tests. Experimental investigations were conducted on Au, Cu, and Pd-coated Cu bonding wires, each with a diameter of 25 µm, using both low- and high-frequency excitation. The lifetime of the wire bond obtained from these tests ranged from 100 to 1,000,000 cycles. This proposed testing method offers material lifetime data in a significantly shorter timeframe and requires minimal sample preparation. Additionally, finite element simulations were performed to quantify the stresses at the wire neck, facilitating comparisons to conventional testing methods, fatigue test results under various operating conditions, material models, and design evaluations of the fine wire bond reliability in LED and microelectronic packages.

Increasing the Reliability of Aluminum Wirebonds by Thermal Treatments: Analysis and Implementation

In this work we studied the effect of a post-bonding thermal treatment on thick aluminum wirebonds lifetime in IGBT power modules during power cycling at different temperature swings. A reliability improvement of up to 44% is demonstrated for the bonds located at the center of the chip and seeing the highest thermal treatment temperature. The physical phenomena occurring during the thermal treatments and during power cycling are studied using microstructure analysis (Scanning Electron Microscopy techniques) and nanoindentation. Softening of the material results from recrystallization and/or recovery during thermal treatment, whereas during power cycling the thermal treated material hardens due to strain accumulation and defect formation. Despite the hardening our data suggests a decrease in crack growth rate at the second half of the testing time. We implemented an approach for applying thermal treatments during typical operating conditions in a converter by controlling the off-state losses of a device in a multichip configuration. The stability and the limits of this approach are studied experimentally and described by an electrothermal model. This study allows us to conclude on a realistic process window for online thermal treatments, by considering both material constrains and practical temperature control limits.

Digital Twins and Smart Manufacturing for Wire Bonding

Low cost, excellent flexibility, and high yield rate have long been the drivers of wire bonding technology. In the past decade, advancements in wire bonding technology have significantly improved wire bond reliability and strengthened the adoption of the technology while maintaining its competitive advantage. Digital twins of wire bonding can now simulate and optimize 3D wire loop shapes to facilitate design-for-manufacturing (DFM), increase design flexibility, reduce product development time, and improve overall package yields. In particular, the benefits of digital twins have been realized in system-in-package (SiPs), large stack-die memory applications, and complex high pin count packages with multiple looping tiers. With increasing package complexity and modular package configurations, the need for smarter functionalities is imperative. More recently, technological developments in wire bonding have been targeted toward furthering design, quality, and time-to-market (TTM) from an Industry 4.0 smart manufacturing perspective. In this paper, we will introduce new digital twin simulation techniques to detect potential interference between wire bond capillaries and wire loops, various dies, passive components, and other structures within the package. These advanced capabilities are demonstrated on a real application and shown to help in the detection of design issues early in the product cycle and aid in the selection of capillary, wire, as well as optimization of the package layout. All these factors significantly improve the overall TTM of semiconductor packages. Technologies that provide improvements via autonomous monitoring and optimization are also strongly desired. We will also explore new on-bonder process monitoring capabilities to detect wire sway such that wire shorts and resultant yield losses can be minimized. Additionally, vision-guided enhancements to on-bonder loop height monitoring capabilities will also be discussed. These new advancements significantly improve production quality and yield, paving the way for smarter factories

Advantages of the extended finite element method for the analysis of crack propagation in power modules

• XFEM and Level set methods with submodelling has been implemented in this study. • Method easily allows inclusion of crack growth in IGBT wire bond reliability analysis • Bond wire diameter and loop height significantly affect IGBT wire bond reliability. • Wire bond degradation parameter values decrease with increasing crack length. • For similar load density, smaller wire diameter produces longer wire bond lifetime. The techniques of extended finite element method, level set method and the submodelling approach are implemented in this study to model crack and crack growth in ultrasonically bonded thick aluminium wire for the IGBT power electronics modules under different loading conditions for the purpose of lifetime prediction and reliability assessment during design and manufacturing stages. The crack growth and lifetime prediction were performed under cyclic fatigue passive thermal cycling and active power cycling for the bond wire lift-off failure mechanism while the J-integral for different heel crack lengths are predicted under mechanical loads. The analyses showed that the techniques implemented in this paper are effective for modelling such complex geometries and loading conditions and can easily be integrated in a virtual design platform for power electronics. The accuracy of the technique is evaluated by comparing with trends in the published experimental tests and simulation results as well as the standard finite element method which are all in a good agreement. The wire bond crack growth rate under cyclic loading is strongly influenced by the bond thickness and loading conditions.

Effect of post bonding annealing on the reliability of Al based wire bondings in IGBTs

The reliability of Aluminium wire bonds in IGBTs is reported to be positively affected by a high temperature ultrasonic bonding or a post annealing treatment after wire bonding. This study focusses on the effect of the later and aims to explain the increase in lifetime recorded after power cycling tests on treated vs untreated modules. The reliability enhancement is linked to the microstructure modification of the Al wire/metallization interface as a result of the heat treatment. Using scanning and transmission electron microscopy, the microstructure evolution of heat-treated modules after power cycling is analyzed. The damage mechanisms of the heat treated, and non-treated Al top interconnects are compared. It is observed that the heat treatment improves the bonding interface thus slowing down the degradation of the wire bonds.

Impact of heat treatment on the lifetime of wire-bonded power modules

Wire bondings in power modules are one of the weakest links in packaging, often causing an entire power module to fail. Thermo-mechanical stresses in the wire bonds related to CTE mismatch induce cracks that propagate in a region close to the bonding interface. In this paper, Scanning Electron Microscope (SEM) analysis after a bonding process clearly shows small grains and a different texture close to the interface of the wire and the die metallization. In order to improve the reliability of wire bonds, heat treatment after power module manufacturing is proposed. Heat treatment has a positive effect on the bonding region by increasing the grain size, reducing the dislocation density and merging the grains of the wire and the metallization. Furthermore, power cycling has been shown to increase the lifetime of the heat-treated power modules compared to a control comprising the same non-treated (as-delivered) IGBT power modules.

Failure Analysis of Aluminum Wire Bonds in Automotive Pressure Sensors in Thermal Shock Environments

Wire bonding remains one of the most widely adopted interconnection techniques in the field of electronic packaging. At present, the most effective way to ensure a long life and high reliability of wire bonds is to improve the bonding quality. In this study, both experiments and finite element analysis (FEA) were employed to develop a fundamental understanding of wire bond degradation. Sensors with two protective silicone gels were loaded with the same thermal shock at a temperature ranging from $- 40^{\circ }\text{C}$ to 125°C, and the switching time was shorter than 10 s. The number of thermal shock cycles for the aluminum wire covered with transparent silicone reached 1200, but the maximum number of cycles for the other wire only reached 454. The experimental results indicated that the chosen transparent silicone performed better than did the black silicone originally selected, which was also verified by the simulation results. In addition, bond pull and shear tests were performed. The results revealed no degradation of either the Ag-Al or Ni-Al bonding joints under thermal loading. In summary, the root cause of failure was found to be improper protection silicone application, which, as often ignored in analysis, accelerated thermal fatigue of the aluminum wires. An explanation of the observed trend and a recommended aluminum wire bonding method were also provided.

A Way to Reduce Leakage Current and Improve Reliability of Wire-Bonds for 300-A Multichip SiC Hybrid Modules

In this article, pressureless sintering of nanosilver paste is proposed to enhance the reliability of wire-bonds with SiC chips by both alleviating thermomechanical stresses and enhancing thermal coupling of bonding wires and chips. A multichip 1200-V/300-A SiC hybrid module with six Si IGBTs and 12 SiC Schottky barrier diodes (SBDs) is demonstrated. The lifetime of the wire-bonds with the SiC SBD bonded by the pressureless sintered nanosilver is ~27.9% longer than that by the high-temperature solder under power cycling with constant temperature swing. The lifetime of the wire-bonds with the IGBT also bonded by the pressureless sintered nanosilver is ~46.2% longer than that by the high-temperature solder under power cycling with constant conduction current. Furthermore, not only the cost of 1700-V SiC SBDs is quite similar to that of 1200-V ones but also the leakage current of the 1200-V/300-A SiC hybrid module can be reduced greatly using 1700-V SiC SBDs as free-wheeling diodes instead of the regular 1200-V ones. Considering the much larger leakage current of a SiC SBD compared with that of a Si p-i-n diode. It is feasible to use a SiC SBD with higher blocking voltage to reduce the significant leakage current of the free-wheeling SBD with almost no cost increase.

Wire-Bonding Reliability Evaluationa

Abstract In microelectronic devices, wire bonding is the most common first-level interconnection method between die and lead. Failure of wire bonding causes component failure. Component failure may lead to system or sub-system failures, which often have very expensive consequences. Such failures are even more severe in the harsh operating conditions of the Oil and Gas industry, where services such as rig charge are extremely expensive. We have developed a robustness-evaluation method for microelectronic components using construction analysis.

Controlling Extrinsic Chloride Ions Effect on Copper Wirebond Reliability

Abstract Copper (Cu) wirebond (WB) reliability in encapsulated microelectronic devices is influenced by intrinsic and extrinsic chloride ions. Previous work showed that intrinsic extractable chloride (Cl) ions that are part of the epoxy mold compound (EMC) can cause Cu-Al intermetallic (IMC) or Al pad corrosion under moisture-temperature reliability conditions. Another mode of Cl corrosion occurs due to the entrapment of Cl foreign material (FM) particles that can release Cl ions after molding the device. Intrinsic EMC and extrinsic Cl ions in encapsulated EMC must be defined, analyzed, and controlled to limit the potential for corrosion. Extrinsic Cl ions from FM (Foreign Material) particles can originate from human sources, the environment, assembly processes, and assembly tools. This paper focuses on extrinsic Cl ions from Cl-FM. Cl-FM embedded in EMC can be determined by dissolving the EMC in a solvent followed by filtration. The isolated FM was characterized by various techniques including: Scanning Electron Microscopy - energy-dispersive X-ray (SEM – EDX) and Fourier-transform infrared spectroscopy (FTIR) to determine the structure of the Cl-FM compounds. The FTIR Analysis determines the presence of C-Cl bond by identifying stretching bond frequency in the region of 800 – 600 cm−1 that determines if the Cl-FM particle is organic. The combination of analytical techniques was used to identify the source of the Cl-FM. The types of Cl FM particles discovered were both organic and inorganic in nature, and of different shapes and sizes. The smaller size particles < 30μm posed a challenge for some particle type identification accuracies. Airborne particles are one of the main sources of Cl FM particles that can be entrapped in the EMC. Airborne particles are created by environmental dust, human wear, abrasion and handing, and machine maintenance. The primary Cl FM particles were found to be carbon-chlorine polymers such as polyvinyl chloride (PVC), Polyvinylidene chloride (PVDC), and inorganic chlorides including metal chlorides. Many of the EMC materials found to have entrapped natural and synthetic fibrous materials with embedded Cl compounds. The 175°C mold process and 260°C reflow thermal effect degrading the Cl FM particle in the EMC matrix could generate Cl depending on the additives and modifiers. Investigations were performed to develop hypotheses of how Cl FM particles are generated in the EMC and how the FM particles could be controlled.

Effect of copper over-pad metallization on reliability of aluminum wire bonds

Recently, there have been moves to replace Si power devices with SiC ones, which will require new materials with higher thermal conductivity for power module assemblies owing to their higher operating temperatures. Al wire bond interconnections suffer from a mismatch in the coefficient of thermal expansion (CTE) between the SiC chip and the wire material, leading to a degradation of the power module reliability owing to the higher junction temperature (Tj) operation caused by the current density increase. Various studies have been conducted to improve the reliability of such interconnections. In this study, Al wires were bonded on a thick Cu over-pad metallization (OPM) layer that was formed on an Al pad of a SiC Schottky barrier diode, and active power cycling tests were performed while changing Tjmax to investigate the contribution of such a thick Cu-OPM layer on the reliability of Al wire bonds. Compared with the case of Al wire bonds on an Al pad, in active power cycling tests, the lifetime of Al wire bonds on a 25 μm-thick Cu-OPM layer was 1.3-times longer at ΔTj = 75 °C, and 1.5-times longer at ΔTj = 100 °C. The results of Joule heating analysis and elastic thermal-stress analysis showed that the lifetime prolongation effect of Al wire bonds on Cu-OPM was not derived from the heat dissipation effect of the thick Cu-OPM layer, but from a stress-reduction effect obtained by keeping the Al wire bonds away from the SiC diode chip, with which the CTE mismatch is large.

Life prediction of copper wire bonds in commercial devices using principal component analysis (PCA)

Copper has been widely adopted as a viable alternative to gold for wire bonding, due to its lower cost, better electrical and thermal conductivity, lower tendency for wire sweep due to a higher modulus and slower intermetallic compound (IMC) formation with aluminum bond-pad. However, these IMCs can cause an increase in resistance and separation between bonding interface which causes an open circuit. Wire bond and component reliability must consider all factors in combination with the change of wire bond materials and processes. How can users of off-the-shelf components determine the effects of wire bond material changes on the reliability of the components in their systems? How will these changes affect high reliability applications such as automotive, military and harsh environments?Although physics-of-failure based models can represent the failure mechanisms individually, the complex nature of the mixed failure mechanism has inhibited development of an analytical equation to represent it. In addition, geometrical and material characteristics of the entire package along with bonding process parameters play a crucial role in magnitude of stress experienced by these bonds, portraying difficulty in developing one such equation for use to all copper wire bonded devices. This study has aimed to develop a data-based predictive method based on the principal component analysis technique to provide an estimate of the wire bond time to failure for plastic encapsulate components. Extensive thermal cycling experiments have been performed on multiple commercial devices to obtain training data for the model. This method of wire bond fatigue and failure prediction is an adaptive technique which can achieve greater accuracy as more data is added. This method aims to provide a life-time estimate of copper wire bonded component with inputs such as initial geometrical, material properties, and wire bond related attributes for a specific package.

Deriving lifetime predictions for wire bonds at high temperatures

We report a method to predict wire bond lifetimes. Wire bond resistance increase due to thermal stress can be modelled by the Arrhenius equation, permitting prediction of wire bond reliability in a product prior to qualification if sufficient experimental data is collected and statistically analysed. Activation energies for various experiment “legs” are determined by stressing a number of wire bonds at 3 different temperatures, then, using survival analysis techniques for accelerated failure time models, extrapolating results to use conditions. Example lifetime predictions for Cu and PCC wire bonds on Al pads are shown to illustrate the method, using a small number of test dies that incorporate four-wire resistance measurements of wire bond pairs, with two ball bond sizes and two different wire types, stressed at precise temperatures with in-situ resistance monitoring in the University of Waterloo's “mini-oven” reliability test systems. These results show that typical Cu wire bonds on Al bond pads can be highly reliable up to 163 °C without encapsulation or 155 °C with encapsulation, with estimated lifetimes of 12,000 h with <1 ppm failure rate, assuming a failure condition of 10% resistance change.

Complete elimination of Ag3Al in Ag wire bonds on Al by alloying In into Ag

During the electronic packaging process, when the silver (Ag) alloy wire bonds on aluminum (Al) pads, it is often desirable to avoid the formation of Ag3Al because of its low fracture toughness and low corrosion resistance. The current work reports a method to eliminate the Ag3Al through alloying indium (In) into Ag. The corresponding mechanism is studied through transmission electron microscopy (TEM) and thermodynamic modeling. The experimental results show that the formation of Ag3Al leads to the repelling of In atoms into unreacted Ag solid solution when the In concentration is low, but the Ag3Al can be fully eliminated and replaced by an Ag–In–Al ternary phase when the concentration of In is at 12%. We establish an analytical thermodynamic model for the nucleation process of Ag3Al that considers the effects of In doping, and successfully explains the underlying reason for the elimination of Ag3Al: it has to do with the necessity of repelling In into unreacted region. Reaction kinetics are further discussed and the deceleration in Ag–Al inter-diffusion is attributed to the solute–vacancy attraction. A study of defects in Ag–Al bonding wire system is conducted and the growth rate of voids is found to be low due to small volumetric change during phase transformation, which also reduces the growth rate of alumina. Compared to Ag3Al, Ag–In–Al ternary phase is experimentally proven to be softer, tougher, and more corrosion resistant, which would contribute to enhanced wire bond reliability and perhaps an increase the market share of Ag alloy bonding wires.

Failure Mode and Mechanism Analysis for Cu Wire Bond on Cu/Low-k Chip by Wire Pull Test and Finite-Element Analysis

In this paper, failure mode and mechanism analysis on Cu wire bond and bond pad reliability for Cu/low-k chip are investigated through wire pull test and finite-element analysis (FEA). The wire pull test has been carried out for the bonded Cu wires with changing pull position to reveal different failure modes. Failed load is monitored and failure mode is analyzed for different wire pull test conditions. It is observed that the pull position influences failed pull force and failure mode. Failure modes include broken wire neck and wire wedge, ball lift, and pad peel and the failed force decreases with a changing pull location from the ball bond toward the wedge bond. FEA simulation is performed to help further understand failure mechanism and establish failure criteria. Finally, failure mechanism and criteria are presented for different failure modes and materials. In addition, the influence of wire loop height is also studied.

Effective decapsulation of copper wire-bonded microelectronic devices for reliability assessment

The wire bonding industry has made a major shift in wire materials from gold to copper, primarily due to cost concerns. Copper wire-bonds are now present in many commercial off-the-shelf (COTS) devices but minimally used in automotive, industrial, or military-grade applications due to lack of detailed understanding about reliability concerns. A thorough study of wire bond reliability includes performing bond shear and pull strength measurements before and after stress testing. This in turn requires a special decapsulation procedure for copper wire-bonded devices because, unlike gold, copper is chemically potent. Many techniques for copper wire-bonded device decapsulation exist and can be categorized into laser-, plasma-, and acid-based processes. This paper reviews some of these techniques and discusses the decapsulation mechanism, which involves decomposition of the epoxy resin. By understanding the decapsulation mechanism and available techniques, a unique decapsulation method was developed. The effectiveness of this method is presented along with scanning electron microscopy (SEM) images of the results, which indicate minimal etching of copper wire bonds. The critical parameters of this technique are also identified, a suitable range of input for each parameter is analyzed theoretically, and a design of experiment (DOE) is conducted to find optimal values for each parameter. Several SEM images are provided to show both the good and bad results from the DOE. An image method for measuring effectiveness of decapsulation is also presented.

High-Temperature Reliability of Wire Bonds on Thick Film

Abstract In a harsh environment, wire-bonded interconnects are critical for overall reliability of microelectronic assemblies. Aluminum is the dominating metallization of the die wire bonding pads and aluminum wires are used to achieve monometallic bonding system on die side. On the substrate side, a monometallic connection is not readily available and typically involves expensive aluminum thin-film deposition or labor-intensive bonding tabs. Nickel-palladium-gold galvanic or electro-less plating stacks are also used to improve bondability and reliability of non-monometallic Al wire bonds on the substrate side. However, these plating stacks do not perform well after excursions above 330°C that are needed for the attachment of die and passives prior to wire bonding. At these temperatures, both palladium and nickel diffuse through the gold and form surface oxides that degrade wire bondability. In monometallic wire-bonding schemes, in addition to aluminum wires gold wires within same assembly are often also needed, for example, when some die is only available with gold-plated bond pads, or to connect substrates to gold-plated pins of hybrid housings. A universal substrate metallization, compatible with aluminum wire and gold wire, is therefore desirable. Thin-film substrates produced by sequential deposition and etching of gold metal, barrier metals, then aluminum metal is a good working solution, but it can be as much as ten times more expensive than other types of substrates. Printed thick-film metallization, a well-established technology, have been widely used for hybrid substrates. Silver-based thick films are inexpensive and capable of accepting aluminum and gold bonds. However, the silver-aluminum bonds are seldom used because of intermetallic formation and subsequent degradation triggered by multiple factors like temperature, humidity, and the presence of halogens. Pd and Pt are often added to the Ag thick films to decrease this effect, but potential usability and the reliability of these formulations in extreme temperature environments is not well researched. For this study, samples of Pt/Ag thick-film metallization were printed on Al2O3 substrates, and 25-um and 250-um aluminum wires and 50-um gold wires were wedge bonded in daisy chain to the substrate. The test vehicles were subjected to high-temperature testing at 260°C and 280°C. Thermal cycling tests from −20°C to 280°C were also performed. Mechanical and electrical characterizations of the wire bonds were conducted periodically. These tests included resistance and pull-strength measurements. Failure analysis of the bond joints was performed to understand the results of the tests. The 250-um Al wire and 25-um Al wire showed no significant changes until a critical time-at-temperature was reached. After reaching this temperature, the wire/substrate interface resistance rapidly increased to values as high as 40 Ohms for the 25-um Al wires. However, the pull strength remained within standard throughout the tests of up to 1200 hours. The relationship between time to failure and the temperature is presented in the paper. There was a four times life increase of bonds with every 20°C. With gold wires, no dramatic increase of bond resistance was observed, only a slight increase with time. The pull strength of Au wires remained stable throughout the time at high temperature. The tested Ag/Pt thick film metallization was found to be compatible with bonding of the gold wires and the aluminum wires for high-temperature applications up to an Arrhenius equivalent of 800 hours at 260°C. Additionally, Parylene HT coating was vapor-deposited on one set of 250-um Al wire-bonding samples. This set of samples demonstrated doubling of its useful life as compared to the uncoated samples.