High Temperature Storage Life Research Articles

Development of Wafer Level Package Platform for High Reliability Crossover MCUs

Fan in and fan out wafer level packages are primarily used in the industry for applications in handheld consumer electronic products. The key benefits of wafer level package (WLP) are small form factor, reduced cost, improved electrical and thermal performance. WLP investigated in this study are directly surface mounted on PCB and have no intermediate substrate. Direct mount of package on PCB, leads to significant CTE mismatch between the package and board which stresses the package solder joint, leading to cyclic fatigue induced solder joint cracking. To overcome the solder joint cracking, stiffer solder alloys have been evaluated. However, higher stiffness of the solder alloy shifts the cyclic stress induced failure, from the solder joint to the package metal interconnect layers. Moreover, WLP on advanced silicon node have fragile low-k and extremely low-k back end of line dielectric layers that also crack or delaminate in cyclic fatigue. In this work extensive WLP platform development has been done with following DOE variables; multi-layer package routing, dielectric materials, solder alloys, solder ball pitch and diameter. Developed packages passed and outperformed the following product reliability qualification conditions: high temperature storage life (150°C, 2000 hours), highly accelerated stress test (110°C / 85%RH / Bias, 528 hours), application level temperature cycling ((-40 °C to 125 °C, 600 cycles), board level temperature cycling (-40 °C to 125 °C, 500 cycles) and board level drop test (1500g/0.5ms, 30 drops). Excellent reliability, functional performance, and successful chip package integration was achieved for WLP for crossover MCU products.

Development of high performance flip chip ball grid array (FCBGA) packages for automotive application processors

Automobiles have witnessed rapid proliferation of infotainment, driver assistance and autonomous driving features which have led to significant increase in semiconductor content per car. However, this has also required increased integration of device functionality to meet the new automotive requirements for in-vehicle networking, autonomous driving, infotainment, and sensor integration. Advance technology/packages are needed to provide ideal solutions for automotive grade reliability, high electrical performance, and multi-function integration for automotive application processors. To address these requirements, innovative packages including Flip Chip Ball Grid Array (FCBGA) are the potential solutions. In this study FCBGA packages are developed for automotive processor application and qualified for AEC2 qualification tier. To achieve higher performance and reliability, different package substrate materials such as core dielectric and build-up dielectric were evaluated. Mechanical modelling and simulation of package reliability and influence of key material properties such as coefficient of thermal expansion (CTE), modulus of elasticity (E) and glass transition temperature (Tg) was used to provide guidance for the selection of substrate and assembly materials. Developed packages met all the product performance requirements and passed package qual conditions of high temperature storage life (150°C, 500 hours), temperature cycling (-55 °C to 125 °C, 1000 cycles), temperature humidity bias (85 °C, 85% RH, 1000 hours) and board level temperature cycling (-40 °C to 125 °C, 1000 cycles).

Effects of Commercial No-Clean Flux on Reliability of Fine Pitch Flip-Chip Package With Solder Bumps and Copper Pillars

In this work, two commercial no clean fluxes, namely, extremely low residue no-clean flux (NCF) (NC-1) and ordinary NCF (NC-2), were used for the preparation of a fine pitch flip-chip package with a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7.6\,\times \,7.6$ </tex-math></inline-formula> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> Si die on a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$17\,\times \,17$ </tex-math></inline-formula> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> organic substrate. One water-soluble (WS) flux was also used for comparison. Moisture sensitivity of the package was evaluated using JESD22-A113D (30 °C/60% relative humidity (RH), 192 h, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3\times $ </tex-math></inline-formula> reflow at 260 °C). Thermal cycling tests were performed following JESD22-A104D (−65 °C to 150 °C). The high-temperature storage life (HTSL) of the packages was investigated using JESD22-A103C (175 °C). Underfill delamination or voids in the package were investigated by confocal scanning acoustic microscopy (C-SAM). Failure characteristics of the packages were also studied using scanning electron microscopy (SEM). After moisture sensitivity level (MSL) test, vehicles prepared by NC-1 and NC-2 showed failure. SEM images revealed severe delamination between underfill and solder mask in the presence of amine/amide and carboxylic acid-based NCF residue. Solder bump crack were found at < 500 cycles for samples prepared with NC-1 which contains tertiary amine and long carbon chain (C8:C10:C12) carboxylic acid-based. However, failure occurred at < 1500 cycles for NC-2 containing secondary amide and shorter carbon chain length (C3) carboxylic acid. Samples prepared using WS did not show any failure for up to 2000 cycles. Thus, NCF-treated assemblies performed poorly in moisture sensitivity and temperature cycling tests.

MAXQFP: NXP's new package solution for automotive application

Abstract 172-lead (16x16 mm body size) and 100-lead (10x10 mm body size) MAXQFP's and 172 MAXQFP_EP (exposed pad) for automotive industry are introduced. The advantage of MAXQFP as compare to standard LQFP/QFP packages will be outlined. Thermal &amp; mechanical simulation results were performed to prove its advantage over conventional LQFP and LQFP_EP. The challenges in manufacturing, designs and concerns of tighter lead pitches for MAXQFP are briefly addressed. Methods and data to resolve these challenges will be shown. For example, Sn whisker and Sn migration both are concerns to MAXQFP because of smaller distance between adjacent leads. The board-level solder joint reliability (SJR) has been collected to prove it is AEC G1 compliant. Visual inspection methods and requirements on AOI (automatic object inspection) systems on solider joints of J-leads of MAXQFP for are proposed. Standard AEC G1 component level reliability stresses defined at AEC Q100 which are TC (temperature cycling), HTSL (high temperature storage life), THB (Temperature Humidity Biased) and uHAST (un-biased HAST) tests are summarized Since Cu wires were used, AEC Q006 data are also collected. Assembly challenges are described. Future works will be summarized.

Gold wire bond study for automotive application

In this publication, the influence of bond wire material properties (Au 2N/4N), and plasma pre-treatment on the wire-bond strength is investigated based on Automotive Electronics Council Qualification (AEC-Q100) and customer requirements. The wire pull force capability is compared, and growth of the Au/Al intermetallic phase (IMP) is analyzed with scanning electron microscope (SEM) cross sections after High Temperature Storage Life (HTSL, 150 °C), Temperature Cycling (TC, −65 °C – 150 °C) and unbiased Humidity Accelerated Stress Test (uHAST, 130 °C/85% relative humidity (RH)). The effect of plasma treatment prior bonding on 2N and 4N wires is discussed and compared to the results without plasma treatment prior wire bonding. Furthermore, test acceleration by using elevated test temperatures (HTSL, 250 °C) is shown and the wire capability compared.

Effects of alloying elements in high reliability copper wire bond material for high temperature applications

Recently, a shift from Au bonding wire to Cu bonding wire is expected for automotive application. Palladium coated copper (PCC) wire is strong candidate since it is widely used in LSI packages owing to its high performance and low cost. In order to apply PCC wire to automotive devices, long-term reliability specific to automobiles including stable operation under harsh environment with high temperature and humidity is required. However, pitting corrosion at the wedge bond portion was reported with PCC wire under high temperature storage life (HTSL) test. Depending on the surrounding environment such as mold compound, it is difficult for conventional PCC wire to achieve the target of automotive application. A newly developed PCC wire (EX1R) has thus developed. By using additive element in Cu core, halide induced interface corrosion and also pitting corrosion can be prevented successfully. In this paper, effect of additive element on the corrosion resistance will be discussed. The result shows that additive element forms protective passivation layer on the intermetallic compound (IMC) and Cu surface. Thereby, EX1R improves bond reliability even under severe reliability test condition.

Accelerated Stress Tests and Statistical Reliability Analysis of Metal-Oxide/GaN Nanostructured Sensor Devices

In this work, sensor die/process and packaging reliabilities of metal-oxide/GaN nanowire-based gas sensors have been studied for the first time, using industry standard accelerated lifetime tests, such as- High Temperature Operating Life, High Temperature Storage Life, Temperature Cycling Test and Highly Accelerated Stress Test. The metal-oxide functionalization used for sensing ethanol exposure in this study is ZnO. For all the tests, sample ZnO/GaN devices have been exposed to 500 ppm of ethanol in dry air at room temperature (20°C) to observe and record the degradation of signal to noise ratio (SNR) as a function of stress time and number of thermal cycles. Although no complete device failure was observed in any of the performed tests, gas sensing response kept decreasing gradually due to increasing stress. The lowering of the sensor response is believed to be due to gradual phase transformation of the receptor ZnO and baseline resistance increase. The method for estimating failure rate and lifetime of sensor devices has been discussed in detail. Using statistical data from the performed accelerated stress tests, chi-square distribution has been implemented to predict the failure rate and lifetime of GaN nanostructured sensor devices. The mean-time-to-failure (MTTF) of the stressed devices of this study is about 4 years.

High bond reliability of newly developed silver alloy bonding wire

Abstract In this paper, a new type of silver (Ag) alloy bonding wire is introduced, and its bonding property and long term reliability are demonstrated. The new Ag wire, called GX2s, is developed as a cost-effective alternative to gold (Au) wire targeting at automotive electronics. The wire material is doped with added element, and its electrical resistivity is much lower than the conventional palladium (Pd) doped Ag wire. Highly accelerated stress test (HAST) and high temperature storage life (HTSL) test were carried out along with other bonding evaluations. The results show that GX2s has good bonding property and excellent long term bond reliability. Microstructural analyses of bond interface after the reliability tests were also conducted to investigate its improving mechanism. GX2s is a suitable alternative to Au wire for many applications including high temperature automotive devices.

Luminous Efficiency of Pd-Doped Ag-Alloy Wire Bonded LED Package after Reliability Tests

In this study, binary Ag-alloy wires were doped with different Pd concentrations, and each wire was encapsulated in an LED package. The initial optical characteristics were tested, and reliability was tested with the high temperature storage life (HTSL), high temperature operating life (HTOL) and wet high temperature operating life (WHTOL). The luminous efficiency of the Ag-alloy wire LED package was about 2% higher than that of the Au wire package, but the addition of 6% Pd to the Ag-alloy wire decreased the luminous efficiency to close to that of the Au-wire LED package. This was due to the high reflectivity of silver in the blue wavelength region, as compared to the low reflectivity of palladium. After 1,000 hours of HTOL and WHTOL, the results showed that the performance of luminous flux maintenance increased with increasing Pd content, indicating that Ag-alloy wires doped with a sufficient amount of Pd can inhibit degradation due to oxidation reaction and thermal and humidity aging. Therefore, binary Ag-Pd alloy wires produced with specific drawing and annealing processes are suitable for mid-power white light LEDs in lighting applications.

Copper Ball Voids: Failure Mechanisms and Methods of Controlling at High Temperature Automotive Application

Since 2008, fine gauge (≤ 35 μm diameter) copper (Cu) wire has been rapidly replacing fine gauge gold (Au) wire in consumer, commercial, and industrial products [2–4]. The first wave of Cu wire products used bare, uncoated Cu wire which is soon to known having Cu-Al IMC corrosion induced by mobile chlorine ions in the epoxy mold compound system when IC parts are subjected to moisture related package stress tests such as biased HAST (Highly Accelerated Stress Test) [1–7]. Additionally, when comparing to Au wires, the 2nd bond process window of bare Cu wire can be very narrow and becomes a concern of moving into HVM (high volume manufacturing) [8]. Thus, palladium-coated Cu (PdCu) wire was introduced to the semiconductor assembly market aiming to provide more margin of passing biased HAST and enhance 2nd bond process capability [9–13]. However, the use of Pd-Cu wire is not a panacea to all Cu wire bond problems. One unique anomaly for Pd-Cu wire is the Cu ball void [1] which is observed only with Pd-Cu and not bare Cu ball bonds during HTSL (high temperature storage life) tests. The mechanism of forming Cu ball voids was proven to be the galvanized corrosion mechanism with Pd-Cu coupling. Significant factors affecting the formation rate of Cu ball voids are found to be baking temperature, EFO current settings, bonding parameters and mold compound additives (sulfur). Both anodic and cathodic chemical reactions will be proposed for Cu voids in this paper. Even though Cu void can be considered as a cosmetic defect for the majority of application since the peak temperature of device mission profile is always no larger than 175C. The application at extreme high temperature (for example, 190C) can actually cause electrical failure at the ball bon region due to the Cu void formation in terms of size and location at the Cu-Al IMC region. The main effect is due to the selected mold compound having high amount of metallic adhesion promoter which is sulfur-based and extensive high temperature storage test condition (190C). The FIB/SEM picture of failing ball bond due to Cu voids from this particular device will be presented in the paper. Thus, a newly developed doped Cu wire without Pd coating has been proposed by many wire suppliers to overcome Cu ball voids. However, doped Cu wires without Pd coating have suffered the same high volume manufacturing issues observed by bare Cu wires. For example, short tail and mean time between assist (MTBA) for doped Cu wires without Pd coating are both as poor as bare Cu wires. We will present high temperature storage test results obtained by doped PdCu wires in this paper. To balance high volume manufacturing issues and Cu void formation, doped PdCu wires are also proposed recently. Several doped PdCu wires whose extensive high temperature storage results (220C) will be presented in this paper. The worst case mold compound with high amount of sulfur based adhesion promoter has been used to test the effectiveness of these new wire types. At such harsh testing condition, there is one doped PdCu wire in our test can actually survive without electrical failed ball bond due to Cu voids. Factors of effectiveness of doped PdCu wires will be discussed in this paper. Authors have chosen to focus on Cu voids at both 1st bond (ball bond) and 2nd bond (wedge). 20 um wire diameter has been used for all test vehicle in this study. All controlling factors of eliminating Cu voids will surely be included at the end of this paper.

Power Semiconductor SMD Package Embedded in Multilayered Ceramic for Low Switching Loss

We propose a multilayered-substrate-based power semiconductor discrete device package for a low switching loss and high heat dissipation. To verify the proposed package, cost-effective, low-temperature co-fired ceramic, multilayered substrates are used. A bare die is attached to an embedded cavity of the multilayered substrate. Because the height of the pad on the top plane of the die and the signal line on the substrate are the same, the length of the bond wires can be shortened. A large number of thermal vias with a high thermal conductivity are embedded in the multilayered substrate to increase the heat dissipation rate of the package. The packaged silicon carbide Schottky barrier diode satisfies the reliability testing of a high-temperature storage life and temperature humidity bias. At 175 °C, the forward current is 7 A at a forward voltage of 1.13 V, and the reverse leakage current is below 100 μA up to a reverse voltage of 980 V. The measured maximum reverse current (IRM), reverse recovery time (Trr), and reverse recovery charge (Qrr) are 2.4 A, 16.6 ns, and 19.92 nC, respectively, at a reverse voltage of 300 V and di/dt equal to 300 A/μs.

The reliability of Ag wedge bonding with various bonding pads for power devices

Abstract Recent years, with the development of intelligent vehicles, power devices would be widely used. But traditional Si power devices have problems under high temperature. Now, there is a tendency that using SiC instead of Si in power devices, as SiC has a higher band gap 3.25 eV comparing with 1.12 eV of Si. So that SiC power devices can withstand higher temperature and voltage. Also SiC power devices have the advantages of lower parasitic parameters, smaller device size and shorter response time. In this study, to investigate the reliability of Ag wedge bonding, Ag wires were bonded on Al pad and Au-Ni pad. And then we did shear test after high temperature storage life test (HTSL). Finally, we used energy dispersive X-ray spectroscopy (EDS) to do cross-section observation. The results show that, for Al pad, the shear strength has decreased after annealing at 300°C with mold packages, cracks and corrosion were observed. For Au-Ni pad, the shear strength has increased after annealing, and no cracks or corrosion formed. So Ag bonding wire is proposed as an alternative to Al bonding wire for selected metal pads in power devices.

High-Temperature Reliability of Copper Wire-Bonded Packages Encapsulated with Mold Compounds Containing Sulfur Compounds

Cu wire-bonded (CuWB) packaging is more susceptible to corrosion than traditional inert gold wires. CuWB reliability greatly depends on the compatibility of Cu wire with the surrounding encapsulating mold compound as this matrix can provide a corrosive environment leading to reliability issues. Many mold compounds contain specific components, which are sulfur-based compounds. Since the reliability testing of an encapsulated packaged device involves thermal treatments, such as the high-temperature storage life (HTSL) test, there is a concern that corrosive sulfur compounds can be produced at high temperatures (e.g., 150°C and 175°C), endangering CuWB reliability. This article describes detection methods of sulfur compounds produced from mold compounds, if any, at high temperatures such as 175°C and CuWB die package reliability with mold compounds containing sulfur compounds. The dynamic headspace concentration-gas chromatography-mass spectroscopy analysis technique was used to test liberation of gaseous and volatile sulfur compounds from mold compounds at temperatures 25°C, 150°C, 175°C, and 200°C. No gaseous sulfur compounds were detected by chromatographic methods within the time period of the experiments. To determine sulfur-containing anionic species present in the mold compound matrix, such as sulfide, sulfite, sulfate, and thiosulfate, ionic compounds were extracted to water and analyzed by ion chromatography. Upon analysis, the only sulfur-bearing anion found in the samples was sulfate. Thermally treated mold compounds for 2,000 h at 150°C and for 1,000 h at 175°C were also extracted and analyzed to determine possible decomposition of sulfur compounds due to the thermal aging process. Corrosion due to sulfur compounds and reliability of CuWB was evaluated by HTSL for 2,000 h at temperatures of 150°C and 175°C with devices packaged with mold compounds containing sulfur compounds. CuWB ball bond-Al interface and Cu stitch bond integrity were evaluated by focused ion beam-scanning electron microscopy with energy-dispersive x-ray spectroscopic analysis and wire pull and ball shear testing of CuWB ball bonds. No reliability issues due to sulfur compounds were found with mold compounds containing sulfates up to ∼45 ppm.

Electrical and Reliability Performance of Molded Leadless Package for High-voltage Application

This paper investigates the influence on electrical and reliability performance of molded leadless package for high-voltage power integrated circuit application. Semiconductor devices are mostly encapsulated by using epoxy molding compounds which act as protection for the ICs from damage to the harsh environment. Quad Flat No Lead was selected since the application requirement for compact AC to DC portable adapter charger and more input and output pin. High-voltage package was designed based on the IPC-2221 standard specification and creepage distance was calculated under external component lead, uncoated. Two epoxy molding compounds were used namely as type A and B. Key properties of EMCs were identified such as ionic content, glass transition temperature and volume resistivity. The electrical tested at room temperature on high-voltage leakage current at 700V showed EMC B has no failure compared with EMC A. On top of that, electrical parametric distribution showed that the Cpk of EMC B was extremely robust compared with EMC A. Reliability test was conducted for high temperature operating life test at 115˚C and EMC B was passed up to 1000hours while EMC A was failed. Meanwhile, High Temperature Storage Life test at 150˚C and Temperature Humidity Bias Test at condition 85˚C, 85% relative humidity showed that EMC B was passed for 1000hours but EMC A was failed at 168hours. However, both compounds A and B were passed delamination criteria tested by scanning acoustic tomography technique before and after subjected to moisture sensitivity level 1.

Reliability and Failure Modes of Solid-State Lighting Electrical Drivers Subjected to Accelerated Aging

An investigation of an off-the-shelf solid-state lighting device with the primary focus on the accompanied light-emitting diode (LED) electrical driver (ED) has been conducted. A set of 10 EDs were exposed to temperature humidity life testing of 85% RH and 85 °C (85/85) without an electrical bias per the JEDEC standard JESD22-A101C in order to accelerate the ingress of moisture into the aluminum electrolytic capacitor (AEC) and the EDs in order to assess the reliability of the LED drivers for harsh environment applications. The capacitance and equivalent series resistance for each AEC inside the ED were measured using a handheld LCR meter as possible leading indications of failure. The photometric quantities of a single pristine light engine were monitored in order to investigate the interaction between the light engine and the EDs. These parameters were used in assessing the overall reliability of the EDs. In addition, a comparative analysis has been conducted between the 85/85 accelerated test data and a previously published high-temperature storage life accelerated test of 135 °C. The results of the 85/85 acceleration test and the comparative analysis are presented in this paper.

High Temperature Reliability of Copper Wire - Bonded Packages Encapsulated with Mold Compounds Containing Sulfur compounds

Copper wire-bonded (CuWB) packaging is more susceptible to corrosion than traditional inert gold wires. CuWB reliability greatly depends on the compatibility of Cu wire with the surrounding encapsulating mold compound as this matrix can provide a corrosive environment leading to reliability issues. Many mold compounds contain specific components which are sulfur-based compounds. Since the reliability testing of an encapsulated packaged device involves thermal treatments such as high temperature storage life (HTSL) test, there is a concern that corrosive sulfur compounds can be produced at high temperatures, e.g. 150 °C and 175 °C, endangering CuWB reliability. This paper describes methods of detection of sulfur compounds produced from mold compounds, if any, at high temperatures such as 175 °C and CuWB die package reliability with mold compounds containing sulfur compounds. Dynamic Headspace Concentration-Gas Chromatography–Mass Spectroscopy (DHC-GC-MS) analysis technique was used to test liberation of gaseous and volatile sulfur compounds from mold compounds at temperatures 25 °C, 150 °C, 175 °C, and 200 °C. No gaseous sulfur compounds were detected by chromatographic methods within the time period of the experiments. In order to determine sulfur containing anionic species present in the mold compound matrix, such as sulfide, sulfite, sulfate and thiosulfate, ionic compounds were extracted to water and analyzed by Ion Chromatography. Upon analysis, the only sulfur bearing anion found in the samples was sulfate. Thermally treated mold compounds for 2000 hours at 150 °C and 1000 hours at 175 °C were also extracted and analyzed to determine possible decomposition of sulfur compounds due to the thermal aging process. Corrosion due to sulfur compounds and reliability of CuWB (bare Cu-25 μm wire diameter) were evaluated by HTSL for 2000 hours at temperatures of 150 °C and 175 °C with devices packaged with mold compounds containing sulfur compounds. CuWB ball bond – Al interface and Cu stitch bond integrity were evaluated by FIB (Focused Ion Beam) - SEM (Scanning Electron Microscope) with EDX (energy dispersive X-ray spectrometer) analysis and wire pull and ball shear testing of CuWB ball bonds. No reliability issues due to sulfur compounds were found with mold compounds containing sulfates up to about 45 ppm.

Copper wire interconnect reliability evaluation using in-situ High Temperature Storage Life (HTSL) tests

This paper describes the use of in-situ High Temperature Storage Life (HTSL) tests based on a four point resistance method to evaluate Cu wire interconnect reliability. Although the same set up was used in the past to monitor Au–Al ball bond degradation, a different approach was needed for this system. Using conventional statistical methods of failure probability distributions and a fixed failure criterion were found to be unsuitable in this case. Besides this, tests usually take very long until a sufficient percentage of the population have failed according to that criterion. A simple physical model was used to electrically quantify ball bond degradation due to the prevailing failure mechanism in a substantially smaller amount of test time. The method enabled the determination of activation energies for a number of moulding compounds and is extremely useful for a fast screening of such materials regarding their suitability for Cu wire.

Evolution and investigation of copper and gold ball bonds in extended reliability stressing

This paper discusses the microstructure evolution of copper (Cu) and gold (Au) ball bonds after various extended reliability stresses such as biased highly accelerated temperature and humidity test (HAST), unbiased highly accelerated temperature and humidity test (UHAST), temperature cycling (TC), and high temperature storage life (HTSL) in BGA package. Objective of this study is to study the microstructure evolution and changes after long hours and long cycles of component reliability stressing and its predicted failure mechanisms and to determine the long-term reliability comparison with combination of bonding wires in HAST, UHAST, and TC. Secondary electron microscopy (SEM) and energy dispersive X-ray (EDX) have been carried out to understand the respective microstructure of failed samples in HAST, UHAST, TC, and HTSL long-term reliability failures. Respective failure mechanisms of copper and gold ball bonds carrion under HAST and UHAST, ball bond lifting in TC and HTSL have been analyzed and proposed. The evolution of surface morphology, including copper and gold ball bond micro cracking, gold ball bond Kirkendall microvoiding and intermetallic compound (IMC) formation, was studied in FBGA package with copper and gold ball bonds during various reliability stresses. Biased HAST, UHAST, TC, and HTSL mechanisms were proposed to explain the observed morphological changes and the resulting ball bond wear out modes after extended reliability stresses. Weibull reliability analyses have been established to compare the performance of copper and gold ball bonds under humid and dry environmental tests.

Effects of Bonding Wires and Epoxy Molding Compound on Gold and Copper Ball Bonds Intermetallic Growth Kinetics in Electronic Packaging

This paper discusses the influence of bonding wires and epoxy mold compounds (EMC) on intermetallic compound (IMC) diffusion kinetics and apparent activation energies (E aa) of CuAl and AuAl IMCs in a fineline ball grid array package. The objective of this study is to study the CuAl and AuAl IMC growth rates with different epoxy mold compounds and to determine the apparent activation energies of different combination of package bills of materials. IMC thickness measurement has been carried out to estimate the coefficient of diffusion (D o) and E aa various aging conditions of different EMCs and bonding wires. Apparent activation energies (E aa) of both wire types were investigated after high temperature storage life tests (HTSL) for both molding compounds. Au bonds were identified to have faster IMC formation, compared to slower IMC growth of Cu. The E aa obtained for CuAl IMC diffusion kinetics are 1.08 and 1.04 eV with EMC A and EMC B, respectively. For AuAl IMC diffusion kinetics, the E aa obtained are 1.04 and 0.98 eV, respectively, on EMC A and EMC B. These values are close to previous HTSL studies conducted on Au and Cu ball bonds and are in agreement to the theory of HTSL performance of Au and Cu bonding wires.Overall, EMC B shows slightly lower apparent activation energy (E aa) valueas in CuAl and AuAl IMCs. This proves that the different types of epoxy mold compounds have some influence on IMC growth rates.

Superior performance and reliability of copper wire ball bonding in laminate substrate based ball grid array

PurposeThe purpose of this paper is to provide a systematic method to perform long‐term reliability assessment of gold (Au) and copper (Cu) ball bonds in fineline ball grid array package. Also with the aim to study the apparent activation energies (Eaa) and its associated wearout mechanisms of both Au and Cu wire in semiconductor device packaging. This paper discusses the influence of wire type on the long‐term reliability and mechanical performance after several component reliability stress tests.Design/methodology/approachA fineline ball grid array (FBGA) package with Cu and Au wire bonds was assembled with green molding compound and substrate. Samples are subjected for long‐term high temperature storage bake test at elevated temperatures of 150°C, 175°C and 200°C. Long‐term reliability plots (lognormal plots) are established and Eaa of both ball bonds are determined from Arrhenius plots. Detailed failure analysis has been conducted on failed sample and HTSL failure mechanisms have been proposed.FindingsReliability results show Au ball bond in FBGA package is observed with higher hour‐to‐failure compared to Cu ball bonds. The Eaa value of high temperature storage life (HTSL) reliability for Au ball bond is lower than Cu ball bond. Typical HTSL failure mechanism of Au ball bond is induced by micro‐voiding and AuAl intermetallic compound (IMC) micro‐cracks while CuAl IMC micro‐cracking (induced by Cl− corrosion attack and micro‐cracking) caused wearout opens in Cu ball bond. These test results affirm the test‐to‐failure data collected is a useful method for lifetime prediction and Eaa calculation.Practical implicationsThe paper reveals higher reliability performance of Cu ball bond in FBGA flash memory package which can be deployed in flash memory FBGA packaging with optimised package bill of materials.Originality/valueThe test‐to‐failure methodology is a useful technique for wearout reliability prediction and Eaa calculation.