Query: An evaluation of effects of molding compound properties on reliability of Ag wire components

Candidate papers:

abstract: Silver (Ag) bond wires are increasingly used in semiconductor components to replace gold (Au) bond wires, and applications for these components are expanding from consumer to high reliability electronic systems. To assess the impact of this technology transition on the overall component reliability, extended reliability testing beyond the typical JEDEC component qualification testing is needed. Additionally, key packaging materials, such as molding compounds, also need to be re evaluated as they may interact with the Ag wire bond differently from Au wire bonds and introduce new failure mechanisms under different conditions. In this work, we investigate the impact of molding compound chemistry and testing condition on the reliability performance by testing a range of commercially available Ag wire bonded components. The composition of the molding compound is analyzed and concentrations of key elements that contribute to bond wire bonding pad interface corrosion are reported. These components are subjected to acceleration tests, including temperature humidity bias and high temperature storage tests. As a control, Au wire bonded components are also subjected to the same acceleration tests. Failure rates and mechanisms for the experimental conditions are determined based on resistance measurements and cross section analyses of microstructures and discussed in terms of interactions between the test conditions, the chemistry of the molding compounds, and wire bond composition. Reliability testing and analytical results demonstrate the importance of controlling molding compounds composition and properties and provide guidelines for the selection of these materials for different applications. In particular, improved and better controlled packaging material formulations will be needed for high reliability and mission critical electronic systems to ensure the long term reliability of components using Ag bond wires.
author_names: Keisuke Yazawa

Matthew Parsons

Azzedin Jackson

Wenhao Chen

Alexander Campbell

John E Blendell

Carol A Handwerker

Peng Su
title: An Evaluation of Effects of Molding Compound Properties on the Reliability of Ag Wire Bonded Components
venue: 2017 IEEE 67th Electronic Components and Technology Conference (ECTC)
year: 2017

abstract: Adhesion and interface compositions of epoxy phenolic molding compounds (EMCs) for high temperature plastic packages are studied. Interfaces are obtained by molding two EMCs onto aluminum oxide hydroxide surfaces (oxide onto thin film of AlSiCu) and two die passivation layers consisting of fluorinated polyimide and cyclotene. One compound (A) is a "green" type, containing organic phosphorous based flame retardant, and the other compound (B) is a conventional type containing antimony (III) oxide and bromined resin flame retardants. A high temperature storage test at 250 degC is employed to study chemical modifications occurring at the previously mentioned interfaces. A high temperature reverse bias test at 225 degC is employed to study the influences of the EMC chemical formulations on the reliability of plastic packages for SiC based power MOS devices. Green compound A shows poor adhesion onto Al oxide and high adhesion strength onto both polymer passivations. The failure mechanism is mainly cohesive on the polymer passivations. The conventional compound B shows a high degree of delamination because of poor adhesion compared with the green compound. SiC based power MOS devices assembled in plastic packages with compound A show better reliability under HTRB test at 225 degC compared with compound B.
author_names: Antonino Scandurra

Giuseppe Francesco Indelli

Roberto Zafarana

Angelo Cavallaro

Emanuele Scrofani

Jean Paul Giry

Sebastiano Russo

Mietek Bakowski
title: Molding Compounds Adhesion and Influence on Reliability of Plastic Packages for SiC Based Power MOS Devices
venue: IEEE Transactions on Components, Packaging and Manufacturing Technology
year: 2013

abstract: Wire bonding on Al pad packages with an innovative annealing twinned Ag 8Au 3Pd alloy wire results in a sufficient interfacial intermetallic layer at the initial as bonded stage, while its growth during the further temperature cycling test and pressure cooker test is very slow. Even after prolonged high temperature storage at 150degC for 500 h, the thickness of its intermetallics is only around 1.7 mm. In contrast, a very thin CuAl<sub>2</sub> intermetallic layer appears at the interface of the Pd coated Cu wire bonded package, and a thick layer of Au<sub>8</sub>Al<sub>3</sub> intermetallic compounds forms in the Au wire package, which grows to a thickness of around 4.0 mm after high temperature storage at 150<sup>deg</sup>C for 500 h. Energy dispersive X ray spectrometry analyses indicate that AgAl<sub>2</sub> Au<sub>8</sub>Al<sub>3</sub> and CuAl<sub>2</sub> are the main intermetallic phases formed in the packages bonded with Ag 8Au 3Pd, and Au and Pd coated Cu wires, respectively. However, an additional Pd containing Ag<sub>2</sub>Al layer found at the AgAl<sub>2</sub>/Al interface of Ag 8Au 3Pd wire bonded package can interrupt its intermetallic reaction, and the annealing twins can further slow the intermetallic growth.
author_names: Tung-Han Chuang

Che-Cheng Chang

Chien-Hsun Chuang

Jun-Der Lee

Hsing-Hua Tsai
title: Formation and Growth of Intermetallics in an Annealing Twinned Ag 8Au 3Pd Wire Bonding Package During Reliability Tests
venue: IEEE Transactions on Components, Packaging and Manufacturing Technology
year: 2013

abstract: Solder materials demonstrate evolving microstructure and mechanical behavior that changes significantly with environmental exposures such as isothermal aging and thermal cycling. These aging effects are greatly exacerbated at higher temperatures typical of thermal cycling qualification tests for harsh environment electronic packaging. In the current study, mechanical measurements of thermal aging effects and material behavior evolution of lead free solders have been performed. Extreme care has been taken so that the fabricated solder uniaxial test specimens accurately reflect the solder materials present in actual lead free solder joints. A novel specimen preparation procedure has been developed where the solder uniaxial test specimens are formed in high precision rectangular cross section glass tubes using a vacuum suction process. The tubes are then sent through a SMT reflow to re melt the solder in the tubes and subject them to any desired temperature profile (i.e. same as actual solder joints) Using specimens fabricated with the developed procedure, isothermal aging effects and viscoplastic material behavior evolution have been characterized for 95.5Sn 4.0Ag 0.5Cu (SAC405) and 96.5Sn 3.0Ag 0.5Cu (SAC305) lead free solders, which are commonly used as the solder ball alloy in lead free BGAs and other components. Analogous tests were performed with 63Sn 37Pb eutectic solder samples for comparison purposes. In our total experimental program, samples have been solidified with both reflowed and water quenching temperature profiles, and isothermal aging has been performed at room temperature (25 degC) and elevated temperatures (100 degC, 125 degC and 150 degC) In this paper, we have concentrated on reporting the results of the room temperature aging experiments. Variations of the temperature dependent mechanical properties (elastic modulus, yield stress, ultimate strength, creep compliance, etc. were observed and modeled as a function of room temperature aging time. Microstructural changes during room temperature aging have also been recorded for the solder alloys and correlated with the observed mechanical behavior changes
author_names: Hongtao Ma

Jeffrey C Suhling

Pradeep Lall

Michael J Bozack
title: Reliability of the aging lead free solder joint
venue: 56th Electronic Components and Technology Conference 2006
year: 2006

abstract: Technical Introduction to the Second Edition. Ultrasonic Bonding Systems and Technologies (Including Ultrasonic Wire Bonding Mechanism) Some Aspects of Bonding Wire Characteristics That can Affect Bonding, Reliability, or Testing. Wire Bond Testing. Gold Aluminum Intermetallic Compounds and Other Metallic Interface Reactions Encountered in Wire Bonding. Bond Failures Resulting from Gold Plating Impurities and Conditions. Cleaning to Improve Bondability and Reliability. Mechanical Problems in Wire Bonding. High Yield and Fine Pitch Wire Bonding. Wire Bonding to Multichip Modules and Other Soft Substrates. Glossary. Index.
author_names: George G Harman
title: Wire Bonding in Microelectronics: Materials, Processes, Reliability, and Yield
year: 1997

abstract: Customers demand various functions from their applications and, in order to satisfy these demands, module packages must be multifunctional. This applies to power module packages that include power devices, components and control ICs. The modules must also have substrates in order dissipate heat from operating power chips as well as a PCB to create multifunctional circuits. Occasionally, specific clips are used instead of wire interconnections and the inner structures of the power module packages become complicated by a customer's design requests. When those power module packages accept epoxy molding compound (EMC) it may become difficult to achieve good `flowability, perfect molded packages, and stable wire sweep index and it may also be hard to avoid wire sagging risk. Finite element analysis (FEA) for semiconductor encapsulation early in the design phase is now essential to finding out target designs and proper quality of flow. FEA also helps to recommend proper runner systems, gate design, and the number of gates, which also helps to save time and money when producing the initial mold die. This paper will compare and discuss the limitations of the flow pattern, wire sweep, air vent effect, and air trap between the result of commercial FEA software, Moldflow(tm) and the real samples.
author_names: Taekkeun Lee

Aimee Lim

Young-sun Ko

Taewoo Lee

Byoungok Lee
title: The evaluation of flowability and wire sweep by epoxy molding compound for power module packages using Moldflow(tm)
venue: 2013 14th International Conference on Thermal, Mechanical and Multi Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE)
year: 2013

abstract: 1. Introduction 2. The structure of cellular solids 3. Material properties 4. The mechanics of honeycombs 5. The mechanics of foams: basic results 6. The mechanics of foams refinements 7. Thermal, electrical and acoustic properties of foams 8. Energy absorption in cellular materials 9. The design of sandwich panels with foam cores 10. Wood 11. Cancellous bone 12. Cork 13. Sources, suppliers and property data Appendix: the linear elasticity of anisotropic cellular solids.
author_names: Lorna J Gibson

M F Ashby
title: Cellular solids: Structure properties
year: 1988

abstract: Free air ball processed using coated silver (Ag) wire is soft similar to gold (Au) wire and enables bonding of stacked devices with over hangs. The bonded ball shear/pull, dimensions and stitch pull satisfied internal specifications and customer requirements including folded loop. Moreover, reliability of coated Ag wire bonds when molded using green epoxy mold compound (EMC) containing chlorine (Cl) \lt15$ppm, sulfur (S) \lt10$ppm, formulated with ion catcher and pH between 5 and 7, free of bromine and antimony, revealed reliable bonds. Two of the case studies of coated Ag ball bonds exhibit:*No failure until 3000h on high temperature storage (HTS) test at $175^\circ}\mathrm{C} and $150^\circ}\mathrm{C}*No failure until 1000h on unbiased highly accelerated stress test (uHAST) at $110^\circ}\mathrm{C} 85%RH*No failure until 504h on biased HAST at $130^\circ}\mathrm{C} 85%RH, +20V*No failure until 384h on uHAST, 2000h on HTS at $150^\circ}\mathrm{C} and 2000cycles on thermal cycling at 55^\circ}\mathrm{C} to 125^\circ}\mathrm{C}*Examining EMC formulated with pH 3 to 6 passed 2000h on HTS testing at $175^\circ}\mathrm{C} thereafter bond failed and showed high electrical resistanceThe reported results are based on electrical contact resistance measurement for the condition not to reduce below 10% of time zero bond resistance. The slower failure rate of Ag ball bonds showed EMC formulated with 5 to 7 pH is compatible than formulated with 3 to 5 pH.
author_names: Sarangapani Murali

B Senthilkumar

Tan Swee Seng Eric

Wong Chin Yeung Jason
title: Coated Silver Wire Bond: Reliability of Epoxy Molded Device
venue: 2018 IEEE 20th Electronics Packaging Technology Conference (EPTC)
year: 2018

abstract: Gold is commonly used in the field of electronic manufacturing as bonding wire that connects the IC chip and circuit board. The effect of trace elements on the mechanical properties of 4N gold wire has not been widely investigated for some years despite the important of wire bonding and the move towards fine pitch applications. The objective of this study is to determine the effect of mechanical properties of two type of gold wire (wire A and wire B) on looping and pull strengths. Both wires with diameter of 25.4mm were bonded using K&S Maxum by maintaining the temperature at 200oC. Due to the element analysis, atomic percentage of Ca in wire B is higher than wire A. Pull strength increase with the increasing of the trace element. The higher pull strength of wire B could improve the yield strength, elastic modulus and recrytallization temperature. Keyword: Wire bonding, Ultrasonic (USG) current, QFN packaging, ball bonding
author_names: Azman Jalar

S A Radzi

Shahrum Shah bin Abdullah

Mohd Faridz Mod Yunoh

Mohamad Firdaus Rosle
title: Effect of mechanical properties of gold wire on looping behavior and pull strength for QFN Stacked Die Package
year: 2009

abstract: Silicon carbide (SiC) power modules with Ag sinter bonding die attach were designed on the basis of thermal stress analysis for reliable high temperature operations. Both the finite element analysis (FEA) simulations and preliminary experiments confirmed that inserting the direct bonded copper (DBC) substrates can effectively reduce the maximum thermal stress in the module. A prototype SiC power module using sintered Ag die attach with a DBC substrate was designed and fabricated. The modules exhibited excellent durability in power cycling between 65 degC and 250 degC up to 20 000 cycles. FEA calculations of cumulative thermal strain and stress distributions adequately predicted the initial cracking position in the specimens after prolonged power cycles, observed by scanning electron microscopy.
author_names: Kazuhiko Sugiura

Tomohito Iwashige

Kazuhiro Tsuruta

Chuantong Chen

Shijo Nagao

Tsuyoshi Funaki

Katsuaki Suganuma
title: Reliability Evaluation of SiC Power Module With Sintered Ag Die Attach and Stress Relaxation Structure
venue: IEEE Transactions on Components, Packaging and Manufacturing Technology
year: 2019