Query: semiconductor wirebond IMC images

Candidate papers:

abstract: Microelectronics wirebonding is used in the vast majority of semiconductor assembly and packaging operations worldwide. In the last few years, much of the manufacturing that traditionally had been gold (Au) wirebond has switched to using copper (Cu) wire. Once a wirebond "recipe" is established in manufacturing, reliability is checked by Bond Pull Strength test (Mil Std 883G method 2011) and Bond Shear test (JEDEC JESD22 B116A) Both industry standards were established based on gold (Au) wirebonds. Cu wire is stronger and stiffer, producing higher values than Au in both pull and shear tests when well bonded, so companies are comfortably complying with the old Au reliability limits while using Cu wire. But in fact, Cu intermetallic (IMC) growth and bonding is quite different than for Au, and failure modes in the shear test can be different for Cu than for Au. A new committee is active to revise the JESD22 B116A method to cover Cu wirebond as well as Au. BYU Idaho students have responded to recent interest in switching from Au to copper Cu wire, modeling both the bond pull strength and bond shear tests using finite element methods. Simulations include the various ball bond wire types (Au, Cu, and silver (Ag) alloys) ball sizes, pad aluminum (Al) thicknesses, and IC bond pad structures in silicon wafers. Results show how stresses imparted to the bond pad in these reliability tests change when switching wire types, etc. helping to explain the physical results as well as to indicate potential issues in the interpretation of failure modes.
author_names: Stevan Hunter

Levi Hill
title: Microelectronics wirebond pull and shear test simulations using finite element method
venue: 2014 IEEE Workshop On Microelectronics And Electron Devices (WMED)
year: 2014

abstract: Gold wire bonding has been widely used as first level interconnect in semiconductor packaging. The increase in the gold price has motivated the industry search for alternative to the gold wire used in wire bonding and the transition to copper wire bonding technology. Potential advantages of transition to Cu Al wire bond system includes low cost of copper wire, lower thermal resistivity, lower electrical resistivity, higher deformation strength, damage during ultrasonic squeeze, and stability compared to gold wire. However, the transition to the copper wire brings along some trade offs including poor corrosion resistance, narrow process window, higher hardness, and potential for cratering. Formation of excessive Cu Al intermetallics may increase electrical resistance and reduce the mechanical bonding strength. Current state of art for studying the Cu Al system focuses on accumulation of statistically significant number of failures under accelerated testing. In this paper, a new approach has been developed to identify the occurrence of impending apparently random defect fall outs and pre mature failures observed in the Cu Al wirebond system. The use of intermetallic thickness, composition and corrosion as a leading indicator of failure for assessment of remaining useful life for Cu al wirebond interconnects has been studied under exposure to high temperature and temperature humidity. Damage in wire bonds has been studied using x ray Micro CT. Microstructure evolution was studied under isothermal aging conditions of 150degC, 175degC, and 200degC till failure. Activation energy was calculated using growth rate of intermetallic at different temperatures. Effect of temperature and humidity on Cu Al wirebond system was studied using Parr Bomb technique at different elevated temperature and humidity conditions (110degC/100%RH, 120degC/100%RH, 130degC/100%RH) and failure mechanism was developed. The present methodology uses evolution of the IMC thickness, composition in conjunction with the Levenberg Marquardt algorithm to identify accrued damage in wire bond subjected to thermal aging. The proposed method can be used for quick assessment of Cu Al parts to ensure manufactured part consistency through sampling.
author_names: Pradeep Lall

Shantanu Deshpande

Luu Nguyen

Masood Murtuza
title: Prognostication of copper aluminum wirebond reliability under high temperature storage and temperature humidity
venue: 2014 IEEE 64th Electronic Components and Technology Conference (ECTC)
year: 2014

abstract: Currently, semiconductor packaging is using Gold (Au) wirebonding as the main connection from chip to the lead frame or substrate. Increases in Au price, causes suppliers to look at another alternative wire alloy as such Copper (Cu) wire. Cu wire is another option rather than Au wire due to Cu has higher tensile strength, better elongation and electrical and thermal conductivities. Cu wire has outstanding ball neck strength after the ball formation process [1] high loop stability and high stiffness, which results in lower wire sweeping during encapsulation. These will lead to Cu wire able to have longer, lower loop profiles [2] and minimize wire sagging for fine and ultra fine pitch wirebonding application. Another proposed alloy for wire bonding is Silver (Ag) wire. Ag has the best electrical and thermal conductivities compare to the three kinds of wires material. Ag wire has low Young's modulus compare to Cu and it is another option for replacing Au wire in wirebonding. In this paper, we shall discuss the three types of alloy wire in term of comparing the bonding quality. These will include the disadvantages and advantages of individual by comparing ball shear measurement. The silicon chip surface after bonding will be checked to confirm any crack observed on the bond pad surface occurred after ball shear for each type of wire. IMC growth for the three types of wire will be carried out at 175degC for 0hr to 504hrs will be discuss and the bond interface will be observed using the high power optical microscopy and scanning electron microscopy (SEM)
author_names: Norhanani Binte Jaafar

Eva Wai Leong Ching
title: Comparison of Au/Al, Cu/Al and Ag/Al in wirebonding assembly and IMC growth behavior
venue: 2016 IEEE 18th Electronics Packaging Technology Conference (EPTC)
year: 2016

abstract: Gold wire bonding has been widely used as first level interconnect in semiconductor packaging. The increase in the gold price has motivated the industry search for alternative to the gold wire used in wire bonding and the transition to copper wire bonding technology. Potential advantages of transition to Cu Al wire bond system includes low cost of copper wire, lower thermal resistivity, lower electrical resistivity, higher deformation strength, damage during ultrasonic squeeze, and stability compared to gold wire. However, the transition to the copper wire brings along some trade offs including poor corrosion resistance, narrow process window, higher hardness, and potential for cratering. Formation of excessive Cu Al intermetallics may increase electrical resistance and reduce the mechanical bonding strength. Current state of art for studying the Cu Al system focuses on accumulation of statistically significant number of failures under accelerated testing. In this paper, a new approach has been developed to identify the occurrence of impending apparently random defect fall outs and pre mature failures observed in the Cu Al wirebond system. The use of intermetallic thickness, composition and corrosion as a leading indicator of failure for assessment of remaining useful life for Cu al wirebond interconnects has been studied under exposure to high temperature and temperature humidity. Damage in wire bonds has been studied using x ray Micro CT. Microstructure evolution was studied under isothermal aging conditions of 150degC, 175degC, and 200degC till failure. Activation energy was calculated using growth rate of intermetallic at different temperatures. Effect of temperature and humidity on Cu Al wirebond system was studied using Parr Bomb technique at different elevated temperature and humidity conditions (110degC/100%RH, 120degC/100%RH, 130degC/100%RH) and failure mechanism was developed. The present methodology uses evolution of the IMC thickness, composition in conjunction with the Levenberg Marquardt algorithm to identify accrued damage in wire bond subjected to thermal aging. The proposed method can be used for quick assessment of Cu Al parts to ensure manufactured part consistency through sampling.
author_names: Pradeep Lall

Shantanu Deshpande

Luu Nguyen

Masood Murtuza
title: Prognostic indicators for Cu Al wirebond degradation under operation at elevated temperature and combined temperature humidity
venue: 2014 International Conference on Prognostics and Health Management
year: 2014

abstract: In today's trend in semiconductor wirebonding assembly process, Copper (Cu) wire was presented as viable solution and alternative cost saving options to gold (Au) wire. The use of Cu wire found to be even better than Au, because of its high thermal conductivity, great electrical property and importantly low cost value. However, Cu have some challenges that needs to carefully understand, it natural nature such as its inherent material hardness, easily to get oxide, the growth of Cu/Al intermetallic compound (IMC) and others. In this paper it will discuss the process experimentations on how those challenges are addressed and studied primarily on understanding the formation of intermetallic compound, its relationship to the bondability response. An accelerated stress test prior to the formal qualification stress has been assessed as way to determine how good the bonding process is by evaluating a different wirebonding parameter combination. The findings of the study suggest that IMC formation can be improved by applying an initial USG (ultrasonic generator) Power also known as USG "pre bleed" parameter as compared to the conventional wirebonding parameter. Accelerated stressing on un molded units through Autoclave test was use to assess and mitigate the potential reliability risk. The accelerated stressing found out more presence of ball lift failure break mode which corresponds to a low wirepull reading on conditions with a bulk of non IMC on effective bonding area. These theorized to translate a potential failure mode in the real electrical testing environment.
author_names: Allen M Descartin

Song Meijiang

Li Jun

Yan Beiyue
title: Non continuous IMC in copper wirebonding: Key factor affecting the reliability
venue: 2015 16th International Conference on Electronic Packaging Technology (ICEPT)
year: 2015

abstract: In today's trend in semiconductor wirebonding assembly process, Copper (Cu) wire was presented as viable solution and alternative cost saving options to gold (Au) wire. The use of Cu wire found to be even better than Au, because of its high thermal conductivity, great electrical property and importantly low cost value. However, Cu have some challenges that needs to carefully understand, it natural nature such as its inherent material hardness, easily to get oxide, the growth of Cu/Al intermetallic compound (IMC) and others. In this paper it will discuss the process experimentations on how those challenges are addressed and studied primarily on understanding the formation of intermetallic compound, its relationship to the bondability response. An accelerated stress test prior to the formal qualification stress has been assessed as way to determine how good the bonding process is by evaluating a different wirebonding parameter combination. The findings of the study suggest that IMC formation can be improved by applying an initial USG (ultrasonic generator) Power also known as USG "pre bleed" parameter as compared to the conventional wirebonding parameter. Accelerated stressing on un molded units through Autoclave test was use to assess and mitigate the potential reliability risk. The accelerated stressing found out more presence of ball lift failure break mode which corresponds to a low wirepull reading on conditions with a bulk of non IMC on effective bonding area. These theorized to translate a potential failure mode in the real electrical testing environment.
author_names: M D Allen

Meijiang Song

Jun Li

Bei-yue Yan
title: Non continuous IMC in copper wirebonding: Key factor affecting the reliability
year: 2015

abstract: Gold wire bonding has been widely used as first level interconnect in semiconductor packaging. The increase in the gold price has motivated the industry search for alternative to the gold wire used in wire bonding and the transition to copper wire bonding technology. Potential advantages of transition to Cu Al wire bond system includes low cost of copper wire, lower thermal resistivity, lower electrical resistivity, higher deformation strength, damage during ultrasonic squeeze, and stability compared to gold wire. However, the transition to the copper wire brings along some trade offs including poor corrosion resistance, narrow process window, higher hardness, and potential for cratering. Formation of excessive Cu Al intermetallics may increase electrical resistance and reduce the mechanical bonding strength. Current state of art for studying the Cu Al system focuses on accumulation of statistically significant number of failures under accelerated testing. In this paper, a new approach has been developed to identify the occurrence of impending apparently random defect fall outs and pre mature failures observed in the Cu Al wirebond system. The use of intermetallic thickness, composition and corrosion as a leading indicator of failure for assessment of remaining useful life for Cu al wirebond interconnects has been studied under exposure to high temperature and temperature humidity. Damage in wire bonds has been studied using x ray Micro CT. Microstructure evolution was studied under isothermal aging conditions of 150degC, 175degC, and 200degC till failure. Activation energy was calculated using growth rate of intermetallic at different temperatures. Effect of temperature and humidity on Cu Al wirebond system was studied using Parr Bomb technique at different elevated temperature and humidity conditions (110degC/ 100%RH, 120degC/ 100%RH, 130degC/ 100%RH) and failure mechanism was developed. The present methodology uses evolution of the IMC thickness, composition in conjunction with the Levenberg Marquardt algorithm to identify accrued damage in wire bond subjected to thermal aging. The proposed method can be used for quick assessment of Cu Al parts to ensure manufactured part consistency through sampling.Copyright (c) 2014 by ASME
author_names: Pradeep Lall

Shantanu Deshpande

Luu Nguyen
title: High Temperature Storage and HAST Reliability of Copper Aluminum Wirebond Interconnects
year: 2014

abstract: Space Domain Reflectometry (SDR) is a new technique that has already shown to be a reliable non destructive method to image open failures in semiconductor chips by pumping a high frequency signal into the open trace. We show in this paper that SDR can be used to accurately find a breakage location in copper wire bond that failed during stress test.
author_names: Jan Gaudestad

V Talanov

Antonio Orozco

Khai Ling Khoo
title: Open localization on copper wirebond using Space Domain Reflectometry
venue: 2013 IEEE International Reliability Physics Symposium (IRPS)
year: 2013

abstract: Wearout reliability and high temperature storage life (HTSL) activation energy of Au and Pd coated Cu (PdCu) ball bonds are useful technical information for Cu wire deployment in nanoscale semiconductor device packaging. This paper discusses the influence of wire type on the wearout reliability performance of Au and PdCu wire used in fine pitch BGA package after HTSL stress at various aging temperatures. Failure analysis has been conducted to identify the failure mechanism after HTSL wearout conditions for Au and PdCu ball bonds. Apparent activation energies (Eaa) of both wire types are investigated after HTSL test at 150 degC, 175 degC and 200 degC aging temperatures. Arrhenius plot has been plotted for each ball bond types and the calculated Eaa of PdCu ball bond is 0.85 eV and 1.10 eV for Au ball bond in 110 nm semiconductor device. Obviously Au ball bond is identified with faster IMC formation rate with IMC Kirkendall voiding while PdCu wire exhibits equivalent wearout and or better wearout reliability margin compare to conventional Au wirebond. Lognormal plots have been established and its mean to failure (t50) have been discussed in this paper.
author_names: Chong Leong Gan

Uda Hashim
title: Reliability Assessment and Activation Energy Study of Au and Pd Coated Cu Wires Post High Temperature Aging in Nanoscale Semiconductor Packaging.
venue: Journal of electronic packaging
year: 2013

abstract: To ensure a reliable Cu wire bond on Al bond pad, Freescale has learnt that good IMC plays a very important role. However, unlike Au/Al IMC measurement method which has been well established, Cu/Al IMC measurement method is still relatively new in semiconductor industry. This study was aimed to establish an effective chemical solution to etch off Cu bonded ball to check IMC coverage at the entire ball bond to bond pad interface, with consistent and reliable result. In this paper, effect of chemical etching solution on Cu/Al IMC result was studied by using different combination of Nitric Acid molar concentration. The key factors were found to be etching temperature and different combination of Nitric Acid molar concentration. The chemical etching method was carefully designed to etch away Cu wire while only retaining the Cu/Al IMC on Al bond pad. The test vehicle used was 668TePBGA II. Samples were baked at 175C for 48hrs. Cu ball bond was then removed with different combination of Nitric Acid molar concentration. After etching, IMC was inspected under 500x microscope magnification. Images were taken and software was used to accurately calculate IMC with reference to effective bonded ball area. SEM/EDX was used to confirm the presence of Cu/Al IMC on the surface of Al bond pad. EDX was used to analyze the phase diagram of Cu Al system to identify the possible IMCs formed between Cu and Al. Through this study, Cu/Al IMC phases were found to be Cu9Al4 (69.2 atomic Cu) Cu3Al2 (60.0 atomic Cu) Cu4Al3 (57.1 atomic Cu) CuAl (50.0 atomic Cu) and CuAl2 (33.3 atomic Cu) The result showed that Nitric Acid concentration from 9 to 11 mol/L yielded the most reliable and repeatable IMC result. Apart from that, other advantages of the final recipe included low price and reasonable short etching time.
author_names: C C Yong
title: Effect of chemical etching solution on Cu/Al IMC result
venue: 2012 14th International Conference on Electronic Materials and Packaging (EMAP)
year: 2012