Advancements in Silver Wire Bonding

2017 ◽  
Author(s):  
Subramani Manoharan ◽  
Chandradip Patel ◽  
Patrick McCluskey
Keyword(s):  
Failure Modes ◽  
Copper Wire ◽  
Gold Wire ◽  
Good Alternative ◽  
Wire Bonding ◽  
Silver Wire ◽  
Process Window ◽  
Fine Pitch ◽  
Wire Bonds ◽  
Copper Wire Bonding

Silver is a leading competitor to gold and copper in fine pitch wire bonding used in the interconnection of microelectronic devices. Primary material for wire bonding has been gold, which gave way to copper in order for original equipment manufacturers to realize cost benefits. However, copper wire bonding has exhibited several reliability issues, especially in industrial and high temperature applications. Corrosion is the major problem, which was mitigated by coating the wire with palladium, which increased overall cost of production. Other concerns include harder free air ball (FAB) leading to under pad metallization cracking, smaller process window, excessive aluminum splash especially in fine pitch bonding, and lower throughput and yield arising from the hardness and stiffness of copper. Due to the above concerns, automotive, military and aerospace industries are still reluctant to fully adopt copper wire bonding. Light emitting diodes (LEDs) are also not manufactured with copper wires due to its low reflectance. Some of these industries are still using gold wire bonds in most of their packages, but are continually looking for an alternative. Silver wire bonds have good electrical and thermal conductivity, are less prone to corrosion than copper, have low melting points and comparable hardness to gold. Also, cost of silver has been shown to be similar to that of palladium coated copper wire, hence making it a good alternative. Silver wire bonding, a relatively new area of research, has attracted a lot of research focused on wire dopant material, bonding process, quality and reliability. This paper is aimed to serve as a comprehensive review of research done in this area, by summarizing the literature on silver wire bonding, establishing benefits and drawbacks over other wire bond materials and indicating reliability concerns along with failure modes and mechanisms.

Reliability Study of Silver, Copper and Gold Wire Bonding on IC Device

2014 ◽  
Vol 2014 (1) ◽  
pp. 000850-000855
Author(s):  
Hongtao Gao ◽  
Jun Lu ◽  
Richard Lu ◽  
Wei Xin ◽  
Xiaojing Xu ◽  
...  
Keyword(s):  
Shear Strength ◽  
Copper Wire ◽  
Gold Wire ◽  
Wire Bonding ◽  
Silver Wire ◽  
Ball Shear ◽  
Significant Difference ◽  
Copper Wire Bonding ◽  
Bonding Wires ◽  
Ball Shear Strength

Copper wire bonding in IC packages is not always suitable for devices with active circuit under bonding pad because higher bonding power required for copper wire bonding may cause top aluminum metal splash and mechanically impact the circuit underneath. Silver wire is an alternative solution to this problem based on its physical properties and lower cost compared to gold wire. Ag88%Au8.5%Pd2.5%X1% and Ag95%Au1.5%Pd2.5%X1% alloyed silver wires are used in the study to compare with copper and gold wires of 99.99% in purity. As bonding power plays a dominating role in wire bonding, we focused on the effects of silver, copper and gold bonding wires with different bonding power on the top aluminum metal splash of power device by Optical Microscope(OM) and Scanning Electron Microscope(SEM). The ball shear strength of the bonding wires with different bonding power in samples without mold compound encapsulation was investigated before and after 24, 48, 96 and 192 hours of pressure cooker test (PCT). The intermetallic compound (IMC) formed between silver and aluminum was confirmed by focus ion beam (FIB) and transmission electron microscope (TEM). Although the top surface of the silicon device shows no significant difference after aluminum layer removal for all three wire types, the severity level of vertical deformation and side splash of aluminum layer due to copper wire bonding is much more than silver or gold wire using same amount of bonding power. Ball shear strength of non-encapsulated silver wire decreases dramatically after PCT aging compared with copper wire or gold wire and some samples show zero shear strength after PCT 96 hours and PCT 192 hours for silver wires doped with Pd/Au. Furthermore, larger bonding power induces higher ball shear strength. The major IMC compositions between silver and aluminum are Ag3Al and Ag2Al. A thermo dynamic model was built to explain why silver wire is prone to corrosion compared with copper wire by humidity although copper is easier to be ionized than silver. No electrical test was performed as the samples cannot be tested without package encapsulation and singulation. Furthermore, silver wire samples in SO8 package with mold compound encapsulation were subjected to highly accelerated stress test (HAST), PCT, temperature cycle test (TCT) after MSL1 preconditioning test as well as high temperature operation life test (HTOL) according to JEDEC procedures. The encapsulated samples using either Ag 88wt% or Ag95wt% alloys all passed MSL1 and PCT/HAST/TCT/HTOL. Drain to source on-resistance (Rdson) of the device including package parasitics was measured and it has no significant difference between silver wire and gold wire. The results from this study shows promising data using silver alloy wires but care should be taken to further understand the degradation of silver-aluminum interface under severe humidity condition. Using other metallization on silicon top surface such as NiAu or CuAu can significantly alleviate the interface problem related to AgAl.

Fine Pitch Cu Wire Bonding – As Good As Gold

2010 ◽  
Vol 2010 (1) ◽  
pp. 000650-000655
Author(s):  
Bernd K. Appelt ◽  
William T. Chen ◽  
Andy Tseng ◽  
Yi-Shao Lai
Keyword(s):  
Raw Materials ◽  
Copper Wire ◽  
Commodity Prices ◽  
Gold Wire ◽  
Wire Bonding ◽  
Fine Pitch ◽  
Methodical Approach ◽  
Copper Wire Bonding ◽  
Gold Wires ◽  
The Impact

Fine pitch wire bonding has traditionally been the domain of gold wires. The significant increase in gold commodity prices has driven a continuous reduction in wire diameters to minimize the impact of the raw materials cost of the wire. This has reached a point now where copper wires are beginning to displace gold wires despite the technical challenges associated with copper wires. The basic challenges like propensity for oxidation, hardness and propensity for corrosion can be managed with the appropriate investment in tooling and infrastructure. Doubts are persisting about yield and reliability. With a very methodical approach to developing the process controls, it can be demonstrated that yields are as good as those for gold despite the fact that copper bonds are not reworkable. Likewise, the typical JEDEC reliability tests can be full filled. Here, an extensive effort has been placed on extended JEDEC testing to demonstrate that with good process control and proper materials choices, test durations of more than 2x can be passed. This excellent performance demonstrates that copper wire bonding can be as good as or better than gold wire bonding.

Failure Analysis on Power Trench MOSFET Devices with Copper Wire Bonds

2011 ◽  
Author(s):  
Huixian Wu ◽  
Arthur Chiang ◽  
David Le ◽  
Win Pratchayakun
Keyword(s):  
Failure Analysis ◽  
Copper Wire ◽  
New Technology ◽  
Analytical Techniques ◽  
Wire Bonding ◽  
Bonding Process ◽  
Wire Bonds ◽  
Copper Wire Bonding ◽  
Wet Chemical ◽  
Microelectronic Components

Abstract With gold prices steadily going up in recent years, copper wire has gained popularity as a means to reduce cost of manufacturing microelectronic components. Performance tradeoff aside, there is an urgent need to thoroughly study the new technology to allay any fear of reliability compromise. Evaluation and optimization of copper wire bonding process is critical. In this paper, novel failure analysis and analytical techniques are applied to the evaluation of copper wire bonding process. Several FA/analytical techniques and FA procedures will be discussed in detail, including novel laser/chemical/plasma decapsulation, FIB, wet chemical etching, reactive ion etching (RIE), cross-section, CSAM, SEM, EDS, and a combination of these techniques. Two case studies will be given to demonstrate the use of these techniques in copper wire bonded devices.

Reliability Assessment of Cu-Al WB Under High Temperature and High Voltage Bias Application

2020 ◽  
Author(s):  
Pradeep Lall ◽  
Sungmo Jung
Keyword(s):  
High Temperature ◽  
High Voltage ◽  
Galvanic Corrosion ◽  
Copper Wire ◽  
Ionic Transport ◽  
Gold Wire ◽  
Process Window ◽  
Voltage Bias ◽  
Wire Bond ◽  
Wire Bonds

Abstract Electronics in automotive underhood environments may be subjected to high temperature in the range of 125–200°C. Transition to electric vehicles has resulted in need for electronics capable of operation under high voltage bias. Automotive electronics has simultaneously transitioned to copper wire-bond from gold wire-bond for first-level interconnections. Copper has a smaller process window and a higher propensity for corrosion in comparison with gold wire bonds. There is scarce information on the reliability of copper wire bonds in presence of high voltage bias under operation at high temperature. In this paper, a multiphysics model for micro galvanic corrosion in the presence of chlorine is introduced. The diffusion cell is used to measure the diffusivity of chlorine in different pH values and different temperatures. Diffusivity measurements are incorporated into the 3D ionic transport model to study the effect of different environmental factors on the transport rate of chlorine. The tafel parameters for copper, aluminum and intermetallics have been extracted through measurements of the polarization curves. The multiple physics of ionic transport in presence of concentration gradient, potential gradient is coupled with the galvanic corrosion.

Fine pitch copper wire bonding on 45nm tech Cu/low-k chip with different bond pad metallurgy

2011 ◽  
Author(s):  
Leong Ching Wai ◽  
Norhanani Binte Jaafar ◽  
Michelle Chew ◽  
Sivakumar ◽  
Gunasekaran ◽  
...  
Keyword(s):  
Copper Wire ◽  
Wire Bonding ◽  
Fine Pitch ◽  
Copper Wire Bonding ◽  
Low K

The Microelectronic Wire Bond: Past, Present, and Future

2010 ◽  
Vol 2010 (1) ◽  
pp. 000462-000469
Author(s):  
Harry K. Charles
Keyword(s):  
Copper Wire ◽  
Low Cost ◽  
Bond Formation ◽  
Wire Bonding ◽  
Testing Methods ◽  
Wire Bond ◽  
Fine Pitch ◽  
Wire Bonds ◽  
Ball Bonding

Since its very inception, the microelectronic wire bond has been the dominate form of first-level interconnection (chip to package or substrate). Wire bonds account for over 80% of first-level chip interconnections made by the microelectronic industry each year. Wire bonding is reliable, flexible, and low cost when compared to other forms of first-level interconnections. In this article a brief discussion of wire bonding is presented along with bond formation fundamentals. Aspects of wire bond reliability will be explored in conjunction with methods of wire bond testing. Particular attention is given to fine pitch bonding, bonding to stacked die, higher frequency bonding, ball bonding with copper wire, and advanced bond testing methods.

Copper Wire Bonding: R&D to High Volume Manufacturing

2012 ◽  
Vol 2012 (1) ◽  
pp. 000638-000649 ◽  
Author(s):  
Bob Chylak ◽  
Horst Clauberg ◽  
John Foley ◽  
Ivy Qin
Keyword(s):  
Copper Wire ◽  
Leading Edge ◽  
Relative Sensitivity ◽  
High Volume ◽  
Gold Wire ◽  
Wire Bonding ◽  
Bonding Process ◽  
Wire Diameter ◽  
Bond Quality ◽  
Copper Wire Bonding

During the past two years copper wire bonding has entered high volume manufacturing at a number of leading edge OSATs and IDMs. Usage of copper wire has achieved 20% market share and is expected to exceed 50% within three years. Products spanning the range from low pin count devices with relatively large wire diameter to FPGA's with nearly one thousand wires at 20 μm or even 18 μm wire are now using copper wire. This paper will discuss the requirements for developing a robust copper wire bonding process and then moving it to high volume manufacturing. Process optimization begins with the selection of the appropriate wire diameter, ball diameter, bonding tool and bonding process type. These are functions not only of the bond pad opening, but also of the pad aluminum thickness and relative sensitivity of the pad to damage. Proper optimization depends on the availability of new and modified bond quality metrologies, such as extensive reliance on cross-sectioning and intermetallic coverage measurements. The bonding window of a copper wire bonding process is defined in substantially new terms compared to optimization in gold wire bonding. Once an optimized process has been developed in the lab on a single bonder, it needs to be verified. Copper wire bond processes are much less forgiving with respect to the acceptable variability on the manufacturing floor. To ensure that the process is stable, a low volume pre-manufacturing test is highly recommended. This not only makes sure that the process is stable across multiple bonders, but also ensures the adequacies of manufacturing controls, incoming materials quality and sufficient equipment calibration and maintenance procedures.

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