By using fluorocarbon gases for aluminum (Al) pad open plasma etch, the pad inevitably has a thin surface remnant layer of Al-oxyfluoride (AlOF) by-product. This layer is chemically stable and does not directly cause issues in chip testing or wire bonding. This is true until open Al pads were exposed to a humid environment causing pad corrosion over time. The F-assisted corrosion created so-called black mushroom (BM) defects on the Al pads according to the defects appearance, resulting in the non-stick pads for wire bonding. Experimental tests were carried out to induce the Al pad corrosion via placing random fab-out wafers in a cassette pod hosting about 90% RH over a period up to a week. Optical imaging revealed BMs nucleated, primarily at Al grain boundaries. BMs were found all to be composed of O, F, and Al. In the cross section, BMs were shown to have separations of F-rich region next to Al and O-rich region towards the surface. In addition, BMs were composed of small crystallites and were porous. The former indicates an ionic bonding involving in O, F, and Al. The latter indicates the corrosion generated gaseous byproduct. A moisture (H 2 O) involved cyclic chemical reaction incorporating these analyses has been formulated. Factors to prevent BM formation were discussed.

Copper ball bonding is the most widely used interconnection method in microelectronic packages. It has enabled many modern technologies, but the bond can fail due to corrosion. This paper concerns quantitative analyses of corrosion products of passing and failing copper ball bonds, and correlation with the corrosion thermodynamics. The role each element in the aluminum-copper intermetallic compound plays during crevice corrosion is described, and relative abundances of the oxidized elements are estimated. New insights regarding mechanisms of the highest vulnerability to corrosion attack in the thin film-stack across the bond are presented. Limited data indicate the same corrosion mechanisms for Au ball bonds.

Currently, wire bonding is still the dominant interconnection mode in microelectronic packaging, and epoxy molding compound (EMC) is the major encapsulant material. Normally EMC contains chlorine (Cl) and sulfur (S) ions. It is important to understand the control limit of Cl and S in the EMC to ensure good Au wire bond reliability. This paper discussed the influences of Cl and S on the Au wire bond. Different contents of Cl and S were purposely added into the EMC. Accelerated reliability tests were performed to understand the effects of Cl, S and their contents on the Au wire bond reliability. Failure analysis has been conducted to study the failure mechanism. It is found that Cl reacted with IMCs under humid environment. Cl also caused wire bond failure in HTS test without moisture. On the other hand, the results showed that S was not a corrosive ion. It was also not a catalyst to the Au bond corrosion. Whilst, high content of S remain on the bond pad hindered the IMCs formation and caused earlier failure of the wire bond.

Copper (Cu) material was extensively studied in the past years and widely implemented in high volume wire bonding process as a replacement of Gold (Au) material during semiconductor device fabrication. No doubt, Cu wire provide low cost alternative to gold with higher thermal and electrical conductivity, but it does pose some drawback especially after reliability stress. One of the most common problem was ball lifted after component gone through several reliability stress tests. In this paper, several FA analytical techniques and procedures will be discussed in detail to demonstrate the use of these techniques in ball lifting investigation.

In today’s advanced technology world, electronic devices are playing a key role in modern semiconductor products to improve the energy proficiency. These devices are required to be contamination free especially on the bond pad with good adhesion before wire bonding process at the back end. Contamination on the bond pad leads to reliability issues such as pad corrosion, delamination and failure leading to leakage and open fails of electronic devices. Therefore, detection accuracy and sensibility of contamination is important. Auger analysis is the most suitable technique to check bond pad contamination. Auger electron spectroscopy has the capability of analyzing compositional information with excellent spatial resolution. However, charging, noise or artifact is known to be a major concern to the characterization of insulating materials. This paper outlines the strategy that has been utilized to minimize the artifact, noise or charging impact for Auger investigation on a smaller bond pad surrounded by imide passivation layers. The imide passivation layer normally causes the charging effect during Auger analysis, which makes the Auger analysis difficult to be proceed. In addition to that, the charging effect leads to inaccurate analysis. In this paper, we demonstrate a sample preparation method to minimize the charging and artifact of Auger analysis especially for small bond pads.

Decapsulation of silver wire bonded packages with known techniques often results in damaged silver wires. The chemical properties of silver and silver compounds make silver bond wire inherently susceptible to etching damage by acid, conventional plasma, and oxygen-based Microwave Induced Plasma (MIP). In this paper we solve this problem by developing a specific decapsulation chemistry, based on a hydrogen-containing MIP, for artifact-free decapsulation of silver wire bonded packages.

An advanced sample preparation protocol using Xe+ Plasma FIB for increasing FA throughput is proposed. We prepared cross-sections of 400 μm and wider in challenging samples such as a BGA (CSP), bond wires in mold compound or a TSV array. These often suffer from FIB milling artifacts. The unsatisfactory quality of the cross-section face is mainly due to extremely different milling rates of the various materials (polyimide, tin, copper, mold compound, platinum), ion beam induced ripples [1] or due to significant surface topography. We explored the usability of the protocol for standard cross-sections and also tested the preparation of TEM lamellae. The process parameters of the proposed approach were compared with the standard methods of Xe+ Plasma FIB FA with respect to preparation time and cross-section quality. Aiming for ultimate results, we incorporated the Rocking stage technique which also greatly improves cross-section quality.

As various types of DRAM package have been developed, new defects in interconnection in chip have been discovered after assembly process such as flip chip bump mount or wire bonding. There are lots of regular inspections in manufacturing process to detect assembly defects, but it is not easy to find all of the defects. We used a method to classify physical failures based on electrical measurements. Conventional open and short tests by using ISVM were used to support the mass production. External voltage sweep is employed to distinguish weak defects from strong defects of interconnection. Finally, a proposed method was verified with statistical analysis of 800,000 FBGA DRAM chips and physical analysis of failure chips.

Bond pull testing, a well-known method in the failure analysis community, is used to evaluate the integrity of an electronic microchip as well as to detect counterfeit ICs. Existing bond pull tests require that the microchip be de-capsulated in order to obtain physical access to the bond wires in the IC package. Bond pull analysis based on simulation and finite element methods also exists but relies on the original model for a bond wire from a CAD design. In this work, we introduce X-ray tomography imaging with 700nm imaging resolution to acquire the 3D geometry details of bond wires non-destructively. Such information can be used to develop more accurate models for finite element analysis based on real size and structure. Therefore, one can test the bond wire strength as a proof of concept for virtual mechanical testing and counterfeit detection in microchips.

Contamination by particles is one of the major causes of failures in integrated circuits. In some cases, particles may absorb moisture leading to electrochemical migration, dendrite growth, and electrical leakage and short failures. This work presents two case studies of particle induced corrosion of copper wire bond that resulted in an electrical failure. In the first case, adjacent pin resistive short failures were found to fail due to corrosion and electrochemical migration at wires that were in contact with calcium chloride particles. Analysis showed that the highly hygroscopic calcium chloride particles absorbed moisture and resulted in corrosion and electrochemical migration of the copper wires. For the second case, an electrical open failure after temperature cycle reliability test was found to be due to an organophosphorus particle being in contact with the wire.

Coating of the Cu bond wire with Pd has been a rather widely accepted method in semiconductor packaging to improve the wire bonding reliability. Based on comparison of a Cu bond wire and a Pd-coated Cu bond wire on AlCu pads that had passed HAST, new insight into the mechanism of the reliability improvement is gained. Our analysis showed the dominant Cu-rich intermetallics (IMC) were Cu3Al2 for the Cu wire, and (CuPdx)Al for the Pd-coated wire. The results have verified the Cu-rich IMC being suppressed by the Pd-coating, which has been extensively reported in literature. Binary phase diagrams of Al, Cu, and Pd indicate that the addition of Pd elevates the melting point and bond strength of (CuPdx)Al compared with CuAl that formed with the bare Cu wire. The improvements are expected to decrease the kinetics of phase transformation toward the more Cu-rich IMC. With the suppression of the Cu-rich IMC, the corrosion resistance of the wire bonding is enhanced and the wire bonding reliability improved. We find that Ni behaves thermodynamically quite similar to Pd in the ternary system of Cu wire bonding, and therefore possesses the potential to improve the corrosion resistance.

Cu wires were bonded to AlSi (1%) pads, subsequently encapsulated and subjected to uHAST (un-biased Highly Accelerated Stress Test, 130 °C and 85% relative humidity). After the test, a pair of bonding interfaces associated with a failing contact resistance and a passing contact resistance were analyzed and compared, with transmission electron microscopy (TEM), electron diffraction, and energy-dispersive spectroscopy (EDS). The data suggested the corrosion rates were higher for the more Cu-rich Cu-Al intermetallics (IMC) in the failing sample. The corrosion was investigated with factors including electromotive force (EMF), self-passivation of Al, thickness and homogeneity of the Al-oxide on the IMC, ratio of the Cu-to-Al surface areas exposed to the electrolyte for an IMC taken into account. The preferential corrosion observed for the Cu-rich IMC is attributed to the high ratios of the surface areas of the cathode and anode that were exposed to the electrolyte, and the passivation oxide of Al with the lower homogeneity. The corrosion of the Cu-Al IMC is just a manifestation of the well-known phenomenon of dealloying. With the understanding of the corrosion mechanisms, prohibiting the formation of Cu-rich IMCs is expected be an approach to improve the corrosion resistance of the wire bonding.

LASER techniques are widely used for pre-opening in combination with a final manual or automated wet chemistry decapsulation. Even if most of the ICs may be opened today, and if opening the recently introduced Ag wires packages have been solved with novel chemical recipes, the need for a greener and safer solution is still there. Plasma techniques combined with LASER can be a promising solution to these challenges. In this paper, after a presentation of the state of the art of the different techniques available in laboratories nowadays, the latest solution combining LASER and acid or plasma etching is presented. The paper compares the results obtained with these solutions on Cu an Ag wires devices with pros and cons for each solution. The results presented show the benefits, the constraints and the limitations of each technique regarding the different types of wires used in industry.

Destructive physical analysis (DPA) is one of the reliability evaluation methods, which observes defects and faults in a device, and it can classify the reliability level of the device. After a description of the current method for Au wires, this paper explains the DPA for a Cu wire device. The DPA for semiconductor devices is divided roughly into three steps: a non-destructive inspection, an assembly process inspection, and a wafer process inspection. Investigation of DPA for Cu wire device includes wire material identification, optimization of decapsulation for Cu wire device and wire pull strength test, and observation of package cross-section. From the result, novel sample preparation (embedding a sample in molding package and forming the package to be suitable for cross-sectional observation by ion polishing) enables the observation of the thin alloy layer at the wire/pad interface.

Performance degradation due to fatigue accumulation from the repetitive switching of high load current is critical to understanding robust power MOSFET product design. In this paper, we present a novel high-current-temperature (HCT) characterization system used to investigate real world powercycling failure mechanisms. The effects of electric current Joule heating, non-uniform temperature distribution and performance deterioration of discrete power devices are discussed. Thermal fatigue of solder joints and thick aluminum wire bonding are common weak spots with regard to power-cycling capability. We report performance failure mechanisms and discuss the superposition of contributing factors in defining root cause. Results discuss various package influences as part of a robust power MOSFET development process.

This paper demonstrates the application of fractography on ductile fracture in gold wire bonding and brittle fracture in micro lateral crack of silicon chip. Different separation mode of a lifted wire ball was mapped through the study of various sizes of dimples, ductile zone and non-welded area. Multiple Focus Ion Beam (FIB) cuts were required at lateral crack area in order to expose the horizontal fracture features to determine the crack propagation direction.

Lifted bond balls in Integrated Circuit (IC) have numerous failure mechanisms. A simple external curve can confirm the open, and with package decapsulation, lifted balls can be readily observed. However, the exact cause can be difficult to identify. Most often, a cross section through the balls was performed, but it is far from being able to reveal the reason for lifted bond balls. A comprehensive FA approach is needed. Performing failure analysis through the back side of the die using Scanning Acoustic Microscopy (C-SAM) and Infra Red (IR) inspection helps to observe the conditions of the bond pads. Pulling the die from the mold compound can provide a pristine view of the bond ball-bond pad interface. This allows the detection of contaminants, both organic and inorganic, which cross sections cannot provide.

This paper describes how scanning acoustic microscopy can be used to inspect materials under the chamfer of electronic device packages. The technique involves the use of copper tape to locate the areas affected by the chamfer during X-ray radiography. The results are then correlated with known critical package and assembly geometries to determine how far parallel lapping should proceed to ensure that the areas of interest will become observable under acoustic microscopy without interfering with the functionality of the device.

Cu needs a higher level of ultrasound combined with bonding force to be bonded to the Al pad properly, not just because Cu is harder than Au, but it is also harder to initiate intermetallic compounds (IMC) formation during bonding. This increases the chances of damaging the metal/low k stack under the bondpad. This paper presents a fundamental study of IMC as well as one example of a failure mode of Cu/Al bonded devices, all based on detailed analysis using scanning electron microscopy, scanning transmission electron microscopy, energy dispersive spectrometers, and transmission electron microscopy. It presents a case study showing a corrosion mechanism of Cu/Al ballbond after 168hr UHAST stress. It is observed that all Cu9Al4 was consumed, while very little copper aluminide remained after 168 hours of UHAST stressing.

In this paper we will discuss an empirically discovered technique to remove residual solder bumps or remnants using reflow and wicking to a gold plated surface rather than mechanical or chemical means. Extraction of flip chip ICs, for the purpose of repackaging, can leave bond pads in inconsistent and undesirable conditions such as 1) retaining remnants of the solder bumps or 2) damaged or eliminated pad metal caused by acid or mechanical means used to separate the IC from the board. These conditions hinder subsequent wire bonding and probe card use. Though other techniques have been found to be suitable at times, the technique described in this paper consistently leaves the bonding area in an acceptable, more predictable condition, as the bulk of the solder bump material is removed. This lends to a higher wire bonding success rate.