Bond Pad Opening Research Articles

Single chip integration of MWCNTs/SiO2 thin film humidity sensor based on standard CMOS IC process

Miniaturization, integration and high performance are key requirements for the present humidity sensor development. One kind of single chip integrated MWCNTs thin film humidity sensor based on standard CMOS IC process was proposed in this paper. The sensor was designed and realized with MWCNTs/SiO2 thin film coated on exposed interdigital electrodes on chip, which was achieved by arrange PADs (bond pad opening) array on the top layer of layout by 0.5μm DMDP 18V process, at maximum exposure of the interdigital patterned metal2 electrodes. The sensor was surrounded by the heating cells formed by paralleled polysilicon resistors, which can accelerate desorption of condensed vapors and thus lower the humidity hysteresis, and provide good long time stability at high humidity environments. As the film was fabricated onto the electrodes in post process, it has great IC compatibility. The sensor has high sensitivity of 270% at 200kHz and 120% at 50kHz under sine source signal, and a fast response and recovery of 5s and 7s, respectively. It was found that nano SiO2 dispersed in film and middle frequency AC source on sensor can both reduce fluctuation of electron waves, and further lower the sensor’s inherent noise. Besides, given the 30μm interdigital finger gap, sensors with MWCNTs of 4–6μm length has apparently lower current noise than those with 1–2μm tubes under 4kHz source signal. The chip is simple and compact, and low cost, and has good long time endurance in high humidity environments.

Copper Wire Bonding: R&D to High Volume Manufacturing

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.

Exploiting CMOS Technology to Enhance the Performance of ISFET Sensors

This letter presents a novel method for fabricating ion-sensitive field-effect transistor (ISFET) devices in unmodified CMOS technologies. Conventional CMOS ISFETs utilize the protective passivation coating as the sensing membrane, with the sensed potential being coupled down to the floating MOS gate via a stack of conducting and insulating layers. The proposed structure minimizes the use of these layers by exploiting the passivation-opening mask, normally intended for bond-pad openings. Parasitic effects such as reduced transconductance and trapped charge within the floating gate structure are minimized, resulting in a lower VT and improved chemical transconductance efficiency. Other characteristics, including chemical sensitivity, reference leakage current, and noise power, are at comparable levels with conventional CMOS-based ISFET devices.

Formation and Growth of Intermetallic Compounds in Cu–Au and Au–Al Systems for Copper on Gold Bonding

Copper (Cu) ball on gold (Au) bump (COG) bonding is developed as a practicable approach to solving the challenges posed by Cu wire bonding on large integrated circuit devices. In the COG bonding, there are two different interfaces, Cu-Au and Au-Al couples, which is totally different from either Cu or Au wire bonding. In this paper, the COG bonding was studied on a typical experimental chip of 69-μm bond pad opening and four-layer central via pattern design with current wire bonders. Tests of wire pull, ball shear, and crater were adopted in investigating the bonding strength at the interfaces and the potential damage of the underlying metals of bond pads after the COG bonding. The intermetallic compounds (IMCs) formation at the two interfaces, Cu-Au and Au-Al couples, were studied in detail on the cross-sectioned assembled samples. Two reliability tests, high-temperature baking (HTB) and temperature cycle (TC) were also used to investigate the IMC change and growth. The results showed that qualified bonding strength on all of bond pads existed and no damage such as crack and crater was observed on the underlying metals of the bond pads after removing Al metallization. At the Au-Al interface, a comparable Au-Al IMC was formed on as-bonded samples, and it gradually grew thick after the reliability tests and its corresponding content also changed along with temperature and time. At the Cu-Au interface, there was no observable formation of Cu-Al IMC on as-bonded samples. Undergoing 1008 hours HTB at 175°C, only a very thin Cu-Au IMC appeared at the Cu-Au interface. After all, the Cu-Au IMC appearance hardly affects the IC's mechanical performance.

Analysis of the Test Parameters in the Shear Test of BGA Solder Joints

Ball shear test was investigated in terms of effects of important test parameters, i.e. shear height and shear speed, with an experimental and non-linear finite element analysis for evaluating the solder joint integrity of area array packages. A Pb-free solder composition was examined in this work: Sn-3Ag-6Bi-2In. The substrate was a common SMD (Solder Mask Defined) type with solder bond pad openings of 460㎛ in diameter. It could be observed that increasing shear height, at fixed shear speed, has the effect of decreasing shear force, while the shear force increased with increasing shear speed at fixed shear height. Too high shear height could cause some bad effects on the test results such as unexpected high standard deviation values or shear tip sliding from the solder ball surface. The low shear height conditions were favorable for screening the type of brittle interfacial failures or the degraded layers in the interfaces.

Reexamination of the solder ball shear test for evaluation of the mechanical joint strength

Ball shear tests were investigated in terms of the effects of test parameters, i.e., shear height and shear speed, with an experimental and non-linear finite element analysis for evaluating the solder joint integrity of area array packages. Two representative Pb-free solders were examined in this work: Sn–3.5Ag and Sn–3.5Ag–0.75Cu. The substrate was a common solder mask defined (SMD) type with solder bond pad openings of 460 μm in diameter. The microstructural investigations were carried out using scanning electron microscopy (SEM), and the intermetallic compounds (IMCs) were identified with energy dispersive spectrometry (EDS). Shear tests were conducted with the two varying test parameters. It was observed that increasing shear height at a fixed shear speed has the effect of decreasing shear force for both Sn–3.5Ag and Sn–3.5Ag–0.75Cu solder joints, while the shear force increased with increasing shear speed at fixed shear height. Shear heights that were too high had some negative effects on the test results such as unexpectedly high standard deviation values or shear tip sliding from the solder ball. Low shear height conditions were favorable for screening the type of brittle interfacial fractures or the degraded layers in the interfaces.

Optimum Shear Height for Evaluation of Pb-Free Solder Ball Shear Strength

Ball shear test was investigated in terms of the effects of important test parameter, i.e., shear height, with an experimental and non-linear finite element analysis for evaluating the solder joint integrity of area array packages. The substrate was a common SMD type with solder bond pad openings of 460 ㎛ in diameter. It was observed that increasing the shear height, at a fixed shear speed, has the effect of decreasing the shear force. The high shear height could cause some bad effects on the test results such as unexpected high standard deviation values or shear tip sliding from the solder ball surface. The low shear height conditions were favorable for screening the type of brittle interfacial fractures or the degraded layers in the interfaces.

Mechanical strength test method for solder ball joint in BGA package

Ball shear tests were investigated in terms of effects of test parameters, i.e. shear height and shear speed, with an experimental and non-linear finite element analysis in order to evaluate the solder joint integrity of area array packages. The substrate was a common SMD type with solder bond pad openings of 460 μm in diameter. Microstructural investigations were carried out using SEM, and the IMCs were identified with EDS. It was observed that increasing shear height, at fixed shear speed, results in decreasing shear force, while the shear force increased with increasing shear speed at fixed shear height. Excessive shear height could cause some detrimental effects on the test results such as unexpected high standard deviation values or shear tip sliding from the solder ball surface. Low shear height conditions are favorable for screening the type of brittle interfacial fractures or degraded layers in the interfaces.

Characterization of the shear test method with low melting point In–48Sn solder joints

The ball shear tests were investigated in terms of effects of test parameters, i.e. shear height and shear speed, with an experimental and non-linear finite element analysis for evaluating the solder joint integrity of area array packages. A representative low melting point solder, In–48Sn, was examined in this work. The substrate was a common solder mask defined (SMD) type with solder bond pad openings of 460 μm in diameter. The microstructural investigations were carried out using scanning electron microscopy (SEM), and the intermetallic compounds (IMCs) were identified with energy dispersive spectrometer (EDS) and electron probe micro analyzer (EPMA). Shear tests were conducted with the two varying test parameters. It could be observed that increasing shear height, at fixed shear speed, has the effect of decreasing shear force, while the shear force increased with increasing shear speed at fixed shear height. Too high shear height could cause some bad effects on the test results such as unexpected high standard deviation values or shear tip sliding from the solder ball surface. The low shear height conditions were favorable for screening the type of brittle interfacial fractures or the degraded layers in the interfaces. The sensitivity of shear speed in In–48Sn solder is largely higher than those of Sn-based solders.

Application of Auger Electron Spectroscopy and X-Ray Photoelectron Spectroscopy Analysis in Failure Analysis of Wafer Fabrication

In this study, field emission AES and small-area XPS techniques were used to analyze surface composition and depth profiles on discolored bondpads to identify possible root causes for nonstick failure. In wafer fabrication, the discolored bondpad problem was found in the fab process with hot Al alloy metallization, which had resulted in nonstick failure during the assembly bonding process. Analytical results indicated that discolored bondpads with nonstick failure might be due to TiN residue introduced during the bondpad opening etching process. The possible root cause of TiN residue on bondpads was then confirmed to be arisen from ARC (TiN) layer underetched during the bondpad opening etching process. The solution to eliminate TiN residue on bondpads was taken to increase the etch time at the bondpad opening fab process.

APPLICATION OF AUGER ELECTRON SPECTROSCOPY AND X-RAY PHOTOELECTRON SPECTROSCOPY ANALYSIS IN FAILURE ANALYSIS OF WAFER FABRICATION

In this study, field emission AES and small-area XPS techniques were used to analyze surface composition and depth profiles on discolored bondpads to identify possible root causes for nonstick failure. In wafer fabrication, the discolored bondpad problem was found in the fab process with hot Al alloy metallization, which had resulted in nonstick failure during the assembly bonding process. Analytical results indicated that discolored bondpads with nonstick failure might be due to TiN residue introduced during the bondpad opening etching process. The possible root cause of TiN residue on bondpads was then confirmed to be arisen from ARC (TiN) layer underetched during the bondpad opening etching process. The solution to eliminate TiN residue on bondpads was taken to increase the etch time at the bondpad opening fab process.