Pressure Cooker Test Research Articles

Effects of thermoplastic resin content of anisotropic conductive films on the pressure cooker test reliability of anisotropic conductive film flip-chip assembly

The flip-chip technology using anisotropic conductive films (ACFs) is gaining growing interest due to its technical advantages such as environmentally friendly, simpler, and lower cost processes. Electrical performances and reliability of ACF flip-chip assembly depend on thermomechanical properties of ACF polymer resins. In this paper, the changes in ACF resin morphology due to the phase separation of thermoplastics, and subsequent changes of physical and mechanical properties were investigated as a function of thermoplastic contents of ACF formulation. Furthermore, the pressure cooker test (PCT) reliability of ACF flip-chip assemblies with various thermoplastic contents was also investigated. As thermoplastic contents increased, coefficient of thermal expansion (CTE) of ACFs increased, and elastic modulus (E′) of ACFs decreased. In contrast, water absorption rate decreased as thermoplastic content increased. As a result, PCT reliability of ACF flip-chip assembly was improved adding up to 50 wt.% content of thermoplastic.

Moisture-induced failures of adhesive flip chip interconnects

Adhesive flip chip interconnect has been recognized as a promising substitute for solder interconnection due to its fine-pitch, lead-free, and low-temperature processing capabilities. As adhesives are made of polymers, moisture absorption by the polymeric resin remains as one of the principal contributors to adhesive joint failure mechanisms. In this research, the reliability performance of the adhesive flip chip in the pressure cooker test and moisture sensitivity test conditions was investigated. The failure modes were found to be interfacial delamination and bump/pad opening which may eventually lead to total loss of electrical contact. Different sizes of bump/pad opening in the interconnections were discussed in the context of the significance of mismatch in coefficient of moisture expansion (CME) between adhesive and other components in the package, which induces a hygroscopic swelling stress. The effect of moisture diffusion in the package and the CME mismatch were also evaluated from the standpoint of finite element modeling. In this study, it is concluded that hygroscopic swelling assisted by loss of adhesion strength upon moisture absorption is responsible for the moisture-induced failures in these adhesive flip chip interconnects.

Formation of highly moisture-resistive SiN x films on Si substrate by Cat-CVD at room temperature

Silicon nitride (SiN x ) films were prepared with a gas mixture of SiH 4, NH 3 and H 2 on Si wafers at low temperatures using the catalytic chemical vapor deposition (Cat-CVD) method. For fixed flow-rates, properties for the SiN x films depending on substrate temperatures from 20 °C to 100 °C were investigated. The N/Si composition ratio depended little on the substrate temperature. When the substrate temperature was low, the refractive index decreased, the deposition rate increased slightly, the etch rate became large and the internal stress decreased. No variation appeared in the infrared absorption of the films before and after a pressure cooker test. It is found that highly moisture-resistant SiN x films without stress can be obtained at room temperature by using Cat-CVD.

Heat, moisture and chemical resistance on low dielectric constant (low- k) film using Diethoxymethylsilane (DEMS) prepared by plasma enhanced chemical vapor deposition

Resistance of low dielectric constant (low- k) dielectrics, deposited using Diethoxymethylsilane (DEMS) precursor and helium (He) carrier gas with or without oxygen (O 2) reaction gas, against heat, moisture stress and chemical treatment is clarified. The low dielectric constant organosilicate glass (OSG) films deposited using DEMS and O 2 is shown to be the most reliable: the dielectric constant are stable even after a heating test at 700 °C and a pressure cooker test (PCT) for 168 h. This stability is high enough to ensure the low- k properties throughout fabricating multilevel interconnects and long-term reliability after the fabrication. This is due to the stability of Si–CH 3 bonds and more Si–C–Si– bonds, which has high degree of cross-linking. However, the degradation of the dielectric constant occurs after O 2 plasma ashing process. The nitrogen plasma treatment is proposed to prevent the damage from O 2 attack in the low- k films deposited using DEMS precursor.

Lead Free Die Mount Adhesive Using Silver Nanoparticles Applied To Power Discrete Package

Lead-free materials are required to replace conventional lead-containing solder for environmental protection. The Pb-rich solder die mount material in a high-power transistor package is required to be replaced by a silver adhesive paste. The silver paste has disadvantages such as low thermal conductivity and high electrical resistivity, since conduction paths are achieved only by mechanical contacts between silver particles. Recently, a new conductive paste containing silver particles and silver nanoparticles with a particle size of 3–7 nm in diameter was developed. The paste shows very low electrical resistivity of 6×10−6 ohm.cm, since the silver nanoparticles can be fused at temperatures below 200°C. We have been studying the possibility of the paste as a die mount material for high-power transistor packages. It was confirmed that the paste had a very high thermal conductivity of 51 W/mK. We fabricated a high-power transistor package using this paste. As a result, the package showed lower thermal resistance than that fabricated using silver paste or lead-containing solder. Moreover, the package is sufficiently reliable that it passed the thermal cycle and pressure cooker tests. This paste can be applied to a high-power transistor package in place of lead-containing solder.

Interfacial Adhesion of Anisotropic Conductive Adhesives on Polyimide Substrate

There has been steadily increasing interest in using electrically conductive adhesives as interconnecting materials in electronics manufacturing. Simple processing, low processing temperature and fine pitch capability are the major advantages of conducting adhesive technology. A new and innovative connection technology geared towards achieving increased functionality at a lower total system cost is anisotropic conductive adhesive (ACA) interconnection. ACAs, when used for flip chip assembly, provide electrical as well as mechanical interconnections for fine pitch applications. This work deals with adhesion issues between ACA on polyimide materials. The paper presents a reliability assessment of adhesive joints using ACA on polyimide substrate that was conducted by testing samples at various aging temperature, high humidity and high pressure environments. The effects of high temperature and high humidity on the bond strength of ACA joints were measured using 90 deg peel test as well as by microstructural examination. It was found that aging generally caused a decrease in peel strength, especially the results of scanning electronic microscopy showed that the pressure cooker test could most effectively reveal the adhesion behavior.

Diffusion phenomena at the interface between dielectric films and compound semiconductors

AbstractThe diffusion phenomena at the interface between dielectric films and compound semiconductors under two kinds of condition (humid or dry thermal) have been studied by means of secondary ion mass spectrometry (SIMS). Under the humid condition—the pressure cooker test at 121 °C, 100% relative humidity and 2 atm—we confirmed that oxygen diffused into dielectric films of SiNx or SiOxNy from the surface and that both Ga and As diffused into films from GaAs substrates simultaneously. Because such diffusion phenomena did not occur under the dry thermal condition at 120 °C, the diffusion was assumed to be influenced by the existence of water vapour. In addition, we investigated the selective diffusion of Ga from AlGaAs into SiOx under the dry thermal condition with rapid thermal annealing. We found that the diffusion velocities depended on the SiOx growing method and the diffusion into SiOx deposited by sputtering was more remarkable than that by plasma chemical vapour deposition Copyright © 2005 John Wiley & Sons, Ltd.

Effects of hygrothermal ageing and thermal shock on reliability of interfacial adhesion between black oxide coated copper substrate and epoxy resin

Black oxide is a conversion coating applied onto the Cu substrate to improve the interfacial adhesion with polymeric adhesives. A comprehensive study was made to characterize the black oxide coating and the corresponding interfacial adhesion with various types of polymeric resin, aiming to optimize the oxide processing conditions. The reliability of adhesion performance of the coating was evaluated before and after accelerated hygrothermal ageing, such as temperature cycling, pressure cooker test, and moisture sensitivity test followed by thermal shock. The moisture resistance of the substrate with black oxide coating was much higher than the bare Cu substrate, during both the moisture absorption and desorption processes. Thermal cycling alone did not change significantly the adhesion performance of any of the substrates studied. Pressure cooker test was detrimental to adhesion performance of oxide coated Cu substrates. Nevertheless, the residual interfacial bond strengths were consistently much higher for the black oxide coated substrates than the bare Cu surface. Significant delamination occurred between the bare Cu and the moulding compound after the moisture sensitivity test followed by thermal shock, whereas there was virtually no delamination on the black oxide coated samples under the same ageing condition, confirming the higher reliability of interfacial adhesion performance for the latter.

Highly moisture-resistive silicon nitride films prepared by catalytic chemical vapor deposition and application to gallium arsenide field-effect transistors

Moisture resistivity for silicon nitride (SiNx) films prepared by catalytic chemical vapor deposition (Cat-CVD) was examined. SiNx films prepared by Cat-CVD and those by plasma-enhanced chemical vapor deposition (PECVD) were subjected to the pressure cooker test (PCT) in H2O vapor at 2 atm and 121°C for 96 h. It was confirmed after PCT that the intensity of the signal due to Si–O bonds in Fourier-transform infrared absorption spectra remarkably increases for PECVD films although little increase is observed for Cat-CVD films. Low stress of the order of 10 MPa was also obtained for SiNx films prepared by Cat-CVD. SiNx passivation by Cat-CVD brings about low leakage current and high mutual conductance for gallium arsenide self-align-gate field-effect transistors.

Characterization of nonconductive adhesives for flip-chip interconnection

For chip-level interconnection, nonconductive adhesive (NCA) is emerging as one of the promising substitutes for solder interconnection because of its inherent fine-pitch capability and environmental friendliness. The NCA interconnect relies on the mechanical connection between the contacts on the chip and corresponding contacts on the substrate enabled by the compressive stress created as the NCA epoxy cures. The degradation mechanism of NCA technology is, however, relatively less well understood compared to solder interconnects in terms of materials requirements for enhanced reliability performance. This study addresses the impact of material systems employed on the reliability of the packages. This involves characterization of NCA pastes in thermomechanical, hygroscopic swelling, and moisture diffusion properties. The reliability evaluation was carried out using electroless nickel/gold perimeter bumped test chips with daisy-chained connections. Analysis showed that interfacial delamination and open contact were the major failure modes in the NCA package. Pressure cooker test (PCT) performance was improved by using NCA with low-saturated moisture concentration, low coefficient of moisture expansion, and high adhesion. For better performance in the moisture sensitivity test (MST), the key properties required were high shear strength and low moisture diffusivity. Interestingly, filler content shows opposing behavior in the MST versus the PCT. Thus, optimum filler content must be found.

Highly moisture-resistive silicon nitride films prepared by catalytic chemical vapor deposition and application to gallium arsenide field-effect transistors

Moisture resistivity for silicon nitride (SiN x ) films prepared by catalytic chemical vapor deposition (Cat-CVD) was examined. SiN x films prepared by Cat-CVD and those by plasma-enhanced chemical vapor deposition (PECVD) were subjected to the pressure cooker test (PCT) in H 2O vapor at 2 atm and 121°C for 96 h. It was confirmed after PCT that the intensity of the signal due to Si–O bonds in Fourier-transform infrared absorption spectra remarkably increases for PECVD films although little increase is observed for Cat-CVD films. Low stress of the order of 10 MPa was also obtained for SiN x films prepared by Cat-CVD. SiN x passivation by Cat-CVD brings about low leakage current and high mutual conductance for gallium arsenide self-align-gate field-effect transistors.

Stability of Carbon-Doped Silicon Oxide Low-k Thin Films

The impact of and plasma treatments on the properties of low-dielectric-constant (low-k) carbon-doped silicon oxide (CDO) film, deposited by plasma-enhanced chemical vapor deposition, has been investigated. The thermal stability and the effect of moisture penetration on low-k films have also been evaluated. It is found that and plasma treatments of low-k films result in some loss of C content and increase in moisture uptake. This increases the k value and leakage current of the film. The and plasma treatments do not add any N content in the films. Therefore, it does not cause the resist contamination of chemically amplified-type photoresists. High thermal stability of the low-k CDO material is confirmed by isothermal thermogravimetric analysis of the low-k CDO powder and there is no weight loss or change of composition of the low-k CDO film after seven thermal cycles at 425°C for 1 h in ambient. A pressure cooker test of the film carried out at ∼2 atm, 120°C, and 100% relative humidity for 24 h has been found to increase the k value by 7% and leakage current by two orders of magnitude. © 2004 The Electrochemical Society. All rights reserved.

Moisture resistance and thermal stability of fluorine-incorporation siloxane-based low-dielectric-constant material

The low dielectric constant (low- k) of organo-silica-glass (OSG) and fluorine-incorporated OSG (OFSG) materials produced from plasma-enhanced chemical vapor deposition of trimethylsilane are thermally stable to greater than 600 °C. FTIR analysis indicates that SiCH 3 bonds and SiF bonds remain intact to temperatures well above that normally encountered during integrated circuit manufacture, allowing these materials to maintain a low- k value. While OFSG materials proved to have less hydrolytic resistant than their non-fluorinated analogs during high pressure, high temperature water exposure (pressure cooker test), their leakage current was found to be lower than OSG films before and after wafer exposure. The measured properties of OFSG blanket films suggest that this material is sufficiently robust to ensure stability of reliability after the fabrication.

Study of the properties and reliability of EMC packaging material

AbstractThermoplastic nylon powder with a low melting point was added to Biphenyl Epoxy to serve as a forming stress release agent that is intended to reduce the stress resulting from Epoxy Molding Compound (EMC). The purpose of this study was to explore the physical impact and effect on the formed object after adding nylon powder to Biphenyl Epoxy. Mechanical properties were explored through the Izod impact test and the three‐point bending test. Thermal Mechanical Analysis and Dynamic Mechanical Analysis were conducted to probe the coefficient of thermal expansion (CTE) and the glass transition temperature (Tg). The rate of water absorption was measured via a test of the pressure cook test (PCT), and insulation resistance was assessed through the insulating destruction experiment. The results indicate that adding nylon powder increases the fracture energy of the epoxy‐formed material; however, mechanical properties decreased slightly. TMA showed that the CTE (α1) decreased when nylon was added, and DMA revealed that heat resistance decreased slightly. The water absorption rate test and the PCT test showed that the rate of water absorption increased to a small extent, whereas the breakdown voltage (BDV) decreased slightly. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3928–3933, 2003

Electrochemical oxidation of 1-methoxy-2-propanol in direct liquid fuel cells : Qi, Z. and Kaufman, A. Journal of Power Sources, 2002, 110, (1), 65–72

Over 80% of Athabasca, Alberta, Canada oil sands deposits are suitable for in-situ bitumen recovery processes. Steam assisted gravity drainage and cyclic steam stimulation processes are commercially implemented with current bitumen production capacity of about 850,000 bbl/d, which is projected to exceed 5000,000 bbl/d in the next two decades. Efficiency of these processes would be improved by reducing the steam-to-bitumen ratio. For this purpose addition of light hydrocarbons into steam as a solvent to reduce bitumen viscosity has been studied for decades with a limited commercial success. As an alternate strategy to solvent co-injection with steam, reduction of bitumen–water interfacial tension by co-injection of a surfactant, such as biodiesel (fatty acid methyl esters), with steam was proposed (Babadagli et al., 2009. Use of biodiesel as an additive in thermal recovery of heavy-oil and bitumen. In: Paper 049 Presented at the Canadian International Petroleum Conference (CIPC), 16–18 June, Calgary, Alberta, Canada; Babadagli and Ozum, 2012. Oil Gas Sci. Technol.: Rev. IFP Energies Nouvelles 67 (3), 413–421). The present study focuses on three issues: (i) viscosity of bitumen in the neighborhood of the edge of the steam chamber using heat conduction models, where bitumen mobility should be controlled by viscosity and bitumen–water interfacial tension; (ii) generate bitumen recovery data, operating the steam chamber as a pressure cooker; where bitumen mobility should be controlled mainly by viscosity rather than bitumen–water interfacial tension, since the influence of the creeping flow of water-condensed steam is marginally small; and, (iii) measure bitumen content at different heights of the pressure cooker test spent core samples to predict bitumen mobility and permeability. Pressure cooker tests were performed using steam, steam and pentane as a solvent at 5%, 10% and 15% of bitumen by mass, and steam and biodiesel as a surfactant additive at 0.2% and 0.3% of bitumen by mass dosages. Our test results showed that solvent, such as pentane, addition reduced bitumen recovery as the dosage of solvent addition increased from 5% to 15% of bitumen. This observation is interpreted that while solvent addition reduces bitumen viscosity it also increases bitumen–water interfacial tension; the overall effect of which results in reduction of bitumen recovery efficiency. When biodiesel was used as a surfactant additive at 0.2% and 0.3% of bitumen by mass dosage, a slightly increase in bitumen recovery efficiency was observed. Bitumen mobility and bitumen permeability values predicted in this study were one order of magnitude smaller than that of the values reported in the literature; probably resulting from reduced bitumen–water interfacial tension, by the activation of natural surfactants contained in bitumen, promoting bitumen mobility in the field operations. Result of the present study suggests that further tests and modeling studies are needed to understand effects of bitumen viscosity reduction by solvent co-injection and bitumen–water interfacial tension reduction by surfactant co-injection with steam on the efficiency of steam assisted bitumen recovery processes.

Reliability assessment and hygroswelling modeling of FCBGA with no-flow underfill

In the flip-chip ball grid array (FCBGA) assembly process, no-flow underfill has the advantage over traditional capillary-flow underfill on shorter cycle time. Reliability tests are performed on both unmolded and molded FCBGA with three different types of no-flow underfill materials. The JEDEC Level-3 (JL3) moisture preconditioning, followed by reflow and pressure cooker test (PCT) is found to be a critical test for failures of underbump metallization (UBM) opening and underfill/die delamination. In this paper, various types of modeling techniques are applied to analyze the FCBGA-8×8 mm on moisture distribution, hygroswelling behavior, and thermomechanical stress. For moisture diffusion modeling, thermal-moisture analogy is used to calculate the degree of moisture saturation in the multi-material system of FCBGA. The local moisture concentration along the critical interface, e.g. die/underfill, is critical for delamination, because the moisture weakens the interfacial adhesion strength, generates internal vapor pressure during reflow, and induces tensile hygroswelling stress on UBM during PCT. The results of moisture distribution can be used as loading input for the subsequent hygroswelling modeling. The magnitude of hygroswelling stress acting on UBM is found to be greater than the thermal stress induced during reflow, both in tensile mode which may cause the UBM-opening failure. Underfill with lower saturated moisture concentration ( C sat) and coefficient of moisture expansion (CME) are found to induce lower UBM stress and has better reliability results. Molded package generally has higher stress level than unmolded package. Parametric studies are performed to study the effects of no-flow underfill materials, package type (molded vs. unmolded), die thickness, and substrate size on the stresses of UBM during reflow and PCT.

Polymer film deposition with fine pitch openings by stencil printing

It is confirmed that stencil printing with a novel developed printable polyimide paste can be used for polymer film deposition on LSI wafers. A thick polyimide film with openings for solder ball bumping can be deposited on all of the LSIs on a wafer by stencil printing at one time. This stencil printing process does not need an expensive lithography process, providing cost-effective wafer-level chip scale packages (WLCSPs). In this study, a novel polyimide paste was tailored to have a higher thixotropy ratio than conventional printable polyimide materials. The novel printable polyimide paste shows that the viscosity ratio of more than 3.5 at the shear rate of 1 to 10 s −1 and that the viscosity increases rapidly after the shear rate is lowered. Fine spaces of 40 μm between 250 μm openings were obtained for 10 μm thick polyimide films on Si wafers. It has been also confirmed that the new paste shows the variation range of 30 μm at the opening size of 385 μm within 100 continuously printed wafers. Even after the new paste was shear-thinned repeatedly, rheological behavior of the new paste was not changed. This robustness leads to higher efficiency of the materials for mass-producing. From the reliability viewpoint of the printed polyimide films, no peelings were observed on plasma-CVD SiN films after the pressure cooker test under the condition of 127 °C and 0.25 MPa with the humidity of 100% for 300 h. The optimal stencil printing process using the novel developed paste will lead to significant cost reduction of a patterned polymer deposition process. Finally, WLCSPs using the stencil printing of the new polyimide paste have been demonstrated for SRAM LSIs on 8-in. wafers.

Study on underfill/solder adhesion in flip-chip encapsulation

Underfill materials are employed in flip-chip assemblies to enhance solder joint reliability performance. We have studied the adhesion strength of two underfill samples with tin/lead (Sn/Pb) eutectic solder and tin/copper (Sn/Cu) lead-free solder, benchmarked with a copper surface. It was found that the adhesion of underfills and both solder materials was about 1/3 of the adhesion between underfills and copper. The effect of temperature and humidity aging as well as flux residue on adhesion strength was also investigated. A loss of adhesion was observed after the pressure cooker test, but 85/spl deg/C/85% RH aging and flux residue revealed only a slight influence on adhesion strength. Surface analysis was performed on solid surfaces including copper, Sn/Pb eutectic solder, Sn/Cu lead-free solder and cured underfills by using the three-liquid-probe three-component surface tension method with a goniometer. The surface tension of liquid underfills was measured by the pendent drop method, and their contact angles on copper, Sn/Pb eutectic solder and Sn/Cu lead-free solder were also measured with a goniometer. The thermodynamic work of adhesion for underfills with copper and solder surfaces of different conditions was then calculated following these two surface analysis approaches. It was found that the thermodynamic work of adhesion was not correlated with the lap shear strength of underfills with copper and solder materials. Thus, the wetting property of an underfill on a substrate is not the determining factor for its practical adhesion strength. Various possible techniques for improving the adhesion of underfills and solder materials were then considered, and the use of additives in underfill formulations was experimented. However, we have not observed any significant effect of adhesion strength enhancement from any of these additives. Further tests of these additives with the base underfill formulation seemed to reveal a slight possibility to enhance adhesion of underfills and solders by proper manipulation of the underfill and/or flux formulation.

Corrosion study at Cu–Al interface in microelectronics packaging

The interfacial shear (IS) force of copper ball onto aluminium-based bond pad in microelectronics packaging depends on the formation and growth of Cu–Al intermetallic. This paper reports the study on the behaviour of the IS force of the Cu–Al bonds that were subjected to pressure cooker test up to 576h. Initially, the IS force increases with test readout point until 192h, due to Cu–Al intermetallic growth that has strengthened the bonding. However, IS force decreases significantly from 157.4gf at 192h to 97.6gf at final test readout point, 576h. The number of shear-induced cratering shows similar reduction trend after 288h. Result of scanning electron microscopy (SEM) on bonding morphology shows the evidence of crack at the aluminium bond periphery or outer Cu–Al interface and the cracking trend continues at higher time point. Surface analysis of ball-peeled bond pad using X-ray photoelectron spectroscopy (XPS) indicated that the cracks were due to stress corrosion cracking at aluminium that has been stimulated by copper. The concentration of CuO at the surface bonded area was found to be increased at higher readout point and reached 100% at 576h. These results indicated that the Cu–Al bond had been weakened by stress corrosion cracking at outer bond interface and reduced the IS force.

Characterization and reliability of low dielectric constant fluorosilicate glass and silicon rich oxide process for deep sub-micron device application

Fluorosilicate Glass (FSG) with low dielectric constant currently has been replaced as an alternative to SiO 2 for device speed improvement. However, several integration aspects, such as Fluorine (F) distribution, F thermal stability, gap fill capability, capacitance reduction and via resistance of FSG prepared by the high density plasma (HDP) chemical vapor deposition (CVD) method are of concern for sub-0.18-μm devices. In this study, HDP–FSG films show different F concentrations at different locations on an 8-inch wafer. In addition, the FSG film shows poor thermal stability and F diffuses out of the film after high temperature annealing and the pressure cook test (PCT). However, the thermal stability of FSG film can be improved by capping with an oxide layer. The results indicate that silicon rich oxide (SRO) has a better effect at blocking the F diffusion out of FSG films at high temperature than plasma enhanced oxide (PE-OX). For the gap fill capability, HDP-FSG can fill all 0.23-μm gaps and some of the 0.21-μm gaps with an aspect ratio <3.8 but not the 0.19-μm gaps. A 8000 Å HDP–FSG film with 600 Å USG liner and 2000 Å cap layer shows approximately 7.5 to 7.7% capacitance reduction on 0.23/0.23-μm gaps when compared with USG (undoped silicate glass). In addition, FSG has a larger capacitance reduction on the wider metal lines than the thinner metal lines at the same gap size due to a capacitance fringe effect. The via resistance for 0.26 μm unlanded via (which allow minor photo mis-alignment) of HDP-FSG film is also similar to that of USG.