Thermal and hygroscopic reliability of flip-chip packages with an anisotropic conductive film

Thermal and hygroscopic reliability of anisotropic conductive film (ACF) joints in relation to flip-chip bonding force was evaluated by thermal shock and constant temperature/humidity testing. The failure mode by thermal shock testing varied with increasing bonding force, i.e., (1) formation of a conduction gap between conductive particles and Au bump or Ni/Au plated Cu pad at low bonding force and (2) delamination of adhesive matrix from the plated Cu pad on the flexible substrate at high bonding force. The delamination initiated as a crack under a conductive particle and propagated sideward resulting in a complete delamination of the ACF from the Cu pad. However, delamination was observed between the ACF and Au bump on the chip side after the constant temperature/humidity testing for 500 h. A theoretical calculation was also conducted to predict the connection resistance of the ACF joint before and after reliability tests. The calculation showed the importance of the bonding gap between the electrodes.     

The role of water in delamination in electronic packages: degradation of interfacial adhesion

Polymeric electronic packages subjected to standard Joint Electron Device Engineering Council (JEDEC) reliability testing are known to exhibit weakening and failures at the polymeric adhesive interfaces. Coupling agents are typically used as additives in epoxy-based materials to improve package reliability. Coupling agent chemistry and environment conditions, including pH, temperature and applied stress, are known factors that affect the rate of adhesion degradation and jeopardize the long-term reliability of the package. In this study, the subcritical interfacial debonding process is described. The debonding rates of polymers with silane, titanate and zirconate coupling agents were characterized at different temperatures by shear fracture tests and tapered double cantilever beam tests under mechanical loading and simultaneous exposure to controlled acidic environments. An analytical procedure was developed to delineate the material parameters governing adhesion degradation. Elevated temperature and acidity were shown to have a strong effect on package reliability, but mechanical loading was found to have a minimal effect on the rate of adhesion degradation. The effects of the JEDEC testing conditions on interfacial bond degradation are discussed using the chemical kinetic model.     

17—AUTOMATIC MEASUREMENT OF FOLDING TWIST ON TWO-PLY YARN

A new instrument is described for the measurement of folding twist on two-ply yarn for yarns in the range 6 to 35 turns per inch. In the system used, yarn is passed continuously through a mechanical detector consisting of a stylus that rests on the yarn and approximately measures its projected diameter. A photoelectric system converts the measured diameter into an electrical signal, which is electronically processed to give a digital count for each half twist in the yarn. This information is also presented as a curve that continuously monitors the twist and as a print-out of the number of half turns per 10-in. length of yarn. An outline is given of the methods currently in use to measure folding twist.     

Thermosonic bonding of crossed strip Au bumps

Abstract

Gold strip bumps for electronic packaging are bonded using the thermosonic process. The Au strip bumps on the chip and substrate are aligned in a crossed configuration, and ultrasound is applied longitudinally on the chip to form a solid state bond between the crossed strip Au bumps. Deformed bump shapes are calculated numerically, and the shear force and fractured surface profile are measured to evaluate the bond quality. The deformed Au bump shape is similar to a saddle, which provides larger contact surface area and greater friction force. The bond strength of crossed strip bumps reaches the yield strength of Au, which is much higher than that previously obtained for bonding between Au bumps and a planar pad.     

A new epoxy/episulfide resin system for electronic applications — 2: pot life and prepreg storage life evaluation

A new epoxy/episulfide thermosetting resin was evaluated, using a dicyandiamide (DICY) curing agent. The system was found to exhibit a longer pot life and prepreg storage life than the standard epoxy system. The properties are attributable to the change in reaction mechanism caused by the addition of episulfide. The reaction mechanisms were studied using a mono-functional model compound system; the extent of episulfide-amine reaction is relatively high in the epoxy/episulfide system relative to epoxy-amine. A tert-amine salt is probably formed which does not act as a catalyst for the epoxy ring opening, resulting in a greater pot life.     

30—YARN HAIRINESS: A SURVEY OF RECENT LITERATURE AND A DESCRIPTION OF A NEW INSTRUMENT FOR MEASURING YARN HAIRINESS

This paper is intended to supplement one published in 1966 containing a survey of the literature on yarn hairiness, and the review of the literature is brought up-to-date at the time of writing.

A new electronic instrument for measuring yarn hairiness is outlined. This apparatus enables three parameters to be obtained directly and simultaneously, these being hairiness, hair length, and yarn diameter.     

MODEL-BASED DEVELOPMENT OF REAL-TIME SOFTWARE SYSTEM FOR ELECTRONIC UNIT PUMP SYSTEM

A real-time operating system (RTOS), also named OS, is designed based on the hardware platform of MC68376, and is implemented in the electronic control system for unit pump in diesel engine. A parallel and time-based task division method is introduced and the multi-task software architecture is built in the software system for electronic unit pump (EUP) system. The V-model software development process is used to control algorithm of each task. The simulation results of the hardware-in-the-loop simulation system (HILSS) and the engine experimental results show that the OS is an efficient real-time kernel, and can meet the real-time demands of EUP system; The built multi-task software system is real-time, determinate and reliable. V-model development is a good development process of control algorithms for EUP system, the control precision of control system can be ensured, and the development cycle and cost are also decreased.     

29—AN INSTRUMENT FOR MEASURING THE HAIRINESS OF YARNS

An instrument developed at the Shirley Institute and used since 1963 for measuring the hairiness of yarns is described. The basis of the method of counting is the interruption of a light beam by the projecting hairs. Results obtained by means of this instrument have been described previously by Walton.     

Peel strength and peel angle measured by the T-peel test on Cr/BPDA-PDA interfaces

The peel strength and peel angle of Cr/BPDA-PDA interfaces were measured using the T-peel test for Cu/Cr/BPDA-PDA structures. When the Cu/Cr metal film was thin, plastic bending of the metal film occurred during the T-peel test. With a thicker metal film, however, plastic bending of BPDA-PDA polyimide was observed. The critical thickness of the metal film for the transition from metal film bending to polyimide bending became thinner with decreasing yield strength of the metal film. Regardless of the metal film bending or polyimide bending during the T-peel test, the peel strength increased with higher peel angle and the failure mode of the Cr/BPDA-PDA interfaces was cohesive failure within BPDA-PDA.     

Synergistic Toughening of Epoxy–Copper Interface Using a Thiol-Based Coupling Layer

A novel concept of tuning the fracture properties of the interface through the treatment process of the coupling layer according to the cohesive critical strain energy release rate of the epoxy is proposed for optimizing the joint strength between epoxy and copper substrate. In most coupling agent application recipes, the treatment condition design has omitted the influence of the fracture properties of the corresponding adhesive. Conceivably, excessive strengthening of the adhesive–substrate interface may not lead to optimal interfacial strength. Synergistic toughening of the interface takes place when there is simultaneous interfacial debonding and failure of adhesive under a comparable critical stress state. Under critical applied load, energy is concurrently dissipated through the fracture of the interface, the fracture in the adhesive, and possible non-reversible failure processes such as shear yielding or micro-cracking of the adhesive. These combined energy dissipation processes result in extensive energy absorption around the crack tip. The adhesive joint, therefore, becomes more crack resistant. In this study, the interfacial adhesion promotion concept with synergistic toughening was demonstrated using three different epoxy systems bonded to copper substrates modified by a thiol-based coupling layer. The coupling layer was formed by treating the copper substrate with a thiol-based coupling agent. Critical strain energy release rate of the treated tapered double cantilever beam samples in different treatment conditions was measured for each of the epoxy systems. From the failure path analysis, mixed interfacial and cohesive failure was observed. This observation indicated that extensive energy dissipation occurs around the crack tip that results in synergistic toughening of the interface. This work shows the significance of matching the fracture property of the coupling layer with the adhesive. Up to 2.3 times improvement in the critical strain energy release rate was achieved with optimized thiol treatment compared to non-optimized treatment.