Epoxy Die Attach Combined With Face-Up Die Bonding for Improved XYZ Placement Accuracy

Epoxy die attach is widely used in microcircuit assembly and enjoys advantages such as ease of deposition, fast curing, reworkability, and non-toxicity. These qualities also make it suitable for automated mass production. However, this method falls short when high placement accuracy is desired as the die can shift on uncured epoxy leading to die displacement from its original location. Gold to gold face-up bonding is another method utilized in microelectronics packaging given its proven bonding reliability and high placement accuracy for small devices. Nevertheless, it is difficult to achieve a reliable bond using this method for relatively larger devices. The nonplanarity of the bonding collet or the variation in the height of the gold bumps results in a tilted die attach and/or a weak bond between the die and the substrate. Moreover, CTE (Coefficient of Thermal Expansion) mismatch between the die, the gold bumps, and/or the substrate leads to bond failure due to temperature fatigue. This paper discusses a hybrid method to take advantage of the strengths of both methods mentioned above, culminating in a reliable process with high XYZ placement accuracy. To apply this method, epoxy is first dispensed on a gold-plated substrate. Using a flip chip machine, samples with plated gold bumps on their ground side are then placed on the substrate. The gold bumps are mainly used as targets and stand-offs to improve the placement accuracy and to control epoxy glue-line thickness. The force applied on the die, the time the force is applied, and the substrate temperature are controlled for optimum die attach. Moreover, along with the force applied by the vacuum tip, epoxy is partially cured on the flip chip machine heated stage before it is moved to an oven to complete the cure process. Die shear test results before and after temperature conditioning are compared with standard epoxy die attach and gold to gold face-up bonding for identical samples and the advantages are discussed.

Intermetallics Disappearance Rate Analysis in Double Multiphase Systems

Electric corrosion of aluminium and copper is investigated experimentally. It is found that the electric corrosion of copper is higher than the electric corrosion of aluminium. It is also clarified that the intrinsic diffusion coefficient of Cu is higher than the intrinsic diffusion coefficient of Al in each phase, so inert markers move to Cu. Copper has a higher electric conductivity, higher thermal conduction, and lower material cost than gold, so it is possible to use Cu instead of Au for wire bonding in microelectronics packaging, because the thin Al pad (1.2 μm thickness) can prevent gold and copper corrosion. Intermetallics disappearance and Kirkendall shift rates calculation methods are proposed. Methods involve mass conservation law and concentration profiles change during mutual diffusion. Intermetallics disappearance and Kirkendall shift rates in Al-Cu (Al is thin layer on Cu), Cu-Al (Cu is thin layer on Al), Al-Au, Zn-Cu, and Cu-Sn systems are analyzed theoretically using literature experimental data. Diffusion activation energies and pre-exponential coefficients for Cu-Sn system were calculated combining literature experimental results.

Thin Glass Handling Solutions for Microelectronics Packaging

Glass substrates with fine-pitch through-glass via (TGV) technology gives an attractive approach to wafer level packaging and systems integration. Glass can be made in very thin sheets (<100 um thick) which aids in integration and eliminates the need for back-grinding operations. Electrical and physical properties of glass have many attractive attributes such as low RF loss, the ability to adjust thermal expansion properties, and low roughness with excellent flatness to achieve fine L/S. Furthermore, glass can be fabricated in panel format to reduce manufacturing costs. The biggest challenge to adopting glass as a packaging substrate has been the existence of gaps in the supply chain, caused primarily by the difficulty in handling large, thin glass substrates using standard automation and processing equipment. This paper presents a temporary bonding technology that allows the thin glass substrates to be processed in a semiconductor fab environment without the need to modify existing equipment.

Development of a Piezo-Driven Liquid Jet Dispenser with Hinge-Lever Amplification Mechanism

Owing to the quick response, compact structure, high precision, huge blocking force generation, and ease of operation, piezoelectric actuators are urgently being adopted in the field of advanced dispensing for jetting performance improvement and fulfillment of precision requirements in microelectronics packaging, adhesive bonding, and miniaturization industry. This research focuses on the fundamental design and development of a piezo-electrically driven compact fluid dispenser using the principle of a class-one lever for amplification of needle displacement, and enhancement of application areas of the developed jet dispenser. Using fundamental lever principle, geometry-based modelling is carried out to fabricate a working prototype of a normally closed hinge-lever type dispenser. Preliminary experiments are carried out to witness the workability of the fabricated dispenser to deliver 100 dots of working fluid per second that will provide a novel device for dispensing of various fluids, and the proposed amplification mechanism suits various other piezoelectric applications as well.