Void Formation Study of Flip Chip in Package Using No-Flow Underfill

Abstract

The advanced flip chip in package (FCIP) process using no-flow underfill material for high I/O density and fine-pitch interconnect applications presents challenges for an assembly process that must achieve high electrical interconnect yield and high reliability performance. With respect to high reliability, the voids formed in the underfill between solder bumps or inside the solder bumps during the no-flow underfill assembly process of FCIP devices have been typically considered one of the critical concerns affecting assembly yield and reliability performance. In this paper, the plausible causes of underfill void formation in FCIP using no-flow underfill were investigated through systematic experimentation with different types of test vehicles. For instance, the effects of process conditions, material properties, and chemical reaction between the solder bumps and no-flow underfill materials on the void formation behaviors were investigated in advanced FCIP assemblies. In this investigation, the chemical reaction between solder and underfill during the solder wetting and underfill cure process has been found to be one of the most significant factors for void formation in high I/O and fine-pitch FCIP assembly using no-flow underfill materials.

Synchronous curable deoxidizing capability of epoxy–anhydride adhesive: Deoxidation quantification via spectroscopic analysis

“…These cross sectional images by optical microscopy and SEM show complete wetting resulting from the fluxing capability of the epoxy–anhydride binary system that excluded a deoxidizing agent such as carboxylic acids. This novel discovery positively refutes those of previous studies, in which the incorporation of a fluxing agent into epoxy systems is deemed necessary for deoxidizing capability …”

“…Deoxidizing capability is considered important in terms of removing the metal oxide layer because it leads to electrical interconnections. The commonly used deoxidizing agents and antioxidants are organic compounds such as carboxylic acids and alcohols . These fluxing agents either remain in the paste after curing or participate in the epoxy reaction during the bonding process .…”

“…The commonly used deoxidizing agents and antioxidants are organic compounds such as carboxylic acids and alcohols . These fluxing agents either remain in the paste after curing or participate in the epoxy reaction during the bonding process . Low molecular weight unreacted organic acids such as abietic, pimaric, adipic, acrylic, and critic acids may cause corrosion to soldered interconnections .…”

Underfill Flow in Flip-Chip Encapsulation Process: A Review

“…Despite the no-fill and molded underfills resolved the productivity issue of slow underfill flow, the likelihood of occurrence of undesired voiding on the underfilled package greatly increases due to the uncontrolled distribution and rapid flow of underfill fluid, respectively. Additionally, the chemical reaction of fluxing agent in no-flow underfill during the thermal reflow induced void formation [8,9]. Moreover, both no-fill and molded underfills are less versatile as they required specific setups and limited for specific types of underfill fluid and design configuration of the chip packages.…”

Assembly and reliability assessment of 50µm-thick chip stacking by wafer-level underfill film

“…It could remove the oxide layer on solder bump and perform the underfill dispensing in one-step bonding process. Some researchers focus on the materials development such as Nonconductive paste (NCP) [1][2], non-conductive film (NCF) and wafer level underfill (WLUF) [3][4][5][6][7].…”