Ultrasonic Bonding for Flip-Chip Pad and Bump Strength
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Solution Overview
Problem
The reduction of pad size in flip-chip mounting decreases the bond strength between the bump and the pad, posing a challenge in minimizing chip area while maintaining adequate bonding.
Innovation Solution
A method involving the application of ultrasonic waves to bond a pad on the device chip with a bump on a mounting substrate, where the pad is positioned on the lower surface of the device chip and the bump on the upper surface, and a burr formed during dicing is used to prevent damage to the functional element and enhance bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the pad size is reduced to minimize chip area, then the chip area is reduced, but the bond strength between the bump and the pad decreases
Solution Approach 1:
The patent applies ultrasonic vibration to the bonding interface between the bump and pad during the bonding process. The ultrasonic wave is applied from the upper surface of the device chip to the lower surface where the pad is located, creating mechanical vibration that enhances bonding strength even with reduced pad area. This resolves the contradiction by allowing smaller pads while maintaining adequate bond strength through vibration-assisted bonding.
2Productivity
If a dicing blade is used to cut the substrate into device chips, then the substrate is divided into multiple chips, but the functional element may be damaged during the cutting process
Solution Approach 1:
The patent forms a burr on the upper surface of the metal layer before dicing the substrate. This preliminary burr formation creates a protective protrusion that prevents the dicing blade from directly contacting and damaging the functional element during the cutting process. The burr acts as a sacrificial feature that absorbs the cutting stress, thereby protecting the functional element while still allowing efficient chip production.
3Area of moving object
If the pad size is reduced, then the chip area is minimized, but the area of the bond between the bump and the pad becomes insufficient
Solution Approach 1:
The patent utilizes ultrasonic vibration during bonding to enhance the bond area between the bump and pad. The mechanical vibration from the ultrasonic wave applied to the device chip creates dynamic conditions at the bonding interface that increase the effective bond area and bonding strength, compensating for the reduced physical pad area. This allows the bond area to be sufficient even when the pad area is minimized for smaller chip dimensions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method increases the bond strength between the pad and the bump, reduces the chip size by minimizing the bump area, and prevents damage to the functional element during processing.
Implementation Method 1
bonding a pad located on the lower surface of the device chip and the bump by applying an ultrasonic wave to the device chip from an upper surface of the device chip
Data Source
AI summary
A method of fabricating an electronic device, the method including: arranging a device chip with no bump located on a lower surface of the device chip on a mounting substrate including a bump located on an upper surface of the mounting substrate; and bonding a pad located on the lower surface of the device chip and the bump by applying an ultrasonic wave to the device chip from an upper surface of the device chip.