Flip-Chip Bonding Terminal Segmentation for Solder Protrusion Control
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Solution Overview
Problem
The flip-chip mounting method using copper electrodes faces challenges with oxidation, leading to decreased bonding strength and potential electrical shorts due to solder material protrusion, which limits the miniaturization and integration level of semiconductor devices.
Innovation Solution
A method involving a wiring substrate with terminals having a wide and narrow portion, where the copper electrodes are bonded over the narrow portion with a controlled amount of solder material applied to prevent oxidation and protrusion, ensuring reliable connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If solder material is applied in advance onto terminal and projecting electrode surfaces, then bonding strength is improved by preventing oxidation, but solder material protrudes into periphery causing electrical shorts between adjacent terminals
Solution Approach 1:
The terminal is divided into two distinct portions: a wide portion that receives solder material to prevent oxidation and enhance bonding strength, and a narrow portion that prevents solder material protrusion and electrical shorts. This segmentation allows each portion to serve its specific function independently.
Solution Approach 2:
Different portions of the terminal have different widths tailored to specific functions: the wide portion provides adequate solder material containment for strong bonding, while the narrow portion restricts solder material spread to prevent electrical shorts. This local differentiation resolves the contradiction between bonding strength and electrical isolation.
2Productivity
If distance between adjacent terminals is reduced to improve integration level, then miniaturization is achieved, but solder material protrusion causes electrical shorts more easily
Solution Approach 1:
The terminal structure is segmented into wide and narrow portions, where the narrow portion acts as a built-in barrier that prevents solder material from protruding into the space between adjacent terminals. This allows terminals to be placed closer together without increasing the risk of electrical shorts.
Solution Approach 2:
The narrow portion of the terminal serves as an intermediary structure between adjacent terminals, physically blocking solder material from bridging the gap between terminals. This mediator enables higher integration levels while maintaining electrical isolation.
3Ease of manufacture
If copper material is used for projecting electrode instead of gold, then manufacturing cost is reduced, but oxidation resistance decreases leading to decreased bonding strength
Solution Approach 1:
Solder material is applied in advance to the wide portion of the terminal before bonding, creating a protective layer that prevents oxidation of the copper surface. This preliminary action preserves the bonding strength of copper electrodes while maintaining cost advantages.
Solution Approach 2:
The solder material applied to the wide portion acts as an intermediary protective layer between the copper electrode and oxygen, preventing oxidation. This mediator allows copper to be used instead of gold while maintaining bonding strength.
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 approach enhances the bonding strength and reliability of semiconductor devices by preventing oxidation and electrical shorts, allowing for improved miniaturization and integration.
Implementation Method 1
the second solder material is melted by applying heat to the second solder material
Implementation Method 2
the oxidation of the surface of the projecting electrode containing copper (Cu), for example, can be prevented or suppressed by the solder material
Data Source
AI summary
To improve reliability of a semiconductor device, in a flip-chip bonding step, a solder material that is attached to a tip end surface of a projecting electrode in advance and a solder material that is applied in advance over a terminal (bonding lead) are heated and thereby integrated and electrically connected to each other. The terminal includes a wide part (a first portion) with a first width W1 and a narrow part (a second portion) with a second width W2. When the solder material is heated, the thickness of the solder material arranged over the narrow part becomes smaller than the thickness of the solder material arranged in the wide part. Then, in the flip-chip bonding step, a projecting electrode is arranged over the narrow part and bonded onto the narrow part. Thus, the amount of protrusion of the solder material can be reduced.