Bonding Pad Plating Structure to Prevent RDL Undercut
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Solution Overview
Problem
In the manufacturing of fan-out semiconductor packages, the adhesion of dry resist film to redistribution pads is poor, leading to bird's beak formation, which results in undercut formation due to galvanic corrosion during etching and voids under the passivation layer, causing defects.
Innovation Solution
The semiconductor package design includes a bonding pad with sequentially stacked plating patterns, where the first plating pattern has an inclined sidewall with decreasing diameter, and subsequent patterns have different materials, ensuring the redistribution pad's upper surface is covered by gold, thereby reducing undercutting during etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a dry resist film is used in the plating process, then the plating pattern can be formed, but the dry resist film has poor adhesion to the redistribution pad causing bird's beak formation and lifting
Solution Approach 1:
The patent changes the geometric parameters of the plating pattern by forming an inclined sidewall structure where the diameter gradually decreases from the bottom to the top. This parameter modification allows the plating pattern to accommodate the bird's beak formation without compromising adhesion, as the inclined structure provides stress relief and prevents lifting while maintaining effective plating coverage
Solution Approach 2:
The plating pattern is segmented into multiple regions with different diameters - a wider base portion and a narrower top portion connected by an inclined sidewall. This segmentation allows each region to serve different functions: the base provides strong adhesion and coverage, while the tapered top accommodates resist lifting without causing failure
2Manufacturing precision
If the plating pattern fills the space formed by bird's beak, then the space is covered, but undercut is formed in the redistribution pad due to galvanic corrosion in subsequent etching process
Solution Approach 1:
The inclined sidewall plating pattern is formed in advance to counteract the subsequent galvanic corrosion effect. By creating a geometry where the plating extends further at the base than at the top, the structure pre-compensates for the material loss that will occur during etching, preventing undercut formation before it can happen
Solution Approach 2:
The plating process is performed to fill and over-cover the bird's beak space with an inclined structure before the etching process occurs. This preliminary action ensures that when etching happens, the redistribution pad is already protected by the extended base portion of the plating pattern, preventing the harmful undercut effect
3Ease of operation
If passivation layer is formed to expose the plating pattern, then the plating pattern is accessible, but voids are generated and cracks occur later
Solution Approach 1:
The inclined sidewall geometry changes the stress distribution parameters within the plating structure. By creating a gradual taper rather than an abrupt transition, the stress concentrations that would lead to void formation and cracking are eliminated, allowing the passivation layer to be removed and plating exposed without compromising structural integrity
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 design effectively prevents undercutting and void formation, enhancing the reliability and integrity of the semiconductor package by minimizing defects.
Implementation Method 1
A bonding pad is on the redistribution pad of the second redistribution wiring, and the bonding pad includes first, second, and third plating patterns. The first plating pattern is on the redistribution pad, and the first plating pattern has an inclined sidewall with a diameter that gradually decreases with increasing distance from the core substrate.
Implementation Method 2
The second plating pattern is on the first plating pattern. The third plating pattern is on the second plating pattern
Implementation Method 3
The third plating pattern is on the second plating pattern, and the third plating pattern has a diameter that is the same as a diameter of the second plating pattern
Data Source
AI summary
An electronic package includes a redistribution wiring layer having redistribution wiring with a redistribution pad, and a bonding pad on the redistribution pad of the redistribution wiring. The bonding pad includes first, second, and third plating patterns. The first plating pattern is on the redistribution pad, and the first plating pattern includes a first material. Moreover, the first plating pattern has an inclined sidewall so that a diameter of the first plating patter decreases with increasing distance from the redistribution pad so that a first diameter of the first plating pattern adjacent the redistribution pad is greater than a second diameter of the first plating pattern spaced apart from the redistribution pad. The second plating pattern is on the first plating pattern, and the second plating pattern includes a second material different than the first material. The third plating pattern is on the second plating pattern, and the third plating pattern includes a third material different than the second material. Moreover, the second and third plating patterns have a same diameter that is no greater than the second diameter of the first plating pattern.