Wiring Board Opening Edge Positioning for Underfill Resin Flow
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Solution Overview
Problem
In flip chip mounting, the formation of voids within the underfill resin between the semiconductor chip and the wiring board due to inadequate resin flow and insufficient fillet formation at corner portions, leading to reduced bonding strength and potential electrical disconnection.
Innovation Solution
A wiring board design where the opening portion in the solder resist layer has its edge positioned outside the mounting area except for one corner, allowing for improved resin flow and filling without voids, ensuring reliable resin fillet formation at the corner portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the opening portion edge is positioned outside the mounting area, then resin flow is improved and void formation is prevented, but the gap between the solder resist layer and chip becomes smaller in vertical dimension causing quicker resin spread over the solder resist layer than the opening portion
Solution Approach 1:
The patent applies local quality by making the opening portion larger than the chip mounting area in specific regions. The opening portion extends beyond the chip peripheral shape in the vertical direction, creating a resin reservoir that ensures sufficient resin supply to corner portions while maintaining appropriate gap dimensions in horizontal directions. This local enlargement of the opening portion addresses the specific problem of insufficient resin flow to corners without affecting the overall gap structure.
Solution Approach 2:
The patent implements preliminary action by pre-forming the opening portion with dimensions that anticipate the resin filling process requirements. The opening portion is designed beforehand to be larger than the chip mounting area, creating a reservoir that will supply resin during the filling process. This preliminary design ensures that corner portions receive adequate resin before the filling process begins, preventing void formation at critical locations.
2Reliability
If the opening portion is formed to expose pad portions in annular shape, then electrical connection is enabled, but corner portions of the chip mounting area are not sufficiently filled with resin
Solution Approach 1:
The patent applies local quality by differentiating the opening portion dimensions from the chip mounting area boundaries. The opening portion is designed to extend beyond the chip peripheral shape in certain directions (vertical), creating localized resin reservoirs at corner portions. This allows the opening to maintain its annular function for electrical connection while simultaneously providing enhanced resin supply to corner regions for proper fillet formation.
Solution Approach 2:
The patent employs dimensionality change by extending the opening portion in the vertical direction beyond the chip mounting area, rather than merely expanding it in the horizontal plane. This vertical extension creates a three-dimensional resin reservoir that preferentially supplies resin to corner portions during the filling process, addressing the insufficient fillet formation problem while preserving the annular configuration for electrical connection.
3Ease of manufacture
If the opening portion edge is positioned inside the mounting area, then resin filling is simpler, but voids form within the resin due to quicker spread over the solder resist layer than the opening portion
Solution Approach 1:
The patent applies local quality by creating a non-uniform opening portion configuration where the opening extends beyond the chip mounting area in the vertical direction. This localized enlargement at specific regions (corners) ensures adequate resin supply to these critical areas, preventing void formation and maintaining connection reliability, while the overall opening structure remains relatively simple to manufacture.
4Shape
If the opening portion is formed larger than chip size, then resin flow to corner portions is improved, but the gap between the solder resist layer and chip is reduced in vertical dimension
Solution Approach 1:
The patent employs dimensionality change by extending the opening portion primarily in the vertical direction beyond the chip mounting area, rather than uniformly expanding it in all directions. This vertical extension creates a resin reservoir that improves fillet formation at corner portions while minimizing the impact on the horizontal gap dimensions between the solder resist layer and chip. The opening portion acts as a three-dimensional structure that supplies resin vertically to corner regions.
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
Prevents void formation and enhances resin flow to all areas, including corner portions, improving bonding strength and appearance by ensuring complete resin coverage and maintaining insulation properties.
Implementation Method 1
when an underfill resin is filled between the chip and the wiring board, the underfill resin spreads quicker over the solder resist layer than the opening portion by capillary action
Data Source
AI summary
A wiring board between which and a chip to be mounted a resin is filled includes: a substrate body on which a conductor portion to be connected to an electrode terminal of the chip is formed; and an insulating protection film formed on the substrate body and having an opening portion formed therein to expose the conductor portion. The opening portion is formed in such a manner that the edge thereof is positioned along and outside the outer shape of the chip except for a specific corner portion, and that the edge in the specific corner portion is positioned on a side of or inside the outer shape of the chip.