High Density Package Substrate With Bottom Pad To Prevent Laser Drill Punch Through
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Solution Overview
Problem
Existing methods for forming high density package substrates using laser drilling face challenges such as punch through and increased costs due to ultra-thin copper foils, which complicate the process and affect fine line capability.
Innovation Solution
A method involving a double-sided copper clad laminate with an ultra-thin upper and lower copper foil, where a bottom pad is formed on the lower copper foil to prevent punch through, and a seed layer is conformally plated on the through hole, allowing metal to fill the hole without penetrating the pad, thereby avoiding punch through and reducing etching time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thick copper foil (12 μm or 18 μm) is used in full-subtractive process to prevent laser drill punch through, then punch through is prevented, but etching time increases and undercut phenomenon worsens
Solution Approach 1:
The patent applies different copper foil thicknesses to different locations: thick copper foil (12-18 μm) at the bottom layer to prevent laser drill punch through, and thin copper foil (3-7 μm) at the top layer to enable fine line formation and reduce etching time. This spatial differentiation of material properties resolves the contradiction between preventing punch through and reducing etching time.
Solution Approach 2:
The copper clad laminate is segmented into multiple layers with different copper foil thicknesses. The bottom layer uses thick copper foil for mechanical strength and punch through prevention, while upper layers use thin copper foil for fine line capability. This segmentation allows each layer to optimize for its specific function, resolving the time-reliability contradiction.
2Manufacturing precision
If thin copper foil (4 μm) is used in semi-subtractive process to improve fine line capability, then fine line formation is improved, but laser drilling process becomes complicated and costs increase
Solution Approach 1:
The patent uses thin copper foil (3-7 μm) specifically in upper layers where fine line capability is required, while maintaining thick copper foil in the bottom layer for structural integrity. This localized application of thin copper foil achieves fine line precision without requiring the entire structure to use thin material, thereby simplifying the overall laser drilling process compared to using thin copper throughout.
Solution Approach 2:
The copper clad laminate is divided into layers with different copper foil thicknesses optimized for different functions. Upper layers with thin copper foil enable fine line formation, while the bottom layer with thick copper foil provides a robust base for laser drilling. This segmentation resolves the contradiction between fine line capability and process complexity.
3Loss of time
If thin copper foil (4 μm) is used to reduce etching time, then etching time decreases, but probability of punch through increases
Solution Approach 1:
The patent strategically places thin copper foil (3-7 μm) in upper layers to reduce etching time and improve fine line capability, while maintaining thick copper foil (12-18 μm) in the bottom layer to prevent laser drill punch through. This spatial differentiation allows simultaneous optimization of etching time and punch through resistance.
Solution Approach 2:
The multi-layer structure segments the copper foil thickness functionally: thin copper in upper layers for rapid etching and fine line formation, thick copper in bottom layer for mechanical support and punch through prevention. This segmentation resolves the contradiction between reducing etching time and maintaining reliability.
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 prevents punch through and undercut phenomena, reduces etching time, and enhances fine line capability, offering improved cost efficiency and process accuracy compared to conventional methods.
Implementation Method 1
forming the through hole by laser drilling, wherein the through hole passes through the upper copper foil and the substrate
Implementation Method 2
forming a seed layer conformally on the through hole
Implementation Method 3
forming a plated through hole by plating a metal on the seed layer
Data Source
AI summary
The invention provides a high density package substrate and a method for fabricating the same. A double-sided copper clad laminate containing an upper copper foil and a lower copper foil is provided. A bottom pad is disposed on the lower copper foil, aligned to a predetermined position of a through hole. The through hole is formed by laser drilling through the upper copper foil and the substrate, but not through the bottom pad. A seed layer is formed conformally lining the through hole, and a metal layer is formed on the seed layer by plating to form a plated through hole (PTH).