HDI PCB Microvia Copper Filling for Uniform Trace Etching
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Solution Overview
Problem
Conventional methods for manufacturing high density interconnect printed circuit boards (HDI PCBs) face challenges in achieving uniform copper layer thickness and preventing undercut etching due to uneven copper thickness variations, especially with trace widths less than 30 μm, leading to increased complexity and risk of unacceptable width reduction.
Innovation Solution
A method involving the electroless deposition of a conductive layer followed by electrodepositing copper in microvias to form a planar surface with a thickness of 0.1 to 3 μm, eliminating trenches and ensuring uniform copper layer formation without significant height differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional mSAP sequences are used with specific microvia-filling electrolytes, then microvias can be filled with copper, but copper thickness variations occur between microvia pad and patterned copper surfaces
Solution Approach 1:
The patent changes the electrolyte composition parameters by using a conventional general-purpose electroplating electrolyte instead of specific microvia-filling electrolytes, and adjusts process parameters such as copper layer thickness to 0.1-3 μm to achieve uniform copper distribution without thickness variations
Solution Approach 2:
The patent applies homogeneity by using the same conventional general-purpose electroplating electrolyte for both microvia filling and patterned copper surface deposition, ensuring uniform copper thickness and properties across all copper surfaces without differentiation
2Quantity of substance
If thick copper layers are deposited to ensure complete microvia filling, then microvia filling is achieved, but uneven copper layer surfaces result causing etching difficulties
Solution Approach 1:
The patent changes the thickness parameter to a thin copper layer range of 0.1-3 μm, which is sufficient for microvia filling while maintaining surface uniformity and avoiding the uneven surfaces that cause etching difficulties
Solution Approach 2:
The patent applies partial action by depositing only the necessary thin copper layer (0.1-3 μm) rather than thick copper layers, achieving sufficient microvia filling while preventing surface unevenness and subsequent etching problems
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 reduces copper layer thickness variations and minimizes risks during etching, enhancing the reliability and precision of HDI PCBs by ensuring even copper distribution and minimizing etching time for trace-to-trace separation.
Implementation Method 1
The first step of the process is an electroless deposition of copper, distributing a thin metal seed layer (0.35 to 0.6 μm) on the peripheral surface of the copper clad substrate and the inner surface of the microvia
Implementation Method 2
Subsequent electrodeposition of ~3 μm flash copper constitutes the first copper layer
Implementation Method 3
c) electroplating a copper filling in the microvia and a first copper layer on the conductive layer wherein a thickness of the first copper layer is from 0.1 to 3 μm and wherein the copper filling and the first copper layer form together a planar surface
Data Source
AI summary
The present invention refers to a method of preparing a high density interconnect printed circuit board (HDI PCB) or IC substrates including through-holes and/or grate structures filled with copper, which comprises the steps of:a) providing a multi-layer substrate;b) forming a non-copper conductive layer or a copper layer on the cover layer and on an inner surface of the through-hole, respectively on an inner surface of the grate structure;c) forming a patterned masking film;d) electrodepositing copper;e) removing the masking film; andf) electrodepositing a copper filling.