Substrate Structure With Filled Traces to Prevent Copper Migration
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Solution Overview
Problem
Conventional semiconductor packaging technologies face issues with fine circuit pitches due to undercut structures in solder-mask layers, leading to copper migration and potential short circuits between conductive traces, which are exacerbated by the need for precise exposure and development processes that can result in incomplete solder-mask removal or overexposure.
Innovation Solution
A substrate structure design featuring a thin filling layer between conductive traces, with an insulating protective layer having controlled thickness to prevent undercut formation, allowing for effective exposure and encapsulation to avoid copper migration and ensure reliable electrical connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the solder-mask layer thickness is increased to prevent circuit layer exposure and short circuits, then electrical insulation is improved, but undercut structure formation occurs at the bottom of the opening due to insufficient light penetration
Solution Approach 1:
The solder-mask layer is segmented into two distinct layers: a first solder-mask layer with smaller thickness formed on the circuit layer, and a second solder-mask layer with larger thickness formed on the substrate. This segmentation allows the first layer to provide sufficient electrical insulation while the second layer ensures adequate light penetration during exposure, preventing undercut structure formation at the opening bottom.
Solution Approach 2:
Different regions of the solder-mask structure are assigned different thicknesses to fulfill different functions. The first solder-mask layer directly covering the circuit layer is made thinner to allow light penetration and prevent undercutting, while the second solder-mask layer provides additional electrical insulation where needed. This local differentiation of thickness resolves the contradiction between insulation and manufacturing precision.
2Manufacturing precision
If light energy is increased to prevent undercut structure formation, then opening wall precision is improved, but solder-mask material on the circuit layer becomes overexposed and difficult to remove
Solution Approach 1:
The solder-mask layer is divided into two segments with different thicknesses: the first solder-mask layer on the circuit layer is thinner and allows standard light energy to penetrate without causing overexposure, while the second solder-mask layer provides additional protection. This segmentation enables the use of moderate light energy that prevents undercutting without overexposing the solder-mask material on the circuit layer, making removal easier.
Solution Approach 2:
The solder-mask structure employs local quality variation through different layer thicknesses. The first layer directly on the circuit layer has optimized thickness for light penetration and easy removal, while the second layer provides enhanced protection. This local differentiation allows standard light energy to achieve precise opening formation without overexposing critical areas.
3Productivity
If the pitch between conductive traces is reduced to achieve finer circuit designs, then circuit integration is improved, but copper migration occurs due to electron movement when packaging colloid cannot fill undercut structures
Solution Approach 1:
The dual-layer solder-mask structure segments the protection function: the first thin layer allows precise opening formation without undercutting, and the second layer provides additional insulation. By eliminating undercut structures through this segmentation, the patent prevents copper migration paths that would otherwise form in fine-pitch circuits, thereby maintaining electrical connection stability while enabling higher circuit integration.
Solution Approach 2:
The patent applies preliminary anti-action by preventing undercut structure formation at the opening bottom through the optimized first solder-mask layer thickness. This preliminary prevention eliminates the conditions that would lead to copper migration and electrical short circuits in fine-pitch circuits, thereby protecting electrical connection stability before the problem can occur.
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
The design prevents copper migration and short circuits by ensuring complete exposure and encapsulation, enhancing the reliability and manufacturability of semiconductor packages without requiring new materials or processes.
Implementation Method 1
the opening process is carried out by exposure and development
Implementation Method 2
the bottom of the wall of the opening 110 of the solder-mask layer 11 is easily to be corroded by the development solution
Data Source
AI summary
An electronic package and a substrate structure thereof are provided, in which a circuit layer and a filling layer are formed on a substrate body in the substrate structure, where the circuit layer has a plurality of conductive traces separated from each other, so that the filling layer is filled between the plurality of conductive traces, and a portion of a surface of the circuit layer and a surface of the filling layer are covered with an insulating protective layer. Therefore, the insulating protective layer is carried by the filling layer, so that the insulating protective layer can be thin, thereby preventing the phenomenon of copper migration from occurring to the substrate structure in subsequent processes.