Wiring Substrate Conductive Covering Layer Whisker Prevention
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Solution Overview
Problem
The formation of whiskers during etching in the manufacturing of ceramic multilayer wiring substrates leads to short circuits and decreased adhesion strength between wiring layers and the resistor, due to anisotropic etching and undercut issues.
Innovation Solution
A wiring substrate design with conductive covering layers that cover the upper and side surfaces of the wiring layers, preventing whisker formation and undercut, achieved through a method involving electroplating and controlled etching of grounding metal layers to maintain adhesion and prevent short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If etching is performed in the thickness direction to form wiring layers, then wiring layers can be formed on the resistor, but whiskers are generated on the side surface of the film causing short circuits between adjacent wiring layers
Solution Approach 1:
A covering layer is introduced as an intermediary between the film-like conductor portions and the etching process. This covering layer protects the side surfaces of the conductor portions during etching, preventing whisker formation while allowing the etching process to proceed for wiring layer formation.
Solution Approach 2:
The covering layer is formed in advance before etching to prevent whisker generation. By applying the covering layer prior to the etching process, the patent preemptively counteracts the harmful effect of whisker formation that would otherwise occur during etching.
2Ease of manufacture
If etching is performed through inorganic acid or organic acid, then wiring layers can be formed, but anisotropic etching causes undercut at the lower portion of the film-like laminate
Solution Approach 1:
The covering layer acts as a protective intermediary during etching, preventing the etchant from attacking the lower portions of the film-like laminate. This eliminates the undercut phenomenon caused by anisotropic etching while maintaining the ability to form wiring layers.
Solution Approach 2:
The covering layer is applied in advance to protect vulnerable areas before etching occurs. This preliminary protective action prevents the undercut that would otherwise be caused by the anisotropic nature of acid-based etching processes.
3Ease of manufacture
If undercut is formed at the lower portion of the film-like laminate, then etching can proceed, but adhesion strength between the laminate and resistor decreases
Solution Approach 1:
The covering layer serves as a protective intermediary that prevents the etchant from creating undercut at the interface between the film-like laminate and the resistor. By protecting this critical interface during etching, the adhesion strength is maintained while the etching process still proceeds to form the wiring layers.
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 solution effectively suppresses whisker formation and undercut, enhancing the adhesion strength between wiring layers and the substrate, thereby preventing short circuits and ensuring reliable electrical connectivity.
Implementation Method 1
a method involving electroplating and controlled etching of grounding metal layers
Data Source
AI summary
A wiring substrate includes a substrate main body having a first main face and a second main face opposite the first main face; a resistor formed on the first main face; a plurality of first-main-face-side wiring layers which are each formed on the resistor and which each include a grounding metal layer formed of a metal having a resistance lower than that of the resistor and a conductor layer formed on the grounding metal layer; a second-main-face-side wiring layer formed on the second main face; and a via which is formed in the substrate main body and which establishes electrical connectivity between the first-main-face-side wiring layers and the second-main-face-side wiring layer. The wiring substrate further includes a conductive covering layer which covers an upper surface and substantially covers the side surfaces of each of the first-main-face-side wiring layers.