Embedded Pad Wiring Substrate with Localized Surface Roughness
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Solution Overview
Problem
In the manufacturing process of build-up wiring substrates, the roughened surface of the support body is transferred to the pads, leading to reduced solder wettability and reliability of connections between the pads and semiconductor chip electrodes, making it difficult to ensure reliable connections.
Innovation Solution
A wiring substrate design with recessed pads embedded in an insulating layer, where the pads have smooth bottom and inner wall surfaces and a solder resist layer with protrusions covering the pads, enhancing adhesion and preventing peeling due to stress, while maintaining uniform surface treatment layers for improved solder wettability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the support body surface is roughened to improve adhesion of the insulating layer, then adhesion property between the insulating layer and solder resist layer is improved, but the pad surfaces become roughened which reduces solder wettability
Solution Approach 1:
The invention applies different surface roughness characteristics to different regions of the pad structure. The peripheral portion of the pad surface maintains high roughness for strong adhesion with the insulating layer and solder resist layer, while the central portion maintains low roughness for excellent solder wettability. This local differentiation resolves the contradiction between adhesion strength and solder wettability.
Solution Approach 2:
The pad surface is segmented into two distinct zones: a peripheral region with roughened surface for adhesion purposes and a central region with smooth surface for soldering. This segmentation allows each zone to fulfill its specific function independently, eliminating the trade-off between adhesion and wettability.
2Strength
If the pad surface is roughened to enhance adhesion, then adhesion property is improved, but connection reliability between pads and semiconductor chip electrodes deteriorates
Solution Approach 1:
Different surface qualities are assigned to different functional regions: the peripheral pad surface is roughened for mechanical adhesion with surrounding layers, while the central pad surface remains smooth to ensure reliable electrical and mechanical connection with semiconductor chip electrodes through solder joints.
3Reliability
If the entire pad surface is kept smooth to maintain solder wettability, then solder wettability is improved, but adhesion property between the insulating layer and solder resist layer deteriorates
Solution Approach 1:
The invention creates a dual-characteristic pad surface where the central area remains smooth for optimal solder wettability and electrical connection, while the peripheral area is roughened to provide mechanical interlocking and strong adhesion for the insulating layer and solder resist layer.
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 increases the reliability of connections between the wiring substrate and semiconductor chips by improving solder wettability and adhesion, preventing peeling, and maintaining high-frequency characteristics.
Implementation Method 1
when the support body is removed, the roughened surface of the support body is transferred to an insulating layer or the like that has been formed on the support body
Implementation Method 2
The first pad is formed with a recess portion, having a smooth bottom surface, at a center portion of the upper surface of the first pad
Implementation Method 3
The adjacent portion of the solder resist layer protrudes from the peripheral portion of the upper surface of the first pad toward the center portion of the first pad so as to cover above the recess portion
Data Source
AI summary
A wiring substrate includes an insulating layer, a first pad, and a solder resist layer. The first pad is embedded in the insulating layer. The solder resist layer is provided on an upper surface of the insulating layer. The solder resist layer is formed with an opening portion through which the recess portion is exposed. An adjacent portion of the solder resist layer adjacent to a peripheral portion of the opening portion covers a peripheral portion of the upper surface of the first pad and protrudes from the peripheral portion of the upper surface of the first pad toward the center portion of the first pad so as to cover above the recess portion. Surfaces of the first pad being in contact with the insulating layer are smaller in roughness than the upper surface of the insulating layer and the peripheral portion of the upper surface of the first pad.