Segmented Via Wiring for Thermal Expansion Matching in Wiring Substrates
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Solution Overview
Problem
The existing wiring substrates face challenges in maintaining the processability of resin layers due to filler particles, leading to disparities in through hole diameters and reduced connection reliability between via wiring and wiring layers, which affects the thermal expansion mismatch and warpage of semiconductor packages.
Innovation Solution
A wiring substrate design featuring a via wiring structure with a first via portion having a decreasing diameter from the insulation layer to the pad, and a second via portion with an increasing diameter towards the pad, improving connection reliability and thermal expansion coefficient matching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the amount of filler contained in the resin layer is increased to decrease the thermal expansion coefficient, then the thermal expansion coefficient matching between the insulation layer and the electronic component is improved, but the processability of the resin layer using the laser beam is further adversely affected and the bottom diameter of the through hole tends to become further smaller
Solution Approach 1:
The via wiring is divided into two distinct portions: a first via portion extending from the upper surface of the insulation layer to a lower position, and a second via portion extending from the lower position to the upper surface of the pad. This segmentation allows each portion to have different diameter characteristics, with the first via portion having a smaller diameter and the second via portion having a larger diameter at its upper end, thereby compensating for the reduced bottom diameter caused by high filler content in the resin layer.
Solution Approach 2:
Different portions of the via wiring are given different local qualities in terms of diameter. The first via portion has a smaller diameter suitable for penetrating the filler-containing resin layer, while the second via portion has a larger diameter at its upper end to ensure adequate connection area with the wiring layer. This local differentiation resolves the contradiction between maintaining small through hole diameters for processability and ensuring large connection areas for reliability.
2Productivity
If the diameter of the through hole at the bottom is reduced due to laser beam irradiation characteristics, then the wiring density can be increased, but the connection area between the via wiring and the wiring layer is reduced and connection reliability may be decreased
Solution Approach 1:
The via wiring is segmented into two portions with different diameter characteristics. The first via portion has a smaller diameter that allows for high wiring density, while the second via portion has a larger diameter at its upper end that ensures adequate connection area with the wiring layer, thereby maintaining connection reliability despite the reduced bottom diameter.
Solution Approach 2:
The via wiring structure transitions from a single-diameter hole to a two-diameter structure by adding a second via portion that expands upward from the first via portion. This dimensional change in the via wiring geometry allows simultaneous achievement of small bottom diameter for density and large top diameter for connection 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 design enhances the connection reliability between wiring layers and reduces warpage in semiconductor packages by optimizing the via wiring structure and thermal expansion coefficient matching, while maintaining finer wiring patterns.
Implementation Method 1
The irradiation intensity of a laser beam is generally lower at a peripheral portion than at a center portion. The difference in the irradiation intensity generates the disparity in the processability of a resin layer.
Implementation Method 2
forming a transformed portion by heating the pad with the laser beam to transform a portion of the insulation layer that is in contact with the pad around the opening
Implementation Method 3
Filler decreases the thermal expansion coefficient of the insulation layer. Decreases in the difference between the thermal expansion coefficient of the insulation layer and the thermal expansion coefficient of the electronic component limit warpage of a semiconductor package
Data Source
AI summary
A wiring substrate includes a pad, an insulation layer that covers the pad, and a via wiring extending through the insulation layer and connected to the pad. The via wiring includes a first via portion, which has a diameter that is decreased from an upper surface of the insulation layer toward the pad, and a second via portion, which has a diameter that is increased from a lower end of the first via portion toward the pad. The diameter of the second via portion at an upper surface of the pad is larger than the diameter of the first via portion at the upper surface of the insulation layer.