Interconnect Substrate Two-Layer Resin Structure
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Solution Overview
Problem
In flexible interconnect substrates, the use of resin materials with low modulus of elasticity and high coefficient of elongation for insulating layers leads to insufficient stress mitigation of thermal expansion differences between conductive and insulating layers, resulting in reduced adhesion and increased risk of haloing (fracture or delamination) during the desmear process after laser formation of via holes.
Innovation Solution
The interconnect substrate employs a two-layer resin structure, where the first resin layer with higher modulus of elasticity and lower coefficient of elongation covers the conductive layer, and the second resin layer with lower modulus of elasticity and higher coefficient of elongation is used for the insulating layer, effectively mitigating thermal stress and improving adhesion between layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a resin material with low modulus of elasticity and high coefficient of elongation is used as the insulating layer, then the flexibility and wearability of the interconnect substrate are improved, but the adhesion between the conductive layer and the insulating layer deteriorates due to insufficient stress mitigation
Solution Approach 1:
The insulating layer is divided into two distinct resin layers: a first resin layer with low modulus of elasticity and high coefficient of elongation (for flexibility) and a second resin layer with high modulus of elasticity and low coefficient of elongation (for adhesion and stress mitigation). This segmentation allows each layer to perform its specialized function independently, resolving the contradiction between flexibility and adhesion.
Solution Approach 2:
Different regions of the insulating layer are assigned different material properties: the first resin layer (in contact with conductive layer) provides local flexibility, while the second resin layer (upper insulating layer) provides local stress resistance and adhesion. This local differentiation of material qualities enables the structure to simultaneously achieve both flexibility and reliable adhesion.
2Adaptability or versatility
If a resin material with low modulus of elasticity and high coefficient of elongation is used as the insulating layer, then the flexibility is improved, but the resistance to laser thermal energy deteriorates, causing resin damage and adhesion reduction
Solution Approach 1:
The second resin layer acts as an intermediary protective layer between the laser beam and the first resin layer. It absorbs and dissipates the thermal energy generated during laser drilling of via holes, preventing direct thermal damage to the first resin layer and maintaining the overall structural integrity and adhesion of the flexible substrate.
Solution Approach 2:
The second resin layer is positioned in advance to cushion and absorb the harmful thermal effects before they can reach and damage the first resin layer. This prior protective arrangement ensures that the flexible resin material is shielded from laser-induced thermal damage during the via hole formation process.
3Adaptability or versatility
If a single resin material with low modulus of elasticity is used for the insulating layer, then the flexibility is improved, but the stress mitigation capability deteriorates, increasing the risk of haloing during the desmear process
Solution Approach 1:
The insulating layer is segmented into two resin layers with different mechanical properties. The first resin layer maintains flexibility, while the second resin layer provides the necessary stress mitigation capability to prevent haloing during the desmear process. This segmentation allows the structure to simultaneously achieve both flexibility and haloing resistance.
Solution Approach 2:
The insulating layer is constructed as a composite structure combining two different resin materials with complementary properties. The composite design leverages the flexibility of the first resin and the stress resistance of the second resin, creating a unified structure that exhibits both flexible behavior and resistance to haloing during subsequent processing steps.
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 configuration reduces the likelihood of haloing during the desmear process, enhancing the reliability of connections between interconnect patterns by maintaining secure adhesion between the conductive and insulating layers.
Implementation Method 1
the stress caused by a difference in thermal expansion coefficients between the conductive layer and the insulating layer
Implementation Method 2
the first resin layer is made of a resin having a higher modulus of elasticity and a lower coefficient of elongation than the second resin layer
Implementation Method 3
A laser generates a large amount of thermal energy when forming the via holes through the insulating layer
Data Source
AI summary
An interconnect substrate includes an insulating layer having a first resin layer and a second resin layer covering an upper surface of the first resin layer, a first conductive layer having an upper surface and side surfaces covered with the first resin layer, a lower surface of the first conductive layer being exposed from a lower surface of the first resin layer, and a second conductive layer including an interconnect pattern and a via interconnect, the interconnect pattern being disposed on an upper surface of the second resin layer, the via interconnect penetrating through both the second resin layer and the first resin layer to connect the interconnect pattern to the upper surface of the first conductive layer, wherein the first resin layer is made of a resin having a higher modulus of elasticity and a lower coefficient of elongation than the second resin layer.