Package-Substrate PCB Solder-Resist Anchoring
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Solution Overview
Problem
Existing package-substrate-mounting printed wiring boards face challenges in ensuring reliable connections and preventing peeling between solder-resist layers during heat cycles, especially when mounting semiconductor elements and package substrates, due to mismatched thermal expansion coefficients and inadequate anchoring effects.
Innovation Solution
A printed wiring board design featuring an interlayer insulation layer with first and second pads, a first solder-resist layer exposing these pads, conductive posts on the second pads, and a second solder-resist layer filling gaps between the posts, where the second opening portions have a larger diameter than the conductive posts, and both solder-resist layers are made of the same resin to minimize thermal expansion issues and enhance anchoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional solder-resist layers are used with standard opening portions, then manufacturing is simpler, but peeling occurs between layers during heat cycles due to thermal expansion mismatch
Solution Approach 1:
The solder-resist layer is segmented into multiple layers (first and second solder-resist layers) with different opening portions. The first opening portions expose second pads for conductive posts, while the second opening portions expose first pads for bumps. This segmentation allows each layer to serve specific functions and prevents peeling by creating interlocking structures between layers.
Solution Approach 2:
The patent implements a nested structure where the first solder-resist layer with first opening portions is positioned beneath the second solder-resist layer with second opening portions. The conductive posts extend through the first opening portions and are surrounded by the second opening portions, creating a nested arrangement that enhances mechanical interlocking and prevents peeling during thermal cycling.
2Reliability
If larger opening portions are used to accommodate conductive posts, then anchoring is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies local quality by making the opening portions larger than the conductive posts or bumps they accommodate. The first opening portions are sized to accommodate conductive posts with gaps, and the second opening portions are sized to accommodate bumps with gaps. This local enlargement at critical anchoring points provides sufficient mechanical interlocking without requiring ultra-precise dimensional control across the entire structure.
3Adaptability or versatility
If different resins are used for solder-resist layers to optimize performance, then functional properties improve, but thermal expansion mismatch and peeling worsen
Solution Approach 1:
The patent employs homogeneity by using the same resin material for both the first and second solder-resist layers. This ensures matched thermal expansion coefficients between layers, preventing differential expansion and contraction during heat cycles that would cause peeling. The uniform material composition maintains consistent mechanical and thermal properties across the multi-layer structure.
4Reliability
If multiple curing processes are used for different solder-resist layers, then functional properties are optimized, but productivity decreases
Solution Approach 1:
The patent merges the curing processes of the first and second solder-resist layers into a single simultaneous curing step. Since both layers use the same resin material, they can be cured together under identical or compatible conditions, eliminating the need for separate curing cycles. This integration maintains curing quality while significantly improving manufacturing efficiency and productivity.
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 connection reliability by reducing peeling and thermal stress, while using the same resin for both solder-resist layers ensures low cost and high productivity through simultaneous curing, allowing for high-density packaging with small-diameter bumps.
Implementation Method 1
a second solder-resist layer formed on the first solder-resist layer and having a third opening portion exposing the first pads and fourth opening portions exposing surface portions of the conductive posts, respectively. The second opening portions have a diameter which is set greater than a diameter of the conductive posts, and the second solder-resist layer is filling gaps formed between the second opening portions and the conductive posts
Implementation Method 2
Existing package-substrate-mounting printed wiring boards face challenges in ensuring reliable connections and preventing peeling between solder-resist layers during heat cycles, especially when mounting semiconductor elements and package substrates, due to mismatched thermal expansion coefficients
Data Source
AI summary
A printed wiring board includes an interlayer insulation layer, first pads positioned to mount a semiconductor element and forming a first pad group on the insulation layer, second pads forming a second pad group on the insulation layer and positioned along a peripheral portion of the first group, a first solder-resist layer formed on the insulation layer and having first openings exposing the first pads, respectively, and second openings exposing the second pads, respectively, conductive posts formed on the second pads through the second openings of the first solder-resist layer, respectively, and a second solder-resist layer formed on the first solder-resist layer and having a third opening exposing the first pads and fourth openings exposing surfaces of the posts, respectively. The second openings have a diameter greater than a diameter of the posts, and the second solder-resist layer is filling gaps formed between the second openings and the posts.