Circuit Board Pad Opening Layout for Stress-Based Bonding Reliability
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Solution Overview
Problem
Conventional circuit boards face reliability issues due to varying stress applied to different regions, leading to inconsistent bonding strengths between pads and solder balls or insulating layers, as the design of solder resist openings does not consider stress distribution, resulting in separation problems.
Innovation Solution
The circuit board incorporates a protective layer with distinct regions and varying types of openings, including first and second regions with different numbers and configurations of openings, optimizing bonding strengths based on stress distribution and warpage, thereby enhancing physical reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If SMD-type opening region is used, then the opening region width is smaller than pad width providing better protection, but the solder ball bonding strength is reduced causing separation
Solution Approach 1:
The patent applies different opening region types (SMD-type and NSMD-type) to different locations on the pad based on local stress conditions. High-stress areas use NSMD-type openings with larger widths for better solder ball bonding, while low-stress areas use SMD-type openings with smaller widths for better pad protection. This localized differentiation resolves the contradiction by optimizing each region's opening type according to its specific requirements.
2Reliability
If NSMD-type opening region is used, then the opening region width is larger than pad width improving solder ball bonding, but the pad becomes separated from the circuit board
Solution Approach 1:
The patent strategically places NSMD-type opening regions only in areas where the pad has sufficient bonding strength to the insulating layer, while using SMD-type openings in regions where pad-insulating layer bonding is weaker. This spatial differentiation allows the system to utilize the advantages of each opening type without suffering from their respective disadvantages.
3Ease of manufacture
If conventional uniform opening design is used, then manufacturing is simple, but physical reliability is reduced due to stress variation
Solution Approach 1:
The patent introduces spatial variation in opening region characteristics (width, type, position) according to the local stress distribution pattern on the circuit board. The opening region width and type are adjusted based on the distance from the board center and local stress concentration, creating a non-uniform design that enhances overall reliability while remaining manufacturable.
Solution Approach 2:
The patent systematically varies the opening region parameters (width, type, position) as a function of location on the circuit board. Specifically, the opening width and type change based on the distance from the board center and the local stress state, transforming a uniform design into a gradient design that adapts to stress variations across the board surface.
Data Source
AI summary
A circuit board according to an embodiment includes an insulating layer; a circuit pattern layer disposed on the insulating layer; and a protective layer disposed on the insulating layer and the circuit pattern layer and including a plurality of openings, wherein the openings includes a plurality of first openings and a plurality of second openings, wherein the first opening overlaps vertically with an upper surface of a pad of the circuit pattern layer and does not overlap horizontally with a side surface of the pad, and wherein the second opening overlaps vertically with an upper surface of a pad of the circuit pattern layer and horizontally with at least a portion of a side surface of the pad.