Wiring Substrate Connection Pad Level Difference Design
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Solution Overview
Problem
Existing wiring substrates with flat surfaces on connection pads face issues with solder flow causing electric short-circuits and poor image recognition of fiducial marks, leading to inaccurate alignment and mounting of semiconductor chips, especially with narrow pitch connections.
Innovation Solution
A wiring substrate design featuring connection pads buried in an insulating layer with exposed upper surfaces and concave level differences around the periphery, manufactured through electroplating and etching processes, which prevents solder flow and enhances fiducial mark recognition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the pitch of connection pads is made narrower to increase integration density, then the area occupied by connection pads is reduced, but solder flows from the connection pad to the lateral direction causing electric short-circuit between adjacent connection pads
Solution Approach 1:
The invention transitions from a two-dimensional flat pad structure to a three-dimensional structure by forming a convex level difference portion (protrusion) around the connection pad and positioning the fiducial mark in a depressed area. This vertical dimensionality change allows solder to be contained within the pad area while providing distinct recognition features for alignment, thereby preventing short-circuits even at narrower pitches.
Solution Approach 2:
The invention applies different surface characteristics to different regions: the connection pad area has a convex protrusion structure that confines solder, while the surrounding area has a depressed region that provides space for fiducial marks. This local differentiation of surface quality enables both reliable solder joints and precise alignment recognition without requiring larger overall pad spacing.
2Ease of manufacture
If the surface of the wiring substrate on the connection pad side is made flat for ease of manufacturing, then the manufacturing process is simplified, but the accuracy of image recognition of fiducial marks is degraded
Solution Approach 1:
Instead of relying solely on two-dimensional flat surface features for fiducial mark recognition, the invention creates three-dimensional depressed areas surrounding the connection pads. These depressed regions provide distinct visual contrast and spatial definition that significantly improve image recognition accuracy while being formed through the same convex formation process used for pad definition.
Solution Approach 2:
The convex level difference portion and depressed area structure is formed in advance during the pad fabrication process, before the mounting and alignment operations occur. This preliminary creation of recognition features ensures that fiducial marks are clearly defined and easily recognizable during subsequent chip alignment operations, eliminating the need for additional surface modification steps.
3Ease of manufacture
If connection pads are formed with exposed upper surfaces at the same plane as the insulating layer for standard manufacturing, then the manufacturing process is conventional and simple, but solder flows laterally during flip-chip connection causing electric shorts
Solution Approach 1:
The invention modifies the conventional flat pad structure by forming a convex level difference portion that creates a three-dimensional protrusion around the connection pad. This vertical structure acts as a physical barrier that contains solder within the pad area during reflow, preventing lateral flow and electric short-circuits while maintaining compatibility with standard flip-chip mounting processes.
Solution Approach 2:
The convex protrusion structure is formed in advance around the connection pad perimeter, creating a preliminary barrier that prevents solder from flowing laterally during the subsequent reflow process. This pre-formed structural defense counteracts the harmful lateral flow tendency of solder before the short-circuit can occur, while requiring only minor modifications to conventional manufacturing processes.
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 prevents solder flow between connection pads, ensuring precise alignment and mounting of semiconductor chips with narrow pitch connections and improves fiducial mark recognition for high-precision assembly.
Implementation Method 1
forming a metal layer for a connection pad in the concave portion of the supporting plate and the opening portion of the resist, by an electroplating utilizing the supporting plate as a plating power feeding path
Implementation Method 2
forming a ring-like part of the supporting plate around an outer periphery part of the metal layer as a convex level difference portion whose height is higher than other etched surfaces, by etching the supporting plate
Data Source
AI summary
A wiring substrate includes an insulating layer, a connection pad buried in the insulating layer in a state that an upper surface of the connection pad is exposed from an upper surface of the insulating layer and a lower surface and at least a part of a side surface of the connection pad contact the insulating layer, and a concave level difference portion formed in the insulating layer around an outer periphery part of the connection pad, wherein an upper surface of the connection pad and an upper surface of the insulating layer are arranged at a same height.