Buried Conductive Trace Circuit Board with Elevated Pads
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Solution Overview
Problem
Conventional methods for manufacturing circuit boards with buried conductive traces face challenges in forming fine patterns, leading to electrical connectivity issues and difficulties in filling the die gap with underfill material due to flush pad structures and interconnected finger structures, which result in voids and compromised electrical performance.
Innovation Solution
The method involves forming protrusion structures on a copper layer, burying them in a substrate, and using a nickel/gold layer as an etch mask to create elevated pads and fingers, allowing for increased die gap and separate electrical testing of finger structures, thereby facilitating better underfill material flow and avoiding voids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If protrusion structures are formed on copper layer and buried in substrate, then fine circuit patterns can be achieved, but pad structures become flush with substrate surface making die gap filling difficult
Solution Approach 1:
Instead of making pads flush with the substrate surface (conventional approach), the invention inverts the approach by forming elevated pad structures that protrude from the substrate surface. This is achieved by forming protrusion structures on the copper layer before burying it in the substrate, so that after substrate removal, the pads remain elevated rather than flush with the surface.
Solution Approach 2:
The invention transitions from a two-dimensional flush pad structure to a three-dimensional elevated pad structure. By adding the vertical dimension (height) to the pad structures, the invention creates space above the substrate surface that facilitates die gap filling with underfill material, while maintaining the fine circuit pattern precision in the horizontal plane.
2Ease of operation
If finger structures are plated with Ni/Au layer for electrical connection, then external circuitry connection is enabled, but all finger structures become electrically connected making individual testing impossible
Solution Approach 1:
The invention segments the finger structures by forming them as separate, isolated protrusion structures on the copper layer. Each finger structure is individually patterned and separated from others, allowing them to be tested independently. The segmentation is achieved through photolithography patterning that creates discrete finger structures rather than a continuous conductive layer.
Solution Approach 2:
The invention applies local quality by providing different treatments to different regions. Finger structures designated for testing are left with copper only or have different plating compared to those intended for external connection. This localized differentiation allows specific fingers to be electrically isolated for testing purposes while others remain connected for external circuitry interface.
3Strength
If solder mask is formed with non-negligible thickness on flush pad structures, then pad protection is achieved, but solder balls have only small portion protruding making underfill material flow difficult
Solution Approach 1:
Instead of having the solder mask cover the entire pad structure (conventional approach), the invention inverts the relationship by elevating the pad structure above the solder mask surface. The pads protrude through or above the solder mask layer, creating a topographic feature that facilitates underfill material flow and die gap filling while the solder mask still provides lateral protection to the pads.
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 approach enhances the die gap between the chip and substrate, preventing voids in the underfill material and enabling immediate electrical performance testing of finger structures, improving manufacturing efficiency and reliability.
Implementation Method 1
using a nickel/gold layer as an etch mask to create elevated pads and fingers
Implementation Method 2
the carrier is pressed to a soft substrate (130), such as a B-stage Bismaleimide Triazine (BT) substrate such that the protrusion structures (122, 124) of the copper layer (120) are buried on a surface (132) of the substrate (130)
Implementation Method 3
The carriers (110) are separated from the copper layers (120, 140) and the copper layers (120, 140) are then thinned by etching
Data Source
AI summary
A circuit board with a buried conductive trace formed thereon according to the present invention is provided. A buried conductive trace layer is formed on the surface of a substrate and the pads and fingers of the conductive trace layer are heightened to facilitate the subsequent process of molding.