Flip Chip Substrate Layout for Shadow-Based Bonding Inspection
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Solution Overview
Problem
Conventional flip chip packages make it difficult to inspect the bonding between bumps and circuit lines due to their location being shielded by the substrate and chip, hindering visual inspection.
Innovation Solution
A flip chip package design featuring a light-transmissive carrier with a supportive layer that includes openings to reveal shadows of dummy and identification lines and bumps, allowing for visual inspection of bonding accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional flip chip package structure is used with bumps and circuit lines located between substrate and chip, then the package structure is compact and complete, but bonding inspection between bumps and circuit lines becomes difficult due to shielding
Solution Approach 1:
The substrate is divided into a light-transmissive carrier and a supportive layer positioned on its lower surface. The supportive layer contains openings that segment the shielding structure, allowing light to pass through and reveal shadows of bonding features for inspection purposes while maintaining the overall package integrity.
Solution Approach 2:
A supportive layer with openings is introduced as an intermediary element between the light source and the bonding interface. This intermediary structure enables optical access to the bonding area without compromising the mechanical support or electrical functionality of the substrate.
2Measurement precision
If the substrate and chip completely cover the bonding area, then structural integrity is maintained, but visual inspection of bonding alignment becomes impossible
Solution Approach 1:
The patent utilizes shadow contrast created by light transmission through the carrier. The shadows of the identification bump, identification line, and dummy line appear as dark regions against a lighter background, enabling visual detection of bonding alignment through the openings in the supportive layer.
Solution Approach 2:
The inspection capability is extended to a different dimensional approach by viewing the bonding interface through the lower surface of the substrate rather than from the sides or top. Light transmitted through the carrier creates a two-dimensional shadow projection that reveals bonding alignment information.
3Reliability
If identification features are added for inspection, then bonding verification capability is improved, but the patterned metal layer becomes more complex
Solution Approach 1:
A first dummy line is added to the patterned metal layer as a reference feature that copies the structure of the identification line. This dummy line serves as a comparison standard for verifying the alignment and positioning of the identification bump during inspection, enabling accurate bonding verification without requiring complex additional features.
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
Enables accurate inspection of bonding alignment and misalignment of bumps with circuit lines, ensuring correct bonding and alignment through visible shadows, enhancing inspection efficiency.
Implementation Method 1
a light-transmissive carrier has a first surface and a second surface which are opposite
Implementation Method 2
the identification line projects a lead shadow on the second surface; the first dummy line projects a first measurement shadow on the second surface
Data Source
AI summary
In a flip chip package, lines, an identification line and a dummy line are provided on a first surface of a light-transmissive carrier, and a supportive layer is disposed on a second surface of the light-transmissive carrier. Bumps and an identification bump of a chip are bonded to the lines and the identification line, respectively. Shadows of the dummy line, the identification line and the identification bump which are projected on the second surface are visible from an opening of the supportive layer. The shadows can be inspected through the opening so as to know whether the bumps are bonded to the lines correctly.