Flip-Chip Bonding Structure Using Boundary Shadows for Fine-Pitch Inspection
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Solution Overview
Problem
In conventional flip-chip bonding, it is difficult to inspect the correct bonding of bumps to leads due to varying lead pitches, making it challenging to identify the boundary between circuit groups and the position of leads with the smallest pitch after bonding.
Innovation Solution
A flip-chip bonding structure that includes a light-transmissive substrate with distinct circuit groups, boundary circuits, and an identifying member, allowing for easy identification of the boundary between circuit groups and lead positions through projected shadows and an identifying member on the substrate surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If lead pitch reduction and variation are implemented on the circuit board to match smaller chip sizes, then the chip size and bump pitch can be reduced, but the inspection difficulty of bump bonding increases because the position with smallest pitch and boundary between circuit groups cannot be identified after bonding
Solution Approach 1:
A light-transmissive substrate is introduced as an intermediary layer between the chip bumps and the circuit board leads. This substrate allows light to pass through and project shadows of the bumps and leads onto its second surface, enabling visual inspection of bonding positions without being affected by the reduced pitch dimensions. The substrate acts as a mediator that translates the micro-scale bonding structures into visible shadow patterns for easy identification.
Solution Approach 2:
The light-transmissive substrate creates shadow copies of the bumps and leads on its second surface. These shadow copies preserve the spatial relationships and pitch variations of the original structures while being magnified and visible to the naked eye or inspection tools. The boundary circuit shadow and identifying member shadow provide reference copies for determining correct bonding positions.
2Adaptability or versatility
If varying lead pitches are used on the circuit board to accommodate different circuit requirements, then circuit functionality is improved, but the identification of boundary between circuit groups and leads with smallest pitch becomes difficult after bonding
Solution Approach 1:
The light-transmissive substrate utilizes optical properties to create visible shadow patterns that differentiate between various lead groups and circuit boundaries. By transmitting light through the substrate and projecting shadows, the system creates visual contrast that highlights pitch variations and boundary positions, effectively using optical 'color' or intensity changes to encode spatial information that would otherwise be lost due to the varying lead pitches.
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 quick and accurate inspection of bump bonding to leads by recognizing the boundary between circuit groups and lead positions, ensuring correct alignment and bonding.
Implementation Method 1
The light-transmissive substrate has a first surface and a second surface opposite to the first surface
Implementation Method 2
Each of the first leads includes a first bonding portion and projects a first lead shadow on the second surface of the light-transmissive substrate
Data Source
AI summary
A flip-chip bonding structure includes a chip and a circuit board, the chip is bonded to the circuit board by bumps. The circuit board includes a light-transmissive substrate, a first circuit group, a second circuit group, a boundary circuit and an identifying member. The boundary circuit is located between the first and second circuit groups and projects a boundary circuit shadow on light-transmissive substrate. The boundary circuit shadow can be recognized according to the identifying member and is provided to identify the boundary between the first and second circuit groups or identify the position of leads with the smallest pitch.