Annular EFO Wand Structure for Centered Free Air Ball Formation
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Solution Overview
Problem
As semiconductor packages shrink, the smaller bond pad openings lead to a higher likelihood of free air balls (FABs) being offset during the wire bonding process, resulting in unreliable connections due to uneven energy application during the formation of FABs.
Innovation Solution
An annular structure is integrated into the electronic flame off (EFO) wand of a wire bonder, positioned below the capillary to uniformly provide heat to the bond wire, ensuring that the FAB is centered and uniformly formed, reducing the chances of offsetting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional EFO wand is used to create a spark between the bond wire and the wand, then the bond wire is heated to form a free air ball (FAB), but the FAB becomes offset from the center of the capillary due to uneven energy distribution
Solution Approach 1:
The EFO wand tip is modified with an annular heating element that provides non-uniform heat distribution - specifically designed to concentrate heat at the center region of the bond wire while reducing heat at the edges. This local quality change in heat distribution ensures the FAB forms centered within the capillary aperture, directly resolving the centering precision issue while maintaining connection reliability
Solution Approach 2:
The invention changes the thermal parameter distribution along the EFO wand tip surface. By creating an annular heating element with a specific geometry (inner radius and outer radius), the heat generation parameter is modified to produce a controlled temperature gradient across the bond wire cross-section, ensuring uniform FAB formation and proper centering
2Area of moving object
If the size of the FAB is decreased to match smaller bond pad openings, then the FAB can fit through smaller openings, but the FAB is more likely to be offset from the center during formation
Solution Approach 1:
The annular heating element creates a specific local quality pattern where the center region of the bond wire receives concentrated thermal energy while the peripheral regions receive less heat. This localized heat distribution ensures that even when the FAB size is reduced to match smaller bond pad openings, the FAB maintains proper centering during formation, preventing offset issues
Solution Approach 2:
The heating element introduces intentional asymmetry in the thermal field - the heat distribution is deliberately non-uniform across the bond wire cross-section, with higher temperature at the center and lower temperature at the edges. This asymmetric heating pattern compensates for the reduced FAB size by ensuring the molten material coalesces at the center, maintaining centering precision despite the smaller overall FAB dimensions
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 solution enhances the reliability of wire bonding connections by consistently forming centered FABs, reducing the occurrence of off-centered bonds and improving the overall reliability of semiconductor devices.
Implementation Method 1
An electric current is provided to the EFO wand and a spark is created between the bond wire and the EFO wand. The spark generates heat
Implementation Method 2
a spark is created between the bond wire and the EFO wand. The spark generates heat, which melts at least a portion of the bond wire
Data Source
AI summary
An annular structure for an electronic flame off (EFO) wand of a wire bonder is positioned beneath a capillary of the wire bonder. The annular structure provides uniform heat to a bond wire extending from the capillary to form a free air ball (FAB). Because heat is uniformly applied to the bond wire, the FAB is uniformly formed and is centered with respect to the capillary. The FAB is then bonded to a bond pad of a substrate. Because the FAB was uniformly formed and is centered on the capillary, the FAB will also be centered on the bond pad.