Dummy Die Segmentation for BGA Gold Wire Collapse
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Solution Overview
Problem
Conventional packaging technologies face challenges with excessively long gold bonding wires when chips have arrays of bonding pads at the center, leading to wire collapse and high defective rates, especially when pad pitch is dense, and alternative methods like WBGA increase costs or are not suitable for all specifications.
Innovation Solution
The introduction of a package structure that includes dummy dies with redistribution layers connected to gold bonding wires, which are then fixed by epoxy strips or connected to gold fingers, reducing wire length and preventing collapse.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional packaging technology is used with bonding pads at chip center, then the chip can be packaged on BGA substrate, but the gold bonding wire becomes excessively long leading to wire collapse and high defective rates
Solution Approach 1:
The invention divides the bonding path into segments by introducing dummy dies between the chip and BGA substrate. The gold bonding wires are segmented into multiple shorter sections: chip to dummy die, dummy die to dummy die, and dummy die to BGA substrate, rather than one excessively long wire directly from chip to BGA substrate. This segmentation prevents wire collapse and reduces defective rates to below 0.5%.
Solution Approach 2:
Dummy dies are introduced as intermediary elements between the chip and BGA substrate. These dummy dies serve as intermediate bonding points that break the long bonding wire path into shorter segments. The dummy dies are connected to the chip through gold bonding wires and to the BGA substrate through another set of gold bonding wires, effectively mediating the connection and preventing wire collapse.
2Reliability
If WBGA package is used to reduce bonding wire length, then wire collapse is prevented, but package cost increases
Solution Approach 1:
The invention uses dummy dies as temporary, inexpensive intermediary structures that serve their purpose of reducing bonding wire length and then can be removed or left as part of the final package. These dummy dies are simpler and cheaper alternatives to the complex WBGA window structure, achieving the same reliability improvement at lower cost.
3Productivity
If pad pitch is made dense to increase I/O density, then more I/O pads can be accommodated, but wire collapsing happens more frequently leading to short circuits
Solution Approach 1:
By segmenting the bonding path through dummy dies, the invention enables dense pad pitch (50-100 μm) to be used without wire collapse. The segmented bonding path with multiple shorter wires allows the chip to accommodate more I/O pads in a given area while maintaining reliability, as each short wire segment is less prone to collapsing even when pads are densely packed.
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 significantly reduces the defective rate of gold bonding wires to below 0.5% and 20% respectively, improving yield and reducing costs by addressing the issue of excessively long wires without increasing costs or compromising package specifications.
Implementation Method 1
a chip whose bottom is adhered to the BGA substrate by insulating sealant
Implementation Method 2
Two dummy dies are respectively connected to the upper surface of the BGA chip with another insulating sealant
Implementation Method 3
the gold bonding wires are fixed by the epoxy strips on the chips
Data Source
AI summary
A package structure and method for preventing gold bonding wires from collapsing are disclosed. The structure is especially useful for those chips whose two n×1 arrays of bonding pads are on the chip center to be packaged on a BGA substrate. According to the first preferred embodiment, two dies having a redistribution layer formed thereon are introduced outer the bonding pad array on the chip so that the gold bonding wires can be divided into two sections each to connect the bonding pads with the redistribution layer and the redistribution layer with the gold fingers on the BGA substrate. According to the second embodiment, the gold bonding wires are fixed by the epoxy strips on the chips after bonding the bonding pads to the gold fingers but before pouring liquid encapsulated epoxy into a mold.