Dummy Wire Bonds for Semiconductor Die Stack Flatness
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Solution Overview
Problem
Conventional stacked semiconductor die packages tend to warp or tilt upward at the non-wire bonded side, leading to protrusion of the die edge through the encapsulating molding compound, which limits the area available for printing package information and increases the risk of exposure to the external environment.
Innovation Solution
The use of dummy wire bonds, which are configured to exert a force on the semiconductor die, holding them flat against the substrate, thereby preventing tilting and allowing for a flat die stack configuration that maintains the integrity of the package surface for printing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If conventional stacked die packages are used without dummy wire bonds, then the package footprint is efficiently utilized with die stacked on substrate, but the die tend to warp or tilt upward at the non-wire bonded side causing edge protrusion through molding compound
Solution Approach 1:
The wire bonding process is segmented into two distinct functional groups: signal transfer wire bonds that carry electrical signals, and dummy wire bonds that provide mechanical support. This segmentation allows each type of wire bond to be optimized for its specific function, resolving the contradiction between maintaining flatness and avoiding excessive complexity.
Solution Approach 2:
Dummy wire bonds act as intermediary elements that do not carry signals but provide the necessary mechanical support to prevent die warping. These intermediary components mediate between the substrate and the die stack, distributing mechanical forces to maintain flatness without interfering with signal transmission.
2Ease of manufacture
If die are stacked in offset configuration to provide access to bond pads, then wire bonding can be performed, but the non-wire bonded side experiences upward warping and tilting
Solution Approach 1:
The wire bond configuration employs asymmetry by placing signal transfer wire bonds on one side of the die stack for manufacturing accessibility, while introducing dummy wire bonds on the opposite side to provide counterbalancing mechanical support. This asymmetric arrangement maintains both ease of manufacture and die stack stability.
Solution Approach 2:
Dummy wire bonds function as a counterweight mechanism, providing opposing mechanical force to balance the upward warping tendency on the non-wire bonded side. This counterbalancing approach stabilizes the die stack composition while preserving the offset configuration needed for wire bonding accessibility.
3Ease of operation
If die edge protrudes through molding compound surface, then wire bonding can be performed on offset stacked die, but the protruding area becomes a keep out area limiting printing capabilities
Solution Approach 1:
Dummy wire bonds are implemented in advance during the wire bonding process to prevent die warping before encapsulation in molding compound. This preliminary mechanical support action ensures that the die stack remains flat during subsequent packaging and printing operations, maximizing the printable surface area while maintaining wire bonding capability.
4Area of stationary object
If dummy wire bonds are added to hold die flat, then die stack flatness is maintained and printable surface area increases, but the number of wire bonds and manufacturing steps increases
Solution Approach 1:
The dummy wire bonds are merged into the existing wire bonding manufacturing process, utilizing the same equipment, materials, and operational procedures. This integration allows dummy wire bonds to be added without requiring separate manufacturing steps or specialized equipment, thereby minimizing the impact on manufacturing cycle time while achieving the benefit of increased printable surface area.
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
The dummy wire bonds effectively hold the die stack flat, preventing edge protrusion and allowing manufacturers to print on the entire package surface without restrictions, enhancing the reliability and functionality of the semiconductor device.
Implementation Method 1
a set of dummy wire bonds connected between a set of dummy bond pads and a set of contact pads on the substrate, the set of dummy wire bonds configured to exert a force on the plurality of semiconductor die to hold the plurality of semiconductor die down on the substrate
Data Source
AI summary
A semiconductor device is disclosed including a stack of semiconductor die on a substrate, wherein a semiconductor die in the stack is wire bonded to the substrate using dummy wire bonds. Each dummy wire bond has a stiffness so that together, the dummy wire bonds effectively pull and/or hold down the die stack against the substrate.