Stitch Bump Stacking for Semiconductor Package Size Reduction
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Solution Overview
Problem
The increasing number of stacked dies in semiconductor devices leads to longer bond finger lengths, which in turn increases the size of the semiconductor package, making it challenging to achieve smaller package sizes and thinner heights while maintaining device density.
Innovation Solution
The formation of stacked fish-tail shaped stitch bonds using molten balls or stitch bumps between each bond, allowing multiple bond wires to be connected to a single contact point on the bond finger, thereby maintaining a constant bond finger length regardless of the number of dies stacked.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multiple dies are stacked vertically to increase device density, then semiconductor device density is improved, but bond finger length increases causing package size to increase
Solution Approach 1:
The patent transitions from a planar wire bonding approach to a three-dimensional stacked configuration where multiple stitch bonds are arranged vertically along the bond finger. This allows multiple dies to be connected through stacking in the vertical dimension rather than requiring extended horizontal bond finger length, thereby maintaining compact package size while achieving high device density.
Solution Approach 2:
The patent implements a nested structure where stitch bumps are formed between stacked stitch bonds, creating a compact vertical arrangement. Each stitch bond is nested within the vertical stack with stitch bumps providing spacing and structural support, allowing multiple bond wires to be connected to a single contact point through vertical stacking rather than horizontal extension.
2Productivity
If bond finger length is increased to accommodate more stacked dies, then the number of stacked dies is improved, but package size increases
Solution Approach 1:
The patent resolves this contradiction by moving the scaling dimension from horizontal (bond finger length) to vertical (stack height). Multiple dies are accommodated by increasing the vertical stack of stitch bonds rather than extending the bond finger horizontally, thereby increasing the number of stacked dies while maintaining a compact package footprint and volume.
3Reliability
If more contact points are provided on bond fingers to prevent wire damage, then wire bonding reliability is improved, but bond finger length and package size increase
Solution Approach 1:
The patent merges multiple wire bonding connections into a single contact point by stacking stitch bonds vertically. Instead of requiring separate contact points for each die (which would increase bond finger length), multiple stitch bonds are combined at one location, with stitch bumps providing the necessary spacing and protection, thereby maintaining wire bonding reliability without extending package 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 approach reduces the semiconductor device package size and increases density by keeping the bond finger length constant, even with increased die stacking, while preventing damage to existing bond wires during the wire bonding process.
Implementation Method 1
a wire bond machine welds the bond wires 130 between the bonding pads 132 and the contact points 134 utilizing ultrasonic, thermosonic or thermocompression bonding
Implementation Method 2
a wire bond machine welds the bond wires 130 between the bonding pads 132 and the contact points 134 utilizing ultrasonic, thermosonic or thermocompression bonding
Implementation Method 3
a wire bond machine welds the bond wires 130 between the bonding pads 132 and the contact points 134 utilizing ultrasonic, thermosonic or thermocompression bonding
Implementation Method 4
This first bond is forming by melting the end of a bond wire 130 to form a molten ball 138 on the bonding pad 132
Data Source
AI summary
A method for die stacking is disclosed. In one embodiment a first die is formed overlying a substrate. A first wire is bonded to the first die and to a bond finger of the substrate, wherein the first wire is bonded to the bond finger with a first bond. A first stitch bump is formed overlying the first stitch bond, wherein the first stitch bump is formed from a molten ball of conductive material. A second die is formed overlying the first die. A second wire is bonded to the second die and to the first stitch bump, wherein the second wire is bonded to the first stitch bump with a second bond.