Foldback Wire Bond Structure for Small High-Current Bond Pads
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Solution Overview
Problem
Current solder technology struggles to attach to small bond pads on power semiconductors like SiC MOS and GaN, leading to issues with contaminated pads and residues, which are not suitable for high current density applications.
Innovation Solution
A method involving forming a first foldback bond on a contact element using a bonding wire, folding it over, and pressing it onto another contact element, creating a multi-loop connection that minimizes space requirements and allows for high current values by stacking wire bonds alternately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder technology is used for clip attach on small bond pads, then current carrying capacity can be achieved, but contamination and residues occur that are not suitable for high current density applications
Solution Approach 1:
The invention extracts the harmful solder material from the bonding process entirely, replacing it with a solderless wire bonding method that achieves reliable electrical connection without introducing contamination or residues to the bond pad surface
Solution Approach 2:
The invention replaces the chemical/solder-based attachment system with a mechanical wire bonding system that uses controlled deformation and metallurgical bonding through pressure and heat, eliminating the need for solder paste and associated contamination
2Reliability
If multiple wire bonds are stacked to carry high current, then current density requirements are met, but space requirements on the bond pad increase
Solution Approach 1:
The invention transitions from planar arrangement of multiple wire bonds to a vertical stacked configuration, utilizing the third dimension (height) to accommodate multiple bonds while maintaining a compact footprint on the bond pad surface
Solution Approach 2:
The invention implements a nested structure where successive wire bonds are stacked one on top of another, with each bond positioned vertically above the previous one, allowing multiple bonds to occupy minimal horizontal space while collectively carrying high current
3Area of moving object
If bond pad size is reduced by 30% to shrink chip size, then chip dimensions are reduced, but attachment reliability for power interconnects becomes more challenging
Solution Approach 1:
The invention segments the current carrying function across multiple wire bonds rather than relying on a single large bond, allowing the total current capacity to be distributed among several smaller bonds that can be accommodated on reduced bond pad areas
Solution Approach 2:
The invention changes the bonding parameters by using controlled pressure and heat during wire bonding to achieve reliable metallurgical bonds on small pads, where the bonding force and temperature are optimized for small-area attachments
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 method enables efficient electrical connections on small bond pads by minimizing space requirements and ensuring a flat surface for successive wire bonds, facilitating high current performance.
Implementation Method 1
The bonding connection being formed alternatingly between the two contact elements may be referred to as cross-chain bonding
Implementation Method 2
The bonding processes described herein may in various embodiments include thermosonic or ultrasonic bonding
Data Source
AI summary
A method of forming an electrical connection is provided. The method may include: forming a first foldback bond on a first contact element by bonding a first section of a first bonding wire to the first contact element; folding the first bonding wire to arrange a second section of the first bonding wire over the bonded first section; and pressing the second section onto the first section, bonding a third section of the first bonding wire to a second contact element, and bonding a fourth section of the first bonding wire onto the first foldback bond.