Non-Circular Ball Bonds for Fine-Pitch Bond Pad Alignment
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The increasing demand for finer pitch semiconductor devices poses challenges in wire bonding due to tighter tolerances and higher chances of defects, as conventional ball bonds may not be properly centered or shaped, leading to short circuits and reduced bonding strength.
Innovation Solution
The use of capillaries with non-circular distal openings, such as stadium, oval, or rectangular shapes, to form ball bonds with non-circular footprints that have a longer length and shorter width, providing greater contact area and symmetry, which can be tailored to match the dimensions of the bond pads, thereby improving bonding strength and preventing short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If smaller ball bonds are produced by using finer wires and/or capillaries with smaller diameters, then the ball bond size is reduced to accommodate fine pitch devices, but the surface contact area with bond pads is reduced resulting in weaker bonding strength and reduced current flow
Solution Approach 1:
The patent applies asymmetry by changing the capillary opening from a conventional circular shape to a non-circular shape (such as oval, rectangular, or stadium shape). This asymmetric opening shape creates an asymmetric ball bond footprint that can be optimized to match the rectangular geometry of bond pads, thereby increasing the contact area and bonding strength even when using finer wires for small pitch applications
Solution Approach 2:
The patent changes the geometric parameters of the capillary opening (from circular to non-circular with specific aspect ratios) to transform the ball bond footprint shape. This parameter change allows the ball bond to conform to the bond pad geometry, maximizing surface contact area and improving both bonding strength and current flow capabilities despite reduced ball bond size
2Ease of manufacture
If conventional circular ball bonds are used, then the wire bonding process is simple, but the ball bonds may not be properly centered or positioned on bond pads, resulting in short circuits with adjacent bond pads
Solution Approach 1:
The non-circular capillary opening creates an asymmetric ball bond footprint that naturally aligns with the rectangular bond pad geometry. This asymmetric shape provides inherent positioning guidance that helps center the ball bond on the bond pad, reducing the risk of short circuits while maintaining manufacturing simplicity
Solution Approach 2:
The patent transitions from a circular (isotropic) footprint to a non-circular (anisotropic) footprint by changing the capillary opening geometry. This dimensional change in the footprint shape provides directional alignment characteristics that improve positioning accuracy on rectangular bond pads, enhancing reliability without complicating the manufacturing process
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 enhances the bonding strength and prevents short circuits by ensuring adequate surface contact and alignment with bond pads, even at finer pitches, while maintaining or improving current flow capabilities.
Implementation Method 1
The tip of the capillary then presses and flattens the ball against the surface of the bond pad
Implementation Method 2
molding the ball with the distal opening of the capillary to form the ball into a predetermined shape
Implementation Method 3
heat and/or ultrasonic energy welds the flattened ball to the bond pad to form a ball bond
Implementation Method 4
heat and/or ultrasonic energy welds the flattened ball to the bond pad
Implementation Method 5
Because of surface tension, the molten metal forms a ball at the end of the wire
Data Source
AI summary
A semiconductor device includes an integrated circuit die having bond pads and a bond wires. The bond wires are connected to respective ones of the bond pads by a ball bond. An area of contact between the ball bond and the bond pad has a predetermined shape that is non-circular and includes at least one axis of symmetry. A ratio of the ball bond length to the ball bond width may be equal to a ratio of the bond pad length to the bond pad width.