Stepped Bond Pad Structure for Copper Wire Crack Resistance
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Solution Overview
Problem
The use of copper wire bonds on aluminum pads in electronic component packages leads to reliability issues due to cracking at the interface between the copper wire bond and the aluminum pad, especially under temperature cycling, which can destroy the connection to the circuitry.
Innovation Solution
The formation of stepped bond pads, where the wire bond region is thinner than the rest of the pad, allowing almost all the thinner material to form an intermetallic compound that is less susceptible to cracking, while the thicker portion maintains conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper wire bonds are used on aluminum pads to reduce cost, then material cost is reduced, but cracking occurs at the interface under temperature cycling
Solution Approach 1:
The bond pad is segmented into two distinct regions: a first region with greater thickness and a second region with lesser thickness. This segmentation allows the first region to provide mechanical support and conductivity while the second region forms a controlled intermetallic compound layer, preventing cracking at the wire bond interface.
Solution Approach 2:
Different regions of the bond pad are given different thicknesses to serve different functions. The first region (thicker) provides structural support and electrical conductivity, while the second region (thinner) is optimized for forming a reliable intermetallic compound interface with the copper wire bond, thereby locally optimizing properties to prevent cracking.
2Reliability
If the bond pad thickness is reduced to form intermetallic compound, then cracking resistance is improved, but conductivity may increase
Solution Approach 1:
The bond pad is divided into two regions with different thicknesses. The first region maintains greater thickness to ensure low electrical resistance and good conductivity, while the second region has reduced thickness to facilitate formation of a thin, crack-resistant intermetallic compound layer at the wire bond interface.
Solution Approach 2:
The bond pad structure uses local quality variation where the first region is thicker for conductivity and the second region is thinner for cracking resistance. This localized differentiation allows simultaneous optimization of both electrical performance and mechanical reliability.
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 enhances the reliability of the connection between the wire bond and circuitry by reducing cracking and maintaining low resistance, thus improving the durability of the semiconductor device under temperature cycling.
Implementation Method 1
allowing almost all the thinner material to form an intermetallic compound when the wire bond is formed
Implementation Method 2
form an intermetallic compound when the wire bond is formed
Data Source
AI summary
A method for forming a semiconductor structure includes forming a bond pad over a last metal layer of the semiconductor structure wherein the bond pad includes a wire bond region; and recessing the wire bond region such that the wire bond region has a first thickness and a region of the bond pad outside the wire bond region has a second thickness that is greater than the first thickness.