Semiconductor Package Redistributed Pad for Copper Wire Bonding
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Solution Overview
Problem
The existing wire bonding process for semiconductor packages using copper wires faces limitations due to the insufficient ductility and easy oxidation of copper, which restricts its application to smaller chip pads, and the structural damage caused by the higher hardness of copper bonding wires to aluminum pads during the bonding process.
Innovation Solution
A wire bonding structure is developed that incorporates a re-distribution layer to select a second metallic pad with higher hardness or better bonding properties, such as copper, and designs the pad size and arrangement to increase bonding area and force, while avoiding damage to the original aluminum pad.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If copper bonding wire is used instead of gold wire, then cost is reduced and electrical conductivity is improved, but the wire bonding process becomes more difficult due to copper's insufficient ductility and easy oxidation
Solution Approach 1:
The patent introduces a copper pad as an intermediary layer between the aluminum chip pad and the copper bonding wire. This copper pad serves as a mediator that is compatible with both the aluminum pad (through proper material selection and interface design) and the copper wire (through matched thermal expansion coefficient and conductivity), thereby enabling reliable copper wire bonding without directly exposing the aluminum pad to copper wire bonding stresses
Solution Approach 2:
The patent modifies the bonding parameters and process conditions for copper wire bonding, including optimizing bonding temperature, pressure, and time parameters to account for copper's lower ductility and higher oxidation susceptibility. The copper pad's material properties (thermal expansion coefficient, conductivity) are specifically selected and tuned to match both the aluminum pad and copper wire, enabling successful bonding process
2Length of moving object
If copper bonding wire is used, then wire diameter can be reduced for better heat dissipation, but the higher hardness of copper damages the aluminum pad structure during pressing
Solution Approach 1:
The copper pad acts as a mechanical intermediary that absorbs and distributes the bonding force during wire attachment. By positioning the copper pad between the aluminum chip pad and the copper bonding wire, it serves as a force distribution interface that protects the softer aluminum pad from direct mechanical damage while still enabling effective force transmission for wire bonding
Solution Approach 2:
The copper pad is pre-formed and positioned on the aluminum chip pad before the wire bonding process. This preliminary preparation creates a ready-made bonding surface with appropriate mechanical properties, eliminating the need to directly bond copper wire to the aluminum pad and thereby preventing structural damage to the aluminum pad during the pressing operation
3Area of stationary object
If the chip pad size is reduced, then integration density is improved, but copper wire bonding becomes unreliable due to insufficient pad structural strength
Solution Approach 1:
The patent employs a composite pad structure consisting of an aluminum chip pad combined with a copper pad layer. This composite structure leverages the advantages of both materials: the aluminum provides good electrical conductivity and compatibility with standard chip fabrication, while the copper layer provides enhanced mechanical strength and ductility specifically at the wire bonding interface, enabling reliable bonding on smaller pads
Solution Approach 2:
The copper pad is strategically positioned only at the specific location where wire bonding is required, rather than making the entire chip pad larger. This localized application of copper material provides the necessary mechanical strength and bonding reliability precisely where needed, while maintaining small overall pad dimensions for high integration density
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 solution enhances the bonding force and area between the copper bonding wire and the chip, allowing for successful wire bonding on smaller pads without damaging the original pad structure and increasing the number of input/output contacts by arranging pads in a non-straight line.
Implementation Method 1
the bonding wire is bonded to the second metallic pad
Data Source
AI summary
A wire bonding structure includes a chip and a bonding wire. The chip includes a base material, at least one first metallic pad, a re-distribution layer and at least one second metallic pad. The first metallic pad is disposed on the base material. The re-distribution layer has a first end and a second end, and the first end is electrically connected to the first metallic pad. The second metallic pad is electrically connected to the second end of the re-distribution layer. The bonding wire is bonded to the second metallic pad.