Wafer Probing Needle Tip Diameter Optimization
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Solution Overview
Problem
In wafer probing, high contact forces from probing needles can cause mechanical damage to bonding pads and underlying layers, leading to unreliable wire bonding and increased risk of cracks, necessitating consistent tip diameters for reliable contact without extensive experimental qualification.
Innovation Solution
A method to determine the minimum permissible tip diameter of probing needles by performing contact procedures at varying stresses, measuring indentation depths, and calculating calibration coefficients to predict indentation depth as a function of stress, allowing for adjustment of tip diameters to prevent damage and ensure reliable contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high contact forces are applied by probing needles, then sufficient electrical contact is achieved, but mechanical damage to bonding pads and underlying layers occurs
Solution Approach 1:
The patent changes the geometric parameter of the probing needle tip (tip diameter) to optimize the contact force distribution. By determining a minimum permissible tip diameter based on bonding pad dimensions and material properties, the contact stress is reduced while maintaining sufficient contact force for reliable electrical connection, thereby preventing mechanical damage to the bonding pad and underlying layers
2Reliability
If high contact forces are applied by probing needles, then sufficient electrical contact is achieved, but cracks in the oxide layer beneath the bonding pad occur
Solution Approach 1:
The patent modifies the contact geometry parameter (probing needle tip diameter) to control the stress distribution in the underlying oxide layer. By ensuring the tip diameter meets a minimum permissible value calculated from oxide layer properties and bonding pad dimensions, the induced stress remains below the crack initiation threshold while still providing adequate electrical contact
3Reliability
If extensive experimental qualification is performed to determine safe contact forces, then reliability of wafer probing is improved, but time and resource consumption increase
Solution Approach 1:
The patent performs preliminary calculations to determine the minimum permissible probing needle tip diameter before actual wafer probing operations. By using analytical models that incorporate bonding pad and oxide layer properties, the safe operating parameters are established in advance, eliminating the need for time-consuming iterative experimental qualification while ensuring reliable and damage-free probing
Solution Approach 2:
The patent replaces extensive mechanical experimental qualification with analytical calculations and simulations. By using mathematical models that predict indentation depth and stress distribution based on material properties and geometric parameters, the reliable operating conditions are determined through computation rather than repeated physical experiments
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 risk of mechanical damage and crack occurrence by optimizing probing needle tip diameters, enhancing the reliability of wafer probing and reducing the need for extensive experimental qualification and monitoring.
Implementation Method 1
A chart of indentation depths of the plurality of bonding pads caused by the contact procedures at different stress is determined
Implementation Method 2
At least two different stresses applied to the underlying layer based on the at least two different stresses applied to the bonding pads are determined
Data Source
AI summary
A method of determining a minimum permissible tip diameter of probing needles of a probe card for wafer probing is described. The method includes performing a plurality of contact procedures of at least one probing needle to a plurality of bonding pads on a wafer. The plurality of contact procedures is performed at different stress applied by the at least one probing needle to the bonding pads. A chart of indentation depths of the plurality of bonding pads caused by the contact procedures at different stress is determined. A set of calibration coefficients based on the chart is determined, wherein the set of calibration coefficients allows to compute a predicted indentation depth as a function of stress. The minimum permissible probing needle tip diameter is determined based on an evaluation of the function.