Conductive Ink Pads for Wafer Probing
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Solution Overview
Problem
The shrinking size of integrated circuit pads and tight pad pitch makes it difficult and costly to manufacture and maintain high-precision probe cards for wafer testing, necessitating a method to reduce the need for such high-precision equipment.
Innovation Solution
A pattern of conductive ink, comprising a mixture of conductive particles and wafer bonding thermoset plastic, is applied to the wafer using an ink jet printing system to create large contact pads that are much larger than the bond pads, allowing for easier and less precise probing, and subsequently removed after testing without damaging the wafer surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If probe cards are designed to contact small pads with tight pitch, then testing precision is improved, but manufacturing cost and maintenance difficulty increase
Solution Approach 1:
A conductive ink layer is introduced as an intermediary between the probe card and the bond pads. This ink layer is deposited on the wafer surface and provides large-area contact regions that are easier to probe, while still maintaining electrical connection to the underlying bond pads through conductive pathways.
Solution Approach 2:
The solution transitions from direct point-to-point contact in the horizontal plane to a multi-layer vertical structure. The conductive ink creates elevated contact regions that add a vertical dimension to the probing interface, allowing larger probe contact areas without increasing horizontal pad pitch.
2Measurement precision
If probe cards are designed to contact small pads with tight pitch, then testing accuracy is improved, but maintenance complexity increases
Solution Approach 1:
The conductive ink layer serves as a mediator that absorbs mechanical stress and alignment variations during probing. This protects the underlying bond pads from damage and reduces the precision requirements for probe card positioning, thereby simplifying maintenance.
Solution Approach 2:
The invention changes the contact interface parameters by creating large-area contact regions with the conductive ink, as opposed to small-point contacts. This parameter change makes the probing process more robust to misalignment and reduces wear on both the probes and the wafer surface.
3Ease of operation
If large contact pads are created on the wafer surface, then probing ease is improved, but wafer surface area is reduced
Solution Approach 1:
The conductive ink forms a thin film layer on the wafer surface that provides large contact areas without significantly increasing the vertical profile. This thin-film approach maintains wafer compactness while enabling easier probing through larger contact regions.
Solution Approach 2:
Instead of expanding contact areas in the horizontal plane (which would reduce active wafer area), the solution uses vertical layering with the conductive ink to provide elevated contact regions. This dimensional transition allows large contact areas without consuming additional horizontal wafer real estate.
4Ease of manufacture
If conductive ink is applied to create contact pads, then probe card precision requirements are reduced, but manufacturing process complexity increases
Solution Approach 1:
The mechanical process of creating precise metal interconnect structures is replaced with a chemical/depositional process using conductive ink. This substitution simplifies the manufacturing steps by using solution-based processing rather than complex vapor deposition and patterning sequences.
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 enables wafer testing with lower-cost, less precise probe cards and allows for multiple tests without damaging the contact pads, increasing assembly yield and reducing the risk of pad damage, while maintaining the 2D shape of the features and preserving the wafer's pre-tested condition.
Implementation Method 1
the conductive ink is heated and disposed on a wafer by an ink jet printing system
Implementation Method 2
a pattern of conductive ink, comprising a mixture of conductive particles and wafer bonding thermoset plastic
Data Source
AI summary
A pattern of conductive ink is disposed on the topside of the unsingulated integrated circuits of a wafer, and, typically after wafer probing, the pattern of conductive ink is removed. The conductive ink pattern provides an electrical pathway between bond pads on an integrated circuit and large contact pads disposed on the topside of the integrated circuit. Each of the large contact pads is much greater in area than the corresponding bond pads, and are spaced apart so that the pitch of the large contact pads is much greater than that of the bond pads. In one aspect of the present invention, the conductive ink includes a mixture of conductive particles and wafer bonding thermoset plastic. In another aspect of the present invention, the conductive ink is heated and disposed on a wafer by an ink jet printing system.