Temporary Test Structure for C4 and TSV Electrical Probing
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Solution Overview
Problem
Current methods for testing conductive interconnects, such as C4 solder bumps and TSVs, face challenges in detecting opens and shorts due to their small critical area and limited sensitivity, leading to inefficiencies in product health monitoring and yield loss, especially in 3D and 2.5D integration where traditional probes are physically and mechanically limited.
Innovation Solution
A method is developed to form a temporary test structure by providing a substrate with conductive interconnects, conformally forming an electrical test layer, patterning it to create test locations, and using probes to perform electrical testing before removing the structure, which allows for early detection of defects and reduces damage to the underlying components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional probes are used for testing C4 bumps and TSVs, then testing can be performed, but the probes are physically and mechanically limited and cannot detect opens and shorts effectively
Solution Approach 1:
The patent segments the testing function by creating separate temporary test structures (test pads and test interconnects) that are distinct from the final product structure. This segmentation allows dedicated test access points to be formed that can be probed effectively, while the actual C4 bumps and TSVs maintain their small critical dimensions for the final device.
Solution Approach 2:
The patent introduces temporary test structures as intermediary elements between the probing system and the conductive interconnects. These test structures act as mediators that provide accessible test points for detecting opens and shorts in the underlying TSVs and C4 bumps, overcoming the limitation of direct probing at small critical areas.
2Productivity
If temporary test structures are formed, then 100% KGD testing and early defect detection are enabled, but additional fabrication steps and process complexity are introduced
Solution Approach 1:
The patent applies preliminary action by forming temporary test structures early in the fabrication process, before the final C4 bumps and TSVs are completed. This allows defect detection to occur at intermediate stages, enabling early intervention and yield monitoring without waiting for final assembly testing.
Solution Approach 2:
The temporary test structures are discarded after serving their testing purpose. The method involves forming test structures, performing electrical testing to detect defects, and then removing the temporary structures. This allows the underlying conductive interconnects to be recovered for their intended function without the test structures interfering with the final device performance.
3Ease of operation
If probes apply force to test small pitch features, then electrical testing is achieved, but damage to the device being tested occurs
Solution Approach 1:
The patent creates temporary test structures that are electrical copies or representations of the final conductive interconnects. These test structures replicate the electrical pathways of the TSVs and C4 bumps but are formed with larger, more robust dimensions that can withstand probing forces without damage, thereby protecting the actual delicate interconnects.
Data Source
AI summary
A method of forming a temporary test structure for device fabrication is provided. The method allows for electrically testing conductive interconnects during controlled collapse chip connections (C4) fabrication and/or through-silicon vias (TSVs) during interposer fabrication. The method includes providing a substrate containing a plurality of electrically conductive interconnects extending vertically to top surface of the substrate. A temporary test structure is formed to connect the plurality of interconnects for electrical testing. Electrical testing is performed on the substrate by probing at different test locations on the temporary test structure. All or part of the temporary test structure is removed so as not to affect product performance. The temporary test structure can contain electrical test pads which provide a way to make temporary connections to small interconnect landings or features at extreme tight pitch to fan them out to testable pads sizes and pitches.