Integrated Circuit Pad Segmentation for Bump Support
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Solution Overview
Problem
In flip chip technology, the insulator layer over bonding pads is not strong enough to support solder balls due to holes created during wafer probing tests, leading to potential collapse or slanting of conductive bumps and compromised surface profile uniformity.
Innovation Solution
An integrated circuit structure with a metal pad featuring a probing portion and a bumping portion, separated by a first and second passivation layer, where the second passivation layer has a balanced topography to prevent conductive bump collapse and ensure uniformity, using materials like silicon oxide and polyimide, and a conductive bump positioned in an opening of the second passivation layer to maintain separation from the probing portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an insulator layer is formed over bonding pads to provide electrical connections, then electrical insulation is achieved, but the insulator layer becomes too weak to support solder balls due to holes created during wafer probing tests
Solution Approach 1:
The metal pad is divided into two distinct portions: a probing portion for wafer probing tests and a bumping portion for solder ball attachment. This segmentation allows the probing portion to bear the mechanical stress of probing while the bumping portion provides a stable base for solder balls, eliminating the need for a separate support structure over the entire pad area.
Solution Approach 2:
Different regions of the metal pad are assigned different functions: the probing portion is designed to withstand probing operations, while the bumping portion is optimized for solder ball support. This local differentiation of function allows each region to be optimized for its specific purpose, resolving the contradiction between probing access and solder ball support.
2Measurement precision
If wafer probing tests are performed on bonding pads, then electrical characteristics can be assessed, but holes are created that compromise the insulator layer's ability to support conductive bumps
Solution Approach 1:
By segmenting the pad into probing and bumping portions, the probing operations are confined to a specific area. This prevents probe-induced damage from affecting the bumping area, thereby maintaining surface profile uniformity in the region where conductive bumps will be formed, while still allowing comprehensive electrical testing.
Solution Approach 2:
The first passivation layer acts as an intermediary structure that covers the metal pad and provides mechanical support. It bridges the probing portion and the bumping portion, preventing the propagation of stress and damage from the probing area to the bumping area, thus preserving surface uniformity.
3Ease of manufacture
If a single insulator layer is used over the metal pad, then fabrication is simplified, but the insulator layer cannot provide sufficient support for conductive bumps while maintaining separation from probing areas
Solution Approach 1:
The passivation structure is segmented into two layers: a first passivation layer covering the metal pad and a second passivation layer with an opening for the conductive bump. This layered segmentation provides both mechanical support and precise positioning, ensuring conductive bump stability while maintaining manufacturability through standard multi-layer passivation processes.
Data Source
AI summary
An integrated circuit structure includes a substrate, a metal pad, a first passivation layer, a second passivation layer, and a conductive bump. The metal pad is over the substrate. The metal pad includes a probing portion and a bumping portion laterally connected to the probing region. The first passivation layer is over the metal pad. The second passivation layer is over the first passivation layer and has an opening. The bumping portion is in the opening. The conductive bump is in the opening of the second passivation layer and contacts the probing portion. The probing portion and the conductive bump are separated by the first passivation layer.