Sacrificial Pad Layout for Galvanic Corrosion in EMIB FLI Bumps
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Solution Overview
Problem
The surface finish, particularly gold, in first level interconnect (FLI) bumps acts as a catalyst for the reduction of hydrogen peroxide during seed layer etching, leading to unintended etching of copper FLI bumps when they are electrically coupled to pads with large surface areas, resulting in yield and reliability issues.
Innovation Solution
Incorporating sacrificial pads with a larger exposed surface area than the FLI bumps to preferentially oxidize and supply electrons for the hydrogen peroxide reduction reaction, thereby preventing excessive etching of the FLI bumps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the surface finish (gold) is applied to FLI bumps to enable pitch scaling and reliable assembly yield, then the assembly yield and reliability are improved, but the gold acts as a catalyst for hydrogen peroxide reduction causing excessive etching of copper FLI bumps
Solution Approach 1:
A sacrificial pad made of copper is introduced as an intermediary element between the seed layer etching process and the FLI bump. This sacrificial pad absorbs the harmful catalytic etching effect by providing a larger surface area for the reaction, thereby protecting the FLI bump from excessive etching while allowing the gold surface finish to maintain its beneficial assembly yield properties
2Quantity of substance
If the exposed surface area of the pad is made large to provide sufficient electrons for the reaction, then the electron supply is improved, but the FLI bump becomes more susceptible to over-etching
Solution Approach 1:
The pad structure is segmented into two distinct functional areas: a large-area sacrificial pad region that provides electrons for the reaction, and a protected FLI bump region that maintains precise dimensions. This segmentation allows the system to simultaneously achieve sufficient electron supply and maintain manufacturing precision by spatially separating the electron source from the sensitive interconnect structure
3Ease of manufacture
If the seed layer is completely removed to expose the surface finish, then the surface finish functionality is achieved, but the FLI bump copper is entirely etched away
Solution Approach 1:
The sacrificial pad is prepared in advance with a larger surface area than the FLI bump before the etching process begins. During etching, this pre-positioned sacrificial pad preferentially consumes the etchant and provides electrons, ensuring that when the seed layer is completely removed to expose the surface finish, the FLI bump copper remains protected and is not entirely etched away
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 effectively reduces the over-etching of FLI bumps, enhancing the reliability and yield of electronic packages by ensuring that the sacrificial pads are preferentially etched instead of the FLI bumps, maintaining their integrity and performance.
Implementation Method 1
the surface finish (particularly, the gold of the surface finish) acts as a catalyst for the reduction of hydrogen peroxide
Implementation Method 2
copper is oxidized (etched)
Implementation Method 3
preferentially oxidize and supply electrons for the hydrogen peroxide reduction reaction
Data Source
AI summary
Embodiments disclosed herein include electronic packages and methods of making electronic packages. In an embodiment, the electronic package comprises a package substrate, an array of first level interconnect (FLI) bumps on the package substrate, wherein each FLI bump comprises a surface finish, a first pad on the package substrate, wherein the first pad comprises the surface finish, and wherein a first FLI bump of the array of FLI bumps is electrically coupled to the first pad, and a second pad on the package substrate, wherein the second pad is electrically coupled to the first pad.