Adhesive Layer Protects Passivation Cracking in Flip Chip Solder Bumps
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Solution Overview
Problem
The passivation layer surrounding solder bumps in semiconductor devices tends to crack during the solder reflow process, primarily due to degradation caused by chemical processes involved in forming and removing dry film, which compromises the reliability and integrity of the interconnect structure.
Innovation Solution
A method is introduced that involves forming an adhesive layer over the passivation layer, which remains in place until the solder bumps are formed, reducing cracking by protecting the passivation layer from chemical degradation during the solder bump formation process. This method includes steps such as forming a substrate with active devices, creating contact pads, forming intermediate conduction layers, and patterning a dry film over the adhesive layer before depositing and reflowing solder material to form bumps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If chemical processes are used to form and remove dry film during solder bump formation, then solder bumps can be formed on contact pads, but the passivation layer surrounding the solder bumps cracks due to degradation
Solution Approach 1:
A protective layer is introduced as an intermediary between the chemical processes (dry film formation and removal) and the passivation layer. This protective layer absorbs or shields against the chemical degradation, allowing the dry film processes to proceed while preventing direct damage to the passivation layer, thus eliminating the cracking problem while maintaining manufacturability
Solution Approach 2:
The protective layer is applied beforehand (prior to dry film formation) to preemptively shield the passivation layer from chemical degradation. This preliminary protective action ensures that when subsequent chemical processes occur, the passivation layer is already protected, preventing cracking before it can occur
2Ease of operation
If the passivation layer is exposed during solder bump formation, then access to contact pads is available for solder deposition, but the passivation layer degrades and cracks under thermal and chemical stress
Solution Approach 1:
The protective layer serves as a mediator that allows contact pads to remain accessible for solder deposition while simultaneously protecting the passivation layer from thermal and chemical stress. It enables the manufacturing process to proceed without compromising passivation layer strength
3Manufacturing precision
If dry film is removed after solder bump formation, then excess solder is cleared, but the chemical removal process degrades and cracks the passivation layer
Solution Approach 1:
The protective layer acts as a shield during the dry film removal process, allowing chemical etchants to remove excess solder and dry film residue while preventing these chemicals from degrading the passivation layer. This maintains manufacturing precision for solder bump patterning while preserving passivation layer integrity
Solution Approach 2:
The protective layer is applied in advance before any chemical processes occur, establishing a protective barrier that remains in place during both dry film formation and removal. This preliminary protection ensures the passivation layer is never exposed to degrading chemicals, preventing cracking while allowing precise solder bump formation
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
The adhesive layer effectively reduces cracking in the passivation layer, enhancing the strength and reliability of the solder bump structure without increasing manufacturing costs, thereby improving the longevity and performance of semiconductor devices.
Implementation Method 1
The cracking has been attributed to degradation of the passivation layer caused by the chemical processes used during formation of the solder bumps
Implementation Method 2
reflowing the solder material to form solder bumps
Data Source
AI summary
A flip chip semiconductor device has a substrate with a plurality of active devices formed thereon. A contact pad is formed on the substrate in electrical contact with the plurality of active devices. A passivation layer is formed over the substrate and intermediate conduction layer. An adhesive layer is formed over the passivation layer. A barrier layer is formed over the adhesive layer. A wetting layer is formed over the barrier layer. The barrier layer and wetting layer in a first region are removed, while the barrier layer, wetting layer, and adhesive layer in a second region are maintained. The adhesive layer over the passivation layer in the first region are maintained until the solder bumps are formed. By keeping the adhesive layer over the passivation layer until after formation of the solder bumps, less cracking occurs in the passivation layer.