PPI Pad Oxide Layer Controls Solder Ball Reflow
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Solution Overview
Problem
In the integrated circuit manufacturing process, the existing methods for forming solder balls over Post-Passivation Interconnects (PPI) structures often result in solder balls extending to the neck regions, leading to potential cracking and reliability issues due to uneven oxidation and wetting characteristics of the metal oxide layers.
Innovation Solution
A method involving the formation of a thick metal oxide layer on PPI pads through oxidation, followed by local oxide removal during the reflow process, limits the wettable surfaces to prevent solder balls from reaching the neck regions, thereby enhancing the reliability of the PPI connections by maintaining non-planar surfaces with controlled thickness variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder balls are placed over UBMs and reflowed using existing methods, then the solder balls are formed and connected to PPI, but the solder balls extend to the neck regions causing cracking and reliability issues
Solution Approach 1:
A thick metal oxide layer is formed on the PPI pads through oxidation before solder ball placement. This preliminary oxidation creates a controlled wettable surface that limits solder ball spread, preventing them from reaching the vulnerable neck regions during reflow, thus avoiding cracking while ensuring reliable connections.
Solution Approach 2:
The oxidation process creates a non-uniform oxide layer thickness across the PPI structure. The oxide layer is thickest on the PPI pads where wetting is desired, and thinner or removed from the neck regions where solder spread must be prevented. This local variation in oxide layer quality controls solder ball morphology and prevents harmful extensions.
2Reliability
If a thick metal oxide layer is formed on PPI pads through oxidation, then the wettable surfaces are controlled to prevent solder ball extension, but additional process steps are required
Solution Approach 1:
The oxidation step forming the thick metal oxide layer on PPI pads is merged with the existing reflow process. The oxidation is performed as a preliminary treatment before solder ball placement, and the same thermal processing conditions that form the oxide layer also facilitate controlled wetting during reflow, combining multiple functions into an integrated process sequence.
3Manufacturing precision
If local oxide removal is performed during reflow, then solder balls are prevented from reaching neck regions, but process control complexity increases
Solution Approach 1:
The oxidation process parameters (temperature, time, atmosphere composition) are optimized to create a thick metal oxide layer with specific properties that enable controlled wetting. By adjusting these parameters, the oxide layer thickness and reactivity are controlled to limit solder ball spread to desired areas while preventing extension into neck regions, achieving precision through parameter optimization rather than complex process control.
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 improves the reliability of PPI connections by preventing solder balls from reaching the neck regions, reducing the likelihood of cracking and ensuring stable interconnects during the molding process.
Implementation Method 1
A method involving the formation of a thick metal oxide layer on PPI pads through oxidation
Implementation Method 2
Solder balls are then placed over the UBMs and reflowed
Data Source
AI summary
An integrated circuit structure includes a semiconductor substrate, a metal pad over the semiconductor substrate, a passivation layer including a portion over the metal pad, a polymer layer over the passivation layer, and a Post-Passivation Interconnect (PPI) over the polymer layer. The PPI is electrically connected to the metal pad. The PPI includes a PPI line have a first width, and a PPI pad having a second width greater than the first width. The PPI pad is connected to the PPI line. The PPI pad includes an inner portion having a first thickness, and an edge portion having a second thickness smaller than the first thickness.