Wafer Level Packages With Non-Wettable Solder Collars
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Solution Overview
Problem
Existing wafer level packaging technologies face issues with crack formation and delamination at the interfaces between solder balls and redistribution layers (RDLs) due to thermal cycling, leading to potential failure during electrical testing.
Innovation Solution
The implementation of non-wettable solder collars within the RDLs, which are exposed through enlarged solder mask openings, preventing the solder balls from contacting the solder mask layer and maintaining a controlled circumferential clearance, thereby reducing the likelihood of delamination and crack formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If solder balls are deposited to sizes exceeding the planform dimensions of the solder mask openings, then a structurally robust contact array is produced, but crack formation and delamination can occur within the RDLs at or near the interfaces between the solder mask layer and the BGA solder balls after prolonged thermal cycling
Solution Approach 1:
A non-wettable solder collar is introduced as an intermediary component between the solder ball and the RDL. This collar prevents direct contact between the solder ball and the RDL, thereby eliminating the source of crack formation and delamination while still allowing the solder ball to maintain its structurally robust size that exceeds the solder mask opening dimensions.
Solution Approach 2:
The interface between the solder ball and the RDL is segmented by introducing the solder collar as a separate component. This segmentation isolates the solder ball from the RDL, preventing the propagation of cracks and delamination that would otherwise occur at the direct interface, while preserving the structural robustness of the solder ball contact array.
2Strength
If solder balls are made larger than solder mask openings, then structural robustness is improved, but thermal cycling causes stress concentration at the solder mask-RDL interface leading to cracks
Solution Approach 1:
The non-wettable solder collar serves as a mediator that physically separates the solder ball from the RDL. This intermediary structure prevents stress concentration at the solder mask-RDL interface during thermal cycling, while allowing the solder ball to maintain its larger size for structural robustness.
3Ease of manufacture
If solder balls contact the solder mask layer directly, then manufacturing is simpler, but delamination occurs at the solder ball-RDL interface reducing yield
Solution Approach 1:
The non-wettable solder collar is introduced as an intermediary layer that prevents direct contact between the solder ball and the RDL. This simple structural addition eliminates delamination issues at the solder ball-RDL interface, thereby improving manufacturing yield without significantly complicating the deposition process.
4Manufacturing precision
If solder mask openings are enlarged to accommodate larger solder balls, then manufacturing tolerance is improved, but the solder balls may contact the solder mask sidewalls causing delamination
Solution Approach 1:
The non-wettable solder collar acts as an intermediary barrier between the solder ball and the solder mask layer. This allows the solder mask openings to be enlarged for improved manufacturing tolerance, while the collar prevents the solder ball from contacting the solder mask sidewalls, thereby eliminating the risk of delamination.
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 design effectively minimizes the occurrence of cracks and delamination in RDLs, enhancing the reliability and throughput of wafer level packages during manufacturing and in-field usage.
Implementation Method 1
non-wettable solder collars, which prevent or at least impede the undesired lateral creep of the solder balls during reflow
Data Source
AI summary
Wafer level packages and methods for producing wafer level packages having non-wettable solder collars are provided. In one embodiment, the method includes forming solder mask openings in a solder mask layer exposing regions of a patterned metal level underlying the solder mask layer. Before or after forming solder mask openings in the solder mask layer, non-wettable solder collars are produced extending partially over the exposed regions of the patterned metal level. Solder balls are deposited onto the non-wettable solder collars and into the solder mask openings such that circumferential clearances are provided around base portions of the solder balls and sidewalls of the solder mask layer defining the solder mask openings.