Wafer Chip Scale Packaging With Ball-First Repassivation
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Solution Overview
Problem
Existing wafer level chip scale packaging processes face challenges with edge roughness and bleed out of repassivation materials, leading to missing solder balls, non-fusion of solder, and stress concentration issues.
Innovation Solution
The described process involves solder ball placement followed by repassivation layer formation using additive manufacturing techniques, which reduces material usage and mitigates edge roughness and bleed out effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If spin coating and patterning are used to form the repassivation layer, then precise patterned openings can be achieved, but materials usage is low and process complexity increases
Solution Approach 1:
Solder balls are attached to the conductive structures before the repassivation layer is formed. This preliminary action allows the repassivation material to be deposited only in areas where it is needed for protection and stress relief, avoiding waste on areas that will be covered by solder balls anyway.
Solution Approach 2:
The repassivation step is extracted from the pre-solder ball process and performed after ball attach. This separates the protective function from the patterning function, allowing material to be applied only where needed without requiring precise patterned openings.
2Loss of substance
If printing processing is used to deposit the repassivation layer, then materials usage improves, but edge roughness and bleed out cause missing solder balls
Solution Approach 1:
Solder balls are attached before repassivation layer formation, so the repassivation material does not need to achieve precise edges at solder ball locations. The critical positioning is done by the ball attach process, not the printing process.
Solution Approach 2:
The bleed out effect of printed repassivation material, which was previously harmful by causing edge roughness and missing solder balls, becomes beneficial by providing stress relief and protection at the base of copper pillars without interfering with solder ball placement.
3Reliability
If repassivation material is applied before solder ball placement, then copper protection is achieved, but stress concentration causes solder ball cracking and delamination
Solution Approach 1:
Solder balls are attached to conductive structures before the repassivation layer is formed. This ensures that the solder ball attachment process occurs on clean, exposed surfaces without the interference of repassivation material, achieving strong fusion.
Solution Approach 2:
The repassivation layer is applied locally at the base of copper pillars after solder ball attach, providing stress relief and protection only where needed, without interfering with the solder ball attachment interface.
Data Source
AI summary
Disclosed examples provide methods that include forming a conductive structure at least partially above a conductive feature of a wafer, attaching a solder ball structure to a side of the conductive structure, and thereafter forming a repassivation layer on a side of the wafer proximate the side of the conductive structure. Further examples provide microelectronic devices and integrated circuits that include a conductive structure coupled with a conductive feature of a metallization structure, a solder ball structure connected to the conductive structure, and a printed repassivation layer disposed on the side of the metallization structure proximate a side of the conductive structure.