Wafer Level Package Sidewall Cracking Prevention
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Solution Overview
Problem
Conventional fan-in wafer level packaging (WLP) processes face challenges with sidewall chipping and cracking, leading to yield loss and reliability issues, and current automatic inspections are costly and unable to fully prevent these failures.
Innovation Solution
The implementation of a wafer level package device with a redistribution layer and a molding compound configuration that leaves the metal layer exposed, with molding compound sidewalls extending beyond the substrate sidewalls to prevent cracking and chipping, allowing for a smaller form factor and reduced manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a thick mold compound is added to the sidewalls in fan-out WLP, then the package connections can be arranged on a fan-out area, but the sidewall width increases and the form factor cannot be minimized to match fan-in WLP
Solution Approach 1:
The patent transitions from a traditional thick sidewall structure to a planar fan-out area by changing the dimensional arrangement of package connections. The mold compound is configured to provide a fan-out area on the top surface rather than extending thick sidewalls, allowing connections to be arranged horizontally rather than vertically along the sidewalls.
Solution Approach 2:
The mold compound is selectively applied to provide localized fan-out area where package connections are needed, rather than uniformly thick sidewalls throughout. The compound is positioned specifically to create the necessary connection area while maintaining minimal sidewall width elsewhere.
2Shape
If conventional fan-in WLP is used with minimal sidewalls, then the form factor is minimized, but sidewall chipping and cracking occur leading to yield loss
Solution Approach 1:
The patent applies a mold compound to the sidewalls and corners of the substrate beforehand to provide protective cushioning. This compound layer is applied prior to packaging to prevent chipping and cracking from occurring during subsequent handling and assembly processes, addressing the reliability issue before it manifests.
Solution Approach 2:
The patent uses a composite structure combining the substrate material with mold compound material. The mold compound acts as a protective layer that complements the substrate, providing enhanced mechanical strength and crack resistance while maintaining the minimal form factor of the original substrate.
3Reliability
If automatic inspection is implemented to detect sidewall cracking, then quality assurance is provided, but capital investment increases and throughput is reduced
Solution Approach 1:
The patent implements preliminary protective action by applying mold compound to the sidewalls and corners before packaging. This preventive measure eliminates the need for subsequent inspection to detect cracking, as the protective layer prevents the defects from occurring in the first place, thereby maintaining high throughput without sacrificing quality assurance.
4Ease of manufacture
If fan-in WLP process is used with 8-inch Si wafers instead of 12-inch fan-out WLP, then manufacturing costs are reduced by up to 30%, but sidewall chipping and cracking still occur
Solution Approach 1:
The patent maintains the cost-effective fan-in WLP process with 8-inch wafers but applies local quality enhancement by selectively adding mold compound to the sidewalls and corners. This localized modification provides the necessary protective function without changing the overall cost-effective manufacturing approach, preventing chipping and cracking while maintaining low production costs.
Data Source
AI summary
A wafer level package device may include a molding compound that encapsulates a substrate, a back end of line and front end of line layer on the substrate and a passivation layer of a redistribution layer without encapsulating a metal layer on the passivation layer. The molding compound may eliminate sidewall chipping and cracking as well as reduce the need for back side lamination.