Transparent-Substrate WLCSP to Reduce Sidewall Light Escape
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Solution Overview
Problem
Wafer level chip scale packages (WLCSPs) face challenges in reducing light escape, manufacturing cost, and thickness while maintaining functionality, particularly in applications like foldable electronics where space is limited.
Innovation Solution
The implementation of a transparent substrate with a molding compound layer on the sidewalls to reduce light escape and a method converting a 12-inch semiconductor wafer to an 8-inch wafer for manufacturing, using a transparent die attach film to eliminate the need for caps or lenses, thereby reducing thickness and utilizing existing machinery to minimize costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a transparent substrate is used in WLCSP to allow light passage, then light detection capability is improved, but light escape from sidewalls increases reducing detection efficiency
Solution Approach 1:
The substrate is designed with different optical properties in different regions: the top surface remains transparent for light entry, while the sidewalls are coated with opaque material to prevent light escape. This local differentiation of material properties resolves the contradiction between allowing light passage and preventing light loss.
Solution Approach 2:
The package combines transparent substrate material with opaque coating material to create a composite structure that simultaneously provides light transmission capability and light containment, resolving the contradiction between these two opposing requirements.
2Productivity
If conventional 12-inch wafer manufacturing is used, then production capacity is maintained, but highly specialized machinery is required increasing manufacturing cost
Solution Approach 1:
The patent transitions from 12-inch wafer fabrication to 8-inch wafer fabrication, changing the dimensional scale of the manufacturing process. This allows utilization of existing 8-inch manufacturing infrastructure and equipment, reducing the need for highly specialized 12-inch machinery while maintaining production capacity through the wafer conversion process.
3Productivity
If multiple singulation steps are performed on transparent substrates, then individual packages are separated, but cracking or breaking of substrates increases reducing yield
Solution Approach 1:
The opaque molding compound is applied to the sidewalls before the singulation process. This preliminary action provides structural support and protection to the transparent substrate during the subsequent singulation cutting steps, preventing cracking or breaking that would otherwise occur during package separation.
4Measurement precision
If caps or lenses are added to WLCSP to improve light detection, then detection effectiveness is improved, but package thickness increases
Solution Approach 1:
The patent removes the cap or lens components from the package structure and instead integrates the light detection functionality directly into the transparent substrate with opaque sidewall coating. This extraction of unnecessary components reduces package thickness while maintaining detection effectiveness through the optimized optical path.
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 solution enhances light detection efficiency by minimizing light loss, reduces manufacturing costs by minimizing waste and machinery requirements, and achieves a thinner package suitable for compact electronic devices.
Implementation Method 1
The molding compound layer is formed of an opaque material that is on the sidewalls of the transparent substrate. This reduces the amount of light that escapes from the sidewalls of the transparent substrate
Data Source
AI summary
The present disclosure is directed to a package, such as a wafer level chip scale package (WLCSP), with a die coupled to a central portion of a transparent substrate. The transparent substrate includes a central portion having and a peripheral portion surrounding the central portion. The package includes a conductive layer coupled to a contact of the die within the package that extends from the transparent substrate to an active surface of the package. The active surface is utilized to mount the package within an electronic device or to a printed circuit board (PCB) accordingly. The package includes a first insulating layer separating the die from the conductive layer, and a second insulating layer on the conductive layer.