Image Sensor Package Cover Structure to Prevent Mold Flash
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Solution Overview
Problem
In image sensor molded ball grid array (ImBGA) packaging, issues such as mold flash, foreign matter, scratches, and interface peel-off can occur due to air expansion during thermal processes, affecting the reliability of the packaging process.
Innovation Solution
An image sensor package design incorporating a transparent cover with an inclined or stepped surface, where a mold layer covers the substrate, image sensor, adhesive film, and partial transparent cover surface, with the mold layer's top surface positioned lower than the transparent cover's top surface to enhance contact and prevent peel-off and flash formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional molding process is used in ImBGA packaging, then the packaging can be completed, but mold flash, foreign matter, scratches, and interface peel-off may occur during the process
Solution Approach 1:
The patent applies preliminary action by forming a protrusion on the transparent cover before the molding process, and positioning a mold recess to receive it. This pre-arranged mechanical interlocking structure prevents mold flash and interface peel-off during the subsequent molding and thermal processes, addressing quality issues before they occur.
Solution Approach 2:
The patent applies local quality by creating a specific protrusion structure at the interface between the transparent cover and mold layer, rather than relying on uniform bonding across the entire surface. This localized mechanical interlocking feature concentrates the bonding strength where it is most needed to prevent peel-off and flash.
2Ease of operation
If thermal process according to SMT is performed, then the image sensor can be mounted, but interface peel-off may be generated between the glass and the mold due to air expansion
Solution Approach 1:
The patent applies preliminary action by pre-forming the protrusion and mold recess structures before thermal processing. This mechanical interlocking arrangement is established in advance to counteract the air expansion forces that occur during SMT thermal processes, preventing interface peel-off while maintaining ease of mounting.
Solution Approach 2:
The protrusion structure acts as a cushioning mechanism that absorbs and distributes the stress from air expansion during thermal processes. By having this mechanical interlock in place beforehand, the patent cushions against the forces that would otherwise cause interface peel-off during mounting.
3Area of stationary object
If the mold layer covers the entire transparent cover surface, then complete coverage is achieved, but mold flash may be created on the surface of the transparent cover
Solution Approach 1:
The patent applies preliminary action by pre-forming the protrusion on the transparent cover and the corresponding mold recess before the molding process. This allows the mold layer to cover the necessary areas while the protrusion-mold recess interface prevents excess material from forming flash on the transparent cover surface.
Solution Approach 2:
The patent applies segmentation by dividing the mold layer coverage into two distinct zones: a first region that covers the sensor array region and a second region that covers the logic region and pad region. The protrusion structure creates a clear boundary between these zones, allowing complete coverage where needed while preventing flash formation at the edges.
Data Source
AI summary
An image sensor package includes a substrate and an image sensor on the substrate. An adhesive film is on the image sensor. A transparent cover is on the adhesive film. The transparent cover includes a top surface, a first side surface and a second side surface disposed on the first side surface. The second side surface is inclined with respect to an extending direction of a bottom surface of the transparent cover. A mold layer covers an upper surface of the substrate, a side surface of the image sensor, a side surface of the adhesive film, the first side surface of the transparent cover and a partial portion of the second side surface of the transparent cover. A top surface of the mold layer is higher than a lower end of the second side surface and lower than the top surface of the transparent cover.