Image Sensor Package Adhesive Sealing to Prevent Reflow Cracking
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Solution Overview
Problem
Thermal cycling during solder reflow operations can cause damage to image sensor integrated circuit packages due to expansion of gases within hermetically sealed cavities, leading to delamination or cracking of optical elements.
Innovation Solution
A transparent adhesive film layer is used to mount a glass optical element over the optical sensing circuit, minimizing or eliminating air cavities and providing a consistent, hermetic seal around the optical element and microlenses, thereby preventing delamination and cracking during thermal cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hermetically sealed cavity is formed under the optical element, then the optical element is protected from environmental factors, but thermal cycling causes gas expansion leading to delamination or cracking
Solution Approach 1:
The patent removes the hermetically sealed cavity from the package structure. Instead of sealing the optical element over a cavity containing photosensitive elements, the adhesive extends continuously to cover the optical element and seal against the peripheral region, eliminating the trapped gas volume that causes thermal expansion damage.
Solution Approach 2:
Rather than creating a sealed cavity and accepting thermal expansion risks, the invention inverts the approach by using a continuous adhesive layer that prevents cavity formation altogether. The adhesive serves dual functions: mounting the optical element and providing hermetic sealing without trapping gas.
2Ease of manufacture
If adhesive is applied only peripherally around the optical element, then the optical element can be mounted, but hermetic sealing is compromised allowing moisture ingress
Solution Approach 1:
The patent combines the mounting function and hermetic sealing function into a single continuous adhesive layer. The adhesive extends from the peripheral mounting region across the entire surface to cover the optical element, merging what would traditionally be separate functions performed by different adhesive applications.
Solution Approach 2:
The continuous adhesive layer performs multiple functions simultaneously: it mounts the optical element to the substrate, provides hermetic sealing against moisture and contaminants, and eliminates the need for separate sealing structures. This multi-functional approach simplifies the overall package design.
3Manufacturing precision
If the adhesive layer is thin, then the mounting is precise, but it may not provide sufficient sealing coverage over the optical element
Solution Approach 1:
The patent extends the adhesive coverage in the lateral dimension rather than increasing thickness. The continuous adhesive layer spreads across the entire surface area to provide comprehensive sealing coverage, maintaining thin profile while ensuring complete protection through extended areal coverage rather than increased vertical thickness.
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
The solution effectively prevents delamination and cracking of optical elements during solder reflow operations by minimizing air cavities, ensuring the integrity of the package and maintaining a hermetic seal.
Implementation Method 1
the mounting of the glass optical element die is made by a film layer of transparent adhesive which extends to cover the optical sensing circuit
Implementation Method 2
an encapsulation material body which encapsulates the glass optical element die and the optical integrated circuit die
Data Source
AI summary
An integrated circuit package includes a support substrate having a front side and a back side and an optical integrated circuit die having a back side mounted to the front side of the support substrate and having a front side with an optical sensing circuit. A glass optical element die has a back side mounted to the front side of the optical integrated circuit die over the optical sensing circuit. The mounting of the glass optical element die is made by a layer of transparent adhesive which extends to the cover the optical sensing circuit and a portion of the front side of the optical integrated circuit die peripherally surrounding the optical sensing circuit. An encapsulation material body encapsulates the glass optical element die and the optical integrated circuit die.