Stacked-Die Ambient Light Sensor Package With Separate IR Filter
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Solution Overview
Problem
Existing ambient light sensors in electronic devices face issues with optical mold compounds having high thermal expansion coefficients, which can damage ICs, require costly fillers to match CTE, and attenuate visible light, leading to performance compromises.
Innovation Solution
An integrated filter optical package using an IR-coated glass layer in a stacked die configuration with a non-optical epoxy molding compound, which matches CTE with other components, blocks IR light, and minimizes visible light attenuation, allowing for better stress performance and reduced costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If optical mold compound is used to encapsulate the light sensor, then the light sensor is protected, but the high coefficient of thermal expansion damages the IC and attenuates visible light
Solution Approach 1:
The patent extracts the IR filtering function from the optical mold compound by using a separate IR-transparent epoxy molding compound. This allows the molding compound to provide mechanical protection without the harmful thermal expansion and light attenuation properties of traditional optical mold compounds.
Solution Approach 2:
The patent uses a composite structure combining an IR-transparent epoxy molding compound with a separate IR filter layer. This composite approach allows the molding compound to provide protection while the separate filter layer handles IR blocking, avoiding the trade-offs of using optical mold compound alone.
2Stability of the object's composition
If fillers are added to optical mold compound to match CTE, then thermal expansion is reduced, but manufacturing cost increases and visible light is attenuated
Solution Approach 1:
The patent removes the need for costly fillers by using an IR-transparent epoxy molding compound with inherently low CTE that naturally matches silicon and glass, eliminating the trade-off between CTE matching and manufacturing cost.
Solution Approach 2:
The patent changes the material parameters by selecting an IR-transparent epoxy molding compound with specific CTE properties that match both silicon and glass, achieving thermal stability without requiring additional fillers or compromising visible light transmission.
3Object-affected harmful factors
If IR filter is incorporated into optical mold compound, then IR light is blocked, but visible light transmission is reduced and manufacturing cost increases
Solution Approach 1:
The patent segments the IR filtering function from the molding compound by using a separate IR filter layer. This allows the molding compound to remain transparent to visible light while the separate filter layer blocks IR light, avoiding the trade-off between IR blocking and visible light transmission.
Solution Approach 2:
The patent introduces an IR-transparent epoxy molding compound as an intermediary material that allows visible light to pass through while blocking IR light, eliminating the need to compromise visible light transmission for IR filtering.
4Ease of manufacture
If traditional epoxy molding compound is used, then manufacturing cost is reduced, but IR light reaches the sensor causing inaccurate readings
Solution Approach 1:
The patent extracts the IR filtering capability from expensive optical mold compound and implements it through a separate, cost-effective IR filter layer combined with IR-transparent epoxy molding compound, achieving both low cost and accurate ambient light detection.
Solution Approach 2:
The patent uses a composite structure of IR-transparent epoxy molding compound and IR filter layer that provides both cost effectiveness and accurate IR blocking, improving measurement precision without sacrificing manufacturing advantages.
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 provides improved reliability, reduced costs, and enhanced optical performance by blocking IR light while maintaining visible light transmission, with minimized stress and attenuation, thus ensuring accurate ambient light detection.
Implementation Method 1
A glass infrared (IR) filter is attached to the optical film and embedded in the epoxy molding compound where the exposed surface of the glass filter is exposed to ambient light
Implementation Method 2
An optical film is attached to the light sensitive die and allows visible light to pass through to the light sensitive die
Implementation Method 3
wire bonds, which are also embedded in the epoxy molding compound, electrically connect the light sensitive die to electrical terminations
Data Source
AI summary
An integrated filter optical package including an ambient light sensor that incorporates an infrared (IR) filter in an integrated circuit (IC) stacked-die configuration is provided. The integrated filter optical package incorporates an infrared (IR) coated glass layer to filter out or block IR light while allowing visible (ambient) light to pass through to a light sensitive die having a light sensor. The ambient light sensor detects an amount of visible light that passes through the IR coated glass layer and adjusts a brightness or intensity of a display screen on an electronic device accordingly so that the display screen is readable.