Permeable Gel Package Bubble Restriction
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Solution Overview
Problem
Moisture ingress into cavity-type electronic devices with permeable gel-filled packages can lead to reliability and accuracy issues due to bubble formation at elevated temperatures, causing mechanical deformation and potential failure of sensor measurements.
Innovation Solution
Incorporating a bubble restrictor material with a high modulus of elasticity over the cavity bottom surface, which is permeable to moisture, to prevent bubble formation at the interface with the gel, ensuring that bubbles do not migrate to the exposed surface and maintain the air gap necessary for accurate pressure sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a permeable gel material is used to protect the sensor IC from moisture, then the sensor is protected from moisture ingress, but bubbles form at the gel-cavity interface during elevated temperature processes, causing mechanical deformation and measurement inaccuracy
Solution Approach 1:
The cavity bottom surface is prepared in advance by applying a moisture barrier coating and/or performing plasma treatment before introducing the gel material. This preliminary preparation creates a surface that repels moisture and prevents bubble nucleation sites, so when the gel is later introduced and moisture is present during reflow, the bubbles cannot form at the interface because the surface has already been conditioned to prevent moisture accumulation.
Solution Approach 2:
An intermediary layer or surface treatment is introduced between the gel material and the cavity bottom surface. This intermediary layer acts as a mediator that allows the gel to maintain its moisture-permeable protective function while simultaneously preventing the moisture-gel interaction that leads to bubble formation. The intermediary layer decouples the conflicting requirements of moisture permeability and bubble prevention.
2Reliability
If the gel quantity is increased to ensure complete coverage, then the sensor IC is better protected, but the gel surface deforms more significantly under bubble pressure, potentially contacting the package lid and eliminating the air gap
Solution Approach 1:
The cavity bottom surface is pre-treated with a moisture barrier coating or plasma treatment before the gel is introduced. This preliminary action prevents moisture from accumulating at the interface during subsequent heating processes, thereby preventing bubble formation that would otherwise deform the gel surface and compromise the air gap, allowing the gel to maintain its protective coverage without deformation.
Solution Approach 2:
A surface treatment layer serves as an intermediary between the gel and the cavity bottom, preventing the direct moisture-gel interaction that causes bubble formation and surface deformation. This intermediary allows the gel to maintain its shape and protective function even when in direct contact with the cavity bottom surface.
3Reliability
If bubbles migrate to the sensor IC surface, then mechanical offsets are introduced causing measurement inaccuracy, but the permeable gel allows moisture to reach the sensor interface where bubbles can form
Solution Approach 1:
The cavity bottom surface is pre-conditioned with a moisture barrier coating or plasma treatment before the gel is introduced. This preliminary action creates a surface that prevents moisture accumulation and bubble nucleation, so even though the gel remains permeable to moisture for sensor operation, bubbles cannot form at the interface to migrate to the sensor and cause measurement errors.
Solution Approach 2:
A surface treatment layer acts as an intermediary that decouples the moisture permeability function from the bubble formation problem. The intermediary allows moisture to pass through to the sensor for normal operation while simultaneously preventing the moisture-gel interface conditions that lead to bubble formation and migration to the sensor surface.
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 restricts bubble formation and migration, maintaining the integrity of the air gap and preventing mechanical offsets, thus enhancing the reliability and accuracy of sensor measurements in environmental sensors.
Implementation Method 1
a first material having a relatively high, first modulus of elasticity... the first modulus of elasticity is sufficiently high so that the first material functions as a restrictor of bubble formation
Implementation Method 2
moisture may diffuse through the relatively-permeable, protective gel and lodge on the surface of the package cavity
Implementation Method 3
at elevated temperatures, such as during a reflow process, the moisture may transition to a gaseous state, producing bubbles at the interface between the gel and the package cavity surface
Data Source
AI summary
Embodiments include devices and methods of their manufacture. A device embodiment includes a package housing, at least one electronic circuit (e.g., a sensor circuit), a first material, and a second material. The package housing includes a cavity that is partially defined by a cavity bottom surface, and the cavity bottom surface includes a mounting area and a non-mounting area. The at least one electronic circuit is attached to the cavity bottom surface over the mounting area. The first material has a relatively high, first modulus of elasticity, and covers the non-mounting area. The second material has a relatively low, second modulus of elasticity, and is disposed over the first material within the cavity.