Multilayer Polymer Stress Buffer for Semiconductor Packaging
Solution Overview
Problem
Semiconductor device packaging introduces compressive and shear stress due to mold compound shrinkage, which can alter electrical properties of components like bipolar junction transistors and analog-to-digital converters, leading to performance degradation.
Innovation Solution
A multiple layer stress buffer is formed over sensitive components using a first polymer layer with a lower modulus and a second polymer layer with a higher modulus, applied using ink-jet deposition to reduce stress transmission from the mold compound.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mold compound with filler particles is used to encapsulate the semiconductor die, then the packaged semiconductor device is protected and structurally sound, but compressive and shear stress is applied to the die causing performance degradation
Solution Approach 1:
A stress buffer layer is introduced as an intermediary between the mold compound and the semiconductor die. This buffer layer absorbs and distributes the compressive and shear stress generated during mold compound curing, preventing direct transmission of stress to the die. The buffer layer acts as a mediator that protects sensitive components while allowing the mold compound to provide structural protection.
Solution Approach 2:
The stress buffer layer is formed as a composite structure with multiple layers having different mechanical properties. The first layer has a first modulus and the second layer has a second modulus greater than the first modulus, creating a gradient structure that optimally manages stress transmission. This composite approach allows the buffer to provide both mechanical support and stress distribution.
2Strength
If large filler particles are used in the mold compound, then the mold compound provides adequate structural support, but stress concentration increases causing capacitor mismatch and reduced A/D converter precision
Solution Approach 1:
The stress buffer layer serves as a protective intermediary that prevents direct contact between large filler particles and sensitive components such as capacitors in the A/D converter. By distributing the contact pressure from filler particles across the buffer layer, the direct mechanical influence on capacitor geometry is eliminated, maintaining precision.
Solution Approach 2:
The stress buffer layer functions as a flexible protective film that conforms to the die surface and absorbs localized stress concentrations from filler particles. This thin film structure allows the mold compound to maintain structural integrity while the buffer film protects against stress-induced precision degradation.
3Ease of manufacture
If a single layer stress buffer is used, then the structure is simple and easy to manufacture, but stress transmission is not sufficiently reduced
Solution Approach 1:
The stress buffer is divided into multiple layers with different mechanical properties rather than using a single uniform layer. The first layer with a lower modulus provides initial stress distribution, while the second layer with a higher modulus provides additional structural support and stress management. This segmentation allows each layer to be optimized for specific stress management functions.
Solution Approach 2:
The multi-layer structure utilizes changes in material parameters, specifically the modulus of each layer. The first layer has a first modulus and the second layer has a second modulus greater than the first modulus. This parameter variation allows the buffer system to progressively manage stress from the mold compound, with each layer contributing differently to overall stress reduction effectiveness.
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 stress buffer significantly reduces or eliminates performance degradation caused by mold compound stress, maintaining the integrity of sensitive components within semiconductor devices.
Implementation Method 1
The component is covered with a first polymer layer with a first modulus and at least a portion of the first polymer layer is covered by at least one second polymer layer with a second modulus. The second modulus is greater than the first modulus.
Data Source
AI summary
In a described example, a packaged semiconductor device includes: a semiconductor die with a component proximate to a surface of the semiconductor die; the semiconductor die mounted on a substrate. The component is covered with a first polymer layer with a first modulus and at least a portion of the first polymer layer is covered by at least one second polymer layer with a second modulus and the second modulus is greater than the first modulus. The semiconductor die and a portion of the substrate are covered with mold compound.