Semiconductor Cap Isolating Mold Compound Stress
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Solution Overview
Problem
Mold compound used in semiconductor packaging can apply compressive stress to semiconductor devices, degrading the electrical properties of components such as bipolar junction transistors, analog transistors, and bulk acoustic wave devices, leading to potential device failure.
Innovation Solution
A cap is mounted over selected portions of the active surface of the die, excluding mold compound from contact with these sensitive components, and bonded with an adhesive to create an air pocket that prevents stress transmission from the mold compound.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mold compound is used to encapsulate the semiconductor device, then the device is protected and encapsulated, but compressive stress is applied to the device causing electrical property degradation
Solution Approach 1:
The encapsulation structure is segmented into multiple regions: a first region containing the mold compound and a second region containing the stress-isolating material. This segmentation allows the mold compound to provide encapsulation protection while the stress-isolating material region prevents compressive stress from reaching the semiconductor device, thereby resolving the contradiction between protection and stress avoidance.
Solution Approach 2:
A stress-isolating material is introduced as an intermediary between the mold compound and the semiconductor device. This intermediary material absorbs or blocks the compressive stress generated by the mold compound during curing and cooling, preventing the stress from being transmitted to the device while allowing the mold compound to maintain its encapsulation function.
2Reliability
If mold compound contacts the active surface of the die, then complete encapsulation is achieved, but electrical properties of components degrade due to stress
Solution Approach 1:
The encapsulation structure employs local quality differentiation where different regions have different material properties. The first region uses mold compound for general encapsulation, while the second region uses stress-isolating material specifically at locations where stress would affect electrical components. This localized approach maintains complete encapsulation while protecting electrical properties in critical areas.
3Reliability
If the entire active surface is exposed, then all components are protected from stress, but manufacturing complexity increases
Solution Approach 1:
Instead of protecting the entire active surface uniformly, the invention applies stress-isolating material only in the second region where stress would critically affect electrical components. This partial action approach provides sufficient protection for stress-sensitive components while avoiding the unnecessary complexity of completely covering the entire active surface, thereby balancing reliability improvement with manufacturing simplicity.
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
This solution effectively prevents mold compound-induced stress, thereby reducing or eliminating performance degradation and failure of semiconductor devices, enhancing device yield and reliability.
Implementation Method 1
bonded with an adhesive to create an air pocket that prevents stress transmission from the mold compound
Implementation Method 2
During curing and cooling the mold compound shrinks, and as the mold compound shrinks it applies compressive stress to the semiconductor device
Data Source
AI summary
A described example includes: a die with an active surface; a cap mounted over a portion of the active surface of the die; and mold compound covering the cap and covering portions of the die, the cap excluding the mold compound from contact with the portion of the active surface of the die.