Semiconductor Channels Filled With Polymer for CTE Mismatch Relief
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Solution Overview
Problem
Wafer Level Chip Scale Packages (WLCSPs) face reliability issues due to mismatched coefficients of thermal expansion (CTE) between the semiconductor die and the support substrate, leading to potential electrical shorting and package failure, especially during thermal cycling, which limits the size and functionality of larger devices.
Innovation Solution
Incorporating channels filled with an elastic material, such as a polymer, within the semiconductor device to absorb thermal expansion stresses and strains, thereby matching the CTE of the semiconductor device to the support substrate, reducing the likelihood of cracking and separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the size of the WLCSP is increased, then more electrical connections and functionality can be achieved, but the mismatch in CTE between the WLCSP and substrate causes earlier cracking and separation
Solution Approach 1:
The patent applies local quality by introducing a polymer layer specifically at the interface between the WLCSP and substrate, rather than uniformly throughout the entire device. This localized polymer insertion targets the specific region where CTE mismatch causes stress, allowing the rest of the device to maintain its original properties while the interface region gains enhanced stress-absorption capabilities.
Solution Approach 2:
The patent creates a composite structure by combining the rigid WLCSP and substrate with a flexible polymer layer at their interface. This composite approach integrates materials with different mechanical properties - the rigid semiconductor and substrate provide structural integrity and electrical functionality, while the soft polymer provides stress compliance and CTE matching, resulting in a hybrid structure that leverages the advantages of both rigid and flexible materials.
2Ease of operation
If the WLCSP is coupled to the substrate with solder, then electrical connections are established, but thermal cycling causes expansion mismatch leading to cracking and separation
Solution Approach 1:
The patent applies beforehand cushioning by placing the polymer layer between the WLCSP and substrate before final assembly and thermal cycling occurs. This pre-positioned polymer cushion is designed to absorb and distribute the thermal expansion stresses that will inevitably occur during operation, preventing cracking and separation before they can happen during thermal cycling.
Solution Approach 2:
The polymer layer serves as an intermediary between the WLCSP and substrate, mediating the mechanical and thermal interaction between these two components. Rather than allowing direct contact between the rigid solder joints and the mismatched CTE materials, the polymer acts as a compliant intermediate layer that absorbs expansion differences, reduces stress transmission, and maintains electrical connectivity while protecting against thermal fatigue.
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 enhances the reliability and useful life of the semiconductor device by reducing thermal expansion-induced stress, allowing for the creation of larger devices with additional electrical connections and improved functionality.
Implementation Method 1
mismatch in the coefficient of thermal expansion ('CTE') between the WLCSP and the support substrate... the increase in temperature during operation causes expansion of the WLCSP and the substrate
Implementation Method 2
Incorporating channels filled with an elastic material, such as a polymer, within the semiconductor device to absorb thermal expansion stresses and strains
Data Source
AI summary
A semiconductor device having a channel between active sections or portions of the device is disclosed. An elastic material, such as dielectric or a polymer, is deposited into the channel and cured to increase flexibility and thermal expansion properties of the semiconductor device. The elastic material reduces the thermal and mechanical mismatch between the semiconductor device and the substrate to which the semiconductor device is coupled in downstream processing to improve reliability. The semiconductor device may also include a plurality of channels formed transverse with respect to each other. Some of the channels extend all the way through the semiconductor device, while other channels extend only partially through the semiconductor device.