Semiconductor Package Underfill for Sensor Coil Void Elimination
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Solution Overview
Problem
Current semiconductor packages with mold compound filling gaps between sensor coils and semiconductor dies often experience electrical shorts due to voids formed during the transfer molding process, leading to unexpected failure modes, particularly at the center of the sensor coil.
Innovation Solution
Incorporating a dielectric underfill within the gap between the sensor coil and the semiconductor die before molding, allowing capillary flow to fill the gap completely without trapping gas, thereby eliminating voids and enhancing electrical isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mold compound is used to fill the gap between sensor coil and semiconductor die, then electrical isolation is provided, but voids are formed during transfer molding causing electrical shorts
Solution Approach 1:
The patent applies underfill material to the sensor coil before mounting the semiconductor die, pre-filling the gap area. This preliminary action ensures that when mold compound is later applied, there is no void formation because the gap is already filled with underfill material that displaces air before molding occurs.
Solution Approach 2:
The underfill material serves as an intermediary substance between the sensor coil and semiconductor die. It performs the critical function of displacing air from the gap during assembly, preventing void formation. The underfill acts as a mediator that enables complete gap filling without trapping air bubbles during the molding process.
2Measurement precision
If spacing gap between sensor coil and sensor is reduced to improve sensitivity, then sensor sensitivity increases, but electrical isolation becomes more difficult to maintain
Solution Approach 1:
The patent applies different materials with different properties to different regions: underfill material is applied locally to the gap area between sensor coil and die, while mold compound covers the remaining areas. This local differentiation allows the gap region to have enhanced electrical isolation properties through the underfill, enabling smaller spacing gaps without compromising overall electrical isolation.
Solution Approach 2:
The patent uses a composite approach with two different dielectric materials: underfill material in the critical gap region and mold compound for overall encapsulation. This composite material strategy provides superior electrical isolation in the spacing gap area, allowing reduced gap dimensions while maintaining isolation integrity.
3Reliability
If underfill is added to fill the gap completely, then void formation is eliminated, but device complexity increases
Solution Approach 1:
The patent merges the gap-filling function with the existing underfill process used in semiconductor packaging. By applying underfill material to the sensor coil before die mounting, the gap filling is integrated into the standard assembly sequence, eliminating void formation without requiring a completely new process or additional complex steps.
Solution Approach 2:
The underfill material is applied in a manner that allows it to self-level and self-fill the gap area through capillary action or controlled dispensing. This self-service approach eliminates voids without requiring additional complex filling operations or tools, maintaining process simplicity while achieving complete gap filling.
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 approach significantly reduces the occurrence of electrical shorts, shifting primary failure modes to the edges of the sensor coil where electric field concentrations are highest, thereby improving the reliability and performance of the semiconductor package.
Implementation Method 1
dispensing a dielectric underfill to fill a gap between the sensor coil and the semiconductor die
Data Source
AI summary
A semiconductor package includes a leadframe including a sensor coil between sensor coil leads and further including a plurality of die leads physically and electrically separated from the sensor coil, and a semiconductor die over the leadframe with die contacts electrically connected to the die leads. The semiconductor die includes a sensor operable to detect magnetic fields created by electrical current through the sensor coil, the semiconductor die operable to output a signal representative of the detected magnetic fields via the die leads. The semiconductor package further includes a dielectric underfill filling a gap between the sensor coil and the semiconductor die, and a dielectric mold compound covering the sensor coil and the dielectric underfill and at least partially covering the semiconductor die and the die leads.