Resin-Molded Flow Sensor Packaging for Crack-Free Chip Positioning
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Solution Overview
Problem
Conventional flow sensors using potting resin to fix semiconductor devices suffer from dimensional accuracy issues due to resin shrinkage and require lengthy curing times, increasing manufacturing costs. Additionally, existing mold-integrated structures struggle with accurate air flow detection and are prone to flash or chip cracks during clamping.
Innovation Solution
The proposed solution involves molding and fixing the semiconductor device with the air flow sensing unit exposed, using a resin mold that surrounds the device without continuous contact with three orthogonal walls. This approach includes using springs or elastic films to absorb dimensional variations of the semiconductor device, preventing flash or chip cracks during clamping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If potting resin is used to fix the semiconductor device, then the device is protected and fixed, but the resin shrinkage causes displacement and dimensional accuracy deteriorates
Solution Approach 1:
The resin sealing structure is divided into multiple independent walls rather than a continuous enclosure. Specifically, three walls orthogonal to the air flow sensing unit side are made non-continuous, allowing the semiconductor device to be segmented from complete resin contact in these directions. This segmentation prevents uniform shrinkage-induced displacement while maintaining protection in other areas.
2Reliability
If potting resin is used to fix the semiconductor device, then the device is protected, but a relatively long curing time is required and manufacturing costs increase
Solution Approach 1:
The resin sealing is segmented into multiple walls with gaps, allowing heat to penetrate from multiple directions simultaneously. This multi-directional heat transfer significantly reduces the curing time compared to conventional potting methods where heat must penetrate through a continuous thick resin layer from limited surfaces.
3Manufacturing precision
If the semiconductor device is clamped via mold during molding, then positioning accuracy is improved, but dimensional variation causes flash or chip crack
Solution Approach 1:
An elastic film is introduced as a flexible intermediate layer between the mold clamping surface and the semiconductor device. This elastic film can deform to accommodate dimensional variations in the semiconductor device during clamping, preventing stress concentration that would cause flash or chip cracks, while still providing sufficient clamping force for positioning accuracy.
Solution Approach 2:
The elastic film serves as a pre-prepared cushioning element that absorbs dimensional variations before they can cause damage. By placing this compliant layer in advance between the rigid mold and the semiconductor device, the system is buffered against the harmful effects of dimensional inconsistency during the clamping process.
4Ease of manufacture
If mold integrated structure is used, then air flow sensing unit and lead frame are molded integrally, but the area not surrounded by resin or lead frame allows air to flow into the diaphragm and detection accuracy decreases
Solution Approach 1:
The resin sealing walls are segmented to create a specific enclosure pattern that blocks air flow paths to the diaphragm. By strategically making three walls orthogonal to the air flow sensing unit side non-continuous while maintaining enclosure in other directions, the design prevents air from reaching the diaphragm through the molding structure itself, ensuring detection accuracy.
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 method improves the positioning accuracy of the semiconductor device and the board, reduces resin curing time through heat transfer, and prevents air from flowing into the diaphragm, thereby enhancing the accuracy of air flow detection while minimizing manufacturing costs.
Implementation Method 1
to shorten the resin curing time by the heat transfer from the mold to the resin
Implementation Method 2
capable of absorbing the dimensional variation of the semiconductor device via the deformation of springs or deformation of an elastic film
Data Source
Figure 1A~1C
Figure 2A~2C
Figure 3
AI summary
The invention provides a flow sensor structure for sealing the surface of an electric control circuit and a part of a semiconductor device via a manufacturing method capable of preventing occurrence of flash or chip crack when clamping the semiconductor device via a mold. The invention provides a flow sensor structure comprising a semiconductor device having an air flow sensing unit and a diaphragm formed thereto, and a lead frame having an electric control circuit for controlling the semiconductor device disposed thereto, wherein a surface of the electric control circuit and a part of a surface of the semiconductor device is covered with resin while having the air flow sensing unit portion exposed. The invention further provides flow sensor structure in which surfaces of a resin mold, a board or a pre-mold component surrounding the semiconductor device are continuously not in contact with three walls of the semiconductor device orthogonal to a side on which the air flow sensing unit portion is disposed, and a manufacturing method for absorbing the dimensional variation of the semiconductor device by the deformation of an elastic film in the thickness direction.