Thermal Flowmeter Diaphragm Protection During Mold Pressing
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Solution Overview
Problem
The existing thermal flow meter technologies do not adequately address the vulnerability of the diaphragm structural portion during mold pressing, which can lead to damage and affect measurement accuracy due to improper arrangement of pressing forces.
Innovation Solution
The resin portion is molded in the vicinity of the diaphragm structural portion using a mold such that the mold pressing region does not overlap with the diaphragm structural portion, ensuring the pressing force is applied outside this vulnerable area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the mold is pressed against the upper surface of the semiconductor chip to prevent the flow detection portion from being covered with resin, then the flow detection portion is protected from resin coverage, but the diaphragm structural portion becomes vulnerable to damage due to bending force
Solution Approach 1:
The pressing operation is segmented into two distinct phases: first, the insert presses the flow detection portion to prevent resin coverage; second, the upper mold presses the lead frame to secure components. This segmentation ensures that the diaphragm structural portion is not subjected to pressing force during the critical sealing phase, resolving the contradiction between protecting the flow detection portion and preserving the integrity of the diaphragm structure.
Solution Approach 2:
The insert performs the preliminary action of pressing the flow detection portion before the upper mold applies pressure to the lead frame. By completing the resin prevention action first, the subsequent pressing operation can be applied without risking damage to the diaphragm structural portion, as the critical sealing has already been achieved.
2Manufacturing precision
If the pressing force is applied to the inside of the diaphragm structural portion, then the flow detection portion is effectively sealed, but the diaphragm structural portion may be damaged due to concentrated stress
Solution Approach 1:
The pressing function is segmented between two tools: the insert handles the precise sealing of the flow detection portion by pressing at the optimal location, while the upper mold applies broader pressure to the lead frame. This segmentation allows the insert to achieve manufacturing precision without concentrating excessive stress on the diaphragm structural portion, as the overall pressing load is distributed by the upper mold.
Solution Approach 2:
The insert acts as an intermediary tool that performs the delicate sealing operation on the flow detection portion without directly transmitting large pressing forces to the diaphragm structural portion. By using the insert as a mediator for the precise sealing action, the stress concentration on the diaphragm is minimized while still achieving effective sealing.
3Productivity
If the mold pressing region overlaps with the diaphragm structural portion, then the pressing force is efficiently distributed, but the height and size of the structural portion around the flow detection portion become inconsistent
Solution Approach 1:
The pressing operation is segmented into two phases with distinct pressing regions: first, the insert presses the flow detection portion to prevent resin coverage; second, the upper mold presses the lead frame. This segmentation ensures that the diaphragm structural portion is not subjected to pressing force during the critical sealing phase, resolving the contradiction between protecting the flow detection portion and preserving the integrity of the diaphragm structure.
Solution Approach 2:
Different parts of the assembly are pressed at different times and with different forces: the flow detection portion is pressed locally by the insert to achieve precise sealing, while the lead frame is pressed by the upper mold for general securing. This local quality approach ensures that the diaphragm structural portion maintains consistent dimensions while the flow detection portion is effectively sealed.
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
An objective of the present invention is, in a thermal flow meter having a structure including a resin portion formed in the vicinity of a diaphragm structural portion using a mold, to prevent destruction of the diaphragm structural portion at the time of pressing the mold, in a method of manufacturing the thermal flow meter, including: supporting a gas flow measurement element 200 on support members 102b and 111, the gas flow measurement element 200 including a cavity portion 202 surrounded by a substrate inclined portion 202a inclined to a substrate surface, a diaphragm 201 that covers the cavity portion, and an electrical resistive element formed in the diaphragm 201; and covering the gas flow measurement element 200 and the support members 102b and 111 with the resin portion 104 formed with the mold, to set the mold 14 such that an acting portion of pressure force by the mold that molds the resin portion 104 is positioned outside the substrate inclined portion 202a in the entire periphery of the diaphragm 201.