Stem Protrusion for Flexible Circuit Signal Resonance
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Solution Overview
Problem
Conventional stems with semiconductor elements mounted on flexible printed circuits (FPCs) face issues due to deformation caused by tensional forces, leading to uneven gaps and high frequency signal resonance between the stem and the FPC, which deteriorates high frequency characteristics.
Innovation Solution
The stem design includes a cylindrical body with a protrusion that surrounds the outer circumferential surface of the high frequency signal lead, fitted into a through hole of the stem body, and fixed with a low dielectric constant fixing member, preventing signal leakage and resonance by bonding the protrusion to the grounding pattern of the FPC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the FPC is made flexible to enable mounting, then flexibility and electrical connection are improved, but deformation and gap formation occur causing high frequency signal resonance
Solution Approach 1:
A protrusion is introduced as an intermediary structure between the stem body and the FPC. This protrusion makes contact with the FPC surface to prevent gap formation, thereby eliminating the harmful effect of signal resonance while preserving the flexibility benefit
Solution Approach 2:
The stem structure is segmented into multiple functional parts: the stem body for mounting, the protrusion for gap prevention, and the lead for electrical connection. This segmentation allows each part to address specific issues independently
2Reliability
If the inner diameter of the cylindrical body is increased to prevent signal leakage, then signal resonance is reduced, but the overall size of the stem increases
Solution Approach 1:
Instead of increasing the inner diameter in the radial dimension, the solution introduces a protrusion in the axial dimension (extending downward from the stem body). This dimensional shift allows gap prevention without increasing the stem's overall footprint or volume
Data Source
AI summary
A stem has a stem body that has a first surface to be placed on a flexible substrate, a second surface opposite to the first surface, and a through hole passing through the first surface and the second surface, a cylindrical body that is fitted into the through hole of the stem body, and a lead that is inserted into the cylindrical body and fixed to the cylindrical body with a fixing member and that has an end portion protruding from the first surface of the stem body. The cylindrical body has a protrusion that protrudes toward the flexible substrate from the first surface of the stem body and surrounds an outer circumferential surface of the end portion of the lead.