Double-Sided Capacitor Sensor Package for EMC and Thickness
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Solution Overview
Problem
Magnetic speed sensors face challenges in meeting electromagnetic compatibility (EMC) and electrostatic discharge (ESD) performance requirements while maintaining a compact size and shape, particularly due to the limitations imposed by the thickness of capacitors attached to the same side of the lead frame, which affects the airgap between the sensor and the magnetic encoder gear wheel.
Innovation Solution
A double-sided capacitor attach configuration on the same leads allows for the implementation of physically smaller capacitors with sufficient capacitance, providing high capacitance without increasing the thickness of the sensor package, thereby enabling smaller capacitors that meet EMC/ESD requirements and allowing for both straight and folded sensing configurations without a separate capacitor compartment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If capacitors are attached to the same side of the lead frame, then the sensor package can be manufactured with a simple structure, but the package thickness increases due to capacitor thickness
Solution Approach 1:
The patent transitions from single-sided capacitor attachment to double-sided attachment, utilizing the third dimension (z-axis) by attaching capacitors to both the front and back sides of the lead frame. This dimensional change allows the total capacitance to be achieved with thinner individual capacitors, thereby reducing the overall package thickness while maintaining structural simplicity.
2Reliability
If larger capacitors are used to meet EMC/ESD requirements, then electromagnetic compatibility performance improves, but the sensor package size increases
Solution Approach 1:
The patent segments the total capacitance requirement into multiple smaller capacitor units distributed across both sides of the lead frame. Instead of using one or two large capacitors, multiple smaller capacitors (e.g., four capacitors of 100nF each) are attached, with some on the front side and some on the back side. This segmentation achieves the required total capacitance (e.g., 400nF) for EMC/ESD performance while keeping individual capacitor sizes small, thus reducing the overall package volume.
3Volume of moving object
If capacitors are placed close to the sensor to maintain compact size, then package size is reduced, but output pulse smoothing occurs
Solution Approach 1:
By utilizing double-sided attachment, the patent can position capacitors on both the front and back sides of the lead frame, effectively distributing them in three-dimensional space. This allows capacitors to be placed close to the sensor mounting area without being stacked vertically, maintaining compact package size while preserving signal integrity by avoiding excessive capacitance concentration that would cause pulse smoothing.
Data Source
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AI summary
A sensor package includes a lead frame, a sensor component, and first and second capacitors. The lead frame has a sensor mounting area and first and second leads. The sensor mounting area, the first lead, and the second lead are characterized by a first side and a second side. The sensor component is attached to the first side of the sensor mounting area of the lead frame. The first capacitor is interconnected between the first and second leads, with the first capacitor being attached to the first side of each of the leads. The second capacitor is interconnected between the first and second leads, with the second capacitor being attached to the second side of each of the leads. The first and second capacitors are arranged in stacked relation with one another on opposing sides of the leads, and the sensor component and capacitors are located in a single housing.