MOSFET Source Pad Segmentation for Accurate Current Sensing
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Solution Overview
Problem
The accuracy of current semiconductor devices in sensing current flowing through power MOSFETs is compromised due to variations in the bonding position of metal plates, leading to inconsistent current ratios between power MOSFETs and sense MOSFETs, which degrades the reliability of the semiconductor device.
Innovation Solution
A semiconductor device design where a semiconductor chip with a main MOSFET and a sense MOSFET is bonded to a chip mounting portion and sealed in resin, with a conductor plate bonded to a source pad for current output, and a control circuit is used to manage the MOSFETs, ensuring accurate current sensing and control by maintaining the sense MOSFET's source voltage equal to the power MOSFET's source voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a metal plate is bonded to the bonding pad of the semiconductor chip, then large current can be handled, but bonding position displacement causes variation in current ratio between power MOSFET and sense MOSFET
Solution Approach 1:
The source pad is divided into two separate pads: a first source pad for current output and a second source pad for sensing. This segmentation allows the metal plate to be bonded to the first source pad while the second source pad remains unaffected, eliminating the coupling between bonding position variations and sensing accuracy.
Solution Approach 2:
A coupled portion between source wires is introduced as an intermediary element. This coupled portion is positioned to overlap with the metal plate, creating a controlled interaction that compensates for bonding position variations and maintains consistent current ratio between power MOSFET and sense MOSFET.
2Area of moving object
If sense MOSFET area is made smaller than power MOSFET area, then device miniaturization is achieved, but current sensing accuracy may be compromised
Solution Approach 1:
The patent applies different qualities to different regions: the sense MOSFET is minimized in area while the first source pad is optimized for current handling with metal plate bonding, and the second source pad is optimized for sensing. This local differentiation allows each component to perform its function optimally without compromising overall accuracy.
3Ease of manufacture
If bonding position is allowed to vary, then manufacturing flexibility is improved, but current ratio consistency between power MOSFET and sense MOSFET deteriorates
Solution Approach 1:
By segmenting the source pad into two separate pads with distinct functions, the patent allows bonding flexibility on the first source pad while maintaining consistent sensing on the second source pad, thus preserving current ratio consistency despite bonding position variations.
Solution Approach 2:
The coupled portion acts as a mediator that maintains electrical relationship stability between the two source pads, ensuring that current ratio consistency is preserved even when bonding position varies.
Data Source
AI summary
A semiconductor device is improved in reliability. A power MOSFET for switching, and a sense MOSFET for sensing a current flowing in the power MOSFET, which is smaller in area than the power MOSFET, are formed in one semiconductor chip. The semiconductor chip is mounted over a chip mounting portion, and sealed in a resin. To first and second source pads for outputting the current flowing in the power MOSFET, a metal plate is bonded. A third source pad for sensing the source voltage of the power MOSFET is at a position not overlapping the metal plate. A coupled portion between a source wire forming the third pad and another source wire forming the first and second pads is at a position overlapping the metal plate.