Magnetic Sensor Lead Frame Projecting Portion Adhesion
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Solution Overview
Problem
Magnetic sensors face issues with crack occurrence between the resin package and the lead frame during manufacturing, leading to displacement and changes in sensor output due to the flow of resin, which existing methods fail to address effectively.
Innovation Solution
Incorporating a projecting portion on the lead frame with a surface material having a higher ionization tendency than silver, such as copper, to enhance adhesivity with the epoxy-based resin package, preventing crack formation by improving oxidation and adhesion properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If resin is poured into molding tool to seal semiconductor element, then sealing is achieved, but displacement of lead frame and semiconductor element occurs due to resin flow
Solution Approach 1:
The projecting portion extending from the die pad is designed to be sandwiched and supported by the molding tool during the resin pouring process. This projecting portion acts as a preliminary restraint that prevents displacement of the lead frame and semiconductor element caused by resin flow pressure, thereby maintaining position accuracy while achieving proper sealing.
2Stability of the object's composition
If projecting portion is added to prevent displacement of lead frame, then position stability is improved, but crack occurrence between package and lead frame increases
Solution Approach 1:
The patent applies copper plating (or leaves unplated) specifically on the projecting portion that contacts the package, while other portions may have different plating. This local material differentiation ensures good adhesivity at the package interface, preventing cracks while maintaining the position stability function of the projecting portion.
Solution Approach 2:
The lead frame employs a composite plating structure with different materials (silver and copper) on different portions. The copper-plated or unplated projecting portion provides good adhesivity with the epoxy-based resin package, preventing crack occurrence, while the silver-plated external connection pad provides good adhesivity with bonding wire.
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 configuration effectively prevents crack occurrence between the package and the lead frame, stabilizing the stress applied to the semiconductor element and maintaining consistent sensor output over time.
Implementation Method 1
material having a higher ionization tendency than an ionization tendency of silver is more likely to be oxidized than silver
Implementation Method 2
The epoxy resin which configures the package employs material having a good adhesivity with oxygen
Data Source
AI summary
A magnetic sensor includes a semiconductor element, a lead frame, a bonding wire, and a package. The lead frame includes a die pad to which the semiconductor element is attached and an external connection lead. The bonding wire connects the external connection lead with the semiconductor element. The package seals the semiconductor element, the die pad, the external connection pad, and the bonding wire. The package is made of epoxy-based resin. The lead frame further includes a projecting portion extending from the die pad, the projecting portion is exposed from the package at a position different from a position of the external connection lead, and a partial surface of the projecting portion which contacts with the package is made of material having a higher ionization tendency than an ionization tendency of silver.