Surface Mount Metal Oxide Varistor with Bent Leads for Automated Assembly
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Solution Overview
Problem
Conventional metal oxide varistor (MOV) devices are incompatible with high-speed, automated assembly processes due to the need for soldering wire leads on both sides of a printed circuit board, have a large form factor, and fail to withstand high operating temperatures necessary for meeting the AEC-Q200 stress resistance standard.
Innovation Solution
A surface mount metal oxide varistor device with a plastic device body and 'L'-shaped lead frame portions that are bent into flat abutment with the device body, allowing for high-speed pick and place installation and compact form factor, and utilizing a heat-resistant polymer body to withstand temperatures up to 125 degrees Celsius.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wire leads are inserted into through holes and soldered on both sides of PCB, then reliable electrical connection is achieved, but installation speed decreases and automation becomes difficult
Solution Approach 1:
The device separates the electrical connection function into two distinct parts: the lead frame portions that make contact with PCB pads on one side only, and the bent leads that provide mechanical support and additional contact points. This segmentation allows the device to be mounted using standard surface mount technology without requiring through-hole penetration, enabling automated pick-and-place installation while maintaining reliable electrical connection through the lead frame contact tabs.
Solution Approach 2:
The leads are bent into a curved configuration that extends from the MOV chip, through the device body, and makes contact with the PCB from the opposite side. This three-dimensional lead arrangement transforms the traditional two-dimensional PCB mounting problem into a three-dimensional solution, allowing electrical connections to be established without penetrating the PCB thickness, thereby enabling surface mount installation and automated assembly.
2Reliability
If conventional MOV device structure is used, then electrical protection function is provided, but device height increases and form factor becomes large
Solution Approach 1:
The lead frame portions and contact tabs are nested within the device body housing, with the bent leads tucked inside the device structure. This nesting arrangement minimizes the external dimensions of the device, particularly the height, while maintaining all necessary electrical connection points and protective functions. The compact internal arrangement allows the device to fit within smaller PCB real estate.
Solution Approach 2:
Instead of extending leads vertically outward from the MOV chip, the leads are bent into a configuration that routes them through the device body and makes contact with the PCB from the opposite side. This dimensional reconfiguration reduces the device's height profile while maintaining electrical connectivity, transforming a vertical extension problem into a through-body routing solution.
3Object-affected harmful factors
If epoxy coating is used for protection, then environmental protection is provided, but temperature resistance decreases and AEC-Q200 standard cannot be met
Solution Approach 1:
The device employs a composite protective structure combining a molded device body made from temperature-resistant materials with integrated lead frame portions. This composite construction replaces the epoxy coating with a thermally stable housing material that can withstand high operating temperatures while providing equivalent or superior environmental protection against moisture and contaminants, enabling compliance with the AEC-Q200 automotive standard.
Solution Approach 2:
The invention removes the epoxy coating from the protective function and extracts this role to the device body housing. By separating the protective function from the bonding material, the design can use thermally stable molding materials for the housing while eliminating the temperature-limited epoxy layer, thereby achieving both environmental protection and high-temperature resistance required for automotive applications.
Data Source
AI summary
A metal oxide varistor (MOV) device including a MOV chip having first and second electrodes disposed on opposing side thereof, a first lead frame portion including a first contact tab electrically connected to the first electrode and a first lead contiguous with the first contact tab and extending away from the MOV chip, a second lead frame portion including a second contact tab electrically connected to the second electrode and a second lead contiguous with the second contact tab and extending away from the MOV chip, and a device body encasing the MOV chip, the first contact tab, the second contact tab, and portions of the first and second leads, wherein the first and second leads extend out of the device body and are bent into flat abutment with a bottom surface of the device body.