In-Vehicle Module Sn-Based Solder Layer Oxidation Resistance
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Solution Overview
Problem
In-vehicle electronic modules face challenges in maintaining stable long-term electrical continuity and resisting harsh environments, such as high temperatures and humidity, without using noble metals, while also requiring cost reduction and high reliability, especially in the engine compartment.
Innovation Solution
The use of a Sn-based solder layer containing Ag-Sn intermetallic compounds on the connection terminal, with a thickness of 3 µm or more, combined with a Cu wiring and Cu-Sn reaction layer, and a protective coating of thermally and chemically stable liquid oil, to ensure low contact resistance and reliability under severe conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thin plating film of Sn or Sn-based lead-free solder with a thickness of 0.5 µm to 2.0 µm is used, then cost is reduced and environmental preservation is improved, but contact electrical resistance increases under high-temperature exposure and temperature cycling
Solution Approach 1:
The patent changes the critical parameter of plating thickness from the conventional 0.5-2.0 µm range to 3 µm or more. This parameter change ensures that the Sn-based solder layer maintains sufficient thickness to prevent excessive contact resistance under high-temperature exposure and temperature cycling, while still avoiding the need for expensive noble metal plating processes
Solution Approach 2:
The patent employs a composite material structure consisting of a Cu wiring layer, a Cu-Sn reaction layer, and an outermost Sn-based solder layer containing Ag-Sn intermetallic compounds. This composite structure combines the advantages of different materials: Cu provides electrical conductivity, the Cu-Sn reaction layer provides mechanical bonding, and the Sn-based solder layer with Ag-Sn intermetallic compounds provides oxidation resistance and low contact resistance under severe environmental conditions
2Reliability
If noble metals such as Ni/Au plating are used on connector terminals, then contact resistance is reduced and reliability is improved, but manufacturing cost increases significantly
Solution Approach 1:
The patent replaces expensive noble metals (Ni/Au plating) with a cheaper Sn-based solder layer that forms a durable surface structure through the formation of Ag-Sn intermetallic compounds. This substitution maintains low contact resistance and reliability under severe environmental conditions while significantly reducing manufacturing costs by eliminating the need for costly noble metal plating processes
Solution Approach 2:
The patent changes the material composition parameter from noble metals to Sn-based solder containing Ag-Sn intermetallic compounds. This material substitution, combined with increased thickness to 3 µm or more, achieves comparable or superior performance in maintaining low contact resistance under high-temperature exposure and temperature cycling without the high cost of noble metals
3Adaptability or versatility
If the connector is used in harsh environments such as engine compartment with high temperature and humidity, then functional requirements are met, but contact resistance increases and reliability deteriorates over time
Solution Approach 1:
The patent employs a composite material structure with Cu wiring, Cu-Sn reaction layer, and an outermost Sn-based solder layer containing Ag-Sn intermetallic compounds. This composite structure provides excellent environmental resistance: the Sn-based solder layer and Ag-Sn intermetallic compounds resist oxidation and corrosion in high-temperature and high-humidity conditions, while maintaining low contact resistance and electrical continuity over time
Solution Approach 2:
The patent performs preliminary action by forming a thick Sn-based solder layer with Ag-Sn intermetallic compounds on the connection terminal surface before the connector is subjected to harsh environmental conditions. This pre-formed protective layer prevents oxidation and corrosion during subsequent high-temperature exposure and temperature cycling, ensuring long-term reliability and stable electrical continuity
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 solution provides a low-cost, high-reliability electrical connection that maintains low contact resistance and resistance to mechanical vibrations and temperature cycles, even in harsh environments, by forming a hard Ag-Sn intermetallic compound at the contact interface and using a protective oil to prevent oxidation.
Implementation Method 1
an outermost surface of a connection terminal inserted into a mating connector to obtain electrical continuity includes a Sn-based solder layer containing an Ag-Sn intermetallic compound
Implementation Method 2
a protective coating of thermally and chemically stable liquid oil, to ensure low contact resistance and reliability under severe conditions
Data Source
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AI summary
There is a problem that contact resistance increases due to formation of an oxide film on a contact interface or biting of abrasion powder caused by micro-sliding when a contact connecting portion of a connection terminal including non-noble metal members is exposed to high temperature environment or a repetitious temperature cycle. An object of the present invention is to provide an in-vehicle electronic module that has connection reliability equivalent to that of the conventional in-vehicle electronic module even when being placed in the environment of an engine compartment and can achieve cost reduction by reducing the number of parts and assembly steps. The electronic module includes a mounting board having a circuit board on which an electronic component is mounted, and a case member for accommodating and protecting the mounting board from surrounding environment, The electronic module has a connection structure in which a portion of the circuit board is protruded to the outside through an opening of the case and inserts a board terminal into an external female connector to obtain electrical continuity, and a portion of the case member forms a connector housing that receives the female connector and isolates a space in which the board terminal is present from surrounding environment and an insulating resin member for fixing the circuit board in the case is integrally molded or joined with the circuit board.