Switch with Sealed Resin Case to Prevent Solvent Permeation

Solution Overview

Problem

Existing push switches face contact failures and corrosion due to solvent permeation through through holes during reflow soldering, which can lead to mounting defects and impaired product flatness, as conventional methods like adhesive insulating sheets fail to reliably prevent solvent ingress.

Innovation Solution

A switch design where a second molded resin closes and covers the through holes of a first molded resin, forming a case that houses a movable member, eliminating the boundary between the two resins on side surfaces to prevent solvent permeation, and a manufacturing method involving insert molding to integrate fixed contacts and a movable member within a sealed resin structure.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If adhesive insulating sheets are used to cover the bottom surface of the case, then solvent permeation is partially prevented, but the resistance to solvent remains weak and swelling occurs during reflow soldering

Engineering Contradiction:

Improvesolvent permeation preventionVSAvoidsolvent resistance

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The invention extracts and eliminates the through holes from the case structure by forming a sealed bottom surface that completely closes the openings. This removes the penetration paths that allow solvent to reach the metal plate interface, fundamentally solving the solvent permeation problem rather than just providing partial resistance.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention uses a composite structure combining molded resin case with adhesive insulating sheets in a specific configuration. The insulating sheets are positioned to seal the bottom surface and cover the through holes, creating a multi-layer barrier system that prevents solvent penetration while maintaining structural integrity during reflow soldering.

Inventive Principle:

Principle #40Composite materials

2Object-affected harmful factors

If adhesive insulating sheets are used to cover the bottom surface of the case, then solvent permeation is partially prevented, but air expansion during reflow soldering causes the insulating sheet to swell and impair product flatness

Engineering Contradiction:

Improvesolvent permeation preventionVSAvoidproduct flatness

Core Design Contradiction:

Object-affected harmful factorsVSShape

Solution Approach 1:

The invention extracts and eliminates the through holes from the case structure by forming a sealed bottom surface that completely closes the openings. This removes the penetration paths that allow solvent to reach the metal plate interface, fundamentally solving the solvent permeation problem rather than just providing partial resistance.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention uses a composite structure combining molded resin case with adhesive insulating sheets in a specific configuration. The insulating sheets are positioned to seal the bottom surface and cover the through holes, creating a multi-layer barrier system that prevents solvent penetration while maintaining structural integrity during reflow soldering.

Inventive Principle:

Principle #40Composite materials

3Ease of manufacture

If through holes are formed in the case for insert molding, then metal plates can be supported and fixed, but solvent can enter the interface between metal plates and molded resin causing contact failure and corrosion

Engineering Contradiction:

Improveinsert molding processVSAvoidelectrical contact reliability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The invention extracts and eliminates the through holes from the case structure by forming a sealed bottom surface that completely closes the openings. This removes the penetration paths that allow solvent to reach the metal plate interface, fundamentally solving the solvent permeation problem rather than just providing partial resistance.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The adhesive insulating sheets are pre-positioned on the bottom surface of the case before the insert molding process. This preliminary action ensures that when the through holes are formed and metal plates are inserted, the solvent barrier is already in place, preventing solvent penetration during subsequent mounting processes.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS10068723B2Switch and method for manufacturing same

Publication Date: 2018.09.04 CITIZEN ELECTRONICS CO LTD

AI summary

A switch that more reliably prevents solvent permeation from the outside, and a manufacturing method thereof are provided. The switch includes a first molded resin molded integrally with a plurality of fixed contacts by insert molding, a movable member disposed above the first molded resin to bring the plurality of fixed contacts into and out of contact with each other, and a second molded resin molded so as to close a through hole of the first molded resin formed by a pin supporting the plurality of fixed contacts at a time of the insert molding.