Flexible Wiring Module Structure for Visible Solder Fillet Inspection
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Solution Overview
Problem
Existing visual inspection methods for solder joining in flexible printed boards are unreliable due to thin fillets formed on the inner edge surfaces of through-holes, which affect the reliability of the connection.
Innovation Solution
A wiring module design featuring a metal piece with a projecting portion that includes a plated portion on the inner peripheral surface and a non-plated portion at the end surface of the projecting end, allowing for concentrated fillet formation and easier detection during visual inspection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If solder joining is performed on the inner edge surface of a through-hole in a metal piece, then the connection strength is improved, but the fillet becomes thin and difficult to detect during visual inspection
Solution Approach 1:
The invention transitions the fillet formation from a two-dimensional surface (inner edge surface of through-hole) to a three-dimensional structure by adding a projecting portion that extends upward. This dimensional change creates a new surface (top surface of projecting portion) where the fillet can be formed and easily detected from above, while maintaining the connection strength benefit of inner edge surface soldering.
Solution Approach 2:
The projecting portion acts as an intermediary structure between the through-hole inner edge surface and the external inspection view. It provides a platform that allows the fillet to be formed on the inner edge surface for strength, while simultaneously presenting a detectable top surface for visual inspection, thus mediating between the conflicting requirements.
2Ease of manufacture
If the entire metal piece surface is plated, then solderability is improved, but the fillet becomes difficult to detect during visual inspection
Solution Approach 1:
Instead of uniform plating across the entire metal piece, the invention applies plating selectively to specific locations: the inner edge surface of the through-hole and the top surface of the projecting portion. This local quality approach ensures solderability where needed while creating a visually distinct plated top surface that facilitates fillet detection, avoiding the inspection difficulty caused by complete plating.
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
Enhances the reliability of visual inspection in solder joining by ensuring the fillet is easily detectable and the connection strength is improved through controlled fillet formation.
Implementation Method 1
the plated portion is provided at an inner peripheral surface of the projecting portion facing the through-hole... a portion of the metal piece connected to the land via solder is plated with tin as plating exhibiting excellent solderability
Implementation Method 2
the non-plated portion is provided at an end surface of a projecting end of the projecting portion... the fillet formed on the plated portion by solder joining is visually checked by an inspector
Data Source
AI summary
Provided is a wiring module including a flexible printed board; and a metal piece, in which the flexible printed board has a land and a wiring connected to the land, the metal piece has an upper surface, a lower surface, a through-hole, and a projecting portion, the lower surface of the metal piece is solder-joined to the land, the through-hole is formed in a thickness direction of the metal piece, the projecting portion is formed so as to project from at least part of an edge of the through-hole to above the upper surface of the metal piece, the projecting portion has a plated portion and a non-plated portion, the plated portion is provided at an inner peripheral surface of the projecting portion facing the through-hole, and the non-plated portion is provided at an end surface of a projecting end of the projecting portion.