Flexible Substrate Cap Structure to Prevent Solder Joint Disconnection

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Solution Overview

Problem

The flexible substrate in semiconductor devices is prone to disconnection due to sharp bending near the solder joining portion, especially with increased thickness, leading to potential disconnection under large stress.

Innovation Solution

A semiconductor device design featuring a flexible substrate with a cap covering the solder-joined end and guide slopes on the cap's inner surface to facilitate gentle bending, preventing sharp bends at the solder joining portion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If the flexible substrate thickness is increased, then the substrate strength is improved, but the substrate becomes more prone to disconnection under large stress

Engineering Contradiction:

Improvesubstrate strengthVSAvoidsubstrate connection reliability

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The cap is designed with a guide slope that gently guides the flexible substrate into position before it reaches the solder joint. This gradual transition prevents sudden stress concentration at the connection point, cushioning the impact of bending forces before they reach the vulnerable solder joint area.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The cap acts as an intermediary component between the flexible substrate and the rigid mounting structure. The guide slope within the cap creates a transition zone that mediates the stress between the flexible substrate and the fixed position, preventing direct transmission of sharp bending forces to the solder joint.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of operation

If the flexible substrate is sharply bent near the solder joining portion, then the substrate can be connected to the inspection jig or circuit substrate, but the substrate may be disconnected

Engineering Contradiction:

Improvesubstrate connection easeVSAvoidsubstrate connection reliability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The guide slope in the cap introduces a curved, gradual transition path instead of a sharp angle. This curvature allows the flexible substrate to bend smoothly along the slope's contour, distributing the bending stress over a larger area and avoiding concentration at the solder joint, thereby preventing disconnection while maintaining connection capability.

Inventive Principle:

Principle #14Spheroidality (Curvature)

3Reliability

If a cap with guide slope is added to cover the solder-joined end, then the flexible substrate is protected from sharp bending, but the device complexity increases

Engineering Contradiction:

Improvesubstrate connection reliabilityVSAvoiddevice structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The cap combines multiple functions into a single component: it provides mechanical protection for the solder joint, guides the flexible substrate into proper position through its guide slope, and prevents sharp bending. This merging of protection, guidance, and positioning functions into one element adds reliability without proportionally increasing overall device complexity.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS20250248015A1Semiconductor device

Publication Date: 2025.07.31 MITSUBISHI ELECTRIC CORP

AI summary

An optical device (1) includes a feedthrough substrate (2). The feedthrough substrate (2) is connected to one end of the flexible substrate (3). A cap (4) covers the one end of the flexible substrate (3). The feedthrough substrate (2) includes a second wiring pattern (8) joined to the first wiring pattern (12) at the one end of the flexible substrate (3) by solder (13). The guide slope (15a, 15b) is provided on an inner surface of the cap (4).