Knowledge Resources Why is it necessary to use hot melt glue and heat shrink tubing? Secure Flexible Thread to Rigid Board Connections
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Tech Team · 3515

Updated 1 week ago

Why is it necessary to use hot melt glue and heat shrink tubing? Secure Flexible Thread to Rigid Board Connections


Connecting flexible conductive threads to rigid circuit boards is a critical structural challenge because these threads are inherently fragile and cannot be directly soldered to hard components. To solve this, hot melt glue is applied to the connection nodes to provide essential mechanical reinforcement and electrical insulation, preventing the joint from loosening. Heat shrink tubing is then added over the glue to significantly increase tensile strength and wear resistance, ensuring the connection survives the physical stress of daily wear.

The interface between soft textiles and rigid electronics is a high-risk failure point. This two-step reinforcement process transforms a delicate electrical contact into a rugged structural bond, ensuring stable data collection even during vigorous activity.

The Core Challenge: Material Mismatch

The Fragility of Conductive Threads

Unlike standard copper wire, flexible conductive sewing threads lack the structural integrity to withstand direct attachment to rigid materials.

They cannot be soldered directly to a circuit board in the traditional manner without risking immediate breakage or poor connectivity.

The Stress of Movement

Wearable technology is subject to constant physical motion, bending, and stretching.

Without reinforcement, the energy from these movements creates stress concentrations at the connection point, causing the joint to loosen or snap entirely.

The Role of Hot Melt Glue

Mechanical Reinforcement

Applying hot melt glue creates a robust anchor at the connection node.

This shifts the mechanical load away from the delicate thread-to-board contact, absorbing the stress caused by movement.

Electrical Insulation

Beyond physical strength, the glue encapsulates the connection point.

This provides vital electrical insulation, preventing short circuits that could occur if the exposed conductive thread touched other components or conductive elements.

The Function of Heat Shrink Tubing

Increasing Tensile Strength

While glue anchors the joint, heat shrink tubing acts as an external exoskeleton.

It compresses the entire assembly, significantly increasing the tensile strength so the thread cannot be easily pulled out of the glue.

Enhancing Wear Resistance

Wearables face constant friction against skin or other fabric layers.

The tubing protects the underlying glue and thread from abrasion, ensuring the connection remains intact during complex wearing environments.

Understanding the Trade-offs

Added Bulk and Rigidity

While this method ensures durability, it inevitably adds volume to the connection point.

The combination of glue and tubing creates a small, rigid "capsule" that may interfere with the drape of very lightweight fabrics or cause minor discomfort if placed in sensitive areas.

Repair Difficulty

Once the glue has set and the tubing has shrunk, the connection is permanent.

Modifying or repairing the joint requires cutting away the reinforcement, which can be difficult without damaging the underlying circuit board or thread.

Ensuring Connection Longevity

To ensure your wearable electronics function reliably, assess your specific requirements:

  • If your primary focus is high-impact activity: Use both hot melt glue and heat shrink tubing to maximize tensile strength and prevent data loss during vigorous movement.
  • If your primary focus is component safety: Prioritize the hot melt glue application to ensure the node is fully insulated and protected from short circuits.

By treating the connection as a structural system rather than just an electrical one, you ensure your wearable device remains robust in any environment.

Summary Table:

Component Primary Function Key Benefit
Hot Melt Glue Mechanical Anchor & Insulation Prevents loosening and short circuits
Heat Shrink Tubing External Protection Increases tensile strength and wear resistance
Conductive Thread Signal Transmission Provides flexibility for smart textiles
Rigid Circuit Board Data Processing Serves as the electronic brain of the device

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References

  1. Wei Guo, Lei Jing. PIFall: A Pressure Insole-Based Fall Detection System for the Elderly Using ResNet3D. DOI: 10.3390/electronics13061066

This article is also based on technical information from 3515 Knowledge Base .

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