SIG Vision Measuring Machine: Precision Dimension Measurement Solution for FPC Flexible Printed Circuits

Introduction

Flexible Printed Circuits (FPC), known for their thin profile, bendability, and 3D routing capabilities, have become indispensable components in consumer electronics, automotive electronics, medical devices, and more. However, the flexible substrate of FPC is prone to deformation and uneven expansion/contraction during manufacturing. Even tiny deviations in line width, hole position, or alignment accuracy can cause signal transmission failures or final assembly defects.

SIG’s self-developed fully automatic vision measuring machine offers a non-contact, high-throughput, high-accuracy optical dimensional inspection solution. It covers everything from 2D contour measurement to 3D topography evaluation, enabling FPC manufacturers to achieve robust quality control.

Core Measurement Items for FPC Flexible Circuits

FPC consists of a conductive layer (high-purity electrolytic/rolled copper foil, purity ≥99.7%) and a dielectric layer (polyimide PI or polyester PET). Precision dimensional inspection focuses on the following key parameters:

1. Line Feature Measurement

The SIG vision measuring machine accurately measures line width and line spacing. For high-density FPC products, line width/spacing can be as tight as 25–40 µm, with tolerance requirements typically within ±5 µm. Equipped with a high-resolution color industrial camera, telecentric optical system, and intelligent edge-detection algorithms, the system quickly captures circuit contours and reliably identifies open circuits, shorts, notches, and pinholes.

2. Pad and Gold Finger Inspection

Measures pad diameter, positional accuracy, and gold finger width to ensure proper coverlay alignment without pad exposure. In foldable smartphones, smartwatches, and other consumer devices, the dimensional precision of gold fingers directly affects signal transmission reliability.

3. Hole and Via Inspection

High-accuracy measurement of via diameter, hole-to-hole spacing, and layer-to-layer registration deviation in multilayer boards. For multilayer rigid-flex boards, the SIG hybrid vision measuring machine uses coaxial illumination to penetrate semi-transparent solder masks, clearly capturing underlying circuit features and controlling interlayer misalignment to ≤10 µm.

4. Expansion/Shrinkage and Flatness Evaluation

During lamination (temperatures above 170 °C), the difference in expansion/contraction coefficients between copper and polyimide induces internal stress, causing substrate deformation and circuit pattern distortion. The SIG vision measuring machine can be optionally equipped with a laser sensor to automatically scan multiple height points, calculate expansion/shrinkage values, and output a color deviation map that visually displays flatness and warpage distribution. This helps avoid hole position shifts and loss of processing accuracy caused by deformation.

Industry Pain Points: Why Traditional Inspection Falls Short

FPC’s flexible substrate presents three major challenges for dimensional measurement:

• Contact-induced errors – Traditional contact probes can scratch or deform the flexible material, leading to false readings.
• Low efficiency & human error – Microscopes and projectors rely on manual point-to-point measurement, which is slow and prone to operator variation, making them unsuitable for mass production.
• Bending-induced AOI misjudgment – Transport-related bending of FPC panels can cause AOI false-failure rates as high as 18%, with line-width errors accounting for 60% of those misjudgments.

SIG Vision Measuring Machine: Technological Breakthrough for FPC Dimensional Measurement

The SIG fully automatic vision measuring machine incorporates imported 0.1 µm resolution glass scales, Class H linear guides, and a granite base, achieving repeatable measurement accuracy of ±1.5 µm in compliance with ISO standards. The system features a motorized zoom lens, a high-definition industrial camera, and 256-level programmable LED illumination to clearly resolve micron-scale circuit features.

Fully Automatic CNC Batch Inspection

With intelligent measurement software, users can predefine measurement paths for unattended batch inspection. Single-part inspection time is reduced to seconds. Measurement results are automatically uploaded and can be used to generate SPC statistical reports, providing real-time monitoring of process capability and early warning of potential quality issues.

2.5D / 3D Composite Measurement Expansion

Optional contact probes or laser sensors enable 2.5D/3D data fusion for high-precision analysis of FPC flatness, warpage, and step heights – solving the traditional trade-off between throughput and true 3D accuracy in optical measurement.

Industry Application Scenarios

Conclusion

As FPC technology moves toward higher density, finer lines, and more layers, the SIG fully automatic vision measuring machine – with its non-contact, high-efficiency, high-accuracy optical dimensional measurement capabilities – is gradually replacing some traditional inspection methods and becoming an essential quality control tool for FPC manufacturers. Whether for 2D circuit feature measurement or 3D flatness and warpage evaluation, the SIG vision measuring machine provides stable and reliable data to help reduce costs, increase efficiency, and improve product yield.

For more technical specifications and application solutions of the SIG fully automatic vision measuring machine, please visit the Sinowon official website: www.sinowon.com