Introduction to FPC Defect Detection Process

Flexible circuit board (FPC for short) is a printed circuit board made of flexible substrate. It is used in the downstream industries of the electronics industry to manufacture various high-efficiency and thin electronic products, such as mobile phones, tablets, smart wearable devices, etc., and has become an important bridge for connecting modules and signal transmission.

The process of FPC manufacturing is complex, with high defect rate, many types of defects and high scrap rate. Many types of defects such as wrinkles, indentations, scratches, notches, residual glue, foreign matter, etc. in areas such as FPC gold fingers, EMI, and board surfaces all pose great challenges to detection.

Traditional manual inspection is for production line employees to check the finished product defects with the naked eye, and visually inspect under a magnifying glass, focusing on the problems of surface residual glue, discoloration, gold finger tinning, tin beads, IC pin empty soldering, continuous soldering, etc.

Inspection process

AOI automatic optical inspection is a full inspection of products in the back-end process.

Common problems include:

due to the uneven surface of FPC, it is often accompanied by a high AOI misjudgment rate;

when producing ultra-fine FPC boards, the detection difficulty increases because of the smaller line width, line spacing and aperture;

gold finger offset is prone to occur in the process, affecting the client's inability to assemble, and then causing functional failure. If the early defects are not fully detected, the FPC will be scrapped and the raw material cost will be lost.

Defect types

1, Gold finger wrinkles, gold finger crushing, gold finger scratches, gold finger foreign matter, protective film foreign matter, gold surface dirt, gold surface foreign matter, gold surface scratches, EMI scratches, EMI damage, QR code text missing, QR code blur, board foreign matter, gold surface tinning.

2, Residual glue, back glue bias/breakage, burrs, pen marks, PI residue, oil film shedding, oil replenishment, ink dirt.

Imaging scheme

Generally, different imaging schemes are used in different inspection areas, and multiple imaging is formed to achieve comprehensive scanning of FPC.

In terms of lighting design, parallel coaxial light sources, planar shadowless light sources, etc. can be selected to provide uniform lighting conditions, so that defects such as foreign matter, damage, and wrinkles on the product surface are more prominent to meet the inspection requirements.

In terms of cameras, high-resolution color cameras are generally used to obtain high-precision imaging effects.