FR4 semi-flexible PCB type PCB manufacturing process

The importance of rigid flexible PCB cannot be underestimated in PCB manufacturing. One reason is the trend toward miniaturization. In addition, demand for rigid rigid PCBS is on the rise due to the flexibility and functionality of 3D assembly. However, not all PCB manufacturers are able to meet the complex flexible and rigid PCB manufacturing process. Semi-flexible printed circuit boards are manufactured by a process that reduces the thickness of the rigid board to 0.25mm +/- 0.05mm. This, in turn, allows the board to be used in applications that require bending the board and mounting it inside the housing. The plate can be used for one-time bending installation and multi-bending installation.


Here’s an overview of some of the attributes that make it unique:

FR4 semi – flexible PCB characteristics

L The most important attribute that works best for your own use is that it is flexible and can adapt to available space.

L Its versatility is increased by the fact that its flexibility does not impede its signal transmission.

L It’s also lightweight.

In general, semi-flexible PCBS are also known for their best cost because their manufacturing processes are compatible with existing manufacturing capabilities.

L They save both design time and assembly time.

L They are extremely reliable alternatives, not least because they avoid many problems, including tangles and welding.

PCB making procedure

The main manufacturing process of FR4 semi-flexible printed circuit board is as follows:

The process generally covers the following aspects:

L Material cutting

L Dry film coating

L Automated optical inspection

L Browning

L laminated

L X-ray examination

L drilling

L electroplating

L Graph conversion

L etching

L Screen printing

L Exposure and development

L Surface finish

L Depth control milling

L Electrical test

L Quality control

L packaging

What are the problems and possible solutions in PCB manufacturing?

The main problem in manufacturing is to ensure accuracy and depth control milling tolerances. It is also important to ensure that there are no resin cracks or oil spalling that could cause any quality problems. This involves checking the following during depth control milling:

L thickness

L Resin content

L Milling tolerance

Depth control milling test A

Thickness milling was performed by mapping method to conform to thickness of 0.25 mm, 0.275 mm and 0.3 mm. After the board is released, it will be tested to see if it can withstand 90 degree bending. Generally, if the remaining thickness is 0.283mm, the glass fiber is considered damaged. Therefore, the thickness of the plate, the thickness of the glass fiber and the dielectric condition must be taken into account when conducting deep milling.

Depth control milling test B

Based on the above, it is necessary to ensure a copper thickness of 0.188mm to 0.213mm between the solder barrier layer and L2. Proper care also needs to be taken for any warping that may occur, affecting the overall thickness uniformity.

Depth control milling test C

Depth control milling was important to ensure that the dimensions were set to 6.3 “x10.5” after the panel prototype was released. After this, survey point measurements are taken to ensure that 20 mm vertical and horizontal intervals are maintained.

Special fabrication methods ensure that the depth control thickness tolerance is within ±20μm.