When the FPC is bent, the types of stress on both sides of the heart line are different. The inner side of the curved surface is pressure and the outer side is tension. The size of the stress is related to the thickness of the FPC and the bending radius. Excessive stress will lead to FPC layers and copper foil breaks. Therefore, the layer pressure structure of the FPC should be arranged reasonably during design to make the layer pressure at both ends of the central line of the curved curved surface as symmetrical. Calculate the curved radius based on different applications.
Conditions 1. The curvature of the unilateral flexible line board is shown in the figure below:
Its curved radius can be calculated according to the following formulas:
R = (c/2) [(100-eb)/eb] -D
These:
R = bending radius (unit μM)
C = copper skin thickness (unit μM)
D = Cover thickness (unit μM)
EB = copper skin allows deformation (calculated at a percentage rate)
The types of copper and the deformation of copper skin are different.
A. The deformation of copper pressing copper plate is ≤16%
The deformation of the copper skin during copper electrolysis is ≤11%.
In addition, the deformation of the same material copper skin on different use occasions is also different. For a bending occasion, the limit of the critical state of the break is used (the value of the delay copper, the value is 16%). In the bending installation design, the deformation values (10%, pair of copper) specified by IPC-MF-150 are used. For dynamic applications, the deformation of copper skin is 0.3%. In magnetic head applications, the deformation of copper skin is 0.1%.
At the same time, the radius of the curved plate is set by setting the deformation allowed by the copper plate.
Moving: The scenarios of this type of copper skin can be achieved through deformation. For example, the phosphorus and copper shifts in the IC card seat, that is, the part of contact with the chip after the IC card is inserted. This application scenario is flexible.
Example: 50 μM polytamide, 25 μm glue, so D = 75 μm, C = 35 μM Flexible plate total thickness T = 185 μm
Bending at a time, 16%= 16.9μm, R/T = 0.09
With 10% R = 80 μm or R/T = 0.45 Bend installation
Dynamic bent, 0.3% R = 5.74 mm, R/T = 31
In the scene shown above, the connector is needed to be inserted, and the “dynamic bend” is required. The curved radius is controlled to the> 6 mm, and the diameter> 12 mm.
Great algorithm: about 50 times the total thickness.
2. Double panel
These:
R = bending radius, unit μM
C = copper skin thickness, unit μM
D = coating thickness, unit μM
EB = copper skin deformation, calculate at a percentage rate.
The EB value is the same as the above value.
D = The thickness of the medium of each layer μM
for example:
Lower substrate thickness: 50 μM polytamide;
2X25 μM glue;
2X35 μM copper, d = 100 μm; C = 35μm
Coating thickness: 25 μM polytamide film; 50 μm glue layer d = 75μm
Total thickness: t = 2 d+2+2 c = 320μm
According to the equation:
Bending at one time, EB = 16% R = 0.371μm, R/T = 1.16
EB = 10% R = 0.690 mm Bend installation,
R/T = 2.15 dynamic bending, EB = 0.3% R = 28.17 mm, R/T = 88