Both rigid and flexible materials make up traditional rigid-flex PCBs. Most of the time, the current production method involves pattern-plating the rigid and flexible substrates before laminating the rigid and flexible substrates with an adhesion agent. Pre-pregs that do not flow are often used to make the adhesion agent’s materials. Making flexible materials costs a lot of money. Rigid-flex PCB development is impeded by the fact that multilayer rigid-flex PCB currently costs 5–7 times as much as traditional multi-rigid PCB.
However, when compared with rigid materials, flexible materials’ changes are significantly larger and will always change in size. When laminating, the inconsistent expansion and contraction of rigid and flexible materials may cause circuit patterns of the same size to dislocate, reducing product reliability.
Semi-Flexible PCB
The most common method for making semi-flex PCBs is to bend FR-4 materials and make PCBs using the same method that is used for making rigid PCBs. Then, to meet the requirements of the assembly bending connection, thinning of areas is needed to bend to get a certain degree of flexibility using deep milling technology.
Major Characteristics of Semi-Flexible PCB
· Low Cost
Utilizing epoxy resin FR-4 material, semi-flex PCB technology was initially utilized in accordance with the standard PCB procedures. The traditional multilayer material is then selectively thinned by depth milling to achieve a certain degree of flexibility. This method only requires one more manufacturing step than the production of double-sided and multilayer PCBs, and the manufacturing procedure is relatively straightforward. It can significantly cut costs compared to flexible PCBs and conventional rigid-flexible PCBs by substituting expensive polyamides and other flexible materials.
· High Reliability
Because it is utilized in the electronics and automotive industries, the semi-flex PCB must meet tough requirements. When having the features mounted in the same state and plane, the semi-flex PCB not only saves money when the final assembly requires the PCB to stack, but it also reduces the welding point and entangled connectors limit. The flexible part can meet the requirement of bending to the final shape after the assembly is finished without the flexible substrate. It solves the issue of inconsistent expansion and contraction of the flexible substrate and the rigid substrate, thus increasing the electronic product system’s reliability.
Major Applications of Semi-Flexible PCB
Several applications make extensive use of semi-flexible PCBs. Some applications will use these boards because of their high quality and reliability.
1. Automotive
The automotive industry relies heavily on semi-flex PCB. Applications in which the bending area is not subjected to dynamic stress are ideal for this PCB. A semi-flexible PCB can be found in automotive components. Some vehicle components, like airbag systems and anti-lock brakes, are designed with the assistance of this board. This board is also used in engine control systems in automobiles.
2. Industrial Electronics
When making industrial electronics, a semi-flexible PCB can be very helpful. Additionally, this board is highly reliable and flexible.
3. Consumer Electronics
Semi-flex PCBs can be found in hearing aids and cell phones. The consumer electronics industry relies heavily on semi-flex PCBs.
4. Medical Devices
Semi-flex boards are used in a variety of medical devices. Hearing aids and heart monitors are two examples of these devices.
5. Telecommunication
The semi-flex boards are also heavily used by the telecommunications industry. Additionally, satellite and GPS tracker versions of these boards are available.
Potential Challenges and Solutions During Semi-Flexible PCB Production
Controlling the tolerance and precision of depth-control milling is one of the most significant issues with FR4 semi-flex boards. As a result, rigid PCBs need to be flexible enough. There are a few aspects of the depth-controlling milling process that should be fully considered.
· Depth-controlled test A
The manufacturer mills the remaining thickness using the mapping technique. Also, after testing the board under 90° bending, the manufacturer can accomplish this based on the remaining thickness. The most significant factor in the PCB’s failure is damage to the glass fiber bundle.
· Depth-controlled test B
Between L2 and the solder mask, the copper’s dielectric thickness ranges from 0.188 mm to 0.213 mm. Additionally, if the remaining thickness is greater than 0.283 mm, the manufacturer does not perform 90° bending. As a result, mechanical manufacturing can be done with control over the remaining thickness. This must be within 0.245 mm0.213 mm of the tolerance.
· Depth-controlled test C
On the board warpage and machine uniformity, there is a forward effect. This is because of the shrinking size. The manufacturer performs depth-controlled milling in accordance with the predetermined dimensions of 6.3 × 10.5 inches. Machine uniformity will be measured at the mapping point.
There is a unique production method for FR4 6-layer semi-flex PCB fabrication. It is used and developed by the manufacturer to control the depth and maintain thickness. As a result, manufacturing procedures are made easier.
Conclusion
Products made from semi-flex PCBs are mostly used in fields like large machines, data communication, and automotive electronics. They are able to meet the needs of today’s substrate installation interconnected to the greatest extent, which includes three-dimensional installation, low installation costs and time, and high system reliability. The partial flexible performance is realized on the basis of the rigid PCB through a special processing method.
Semi-flex PCB, as compared to rigid-flex PCB in its traditional sense, is capable of satisfying the requirement for local bending installation for a predetermined number of times while also significantly reducing material costs, manufacturing costs, and manufacturing difficulties. In addition, semi-flex PCBs can offer a more stable and complete electrical signal transmission performance, partially substituting for rigid-flex PCBs in some applications. With the rapid growth of the rigid-flex PCB market, the application of semi-flex PCB will be promoted to a greater extent.
