Flexible circuits (also variously referred to around the globe as flex circuits, flexible printed circuit boards, flex print, Flexi-circuits) are members of electronic and interconnection family. They consist of a thin insulating polymer film having conductive circuit patterns affixed thereto and typically supplied with a thin polymer coating to protect the conductor circuits. The technology has been used for interconnecting electronic devices since the 1950s in one form or another. It is now one of the most important interconnection technologies in use for the manufacture of many of today’s most advanced electronic products.
High Temperature and High-Density Applications
In many cases, flex circuits are made of polyimide or a similar polymer. This material dissipates heat better than most rigid circuit board materials. For this reason, flexible circuits can be placed in inconvenient locations where heat would impact the performance of a rigid circuit board.
Flexible circuit boards can be designed to withstand extreme temperatures – between -200° C and 400° C – which explains why they are so desirable for borehole measurements in the oil and gas industry.
In fact, because of these conditions, and the need for small, unobtrusive devices in most industrial environments, flexible circuits represent the first choice for engineering design in most industrial sensor technologies.
High-temperature resistance comes usually comes with good chemical resistance and excellent resistance to radiation and UV exposure as well. Combined with the ability to control impedances in high-density circuit board designs, flexible circuit designs offer many benefits to manufacturers.
Comparison between the Poyester (PET) and Polymide(PI) material
The flex pcb raw material and stack up will decide the flex circuit quality. According to the market demand, there are three types of base raw material used for Flexible circuit board. Poyester(PET), adhesive Polymide (PI) and adhesiveless Polymide (PI) .
Do you know the difference between the PET and PI material? If not, let us learn about it together now.
Attached is a form for your reference, hope it will be helpful you. And you can choose the right raw material according the below form.
| Features | Polyester(PET) | Adhesive Polymide | Adhesiveless Polymide |
| Flexibility (2mm radius) | Bad | Good | Best |
| Tear strength | 800g | 500g | 500g |
| Strip strength in the air | 1050N/M | 1750N/M | 1225N/M |
| Eatching>=20% | BEST | Bad | Good |
| Working temperature | 80 | 85~165 | 105~200 |
| Chip | Bad | Good | Best |
The advantages and disadvantages of the PET and PI materials
| Material | Advantages | Disadvantages |
| PET | fewer production process; cheaper price; less lead time. |
cannot pass through the soldering flow process; cannot work in high-temperature conditions. |
| PI(Polymide) | easily bend； can work in high-temperature conditions. |
more expensive than PET |
Why Not Make All Circuit Boards Flexible?
Flexible circuit boards are certainly useful, but they are not going to replace rigid circuit boards for all applications. Cost efficiency is the main obstacle to implementing an exclusively flexible circuit board design in a consumer product. Rigid circuit boards are less expensive to manufacture and install in a typical automated high-volume fabricating facility.
Typically, the ideal solution for an innovative product is one that incorporates flexible circuitry when necessary and employs solid, reliable rigid circuit boards where possible to keep manufacturing and assembly costs down.
Some manufacturers even use hybrid rigid-flex printed circuit boards expressly for this purpose. This is common in laptop computers and medical devices, where rigid circuit boards can be connected to one other using ribbon-like flexible circuits. These boards can be compounded and designed to meet any number of engineering needs by focusing on the respective strengths of each circuit board base technology.
KKPCB creates both flexible and printed circuit boards for product manufacturers. Enjoy a consultation with one of our sales reps to find out if your product prototype design is best served by flexible or rigid circuit board types.
Check KKPCB Flex PCB manufacturing capabilities in the following table:
| Item | Capability |
| Layer | 1-12 |
| Board thickness (without stiffener) | 4-40 mil |
| Tolerance of single layer | ±1.0 mil |
| Tolerance of double‐layer (≤12mil) | ± 1.2 mil |
| Tolerance of multi‐layer (≤12mil) | ± 1.2 mil |
| Tolerance of multi‐layer (12mil‐32mil) | ±5% |
| Tolerance of board thickness (including PI stiffener) | ±8% |
| Min. board size | 0.0788” *0.1576” (without bridge) 0.3152” * 0.3152” (with bridge) |
| Max. board size | 8.668” * 27.5” |
| Impedance control tolerance | ±5Ω (≤50Ω), ±7% (>50Ω) |
| Min. coverlay bridge | 6 mil |
| Min. bend radius of single layer | 3‐6 times of board thickness |
| Min. bend radius of double‐layer | 7‐10 times of board thickness |
| Min. bend radius of multi‐layer | 10‐15 times of board thickness |
| Min. mechanical drill hole | 4 mil |
| Inner Layer Trace / Space | 2 / 2 mil |
| Outer Layer Trace / Space | 2 / 2 mil |
| Solder mask color | Green / Black |
| Surface treatment | HASL, ENIG, ENEPIG, Electrolytic Nickel Gold, Soft gold, Hard gold, Immersion silver and OSP, Immersion tin |
| Laser accuracy (Routing) | ±2 mil |
| Punching accuracy (Routing) | ±2 mil ‐ ±6 mil |
KKPCB conducts research on special processing technologies such as ordinary double-sided boards, thick copper circuit boards, high-frequency circuit boards, HDI circuit boards, rigid-flexible circuit boards, FPC flexible boards, buried blind hole circuit boards, and IC carrier boards. Provides PCB design, PCB layout, PCB prototyping and PCB assembly services.
