In the making of Printed Circuit Boards (PCBs), some materials are outstanding. For the flexible circuits, the use of Flexible Copper Clad Laminate (FCCL) has become a trend. In this article, you will learn about what the FCCL PCB means.
The Background
Flexible Copper Clad Laminate or FCCL PCB is a sub-section of the broader Copper Clad Laminate (CCL). It is categorized based on the mechanical rigidity of the CCL.
The FCCL is one of the two circuit board laminates categorized based on the mechanical rigidity. The other is the Rigid Copper Clad Laminate (RCCL).
What is Flexible Copper Clad Laminate?
This is the base or core laminate/component of the Flexible Printed Circuit Board (FPCB). As the key or main material, it plays an important role in the functions of the circuit board.
It is also worth noting here that the FCCL features the layers of Polyimide and copper foil, which, in turn, are used as an insulator and electrical conductor for the board.
How Does the Copper Clad Laminate Stack-Up?
The composition of this material includes the lamination of copper foil onto the Polyimide Film (PI).
Also, the laminate comprises both the Thin Copper Foil and Polyimide Film (PI). While the film acts as the insulating substrate material, the thin copper foil is used as an electrical conductor on the surface.
The Broad Classifications of FCCL PCBs
The Flexible Copper Clad Laminate (FCCL) can be broadly grouped into:
- Single-sided
- Double-sided and;
- Multi-sided FCCL PCBs
Now, these classifications are based on the number of sides that the board has – and the trace density. For the single-sided, it means that the circuit board has only the copper foil on one side, while the double-sided means the inclusion of copper foil on both sides. For the multi-sided boards, we are looking at the ones with copper foil on more than two (2) sides.
The Classifications Based on the Structures
The Flexible Copper Clad Laminate (FCCL) PCB can be further classified, grouped or divided into other sub-categories, based on the structures of the product. In this case, the major divisions are based on whether the circuit board uses adhesive or not.
Also, the consideration is whether adhesive is added in-between the copper foil(s) and Polyimide Film (PI). Irrespective of the presence of adhesive or not, the FCCL can still be used to fabricate the flexible PCBs.
The adhesive Flexible Copper Clad Laminate is also called 3L-FCCL, while the non-adhesive or “adhesiveless” is called the 2L-FCCL.
Differentiating between the Adhesive and Non-Adhesive FCCL
The major differences between the two is that the adhesive FCCL features adhesive in-between the Polyimide Film (PI) and the copper, while the non-adhesive doesn’t.
Another difference between the two is that the non-adhesive Flexible Copper Clad Laminate (FCCL) costs more than the FCCL using adhesive.
In terms of the production capabilities and or applications, you can also differentiate between the two. On the one hand, the adhesive FCCL is ideal for manufacturing the following kinds of flexible circuit boards:
- Simple flexible boards
- Double-sided flexible circuit boards and;
- Single-sided flexible circuit boards.
On the other hand, the non-adhesive FCCL is ideal for manufacturing the following types of flexible boards:
- High-density SMDs, especially the ones with overlay openings.
- Multilayer circuit boards
- Rigid-flexible circuit boards
- Impedance-controlled circuit boards and;
- High-Density Interconnect (HDI) PCBs.
What You Need to Know About FCCL PCBs
Before choosing to work with this material or laminate, take note of the following points:
a. The Need for Desired Thickness
There is a need to attain both the desired thickness and controlled impedance. For this reason, there may be a need to combine the different thicknesses of the following:
- Coverlay
- Flexible Copper Clad Laminate (FCCL)
- Adhesive
Note that the combination is commonly required for special applications/uses.
b. The FCCL Copper Pour Design
The term, “copper pour” means the cross-hatched or solid area on a bare PCB, and this area must be filled with copper.
The functions of copper pour include:
- Reducing the number of etching materials required for producing circuit boards.
- Being used to make connections on the circuit boards and;
- Improving the flexible bending capability of the Flexible Printed Circuit Board (FPBC).
There are different kinds of copper pour, such as cross-hatching/cross-hatched copper, hatching pour and solid copper pour.
Differences between the Copper Pours
While the functions of these pours border on improving the circuit boards’ bendability, reducing the etching materials used and improving connections – they also differ individually.
Here is how they compare:
Solid Copper Pours
It has become common practice for circuit board designers to use the solid areas of copper pour as the ground layers that cover the remaining areas outside the stand-off regions, the traces and the pads.
The solid copper pour can also be used to provide better resistive characteristics for the circuit board.
Hatched Copper Pour
The hatched copper pour has its role to play in the FCCL PCB. Among many other functions, it supports the adjustment of the impedance of high-frequency traces. This comes in handy for the improvement of the impedance capabilities.
Cross-Hatched Copper Pour
This type of copper pour is used to make a balance the dilatation and heat on both sides of the Printed Circuit Board (PCB). This goes a long way to avoid warping of certain PCB substrate(s).
c. The Bending Capabilities
One of the unique attributes of the Flexible Copper Clad Laminate (FCCL) is the improved bending it offers. This is because of the base or primary material comprising the lamination of copper foil onto Polyimide Film (PI). This supports the realization of the ideal product design, with a special concentration on the sliding, bending and folding attributes.
Despite improving the bendability and foldability of the Flexible PCBs, the FCCL might have some discrepancies. An example is the thickness of the FCCL, whereby if one is adhesive and the other is not, then, the flexibility and bending of the non-adhesive FCCL becomes more prominent than that of the adhesive FCCL.
Wrapping Up
Flexible Copper Clad Laminate (FCCL) helps to bolster the flexible bending of the flexible circuit boards. For the best results, use only the adhesive or the non-adhesive, as using the two makes the non-adhesive more prominent.
Nevertheless, you can do without any of the two and the FCCL can still be used to fabricate and manufacture flexible Printed Circuit Boards (PCBs).
