The Rigid-flex Pcb Fabrication And Manufacturing Process

By Author: Ryan
Total Articles: 75
Comment this article

The production of flexible PCBs may appear to be even more difficult than the rigid PCB fabrication procedure. However, many of the same procedures employed in the essentially equivalent flex PCB manufacture of rigid boards are used. This manual gives a comprehensive explanation of all the stages involved in producing flex PCBs. These procedures, which use various material sets as shown in an earlier tutorial, are quite comparable to rigid flex PCB construction procedures.

Flex Build-Ups


The methods listed below demonstrate how to create a standard double-sided flex circuit.

To plate a key, either epoxy or acrylic glue is utilized, or sputtering is employed.

Either chemical plating is applied to the seed layer or lamination to the adhesive is used to add copper foil. Rolls of annealed copper can be laminated without glue thanks to more recent production techniques offered by material suppliers.

The most popular method of drilling via pad holes is mechanical. By merging them from different reels on drums, drilling between work plates, and then ...
... rolling out to other reels on the other side of the drilling machine, numerous plated flex substrates may be drilled at once. Pre-cut flex panels can be joined with stiff blanks and drilled in the same manner as rigid cores, albeit registration is more meticulous and alignment precision is less accurate. Laser drilling is an option for extremely small holes, but it is quite expensive because each film must be drilled independently. For better precision (microvias), Excimer (ultraviolet) or YAG (infrared) lasers would be used, whereas CO2 lasers would be used for medium holes (4+ mils). Punching out large holes and cuts is a distinct procedural step.

After the holes are drilled, copper is chemically plated and then deposited in the same manner as rigid PCB cores (commonly referred to as Cuposit).In contrast to a typical low-cost rigid PCB, which might only have a cuposit of 12 mil, through-hole plating in flex circuits is advised to be at least 1 mil thick to offer mechanical support to the pad or through.

Before chemically etching the copper, a photosensitive etch resist is deposited onto the film surfaces. The resist is exposed and developed using the required mask pattern.


The etch resist is chemically removed from the flex circuit from Rigid Flexible PCB Manufacturer after exposed copper has been etched.

Coverlay layers that are trimmed to size serve as protection for the top and bottom portions of the flex circuit. Parts of the flexible circuit may have components placed on them; in this case, the coverlay also serves as a solder mask. Additional polyimide film with adhesive is the most used coverlay material, while several procedures do not require glue. The coverlay is effectively printed into the flex circuit using the photo-imageable solder mask, which are the same material used on rigid board parts in the adhesive-free technique. Screen printing is another alternative for coarser, less expensive patterns, with UV exposure serving as the topcoat film's final cure. The main distinction is that whereas an overcoat is an applied material covering that has to be cured, a coverlay is a laminated film.

Cutting off the flex circuit is the last stage in the creation process. Blanking is a common term to describe this. The hydraulic punch and die set method of blanking in huge volumes is cost-effective but has somewhat expensive tooling expenses. However, this technique enables the simultaneous punching out of several flex circuits. A blanking knife is utilized for prototype and low-volume runs. The blanking knife is essentially a long razor blade that has been twisted into the outline of the flex circuit and attached to a backing board's routed slot (MDF, plywood, or thick plastic such as Teflon). The blanking knife is then placed into the flex circuits to be cut out.

Routing and Lamination


The procedure continues if the flex circuit is to be a component of a rigid/flex combined stack-up, which is what we are interested in. We now need to laminate a flexible circuit between the hard portions. Due to the absence of glass fiber, this core layer pair is significantly thinner and more flexible than a pair of individually drilled, plated, and etched core layers. However, depending on the intended use, PI and glass might be used to create a less flexible layer. This has to be eventually framed in a panel that mates with the rigid board panel parts as well because it is being laminated between stiff sections. Flex circuits are temporarily attached to a stiff backing board made of MDF or FR-4-style materials when they are not being integrated with rigid parts.

Along with the stiff and any other flexible parts, the flex circuit is laminated into the panel using extra glue, heat, and pressure. Except when building multi-layer flex, neighboring laminated flex portions are not used. This often implies that each flex section has a maximal copper layer count of two to retain flexibility. Rigid pre-pregs and cores or PI bonding sheets with epoxy or acrylic adhesives are used to separate these flex parts.

In essence, each stiff panel is routed out independently in the locations where the flex will, well, flex. You can get an illustration of how a rigid flex PCB may be laminated, with two 2-layer flex circuits sandwiched between three stiff parts.

Due to the difficulty of manufacturing stiff flex PCBs, they are often less expensive. However, employing stiff flex PCBs can make the product less expensive all around. You'll save money on the cost of assembly, which in certain cases requires manual work since wired interconnects are substituted with conductive layers of flexible material.

Conclusion


There is no requirement to place a wire harness in the enclosure it is mounted on since a rigid-flex PCB is a complete circuit on its own. Such wiring requires a lot of time and adds to the price of the product per unit. Since all the subcircuits are already linked when the rigid-flex PCB is built, automated testing of the PCB is very simple. Eliminating connection problems before the components are put together can also save waste and costs. Designing a rigid-flex PCB is far more difficult than designing a traditional rigid PCB. Rigid-flex, however, is employed in some designs for excellent reasons, notably when fitting the board into small places.

High Quality PCB Co., Limited is a leading PCB(Printed Circuit Board) Manufacturer in China since 1995. Dedicated to the technologies innovation, being engaged in IC Substrates, High-Density Interconnect PCB, Multi-layer PCB, Rigid Flexible PCB, Flexible, Radiofrequency PCB.