Flexible printed circuit: Innovations and New Technologies

1. Flexible printed circuit: Innovations and New Technologies

2. Introduction Flex printed circuit boards are at the heart of most modern day electronics, it is the circuit board that provides the density to the electronic. The high density electronics have eyes for a much thinner FPC than the conventional ones. The conventional FPCs comprises of three layers formed by copper, polyimide and bonding adhesives. The three layered circuits are being replaced by two-layer circuits that equate to the copper being directly placed on the polyimide without the help of any adhesives. The process of manufacturing a flexible printed circuit is a very complex one within itself. The manufacturing of the circuit can be affected by a shift, as tiny as 0.01mils. The FPCs themselves aren’t very huge in their size, so a small shift could have a major impact on the manufacturing of the circuit board. The manufacturing of a flexible printed circuit is a much more complex than that of a rigid PCB. With regards to this, there have been multiple innovations in the manufacturing process of the flexible printed circuits. Here are some of the inventions in the manufacturing world of FPCs:

3. Laser drilling of flex panels Laser drilling and routing are everyday processes in the manufacturing of a flexible printed circuit. A high density manufacturing process requires the need of a ultra-violet laser drilling technology. It is used to drill circuit boards that are under 70 µm. The laser drilling machines enables a high accuracy in the alignment that ensures the best registration of vias. This is acquired as the laser drilling machine possesses the capability to acquire the targets on panels. Laser drilling has lately been adopted for the new roll-to-roll production mode. It has been used in the sheet-based production for a long time.

4. Automated optical inspections FPC products are single or double sided more often than not. These circuits did not go through the AOI inspection earlier, but in the last five years fine-line flex has become an important factor in the integration of the Smartphone interconnect. This has led to a demand for higher quality of the single and double sided FPCs, which has risen up a compulsion for the AOI-level inspection. AOI is a process that involves multiple verification stages and includes manual handling of the panel sheets. The manual process is a challenging process for the individuals as the FPC sheets are thin and delicate, this leads to a high accumulation of scrap.

5. Automated optical shaping As the core of the fine-line double-sided FPC is lesser than 30 µm, manual repair or rework is not an option that can be indulged into. It created many defective FPCs, which have to be scrapped on immediate basis. As the innovations have taken the front seat, fully automated copper shaping solutions have been innovated over the past three years to enable seamless shaping and saving fine FPCs. This automated optical shaping solution uses advanced fluorescent-based imaging and laser ablation tools working together in a closed-loop shaping system. This negates the possibility of fine shorts, removes penetration and excludes the damage to the FPC. With the help of this technology the damaged FPCs can be repaired and restored easily with a hassle free process, this leads to lesser wastage and a seaming drop in the production costs.

6. Direct imaging The need for direct imaging is increasing in building the FPCs for Smartphone interconnections. This is becoming necessary to be taken up as the thin flex products do not have reinforcing glass fiber, this leave them without the ability to move and deform throughout the production process. The deformations that occur during the process are accumulated and next to be fixed at the solder mask stage. Direct imaging is becoming a process of high yield and an increase in the use of this process can be noticed evidently.

7. Roll to roll processing The sizes of the sheet to sheet processes incurred many small steps and yielded small substrate sizes, hence has been replaced by the roll to roll processing. Roll to roll processing of FPCs is a continuous process and generally does not include break-ups yielding a flexible printed circuit that is 100m long. With the use of this method, the product efficiency rises as numerous small FPCs can be produced in a single batch of a long continuous yield of the roll to roll process.

8. Conclusion Innovations in all the fields are running rampant with the growth of economies all over the world, and the with the use of FPCs in almost every electronic device and high-density electronic product; innovations in their production process are much appreciated and are being adopted on a rapid pace by the leading FPC manufacturers.

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