Dec 17 2015

The Basic Process of Making the Inner Core in PCB Fabrication

There are some differences in procedures between making a home-made DIY printed circuit board (PCB) and manufacturing it in large quantities. This article will discuss the basic process of making the inner core of a design during PCB fabrication when made in large quantities by a professional manufacturer. Pcbnet is one stop solution to know more about PCB fabrication and process of Inner Core  manufacturing.

The first step in inner core PCB fabrication is making the design or layout of the board. Usually, this is done with computer-aided design (CAD) software. Previously, before CAD programs were invented, the layout is manually drawn and traced on a substrate board. The manual process is a lot more time-consuming and labor-intensive but it is still being used today, albeit very rarely, only in home-made PCBs with very simple designs.

The industry accepted output format of a CAD PCB design is called Extended Gerber (RS274X). The Gerber format is a two-dimensional vector picture format that illustrates the different parts of a PCB design such as the copper layers, holes, legends and masks. It contains the whole illustration of a PCB design with no need of other supplemental files. This means that it is a standalone file that describes PCB layers completely. This makes manufacturing a lot easier and faster.

PCB fabricationAfter the file is validated by a process engineer, the design is now ready to be photo-tooled. For modern PCB fabrication companies, the use of a device called photo plotter is common. The photo plotter converts the Gerber file into a hard copy image by using lasers to print it on a film. The film is developed to be used for mass production.

Only one layer of PCB design is printed in a single film. For multi-layered PCBs, several films are put on top of each other and aligned to create the final layout. This final layout is then registered into an imaging device.

Meanwhile, the PCB base or board is also being prepared. The base is usually made of fiberglass for strength and easy manipulation. A cheaper alternative is a phenol board. The base is coated with copper either on one side only (for single sided laminate) or on both sides (for double sided). Multi-layer configurations are the typical mass produced PCBs, and it requires a more complex process of photo imaging.

In this instance of making the inner core of a PCB, the fiberglass base, copper coatings, photo resist, and the resulting printout containing the prepared designs are stacked on top of one another and pressed with strong UV light to solidify the external coating and show the copper patterns.

The hardened board is then drenched with a chemical to soften the exterior for etching. After etching, the board is cleaned, dried, and made sure that no unwanted photo resist and printout stayed. What remained now is a board covered with the etched photo resist, in which underneath it is the designed copper pattern. The exposed and unnecessary copper pattern is again etched away to leave the photo resist pattern. Finally, the photo resist is peeled off to display the designed copper pattern on the board.The basic board is now finished. This basic board is used as the inner core for multi-layer PCB configurations.

In multi-layer PCB fabrication, once the basic board or inner core is loaded in the production line for assembly, any errors in the output can no longer be revised. Because of that, a thorough automatic optical inspection (AOI) is done either manually by certified company engineers or by a computer scanning program. Any inaccuracies are immediately shown after the scan for correction before mass production.

The process of making the PCB’s inner core is just the initial phase of producing a consumer-ready PCB product. Some of the subsequent processes are bonding (for multi-layer), drilling, plating, soldering, and testing, all of which are necessary to provide the best and most efficient product.

Written by Malcolm Wagner