A must know about Insights of PCB manufacturing techniques

The demand of more advanced and complex machines that can deliver what is required by the customer is increasing day by day. From military and defense sector to automation industry, consumer electronics, IoT, Medical and computer sciences, Advance research on wireless communication and microwave engineering all these sectors demand a great deal of high tech instruments, machines, equipment and devices the back bone of which is what we call “PCB”.
While we are developing our understanding in the depths of PCBs and its details, in this article we shall discuss various aspects of PCB manufacturing process, raw materials used, types of PCBs, surface finish methods, cost of manufacturing, quality, delivery time and finally tips for choosing reliable PCB manufacturer or supplier.

What is Printed Circuit Board Manufacturing..?

PCB is an acronym of “Printed Circuit Board“. The PCB can provide mechanical support to electronic components. It is actually a base or platform for components to reside upon and to interconnect with each other by means of copper tracks or traces. You may have noticed in many electronic products the green thick boards on to which small and large electronic components are stick on one side and on the other side the metallic sharp points of welding are seen. This green thick board is actually PCB “Printed Circuit Board” also called PWB “Printed Wiring Board“.
PCBs are actually divided into three categories

1- Single Sided 2- Double Sided and 3- Multilayer PCBs

The single sided PCBs are those having components on top layer and connections and tracks on bottom layer. The double sided are those having components and solder pads or holes with traces/tracks on top and bottom both. Multilayer PCBs have component on top and bottom and solder pads and holes and tracks on top and bottom layers both as well as there are internal layers that contains buried and blind vias to interconnect components on top and bottom. The vias are the small opening in PCBs that is used to connect the top and bottom and inner layers with each other. The blind via is the one that has one end at either on top or bottom and other end is somewhere inside the inner layers. The buried via is the one having both ends “buried” inside the inner layer. The solder pads are made of solder paste on PCBs onto which SMT components are soldered. The plated through holes made by boring or drilling in the PCB are used to mount THT components

Different Layer PCB Manufacturing Process

Single Layer PCB manufacturing Process:
This process is not for mass manufacture but for single prototype development of single layer PCB for hobbyists. All materials used here is easily available and this PCB can be made in home easily
Step-1: Design the PCB layout from the schematics on any CAD EDA tool like Altium. Then create Gerber files and print your layout on the OHP sheet using laser printer.

Step-2: The fiber glass FR4 substrate base material is used. The copper clad is laminated on one side after soaking in epoxy resin.
Step-3: Rub the copper side of FR-4 with steel wool to remove oxide and photo resists if any.
Step-4: Place the OHP sheet on top of the copper side of FR-4
Step-5: Place the white paper on top of the OHP sheet and press with iron. The heat will cause the ink to stick to the copper plate exactly as it is on OHP
Step-6: Allow the PCB to cool and slowly remove OHP sheet.

Step-7: Now make a solution of Ferric Chloride and dip the PCB in the solution for 30 minutes. This solution will eat away the copper that is exposed to ink. Hence leaving the copper that is under the ink. This is called etching of unwanted copper.
Step-8: Remove the PCB and wash with cold water and rub with steel wool to clear the ink the resulting conductive copper tracks are created as per circuit diagram.
Step-9: Carefully drill on pads
Step-10: Put the components in drill holes and solder them

Step-3: The two separate photo films (negative) are created for top and bottom. The black ink is used to prevent the UV rays passing and hence makes the copper trace and pads.
Step-4: The photo resist film is placed on the entire substrate board. After that, the top film is placed upon the photo resist film.
Step-5: The stack of copper clad FR-4 substrate, photo resist and photo film is then exposed to Ultra Violet (UV) radiation. The black ink will protect the UV rays to penetrate through the resist and thus this resist beneath will be washed off.
Step-6: The photo resist that is exposed directly to UV will harden (polymerize) hence creating pads and tracks.

Step-7: The steps 4-6 are repeated for bottom layer also
Step-8: Next the solution of ferric chloride is prepared and the PCB is dipped to etch away unwanted copper from top and bottom side that is not beneath the photo resist.
Step-9: After unwanted copper is etched away, the wanted copper under the photo resist is protected and not etched away. Now photo resist is removed using another chemical solution
Step-10: Now the PCB with exposed copper tracks and pads is ready. It is time to drill holes and vias as per the drill file generated with extended Gerber. The via is used to connect the top and bottom layers components pads.
Step-11: The registration holes are bored to secure the board in place so it will not move to protect missed drill hits or misalignment of holes. Now the automated machine that is fed drill guide with extended Gerber files will automatically bore holes in PCB.
Step-12: Electro less Plating copper is now done using chemical deposition. The PCB undergoes chemical baths and surface of panel gets 1 micron thick copper. This copper is then deposited upon the walls of drills bored in the previous step. Next the panel plating is done.

Step-13: Solder mask epoxy ink is applied. There are various colors available green, blue and red. Green is widely used. The PCB is moved to oven to secure the solder mask appropriately.
Step-14: Surface Finish is done ENIG , HASL (Hot Air Solder Leveling)
Step-15: Final electrical testing

Multilayer Layer PCB manufacturing Process:

First you should know about your PCB stack up. The stack up is the sandwich of layers formed during PCB fabrication process. The stack up can have up to 30 layers or even 50 to 100 layers for very complex, high density interconnect (HDI) PCBs. Another thing is the size of your PCB, it does not matter how small or large your PCB is, when it comes to manufacturing on large scale, the PCB design is replicated on single larger copper clad material board that is usually 18 x 24 square inch. This is called PCB Panel. The panel is then cut into individual boards. The panel size is chosen such that it fulfills the MOQ (Minimum Order Quantity) as order by customer and adjust as many individual boards on panel as possible.