The printed circuit boards form the main skeleton of most electronic devices. These are devices that have triggered major advancements in the area of electronics especially computational devices such as calculators, smartphones, computers, and other appliances. For clarity, a PCB routes electrical signals through electrical components to satisfy the required need or task. In simple words, the PCB directs electricity where to go hence ensuring that the electronics are brought to life.
To achieve these tasks, PCB has copper traces that form the substrate where the electrical signals flow from component to component. These copper routes will always determine the purpose of each PCB.
Before starting the process of printed circuit board design, the designers are advised to visit the nearest fab houses and explain the intended purpose of their designs face to face and also lay down their PCB manufacturing conditions and demands. This is very helpful as it will save the designers from making any errors that can originate from the design stage.
We are presenting this article in order for every designer to be conversant with the step-by-step PCB manufacturing process. Hopefully, most designers will come across this in order to understand how the design process is done and avoid most errors that may be witnessed during the process.
Steps for PCB manufacturing
1. The design and the output.
Printed circuit boards must be compatible with designs that have been created using the design tools. The most used PCB design tools include; Kicad, Proteus, EasyCAD, Orcad, and many others. Before beginning the design, the designer should contact the manufacturer to inquire about their favorite design tools so that to avoid making mistakes in the process.
- After doing the design and it is approved for manufacturing, the designer will generate manufacturing files as per the designers’ specifications.
- The most used file is the GERBER extension file which is also known as the IX274X
- GERBER files carry around very important information like the copper tracking layers, the components notations, apertures, drill drawing, and many others.
- At this point, all the design requirements are fine-tuned to ensure that they have been met.
- After a close examination, the board is forwarded to the fab house for manufacturing.
- To ensure that the design is fit for manufacturing, all the PCB fab houses run the Design For Manufacture (DFM) check before taking the circuit through the manufacturing process.
2. From file to Film
The PCB manufacturing will begin once the designer has generated the manufacturing files and the manufacturer has performed the DFM check.
- The fab houses have a special type of printer called the plotter which is used for making the photo films of the printed circuit boards. These prints will be used to image the printed circuit boards.
- Plotters, although they are laserjet printers, they are not standard laserjet printers.
- They use highly precise technology to provide a detailed outcome of the PCB to be manufactured.
- At the end of the printing, we must be able to come up with the result of a photo in black ink.
- For the printed photo, the black ink represents the conductive copper traces and the other remaining clear part represents the non-conductive layers of the oriented circuit board.
- The outer layer is different, clear represents the conductive copper layer and the clear indicates the parts that are to be etched away.
- The plotter is used to generate this perfect film and the film is stored in a safe place to prevent contamination.
3. The inner layer printing: Where does the copper layers go?
The creation of the film in the above step is for mapping of the copper paths. In this step, we shall be print the figure of the film on the copper foil.
- Here we are preparing to start making the actual PCB. Remember that the simplest form of PCB is made up of laminate board which has epoxy resin as the core material and the glass fiber which also is referred to as the substrate material.
- The laminate is the receiving body of the copper that forms the substrate material.
- The copper laminate material is first cleaned then passed through the decontaminate substance. During this stage, it is very important to ensure that no dust material settles on the substrate. The cleanliness of the PCB is very vital.
- The availability of the dirt on the PCB might cause the circuit to have a short or open circuit.
- Next, the cleaned substrate layer receives a photoresist which is a photo-sensitive layer that comprises a photoreactive layer that hardens moments it is exposed to UV rays.
- The film is fitted into pins that hold them, into the laminate panel.
- The film and the board are passed through a blast of ultraviolet rays. Light will pass through the clear parts of the film and harden the photoresist substance that is under it and on the copper.
- The black ink that was printed by the plotter will always prevent the protected areas from hardening since these areas are slated for removal.
- Then the board is washed with an alkaline substance to remove the photoresist material that was not hardened.
- Then it is passed through pressure wash to remove anything that had not been washed by the alkaline and passed through the drier.
- A technician examines the board physically to ensure that there is no error incurred during the process. He also ensures that all the resists present represents the copper that will remain during the final stage of the process.
- This process is only suitable for boards with two or fewer layers. For multilayer PCB more steps are needed in the process.
4. Unwanted copper removal process.
During the process, there is a need to remove the unwanted copper material. This can be done by the use of a stronger material. here we shall be using the copper solvent solution to achieve our goal. As we do this, the wanted copper parts remain protected by the photoresist material.
- Not all copper materials have a similar process. Some heavy copper PCBs require a lot of solvents to be etched.
- Now that we have etched away from the unwanted copper material, the remaining copper material covered by the hardened resins needs to be cleaned. The hardened photoresistor needs to be washed away.
- We shall end up with a glittering board with only the copper material suitable for the end product.
5. Optical inspection and layer alignment.
After cleaning all the layers, they require alignment punches to ensure that they are well aligned. The registration holes will align the inner layers to the outer ones. The technician will use the optical punch machine to align and punch the layers.
6. Layering up and bonding.
This is the stage where the circuit board takes shape. Al the separate layers are reunited here. With the layer accurate, ready, and confirmed, they only need to be joined together.
- The outer layers are joined with the substrate.
- This process is carried out in two processes that are the layering-up and bonding.
- The outer layer is made up of fiberglass together with epoxy resin.
- A thin copper foil covers the top and the bottom layers of the PCB substrate which contains the copper traces for conduction.
- Bonding is done on a heavy steel table that has metal clamps.
- The prepreg layer is the first one to be placed, then the substrate layer follows the prepreg layer before you finally place the copper sheet. Finally, the sheet of the prepreg sits over the copper layer.
- Then this is prepared by pressing.
- The entire operation is done automatically by bonding press computer.
Holes are bored into the stack board. All the components that are planned to be fitted on the board are done so using the drilled holes. The drill holes will determine the accuracy of fixing these components.
- The x-ray locator is used to locate where drill holes will be done.
- Before the drilling operation is started, it is advisable you place a board of buffer below the board to ensure that the holes drilled maintain the high level of cleanliness.
- A computer is used to control the drilling machine. The machine will use files received from the designer to locate the exact location of each hole to be drilled.
- After drilling is complete, the entire holes undergo a cleaning process.
8. Plating and deposition of copper.
After drilling, the panel moves to the next stage which involves plating. In this stage, different plates are fused together using the method of chemical deposition.
- After sparkling cleaning of the panel, it undergoes a series of chemical bathing where a thin film of chemical is deposited on the surface of the panel. The copper will go into the holes that had been recently drilled.
- Computers are used to control the whole deposition process so that it can be as accurate as possible.
9. The imaging of the outer layer.
In step three, we imaged the panel with the photoresist. This process is repeated in this stage only that we only image the outer layer of the panel that has the PCB design.
- The process starts with layers in a sterile room to prevent any contaminations on the surface of the PCB.
- Thereafter we apply a layer of the photoresist on the surface of the panel. The prepped surface is then passed through the yellow room.
- The ultraviolet rays affect the surface of the panel.
- The goodness is that the yellow light UV rays do have not enough wavelength to affect the photoresist layer.
- Hold the black ink transparencies together then blast the surface with UV rays to harden the photoresists.
- The surface is then passed through a machine to remove the photoresist that was not hardened due to protection by the black ink.
- Inspect the outer layer to ensure that it is in good condition as expected.
Here we are forced to go back to plating room like we had done in step 8 and do the electroplating of the plate with a thin layer of copper. In the process, the exposed section of the panel from the outer layer section we receive the electroplating of the copper.
- Sometime the process mu involve tin plating so that we can be able to clean up the unremoved copper that remained during the etching process.
- This tin will cover the amount of copper that is not to be etched away and etching will remove only the copper that is not tinned.
11. The final etching
As stated earlier, the tin will protect the wanted copper from etching. The unwanted copper foil and the copper below will be under the etching process.
- The etching will be done using the method of chemical removal.
- After this final etching to remove the copper material, we shall have a clear indication of the contacting and connecting copper paths remaining on the plate.
12. Application of the solder mask.
Before this process, the panel is cleaned nicely and covered with the epoxy solder ink before applying the solder mask on both sides.
- Then the board is passed through a blast of ultraviolet rays which passes through the solder mask photo.
- The covered portion will remain unhardened and will undergo removal to have a complete board.
- Then the board will finally go via an oven to cure the soldering mask.
13. Surface finishing
Sometimes we would like our PCBs to have different abilities and this makes us electroplate our PC Bs with either gold or silver.
- You will find some PCBs with hot air-leveled pads. This is done in this stage and it will always result in the uniform pad.
- PCB manufacturing firms can generate different types of finishing depending on the customer and designers’ needs.
Almost all finished PCB will receive inkjet writing on its surface which will be used to indicate all the needed information about the PCB.
- Then the PCB lastly passes through the final coating, plating, and the curing stage.
15. Electrical tests.
As the final precaution, the technician must perform electrical tests on the PCB to ensure that it is functioning as expected.
- The automated system is used to do the electrical tests on the PCB and confirm its conformity with the design.
Machines and equipment used in the mounting of components in PCB manufacturing.
PCB drilling machine; even though we have said that the SMD is mounted on the surfaces, remember that there needs to be a connection between layers of the PCB boards. this is done via vias which are very tiny holes drilled on the board. This is done by the use of the drilling machine.
Wave soldering machine; this is used for the soldering process. It is also very important in the mass production of the boards.
The PCB brushing machine; we have talked about via drilling. Now after the drilling process is done, we have debris that is deposited. This debris is removed by the PCB brushing machine.
Pick and place machine; this picks the components, rotates them to the required direction, and places them on the PCB board in preparation for the components solder.
The PCB cleaning machine; does all the necessary cleaning that is required on the board. It also ensures that the board is very dry and free from any form of moisture.
Solder paste printing machine; this is for printing the solder paste to attach the components on the board. It ensures that the process is easy and first.
Reflow oven; this does the actual soldering of the boards.it ensures that the process is done in an effective way. We have three types that are currently common in the market; vapor phase oven, infrared oven, and convection oven.