A printed Circuit Board (PCB) holds different electronic components in one place and connects them all with the help of a copper sheet’s conductive traces that are laminated on an insulator substrate. PCB not only provides electronic support for electronic devices but also provides mechanical support. PCB manufacturing procedure involves several difficult steps from PCB design, PCB fabrication and PCB assembly. So, very skilled workers and very experienced professionals are needed to produce perfect circuit boards. To attain a certain level of accuracy and reliability, different computer-aided software and advanced machines are used in PCB design, PCB manufacturing and PCB assembly processes.
In the PCB design for manufacturing stage, many different kinds of software are used according to the purpose and budget of different designers, popular ones like Altium Designer, KiCad, EasyEDA, PADS, etc.
In the PCB manufacturing processes, a lot of PCB manufacturing equipment is used, such as lamination equipment, drill machine, copper etching and plating line, surface treatment line, laser direct imaging (LDI) equipment used in copper and solder mask process, printing machines, profiling machines, e-testing machines, AOI, etc.
In the PCB Assembly process, pick and place equipment, reflow oven, wave soldering machine, AOI machine, first-article tester, x-ray inspection machine, lots of loaders and feeders, testing fixtures., etc are used.
PCB Manufacturing Process:
Different steps of the PCB board manufacturing process are jotted down in sequential order. Before going to the detailed steps, we need to get clear:
What is PCB manufacturing?
PCB manufacturing can mean just the process of bare PCB fabrication, but it can also mean the whole process from circuit board design to PCB fabrication and PCB assembly. Here, we talk about the whole process from deign to finished circuit boards.
1. Schematic Diagram Design
Logical representation of different electronic components, and electronic circuitry is generally considered as schematic diagrams or schematic design. The designer is responsible for designing a blueprint for the PCB using different symbols and notations for each electronic component having different numbers of pins which are connected in a way to make a closed loop circuit allowing current to flow. These blueprint designs are created using computer-aided software like Altium Designer and P-CAD.
2. PCB Diagram/PCB Layout
Using the same EDA software as Altium Designer and P-CAD, PCB designer designs different aspects of PCB like PCB dimensions, number of layers, and PCB packages (PCB footprints) for different electronics components either through-hole or surface-mount. In this step of PCB manufacturing, designers suggest placements of components on the board and join them according to the schematic diagram. PCB designers can visualize how the final PCB will look, when fabricated, in 2D and 3D.
Once the PCB diagram is ready, the PCB designer exports the PCB diagram in Gerber format which will be further used to fabricate the design in hardware. BOM (Bill of Materials) is also created in this step in which the procurement of components is listed in a Microsoft Excel file or other tabular format file, having all necessary data i-e nominal operating and output voltages, current, temperature, etc.
3. Printing circuits from PCB Design
Prior steps are related to software-based designing of PCB, from this step onward, there will be printing and fabrication of the PCB diagram and PCB printed circuit board manufacturing. A special printer known as Plotter Printer is used to print PCB diagrams which prints PCB’s negative-like films comprised of two different colors, one for conductive parts and the other for non-conductive. Different approaches are used to fabricate double-sided PCB and multi-layered PCB, as below:
Double Sided PCB Design
Printing circuits and etching of double-sided PCB design is quite simple, comprising of the following two steps,
Circuits Printing: Designed copper circuits are printed on the copper foil layers to form the structure of PCB traces. Later, to reveal the blueprint of the design, that copper layer is etched away. Photosensitive film is applied to PCB structure which hardens on passing ultraviolet light and revealing copper traces. After this process, an alkaline solution is used to wash the board, sometimes washing the board with higher pressure to remove the excessive photoresist film.
Copper Etching: This step helps to remove all extra and unwanted copper from the board. After covering all required copper, a chemical solution is applied on board which removes all unwanted copper. In this step covering of wanted copper is important. And also, accurate etching is also very critical.
Multi-Layer PCB Design
Multi-layer PCB fabrication requires additional steps, mostly are like double-sided but different steps are repeated for each layer. Following are common steps used in the fabrication of multi-layer.
Inner Layer Circuits Imaging: In this step, a plotter print is used to print the designed copper circuits to produce the film.
Inner Layer Copper Trace Etching: This includes the removal of excessive copper from the base laminates.
Inner Layer AOI: Another automated machine is used to perform Automated Optical Inspection (AOI) to check for any incomplete traces or any unwanted resist on the inner layer of the PCB.
Inner layer Brown Oxide: Brown oxide is also called black oxide; it is used among the inner layer of PCB to ensure copper foil bonds with epoxy resin (prepreg) properly.
Post Etch Punch: An automated machine known as Optical Punch, is used to align layers using the registration holes as discussed earlier.
Alignment: X-rays were used to check the proper placement and alignment of layers of PCB. After this x-ray alignment, there is a drilling process for through-hole components and vias according to the PCB blueprint provided by the designer. After this, the next steps are common for both multilayer and double-sided PCBs.
Layup: During this step machine is used to align, provide heat to layers, and bond the inner layers of PCB with copper film and laminate material.
Lamination: This step is responsible for holding all the layers of PCB tightly considering insulation among them. To do so heat and pressure is used to dissolve the epoxy which results in the bonding of layers.
After lamination, the remaining two processes, Circuit Printing and Copper Etching are the same as double-sided PCB design.
4. Application of Solder Mask and Silkscreen
Before applying the solder mask, PCB is thoroughly cleansed and then put in the oven. UV light of the oven indicates the areas of PCB with no solder mask, while other areas are baked for solder mask. Solder mask gives a green color to PCB which protects PCB from oxidation and corrosion.
The printing of components’ part numbers, warning labels, logos, and other related data on PCB is the application of silkscreen also known as legend printing. This printing is done using an inkjet printer.
5. Surface Finishing the PCB
Surface finishing of PCB involves the plating of the surface to protect exposed copper and improve solderability. This step is important to create a sustainable and reliable connection between PCB and electronic components. Protecting exposed copper involves the protection of from oxidizing of exposed copper due to air, while solderability enhancement means enhancing the soldering of components on the PCB.
6. PCB Test and Inspections
This is a very critical step. When PCBs are finished, we need to do 100% open and short circuit testing, to make sure the PCBs are 100% functional well. Besides, we will also do many other tests and inspections:
- Microsection Check
- Impedance Test
- Solderability Test
- Thermal Test
- AOI Inspection
- Visual Inspection
7. PCB Assembly
In this step, all electronic components will be soldered, and then a fully functional circuit board is finished. In this step, we normally use both PTH assembly and SMT assembly for different kinds of components.
8. PCBA Testing
Of course, necessary inspection and testing need to be done, just like the AOI test, in-circuit testing, X-ray inspection, functional test and visual inspection. Here are a few we have done for all our PCBs.
- AOI Test
- First-article Check
- ICT Test
- X-ray inspection
- Functional Test
- Ageing Test
- Environmental Test
- Visual Defects Inspection
The above are the main PCB manufacturing process steps. But there are a lot of more minor steps. Please visit our website for the detailed processes.