If you are wondering, “How are PCBs made?”, you have reached the right page. A PCB (printed circuit board) is manufactured via a long and complex process comprising various steps. If any of the steps are not carried out with utmost attention, the finished product may not perform well. Additionally, the performance of the PCB may be negatively affected in case any step is skipped or the procedure is cut back. Therefore, it is crucial to ensure that every step is monitored well and no step should be taken lightly.
Now, while all PCBs are prodik-uced by a similar standard procedure, a few steps of the process vary depending on the type of PCB. Single-sided PCBs, double-sided PCBs and multilayered PCBs are different from each other in terms of structure and functioning. And therefore, their manufacturing process also differs slightly. Remember, the more the number of sides in a PCB, the greater the complexity of its manufacturing process. So, to understand how to produce PCBs, you first need to know what kind of PCB you need.
Once it is clear what type of PCB is to be manufactured, and all the steps are carried out with care, you get a fully-functioning printed circuit board that helps your device run smoothly. Continue reading to decode “how are circuit boards manufactured” in this step-by-step guide.
|Table of Contents
1. Design and DFM
Before getting on with the manufacturing of a PCB, it is necessary to clearly define its functioning. Based on the functions a PCB is expected to perform, its design is curated. PCB designers use various software to lay out a design blueprint. This step does not end here. The designer also performs an examination to check if there are any errors in different parts or aspects of the design. After the examination, the design department sends the design to the fabrication department for the building of the PCB. Here, another examination, called the Design for Manufacture (DFM) check, is carried out.
Read further to understand the next steps in this guide explaining, “how are printed circuit boards manufactured”.
2. Base Substrate Chosen
Once the design is thoroughly reviewed by engineers, and they ensure that there is no incorrect structure or missing component, the next step begins.
To hold different components, PCBs need a substrate. Therefore, most commonly glass fibre and epoxy resin (insulating material) are used as a substrate. There is copper on both sides of the base PCB material. We need to choose the proper substrate for different circuit boards. The most widely used material is glass-reinforced epoxy, which is also called FR-4. Besides, ceramic, polyimide and metal core materials are also used.
3. Substrate Cutting
When we have chosen the base material, it is time to start real production. Normally, the base materials are supplied in very big sheets to save costs in production and transportation; they are also suitable for PCB manufacturers to produce PCBs with any dimension.
But a big sheet with 41×47’’ is not convenient in production, so we need to cust these big sheets into small pieces, like 18×24’’ which is easy to handle. But we can cut into other dimensions if you want, according to the size of the printed circuit boards.
4. Inner Layer Pattern Printing
Before starting with this step, you should understand some terms. The laminate panel works as the body of the structure. Resist is a type of photo-sensitive film. Photo-reactive chemicals are used to make the “resist” as they harden when exposed to ultraviolet light. Continue reading to learn how to manufacture PCB boards.
Now, the process of printing the design to the laminate begins. And once the printing is completed, everything is again aligned with the help of registration holes.
This includes printing the design of the PCB using a special printer called a “plotted printer”. By this process, fabricators obtain a film showing all the details of the PCB. This film is similar to transparencies used for presentation purposes in educational institutes. The film works like a “negative” as the colours used to represent the layers are reversed from that in the board.
On the inside layer, clear ink is used to represent the non-conductive areas, whereas copper traces and circuits are shown with black ink. For the outside layer, the same colours are used but in a reversed manner. That is, the non-conductive areas are shown with black ink and clear ink is used to show the conductive areas.
If a multilayered PCB is being manufactured, then separate films for each layer are printed. These layers and films are then aligned with the help of a registration hole punched in them.
4. Exposure to UV Light
Fabricators then expose the laminate and resist with ultraviolet light. The hardened part of the resist indicates the copper pathway. As you know, printing includes the use of black ink, this now comes in handy as it prevents the hardening of resist in required areas. An alkaline solution wash helps in removing the photoresist from these areas. The board is dried and a technician analyses the board for any errors before moving on to further steps.
5. Unneeded Copper Removal
Extra copper should be removed from the board for it to function well. To carry out this step, the necessary copper is first covered so that it is not exposed to the chemical used to remove excess copper. This process is known as etching. The time taken in this step depends upon the type and size of PCBs. You must have understood by now how PCB manufacturing processes vary from PCB to PCB.
6. Inner Layer AOI Inspection
Once all the layers are cleaned and aligned (as per the drilled holes), they are layered together. For this, a machine is used to drill a pin through the registration holes. A different machine, an automated optical inspection (AOI) machine, is then used to examine the board for any errors. Note that a board with defects may have short circuits or it may fail to perform desired functions. Therefore, this is one of the most important steps in this series of “how is a PCB manufactured: step by step guide”.
An examined board with zero defects will be forwarded to the next process.
7. Lamination and Pressing
Once all the layers are aligned with the optical punch, a technician fuses them together. First, they set them in the right order and then, use metal clamps to hold them in place as lamination takes place.
A special press table with an alignment basin is used for this process. An epoxy layer, also called pre-impregnated or pre-preg, is placed first at the base of the basin. This is followed by a substrate layer and a copper foil layer, respectively. More sheets of prepreg layer are placed before finishing off with a press plate (copper layer).
As most of the procedure describing how to manufacture PCB boards includes machines and machine-regulated steps, the pressing process is also carried out with the help of another machine. Pins punched through the layers help keep them in place. If needed, the pins can be removed later.
What helps in the fusion of layers is the melting of epoxy and the pressure applied by the machine.
8. Drilling and Plating
Computer-guided drilling is necessary to expose the inner layers after lamination. The drill spots are located by an X-ray machine to avoid errors. Another copper-removal session is conducted after this step.
A drilled, fused and cleaned PCB again goes through a series of chemical washes. The purpose of one of these chemical washes is to deposit a very thin copper layer on the outer layer and the drilled holes.
You might think that this report describing “how PCBs are made” is about to end soon. But wait, a few steps are still left. Continue reading!
9. Outer Layer Imaging
This process includes the application of photoresist, similar to as described earlier. First, the outer layer is covered with photoresist, then UV light exposure takes place. The process is completed with the removal of excess photoresist before proceeding further.
10. Plating and Etching
Similar to the process of plating described in step 9, another thin copper layer is applied to the panel. To protect this copper layer from being etched off, a thin tin guard is plated to the panel.
Next comes the etching. Yes, you guessed it right! Again, as before, unwanted copper is removed with chemical solutions. The required copper is safe under the tin guard. All the connections in a PCB are established now, thanks to this step.
11. Solder Mask Application
Now, how to produce PCBs that function well, if the solder mask is not applied. Therefore, after cleaning all the panels properly, the technicians move on to the next step. Here, they apply epoxy with the solder mask film. The typical green-coloured look of a PCB is obtained with the solder mask application. Again, for the removal of undesired solder masks, UV light is used.
12. Silkscreening, Surface Finish and Testing
How PCBs are made and how they perform, depends essentially on this final stage.
Silkscreening refers to the process of printing essential information, like company ID codes, warnings, manufacturer’s identification marks, etc., on the PCB. So, after the solder mask application, PCBs are made to go through the process of silkscreening. Usually, an inkjet printer is used for this process. Then, another session of coating and curing takes place.
Now, to strengthen the quality and the bond of the solder, a surface finish is applied. The commonly used surface finishes are HAL, ENIG, OSP, immersion tin, immersion silver, ENEPIG, and hard gold plating.
Finally, a technician performs testing to ensure that the PCB is functioning as per the requirement and its design. The PCBs are good to be installed after cutting and inspection phases are carried out.
So, this detailed guide explaining “how to manufacture PCB boards” is now complete.
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