PCBs are the backbone of all major electronics. These amazing inventions appear in almost all computing electronic devices, including simpler devices such as digital clocks, calculators, etc. For starters, a PCB transmits electrical signals through an electronic device, fulfilling the electrical and mechanical circuit requirements of the device. In short, the PCB tells where the power goes, bringing your electronics to life.
The PCB conducts current around its surface through a network of copper paths. The complex copper wiring system determines the unique role of each printed circuit board.
Before PCB design, circuit designers we recommend you to visit the PC board workshop and discuss the PCB manufacturing needs face to face with the manufacturer. It helps prevent designers from finding any unnecessary mistakes during the design phase. However, as more companies outsource their PCB manufacturing consulting to overseas suppliers, this becomes impractical. Therefore, we present this article to properly understand the PCB manufacturing steps. Hopefully it provides circuit designers and newcomers to the PCB industry with a clear view on how to make printed circuit boards and avoid making those unnecessary mistakes.
Detailed steps of PCB printed circuit board manufacturing process
1. Design and output
The boards should be strictly compatible and designers create a PCB layout using PCB design software. Commonly used PCB design software includes Altium Designer, OrCAD, Pads, KiCad, Eagle, etc. Note: Before PCB fabrication, designers should inform their contract manufacturers about the version of the PCB design software used to design the circuit, it helps avoid problems caused by differences.
Once a PCB design is approved for production, designers export the design to a format supported by their manufacturer. The most commonly used program is called Extended Gerber. The 1980's baby food ad campaign sought beautiful babies, and this software created some beautifully designed offspring. Gerber is also named IX274X.
The PCB industry has extended Gerber as the perfect output format. Different PCB design software may require different Gerber file generation steps, all of which encode comprehensive important information including copper trace layers, drill maps, apertures, component symbols and other options. All aspects of the PCB design are checked. The software executes a supervisory algorithm on the design to ensure that no errors are found. Designers also checked plans for elements related to track width, board margins, trace and hole spacing, and hole size.
After a thorough inspection, the designer forwards the PCB files to PC Board Houses for production. To ensure the design meets the smallest tolerances in the manufacturing process, almost all PCB Fab Houses perform a Design for Manufacture (DFM) check prior to board fabrication.
2. From document to film
After the designer outputs the PCB schematic file and manufacturer, the PCB printing begins with DFM inspection. Manufacturers use a special printer called a plotter to make photo film of the PCB to print the circuit board. Manufacturers will use these films to image PCBs. Although it is a laser printer, it is not a standard laser inkjet printer. Plotters use incredibly precise printing techniques to provide highly detailed thin films of PCB designs.
The final product results in a PCB negative photo of the plastic using black ink. For the inner layers of the PCB, the black ink represents the conductive copper portion of the PCB. The remaining transparent portions of the image represent areas of non-conductive material. The outer layer takes the opposite pattern: the copper color is clear, and the black refers to the areas that are etched away. The plotter automatically develops the film and the film is stored securely to prevent any unwanted contact.
Each layer of PCB and solder mask has its own clear and black film. In total, a two-layer PCB requires four pieces: two for the layers and two for the solder mask. It is worth noting that all films must correspond perfectly to each other. When used harmoniously, they draw PCB alignment.
To achieve perfect alignment of all films, holes should be punched in all films. Determine the accuracy of the holes by adjusting the table on which the film is placed. The holes are punched when a tiny calibration of the table results in the best match. In the next step of the imaging process, these holes will fit the dowels.
3. Printing the inner layer: where is the copper wire?
The movie creation in the previous step was designed to graph the copper path. Now it's time to print the graphics from the film onto the copper foil.
This step in PCB manufacturing prepares the actual PCB to be made. The basic form of PCB consists of laminates whose core material is epoxy resin and fiberglass, also known as substrate material. Laminate is an ideal body to receive the copper that makes up the PCB. The substrate material provides a strong and dust-proof starting point for the PCB. Copper is pre-bonded on both sides. The process involves trimming the copper to reveal the thin film's design.
In PCB construction, cleanliness is important. Clean the copper side laminate and pass it to a decontaminated environment. At this stage it is important that no dust particles are deposited on the laminate. The wrong dirt can cause a circuit to short or remain open.
Next, the cleaning panel receives a layer of photosensitive film called photoresist. Photoresists include a layer of photoreactive chemicals that harden after exposure to ultraviolet light. This ensures an exact match from photographic film to photoresist. These films fit onto the pins, securing them to the laminate.
The film and circuit board line up and receive UV light. The light passes through the transparent portion of the film, hardening the photoresist on the copper below. The black ink from the plotter prevents light from reaching areas that shouldn't be hardened and can remove them.
After the board was ready, any photoresist that was washed with an alkaline solution did not harden. A final pressure wash removes anything else left on the surface. The board is then dried.
As the product emerges, the resist covers the copper areas appropriately to maintain the final form. Technicians check the board to make sure no errors occur at this stage. All the resist present at this point represents the copper that will be present in the finished PCB.
This step only applies to boards with more than two layers. Simple double-layer boards can be drilled directly. Multilayer boards require more steps.
4. Remove Unwanted Copper
With the photoresist removed and the hardened resist covering the copper we want to keep, the board goes to the next stage: unwanted copper removal. Just like alkaline solutions remove resist, stronger chemicals will remove excess copper. A copper solvent solution bath removes all exposed copper. At the same time, the desired copper remains fully protected under the hardened layer of photoresist.
Not all copper plates are the same. Some heavier boards require larger amounts of copper solvent and different exposure times. Also, heavier copper boards require extra attention to track spacing. Most standard PCBs rely on similar specifications.
Now that the solvent has removed the unwanted copper, the hardened resist protecting the preferred copper needs to be washed away. Another solvent accomplishes the task. The board now flashes only the copper substrate needed for the PCB.
5. Layer Alignment and Optical Inspection
With all layers clean and ready, the layers need to be aligned punched to make sure they all line up. Alignment holes align the inner layer with the outer layer. Technicians put the layers into a machine called an optical punch, which corresponds exactly, and thus punches the holes accurately.
Once the layers are put together, there is no way to correct any errors that occur with the inner layers. Another machine performs an automated optical inspection of the panels to confirm that they are completely free of defects. The manufacturer received the original Gerber design as a model. The machine scans the layers using a laser sensor and proceeds to electronically compare the digital image to the original Gerber file.
If the machine finds inconsistencies, the comparison is displayed on the display for the technician to use for evaluation. Once the layer passes inspection, it goes to the final stage of PCB production.
6. Layering and bonding
At this stage, the circuit board is formed. All individual layers await their union. With the layers prepared and confirmed, they just need to be fused together. The outer layer must be attached to the substrate. The process takes place in two steps: layering and bonding.
The outer material consists of fiberglass panels pre-impregnated with epoxy resin. This shorthand is called prepreg. A thin copper foil also covers the top and bottom of the original substrate, which contains the copper trace etching. Now, it's time to clip them together.
Bonding takes place on a heavy duty steel table with metal clips. The layers fit securely onto pins attached to the table. Everything must fit snugly to prevent shifting during alignment.
The technician first places the prepreg layer on the alignment groove. Before placing the copper plate, the base layer is attached to the prepreg. Additional prepreg pieces are placed on top of the copper layer. Finally, the aluminum foil and copper press plate are stacked. Now it's ready to be pressed.
The entire operation runs through the automatic program of the bonding press. The computer coordinates the process of heating the stack, the point at which pressure is applied, and when the stack is allowed to cool at a controlled rate.
Next, a certain amount of unpacking occurs. All layers are molded in a super sandwich PCB, and technicians only need to unpack the multilayer PCB product. It's a simple matter of removing the limit pins and discarding the top pressure plate. The goodness of the PCB wins out from the case of the aluminum laminate. The copper foil included in the process still contains the outer layers of the PCB.
7. Drilling
Finally, drill holes in the stacking board. All subsequent components, such as copper connections through holes and leads, rely on precision drilling for precision. The hair width of the drilled holes is - the diameter of the drill is 100 microns, while the hair is 150 microns on average.
To find the location of a borehole target, the X-ray locator identifies the correct borehole target point. Then, drill the appropriate pilot holes to secure a series of more specific stacks of holes.
Before drilling a hole, the technician places a plate of cushioning material under the drill bit target to ensure the hole is clean. promulgated. The exit material prevents any unwanted tearing at the drill exit.
The computer controls every nudge of the drill - it's only natural that products that determine machine behavior depend on computers. A computer-driven machine uses the original designed drill file to identify the appropriate location for the drill.
The drill uses a pneumatic spindle, which rotates at 150,000 rpm. At this speed, you might think drilling happens in an instant, but there are a lot of holes that need to be drilled. The average PCB contains over 100 complete holes. During drilling, each bit needs its own special moment, so it takes time. These holes later accommodate vias and mechanical mounting holes for the PCB. After electroplating, the final gluing of these parts takes place later.
After drilling is complete, the extra copper lines the edges of the production panels to be removed by analysis tools.
8. Electroplating and copper deposition
After drilling, the panels are moved to plating. The process uses chemical deposition to fuse the different layers together. After thorough cleaning, the panels go through a series of chemical baths. In the bath, the chemical deposition process deposits a thin layer - about 1 micron thick - of copper on the surface of the panel. Copper goes into the most recent drill hole.
Before this step, the inner surface of the hole exposes only the fiberglass material that makes up the interior of the panel. The copper bath completely covers or plated through the hole walls. By the way, the entire panel receives the new copper layer. Most importantly, the new hole is covered. The computer controls the entire process of dipping, removal and disposal.
9. Outer layer imaging
In step three, we apply photoresist to the panel. In this step, we do it again - except this time, we image the outer layers of the panel with the PCB design. We start with the layers in a sterile room to prevent any contaminants from adhering to the surface of the layers, then apply a layer of photoresist to the panel. The prepared panel goes into the yellow room. UV light affects photoresist. UV levels at yellow wavelengths are not sufficient to affect the photoresist.
Black ink transparencies are pinned to prevent misalignment with the panel. With the panel and stencil in contact, the generator illuminates them with high UV light, which hardens the photoresist. The panel then goes into a machine that removes the unhardened resist, protected by the opacity of the black ink.
The process is the opposite of the inversion of the inner layer. Finally, the outer plate is inspected to ensure that all unwanted photoresist has been removed in the previous stage.
10. Electroplating
We go back to the electroplating room. As we did in step 8, we plated the panel with a thin layer of copper. The exposed portion of the panel from the outer photoresist table received copper plating. After the initial copper plating bath, the panels typically receive tin plating, which allows all copper remaining on the board to be removed for removal. In the next etch stage, tin protecting parts of the panel means keeping the copper covered. Etching removes unwanted copper foil from the panel.
11. Final Etching
Tin protects the required copper at this stage. Unwanted exposed copper and copper under the remaining resist layer undergoes removal. Again, a chemical solution is applied to remove excess copper. At the same time, tin protects the valuable copper at this stage. The conductive areas and connections are now properly established.
12. Solder mask application
Before applying the solder mask to both sides of the board, clean the panel and cover with epoxy solder mask ink. The circuit board receives UV light through the solder mask to photographic film. The covered portion remains unhardened and will be removed. Finally, the board goes into the oven to cure the solder mask.
13. Surface treatment
To add extra soldering capability to the PCB, we electroless plating them with gold or silver. At this stage, some PCBs can also receive hot air flat pads. Hot air leveling results in an even pad. This process results in the creation of a surface finish. PCBCart can handle many types of surface treatments according to the specific requirements of customers.
14. Screen printing
The near-finished circuit board receives inkjet writing on its surface to indicate all the important information related to the PCB. The PCB finally goes to the final coating and curing stage.
15. Electrical test
As a last resort, technicians conduct electrical tests on the PCB. Automated procedures confirm the functionality of the PCB and its consistency with the original design. At PCBCart, we offer an advanced type of electrical testing called flying probe testing, which relies on moving probes to test the electrical performance of each net on a bare circuit board.
16. Analysis and V-Scoring
Now we come to the final step: cutting. Cut out different boards from the original panels. The approach taken either centers around the use of routers or V-grooves. The router leaves small tabs along the edge of the board, while the V-grooves cut diagonal channels along the sides of the board. Both ways allow the board to be easily ejected from the panel.
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