PCB Manufacturing Techniques

What is PCB??

The printed circuit board (PCB) acts as the linchpin for almost all of today’s modern electronics.PCBs, bring electronics to life by routing electrical signals where they need to go to satisfy all the device’s electronic requirements. PCBs are the boards that are used as the base in most electronics – both as a physical support piece and as the wiring area for the surface-mounted and socketed components. PCBs are most commonly made out of fiberglass, composite epoxy, or another composite material. For this to happen, PCBs are laid with a network of paths outlined in the traces. It’s these copper pathways that allow PCBs to direct electrical currents around their surface.

Step 1: Types of PCB

There are three main types of circuit boards that get manufactured on a consistent basis:

Single-Sided Circuit Boards: which is a type of PCB which comes with only one layer of conducting material on one side of the board and other side is used for incorporating different electronic components. these boards, when made with an FR4 (glass fibre based board) base, have rigid laminate of woven glass epoxy material, which is then covered on one side with a copper coating that is applied in varying thicknesses depending on the application

Double-Sided Circuit Boards: are the same as single-sided PCBs, but the difference is they have two-sided traces with a top and bottom layer. Double-sided PCBs can mount conductive copper and components on both sides of the printed circuit board so that the traces can cross over each other. Double-sided boards have the same woven glass epoxy base as single-sided boards — however, in the case of a double-sided board, there is the copper coating on both sides of the board, also to varying thicknesses depending on the application

Multi-Layer Boards: These use the same base material as single and double-sided boards, but are made with copper foil instead of copper coating — the copper foil is used to make “layers,” alternating between the base material and copper foil until the number of desired layers is reached.

Step 2: How Are PCBs Made?

Step 1: Design and Output

The beginning step of any PCB manufacture is, of course, the design. PCB manufacture and design always start with a plan: the designer lays out a blueprint for the PCB that fulfills all the requirements as outlined using any program as Gerber.

Step 2: From File to Film

After all the checks are complete, the PCB design can be printed. Manufacturers use a special printer called a plotter, which makes photo films of the PCBs, to print circuit boards. Manufacturers will use the films to image the PCBs. Although it's a laser printer, it isn't a standard laser jet printer. Plotters use incredibly precise printing technology to provide a highly detailed film of the PCB design. The final product results in a plastic sheet with a photo negative of the PCB in black ink. The inside layers of the PCB are represented in two ink colors:

Black Ink: Used for the copper traces and circuits of the PCB

Clear Ink: Denotes the non-conductive areas of the PCB, like the fiberglass base.

Step 3: Where Will the Copper Go?

Now it's time to print the figure on the film onto a copper foil. This step in PCB manufacturing prepares to make actual PCB. The basic form of PCB comprises a laminate board whose core material is epoxy resin and glass fiber that is also called substrate material. The laminate serves as an ideal body for receiving the copper that structures the PCB. Substrate material provides a sturdy and dust-resistant starting point for the PCB. Copper is pre-bonded on both sides. The process involves whittling away the copper to reveal the design from the films. In PCB construction, cleanliness does matter. The copper-sided laminate is cleaned and passed into a decontaminated environment. During this stage, it's vital that no dust particles settle on the laminate. An errant speck of dirt might otherwise cause a circuit to be short or remain open. Next, the clean panel receives a layer of a photo-sensitive film called photoresist. The photoresist comprises a layer of photoreactive chemicals that harden after exposure to ultraviolet light. This ensures an exact match from the photo films to the photoresist. The films fit onto pins that hold them in place over the laminate panel.

The film and board line up and receive a blast of UV light. The light passes through the clear parts of the film, hardening the photoresist on the copper underneath. The black ink from the plotter prevents the light from reaching the areas not meant to harden, and they are slated for removal. After the board becomes prepared, it is washed with an alkaline solution that removes any photoresist left unhardened. A final pressure wash removes anything else left on the surface. The board is then dried. The product emerges with resist properly covering the copper areas meant to remain in the final form. A technician examines the boards to ensure that no errors occur during this stage. All the resist present at this point denotes the copper that will emerge in the finished PCB.

Step 4: Removing the Unwanted Copper

With the photoresist removed and the hardened resist covering the copper we wish to keep, the board proceeds to the next stage: unwanted copper removal. Just as the alkaline solution removed the resist, a more powerful chemical preparation eats away the excess copper. The copper solvent solution bath removes all of the exposed copper. Meanwhile, the desired copper remains fully protected beneath the hardened layer of photoresist. Now that the solvent removed the unwanted copper, the hardened resist protecting the preferred copper needs washing off. Another solvent accomplishes this task. The board now glistens with only the copper substrate necessary for the PCB.

Step 5: Layer Alignment and Optical Inspection

With all the layers clean and ready, the layers require alignment punches to ensure they all line-up. The registration holes align the inner layers to the outer ones. The technician places the layers into a machine called the optical punch, which permits an exact correspondence so the registration holes are accurately punched.
Once the layers are placed together, it's impossible to correct any errors occurring on the inner layers. Another machine performs an automatic optical inspection of the panels to confirm a total absence of defects. The original design which the manufacturer received, serves as the model.

Step 6: Layer-up and Bond

In this stage, the circuit board takes shape. All the separate layers await their union. With the layers ready and confirmed, they simply need to fuse together. Outer layers must join with the substrate. The process happens in two steps: layer-up and bonding.
The outer layer material consists of sheets of fiberglass, pre-impregnated with epoxy resin. The shorthand for this is called prepreg. A thin copper foil also covers the top and bottom of the original substrate, which contains the copper trace etchings. Now, it's time to sandwich them together.A technician begins by placing a prepreg layer over the alignment basin. The substrate layer fits over the prepreg before the copper sheet is placed. Further sheets of prepreg sit on top of the copper layer. Finally, an aluminum foil and copper press plate complete the stack. Now it's prepped for pressing.

The entire operation undergoes an automatic routine run by the bonding press computer. The computer orchestrates the process of heating up the stack, the point in which to apply pressure, and when to allow the stack to cool at a controlled rate.

Step 7: Drill

Finally, holes are bored into the stack board. All components slated to come later, such as copper-linking via holes and leaded aspects, rely on the exactness of precision drill holes. The holes are drilled to a hairs-width - the drill achieves 100 microns in diameter, while hair averages at 150 microns.To find the location of the drill targets, an x-ray locator identifies the proper drill target spots. Then, proper registration holes are bored to secure the stack for the series of more specific holes.

Before drilling, the technician places a board of buffer material beneath the drill target to ensure a clean bore is enacted. The exit-material prevents any unnecessary tearing upon the drill's exits. A computer controls every micro-movement of the drill - it's only natural that a product that determines the behavior of machines would rely on computers. The computer-driven machine uses the drilling file from the original design to identify the proper spots to bore.

Step 8: Plating and Copper Deposition

After drilling, the panel moves onto plating. The process fuses the different layers together using a chemical deposition. After a thorough cleaning, the panel undergoes a series of chemical baths. During the baths, a chemical deposition process deposits a thin layer - about one micron thick - of copper over the surface of the panel. The copper goes into the recently drilled holes. Prior to this step, the interior surface of the holes simply exposes the fiberglass material that comprises the interior of the panel. The copper baths completely cover, or plate, the walls of the holes. Incidentally, the entire panel receives a new layer of copper. Most importantly, the new holes are covered. Computers control the entire process of dipping, removal, and procession.

Step 9: Outer Layer Imaging

In Step 3, we applied photoresist to the panel. In this step, we do it again - except this time, we image the outer layers of the panel with PCB design. We begin with the layers in a sterile room to prevent any contaminants from sticking to the layer surface, then apply a layer of photoresist to the panel. The prepped panel passes into the yellow room. UV lights affect photoresist. Yellow light wavelengths don't carry UV levels sufficient to affect the photoresist. Black ink transparencies are secured by pins to prevent misalignment with the panel. With panel and stencil in contact, a generator blasts them with high UV light, which hardens the photoresist. The panel then passes into a machine that removes the unhardened resist, protected by the black ink opacity. The process stands as an inversion to that of the inner layers. Finally, the outer plates undergo inspection to ensure all of the undesired photoresists was removed during the previous stage.

Step 10: Plating

We return to the plating room. As we did in Step 8, we electroplate the panel with a thin layer of copper. The exposed sections of the panel from the outer layer photoresist stage receive the copper electroplating. Following the initial copper plating baths, the panel usually receives tin plating, which permits the removal of all the copper left on the board slated for removal. The tin guards the section of the panel meant to remain covered with copper during the next etching stage. Etching removes the unwanted copper foil from the panel.

Step 11: Final Etching

The tin protects the desired copper during this stage. The unwanted exposed copper and copper beneath the remaining resist layer undergo removal. Again, chemical solutions are applied to remove the excess copper. Meanwhile, the tin protects the valued copper during this stage. The conducting areas and connections are now properly established.

Step 12: Solder Mask Application

Before the solder mask is applied to both sides of the board, the panels are cleaned and covered with an epoxy solder mask ink. The boards receive a blast of UV light, which passes through a solder mask photo film. The covered portions remain unhardened and will undergo removal. Finally, the board passes into an oven to cure the solder mask.

Step 13: Surface Finish

To add extra solder-ability to the PCB, we chemically plate them with gold or silver. Some PCBs also receive hot air-leveled pads during this stage. The hot air leveling results in uniform pads. That process leads to the generation of surface finish. PCBCart can process multiple types of surface finish according to customers' specific demands.

Step 14: Silkscreen

The nearly completed board receives ink-jet writing on its surface, used to indicate all vital information pertaining to the PCB. The PCB finally passes onto the last coating and curing stage.

Step 15: Electrical Test

As a final precaution, a technician performs electrical tests on the PCB. The automated procedure confirms the functionality of the PCB and its conformity to the original design. At PCBCart, we offer an advanced version of electrical testing called Flying Probe Testing, which depends on moving probes to test electrical performance of each net on a bare circuit board.

Step 16: Profiling and V-Scoring

Now we've come to the last step: cutting. Different boards are cut from the original panel. The method employed either center on using a router or a v-groove. A router leaves small tabs along the board edges while the v-groove cuts diagonal channels along both sides of the board. Both ways permit the boards to easily pop out from the pane