Double layer PCBs can be used for many different types of projects. They also offer more design options at a lower price than multilayer boards.
Unlike single-sided PCBs, double-sided PCBs have copper on both sides. This makes them ideal for achieving high-density circuits without signal crosstalk. To make a double-sided PCB, you’ll need to know how to use an ohmmeter and perform a visual inspection for defects.
Electroless copper
Double-layer PCBs offer more design options and precision than single-layer ones. However, these circuits are more complex to manufacture and require more attention to detail. This includes preparing the substrate, designing a layout with CAD tools, drilling and etching. They also require a high-precision copper plating process for accurate connections. These processes are essential for creating reliable, durable circuit boards.
The first step in double layer pcb manufacturing is to prepare the copper-clad board by cleaning it with an alkaline detergent solution and etching it. Once it is clean, a photoresist film is applied to the surface. Then, the conductive patterns on the screen are transferred to the board through a UV light. After this, the holes on the PCB are plugged with nickel and gold.
The next step is to metallize the non-conductive bare holes by using electroless copper precipitation. After this, the copper is plated on both sides of the board to form plated through holes (PTH). This ensures that electrical signals can travel between layers. Lastly, the PCB is coated with a surface finish, which protects it from oxidation and corrosion. Several types of surface finishes are available, including HASL, OSP, ENIG, immersion tin, and immersion silver.
Photoresist film
Photoresist is a type of light-reactive compound used in double layer PCB production. It is available in both liquid and dry film form. When exposed to UV light, it changes shape and becomes resistant to etch solutions. This process is called photolithography and allows technicians to transfer a computer-generated pattern onto the substrate. The pattern is transferred by using a photomask that lets through or blocks certain wavelengths of light.
There are three types double layer pcb manufacturing of photoresist, categorized by their chemical structures. Negative photoresist includes a photoinitiator that reacts with ultraviolet light to produce free radicals and facilitate cross-linking reactions. This renders the unexposed sections of the photoresist insoluble.
The photoresist can be applied to the board either by spraying or electrically. Choosing the right application method can significantly improve the quality of the resist coating. Proper coating conditions are key to achieving precision and circuit accuracy. In addition, the manufacturer should have a good design rule check and be able to meet delivery commitments. A good manufacturing partner will also offer transparent pricing and be clear about their rework and test fees.
Circuit printing
Double layer PCBs are ideal for a variety of applications, including consumer electronics, telecommunications, automotive and industrial controls. They feature a non-conductive substrate like FR-4 fiberglass with copper layers bonded to both sides. The copper layers serve as conductive surfaces that transmit signals between mounts on the board. These signals are transferred through traces that run along the conductive surface and are often grouped together to reduce signal interference. Careful planning of these traces ensures that they are routed properly.
The next step is circuit printing, where a negative image of the PCB’s copper surface gets transferred to the panel using a photosensitive material called photoresist. The photoresist is exposed to UV light and hardens.
The final step is lamination, where the copper-clad cores and prepreg layers are stacked together and bonded with an epoxy resin. This process ensures that the layers are precisely aligned to prevent voids and disconnected vias. To achieve this, modern systems use optical alignment and precision pins to accurately place the layers. Then, they are heated and pressed under controlled conditions to bond them. This ensures that there is no air entrapment and allows for accurate pressure control.
Etching
The etching process is an important step in double layer PCB manufacturing. It involves immersing the board in a solution that removes excess copper and creates the circuit pathways. It is crucial to follow the steps precisely – a double layer pcb small mistake can ruin the entire board. The PCB will then be passed through an automated optical inspection to make sure that the pathways are correct.
The next step is imaging the inner layer. This is done using a plotter printer and a solder mask film. The machine makes registration holes to ensure that the films line up properly. After the inner layer is imaging, it is exposed to UV light. This hardens the chemicals in the areas that will not wash off during etching. The unhardened areas are then removed by a chemical called tin stripping solution.
Once the etching is complete, it’s time to install the components. This is a tricky task because double-sided PCBs have more complex layouts, requiring careful placement. It is important to use the right tools and materials, and to clean the pieces carefully.
Drilling
Drilling is one of the most important steps in double layer PCB manufacturing. It is the process that makes vias and provides connectivity between different layers of the board. It also ensures that the components are compactly placed and that the electrical signals are uninterrupted. It is a critical bottleneck in the PCB fabrication process, and it’s essential to find a fabricator with high-quality drill technology.
When drilling multilayer PCBs, X-ray alignment is crucial for accurate positioning of the holes. Once the hole is drilled, it’s coated with copper plating, which allows electrical current to flow through the hole without interference. This step is called plated through hole (PTH).
To make double-layer PCBs, manufacturers start with a substrate material such as FR4. They then add copper on both sides to create the circuit boards. After that, they drill tiny holes called vias to connect the copper traces. During the process, the manufacturer uses a technique called back drilling to reduce signal reflection from the via stubs. There are also alternative construction techniques that can be used to minimize stub length, such as laser-drilled vias and blind and buried vias.
