As we already know that printed circuit boards are the core basis of any electronic device. There is no concept of any electric equipment without printed circuit boards because these boards are the way of communication with the device. Also, these boards make sure that signals and other electric charges are flowing well. In the past, printed circuit boards were designed to be simple and for relatively smaller devices but nowadays, circuit boards are more complex. Today’s world of electronics is saturated with a variety of printed circuit boards such as flexible, multi-layered, having different colors, and many more. Simple electronics can use simple PCBs or single-layer PCB for working well. But if we consider sophisticated and heavy electronics particularly, then we need to use heavy printed boards also. That’s the reason multilayer printed board circuits were introduced. The layers may vary in every multilayer circuit depending upon the requirement of the electronic device. With the increasing demand for complex electronics, multilayer circuit boards are the best choice to deal with complexity. Moreover, multilayer circuit boards tend to have a small size.
What is multilayer PCB?
Printed circuit comes in many forms like single layers and double layers. We can say that single-side PCB double-side PCB are combined to make multilayer PCB. Multilayer PCBs come as a combination of several layers. Multilayer printed circuit board is the ones having more than two layers of conductive copper foil. Multilayer circuit boards have several layers put together having a protective heat sheet for insulation purposes. The manufacturing is made in such a way that two layers are connecting on the surface of the circuit board. The electrical connections can be achieved by plating holes and blind vias. More area is required for wiring in multilayer circuits because of an increasing number of layers. There should be space for dielectric material that will act as an insulator between two double layers of the circuit. A conductive metal will be attached to each side of the substrate layer of the multilayer board. For joining insulating material, a special kind of adhesive material is used for joining layers of the circuit board. There is a solder mask on each outer edge of the multilayer board. These boards are convenient in devices that require a high number of connections.
Multilayer PCB Manufacturing – Up to 32 layers
The manufacturing process for all the printed circuit boards is almost the same. The difference comes in the layers stack up, copper traces, ground layers, insulating and dielectric materials. The list of materials that generally requires for multilayer PCB manufacturing is as follows:
- Copper foils
- The skeleton of the board
- Kind of adhesive material for combining several layers of the boards
- Solder ink
- Marking ink
- Silver, alloy, or other metals for surface treatment
Now, once materials have been decided, you need to follow these steps for manufacturing a 32 layers printed circuit board:
Cutting:
In this step, you need to cut the copper clad as required by the production line. Generally available sizes in the market are 36 inches by 48 inches. Size may vary as per user requirements. It should consider using raw material in the printed board manufacturing for increasing efficiency.
Alignment of the layers:
Some stack-ups include a significant number of layers in multilayer PCBs for alignment purposes. Alignment is needed for the proper current flow within the circuit board. Plated through-holes should be positioned correctly for the ease of signal and charge flow.
Inner film:
The inner circuit pattern is shared to the printed circuit board by the inner dry film. The conductive graphics are formed for producing printed circuit boards. The inner film is vital for various processes such as etching of the inner layer, exposure, development, and sticking of the layers. The wiring width should be kept minimized because the minimum width can control the spacing of the wiring. Safety distance should be considered while designing a circuit.
Colour oxidation:
Oxidation can be done in black and brown colors, the purpose is to remove contaminants like and impurities from the surface of the circuit board. The oxidized surface will not be affected by moisture so chances of delamination are quite low.
Drilling:
Drilling is done for making plated through holes so that different layers of printed circuit boards can be attached.
Copper foiling:
Metalizing the through-hole is another important step to take. For this purpose copper and other resins are used. In the metalizing stage, the designer should select the right diameter for thickness.
Pattern plating:
In this process, copper is masked off from most of the surface of the circuit, and plating is done only on traces and pads specifically. An electrophoretic resisting material is required before plating the circuit board.
Solder masking:
This is the common process while manufacturing a printed circuit board. The layer of solder mask usually green is applied on the surface of the board. Solder mask serves the board in several ways. It prevents the board from short circuit, disconnection, lines due to moisture, insulation by bad operations, resistance, and many other exhausting moments as well.
Making profile:
The manufacturing process of the printed circuit board is done so far but it is in panel mode. So you need to profile it to give it a shape. For this purpose, separate the delivery graphics. Engineers should take care of the design and edge of the circuit while profiling it.
Testing:
The printed circuit board is ready to go for the test. The mentioned steps do not include much detail but you can an idea of how a printed circuit board can be manufactured.
There are some limitations also while designing a printed circuit board. An engineer must need to take care of the upcoming issues and limitations while design a multilayer circuit board. Once the designing phase is done, the printed board can go for packaging. Moisture-proof and vibrating resistant packaging is appreciated for this purpose.
Advantages of Multilayer PCB
If we see in the past, the electronic industry has been evolved very much now. When the heavy electronics performing multiple tasks were made, the devices required the heavy printed boards too. PCBs were limited in past having many problems of noise, crosstalk, capacitance and stray, etc. Moreover, the design of those PCBs did not offer enough constraints. Even single and double-sided PCBs were not doing that great for heavy devices. This was the era when multilayer PCBs came into being. Multilayer PCBs came into various sizes and constraints to deal with the needs of expanding applications. This is a fact that an odd number of layers in the circuit can cause some issues so even numbers of layers are preferred in heavy devices such as smartphones and computer devices. So we can say there are several benefits of multilayer printed circuit boards from a technical point of view. Some of them are given below:
- One of the significant benefits of multilayer PCBs is their size. The size is relatively low as compare to any other PCBs. In the modern age when smaller devices such as smartphones, laptops, and other electronic devices are in small size, the smaller PCB is appreciated.
- Power is distributed in a better way in a multilayer printed circuit board. When high-speed circuit switching occurs multilayer circuit helps in absorbing the power spikes.
- The functionality of the circuit board can be increased by using multilayers in a PCB.
- Multilayer PCBs are reliable and high-quality products as compare to other PCBs.
- High speed and higher capacity can be achieved by multilayer circuit boards due to their innate electric properties.
- The manufacturing process of multilayer PCBs offers both rigid and flexible circuit boards. However flexible circuit boards are preferred for better functionality.
- The density of assembly is higher in multilayer PCBs.
- Due to lightweight construction and small sizes, multilayer PCBs are highly reliable and durable in their working manner. They can deal with unexpected heat and pressure problems in an electronic device.
Disadvantages of Multilayer PCB
Although multilayer PCBs are doing great for heavy and complex devices these types of PCBs are not suitable for every electronic device. Especially for the cheap and light devices, these PCBs can create some issues. Some of the drawbacks of multilayer PCB are mentioned below:
- The significant problem with multilayer PCBs is they are very costly as compare to simple PCBs. The designing process of these PCBs requires an extensive amount of work and expertise as well. Due to high costs and difficult procedures, the laboring process is hard to manage. It is difficult to deal with any problem in the manufacturing process.
- The construction of multilayer PCBs is complicated. Even a small mistake can result in a useless product.
- It is hard for manufactures to carry the machinery for making these PCBs as the machinery is so expensive.
- As mentioned before, designing a multilayer PCB is an extensive process so an experienced designer is required other it can be problematic.
Apart from its drawbacks, 32 layer-multilayer PCBs are still doing excellent for modern electronic devices.
