Printed circuit boards (PCBs) are boards exclusively used in electronic products. Printed Circuit Boards form the sub-structure of most of the electronic devices. PCBs were invented by Paul Eisler in 1936 and incorporated into a radio set. These boards started to become the backbone of electronics primarily due to the onset of integration technology in this domain. PCBs became the new go-to base for commercial products, testing of new devices, and any do-it-yourself projects.
What are PCBs Made of and How are PCBs Designed?
PCBs are mostly rigid boards with copper-clad laminates made of FR-4 material and copper sheets. They are non-conductive in nature having conductive copper lines etched onto them to carry current from one node to another. PCBs are basically supportive mediums used for holding different assemblies of devices together. They are used to make the incorporation of an electronic circuit easy. As far as the name is concerned, Printed Circuit Board; printed is there as all the conductive lines present on this board as connectors are etched according to the pattern printed on it by photosensitive films. PCB design software is used to design the circuit and then by using special types of printers and papers, a negative of the circuit is obtained and consequently, is printed on a copper clad, thereby resulting in a PCB board. Although the process seems to be very simple, it is not so point-to-point. The process of PCB design is easy yet complicated.
How to Design a PCB that is Easy to Produce?
The complexity of the PCB production process is completely reliant on the type of PCB board we have designed. A board with a simpler design is easier to produce than one with a complex design. However, there are other factors responsible for making a PCB easy or difficult to produce. A circuit board that is easy to produce will save a lot of cost and time, so it is critical to have a design that is friendly for PCB production. Here, we will talk about how to design PCBs that are easy to produce.
1. Fewer Layers of PCB Board: PCBs are of different kinds and heavily govern the type of manufacturing process for the board. The main types of PCBs highlighted during manufacturing are Single-layer PCBs, Double-layer PCBs and Multi-layer PCBs. As the name speaks for itself, Single layer PCBs consist of only one plate or layer of sheet having conducting lines of copper, and double-layer PCBs have two layers of copper traces, while multilayer PCBs consist of many layers of multi-circuits etched on them and all the layers are connected with each other by drilling holes in the layers. Single-layer PCBs and Double-layer PCBs are much easier to produce than multi-layer PCBs as no inner layers or lamination are needed. Of course, single-layer PCBs are easier than double-layer PCBs since no copper plating is needed. So, try to use as few layers as possible in your PCB design process, which is very helpful for an easy-to-produce PCB.
2. Standard Size of PCB Boards: Generally, PCB boards have different shapes and dimensions according to the applications. These boards are used in electronic products for prototyping and mass production of projects and devices. For most of the electronic devices, the PCB dimension should be less than 18*24 inches. It helps in making the PCB design services easier for a manufacturer and makes the mass production of PCB boards feasible. When a large number of PCB boards of the same size are ordered in bulk, the process of repeating the same steps becomes convenient and less prone to errors. On the contrary, if each board has an extremely large size, extra precautions need to be taken for their production; thus complicating the process. So we need to avoid very big sizes in our PCB design.
3. Design of Fewer Circuits: It is known PCBs have lots of electronic circuits traced onto them. Conceding the design of the circuit is simple and has fewer lines; it is easier to draw and trace on the board. A design with intricate conducting lines is a tough nut to crack and takes patience, knowledge and field experience for its precise production. If the copper trace width and spaces are too small in the PCB design, it will bring a lot of difficulties in PCB production, especially if the copper trace is less than 3mil; it is very challenging in the etching process.
4. More SMT Assembly and Less PTH Assembly: There are two ways to connect electronic components on PCB boards viz holes and surface mount devices. Components are connected manually on PCBs with hole provision by soldering. Surface mount devices called as SMDs are directly connected to the surface of boards. Surface mount technology is a serviceable methodology deployed to install electronic components on board and it is a much easier method to manufacture PCBs. A lot of time and cost will be saved by using as much SMT assembly as possible in PCB design.
All the above factors are used to determine the complexity and difficulty level of designing and producing a PCB board. Having a PCB board designed with fewer layers, simple circuit design, SMD assembly and of standard size is easy to produce and involves simple and fewer steps to manufacture. The process is adequately discussed below in step-by-step to show how PCB design helps to make PCB production easier.
Main Steps in PCB Production Which are Closed Related to PCB Design:
- PCB Design Software: Firstly we need to know how to design a PCB board. An electrical circuit board is designed by the engineer, innovator or designer in PCB design computer software such as Altium Designer, OrCAD, Pads, KiCad, Eagle CAD and EasyEDA. After the printed circuit board design is checked, it is converted to a Gerber file before being sent to the PCB manufacturer for production. It is better to use commonly used PCB design software to avoid mistakes during the transformation of different kinds of software.
- Copper Clad Laminate: Laminate forms the basic structure of a PCB board and is made of FR-4, ceramic, metal, PTFE, polyimide., etc. However, a non-conducting surface is of no help in this scenario; a conducting surface is required to replace the wires used prior to PCBs to ensure two or more circuits are connected properly. To make the laminate conducting, it is layered with an appropriate blanket of copper followed by washing off any extra resin or dust particles and is called a Copper Clad. Usually, PCB manufacturers will buy the CCL (copper-clad laminate) from different material suppliers according to the PCB design files, which will specify which material should be used. Since FR-4 material is the most widely used material with excellent electronic performance and is also cost-effective, PCB engineers should think about this in PCB board design.
- Copper Trace Etching: The process of imprinting PCB layouts printed on negative films on copper clad is defined as Tracing and is the most delicate and intricate step of the whole PCB manufacturing process. Negative films consist of different regions, signifying the outer and inner layers. It has transparent regions and some regions which are made opaque by black ink. The logic behind having two different regions is to allow UV light to pass only through the transparent regions to make conducting channels as per the diagram and is blocked by black ink for the areas with no conducting areas. UV lights have the property of hardening photoresist when in contact and thereby imaging the layouts onto the copper clad resulting in a board with copper all over its surface and some lines or traces hidden by hard photoresist.
To remove unwanted copper from the board except lines below photoresist channels, is known as the Etching process and is catalysed by Ferrous chloride solution in the ratio of 1:1.Ferrous chloride is alkaline in nature and eats away all the unwanted copper present. Acetone is utilized to remove the protective covering of photoresist from required copper channels, thereby giving out an almost complete PCB board. The copper trace is exactly etched according to the PCB designing.
So we can see copper etching is a very complex process; too small traces in printed circuit board design will bring huge difficulty to the copper etching process.
- Drilling and Copper Plating: The dilling process is used to connect the copper wires between two copper layers. These small holes are drilled by very tiny metal pins. For example, 0.2mm via holes need to be drilled by 0.3mm metal metal drill bits. If the holes are smaller than 0.2mm, we need to use drill bits smaller than 0.3mm, but such small drill bits are easier to get broken. Also, it is more difficult to plate copper into small holes less than 0.2mm. So, PCB designers should keep in mind designing drills with 0.2mm or bigger drill sizes in PCB board design.
- Solder Mask and Silkscreen: A solder mask is applied on the PCB surface, its safety against moisture, oxidation corrosion, and dust, maintaining the isolation of each path from the other. Silkscreen has the additional responsibility of making the board easier to utilize by adding all the information graphics like symbols, logos, ratings on it with the help of an Inkjet Printer. So we should choose the most usual colours in PCB design. For the solder mask, we should choose green, white or black, and for the silkscreen, we should choose white, black or yellow.
- Surface Treatment: Now that the board is almost ready, a layer of protective metal coatings is applied to protect the copper pads, which is also easier in PCB assembly. The most commonly used surface treatment is HAL, ENIG, OSP, and immersion tin, silver, ENEPIG, and hard gold plating. Generally speaking, we should use the most common and cost-effective option in our PCB board design.
- Electrical Testing: With the final product in hand, it needs to go through a final electrical testing before being launched in the market to ensure the conductivity of each trace and to check its other parameters. PCB designers should keep in mind that copper pads for testing pins need to be kept properly to make sure all circuits can be tested.
Although the foundation steps of simple and complex PCB production remain the same, there lies a huge difference between the manufacturing processes of PCBs that are easy to produce and those which are more complex in production, both in terms of production difficulty and cost. So, PCB designers should always think carefully about how to design PCBs that are easy to produce to save time and cost.