PCB is an abbreviation for printed circuit board which comes with lines, paths. It incorporates traces on a single panel to electrically connect different electronic components. It comprises substrate material that is usually fiberglass on which copper foil is laminated to provide a conductive path throughout the board’s entire surface. Single-sided PCB has a conductive layer on one side of PCB. In contrast, a double-sided PCB comes with a conductive copper layer on both sides of the board. Double-Sided PCB, also known as two-layer PCB, has two conductive copper layers, one on each side of the board. Through-Hole Technology and Surface-Mount Technology are two separate ways to attach components to these boards. Both technologies have advantages and drawbacks that depend on the preferences and specifications of an application.
What is Single-Sided Design?
Single-sided design reduces the PCB cost, and they are still popular because they are so cheap to manufacture. If the design is simple enough, then one must use a single-sided board. However, the single-sided design requires some unique techniques, which aren’t necessary once you go to double-sided and multilayer structures. It is undoubtedly more challenging than a double-sided layout because it requires various jumper links. It is all about a balance between board size and the number of jumper links needed. Almost every single-sided PCB requires some jumper links, so it is crucial to minimize these. On a single-sided surface, part positioning is much more critical. Instead of conveniently aligning parts, the component placement tries to have the shortest paths possible. The double-sided design provides an extra degree of freedom for designing your board. Things that were next to impossible on a single-sided board become relatively easy when adding extra layers. Double-sided design allows using good ground plane techniques required for high-frequency designs.
Single sided board stack up
What is Double-Sided PCB Design?
Nowadays, in the first step, we design and simulate a circuit schematic in a computer application. There are numerous simulation software programs available that we will discuss later. After the initial simulation, the next step is to prepare a prototype. In the old days, experts manually made PCBs by using adhesives, taps, pads, etc. Today, however, CAD applications allow seamless integration of circuit schematic design and PCB prototyping. Many companies provide circuit design and PCB manufacturing services. PCB design requires a great deal of knowledge to position hundreds of components and thousands of tracks into an intricate pattern to fulfill a whole host of physical and electrical requirements. Appropriate PCB design is an integral part of an entire circuit design process. Being a part of an electrical circuit, PCB traces have resistance, inductance, capacitance, and the PCB layout may make or break the design’s operation and electrical performance.
Double sided PCB stack up
The PCB Layout
Before starting the PCB layout process, we should have an accurate schematic diagram. An excellent schematic design streamlines the PCB design process. These two processes are interwoven as a PCB converts a schematic into its manufactured version. A good and neat schematic would create a professional PCB.
The PCB Measuring Units
Before forwarding a PCB layout for manufacturing, we must check the uniformity of our measurement units. PCB design industry still uses imperial units because the majority of electronic components manufacturing involves imperial pin spacing. For example, one mil (1 thou) is equal to 0.1 inches (2.54 mm) and is used by PCB designers and manufacturers worldwide. Newer surface mount parts use metric pin spacing and dimensions. Many component datasheets also have metric measurements, even though the datasheet lists spacing in an imperial grid. One inch is also commonly known as one pitch. Hundred ‘thou’ serves as a reference point for all aspects of PCB design. Many common component lead spacings are multiples or fractions of this basic unit. 50 and 200 thou are the most common. The IPC has metricized all its standards and rarely refers to imperial units.
PCB Grids and Views
There are two types of grids in a PCB Layout design, a visible grid and a snap grid. The visible grid is an on-screen grid of lines or dots which acts as a background behind your design and dramatically helps you line up components and tracks. The snap grid is one where the cursor snaps into fixed grid positions while placing parts and tracks. In PCB design, laying out parts according to the grids is essential, especially in CAD applications. The grid keeps the components neat and symmetrical. It makes the placement of components easier as the layout grows in size and complexity. The standard grid dimensions include 100, 50, 25, and 10 thou.
Furthermore, components on a PCB layout are placed according to the through-the-board method. In this method, various layers are stacked on top of each other, and the designer views from the top of the board. The only time you will look at your board from the bottom is for manufacturing or checking purposes.
What is PCB Tracks?
Tracks are the actual connections between various components. There are no standard sizes for the track. Instead, they typically depend on the electrical needs, the available space, and the optimum clearance. Larger width tracks have lower resistance and inductance, are easier to etch, and cheaper to manufacture. The lower-width tracks need greater care from the manufacturer to align and etch the board, resulting in a higher cost. Good design practice keeps traces as wide as possible and reverts to thinner tracks when required to meet clearance. Changing track from large to small and then back to large is called necking. This is necessary when you have to lay track between IC or component pads. In practice, the amount of current flowing through a track dictates its size. The maximum tolerable temperature rise of the copper’s track and thickness on the PCB also affects the size. Every track has a certain amount of resistance, so the track dissipates heat like a resistor. The wider track keeps the resistance low.
PCB Vias and Pads
A pad is a copper surface that allows soldering the component to the board. It mechanically supports the component. A via is a pad with a plated hole drilled in its center in the form of a copper cylinder. Vias electrically and thermally connect traces, pads, and polygons on various PCB layers. Pad measurements, dimensions, and shapes depending on the component type and board assembly and manufacturing process. The pad-hole ratio is a vital parameter that helps decide optimum diameters for pad and holes. The Pads are usually used for surface-mount components, whereas vias are used for through-hole parts. The Pads for leaded elements such as resistors, capacitors, and diodes are generally round. Dual In-Line (DIL) components like IC’s often use rectangular or oval-shaped pads. Many surface mount components use rectangular pads. Vias link the tracks from one side of the board to another. Vias are created with electrically coupled holes, called Plated Through Holes (PTH). Making a via connect two layers is usually called stitching because it efficiently stitches both layers electrically together.
PCB Polygons and Clearances
Polygons are available on many PCB packages. A polygon automatically fills in the desired area with copper while meandering around other pads and tracks. The polygons are particularly handy in laying down ground planes. Ensure to place polygons after positioning all the traces and pads.
Electrical clearances are an essential requirement for all boards. Very tight clearance between tracks and pads leads to hairline shorts and various other etching problems during the manufacturing process. The smaller clearances make it very hard to find faults after assembling the board. It is better not to push the limits of the PCB manufacturer. It is better to stay above their recommended minimum spacing unless absolutely necessary.
Double-Sided PCB Manufacturing
PCB manufacturing involves various highly specialized processes. It is the PCB schematic and layout designer’s job to optimize the design according to the manufacturing. Some critical steps are listed below.
- An automated pick-and-place machine manufactures the PCB in an industrial setting. A readymade copper-clad PCB board comes in the form of a panel. The designer should fit as many circuits as possible to a single panel to minimize the manufacturing cost.
- Tooling strips on the top and bottom of a panel allow swift and automatic handling of the board. Tooling strips are blank board strips that extend the length of the board on the top and bottom. If necessary, they provide tooling holes, fiducial points, and other manufacturing data.
- Fiducial markings on PCB tooling strips are optical orientation and alignment aids. Automated pick and place machines use them to match the board and identify reference points. The machine’s video camera will locate the core of fiducial marks and use them as a reference point. A circular pad on the copper sheet should serve as the fiducial symbol. A solder mask must not cover any fiducial mark.
- Assume that a copper region is attached to a surface mount pad. The copper region would then serve as a very powerful heat sink. When soldering, the heat would flow away from the pads. Dry joints and other soldering issues can occur as a result of this. In these cases, a thermal relief link, made up of many smaller tracks, links the pads to the copper plane.
What is PCB Soldering?
Soldering considerations need to take into account when laying out your board. There are three basic soldering techniques
- Manual soldering
- Wave Soldering
- Reflow Soldering
For prototypes and small-scale manufacturing, manual hand soldering is the conventionally used process. Surface mount and through-hole technologies benefit from wave soldering. The whole board passes over liquid solder. Bridging may be prevented by utilizing solder caps. There would be no solder behind larger components since the board goes through the wave solder machine in one direction. Before wave soldering, an adhesive binds surface mount devices to the frame. For all surface-mount parts, reflow soldering is preferable. With the aid of solder stencils, the bare board is first covered with a solder paste mask over the pads. Then each part is mounted, and often an adhesive is used to keep them in position. After that, the whole board is baked in an ultraviolet or nitrogen oven. On the pads and part leads, the solder paste melts or reflows, forming a solid joint.
For through-hole applications, there is a newer reflow approach known as pin-in-paste or invasive reflow. For PCBs comprising both through-hole and surface-mount parts, manufacturers often mix wave and reflow soldering. While wave soldering is less costly, it restricts part placement choices. Reflow soldering is more time-consuming and expensive, but it allows for highly dense surface-mount packaging.
What are Double-Sided PCB Applications?
Double-sided PCBs are relatively cheaper than multilayer PCBs. Double-sided PCBs offer Increased circuit density and incorporate more components that effectively increase the circuit’s density. It’s better to have some parts connected to the bottom side rather than all on one side. Using two sides instead of one makes for a smaller total board size that can be essential when designing lightweight, integrated systems. The durability is extreme as the holes are chemically polished and enabled to ensure proper plating and communication between the top and bottom layers. Having cooper at both sides allows double-sided PCB to be more flexible.
Double-sided PCBs feature a moderate complexity level and are primarily used in a wide range of applications and deemed valuable when a single layer or multiplayer PCB fails to fulfill the project’s requirement. Double-sided PCB helps reduce cost by providing more area to place components on shorter boards. They also permit closer routing traces compared to single-sided PCB. Suppose the board needs to provide a current to other shields or slaves. In that case, they can sink or source current by using the bottom layer as a ground copper pour.
Following are some practical applications of double-sided PCBs.
- Power Converters, such as rectifiers, inverters, DC-DC converters, Ac-AC converters, and UPS
- Automotive dashboards and various other vehicle circuits
- Power system monitoring, test equipment, and control relays
- Instrumentation, HVAC, and Vending machines
- Power supplies, Regulators, and Industrial control equipment
- The traffic control system and LED lighting
- Power amplifiers, cellphones, and printers
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