How should a PCB be designed?

An electronic engineer first selects the components that are required to carry out the operations of the finished product and then determines the most effective way to electrically link those components to one another on the printed circuit board (PCB).

You can include notes about the material type, specifications, UL requirements, solder mask, and test requirements in the drawing. 

The drawing gives the manufacturer a lot of information, such as the dimensions of the printed circuit board, the sizes and positions of the holes, and the general mechanical definition.

CAD: the creation of physical objects using computer programs

PCB layouts were formerly hand-drawn on mylar film, but today they are developed with computer-aided design (CAD) software. In the past, pcb schematic diagram layouts were manually replicated. 

The use of CAD software allows for the automatic determination of routes for drivers, hence minimizing the amount of labor that must be performed manually. 

The majority of CAD providers make a library of various component shapes and sizes available to their customers. Outlines are what you call these various forms and sizes. The term “footprint” refers to the region of the board that these components touch when they are installed.

The selection of materials

Because there is a wide range of possible combinations of copper thicknesses, epoxy characteristics, and varieties of glass fabric, the designer is responsible for defining those combinations. 

A multilayer printed circuit board’s prepreg, which is the agent that ties the layers together, has a composition that is an important factor to take into consideration. 

The term “prepreg” refers to a glass cloth that has been impregnated with epoxy and then partially cured. It is also known as “B-stage resin.” The thermal, electrical, and chemical properties are the fundamental ones.

Specifications for the various finishes available on metals

Copper is the conductor that is used on the majority of printed circuit boards (pcbs), and if it is not properly protected, it may tarnish, which will hinder the correct soldering of components to the bare board. 

A metal that does not tarnish or slowly tarnishes is applied to the exposed copper surfaces of the PCB so that they are protected. 

There is a wide range of prices, usable lives, levels of reliability, and assembly processes for metal surface treatments. The following is a list of some of the most common surface finishes:

• The Printed Circuit Board (PCB) is dipped into a pool of molten (tin-lead) solder during the Hot Air Solder Leveling (HASL) process.
• ENIG, or electroless immersion gold, is widely considered to be one of the most effective and widely used rohs finishing processes. ENIG has fantastic wetting, coplanarity, oxidation, and pot life properties.
• Immersion silver
• Organic Solderability Preservative (OSP): OSP is a rohs-compliant organic substance that is based on water and is an organic compound that selectively attaches to copper. It then provides an organic/metallic layer that protects the copper while it is being soldered.
• HASL Lead-Free is a cast bath that does not contain lead and is also free of rohs. In order to achieve the same outcomes, a nickel-modified alloy is utilized.

Establishment of the accounting record sheet

A stacking sheet is created by the designer as the final phase in the design process. This sheet provides an overview of the board.

• Creating data for the manufacturing process
• Specifications either internal or for the industry
• Underwriters Laboratory (UL) Specifications custom specifications test requirements.

Design handoff to the manufacturing company.

The following are the formats for data transfer that are used the most frequently:

• Gerber and its descendant, Gerber RS-274X.
• ODB++, gencam and PIC-D-350.

Converting designs for various tools

The transmission of electronic data that has been received from the designer is the first step in the manufacturing process. 

This step is carried out with the assistance of specialized software known as computer-aided manufacturing (CAM) software. CAM gives the maker the ability to do the following:

• The development of photographic equipment and penalization techniques
• The penalization process includes the creation of several PCB pictures, which are then used to fill the whole surface of the laminate panel in the most cost-effective manner possible. 
• Additional or Auxiliary Duties: The panel receives layer numbers, UL symbols, borders, and test coupons as additional components. After that, it is sent to the photographic plotter, which is a machine that uses laser light to draw the image onto panels during the imaging process. The completed drawing is then made on the photographic film.
• Another way of applying or exposing the HOT BED circuit board PCB Design to the build panel is called Laser Direct Imaging (LDI). This process involves directly imaging the circuit onto the build panel using a strong laser.

The creation of data for routing and scanning

In order to transmit numerically controlled (NC) drill and routing data to the drill section, you must first generate these data.

The programming of data for inspection and testing

Automated Optical Inspection (AOI) is utilized by manufacturers in the process of locating breaks or shorts in PCB routing. As a point of reference, the manufacturer will either use a gold plate or CAD data while programming the AOI memory. 

The board that is currently being inspected is scanned by the AOI machine, and the results are compared to the gold board. In the event that there was a discrepancy, the system pinpointed the exact position of the errors.

Electrical tests are performed on the bare board to validate that the design specifications from the beginning are being adhered to. The testing can be done in two different ways.

The Gold Board Test is a technique that is utilized most frequently in situations in which the Gerber or electronic data required to construct the artwork utilized by the printed circuit board manufacturer is unavailable. 

This testing method is still used for legacy goods, which typically consist of simple circuit boards with 2, 4, or even 6 layers.

This technique can be utilized in the event that Gerber data is readily available. Network List Test It is complete once all networks, which are defined as a series of points along a circuit, can be recovered from the information that was provided. 

In contrast to the gold plate test, which is a comparative examination, the connection list test examines every point to guarantee high levels of confidence in the system’s electrical soundness. The actual PCB schematic sketch is only one step away from this true point-to-point electrical test that was performed.

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