Almost all electronic devices are made up of one or more printed-circuit boards. The printed circuit board not only holds the components and ICs together, but also facilitates the interconnections between each component. Large volumes of PCBs are manufactured for computers, portable electronics, and entertainment equipment every day. In addition, PCBs are also made for manufacturing, testing equipment, and spacecrafts.
Every electronics engineer out there, at some point in time, will have to design their own PCBs. To be successful in the PCB assembly industry, technicians and engineers must have the ability to construct a high-quality, all-purpose PCB. They definitely must learn how to do this with utmost confidence that the final product will not only meet the objective, but if possible exceed it.
Basic PCB Design Process
PCB design and PCB assembly start off by recognizing that there’s a need for a specially designed PCB. After finding out why there is a need for a particular PCB, designers should then decide on a final concept. This final design concept includes, but is not limited to, the specific functions that PCB must perform and have, circuit placements, circuit interconnection, design features, and the final dimensions.
In addition, the ambient temperature that the PCB will be operating in should also be addressed. Once the ambient operating temperature is determined, the designer should then use this information to specify what kind of material should be used to build the PCB. PCB materials and components should be selected accordingly to ensure operation under all forms of duress that the printed circuit board may be submitted to during its operational lifetime.
The PCB schematic should be drawn according to the final concept. The detailed schematic should illustrate the electrical implementation of each PCB function. Once the schematic is drawn, the designer can then make an accurate projection as to the PCB’s final dimension.
Bill of Materials
Before PCB assembly can proceed, a BOM, or bill of materials must be created in concurrence with the creation of the schematic. To efficiently select the components for the PCB, the designer must analyze the current node levels of the circuit and their maximum operating voltages. After the picking the electrically acceptable components, they then should be considered again based on size, availability, and budget.
Keep in mind that the schematic should be kept updated with the Bill of Materials at all times. Remember that the Bill of Materials should indicate the component’s quantity, value, part number, reference designators, and PCB footprint. These five aforementioned requirements are crucial since they indicate how many of component are required, explain the dimensions of each part for space allocation, and explain circuit locations and identifications while exactly recounting the circuit elements used for substitution and purchasing.
Documentation plays a big part in PCB assembly and design. The PCB’s documentation must include hardware dimensional illustrations, BOM, schematic, layout file, assembly instructions and drawings, component placement, and Gerber file set. Although not required, user guides are also useful. The Gerber file is actually jargon for the output layout files that are utilized by the manufacturers to make the PCB.
A complete Gerber file set must have the following:
• Net list file
• Drill legend
• Assembly illustration bottom and top
• Paste mask bottom and top
• Solder mask bottom and top
• FAB outline
• Drill file
• Component map
• Metal layers
• Silkscreen bottom and top
The one that controls the whole PCB assembly project is the PCB schematics, so completeness and accuracy are crucial for success. Schematics include information that is needed for proper circuit operation. Schematics should always include information such as pin numbers, ratings, component values, and pin numbers.
After schematic details, the next in the process is component placement. PCB component placement is determined according to function, thermal management, and electrical noise considerations. Package sizes and placements are often reconsidered and changed based on cost and size. Components that are sucking up power greater than 10mA or conducting more than 10mW should powerful enough to warrant additional electrical and thermal considerations.
Of course, power management parts should make use of power planes or ground planes for heat management. Create high-current connections in accordance to reasonable drops in voltage for the connection.
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