How to Read a PCB
There are some basic things that you should know when trying to understand how to read a PCB. For instance, you need to understand what a resistor is. A resistor is a piece of metal that has a measurable resistance. Usually, a resistor is marked with an ohm measurement mark. The ohm symbol looks like the Greek letter Omega. The value 100MO means one hundred megaohms. You should also know how to identify a capacitor. Lastly, a board may be marked with traces or components.
Analyzing a board along the signal flow
The design of a PCB can be complicated. Many of the components are layered with a different signal flow. This can cause signal integrity issues when high-speed transmission lines must pass through dense via areas or split planes. Analyzing a board along the signal flow can help you determine which components should be placed where to minimize signal integrity problems.
The distribution properties of a PCB will greatly affect the signal, particularly at high frequencies. For example, high-frequency communication systems will often suffer from ground return, which occurs when the signal current changes rapidly with the external magnetic field. This causes reverse current flow in the surrounding conductors. This effect is illustrated by a ground plane diagram.
The first step in identifying components on a PCB is to identify the board. There are many PCBs marked with codes and acronyms to help you determine the application. For example, a DMCB board is the DOS Main Control Board for a GE Mark V computer. Another example is a daughterboard, which attaches to the motherboard and allows access to the CPU and memory.
Each component has a marking on its body and packaging. This marking will show its value, polarity, and tolerance. In addition, there may be a color-coded band that indicates the resistance. The bill of materials will also list the component parts and their quantities. There are also reference designators that show where the components are located.
When reading a PCB, you need to identify traces. These are not wires, but are the pathways through which electrical current flows. Each path has a specific resistance, and it is important to consider this when selecting trace widths. The resistance of a path can be determined by its temperature rise, which shows how hot the trace will become when current flows through it. The temperature rise is usually the difference between the operating temperature and the maximum operating temperature.
The signal pulse on a trace travels at a rate of 84-85 picoseconds per inch in air. The signal travels at about 11.8 inches per nanosecond in vacuum, and about 145 picoseconds per inch for a common dielectric material. The propagation delay of an electrical signal depends on the design specifications, but there is a general guideline that you can follow for most PCBs.
Cleaning a board
Cleaning a PCB is a delicate process that requires a certain amount of care. Most PCB contamination is caused by the flux residues that accumulate after assembly. To get rid of this, you can use a solvent or an abrasive to clean the board thoroughly. Paper towels and kimwipes are good options to soak up the solvent or abrasive. After cleaning, make sure to wipe the board clean to remove any remaining lint.
Different types of solvents are used for PCB cleaning. Some of these solvents are mild, while others are flammable. Cleaning a PCB with a solvent can improve its performance. You can use foam or cotton swabs that are saturated with a mild solvent. Many pump dispensers sell this type of cleaning solvent. Presaturated wipes that contain isopropyl alcohol can also be used.
Repairing a board
One way to repair a PCB is to remove the damaged components and the adhesive that sticks them to the board. This can be difficult if the adhesive is dry or old. You can use workbench cleaners, which are usually consumer products.
Once you have removed the damaged components, you can use an oscilloscope to check the continuity of the circuit across the board. If you find a burned area, it means the component has failed and has to be replaced. If you don’t know where the failed component is located, you can use tweezers to lift it and replace it.