PCB Sensors

PCB Sensors: Types, Mounting, and Performance

Rush PCB Ltd manufactures all types of printed circuit boards. Many circuit boards meant for industrial use typically have sensors mounted on them. Sensors are necessary to detect changes in ambient conditions. Sensors typically produce an electrical response corresponding to the changes in the environment. They transmit these signals to other elements on the circuit board, where the signals undergo processing. Such elements on the circuit board include passive elements like resistors, capacitors, and transformers, and active elements like transistors, diodes, and integrated circuits.

PCB Sensor Types

Industrial users require many types of PCB sensors. The most common among them are:

  • Flow and Level Sensors
  • Smoke and Gas Sensors
  • Touch Sensors
  • Proximity Sensors
  • Temperature Sensors
  • Sound Sensors
  • Strain and Weight Sensors
  • Color Sensors
  • Position Sensors
  • Humidity Sensors
  • Tilt and Angle Sensors
  • Magnetic Field Sensors
  • Accelerometer Sensors
  • PIR Sensors
  • Ultrasonic Sensors
  • Light Sensors
  • and more.

PCB Sensors

PCBs for Sensors

Most PCB sensors do not require any special type of board. However, some sensitive sensors may require surface cleanliness to avoid inaccurate measurements. Sensors working at high frequencies may require control impedance on the PCB. Guaranteeing good performance from a sensor on a board requires the PCB manufacturing process to follow the standard PCB manufacturing processes, including:

  • PCB Design
  • Gerber Creation
  • Inner Layer Creation
  • Via Drilling
  • Layer Etching
  • Inspection
  • Layer Stacking and Laminating
  • Plating
  • Solder Mask Application
  • Silk Screening
  • Surface Finish Application
  • Testing

Through-Hole Mounting for Sensors

Many sensors have long leads that require a through-hole mounting technique. That means, the PCB will have through-holes on it to allow the sensor leads to anchor. In the case of boards with more than one layer, the through-hole will be typically plated. A plated-through hole will have a thin copper barrel along its hole wall, creating an electrical connection from one layer to another.

The assembler must solder the leads after mounting the sensor properly in the through holes of the board. This anchors the sensor to the board while providing it with the necessary electrical connection to other components. Through-hole mounting sensors may be of the axial type or radial type.

Axial Lead Sensors

This type of sensor has a shape similar to that of a wire jumper. The leads protrude from opposing end points of the sensor, setting up an ideal geometrical axis of conformity. The axial lead sensor typically lies flat on the PCB surface after proper anchoring.

Radial Lead Sensors

In this type of sensor, the leads typically protrude from one side of the sensor. Therefore, after mounting, the sensor assumes an upright position on the board. Radial lead sensors are perfect for use on boards where there is a limited area of space.

Mounting Sensors

Mounting methods for sensors on monitoring locations significantly affect their performance. Broadly, there are four methods of mounting sensors on locations. These are:

  • Magnetic Mounting — using permanent magnets to mount the sensor, suitable for ferromagnetic materials only.
  • Stud Mounting — using studs to mount the sensor. This method provides the most secure and reliable attachment.
  • Adhesive Mounting — using adhesives to fix the sensor on the location.
  • Probe Tips or Stingers Mounting — this method is for sensitive sensors.

There are both advantages and disadvantages of each method of mounting. The user must consider them before deciding on the final technique. This requires considering characteristics such as the location of mounting, surface ruggedness, amplitude range required, accessibility, portability, ambient temperature, and more. Some characteristics can be extremely critical to the effective operation of the sensor. The mounting technique has the maximum effect on the high-frequency operation of the sensor.

Surface preparation is an extremely important step when mounting sensors. For most sensors, the surface must be as flat as possible, free of debris, and without any grease and oil. Some sensors work well if the surface has a light coating of a lubricant before mounting. The coating helps to improve the high-frequency response of the sensor. Users frequently use beeswax, heavy machine oil, or silicone vacuum grease for lubricating the mounting surface.

Conclusion

PCB sensors are an essential factor for consideration for Rush PCB Ltd. Whether the sensor is of the through-hole type or surface mount type, proper component placement is necessary to allow the sensor to perform at its highest capability. An accurate placement of the sensor is crucial for its reliable performance.