Contrinex inductive sensors beat the heat on PCB reflow ovens

Author : Mark Weymouth | Managing Director | Contrinex UK

05 March 2019

Inductive PCB conveyor image

Contrinex’s inductive sensors ‘beat the heat’ on PCB solder reflow ovens by providing exceptional reliability detection of emerging PCBs, overcoming the high-temperature environment and offering longer sensing distances.

The process control system on a reflow soldering oven needed to improve the detection reliability of PCBs to trigger a subsequent operation. The long-distance inductive sensor is mounted above the exit conveyor of the reflow oven and detects each board as it passes out of the oven, triggering a transfer mechanism to move the board automatically to the next process stage.


Key advantages include:

•    Outstanding temperature stability – sensor performance unaffected by elevated temperatures

•    Patented Condist technology of extra distance sensing gives best-in-class operating distances – extended sensing range = 10mm

•    Rugged inductive sensor with metal housing

•    High-quality ASIC sensors with IO-Link interface

•    High performance and high switching frequencies


Customer application advantages include:

•    Improved production OEE as the sensor reliably signals operations after the reflow oven

Inductive PCB conveyor image - Close up

•    Minimal replacement sensor costs, due to the sensor’s long service life

•    Low risk of thermal or mechanical damage because of extended operating distance

Customer application: product quality control test line

During manufacture of PC motherboards, reflow soldering is used to secure components in place on printed circuit boards (PCBs). Following assembly, boards are conveyed into a reflow oven, where the temperature increases progressively to achieve a predetermined thermal profile, melting the solder paste on the boards.

As each board leaves the oven, a sensor must trigger the customer’s control system and activate a transfer mechanism, moving the board automatically to the next process stage.

The ambient temperature immediately adjacent to the oven may reach 80°C (176°F), which has caused unacceptable rates of failure of other manufacturers' sensors in the past, whereas sensors must operate continuously in this environment with ultra-high reliability to achieve the required OEE and throughput.

Extended sensing distances are highly desirable for this application, as several types of motherboard, each with different component heights, pass through the oven. The longer-distance sensing enables the sensor to be positioned further away from the hot boards.

Inductive PCB conveyor image - Video clip

Customer solution:

Contrinex inductive sensors from the Extra Distance family (500 series) are ideal for this application, with their vacuum-encapsulated electronics ensuring excellent resistance to thermal shock and vibration.  Condist technology delivers best-in-class operating distances, and sensors have a continuous rating to 70°C (158°F). Trials confirmed highly stable performance even in the elevated ambient temperatures around the reflow oven, without the need to use high-temperature sensors.

Extra Distance sensors are mounted vertically on steel brackets attached to the exterior of the reflow ovens, sensing the presence of each motherboard as it passes beneath the sensing face. The operating distance is set at 10mm, eliminating the risk of collision with components on the board, and an M12-threaded metal housing allows easy positional adjustment when necessary.

Extra Distance sensors with an industry-standard NPN normally-open configuration connect with the customer’s control system via a flexible PVC sheathed cable. No additional electrical or mechanical protection is required in spite of the adverse operating conditions.

Previously, sensors from other manufacturers did not detect boards reliably and had unacceptably short service lives, causing frequent interruptions to production. Sensor replacement costs were excessive. Contrinex inductive sensors have been reliable and long-lived, providing a professional sensing solution with an attractive total cost of ownership (TCO).

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