Contrinex inductives trusted on PCB reflow ovens

An electronic equipment manufacturer needed to improve the reliability of the detection system fitted to their Printed Circuit Board reflow oven. Long-distance inductive sensors from Contrinex provided a simple solution that reliably detected PCB’s leaving a reflow oven to trigger transfer equipment that moves the board automatically to the next process stage.

Customer application

Reflow soldering ovens are an essential part of the electronic assemble process, being used to secure components in place on printed circuit boards. PCBs which have had solder paste screen-printed onto them are populated with electronic components and connectors before being conveyed into a reflow oven. As the PCB is conveyed through the oven, the temperature increases progressively according to a predetermined thermal profile which melts the solder paste so that it flows around and secures the components, as well as ensuring a robust electrical connection.
As each PCB leaves the oven, a sensor must trigger the factory’s control system to activate an automated transfer mechanism to move the board to the next processing stage.

The ambient temperature of 80°C immediately adjacent to the exit of the oven was causing an unacceptable rate of failure in other manufacturer’s sensors and so Contrinex was approached to see if its sensors could operate with total reliability.

Customer solution

Contrinex’s 500 series of inductive sensors which provide extended sensing distances were ideal for this application. They were able to detect the metal within the PCB and also allow sufficient space for the PCBs with tall components to pass underneath. The longer-distance sensing also enables the sensor to be positioned further away from the heat being radiated off the hot boards.

Best-in-class operating distances, vacuum-encapsulated electronics and excellent resistance to thermal shock and vibration from Contrinex’s Condist technology enable these sensors to provide a continuous 70°C temperature rating.

The inductive sensors are mounted vertically on steel brackets attached to the exterior of the reflow ovens. They are positioned 10mm above the PCBs and their M12-threaded metal housing enables easy adjustment. The 500 series sensors proved to be reliable even in the elevated ambient temperatures around the reflow oven, without needing to use more expensive specialised high-temperature sensors, an area in which Contrinex also excels, offering inductive sensors rated to operate in temperatures up to 230°C.

The factory’s control system required an NPN sensor with a normally open configuration and other than fitting protective sheathing over the sensor’s PVC cable, no additional electrical or mechanical protection was required despite 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. Whilst the sensors were not particularly expensive, the cost of engineers replacing them and interruptions to the manufacturing process was high. The switch to Contrinex inductive sensors provided a reliable sensing solution enabling the customer to achieve the level of machine availability and effectiveness, OEE, that they desired. The total cost of ownership was extremely attractive because the 500 Series extended range inductive sensor cost less than the cost of two of the competitor’s sensors.

Contrinex sensors are available from PLUS Automation.

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