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Essemtec has supplied a machine to a European keyboard manufacturer that has developed a process for the soldering of heat-sensitive, flexible materials such as Mylar – a selective IR oven.

The principle of the soldering process is that the specifically selected wavelength of the IR radiation is absorbed by the solder joint, but not by the foil.

This requires a specific combination of solder, foil and infrared wavelength.

If the combination is right, the foil is nearly transparent for the IR and, therefore, only the solder joints are heated and the foil stays cool.

The keyboard manufacturer requested that Essemtec built a special type of machine for its new process, which protects sensitive materials through selective soldering with infrared radiation.

The complete production line for membrane keyboards includes several process steps.

One of them is the population of the keyboard foils with electronics and switching elements.

For this, Essemtec’s FLX2011-VL flexible production cell was used.

In one run, the machine can dispense and place without moving the foil.

The FLX can dispense up to two different liquids and can place metal domes, LEDs and other electronic components.

For security and easy handling, foils are fixed in carriers that stay with the foil from the first dispensing operation until after soldering.

This way, the foils cannot warp and placed components will not shift during handling and soldering.

After dispensing and placement, the foils are soldered using the selective IR soldering process.

A standard RO300FC reflow system with process-specific adaptations is used for soldering.

The oven features five zones, where the first and last zones are required for handling the foil carriers and the three in between are process zones.

The primary process zone’s function is to condition the foils for proper soldering.

It can preheat or temper the foils using a convection heating module that guarantees homogeneous temperature distribution.

The second process zone is the soldering zone.

The standard convection heating modules have been replaced by IR radiation modules that emit IR radiation with a wavelength in which the Mylar foil is nearly transparent.

Therefore, only the solder joint is heated and the foil stays cool.

In the third process zone, solder joints are cooled using an air convection cooling module.

The foils are then processed further into the output handling zone.

Carriers are controlled by sensors that ensure that only one carrier is inside the process tunnel or on the output platform.

Another carrier will be released at input only if process and output zones are free.

Heating the solder paste creates vapour that may condense inside the oven and contaminate the IR emitters, reducing their efficiency and lifetime.

For this reason, all potentially harmful vapour must be exhausted from the oven, however the exhaust air flow must be in sync with the convection heating and cooling modules.

Essemtec has precisely analysed the flows inside the oven tunnel and invented flow-control systems that prevent vapour, while guaranteeing the efficiency of the convection heating and cooling modules.

Heat energy will only be produced when required and, therefore, the RO300FC is equipped with a standby mode.

If no carrier is inside the oven, both the IR radiation modules and the transport band are stopped.

Only if a carrier is placed on the input loading platform will the heating and transport modules be restarted, saving energy and extending system life.

RO-Control software is used for process setup and control.

This PC software features a fully graphical, easy-to-understand display of the oven status and the temperatures in the zones.

When connected to the network, soldering profiles also can be stored externally and remote support is available via the internet.

RO-Control allows the simulation of soldering profiles and the comparison to solder paste specifications.

Temperatures inside the zones or on the substrate can be recorded, documented and compared with the simulation.

Therefore, RO-Control makes it easy to set up and monitor processes.

The selective soldering oven is based on a RO300FC standard convection oven that has been adapted to the customer’s requirements.

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