The total loss system is a method of applying spray flux that utilizes the minimal amount of material to properly create a satisfactory solder joint. In this process, the flux is sprayed directly onto the PCB from a sealed container. All of the flux from the container is used, either by applying it to the board or it is lost from over spray. This is the main reason why there needs to be a separate venting system for the lost flux removal.
Open systems for applying flux had problems that the total loss spray fluxing system solved. The benefits of using spray fluxers and the total loss system are:
- Can be used with fluxes that don’t foam well
- No need to monitor density
- Titration and chemical measurements of the acid content are unnecessary
All of the above methods were expensive to operate. By not recirculating the flux, the cost and work associated with the tests were eliminated. If the process is set up correctly, all of the flux sprayed on the board will have the same characteristics as the unopened container.
All systems can vary when being used by different consumers because they have different wants and needs for their applications and processes.
There are two distinct variations in the total loss system. One nozzle is used to produce a high pressure fan-shaped spray pattern that covers the entire width of the board and is rapidly pulsed. This ensures an even layer of flux. The other nozzle is moved from side to side to cover the board area. A diagram is seen from my previous post here. They are similar in that fresh flux is sprayed through a nozzle or misted onto the bottom of the PCB. Some spray fluxers mix in some air to help form the mist while others use compressed air to guide the spray. Some apply pressure to the flux in lieu of compressed air.
There are also ultrasonic spray fluxers which use an entirely different approach than mentioned above to disperse the flux. The nozzle utilizes ultrasonic energy to break down the flux into a spray pattern where compressed air forces the droplets into a fan shape for even distribution. It eliminates the mechanics involved in moving the flux nozzle by using certain sensors. The spray therefore only operates when the board is in the right place at the right time. Any other time it is shut off; this minimizes waste of the flux and the loss associated with the total loss system.
Next week I will be talking about Spray Flux Venting.