Question: If you were to begin performng tests to better understand you Wave Solder Machine’s Flux System capabilities and you had a limited amount of resources (both human and capitial resources), in what order of priority would you perform the following tests and why? [Flux Weight (% Solids), Airflow (Velocity), Airflow (Uniformity)]
Answer: In selecting a flux, the first thing you want to check out is: does it improve the soldering compared to the existing flux? This can be done by dipping comparative samples into each flux pot and dipping them in a solder pot and checking the soldering, i.e., what does it look like when the two are compared?
Depending upon the type of flux being evaluated and the fluxing system on the wave, make sure the flux is not going to crystallize and block up the nozzles. Allowing fluxes to sit around for a week or so in small bottles, e.g, pharmaceutical bottle, see if the flux separates an creates crystals. If it does, this many not be the flux for you.
Airflow, uniformity and velocity can all be done at the wave solder system. For uniformity, get a piece of brown paper bag and wrap it around a board and run the board up through the fluxer. Once through the fluxer, remove the board and look at the coverage on the paper. This will tell you whether or not the spray nozzle, or wave generator is wide enough for the product being soldered. As for the velocity. Run another board through the wave, this time with the paper on the top side of the board. You should be able to see flux penetrate through the plated through holes and wet the paper on the top side of the board. This will tell you if you have enough air flow to drive the flux up through the plated through holes.
Last but not least is the flux weight. This is only important to make sure evaporation does not impact the liquid flux in the fluxer system. If the flux is being dispensed through an ultrasonic nozzle the flux is coming for a sealed container and you don’t have to worry about the specific gravity of the flux as the system is always drawing from a clean supply. If the fluxer is a wave or foam fluxer, then you will have to monitor the specific gravity of the flux or the acidic value of the flux, which will be impacted by the evaporation of the solvents within the flux. As the solvents evaporate the fluxes become more active per given volume, so this has to be watched closely. All you need to address this is an acid test kit, which can be purchased from your flux manufacturer.
I would also strongly suggest reviewing J-STD-002 and J-STD-003 for the solderability test for wires, terminals and boards. It is imperative this is done to make sure you’ve qualified the fluxes prior to putting them into use in your soldering system. If the fluxes are not qualified, then auditors can shut down your manufacturing line as you are using non qualified material.
Remember, do not poor the used flux back in the original flux container, as this will contaminate the flux.