|Ask the Experts|
January 5, 2018
Application of Flux for Hand Soldering
Do you know of any tools or materials that will allow for precision application of No-Clean flux for hand soldering operations? We are looking for something that has more precision than the traditional flux pens and don't want to use flux bottles if we cannot control the amount of flux applied. Any information or assistance you can give will be greatly appreciated.
|Expert Panel Responses|
You will achieve the most precise control with paste flux. Paste fluxes come in a variety of formulas optimized for application via dispensing, dipping and printing. Paste flux can be applied more predictably than liquid flux. Unlike liquid flux, paste flux can be dispensed in controlled amounts exactly where needed, and will stay in position until heat is applied. It's also easier to store, not messy, and safer because it's less likely to come in contact with the operator. For hand operations, paste flux is typically packaged in syringes and applied with air-powered dispensers that use a timed air pulse to deposit the same amount every time. In very low-volume operations or when the amount is not critical, syringes can be fitted with hand plungers and the flux applied manually.
Application Engineering Supervisor
Flux-cored solder wire is one way to avoid manual flux application and prevent excessive flux. Typically the flux content could vary between 1-3%. Using a flux-coated preform is a highly precise method of soldering that not only prevents excess flux application, but also ensures that the solder volume is consistent across all locations to be soldered. A preform is solid solder and could be in any shape -- donut / square / circle... A flux-coated preform has a uniform coating of flux over the entire surface of the preform and eliminates the need for manual flux application during soldering. The flux % could be 1-3% by weight.
Technical Manager - Europe
The best way to apply flux with precision is to choose flux gels in a cartridge. By using a fine gauge needle and a hand held air dispensing system, you can apply as much or as little flux as required. The use of a foot controller, with this type of system, allows the operator to apply and stop the flux flow as needed. The fine gauge needle provides a fine application of the flux precisely to the point where the customer chooses it to be placed. The advantage of the flux gel is that it does not flow away from the area it is dispensed. Thanks to the consistency of the material, it is sticky enough to hold the components in place during the rework or fluxing process.
There are two issues her. First is the application of the flux and controlling the volume dispensed, and the second is the movement of the flux once it is on the substrate. Using a gelled rework flux (often referred to as a tacky flux) rather than a liquid flux allows for control of both issues in a single step. The gelled flux typically is suppled in a syringe and can be easily dispensed through a fine gauge needle allowing for control of the volume of material deposited. The rheology of the flux gel prevents spread of the applied flux on the substrate.
Senior Applications Chemist
You can buy your flux loaded into 10cc or 35cc syringes. Use a time pressure dispenser and you can select the needle size, air pressure and dispense time. This system will allow you to control all your variables and precisely deposit your flux prior to your hand soldering operations.
Regional Sales Manager
OK International Inc.
Yes, one method to dispense flux is with a hand held time pressure system (with suck back vacuum so low viscosity materials don't leak out of the nozzle while at rest). Just choose the material and amount of volume on the control box for how much you want dispensed and press on the foot switch for precise application. You can use 5cc, 10cc, or 30cc syringes with standard plastic or metal tip nozzles. Check out the Smart Dispense system from Martin GmbH. http://www.martin-smt.de/
Sales Manager - Martin Products
Indeed, as all of the experts have stated,tacky flux (or gel flux)is the way to go. I did not even think people usedliquid benchtop fluxes anymore, as they burn off too soon, run all over theplace and are difficult to control, and cause oxidation particulates in thesolder joints. Tacky fluxes have proven to be superior in that they stickaround for the whole job, are (in fact) easier to clean, and do not leave asmuch particulate matter embedded in the solder joints. Most operators that I workwith have favored using tacky flux once they learn to use it. Tacky fluxes areavailable in just about any formulation required; no clean, water soluble,halide bearing and halide free.
In addition to the method of application and perhaps more importantly, 'Is the flux appropriate for the application?' If no clean flux is in use, be sure to use a flux that is specifically engineered for rework. Don't use the flux you are using in the wave/selective machine and assume it is formulated for touch up. Talk to your flux vendor for guidance.
Technical Marketing Manager
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