Ask the Experts
January 5, 2018 - Updated
November 15, 2010 - Originally Posted

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.

P. D.

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.

John Vivari
Application Engineering Supervisor
Nordson EFD
Mr. Vivari has more than 15 years of electronic engineering design and assembly experience. His expertise in fluid dispensing and solder paste technology assists others in identifying the most cost effective method for assembling products.

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.

Karthik Vijay
Technical Manager - Europe
Indium Corp.
Currently with Indium Corporation and responsible for technology programs and technical support for customers in Europe. Over 15 yrs experience in SMT, Power, Thermal & Semiconductor Applications. Masters Degree in Industrial Engg, State University of New York-Binghamton.

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.

Doug Dixon
Douglass Dixon is the Chief Marketing Officer for 360 BC Group, a marketing agency with offices throughout the US. 360 BC specializes in consulting and implementing successful marketing programs that utilize the latest in marketing, sales and technology strategies. As an electronics veteran, Dixon has worked in the industry for over 30 years for companies like Henkel, Universal Instruments, Camelot Systems, and Raytheon. Dixon's electronics industry experience includes a broad skill set that includes engineering, field service, applications, product management and marketing communications expertise.

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.

Neil Poole
Senior Applications Chemist
Henkel Electronics
Dr. Poole is a Senior Applications Chemist in Henkel Technologies, electronics assembly materials application engineering group. He is responsible for all of Henkel's assembly products including soldering products, underfills, PCB protection materials, and thermally conductive adhesives.

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.

Edward Zamborsky
Regional Sales Manager
OK International Inc.
Ed Zamborsky is a Regional Sales & Technical Support Manager for Thermaltronics, located in New York. His position requires frequent customer visits throughout North America and the Caribbean and his position encompasses not only sales but the role of trainer and master applications engineer for all of Thermaltronics products. His expertise includes such specialties as hand soldering, convection and conduction reflow techniques, array rework, fluid dispensing equipment, and fume extraction. Ed has authored many articles and has presented many papers on topics such as; Low Volume SMT Assembly, Solder Fume Extraction, SMT Rework, BGA Rework, Lead-Free Hand Soldering, High Thermal Demand Hand Soldering, Lead Free Visual Inspection and Lead Free Array Rework.

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.

Scott Rushia
Sales Manager - Martin Products
Scott Rushia is a Sales Manager with Martin and is responsible for sales and service for Martin's rework and dispensing products. He has over 11 years of experience in the SMT industry and was in the semiconductor industry for 10 years.

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.

Richard D. Stadem
Advanced Engineer/Scientist
General Dynamics
Richard D. Stadem is an advanced engineer/scientist for General Dynamics and is also a consulting engineer for other companies. He has 38 years of engineering experience having worked for Honeywell, ADC, Pemstar (now Benchmark), Analog Technologies, and General Dynamics.

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.

Tim O'Neill
Director of Product Management
Timothy O'Neill is the Director of Product Management for AIM Solder. AIM Solder is a leading global manufacturer of assembly materials for the electronics industry. Mr. O’Neill has 25 years of industry experience is a Certified IPC Specialist.

Mr. O’Neill’s responsibilities include developing product and technical information; he is a technical writer and presenter for industry trade publications and events and has been recognized as a Speaker of Distinction by the SMTA.
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