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May 29, 2006

What is the best method to select a spray fluxer?

I am buying a new wave solder machine to replace a 15 year old machine with a foam fluxer. What is the best method to select a spray fluxer, there seem to be many options.



P.L.

Experts Comments

A spray fluxing system can only do two things for you:

1. Apply wave soldering flux where it needs to be (namely into the plated-holes of your circuit board), and
2. Apply flux in the proper amount

Every feature of a good fluxing system should be geared toward achieving these two goals.

A well-designed fluxing system will penetrate flux into the plated-holes of your circuit board regardless of circuit board width, thickness and hole diameter. Two components of a fluxing system should be looked at carefully to determine its ability to perform this job:

1. The type of spray head, and
2. The fluxing system's ability to control spray head movement (speed and position)

Ultrasonic energy is preferred over conventional air-atomizing and pressure nozzles as it creates smaller flux drop sizes. Nozzle-free spray heads are preferred, as they do not clog. Clogging of air-plenums in nozzle systems is one of the biggest culprits of spray fluxing process breakdown and loss of production time.

Systems that reciprocate the spray head under the circuit board are better than systems with stationary heads. The wider the circuit board, the more difficult it becomes to penetrate plated-holes with flux if you are originating your spray pattern from a single, stationary point. Look for electronically controlled reciprocating mechanisms. Pneumatic band cylinders lack accurate speed and position control, are prone to sticking due to flux residue and shop air contaminates, and require frequent maintenance.

For no clean applications, especially VOC free applications, it is very important to control the amount of flux you apply to each circuit board.

There are three components of a fluxing system that affect flux deposition:

1. Flux flow rate to the spray head
2. Spray head reciprocating speed
3. Spray pattern pitch (overlap between spray strokes)

A good fluxing system will include tools or techniques for measuring and monitoring flux flow rate to the spray head. Varying flux flow rate will affect the quantity of flux applied to the circuit board.

Spray head speed control affects flux deposition. The faster you move the spray head, the less flux applied, and vice versa.

And look for a system that synchronizes spray head movement to the speed of the circuit board conveyor. When conveyor speeds change, you want your fluxing system to adjust to maintain proper spacing between spray strokes.

Finally, look for a robust system built for 24/7 production. It should be modular in design, built from chemically resistant materials, and supported by a solid company capable of assisting you in your time of need.

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Stanley J Soderstrom
Product Engineer
Ultrasonic Systems
Mr. Soderstrom is a veteran of the U.S. Navy where he studied aviation electronics. Stanley has been working in the electronics manufacturing industry for more than 20 years and is considered a top expert in the field of spray fluxing process control.
NOTE: Mr. Soderstron is no longer working at Ultrasonic Systems.

Not all spray fluxers are created equally. First of all make sure the spray fluxer has materials of constriction compatible with your particular flux chemistry. Second make sure the solids content do not create any problems with the nozzle function over time. Also make sure that you have control of flux flow (volume) of deposit as well as droplet formation (Spray pattern). This is more critical the more complex the assembly is as well as type of flux chemistry used.

You have to obtain a properly constructed and adequate control of the nozzle to allow you to deposit uniform sprayed layers of flux. This has to be adequate for you application. Try to avoid sprays that return flux that is unused back to a spray container. This will cause you to make constant adjustments and is not as robust of a process.

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Karl Seelig

Deck Street Consultants
In his 32 years of industry experience, Mr. Seelig has authored over 30 published articles on topics including lead-free assembly, no-clean technology, and process optimization. Karl holds numerous patents, including four for lead-free solder alloys, and was a key developer of no-clean technology.

There are 5 areas that I would look at to evaluate a spray fluxer.

1. Maintenance requirements: Look for a system that has self clean to reduce maintenance and is robust in design to reduce down time.

2. Transfer efficiency: The system shold be rated at 95-98% transfer efficiency to reduce waste.

3. Deposition uniformity: Test the system to insure the spray pattern is uniform over a large aera.

4. Through hole penetration: Test with fax or PH paper on the top of a board to determine hole penteration on different hole sizes and uniformity at the edges of the spray width. The Fluxometer from ECD can also be used for this test and is very usefull.

5. Spray pattern control: Insure that the spray pattern can be controlled to minimize overspray.

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Greg Hueste
Senior Applications Engineer
Speedline Technologies
Greg joined Electrovert in February 1984. Based out of the Electrovert applications laboratory in Camdenton Missouri, Greg has been in the process applications support role since 2000. His primary responsibilities include providing process and machine applications support for the wave soldering lines as well as process, machine and operations training. He also provides applications support for the reflow and cleaner lines. Greg is a PBET certified trainer and holds two patents on wave solder nozzle design.
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