Lead Free Wave Soldering with USI Fluxing Technology

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Lead Free Spray Fluxing

Successful fluxing of circuit boards for lead free wave soldering requires, first and foremost, good flux chemistry. But good flux chemistry alone cannot guarantee soldering success. Flux must be applied to the circuit board in the proper amount and only where it is needed.

Lead brings many benefits to the wave soldering process when using today's lead bearing alloys. Lead increases the solder's "wetting-action", allows solder to melt at a set temperature, and gives solder joints an appealing, shiny, smooth finish. The move to eliminate lead from circuit board assemblies makes the wave-soldering process more difficult. Without lead, solder alloys become sluggish when molten and "wetting-action" decreases dramatically. Higher operating temperatures are required to melt the new lead-free alloys. These alloys may also produce dull, grainy, unattractive solder joints. Proper flux application in the wave-soldering process becomes more critical with these more demanding operating parameters.

Printed circuit boards are not two-dimensional objects, they include plated through holes of varying depths and diameters, protruded by component leads of varying lengths and shapes. Spray fluxing has been proven to be the best method of applying flux to circuit boards for a no-clean process. To successfully apply no-clean flux to these three-dimensional objects, in the proper amount and only where it is needed, a spray fluxer must do the following:

• Apply flux uniformly
• Apply flux into the plated through holes
• Apply flux to the required areas of the board
• Maintain a repeatable process

Lack of one or more of these critical elements will result in a poor soldering process with the following possible consequences:

• Poor fillets
• Insufficient hole fill
• Poor cosmetics
• Excessive residues
• Metal migration

USI's spray fluxing systems feature Ultra-Spray technology with Smart Motion to overcome the challenges associated with the lead-free soldering process. For more information, please call us at 978-521-0095 or e-mail Stan Soderstrom.