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38 SMT007 MAGAZINE I DECEMBER 2022 Cause of the Problem While solder balls can be produced during both SMT reflow and wave soldering, PCB hand soldering during touch-up or rework can result in solder ball formation. When moisture or other impurities entrapped in or on the sur- face of the PCB or component outgas during the hand soldering process, solder balls form. Baking out or cleaning the PCB or the compo- nent and comparing the results can help deter- mine if this is the case. Soldering irons used to reflow solder paste during rework may also heat the paste too quickly and prevent the flux from fully activating, which causes the solder to oxidize and form solder balls. Solutions to the Problem Solder balls form when the flux becomes molten and fails to clean all the soldering sur- faces, which prevents the solder from coalesc- Eliminating Solder Balls in Hand Soldering ing into a single mass. e oxide coating that forms around smaller solder balls inhibits the solder from coming back together. Turning down the temperature of the soldering tip or using a lower tip temperature cartridge may solve the problem. Because the soldering tip can only activate so much of the flux in each amount of time, slow- ing down the wire solder feed rate (Figure 2) or reducing the amount of solder being fed to create the solder joint (Figure 3) can also help prevent solder balls from forming. Fully acti- vating the flux is the key to preventing oxide layers from forming. Utilizing a slightly more active flux that can withstand this temperature ramp is another option for preventing oxide layer forma- tion. Using a hot air or IR reflow source with a slower defined ramp rate can eliminate the solder balling problem when using paste for Knocking Down the Bone Pile by Bob Wettermann, BEST INC. Figure 1: When a solder ball is produced. Figure 2: Feeding solder wire too quickly can lead to solder ball formation.

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