Fill the Void

ABSTRACT Voids in solder joints are a concern for many electronic manufacturers. They create weakness in the solder joints which can lead to mechanical failure. Voids can slow or limit heat transfer away from the component which can lead to thermal failure. Voids can also interfere with electrical signal flow creating problems with the function of the circuit board. Minimization of voiding is beneficial for the life and function of the circuit assembly. Voids are caused by many things. Via holes in pads can cause solder paste to flow away from the solder joint creating voids. Gases from via holes can move upwards into the solder joint creating voids. Incomplete wetting or flow of the solder paste can create gaps or voids in the solder joint. Gasses from solder paste fluxes can be trapped in the solder joint. Regardless of the cause of voids there are ways to minimize voiding. Several methods of minimizing voids are presented in this paper. Stencil design can have a dramatic impact on voiding. Printing solder paste with gas escape routes is an excellent way to reduce voiding. When via in pad designs are used, voiding can be minimized by printing solder paste with a clearance around the via holes. Changes to the reflow profile can help reduce voiding, but the changes need to fit the solder paste. Adding a soak to the reflow profile can drive off volatile materials from certain solder pastes. Lengthening the time above liquidus helps volatile materials to escape from other solder pastes. The solder paste flux has a large influence on voiding. Some solder pastes have a lower potential for voiding than others. A test matrix was designed to validate these methods of minimizing voiding. Void measurements were taken, the data was summarized and a set of recommendations were made. This was all done in an effort to help the reader to “Fill the Void.”