Applications of Solder Fortification with Preforms

ABSTRACT Although many have predicted the demise of through-hole components, they are alive and well with tens of billions assembled each year. In many cases these components are assembled by wave soldering. However, in many mixed product technology products (i.e. SMT and through-hole on the same board), it makes sense to consider assembling the through-hole components using the pin-in-paste (PIP) process. PIP has been successfully used for several decades; however, in many cases it is not possible to print enough solder paste to obtain an acceptable solder joint. In addition to this “solder starved” condition, the large quantity of solder paste used to form the though-hole joint results in excess residual flux. This residual flux can lead to difficulties with in-circuit testing and potential surface insulation resistance concerns. To satisfy the above need, solder performs were developed. These pre-formed pieces of solder typically come in the same sizes as 0402, 0603, and 0805 passive components. The solder preforms are placed by the component placement machines onto the solder deposit. This additional solder assures that an adequate solder joint is formed with a minimum of solder paste and its residual flux. Although PIP was an early application of solder preforms, more recently other “solder starved” applications have emerged, such as radio frequency (RF) shields and connectors. In addition, the use of ultra thin stencils in the assembly of miniaturized components can result in other components being solder starved. These applications are all candidates for solder performs. This paper will cover the design and assembly techniques for using solder performs for “solder fortification”. Several successful applications will be presented. In some of these applications, defects were reduced by 95% after implementing solder performs.