Indium Corporation - Applications of Solder Fortification With Preforms

Authored by: Carol Gowans, Paul Socha, and Ronald C. Lasky, Ph.D., P.E.

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 (i.e. SMT and through-hole on the same board) products, it makes sense to consider assembling the through-hole components with the pin-in-paste (PIP) process. PIP has been successfully used for several decades now; 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 in in-circuit testing and potential surface insulation resistance concerns.


In light of the above need, solder preforms have been developed. These slugs 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 some other components being solder starved and, hence are candidates for solder performs...


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