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Applications of Solder Preforms to Improve Reliability
Keywords: Preforms, PIP Process, Solder Fortification
As early as the 1990s people were predicting the end of through-hole components, but they are alive and well with the numbers of dual in line packages (DIPs) and connectors still measured in the 10s of billions per year. Many of these components are assembled by wave soldering, however in mixed technology (SMT and through-hole on the same board) where the through-hole count is low, it is often advantageous to consider selective soldering or the pin-in-paste process (PIP). PIP is a process in which solder paste is printed over the PWB through-holes. The through-hole components are then placed and the solder join is formed during reflow. PIP has the advantage of eliminating the wave soldering process step. In many cases it is difficult to print enough solder paste to make an acceptable through-hole solder joint. Solder preforms were developed to meet this need. These solder preforms are typically shaped in the form of 0402, 0603, or 0805 passive components. The preforms are typically placed on the appropriate printed solder paste deposit by a component placement machine. The preforms come in tape and reel packaging. Today solder preforms are also used in other “solder starved” applications such as radio frequency (RF) shields, connectors, and under QFN thermal pads. In all cases, the extra solder delivered by the preform is vital to the reliability of the assembled product. In this paper, process design and assembly methods for solder fortification using preforms will be discussed. Four successful solder fortification examples will be presented and along with the associated defect reductions.
Ronald C. Lasky, PhD, PE, Senior Technologist
Indium Corporation of America
Clinton, NY
USA


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