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 preforms.
This paper will cover the design and assembly techniques for using of solder
preforms in the “solder fortification™” needs described above. Several successful
applications will be presented. In some of these applications, defects were
reduced by 95% after implementing solder preforms.
Apex 2011, solder starvation, flux, PIP, pin-in-paste, through-hole, SMT, solder fortification, solder paste, solder preforms
