'Broadband soldering' has become the adopted term for soldering processes that involve a heterogeneous mixture of large and small components on the same board. This is a challenge both for solder materials and for printing processes.

Now a new paper from leading suppliers Cookson and Speedline on the Circuitmart website has reported on a set of experiments aimed at optimising the printing process.

Miniature components today include 01005, 0201 passives to 0.3-0.4mm CSP and BGA. Increasingly there is a need to assemble these next to much larger components, creating a fundamental challenge. There are no significant relevant studies to be found in the literature.

This paper focusses on stencil design and demonstrates that a 3-mil thick stencil with a design that overprints larger components is able to produce results that meet IPC 610D visual inspection criteria.

The study also found that the effect of pad finish was greater than any of the other parameters studied, with OSP finish showing highest paste transfer. There is also a complex interaction between stencil and pad finish.

Use of nitrogen improves reflow characteristics of solder paste with miniature components.

A copy of the paper is available via the Circuitmart website on the reference link below.