Paste in Hole (PIH) Printing with an Enclosed Media Solution

Abstract

Paste-in-Hole (PIH) printing, a.k.a. through-hole printing, pin-in-paste, intrusive reflow, etc., has always been a way to accommodate traditional through-hole components on a mixed-technology SMT assembly using reflow soldering rather than wave to make the through-hole connections. Paste is printed in such a manner to as to fill the through-holes, the through-hole components are inserted, and the assembly is reflowed. Assuming that the TH components can take the heat, successful PIH boils down to three basic issues: 1.) determining the amount of metal needed in the hole to create a good solder joint; 2.) Getting the metal in there; and 3.) Keeping it in there without loss when the through-hole component’s pins are inserted. Over time, changes in technology have made PIH even trickier. For example, early-on, an important issue was the heat tolerance of the through-hole components subjected to reflow temperatures in an oven. Nowadays the shrinking real estate of the PCB with fine-pitch SMT pads closely adjacent to paste-hungry through-holes has raised deposition issues, thus affecting design considerations, and the list goes on from there.

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Stainless steel foil stencils are used to print solder paste and adhesives on bare PCBs. Stencils of varying thickness, and also ‘step’ stencils with varying thicknesses in specific areas for different deposition requirements are used.
Solder Paste, a complex mixture of tiny particles of solder alloy and flux vehicle, is a challenging material to print onto a bare Surface Mount Technology (SMT) PCB.
Traditional metal screens excel in the printing of many electronic materials on rigid and flexible PCBs. These materials include solder masks and resists, fluxes and solder pastes, and especially conductive inks (silver, carbon, silver chloride), and dielectric inks, both used to form conductive traces, capacitor and resistor elements.
MPM stencil printers pioneered Surface Mount Technology (SMT) solder paste printing and continue to lead the industry in performance and excellence in printing electronic materials, including SMT Solder Paste.
PrintingMPM printers are high-speed, high-precision systems for depositing precise patterns of solder paste on printed circuit boards through foil stencils. Available in a wide range of capabilities.Best-in-class printing performance has always neen a hallmark of MPM printing technology, the recognized world standard for reliability, throughput, and high yields.