Effect of Board Clamping System on Solder Paste Print Quality

Abstract

Stencil printing technology has come a long way since the early 80’s when SMT process gained importance in the electronics packaging industry. In those early days, components were fairly large, making the board design and printing process relatively simple. The current trend in product miniaturization has led to smaller and more complex board designs. This has resulted into designs with maximum area utilization of the board space. It is not uncommon, especially for hand held devices, to find components only a few millimeters from the edge of the board. The board clamping systems used in the printing process have become a significant area of concern based on the current board design trend. The primary function of a clamping system is to hold the board tightly in place to provide optimum gasketing during the printing process. There are various types of clamping systems available in the market, including top clamp, snuggers, flippers, and vacuum hold down. Top clamp and snuggers, two primary clamping systems, operate slightly different in providing the mechanism to hold the board. Top clamp, as the name implies, holds the board in place by applying a clamping system (a thin metal foil) on the top of the board. While the snugger works by tightly snugging the board in the Y direction without any foil on top of the board. The current study is designed to investigate the effect of top clamp and Y-snugger on both a specially designed test stencil and production quality cell phone boards. This study will use a 3D Solder Paste Inspection (SPI) system to determine the variation in paste volume and height based on the location of the pad on the board. Various statistical techniques will be used to analyze the SPI data to determine the effectiveness of the clamping system.

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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.