Print Process Characterization for BGA, Fine Pitch BGA and CSP Components

ABSTRACT The goal of this characterization study is to conduct a formal design of experiment, to understand the impact of three important print process parameters, along with BGA, CSP pitch and I/O density on solder paste print quality and volume. The primary objective is to determine an optimum stencil print process for mixed technology PWB, containing various BGA, Fine Pitch BGA (FPBGA) and CSP components, ranging in pitch from 0.5 to 1.27 mm and I/Os from 48 to 784. The experiment was carried out using OSP coated test vehicles, provided by JPL, containing a myriad of BGA and CSP components. No Clean paste was selected for this study, with Type III and Type IV particle size and viscosity ranging from 900-1000 Kcps. Other parameters for the experiment included: Stencil Type – E-Fab Stencil Thickness – 5.65 and 4.65 mils Print Mechanism – Metal Blade 45 degree angle Print Speed – 2 mm/sec Print Pressure – Optimum setting to achieve good rolling of paste in front of the squeegee As part of the experiment, RIT conducted both qualitative and quantitative analysis. The qualitative analysis included visual examination of the actual bricks of paste deposited and recording any anomalies observed. The quantitative analysis involved the measurement of true 3D volume and height of solder paste print. This paper will present the findings of this study in detail.