Critical Variables of Solder Paste Stencil Printing for Micro-BGA and Fine-Pitch QFP

Abstract

Abstract-Stencil printing continues to be the dominant method of solder deposition in high-volume surface-mount assembly. Con trol of the amount of solder paste deposited is critical in the case of fine-pitch and ultrafine-pitch surface-mount assembly. The process is still not well understood as indicated by the fact that industry re ports 52-71% surface-mount technology (SMT) defects are related to the solder paste stencil printing process.The purpose of this paper is to identify the critical variables that influence the volume, area, and height of solder paste deposited. An experiment was conducted to investigate the effects of relevant process parameters on the amount of solder paste deposited for ball grid arrays (BGAs) and quad flat packages (QFPs) of five dif ferent pitches ranging from 0.76 mm (30 mil) to 0.3 mm (12 mil). The effects of aperture size, aperture shape, board finish, stencil thickness, solder type, and print speed were examined. The de posited solder paste was measured by an inline fully automatic laser-based three-dimensional (3-D) triangulation solder paste in spection system. Analysis of variance (ANOVA) shows that aperture size and stencil thickness are the two most critical variables. A linear relationship between transfer ratio (defined as the ratio of the deposited paste volume to the stencil aperture volume) and area ratio (defined as the ratio of the area of the aperture opening to the area of the aperture wall) is proposed. The analysis indicates that the selection of a proper stencil thickness is the key to controlling the amount of solder paste deposited, and that the selection of maximum stencil thickness should be based on the area ratio. The experimental results are shown to be consistent with a theoretical model, which will also be described in this paper.Index Terms-Analysis of variance (ANOVA), area ratio, design of experiment, solder paste, stencil printing, transfer ratio.

Characterization of printed solder paste excess and bridge related defects

“…Effects data presented within individual academic studies [6,7,8] were elicited to generate stencil aperture design paradigms that are based on the following corroborated aspect ratios and their corresponding, validated design rules -also see Figure Using the convention given in Figure 2, aperture volume can be formulated as AL * AW (or AD) * ST. The transfer ratio (TR) of a given solder deposit can be extrapolated by dividing the measured volume by the theoretical volume (which is equitable with the aperture's volume).…”

Optimization of engineering tolerance design using revised loss functions

“…The solder deposited volume data on 264 pads data were from experimental data (Pan et al 2004). The data passed the normality test.…”

Finding and optimising the key factors for the multiple-response manufacturing process

“…In this section, we perform the statistical analysis of solder paste stencil printing data (Pan et al 2004) using an integrated MTGS and desirability function approach.…”

“…The experiment conducted by Pan et al (2004) has four quality characteristics, i.e. the solder paste deposited volume, area, height, and transfer ratio.…”