Automated SPC for the Reflow Process

摘要

This paper will discuss the implementation of real-time automated SPC for the Reflow Process. Topics covered will include: a new statistical method for quantifying the thermal process performance; methods for ensuring that SPC data provides a true representation of process capability; and the value of automated real-time SPC. To realize the full benefit of an SPC program, it is essential to define and set process specific control limits. SPC programs based on "targets" rather than process specific control limits are not capable of reliably predicting process trends, which is the primary function of an SPC program. Developing a fully functional SPC program requires a sufficient data set on which to project process trends. Another key factor in the success of an SPC program is efficiency. An inefficient method of data gathering and analysis is a guarantee of failure, as a program that consumes excess resources will quickly be abandoned. One method for increasing SPC program efficiency is to focus on key process statistics. A statistical method has been developed hat reduces all key process statistics to a single number: the Process Window Index. The calculation of the process Window Index will be defined and its validity as a statistical method for developing Cp and Cpk for the reflow process established. The continuous and automated gathering of data is essential for successful SPC monitoring of the reflow process. Current methods generally rely on periodic profiling, which disrupts production and provides an inaccurate "picture" of the process. Automated Continuous Monitoring Systems for the reflow process have been developed. These systems can provide a data point for every board processed by calculating a "Virtual Profile". A design of experiment (DOE) will be run to establish that the "Virtual Profile" is a leliable method of continuously gathering data on the reflow process. Experiment methods and results will be included. Automated SPC for the reflow process offers significant benefits for Electronics Assemblers. Automated SPC provides a significant sales tool for EMS's, as it allows them to prove to customers that their reflow process is in control and that their facility is dedicated to quality electronics assembly. This paper will be of interest to engineers and managers interested in increasing reflow process efficiency and quality.