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October, 2017 Production


What Yield Troubleshooting Has to Do with Equipment


Utilization By Freddie Chan, General Manager, KIC Asia


the market no longer accepts rework. However, in many assembly operations, equipment utilization is the single largest contributor to profit and cost im- provements. I have had many conversations with engineers about how to improve


E


their processes. For most of them, it is difficult to determine how much the re- flow process contributes to their rate of defects. It is also challenging to figure out the root cause of a particular defect. For example, cold solder on the bot- tom of a component may be caused by either a printing or reflow problem.


Examining Reflow Process engineers generally regard reflow as being responsible for only a


small portion of total defects. Many estimate that it is the cause of less than 10 percent, even 5 percent, of the total. Let’s say a production line is running hour after hour and day after day


without a problem. Suddenly the process engineer catches multiple defects during inspection, through AOI, X-ray, ICT, or another method. The process is shut down to identify the root cause. If the root cause of the PCB assembly defect is made clear during inspec-


IT’S TIME TO RISE UP AGAINST HIGH HEAT, WARPING AND DEFECTS.


tion, then the engineer can go right to the source and fix it. Often, however, the root cause is not immediately apparent. Most engineers that I speak with will then run a thermal profile. But by their own estimation, the reflow oven is only responsible for a small fraction of defects. Why turn to reflow first? We can get pretty good information from all the machines and processes


through SPI and AOI, but not so for the reflow oven. Oven information comes from weekly or daily spot checks, such as running a manual thermal profile. Also, we can see into most of the other machines. The reflow oven is a sort of black box in the production line. This means that the majority of the time, engineers are looking in the


wrong place for defects. It takes a significant amount of time to diagnose an acute yield issue and the entire PCB assembly line must be shut down. This often takes longer than a normally-scheduled thermal profile run, because the thermal profiler and relevant PCB with thermocouples attached has to be re- trieved. This process can take more than 30 minutes each time. Most companies calculate what every hour of unscheduled downtime


costs. The actual numbers vary from factory to factory. The calculations that I have seen indicate that reducing downtime by one hour per week, per PCB assembly line, results in a profit increase of approximately $60,000 per line, per year.


Continuous Process Monitoring Continuous process monitoring and automatic thermal profiling can eas-


ily tell if the thermal process is the culprit or not. No time is wasted looking for a problem where it does not exist, while very expensive seconds are tick- ing away. Should the thermal process be the root cause, then the monitoring system will provide information to help pinpoint where in the oven or process the adjustment needs to be made. This enables the engineer to identify the problem and fix it quickly. This also illustrates the benefit of smart machines in the context of the


ALPHA® Heat has


OM-550. The revolution is coming. taken its


Introducing ALPHA®


Industry 4.0 smart factory, namely how real-time data in an actionable format enables engineers to run production lines and the factory more effectively. The scenario described here represents one of the “low-hanging fruits” that in- stantly leads to significant yield improvements. From this basic capability we can quickly identify other opportunities to improve equipment utilization and yield.


toll on your bottom line long enough. OM-550 HRL1 – the most


revolutionary


advancement in solder paste since the introduction of lead-free. OM-550 cuts the soldering temperature required for SAC alloys by 50°C, while dramatically reducing power consumption and carbon emissions. The result is a highly reliable, cost effective, energy sufficient soldering process with up to 99% less warpage and significantly fewer defects. AlphaAssembly.com


When visualizing the real-time thermal process data in statistical


process control (SPC) charts, negative trends such as a falling Cpk (process ca- pability index) value become apparent. Since changes in a reflow oven tend to


be slow, an SPC chart can provide early information about what might hap- pen in the future. In some cases, it is possible to entirely avoid unscheduled downtime by alerting the maintenance personnel about the trend. They can address the issue during the next preventive maintenance event when the line is already shut down. It’s been said that an average factory in North America runs production


only 67 percent of the time. Thus, about a third of the time the production line does nothing except erode profits. This surprisingly low equipment utilization is caused by many factors beyond yield stoppage, especially the growing num- ber of line changeovers. Continuous process monitoring and automatic oven profiling is an easy


way to improve equipment utilization and reduce downtime. Downtime is ex- pensive. The time saved searching for defects in all the wrong places will


equal greater profits. Contact: KIC, 16120 Bernardo Center Drive, San Diego, CA 92127 % 858-673-6050 E-mail: bjorn@kicmail.com Web: www.kicthermal.com r


See at productronica, Hall B3 Booth 272


liminating defects and fully utilizing equipment are two of the most im- portant areas of focus in electronics assembly. Eliminating defects is important, because poor quality is expensive and a growing segment of


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