Issue link: https://iconnect007.uberflip.com/i/1411055
12 PCB007 MAGAZINE I SEPTEMBER 2021 from desmear through imaging, metallization, plating, etching, and solder masking to elec- trical test in 105 minutes [2,3,4] . Except for the occasional job that had special processes and was diverted to accumulators, the move-wait- queue and set-up times were miniscule. ere is overwhelming evidence in most manufacturing to indicate that the amount of backlog that exists is as much as the company can tolerate. Backlog on the factory floor is in evidence everywhere and there seems to be a variation on Parkinson's Law at work, since: "Work-in-process normally tends to expand to fill the space available." Backlogs are the Problem Since backlog is a fundamental cause of long lead time and lead time can only be controlled if backlog is controlled, let's look at the three major causes of large backlogs: • Lead time inflation • Erratic input to the plant • Inability to plan and control output effectively Lead Time inflation During good times, and as business picks up, companies put more into the factory than they ship out. is builds up the shop backlog, and as a result, they find that their lead times are in- creasing. e plant always feels that if they just had a little more lead time, it would be a sim- ple matter to get jobs completed on schedule. Erratic Input to the Plant Releasing jobs to the manufacturing floor without considering the through-put of each work center always results in a highly erratic input. is results in growing queue times, ex- cessive expediting, and missed delivery dates. Inability to Plan and Control Output Effectively e basic principles of output control are to separate the planning and control of capacity from planning and control of mix. Plan capac- ity requirements in the largest possible groups especially as the manufacturing process ex- pands and becomes more complex. What is Lead Time? Lead time can be defined as the time that elapses between the moment it is determined that an item is needed and ordered, and the moment when the item is available for use. Manufacturing lead time is the actual amount of elapsed time in the factory from the mo- ment that a shop order is released to the fac- tory to the time it is completed. is lead time can be broken into the following elements and descriptions: Lead time = Set-up time + run time + move time + wait time + queue time • Set-up time: e time when the job is sitting at the machine and the machine is being set up (prepared) with the proper tooling or information for this job • Run time: e actual time the job is at the machine and being worked on • Move time: e actual time the job spends in transit • Wait time: is has been separated from queue time so that it could be arbitrarily associated with move time since, in many factories, the dispatching job is not highly organized, and the expediters usually don't get to a job as soon as it is ready to move • Queue time: is is the time the job spends waiting to be worked on because another job is already being run on that machine or process Depending on equipment layout and through-put, a substantial amount of time could be spent waiting for moves. In practice, most of the lead time turns out to be queue time. As an example, the new GreenSource Fab- rication facility is totally automated with digi- tal barcodes or RFID tokens for set-up recipes and lot tracking. I have watched the final out- erlayer process aer lamination and drilling go