We examine the problem of scheduling a set of n independent jobs on a two-stage flow shop with parallel machines for tape mounting and sawing processes for semiconductor packaging. The tape mounting process does not have setup times for switching the job family. However, the next sawing process requires significant setup cost for switching the sawing blade. The due dates and the job release dates are determined to meet the given job schedule at the downstream die attach process. They are agreeable since the time differences between the due dates and the release dates are taken to be constant in order to control the flow time and the work-in-progress inventory. The objective is to minimize the maximum lateness of the jobs. We decompose the two-stage scheduling problem into two single-stage scheduling problems. The scheduling problem for the first stage is defined as a parallel-machine scheduling problem with the job release dates and the due dates. The due dates are given by adding the target flow time at the first stage to the job release dates. The jobs at the first stage are scheduled by the well-known minimum slack rule so that the maximum lateness at the first stage is minimized. The job release dates for the second stage are the same as the job completion times at the first stage. For scheduling the jobs for the second stage, we propose two heuristic rules. First, we modify the well-known ATCS (Apparent Tardiness Cost with Setup first) rule to effectively reduce the number of setups. Second, we propose a look-ahead policy, called look-ahead workload with setup (LWS) rule, to determine when a setup at a machine should be made. The policy considers the future workload of each job family at the machine. By experimenting the proposed scheduling policies, we identify that the LWS has significantly less setups than the revised ATCS rule, but the two rules have close maximum lateness values.
반도체 조립공정에서 Tapemount 와 Sawing 공정의 2단계 병렬장비 스케줄링 문제를 다룬다. Tapemount 공정은 장비 교체시간이 없지만, Sawing 공정은 장비교체비용이 존재한다. 이단계 스케줄링 문제를 각각 한 단계 병렬장비 스케줄링 문제로 나누어서 푼다. 첫번째 단계인 Tapemount 공정은 가용시점 및 납기를 가진 병렬장비 스케줄링 문제이고, 두번째 단계인 Sawing 공정은 가용시점 및 납기, 그리고 교체비용이 있는 병렬장비 스케줄링 문제이다. 첫번째 단계는 기존에 알려진 MS(Minimun Slack) rule 을 이용해서 스케줄링하고, 두번째 단계는 look-ahead workload with setup (LWS) rule 과 기존의 ATCS (Apparent Tardiness Cost with Setup first) rule 을 변형시킨 rule 을 통해 스케줄링한다. 두 가지 rule 에 대해 목적함수 Maximum Lateness 의 최소화와 셋업횟수 최소화에 더 좋은 rule 이 어떤 것인지 비교해본다.
