半導體後段一元化代工服務之訂單分配模式之建構

Abstract

由晶圓製造業者所主導之「半導體後段一元化代工服務(Semiconductor Backend Turnkey Service; SBTS)」為IC設計公司提供從晶圓製造、晶圓針測、晶圓封裝到最終測試的全套代工服務。將訂單分配到各代工廠時，.訂單來到日與交期除具有不確定性外，亦可能分屬於不同之週別。在此情況下，如何逐週進行訂單分配，為一待探究之課題。 承上所述，本文針對訂單分配問題，建構一「逐期訂單分配模式」，將一個月之訂單分為四期接續規劃，每期規劃天數各為七天。且前一期之規劃結果為後一期規劃前之輸入資訊。在規劃前，需先預估各製程規格所需之生產週期時間，使之用於計算最早、最晚末批開工日與最晚完工日。接著，考量已到臨訂單之需求、每一代工廠以各式代工方案所需之生產週期時間等。以最小化成本為目標，包括未能承接成本、超出配置量懲罰成本、不足配置量補償成本與機會成本，設計一整數規劃模式，求解每日各代工廠商以各式代工方案加工各訂單各製程規格之數量，使允諾訂單皆能如期達交。 因訂單類型具有多階段訂單，為確保訂單各階製程能夠如期完工，在逐期訂單分配模式以下述觀念來分配訂單:(1)訂單所需製程階段之最晚末批開工日落在本規劃週期內，則表示此訂單需在最晚末批開工日前開始加工，才能在最晚完工日前如期代工完成。(2)僅訂單所屬製程階段之最早末批開工日落入本規劃週期，則此類訂單毋需在此規劃週期內代工完成，但為避免後期無足夠產能可用，加入一機會成本之概念，使得此類訂單盡可能最大化其加工量。 由案例分析結果指出，當某一製程規格對應之利用率高於85%時，採用悲觀時間為生產週期時間較採用最可能時間為預估值時，能使各代工廠之訂單分配量趨近預定配置量，並降低訂單之總外包成本。

The Semicondutor Backend Turnkey Service (SBTS), implemented by wafer fabricators, provides IC designer the whole outsourcing service package, including wafer manufacturing, integrated circuit (IC) assembly, and final testing. In this situation, how to allocate orders to each firm in each week is worth to be studied. Thus, this thesis proposed a periodic orders allocation model. There are four periods in one mouth, each period includes seven days. The input data of the later period is based on the result of the former period.Before planning, we need to estimate the cycle time of every process specification.Then, the integer programming model is constructed for periodic orders allocation which considers the request of all arrive orders and assigns then to appropriate outsourcing firms with minimum total cost, including order losing cost, overloading cost, shortage cost, and opportunity cost. To ensure each process specification of each order delivered on time, we use the following concepts to allocate orders: (1)If the latest start date for the last batch of an order is within the planning period, then the order need to start working before the corresponding date so as to be completed on time. (2)Only the earliest start date of the last batch is falling into this planning period. For this kind of orders, we use the concept of opportunity cost to make the amount be produced in the period as many as possible to avoid capacity shortage in the following periods. According to the result of cases analysis, when the utilization of a process specification is over 85%, the total amount allocated to each outsourcing company is closer to its prepurchared amount, and the total outsourcing cost is lower when adopting the pessimistic time as the estimated cycle time compared with adopting the most possible time.