Uncertainty estimation by Monte Carlo Simulation applied to Life Cycle Inventory of Cordless Phones and Microscale Metallization Processes

Artikel i vetenskaplig tidskrift, 2004

This paper focuses on uncertainty analysis, that is, how the input data uncertainty affects the output data uncertainty in small but realistic product systems is modeled. The motivation for the study is to apply the Monte Carlo simulation for uncertainty estimation in life cycle inventory and environmental assessment of microelectronics applications. This paper addresses the question whether there is an environmental advantage of using DECT phones instead of GSM phones in offices. The paper also addresses the environmental compatibility of Electrochemical Pattern Replication (ECPR) compared to classical photolithography based microscale metallization (CL) for pattern transfer. Both environmental assessments in this paper consider electricity consumption and CO2 emissions. The projects undertaken are two comparative studies of DECT phone/GSM phone and ECPR/CL respectively. The research method used was probabilistic uncertainty modelling with a limited number of inventory parameters used in the MATLAB tool. For the DECT/GSM study the results reflects the longer DECT technical life which is an environmental advantage. For the Electrochemical Pattern Replication (ECPR)/classical photolithography based microscale metallization (CL) study the results reflects the fewer number of process steps and the lower electricity consumption needed by the ECPR to reach the functional unit. The difference in results is large enough to be able to draw conclusions, as the processes with the highest electricity consumption within the system boundaries have been determined. Based on earlier work a straightforward method to include uncertainty for input life cycle inventory data is used to quantify the influence of realistic errors for input data in two microelectronic applications. The conclusion is that the ECPR technology is more electricity efficient than CL in producing one layer of copper on a silicon wafer having a diameter of 20.32 cm. The conclusion is that the longer technical life of a cordless DECT phone is reflected in an electricity/CO2 comparison with a GSM phone, if use in an office is considered. Reasonable uncertainty intervals used for the input life cycle inventory data for the studied DECT/GSM and ECPR/CL system does affect the outcome of calculation of emission of CO2 but not to the degree that conclusions are not valid. Different uncertainty intervals and probability distributions could apply for different types of data and the interrelated input data dependence should be investigated. Today there exist very few life cycle inventory (LCI) data with the range of uncertainty for input and output elements. It must be emphasized that the upcoming LCI databases should have standard deviation characterized LCI data just as the Swiss ecoinvent LCI database. More inventory parameters and probability distributions characteristic for microsystems could be included and error analysis should be applied to future life inventory methodology, especially for future packaging concepts such as System-In-a-Package and System-On-a-Chip comparisons.