# A Method for Modelling Business-Critical Architecture Decisions in Engineer-to-Order Companies
## 1 Introduction  
Engineer-to-order (ETO) companies are characterised by offering complex products (often including more than 100,000 components) that are engineered and produced only after receiving customer orders, which necessitates engineering activities during the quotation and delivery processes. ETO companies play a crucial role in various industries, including manufacturing, construction, and custom machinery, where tailored solutions are paramount. These industries are now seeing even more product variety with the need for new technologies and solutions as part of the green transition. Nevertheless,the product variety that stems from the ETO characteristics has been shown to have a significant lead time [1; 2] and cost drivers [3; 4] associated with it. Several studies have proposed various methods to help companies address the impact of product variety on engineering [5; 6], manufacturing economies of scale [7; 8], and many other cross-functional disciplines [9] and value-chain activities [10]. Despite these efforts, two main challenges seem to hinder the practical implementation of product architectures when applying the current methodologies. First, the literature suggests that ETO companies are hindered due to the complexity of the architecture models and the large number of decisions that must be made throughout the implementation and maintenance of the architecture. [PERSON] et al. [11] argue that, while the existing models tend to produce thousands of architecture decisions that, in principle, all bring value, relatively few are truly business-critical. With countless architecture decisions to govern, it is difficult for company management to know where to focus their governance efforts. As a result, their efforts are easily lost in non-critical details, and they fail to provide the level of governance needed to successfully reap the benefits of product architectures [12]. Second, although the literature recommends prioritising only critical architecture decisions, the characteristics of ETO companies require an architecture that encompasses decisions in all cross-functional disciplines and across the full value chain. [PERSON] et al. [13] argue that existing methods tend to focus on a select few parts of the value chain or a few functional disciplines; however, the parts of the value chain in focus (typically manufacturing or mechanical engineering) are not always the sole or most critical drivers of the cost and lead time. For example, companies with low product volumes do not see traditional benefits due to economies of scale. In essence, few papers have described a methodology for identifying and prioritising only the business-critical architecture decisions of a product portfolio. Furthermore, the papers that discuss business-critical decisions tend to focus on only one or two parts of the value chain and do not provide guidance on how to structure the analysis cross-functionally and across the full value chain. To address this gap in the literature, we developed a holistic method (the cross-functional architecture matrix, CAM) to support ETO companies in developing modular architectures. The method is tested on three product systems (i.e., cases) in an ETO company in the processing plant industry. Section 2 covers the theoretical background, reviewing the existing literature on product architectures and their impact on business-critical activities in ETO companies. Section 3 describes the materials and methods, detailing the case study approach and data collection techniques such as interviews and workshops used to evaluate the cross-functional architecture matrix (CAM) method. Section 4 presents the results from the case study, demonstrating how the CAM method helps identify and prioritise critical architecture decisions to improve system performance, reduce costs, and shorten lead times.