Issue link: https://iconnect007.uberflip.com/i/1415897
12 SMT007 MAGAZINE I OCTOBER 2021 ly defined as a product performing its expect- ed functions for a designated period under an anticipated set of service conditions. A prod- uct should be designed and built not necessar- ily for the maximum reliability, rather for the operational reliability that is subject to practi- cal requirements and desirability, such as the targeted time-to-market, the acceptable cost to manufacture, the overall manufacturability, and the total cost of ownership. Is Cost a Factor? e total cost of ownership covers the full cycle of making a product from procurement to production to reliable service during a product's life span. Factors such as production yield, defects, rework, a set of product func- tions, and the targeted reliability add up to a product's total cost. An absolute reliability is not always the iso- lated pursuit as reliability does bear a cost. A qualitative relationship between the system cost and the level of system reliability for the pre-shipment and the post-shipment stages can be illustrated in Figure 1. Within the realm of surface mount technolo- gy (SMT), the assessment of the cost requires one to consider the total cost of ownership. is comprises: • Solder material cost per unit weight • Process operational cost • Cost of components • Cost of PCB • Equipment capital expenditure and depreciation • Production yield and defects • Cost of rework, if any • Product reliability Accordingly, a viable product is the result of a tradeoff and a balance among the perfor- mance, manufacturability, cost, and business terms to deliver the expected reliability. How Does SMT Operation Affect Reliability? In the SMT manufacturing operation, the main players of reliability include the PCB bare board, all components before assembly opera- tion, all components aer assembly operation, solder interconnections, and the manufactur- ability. e resulting system's reliability hinges on the quality, practicality, compatibility, and reliability of each of the players, and the inter- play among the players. On the PCB, the sol- derability and planari- ty of surface finish and the PCB internal struc- ture integrity before reflow/wave and oth- er process steps, the PCB internal integrity aer reflow/wave/re- work, and other pro- cess steps are key pa- rameters to watch for. In particular, PCB vul- nerability to high tem- perature excursions es- calates with the level of PCB complexity (e.g., higher number of lay- Figure 1: Reliability vs. cost, pre- and post-shipment.