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84 DESIGN007 MAGAZINE I JUNE 2021 Figure 1: The panel area available for circuit boards and coupons is known as the usable area. in-process inspection tools such as line width checks and coupons. Cost-effective material utilization is defined by a target panel with greater than 75% panel utilization. Raw laminate is the primary cost constitu- ent of a multilayer PCB. Optimizing panel structure around standard base materials while achieving maximum material utiliza- tion on standard panel sizes can have a sig- nificant impact on multilayer board prices and deliveries. e three most preferred sizes are 12x18 inches, 18x24 inches and 21x24 inches. e most effective cost per unit area processed is typically found with larger panel size. e most common panel size is 18x24. For special applications, other panel sizes are provided. e most effective material utilization will be achieved with PCBs or arrays of PCBs where their finished outline fits as efficiently as pos- sible within the useable area of the panel. Test coupons must be within the useable area. e customer may negotiate to have locating holes and/or breakaway tabs for the insertion or sur- face mount equipment located outside the use- able area. is is usually accomplished via the tab-routing process. Material utilization may be increased by employing the scoring pro- cess. is process places grooves on opposite sides of the panel between boards for snapping the boards from the panel. is method allows boards to be butted up against each other, elim- inating the real estate for rout paths, thereby allowing more boards to be placed on the panel. For single- and double-sided product, a 0.500" border is required around the periphery of the panel for tooling purposes. For multilay- ers, this allowance is 0.750." Work with your PCB fabricator to design the most cost-effec- tive array/panel layout for your application. Panel Usable Area e following table can be used to determine the maximum, single 1-up PCB that can fit into a panel. Panel sizes are subdivided into "stan- dard" (most common) and "optional" (cus- tom) classifications. ere are three general modifications to a panel that will reduce the available usable area: 1. Step-and-repeat requirement. 2. Provisions for electroplating edge connectors. 3. Coupon requirements such as MIL spec or impedance. Step-and-Repeat is is the process of reproducing succes- sive images onto a panel. For PCBs without gold-plated edge contacts, the standard step- and-repeat spacing between parts is normally 0.100." Controlled Impedance Coupons PCBs with controlled impedance technol- ogy are processed with test coupons as part