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30 DESIGN007 MAGAZINE I AUGUST 2024 cant cost driver for HDI and ultra HDI PCBs. Designs with BGAs equal to or less than 0.4 mm and multiple rows challenge the capabil- ity of HDI suppliers, which leads to the use of UHDI design parameters and thereby reduces the availability and increases the cost. Material Selection Correct material selection that complies with the performance and functionality of your appli- cation also plays a crucial role in the PCB cost. e most common stackups of standard PCBs are specified with 35 µm Cu on all layers. e manufacturer starts on 17.5 µm Cu on outer lay- ers and 35 µm Cu on inner layers, since the final outer layer Cu thickness reaches approximately 35 µm aer plating. But 35 µm Cu on the inner layers isn't always required and can be replaced by 17.5 µm for the current flowing in many elec- tronic devices. is, in turn, lowers costs. Beyond this, Cu thickness above the standard 35 µm represents a considerable extra cost. e base material choice depends on the PCB technology used for your application and the performance needed. By specifying a spe- cific brand and type of material, you diminish the supplier availability and oen prolong the lead time of the suppliers by adding material purchase time. Seeking advice on the material specification from a specialist like ICAPE can save time and money by ensuring that your choices are based on performance rather than a specific brand and type of material. We recommend specifying the important critical material characteristics for the performance of your application, including glass transition temperature (Tg), coefficient of thermal expansion (CTE), dielectric constant (Dk), dissipation factor (Df ), comparative tracking index (CTI), and maximum operating temperature (MOT). ereby you allow the supplier to provide their offer based upon the most available and cost-optimized material ful- filling your specified criteria. PCB Thickness and Stackup Standard stackups contain only one sheet of prepreg in between each conductive layer. Using two or more sheets of prepreg will increase the PCB cost by approximately 2.5–6 USD/m² per sheet. e most common PCB thickness is 1.6 mm, but could the thickness be reduced to 1.0 mm or 0.8 mm without compromising the mechan- ical or electrical performance? Reducing the thickness can provide direct cost savings on the PCB price of 1–2 USD/m², but it also reduces the weight, leading to large cost savings on the