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32 DESIGN007 MAGAZINE I JULY 2021 If, aer evaluating these factors, you're still not sure if a standard or common thick- ness will work for your design, here are some guidelines to help you choose what will work best for your board. So, You Think You Need a Custom Thickness? If you have read any of our other Design007 Magazine articles, you're probably aware that we consider PCB design as much an art form as a science. As devices demand more and more from boards, PCB design becomes less straightforward. So, if determining thickness is proving difficult during the design phase, we recommend also considering these relevant factors. First, can your PCB be manufactured as designed? Your manufacturer will have pro- duction tolerances. If your board is too thick or too thin, you'll find yourself back at the drawing board. PCB design is a game of millimeters. in- ner PCBs take up less space, so if you are build- ing a device that will fit in your hand, go as thin as necessary to accommodate the space. And once inside the assembly, will it be adequately protected to function properly? Protection from the operating environ- ment is largely about extreme cold or heat. Heat that can threaten functionality doesn't always come from operating in an environ- ment like a car engine or industrial grade oven. Components themselves can generate enough heat to cause an issue, so be sure to determine if you need to prioritize thermal transfer or insulation as you contemplate board thick- ness. PCB weight can be an issue more oen than you might think. Is your board part of a cell- phone, Bluetooth headset, or tablet device? inner boards are lighter and can help give your device that trim figure we all appreciate. Pay careful attention to your connections. PCB edge connectors or PCB trace-based connectors, for example, require a board with thickness matched to fit in the mating portion of the connector. Some through-hole parts have pin lengths that limit board thinness. Keep your ear to the ground for frequency concerns. Layer-to-layer thickness will affect signal integrity, crosstalk, impedance calcula- tion, and signal loss. For high frequency sig- nals, impedance control is a factor in deter- mining the right thickness of your board. ere are trade-offs with board flexibility. Will your product be subjected to excessive shock and vibration? in boards that flex can cause broken connections or components, so be sure it's properly supported in your assembly. Decision Time: Thick or Thin? ough the list of design considerations can theoretically go on forever, drawing conclu- sions about these factors will help with peace of mind about PCB thickness during the tran- sition from design to prototyping. Following are our general recommendations about when to prioritize thicker or thinner boards. Thicker Boards • Your board needs to be durable or isn't well protected in the assembly—or both • Because of its size, the PCB needs to be stiff • Your components require a certain amount of thickness • You have a high layer count, more than six Thinner Boards • Your board is going in a tight space • PCB weight is an issue • If heat is a concern, thinner boards are If your board is too thick or too thin, you'll find yourself back at the drawing board.