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AUGUST 2026 I I-CONNECT007 MAGAZINE 93 or reduced yield, to boards that operate with exces- sive signal loss, are susceptible to thermal damage, or are prone to mechanical breakdown in the field. Signal Integrity Issues If you are designing boards for RF or high-frequen- cy applications, choosing FR-4 can lead to a slew of issues in the field. FR-4 is a solid, cost-effective base for basic circuits, but it opens the door for signal loss, signal reflections, data corruption, and electromagnetic interference (EMI). Thermal Failures If your board needs to operate in a hot environment and you pick the wrong substrate, the result can be solder joint cracking, warping, component failure, and even a melted board. When choosing a sub- strate, pay close attention to CTE, Tg, and thermal conductivity to avoid such issues. Mechanical Failures Polyimide is your best bet for applications requiring a board that can bend or flex. Using rigid materi- als in these instances can lead to delaminated cir- cuits and broken copper or even cause the board to snap. But if your board is designed for structur- ally rigid application, flexible material will not work because of challenges associated with securely mounting components. When your manufacturer gets the first peek at your requirements and design, their job is to ask, "How will we build this?" With modern materials and manu- facturing techniques, more is possible than ever before. A good manufacturing team has the experi- ence and capacity to help you select the materials that are optimal for your project. I-CONNECT007 Matt Stevenson is vice president and general manager of ASC Sunstone Circuits. To read past columns, click here. Read Matt's book, The Printed Circuit Designer's Guide to … Designing for Reality and listen to his podcast series here. Heat Is your board going into space? After assembly, will it have a slew of hot components? I encourage de- signers to carefully evaluate the temperatures their boards will operate in. High heat environments or multiple soldering passes during assembly can cause certain substrates to soften or expand. It's also important to recognize how much heat com- ponents will create and if those temperatures will make one substrate preferable to another. Strength A board's strength is measured in many ways, but all those measures essentially pertain to the board's durability. It is important to choose substrates that will ensure the board can withstand everything the environment throws at it. This is especially so for flexible PCBs and those subject to vibration or re- peated impacts that are often present in military and aerospace applications. Another consideration is excessive moisture absorption that can degrade board performance. Availability Substrate availability issues are becoming more com- mon due to increased demand created by AI-related build-out and geopolitical disruption. Lead times are longer now, and substrate costs are increasing, some- times even for standard materials. This can extend product development windows and drive up the cost of going to market. We encourage designers to con- sider materials availability in their design choices. Manufacturability Manufacturability is a key concern equal to cost considerations. FR-4 is the go-to for ease of manu- facture. Every PCB fabricator works with it. But more designs are requiring other substrate materials that not every manufacturer can offer. Choosing the right manufacturer, one knowledgeable and expe- rienced in the array of substrate materials, ensures the design is functional and structurally reliable, while also helping avoid manufacturing issues. Why It Is Important to Choose Substrate Wisely Choosing the wrong PCB substrate can lead to ev- erything from manufacturing failures, such as rework C O N N ECT T H E D OTS C O N N ECT T H E D OTS