Issue link: https://iconnect007.uberflip.com/i/1514189
JANUARY 2024 I DESIGN007 MAGAZINE 19 When the surface area for component inter- face is restricted, it may justify adopting multi- layer or a multilayer sequential build-up (SBU) PCB fabrication to improve power and ground distribution and allow more efficient sub-sur- face circuit interconnect capability. Base Material Selection Circuit board fabricators and circuit board material suppliers have worked together in establishing a series of standards documents to eliminate misunderstandings between manu- facturers and purchasers, facilitating inter- changeability and end product improvement. Standards allow the fabricator to set up their processes that will meet the quality and reli- ability criteria defined by the customer com- pany. A standard that focuses on materials for printed circuit board fabrication, for example, is IPC-4101, Specification for Base Materials for Rigid and Multilayer Printed Boards. is document is prepared and maintained by IPC member companies. e working members developing and maintaining these standards are experienced in all segments of the product development: engineers, designers, material suppliers, printed circuit board fabricators, and assembly service providers. IPC-4101 includes the requirements for both laminates and prepreg base materials used pri- marily for rigid or multilayer printed circuit boards. Key properties include: • Dimensional stability and flexural strength • Coefficient of thermal expansion (CTE) • Limits of thermally induced Z-axis expansion • Glass transition temperature (Tg) • ermal conductivity and flammability rating At the end of IPC-4101 is a series of detailed specification sheets that furnish key require- ments for both laminate and prepreg mate- rials. e specification sheets are classified by a specific reinforcement type, resin sys- tem, and/or construction. Each variation is assigned a unique specification sheet number and includes copper foil peel strength, resistiv- ity, moisture resistance, moisture absorption potential, and the maximum kV level resulting in dielectric breakdown. Prepreg sheet materials are furnished when adding additional (buildup) circuit layers onto the partially processed base or core sub- strate. e prepreg is a thin woven glass fiber