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62 DESIGN007 MAGAZINE I JULY 2024 Role of solder joint voids: Participants will explore the origins of solder joint voids, under- stand their causes, and analyze their impacts on solder joint efficacy and overall product dependability. Tin whiskers—all you should know: Partici- pants will obtain a comprehensive understand- ing of tin whiskers, including what they are, how they occur, and how to prevent them. Explore our 2024 course schedule at educa- tion.ipc.org to see our entire catalog of self- paced and online instructor-led courses. Are you interested in becoming an IPC online instructor? Tell us about your expertise at go.ipc.org/sme. DESIGN007 Kelly Allen is online instructor- led training manager for IPC. By Beth Turner MACDERMID ALPHA ELECTRONICS SOLUTIONS Chapter 2: Application Overview There are many important things to consider when applying an encapsulant. This chapter is an overview of the application process, we will cover many of the terms and definitions found on a tech- nical data sheet and discuss the primary consider- ations for each of the process stages. It is worth- while considering some of the terms and defini- tions found on a technical data sheet to understand how the different liquid, mixed system, and cured property values can dictate the method chosen to apply materials. Storage It is important to store liquid encapsulants according to the manufacturer's specification to ensure shelf lives are achieved. Single component materials require external energy sources to initi- ate the curing reaction; heat-cure systems should be stored in cool, often sub-ambient temperatures; UV-cure systems should be stored in blackout con- tainers to prevent premature curing. Partial curing can increase the viscosity and cause small gelati- nous clumps to form in the liquid system; this can cause problems during the application, for exam- ple, blocking valves and lines in dispensing equip- ment. Some liquid encapsulants are sensitive to moisture; it is important to keep such encapsulants stored in airtight containers. In addition to the prob- lems above, moisture contamination can also cause unwanted side reactions during the cure process that can lead to undesirable bubbles and voids. The Liquid Properties When asked, "What is the viscosity," the short answer is, "It depends." Most encapsulants in their liquid state exhibit non-Newtonian flow and thus viscosity is not a single number. Viscosity is depen- dent on a variety of factors, including temperature, shear rate, time, and volume. Rheology profiling could be a more useful tool to understand liquid flow properties. It is also important to understand the density of the material to convert between the weight and volume mix ratio, but also to understand the weight contribution an encapsulant will have, to a PCBA or unit. Continue reading... BOOK EXCERPT: The Printed Circuit Assembler's Guide to... Encapsulating Sustainability for Electronics