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The Printed Circuit Assembler’s Guide to… Solder Defects—authored by the experts at Indium Corporation and exclusively available in the I-007eBook library—is specifically dedicated to educating the printed circuit board assembly sector and serves as a valuable resource for people seeking the most relevant information available. What follows is the introduction from this book.
In 2006, much of the world switched from tin-lead to lead-free solder. The European Union’s Restriction of Hazardous Substances (RoHS) directive, which essentially eliminated lead from electrical solder, drove this global move. This change has challenged circuit board assemblers since Pb-free solders melt at temperatures nearly 40°C hotter than lead-containing solders, and they do not flow or wet as well as SnPb solders.
At the same time, the density of electronics has unabatedly increased. This density increase has resulted in exponentially more powerful electronics—the fastest supercomputer of 1996 is outperformed by today’s iPhone 11 Pro—creating another challenge for assemblers. Whereas the 0402 passive was the leading edge in miniaturization in the SnPb era, the 0201, 01005, and smaller passives have emerged for Pb-free soldering. The combined challenges of Pb-free soldering and ever-increasing miniaturization have resulted in new or exacerbated defects in electronics assembly. This book was developed to address this problem, and will address the following defect topics:
- Voiding in SMT Assembly
- Head-in-Pillow and Non-Wet Open Defects
- Tombstoning of Passive Components
- Solder Paste Insufficients
- Solder Balling and Beading
It is also important to recognize that effective electronics assembly is an optimization process—often, minimizing one defect will exacerbate another. So, in addition to the information presented here, when confronted with a process defect or challenge, it is helpful to refer to experts from your materials or equipment suppliers. IPC and SMTA standards should provide further guidance as well, along with the many excellent courses presented by these industry organizations.