Surface mount (SM) assembly is used for many PCB applications. However, plated through-hole (PTH) assembly continues to be used for a number of applications to include mil/aero and medical electronics. High PTH reliability demands tighter fabrication and assembly controls and tolerances. Laser drilling equipment must be up-to-date. Plus, calculations must be accurately performed. Doing so ensures PTH vias and their annular rings are intact when PCBs undergo multiple heat and reflow cycles.It’s always a good idea for OEMs to have a handle on PTH reliability. This is especially important since PCB real estate, components, vias, and annular ring sizes continue to shrink. Here are some tips to follow to assure PTH reliability.

• For lead-free PCBs, select the correct material, solder paste, and flux.
• Assure that your EMS provider and fabricator accurately calculate drill hole and annular ring sizes.
• Connectors and sockets demand greater PTH precision and design attention. Make sure special emphasis is given to this aspect of your PCB design.
• Fully understand that via in pad designs require different chemical compositions than those used in conventional through-hole vias.
• Make sure rework cycles are factored into the PTH design. Inadvertent mistakes at design lead to extra costs during rework.
• Make sure rework cycles are factored into the PTH design. Inadvertent mistakes at design lead to extra costs during rework.
• Be wary of fabricators taking costly shortcuts during ultra quick turn orders. The major consequence is long-term reliability is severely compromised

Inspectors make sure sample vias, annular rings, and holes are within tolerances specified in the fabrication notes and are thoroughly plated. Plus, they have to make sure non-plated holes aren’t mistakenly plated through.